Seismic moment

The 3.2-induced seismic event in 2006 due to fluid injection at the Basel geothermal site in Switzerland was the starting point for an ongoing discussion in Europe on the potential risk of hydraulic stimulation in general. In particular, further development of mitigation strategies of induced seismic events of economic concern became a hot topic in geosciences and geoengineering. Here, we present a workflow to assess the hazard of induced seismicity in terms of occurrence rate of induced seismic events. The workflow is called Forward Induced Seismic Hazard Assessment (FISHA) as it combines the results of for-ward hydromechanical-numerical models with methods of time-dependent probabilistic seismic hazard assessment. To exemplify FISHA, we use simulations of four different fluid injection types with various injection parameters, i.e. injection rate, duration and style of injection. The hydromechanical-numerical model applied in this study represents a geothermal reservoir with pre-existing fractures where a routine of viscous fluid flow in porous media is implemented from which flow and pressure driven failures of rock matrix and preexisting fractures are simulated, and corresponding seismic moment magnitudes are computed. The resulting synthetic catalogues of induced seismicity, including event location, occurrence time and magnitude, are used to calibrate the magnitude completeness and the parameters a and b of the frequency-magnitude relation. These are used to estimate the time-dependent occurrence rate of induced seismic events for each fluid injection scenario. In contrast to other mitigation strategies that rely on real-time data or already obtained catalogues, we can perform various synthetic experiments with the same initial conditions. Thus, the advantage of FISHA is that it can quantify hazard from numerical experiments and recommend a priori a stimulation type that lowers the occurrence rate of induced seismic events. The FISHA workflow is rather general and not limited to the hydromechanical-numerical model used in this study and can therefore be applied to other fluid injection models.

The seismogenic depth and seismic coupling are important inputs into seismic hazard estimates. Although the importance of seismic coupling is often overlooked, it significantly impacts seismic hazard results. We present an estimation of upper and lower seismogenic depth and hypocentral depth and seismic coupling in the transition zone between the Alps, Dinarides and Pannonian Basin, characterized by complex deformation pattern, highly variable crustal thickness, and moderate seismic hazard, supporting the development of the 2021 seismic hazard model of Slovenia. We estimated the lower seismogenic depth using seismological and geological data and compared them. The seismological estimate was based on two regional earthquake catalogues prepared for this study. In the area source model, estimates of lower seismogenic depth from seismological data are deeper or equal to the ones derived from geological data, except in one case. In the fault source model, we analyzed each fault individually and chose seismological lower depth estimates in 12 among 89 faults as more representative. The seismogenic thickness for each individual fault source was determined for seismic coupling determination. The seismic coupling was assessed by two approaches, i.e. we chose the most trusted value from the literature, and the value determined for each fault individually by using the approach based on the updated regional fault and earthquake datasets. The final estimate of seismic coupling ranges from 0.77 to 0.38. We compared the tectonic moment rate based on long-term slip rate using different values of seismic coupling with the seismic moment rate obtained from the earthquake catalogue. The analysis is done for the whole area, as well as for the individual area zones. The analysis of N-S components of estimated slip for the largest faults in the area of west Slovenia shows that the regional geologic and geodetic shortening rates are comparable. The total activity rate of three global seismic source models is compared, which gives up to a 10 % difference. Our results contribute to a better understanding of the seismic activity in the region and the approach for seismic coupling estimation can be applied in other similar regions.

5 – Temporary Seismic Network On 15 January 2018 at 11:51 UTC, an earthquake of 4.9 ML occurred in the Northeast of Arraiolos region near Aldeia da Serra village. The hypocentral location, determined by Instituto Português do Mar e da Atmosfera (IPMA), has coordinates 38.79 N, 7.93 W at 11 km depth. The focal mechanisms determined by P-wave first motion polarities and waveforms inversion indicate a dominance of strike-slip events with nodal plans near NS (left lateral) and EW (right lateral) directions. Due to the lower magnitude, the earthquake didn’t cause damage but was widely felt in the Centre and South of Portugal mainland. In the vicinity of the epicentre, at the Aldeia da Serra village, it reached a maximum intensity VI, having been felt with intensity IV/V in the city of Évora, about 20 km from the epicentre. The event was also felt with intensity III in Lisbon at more than 100 km from the epicentre. This event caused alarm in the population that haven’t felt an earthquake ...

studied in detail to determine possible causes for the observed stronger excitation of surface waves by earthquakes from the Delta region relative to earthquakes of comparable local magnitude in the Peninsular Ranges region. Data from distant stations are complemented with data from aftershock studies using local arrays and, for the Mesa de Andrade earthquake, with data from two strong motion stations. The strong motion records for ihe Mesa de Andrade earthquake show that it consisted of two events, 45 s apart, which produced maximum recorded horizontal accelerations of 0.21 and 0.24g, respectively, at a distance of 18 km from the epicentre. Synthetic seismograms are used to help determine the depth of these events and their source time functions. Both events are relatively simple. The second event is sharp and impulsive and could be thought of as an aftershock, since it has a considerably smaller moment than the first event, even though its recorded acceleration was higher. Comparison of measured parameters shows that while the local magnitude of the Mesa de Andrade earthquake is only 0.2 units larger than the Pino Solo earthquake and its source dimension is -2.2 times larger (source areas -4.8 times larger), its moment is larger by a factor of 6.2-8.5. This is approximately explained by the cY2 scaling law. However, the near source spectra and accelerations recorded on the strong motion accelerograph at Riito, at a distance of about 18 km, are considerably larger than predicted by the scaling law. This is probably a results of high stress drop asperities on the fault surface, although near field focusing (directivity) may also have contributed.

