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NL2020684A - Mixed 2D seismic wave travel time calculation method - Google Patents

Mixed 2D seismic wave travel time calculation method Download PDF

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Publication number
NL2020684A
NL2020684A NL2020684A NL2020684A NL2020684A NL 2020684 A NL2020684 A NL 2020684A NL 2020684 A NL2020684 A NL 2020684A NL 2020684 A NL2020684 A NL 2020684A NL 2020684 A NL2020684 A NL 2020684A
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een
het
van
travel time
reistijd
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NL2020684A
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NL2020684B1 (en
Inventor
Sun Hui
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Univ Southwest Jiaotong
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
    • G01V1/30—Analysis
    • G01V1/303—Analysis for determining velocity profiles or travel times
    • G01V1/305—Travel times
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
    • G01V1/282—Application of seismic models, synthetic seismograms
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/67—Wave propagation modeling
    • G01V2210/671—Raytracing

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Management, Administration, Business Operations System, And Electronic Commerce (AREA)

Abstract

The invention discloses a mixed 2D seismic travel time calculation method comprising inputting relevant parameters and a velocity model; emitting rays in different directions and calculating the information of central rays; calculating the seismic travel time of grid nodes within the ray range by using the wave front construction method; classifying the travel time attributes of grid nodes in the computational area and establishing an initial narrow band; and calculating the seismic travel time of the rest grid nodes by fast marching method. The fast marching method is connected with the wave front construction method through narrow band technology. Seismic travel time calculation precision of a small area near the source is improved by the wave-front construction method. Calculation precision of grid nodes in the rest area is increased by the fast marching method. A 2D seismic travel time calculation method with calculation efficiency and calculation precision is realized.