A generalized form of the directivity function has been used to determine the length and the rupture velocity of four earthquakes with known vertical strike slip faulting. For body wave magnitudes between 5.7 and 7.0, the lengths vary from 18 to 35 km with a rupture velocity of 1-5 kms-l. Seismic moments have been determined from the spectral amplitude densities and the theoretical response to a point source model. From these values, stress drops of 2 to 30 bars and average dislocations of 4 to 160cm have been derived. The products of the average stresses acting at the fault by the seismic efficiency factor are of the order of lo7 dyne cm-' for all four earthquakes; this seems to indicate a minimum strength of the crust under horizontal shear stress of the same order.

This paper presents the overall procedure followed in order to assemble the most recent pan-European strong-motion databank: Reference Database for Seismic Ground-Motion in Europe (RESORCE). RESORCE is one of the by-products of the SIGMA (SeIsmic Ground Motion Assessment; projet-sigma.com) project. RESORCE is intended to be a single integrated accelerometric databank for broader Europe to understand the regional differences in seismic hazard for improving risk studies in Europe and surrounding countries. RESORCE principally updates and extends the previous pan-European strong-motion databank (Ambraseys et al., 2004a) from recently compiled Greek, Italian, Swiss and Turkish accelerometric archives. The updates also include the earthquake-specific literature studies published in recent years. The current content of RESORCE includes 5882 multi-component and uniformly processed accelerograms from 1814 events and 1540 strong-motion stations. The moment magnitude range covered by RESORCE is 2.8 ≤ M w ≤ 7.8. The source-to-site distance interval extends to 587 km and distance information is given by the common pointand extended-source distance measures. The paper presents the current features of RESORCE through simple statistics that also quantify the differences in metadata and strong-motion processing with respect to the previous version of the pan-European strong-motion databank.

Several seismological and paloseismolgical studies and historical reports have indicated that Gulf of Aqaba is characterized by higher seismicity than any other seismogenic sources around Egypt. Accordingly, surrounding areas have been impacted by several destructive earthquakes (AD 1068, AD 1212, AD 1229, AD 1458, and AD 1995). Cities situated around the Gulf of Aqaba have experienced different damage levels due to historical and instrumental earthquakes resulting in considerable fatalities. The Aqaba earthquake which occurred on November 22, 1995 (Moment magnitude (Mw) = 7.3) was the largest recorded earthquake along with the Dead Sea Fault System, strongly felt at Eastern Mediterranean region. Many seismic sequences have ocuuerd in the Gulf of Aqaba in the last decades and some of them continued for almost two years. This paper applies a spectral decomposition method based on a reference site to correct the source spectra from the path and site effects by employing Iterative Leas...

This paper reviews the likely source characteristics, focal source mechanism and fault patterns of the nearest effective seismogenic zones to Greater Cairo Area. Furthermore, M max and ground accelerations related to the effective seismic events expected in future from those seismogenic zones are well evaluated. For this purpose, the digital waveform of earthquakes than M L =3 that occurred in and around Greater Cairo Area from 1997 to 2008 which have been recorded by the Egyptian National Seismological Network, are used to study source characterization, focal mechanism and fault pattern of the seismogenic zones around Greater Cairo Area. The ground motions are predicted from seismogenic zones to assess seismic hazard in the northeastern part of Greater Cairo, where three effective seismogenic zones, namely Abou Zabul, southeast Cairo trend and Dahshour area, have the largest effect to the Greater Cairo Area. The M max was determined, based upon an empirical relationship between the seismic moment and the rupture length of the fault during the earthquake. The estimated M max expected from Abou Zabul, southeast Cairo trend, Dahshour seismic sources are of M w magnitudes equal to 5.4, 5.1, and 6.5, respectively. The predominant fundamental frequency and soil amplification characteristics at the area were obtained using boreholes data and in-situ ambient noise measurement.

In this paper, the shear wave quality factor and source parameters in the near field are estimated by analyzing the acceleration data in Zagros region. Accelerograms recorded by Building and Houses Research Center strong ground motion network have been used. The data have been considered with the magnitude of 4.7 to 6.3 collected from 1999 to 2014. In this approach, the theoretical S-wave displacement spectra conditioned by frequency independent Q was fitted with the observed displacement spectra. The source spectrum of an earthquake can be approximated by the omega-square ω model, which has ω decay for frequencies higher than the corner frequency. By following the mentioned approach, corner frequency, scalar moment, moment magnitude and frequency independent Q for each accelerogram were computed simultaneously, and the estimated error was given in the root-mean-square sense over the frequency range of interest. In this study, the generalized inversion method is used to estimate var...