Description

Mixed 2D seismic travel time calculation method
Technical Field
The present invention relates to the field of seismic travel time calculation, in particular to a mixed 2D seismic travel time calculation method.
Background Art
No. 3, 2009 of Chinese Journal of Engineering Geophysics published “Analysis and Improvement on Calculation Accuracy of Fast Marching Method” by Zhang Shuangjie et al, which introduces two methods for improving the calculation efficiency of the fast marching method: firstly, performing calculating by adopting a high order difference scheme; secondly, performing local precise treatment on grid nodes near the source, so that the high order difference scheme is used for calculation near the source and a low order difference scheme is used for calculation in the rest area. The two methods are also used for calculating the seismic travel time of the homogeneous models, and beneficial experimental results are obtained.
No. 3, 2016 of Global Geology published “Calculation of Fast Marching Method on Seismic Travel-Time Based on Complete Ternary Tree” by Wang Qianlong et al, which introduces an improved fast marching method for calculating seismic travel time. By introducing a complete ternary tree heap sorting method into seismic travel time calculation, the improved method reduces the time to find the minimum travel time in narrow band extension and improves the calculation efficiency of the whole calculation method. Besides, the fast marching method for calculating seismic travel time based on a complete ternary tree is used to calculate the layer model, Mamiousi model and Sigsbee 2a models, and beneficial experimental results are obtained.
As seen from the above examples, although through the fast marching method for calculating seismic travel time, the calculation accuracy can be improved to a certain extent, the realization process is complicated and improvement on the calculation accuracy is also limited.
Summary
The present invention aims to solve the technical problem of providing a mixed 2D seismic travel time calculation method by which a wave front construction method for calculating seismic travel time is seamlessly connected with a fast marching method for calculating seismic travel time together by flexibly using the narrow band technology, namely that the wave front constaiction method with high calculation accuracy is used in a small area near the source, and the fast marching method is used in the rest area to calculate the travel time. While the calculation accuracy of the new method is improved, the high efficiency is still remained.
In order to solve the technical problem, the present invention adopts the technical scheme: 1. a mixed 2D seismic travel time calculation method, comprising the following steps of: step 1: inputting a relevant parameter document and a velocity model, wherein the parameter document contains the grid node number, the grid space and the source position of the velocity model; step 2: emitting rays in different directions from the source and calculating the information of central rays; step 3: calculating the travel time of grid nodes within the ray range by a wave front construction method; step 4: classifying all the grid nodes and dividing the grid nodes into accepted nodes, narrow-band nodes or far-away nodes, namely that if the seismic travel time of one grid node is calculated and all the travel time of surrounding grid nodes is calculated already, then the node is a accepted node, if the seismic travel time of one grid node is calculated but not all the travel time of surrounding grid nodes is calculated, then the node is a narrow-band node, and if the travel time of one node is not calculated yet, the node is the far-away node; step 5: inserting all narrow-band nodes into the narrow band, and establishing an initial narrow band; and step 6: extending the narrow band until the narrow band is empty, wherein in the process, the travel time of the grid nodes is obtained by solving a 2D eikonal equation by the upwind difference method, and the 2D eikonal equation is as shown below: |Vzj = s wherein r is the seismic travel time, s is slowness, V is gradient, and the upwind difference expression of the gradient tenn in the formula is as shown below: wherein /.) 'r , D*Jt , Ayr and Af+"r are forward or backward difference expressions of travel time at the grid node (/, j) in an x or z direction respectively, and the concrete forms are
and
- respectively.
Further, in step 2, the kinematical ray tracing equations are solved by a Runge-Kutta method to get the information of central rays, as shown below:
wherein x, represents spatial position, /r represents slowness, r represents seismic travel time, and v represents the velocity value at a discrete node.
Compared with the prior art, the mixed 2D seismic travel time calculation method disclosed by the present invention has the beneficial effects that: because the seismic travel time calculation precision of grid nodes near the source is improved by the wave front construction method, the accuracy of the fast marching method for calculating grid nodes in the area is improved; and the calculation precision of the whole seismic travel time calculation method is greatly improved at the cost of reducing the calculation efficiency a little.
Brief Description of the Drawings
Fig. 1 shows the flow chart of the mixed 2D seismic travel time calculation method of the present invention.
Fig. 2 shows the schematic diagram of area division by the wave front construction method. Fig. 3 shows the relative error in a homogeneous medium by using the fast marching method. Fig. 4 shows the relative error in a homogeneous medium by using mixed seismic travel time calculation method.
Detailed Description
The invention will now be further described in detains in connection with the accompanying drawings and embodiments.
Fig. 1 shows the flow chart of the mixed 2D seismic travel time calculation method of the present invention. In the method, a reaction flow is shown, as shown below: step 1: inputting a relevant parameter document and a velocity model, wherein the parameter document contains the grid node number, the grid space and the source position; 2)emitting rays in different directions from a shot point and calculating the information of central rays, wherein the emission angle range of the rays is from -90 degrees to +90 degrees, the angle interval between every two adjacent rays is from 3 degrees to 10 degrees, and the kinematical ray tracing equations are solved by a Runge-Kutta method to get the information of central rays, as shown below:
wherein x. represents spatial position, p, represents slowness, τ represents seismic travel time, and v represents the velocity value at a discrete node. step 3: calculating the travel time of grid nodes within the ray range by a wave front construction method, wherein the area is divided into multiple trapeziums by adjacent wave front points on adjacent central rays in the calculation process, and the grid nodes in each trapezium are acquired by interpolating vertex information of the corresponding trapezium; step 4: after the wave front construction method is completed, performing attributive classification on all of the grid nodes and specifying that if the seismic travel time of one grid node is calculated and all the travel time of surrounding grid nodes is calculated already, then the node is a accepted node, if the seismic travel time of one grid node is calculated but not all the travel time of surrounding grid nodes is calculated, then the node is a narrow-band node, and if the travel time of one node is not calculated yet, the node is the far-away node; step 5: moving all narrow-band nodes into a narrow band, and establishing an initial narrow band; and step 6: extending the narrow band until the narrow band is empty, wherein in the process, the travel time of the grid nodes is obtained by solving a 2D eikonal equation by the upwind difference method, and the 2D eikonal equation is as shown below: |Vr| =5 wherein τ is the seismic travel time, s is slowness, V is gradient, and the upwind difference expression of the gradient term in the formula is as shown below:
wherein £Tjr, 1ϊ'χ;τ , ΙΤΛτ and Z)T2r are forward or backward difference expressions of travel time at the grid node (/, /) in an x or z direction respectively, and the concrete forms are
respectively.
The calculation accuracy and stability of the method in disclosed by the present invention will be analyzed and verified below through a homogeneous medium model.
Fig. 3 and Fig. 4 show the relative errors in the homogeneous medium model respectively by the fast marching method and the mixed seismic travel time calculation method, the size of the homogeneous model is 601*601, the grid space is 10m* 10m and the velocity is 1,000 m/s. The maximum length of a single tracked ray in the joint travel time method is 500m. As can be seen from the figure, the calculation precision of the mixed seismic travel time method is greatly improved than that of the fast marching method.
According to the mixed seismic travel time calculation method disclosed by the present invention, the fast marching method is connected with the wave front construction method through a narrow band technology, and the seismic travel time calculation accuracy in a small area near the source is improved by the wave front construction method, so that the accuracy of the fast marching method for calculating grid nodes in the rest area is improved, and a 2D seismic travel time calculation method considering the calculation efficiency and the calculation accuracy is realized.