We present the first detailed estimates of co-seismic slip distribution on faults in the South Iceland Seismic Zone (SISZ), an area of bookshelf tectonics. We have estimated source parameters for two M W 6.5 earthquakes in the SISZ on June 17 and 21, 2000 through a joint inversion of InSAR and GPS measurements. Our preferred model indicates two simple 15 km long, near vertical faults extending from the surface to approximately 10 km depth. The geometry is in good agreement with the aftershock distribution. The dislocations experienced pure right-lateral strike-slip, reaching maxima of 2.6 m and 2.9 m for the June 17 and 21 events, respectively. We find that the distribution of slip with depth may be correlated to crustal layering, with more than 80% of the total geometric moment release occurring in the uppermost 6 km. According to the distributed slip model the middle and upper crust appears to be more apt to generate large displacements than the lower crust. The geodetic estimates of seismic moments are 4.4U10 18 Nm (M W 6.4) and 5.0U10 18 Nm (M W 6.5). The total moment released by the two events equals that generated by several decades of plate motion in the area, but is only a fraction of the moment accumulated in the area since the last major earthquake in 1912.

We estimated source parameters of 216 intermediate-depth (65-150 km) earthquakes (M w 4.0-7.0) in the Pacific slab beneath Japan along using Hi-net data. We made determinations of static stress drop, radiated energy and radiation efficiency, along with estimates of the whole path attenuation, to study the source scaling as a function of earthquake size and depth. Our results show that there is a small increase in the values of the ratio of radiated energy to seismic moment, as a function of seismic moment, which is due to an associated slight increase of static stress drop with earthquake size. We also estimated the radiation efficiency for these events using the static stress drops and radiated energies. The values of radiation efficiency are slightly lower compared to shallow crustal earthquakes. These results indicate that dissipative energy processes may be relatively more important for intermediate-depth earthquakes.

We estimated source parameters of 216 intermediate-depth (65-150 km) earthquakes (M w 4.0-7.0) in the Pacific slab beneath Japan along using Hi-net data. We made determinations of static stress drop, radiated energy and radiation efficiency, along with estimates of the whole path attenuation, to study the source scaling as a function of earthquake size and depth. Our results show that there is a small increase in the values of the ratio of radiated energy to seismic moment, as a function of seismic moment, which is due to an associated slight increase of static stress drop with earthquake size. We also estimated the radiation efficiency for these events using the static stress drops and radiated energies. The values of radiation efficiency are slightly lower compared to shallow crustal earthquakes. These results indicate that dissipative energy processes may be relatively more important for intermediate-depth earthquakes.

A moderate earthquake with local magnitude 5.2 (M L ) occurred off the eastern coast of South Korea on May 29, 2004. This earthquake is one of the largest events near the Korean Peninsula since 1978 when instrumental observations began by the Korea Meteorological Administration. We carried out modeling of regional waveforms and deconvolutions using empirical Green functions to estimate source parameters. The results of the regional waveform modeling show a reverse fault mechanism with a hypocentral depth of 8 km and seismic moment of 5 × 10 16 N • m, which is equivalent to Mw 5.1. Performing the empirical Green function deconvolution, we estimated a fault radius of 1.1 to 1.4 km and an average stress drop of 13.5 MPa, assuming an east dipping fault plane. Assuming a west dipping fault plane, we estimated a fault radius of 1.3 to 2.9 km and an average stress drop of 6.6 MPa.

A moderate earthquake with local magnitude 5.2 (M L ) occurred off the eastern coast of South Korea on May 29, 2004. This earthquake is one of the largest events near the Korean Peninsula since 1978 when instrumental observations began by the Korea Meteorological Administration. We carried out modeling of regional waveforms and deconvolutions using empirical Green functions to estimate source parameters. The results of the regional waveform modeling show a reverse fault mechanism with a hypocentral depth of 8 km and seismic moment of 5 × 10 16 N • m, which is equivalent to Mw 5.1. Performing the empirical Green function deconvolution, we estimated a fault radius of 1.1 to 1.4 km and an average stress drop of 13.5 MPa, assuming an east dipping fault plane. Assuming a west dipping fault plane, we estimated a fault radius of 1.3 to 2.9 km and an average stress drop of 6.6 MPa.

We estimated source parameters of 216 intermediate-depth (65-150 km) earthquakes (M w 4.0-7.0) in the Pacific slab beneath Japan along using Hi-net data. We made determinations of static stress drop, radiated energy and radiation efficiency, along with estimates of the whole path attenuation, to study the source scaling as a function of earthquake size and depth. Our results show that there is a small increase in the values of the ratio of radiated energy to seismic moment, as a function of seismic moment, which is due to an associated slight increase of static stress drop with earthquake size. We also estimated the radiation efficiency for these events using the static stress drops and radiated energies. The values of radiation efficiency are slightly lower compared to shallow crustal earthquakes. These results indicate that dissipative energy processes may be relatively more important for intermediate-depth earthquakes.

A moderate earthquake with local magnitude 5.2 (M L ) occurred off the eastern coast of South Korea on May 29, 2004. This earthquake is one of the largest events near the Korean Peninsula since 1978 when instrumental observations began by the Korea Meteorological Administration. We carried out modeling of regional waveforms and deconvolutions using empirical Green functions to estimate source parameters. The results of the regional waveform modeling show a reverse fault mechanism with a hypocentral depth of 8 km and seismic moment of 5 × 10 16 N • m, which is equivalent to Mw 5.1. Performing the empirical Green function deconvolution, we estimated a fault radius of 1.1 to 1.4 km and an average stress drop of 13.5 MPa, assuming an east dipping fault plane. Assuming a west dipping fault plane, we estimated a fault radius of 1.3 to 2.9 km and an average stress drop of 6.6 MPa.

A moderate earthquake with local magnitude 5.2 (M L ) occurred off the eastern coast of South Korea on May 29, 2004. This earthquake is one of the largest events near the Korean Peninsula since 1978 when instrumental observations began by the Korea Meteorological Administration. We carried out modeling of regional waveforms and deconvolutions using empirical Green functions to estimate source parameters. The results of the regional waveform modeling show a reverse fault mechanism with a hypocentral depth of 8 km and seismic moment of 5 × 10 16 N • m, which is equivalent to Mw 5.1. Performing the empirical Green function deconvolution, we estimated a fault radius of 1.1 to 1.4 km and an average stress drop of 13.5 MPa, assuming an east dipping fault plane. Assuming a west dipping fault plane, we estimated a fault radius of 1.3 to 2.9 km and an average stress drop of 6.6 MPa.

El estudio macrosísmico del terremoto de Murindó (octubre 18 de 1992) ha sido elaborado siguiendo la metodología de Shebalín (1974). El evento sísmico afectó la región del Urabá Antioqueño y el epicentro fue localizado al este del municipio de Murindó, con una Intensidad máxima estimada de Xº (MM). La dirección de máxima elongación trazada para el modelo de ruptura presenta gran concordancia con los datos de buzamiento y azimut de la falla Murindó propuestos por autores como Montes y Sandoval (2001) y , la cual se asocia como la generadora del evento sísmico.

On 5 September 2012, a large thrust earthquake (Mw 7.6) ruptured a densely instrumented seismic gap on the shallow‐dipping plate boundary beneath the Nicoya Peninsula, Costa Rica. Ground motion recordings directly above the rupture zone provide a unique opportunity to study the detailed source process of a large shallow megathrust earthquake using very nearby land observations. Hypocenter relocation using local seismic network data indicates that the event initiated with small emergent seismic waves from a hypocenter ~10 km offshore, 13 km deep on the megathrust. A joint finite‐fault inversion using high‐rate GPS, strong‐motion ground velocity recordings, GPS static offsets, and teleseismic P waves reveals that the primary slip zone (slip > 1 m) is located beneath the peninsula. The rupture propagated downdip from the hypocenter with a rupture velocity of ~3.0 km/s. The primary slip zone extends ~70 km along strike and ~30 km along dip, with an average slip of ~2 m. The associate...

We observed very long period seismic events that are associated with the 1998 activity of Iwate Volcano, northeast Japan. The events show a dominant period of 10 s and duration of 30–60 s, often with accompanying short‐period waves at the beginning and at the end of the long‐period signals. By analyzing the broadband seismograms we find that the source elongates in the east‐west direction for ∼4 km at a depth of 2 km beneath the western part of Iwate Volcano. Results of moment tensor inversions show a source mechanism of mutual deflation and inflation of two chambers located at the western and eastern edges of the source region. The source region coincides with the low seismic velocity zone detected by seismic tomography and is very close to the locations of pressure sources estimated from crustal deformation data. On the basis of these results we infer that the very long period seismic events are generated by transportation and movement of magmatic fluid (hot water and/or magma) in...

A sequence of M 7-class interplate earthquakes and transient postseismic slips following each of these earthquakes occurred along the Japan Trench before the occurrence of the giant earthquake on March 11, 2011. Continuous GPS data detected a significant postseismic deformation with displacements that were much larger than that of the coseismic offset. Moreover, the geodetic inversion results using these observations revealed that the total moment released by these transient slips was much larger than the coseismic ones. This differs from our understanding of the postseismic process that the postseismic deformation and slip are smaller than the coseismic ones. These transient processes may help us understand not only the postseismic process but also the pre-seismic signals indicating the occurrence of the giant earthquake.

A new non-parametric statistic is introduced for the characterization of deviations of the distribution of seismic energies from the Gutenberg-Richter law. Based on the two first statistical log-moments, it evaluates quantitatively the deviations of the distribution of scalar seismic moments from a power-like (Pareto) law. This statistic is close to zero for the Pareto law with arbitrary power index, and deviates from zero for any non-Pareto distribution. A version of this statistic for discrete distribution of quantified magnitudes is also given. A methodology based on this statistics consisting in scanning the lower threshold for earthquake energies provides an explicit visualization of deviations from the Pareto law, surpassing in sensitivity the standard Hill estimator or other known techniques. This new statistical technique has been applied to shallow earthquakes (h ≤ 70 km) both in subduction zones and in mid-ocean ridge zones (using the Harvard catalog of seismic moments, 1977-2000), and to several regional catalogs of magnitudes (California, Japan, Italy, Greece). We discover evidence for log-periodicity and thus for a discrete hierarchy of scales for low-angle dipping, low-strain subduction zones with a preferred scaling ratio γ=7±1 for seismic moments, compatible with a preferred scaling ratio of 2 for linear rupture sizes, and consistent with previous reports. We propose a possible mechanism in terms of cascades of fault competitions.