Claims (2)

1. Een gemengde 2D seismische reistijd berekeningswerkwijze, met het kenmerk dat het de volgende stappen bevat: Stap 1: het invoeren van een relevant parameter document en een snelheidmodel, waarbij het relevante parameter document een roosterknooppunt nummer, een roosteraiime en de bronpositie bevat; Stap 2: het uitzenden van stralen in verschillende richtingen vanuit de bron en het berekenen van de informatie van centrale stralen Stap 3: berekenen van de reistijd voor roosterknooppunten binnen het straalbereik door middel van een golffront constructiewerkwijze Stap 4: classificeren van alle roosterknooppunten en het verdelen van de roosterknooppunten over geaccepteerde knooppunten, smalle-band knooppunten en ver-weg knooppunten, namelijk zo dat indien de reistijd voor een roosterknooppunt berekend ia en alle reistijden voor omringende roosterknooppunten ook reeds berekend zijn, dat dan het knooppunt een geaccepteerd knooppunt is, en indien de reistijd voor een roosterknooppunt berekend is maar nog niet alle reistijden voor omringende roosterknooppunten reeds berekend zijn, dat dan het knooppunt een smalle-band knooppunt is, en indien de reistijd voor een knooppunt nog niet berekend is, het knooppunt een ver-weg knooppunt is, Stap 5: in een smalle band stoppen van alle smalle-band knooppunten en het vaststellen van een initiële smalle band; en Stap 6: het uitwerken van de smalle band totdat de smalle band leeg is, waarbij in de werkwijze, de reistijd voor een roosterknooppunt verkregen wordt door het oplossen van een 2D eikonale vergelijking door een upwind difference werkwijze, en de 2D eikonale vergelijking is als hieronder weergegeven: |V t| = s waarin τ de seismische reistijd is, s de traagheid is, V de gradiënt is, and de upwind difference uitdrukking voor de gradiënt term in de formule is als hieronder getoond:
waarin D~*r, 1Χ·Τ, iXjr en Ι)Χτ forward en backward difference uitdrukkingen zijn van de reistijd op een roosterknooppunt (/, j) in een x of z richting respectievelijk, en de concrete
vormen respectievelijk zijn.
2. Een gemengde 2D seismische reistijd berekeningswerkwijze volgens conclusie 1, met het kenmerk, dat de kinematische straaltraceer vergelijkingen opgelost worden door een Runge-Kutta werkwijze om de centrale stralen te verkrijgen zoals hieronder getoond:
waarin x[ de ruimtelijk positie weergeeft, p, traagheid weergeeft, τ seismische reistijd weergeeft, en v de waarde voor de snelheid op een bepaald knooppunt weergeeft.
NL2020684A 2018-01-23 2018-03-29 Mixed 2D seismic wave travel time calculation method NL2020684B1 (en)

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CN115201901A (en) * 2022-06-30 2022-10-18 中铁第四勘察设计院集团有限公司 Method, device, device and readable storage medium for determining tunnel wavefront travel time

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CN108957538A (en) * 2018-06-21 2018-12-07 成都启泰智联信息科技有限公司 A kind of virtual focus two dimension wavefront construction seimic travel time calculation method
CN114398780B (en) * 2022-01-10 2025-09-23 应急管理部国家自然灾害防治研究院 Seismic imaging travel time data processing method and device
CN117194855B (en) * 2023-11-06 2024-03-19 南方科技大学 Fitting analysis method and relevant equipment for weak anisotropy travel time
CN117607957B (en) * 2024-01-24 2024-04-02 南方科技大学 Seismic wave travel time solving method and system based on equivalent slowness rapid propulsion method
CN118655616B (en) * 2024-06-11 2025-02-14 浙江大学海南研究院 A method, device, medium and product for determining travel time of seismic waves in three-dimensional medium

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NL2020684B1 (en) 2018-11-14

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