We evaluate the seismic moment-frequency relation for the Harvard catalogue in the period 1977-1994. This catalogue is composed of about 12 000 earthquakes. After selection of events in terms of depth and energy, we retain about 8000 data points. We estimate two parameters of the seismic moment distribution: the power exponent b and the cut-off value M m . The method used is a least-squares linear fit on a log-log scale performed over a range selected on the basis of the standard deviation from the histogram. The analysis is carried out for different subdivisions of the Earth in square grids of different sizes. Neither parameter exhibits a dependence on cell size, suggesting the universality of their values and the interpretation of the existence of a cut-off as a finite size effect linked to a finite catalogue length. The variations of the parameters are investigated as a function of time (duration of the catalogue) and versus the number of events used for building up the distribution. Again, b and M m do not depend on time, but M m depends on the number of events, reaching a stable value for N#1000. The only significant change in the parameters is observed for different values of M 0upper in the catalogue, revealing the existence of universality classes.

On May 11 th 2011, a Mw 5.2 earthquake stroke the city of Lorca in the SE Spain. This event caused 9 fatalities, 300 injuries and serious damage on the city and the surrounding areas. The Lorca earthquake occurred in the vicinity of a region bounding two well-known segments of a large active fault, the Alhama de Murcia fault (AMF). The Lorca earthquake offers a unique opportunity to study how strain is accommodated in an inter segment region of a large strike slip fault. We map recent tectonic structures in the epicentral region and we use radar interferometry to analyze the coseismic deformation. Combining these data with seismological ob servations of Lorca seismic sequence we first model the source of the earthquake. Then we analyze the influ ence of our preferred model in the adjacent segments by Coulomb failure stress modeling. The proposed earthquake source model suggests that this event ruptured an area of -4x3 km within the complex structure that limits the Gofiar-Lorca and Lorca-Totana segments of the AMF. The induced static stress change on the adjacent segments of the fault represents a seismic cycle advance equivalent to 200 to 1000 years of tectonic loading.

This paper reviews studies on earthquake energies, seismic efficiency, radiation efficiency, scaled energy and energy-magnitude law conducted by Taiwan seismologists and foreigners who used seismic data from Taiwan to study these problems. Sufficient seismic and geodetic data permits energy measurements from the 20 September 1999 M s 7.6 Chi-Chi earthquake and its larger-sized aftershocks. The results provide significant information on earthquake physics. The issues in this review paper include measures of these physical quantities and related theoretical or analytical studies of these physical quantities made by both Taiwan's seismologists and foreigners who used seismic data of Taiwan to study related problems.

We have taken the seismic moment (M o) values of 79 earthquakes occurring in the Taiwan region that have been published in the Global centroid-moment tensor (CMT) and regional Broadband Array in Taiwan for Seismology (BATS) catalogues for the period 1996–2005 and compared the values determined from the global and regional networks, respectively. M oG and M oB are used to denote the M o values published in the Global CMT and regional BATS catalogues, respectively. Our results show that M oB linearly correlates with M oG and that M oB is, on average, approximately equal to 0.37M oG. This difference may be caused by the use of shorter period seismic waves in BATS for estimating M oB. The moment magnitude evaluated from regional BATS seismograms is about 0.3 less than that estimated from global data.

SUMMARYThis research provides new constraints on the intermediate depth upper-mantle structure of the Hellenic lithosphere using a three-step Rayleigh-wave tomography. Broadband waveforms of about 1000 teleseismic events, recorded by ∼200 permanent broad-band stations between 2010 and 2018 were acquired and processed. Through a multichannel cross-correlation technique, the fundamental mode Rayleigh-wave phase-velocity dispersion curves in the period range 30–90 s were derived. The phase-velocities were inverted and a 3-D shear velocity model was obtained down to the depth of 140 km. The applied method has provided 3-D constraints on large-scale characteristics of the lithosphere and the upper mantle of the Hellenic region. Highlighted resolved features include the continental and oceanic subducting slabs in the region, the result of convergence between Adria and Africa plates with the Aegean. The boundary between the oceanic and continental subduction is suggested to exist along a t...

Joint seismological data and GPS velocities are used to investigate the geodynamics of Aitoloakarnania region (W. Greece). The study area is a thrust and fold belt, located among four rapidly deforming zones, namely the northwestern tip of the Hellenic subduction, the Cephalonia transform fault, the NW Greece collision and the western Corinth rift. During the last decade, several moderate to strong earthquakes occurred in the broader region, providing a large amount of new information. Seismological data used are recent earthquakes, recorded by temporary local and permanent regional networks, and reliable focal mechanisms determined by regional moment tensor inversion and local P-wave first motion polarities. Data from previous microseismic campaigns have also been considered. Hypocentral relocation, traveltime and focal mechanisms inversion were performed in order to investigate the velocity structure and the stress field distribution. A number of continuously recording GPS stations (CGPS) installed in the broader area have been employed. Analysis of the CGPS data with respect to various reference stations resulted to the estimation of the horizontal and vertical deformation on both regional and local scale. Most observations support the concept that the study area constitutes a rigid crustal block bounded by dextral strike-slip deformation imposing counterclockwise rotation. The slight internal deformation observed is characterized by normal, reverse and strike-slip faulting. Although the pattern is quite complex, the deformation appears concentrated and homogeneous at specific depths.

Over the last several decades, mine-induced seismicity has created serious safety and production issues for underground mines worldwide. A significant proportion of the large seismic events resulting in rockbursts have been related to a 'fault slip' mechanism on shear zones. This source mechanism has been the subject of a number of numerical modelling studies in the past and several techniques have been developed to analyse it, but these methods are highly dependent on the strength properties used to simulate (explicitly or implicitly) the non linear response of the rock mass. A methodology is proposed in this paper to estimate non linear ride without considering explicitly the strength properties of the shear zones, considering the premining Limit Equilibrium Strength (LES). As a result of this methodology, observed seismic trends can be reproduced through numerical modelling and if enough data exists to calibrate the model, accurate magnitudes of seismic moment can be reliably forecasted.

New pressure data from a pair of Ocean Drilling Program (ODP) hydrologic borehole observatories at ODP Sites 1173 and 808, located off Japan in the subducting Philippine Sea plate and in the nearby Nankai accretionary prism, respectively, show clear signals associated with an earthquake swarm off the Kii Peninsula that began on September 5, 2004, roughly 220 km away from the observatory sites. At Site 1173, formation pressures rose by 1.0–1.5 kPa at the time of the largest earthquake (Mw= 7.5), then continued to rise to a total anomaly of 4 kPa during the following 200–300 days. These transients are inferred to reflect co-seismic and slow continuing volumetric contraction of the plate by amounts of roughly 0.2 × 10−6and 0.5 × 10−6, respectively. The sign of the estimated strain is consistent with that predicted with a seismic-moment-constrained elastic half-space dislocation model, but the amplitude is much larger, by roughly a factor of 6 at the time of the main earthquake, and by ...

The Mw7.3 1995 Aqaba earthquake is the largest instrumental earthquake along the Dead Sea Fault. We complement previous seismological studies by analyzing co‐seismic ground displacement from differential interferometry computed from ERS images spanning 3 different areas. They are compared with a synthetic model derived from seismological study. Only far‐field deformation related to the main sub‐event could be revealed because the near‐field area lies within the gulf. The interferometric data imply a 56 km long and 10 km wide fault segment, connecting the Elat Deep to the Aragonese Deep, which strikes N195°E and dips 65° to the west, with 2.1 m left‐lateral slip and a 15.5° rake indicating a slight normal component. The geodetic moment compares well with the seismic moment.

SUMMARYThe hydraulic fracturing technique is used for resource production, such as in shale gas/oil extraction and enhanced geothermal systems. The effects of fracturing are often monitored via induced earthquakes, and obtaining as much information as possible from those earthquakes is desirable. The stress drop—calculated from the seismic moment Mo and corner frequency fc—is an earthquake-related parameter that can help identify additional characteristics of the seismicity. To investigate the relationship between stress drops and hydraulically induced seismic events, we estimated the Mo and fc of acoustic emission (AE) events during hydraulic fracturing experiments performed in the laboratory in previous studies using 2 Eagle Ford shale and 10 Kurokami-jima granite samples. We estimated Mo by fitting the theoretical spectra to the observed spectra after correcting for the following effects: (1) frequency response of AE transducers under the installation method used in the fracturin...

Deformation can help predict the presence and severity of an earthquake. SAR image data can be used to calculate postseismic surface deformation using the InSAR and DInSAR methods. DInSAR (Differential Interferometric Synthetic Aperture Radar) is a well-established technology for monitoring subsidence and uplift with millimeter precision. This study uses SAR imagery to detect surface deformation caused by a magnitude M 6.1 earthquake on December 21, 2015, at 01:47:37 WIB in Tarakan Regency, North Borneo. The data used is Sentinel-1 satellite imagery in SLC (single-look complex) format, with a master image from December 18, 2015 (3 days before the earthquake), and a slave image from January 11, 2016 (21 days after). The interferogram generated by the Tarakan earthquake shows deformation patterns radiating in three directions: northeast, southeast-southwest, and southwest-northwest. Tarakan City, located south-southwest of the epicenter, experienced the highest subsidence deformation of 0.001-0.035 meters. On December 21, 2015, the Tana Tidung I Regency area, 33 kilometers southwest of the epicenter, showed the highest uplift deformation (0.019-0.079 meters). The largest uplift in Tana Tidung II Regency (0.069 meters), about 10 kilometers north of the epicenter, occurred near the fault zone. Surface deformation due to the Tarakan earthquake contributes to seismic hazard assessment in North Borneo and indicates other locally active faults. Uplift to the east and subsidence to the west of the epicenter suggest an oblique-normal fault, with dominant strike-slip motion and normal (downward) fault blocks to the west.

We study the rupture process of the Iranian earthquake of 1990 June 20 from broad-band data. We redetermined its moment tensor and source mechanism from long-period surface waves. Then we studied the P and SH broad-band recordings from the GEOSCOPE and IRIS seismic networks. We inverted the body waves using a full waveform modelling. For the inversion we used the gradient method of NBbdek, mixed with a limited exploration of the parameter space. In order to control the resolution of inversion, we proceeded by a stepwise procedure increasing the model complexity with every new inversion. We used the reduction of cost functional as a criterion for the validity of the inverted model. We first inverted the body waves considering a single-point source model. We found that body waves are dominated by a large energy release about 20 s from the onset of the signals. In the next step, fixing fault-plane solution, we inverted for the directivity of the source. We found clear evidence of propagation towards the east of the epicentre. We determined a rupture velocity of -2.5 km s-'. The preceding source inversion reduced the variance of the residuals by about 30 per cent. Further improvement of the fit of the body-wave signals was obtained using an extended line source with constant fault-plane solution. We obtained a very good fit with an asymmetrical model. Initially rupture is bilateral but north-western propagation stops after 10 s. Later rupture continues unilaterally in the south-eastern direction with a rupture velocity of the order of 2.5 km s-'. Finally an inversion was attempted with a line source with varying fault mechanism. The final solution obtained by this procedure reduces the variance of the body-wave residuals by 60 per cent with respect to the variance of the observed body-wave signals. Variations in fault-plane solution along the fault are considered to be well resolved.

Over the last 25 years mining-induced seismicity in the Ruhr area has continuously been monitored by the Ruhr-University Bochum. About 1,000 seismic events with local magnitudes between 0.7 B M L B 3.3 are located every year. For example, 1,336 events were located in 2006. General characteristics of induced seismicity in the entire Ruhr area are spatial and temporal correlation with mining activity and a nearly constant energy release per unit time. This suggests that induced stresses are released rapidly by many small events. The magnitude-frequency distribution follows a Gutenberg-Richter relation which is a result from combining distributions of single longwalls that themselves show large variability. A high b-value of about 2 was found indicating a lack of large magnitude events. Local analyses of single longwalls indicate that various factors such as local geology and mine layout lead to significant differences in seismicity. Stress redistribution acts very locally since differences on a small scale of some hundreds of meters are observed. A regional relation between seismic moment M 0 and local magnitude M L was derived. The magnitude-frequency distribution of a single longwall in Hamm was studied in detail and shows a maximum at M L = 1.4 corresponding to an estimated characteristic source area of about 2,200 m 2 . Sandstone layers in the hanging or foot wall of the active longwall might fail in these characteristic events. Source mechanisms can mostly be explained by shear failure of two different types above and below the longwall. Fault plane solutions of typical events are consistent with steeply dipping fracture planes parallel to the longwall face and nearly vertical dislocation in direction towards the goaf. We also derive an empirical relation for the decay of ground velocity with epicenter distance and compare maximum observed ground velocity to local magnitude. This is of considerable public interest because about 30 events larger than M L C 1.2 are felt each month by people living in the mining regions. Our relations, for example, indicate that an event in Hamm with a peak ground velocity of 6 mm/s which corresponds to a local magnitude M L between 1.7 and 2.3 is likely to be felt within about 2.3 km radius from the event.

SUMMARYEarthquake ruptures and seismic sequences can be very complex, involving slip in various directions on surfaces of variable orientation. How is this geometrical complexity in seismic energy release, here called mechanism complexity, governed by tectonic stress? We address this question using a probabilistic model for the distribution of double couples that is consistent with three assumptions commonly used in regional stress inversions: the tectonic stress is constant, slip vectors are aligned with the maximum shear traction in the plane of slip, and higher shear traction promotes more seismic energy release. We characterize the moment-tensor field of a stress-aligned source process in terms of an ordered set of principal-stress directions, a stress shape factor R, and a strain-sensitivity parameter $\kappa $. The latter governs the dependence of the seismic moment density on the shear-traction magnitude and therefore parametrizes the seismic strain response to the driving st...

The distribution of seismic moment is of capital interest to evaluate earthquake hazard, in particular regarding the most extreme events. We make use of likelihood-ratio tests to compare the simple Gutenberg-Richter power-law distribution with two statistical models that incorporate an exponential tail: the so-called tapered Gutenberg-Richter and the truncated gamma, when fitted to the global CMT earthquake catalog. The outcome is that the truncated gamma model outperforms the other two models. If simulated samples of the truncated gamma are reshuffled in order to mimic the time occurrence of the order statistics of the empirical data, this model turns out to be able to explain the empirical data both before and after the great Sumatra-Andaman earthquake of 2004.

The Mw 7.7 2007 November 14 earthquake had an epicentre located close to the city of Tocopilla, at the southern end of a known seismic gap in North Chile. Through modelling of Global Positioning System (GPS) and radar interferometry (InSAR) data, we show that this event ruptured the deeper part of the seismogenic interface (30-50 km) and did not reach the surface. The earthquake initiated at the hypocentre and was arrested ∼150 km south, beneath the Mejillones Peninsula, an area already identified as an important structural barrier between two segments of the Peru-Chile subduction zone. Our preferred models for the Tocopilla main shock show slip concentrated in two main asperities, consistent with previous inversions of seismological data. Slip appears to have propagated towards relatively shallow depths at its southern extremity, under the Mejillones Peninsula. Our analysis of post-seismic deformation suggests that small but still significant post-seismic slip occurred within the first 10 d after the main shock, and that it was mostly concentrated at the southern end of the rupture. The post-seismic deformation occurring in this period represents ∼12-19 per cent of the coseismic deformation, of which ∼30-55 per cent has been released aseismically. Postseismic slip appears to concentrate within regions that exhibit low coseismic slip, suggesting that the afterslip distribution during the first month of the post-seismic interval complements the coseismic slip. The 2007 Tocopilla earthquake released only ∼2.5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500-km-long North Chile seismic gap.

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To understand the role of the co-seismic moment magnitude, M w , 9.1-9.3 Sumatra-Andaman Earthquake rupture mechanism on the severity of the Indian Ocean Tsunami, we used permanent Global Positioning System (GPS) data and carried out an analysis of co-seismic displacement and tsunami models. Tsunami modelling, validated against independent Jason-1 altimetry data and tsunami arrival time data as determined from tide gauges, was used to analyse the results of five co-seismic slip inversions, using GPS, seismicity and/or uplift data. In this way we determined the most likely slip distribution characterized by slip maxima of ∼ 20 m in the South and ∼20 m in the North. We used both the distribution and temporal evolution of the co-seismic slip as derived from the GPS data. We show that the ∼ 9 min propagation time of the rupture led to constructive interference of waves radiating first from the South and minutes later from the North, strengthening the tsunami in Southern India, Sri Lanka and Thailand. We conclude that the incorporation of permanent real-time GPS stations would represent a valuable component of future tsunami warning systems.

a great (M w 8.3) interplate thrust earthquake ruptured offshore Illapel, Chile, producing a 4.7-m local tsunami. The last major rupture in the region was a 1943 M S 7.9 event. Seismic methods for rapidly characterizing the source process, of value for tsunami warning, were applied. The source moment tensor could be obtained robustly by W-phase inversion both within minutes (Chilean researchers had a good solution using regional data within 5 min) and within an hour using broadband seismic data. Short-period teleseismic P wave back-projections indicate northward rupture expansion from the hypocenter at a modest rupture expansion velocity of 1.5-2.0 km/s. Finite-fault inversions of teleseismic P and SH waves using that range of rupture velocities and a range of dips from 16°, consistent with the local slab geometry and some moment tensor solutions, to 22°, consistent with long-period moment tensor inversions, indicate a 180-to 240-km bilateral along-strike rupture zone with larger slip northwest to north of the epicenter (with peak slip of 7-10 m). Using a shallower fault model dip shifts slip seaward toward the trench, while a steeper dip moves it closer to the coastline. Slip separates into two patches as assumed rupture velocity increases. In all cases, localized *5 m slip extends down-dip below the coast north of the epicenter. The seismic moment estimates for the range of faulting parameters considered vary from 3.7 9 10 21 Nm (dip 16°) to 2.7 9 10 21 Nm (dip 22°), the static stress drop estimates range from 2.6 to 3.5 MPa, and the radiated seismic energy, up to 1 Hz, is about 2.2-3.15 9 10 16 J.

Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.

Despite the surge of great earthquakes along subduction zones over the last decade and advances in observations and analysis techniques, it remains unclear whether earthquake complexity is primarily controlled by persistent fault properties or by dynamics of the failure process. We introduce the radiated energy enhancement factor (REEF), given by the ratio of an event's directly measured radiated energy to the calculated minimum radiated energy for a source with the same seismic moment and duration, to quantify the rupture complexity. The REEF measurements for 119 large [moment magnitude (M w ) 7.0 to 9.2] megathrust earthquakes distributed globally show marked systematic regional patterns, suggesting that the rupture complexity is strongly influenced by persistent geological factors. We characterize this as the existence of smooth and rough rupture patches with varying interpatch separation, along with failure dynamics producing triggering interactions that augment the regional influences on large events. We present an improved asperity scenario incorporating both effects and categorize global subduction zones and great earthquakes based on their REEF values and slip patterns. Giant earthquakes rupturing over several hundred kilometers can occur in regions with low-REEF patches and small interpatch spacing, such as for the 1960 Chile, 1964 Alaska, and 2011 Tohoku earthquakes, or in regions with high-REEF patches and large interpatch spacing as in the case for the 2004 Sumatra and 1906 Ecuador-Colombia earthquakes. Thus, combining seismic magnitude M w and REEF, we provide a quantitative framework to better represent the span of rupture characteristics of great earthquakes and to understand global seismicity.

Inversions of seismic body waves indicate that most large earthquakes involve spatial and temporal heterogeneity of the moment release, but seismic body waves usually lack sufficient bandwidth to constrain the long-period component of the radiation. Analysis of long-period surface waves and free oscillations can constrain the overall source duration and moment; however, most procedures assume simple trapezoidal or boxcar source-time histories, inconsistent with the body wave complexity. We find that source-time function complexity can affect long-period surface waves sufficiently to impact estimates of the source moment tensor, rupture duration and centroid depth. We present a procedure to objectively determine the long-period component of complex source-time functions in which we directly utilize results from body wave analysis. The method is applied to two great normal fault events of June 22, 1977 (Tonga, M,,=8.2) and August 19, 1977 (Indonesia, M,,=8.5). Standard long period analysis procedures underestimate the total slip duration in both cases. The overall source process times of both earthquakes are longer than 120 s. a self-consistent fashion. Our insufficient knowledge of propagation effects on shortperiod surface waves prevents complete resolution of earthquake source process using surface wave data alone. As a result, most long period analyses assume simple moment-rate function parameterizations in the form of boxcars (i.e. ramp dislocation functions) or trapezoids (i.e. Haskell source models), regardless Copyright 1989 by the American Geophysical Union. Paper number 89GL00377. 0094-8276/89/8 9GL-003775 03. O0 of any complexities required by the body wave radiation [e.g.,