Microearthquake location: A nonlinear approach that makes use of a simplex stepping procedure

1988 ◽  
Vol 78 (2) ◽  
pp. 799-815
Author(s):  
Arnfinn F. Prugger ◽  
Don J. Gendzwill
Keyword(s):  
Least Squares ◽  
Velocity Structure ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Simplex Algorithm ◽  
Earthquake Location ◽  
Small Computer ◽  
Monitoring Systems ◽  
Nonlinear Approach ◽  
Direct Iteration

Abstract We present an earthquake location scheme that uses the simplex algorithm in the solution. This method of direct iteration is conceptually simple, does not require derivative calculations, and avoids matrix inversions. The algorithm can be programmed on a small computer and its performance compares favorably with other methods of earthquake location. The method can be used for any velocity structure for which source to geophone times can be calculated. We use a horizontally layered velocity model, and consider both critically and noncritically refracted rays. It is easy to incorporate any time residual misfit norm into the location calculation. We generally use the L1 or L2 (least-squares) norm. The routine we present is used in two different microseismic monitoring systems at two potash mines in Saskatchewan, Canada.

Velocity calibration for microseismic monitoring: A very fast simulated annealing (VFSA) approach for joint-objective optimization

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCB47-WCB55 ◽  
Author(s):  
Donghong Pei ◽  
John A. Quirein ◽  
Bruce E. Cornish ◽  
Dan Quinn ◽  
Norman R. Warpinski
Keyword(s):  
Simulated Annealing ◽  
Velocity Structure ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
S Wave ◽  
Wave Velocities ◽  
Very Fast Simulated Annealing ◽  
Occam’S Inversion ◽  
Synthetic Test ◽  
Ray Parameter

To accurately locate microearthquakes that are genetically related to hydraulic fracture stimulation, a thorough knowledge of the velocity structure between monitoring and fracturing treatment wells is essential. Very fast simulated annealing (VFSA) is implemented to invert for a flat-layered velocity model between wells using perforation or string-shot data. A two-point ray-tracing method is used to find the ray parameter [Formula: see text] for a ray traveling from a source to a receiver. The original traveltime-calculation formula is modified to account for the borehole source-receiver geometry. VFSA is used as a tool to optimize P- and S-wave velocities simultaneously. Unlike previous applications of VFSA, two improvements result from a new study: (1) both P- and S-wave arrival-time misfits are considered in a joint-objective function, and (2) P- and S-wave velocities are perturbed simultaneously during annealing. The inverted velocities follow the true values closely with a very small root-mean-square error, indicating the inverted model is close to the global minimum solution whose rms error should be zero for synthetic examples. Data noise contaminates inverted models, but not substantially in synthetic test results. A comparison of models inverted using VFSA and Occam’s inversion technique indicates that inverted models using VFSA are superior to those using Occam’s method in terms of velocity accuracy.

Transdimensional simultaneous inversion of velocity structure and event locations in downhole microseismic monitoring

Geophysics ◽  
2021 ◽  
pp. 1-92
Author(s):  
Xingda Jiang ◽  
Wei Zhang ◽  
Hui Yang ◽  
Chaofeng Zhao ◽  
Zixuan Wang
Keyword(s):  
Hydraulic Fracturing ◽  
Velocity Structure ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Location Accuracy ◽  
Simultaneous Inversion ◽  
Velocity Models ◽  
Effective Velocity ◽  
Number Of Layers ◽  
Event Location

In downhole microseismic monitoring, the velocity model plays a vital role in accurate mapping of the hydraulic fracturing image. For velocity model uncertainties in the number of layers or interface depths, the conventional velocity calibration method has been shown to effectively locate the perforation shots; however, it introduces non-negligible location errors for microseismic events, especially for complex geological formations with inclinations. To improve the event location accuracy, we exploit the advantages of the reversible jump Markov chain Monte Carlo (rjMCMC) approach in generating different dimensions of velocity models and propose a transdimensional Bayesian simultaneous inversion framework for obtaining the effective velocity structure and event locations simultaneously. The transdimensional inversion changes the number of layers during the inversion process and selects the optimal interface depths and velocity values to improve the event location accuracy. The confidence intervals of the simultaneous inversion event locations estimated by Bayesian inference enable us to evaluate the location uncertainties in the horizontal and vertical directions. Two synthetic examples and a field test are presented to illustrate the performance of our methodology, and the event location accuracy is shown to be higher than that obtained using the conventional methods. With less dependence on prior information, the proposed transdimensional simultaneous inversion method can be used to obtain an effective velocity structure for facilitating highly accurate hydraulic fracturing mapping.

Wave conversions from earthquakes and a new velocity model for the South Carolina coastal plain

1987 ◽  
Vol 77 (6) ◽  
pp. 2143-2151
Author(s):  
Susan Rhea
Keyword(s):  
Surface Layer ◽  
South Carolina ◽  
Coastal Plain ◽  
Velocity Structure ◽  
Velocity Model ◽  
Seismogenic Fault ◽  
Impedance Boundary ◽  
High Impedance ◽  
Hypocentral Parameters ◽  
Converted Phases

Abstract Phase conversions from P to SV and from SV to P occur at a high impedance boundary near the surface in Charleston, South Carolina. Four arrivals (P, converted P, converted S, and S) are observed on three-component records of earthquakes in this area. Using arrival-time differences between paired arrivals of direct and converted phases, a shallow surface layer Vp/Vs ratio of 2.9 was determined. Applying the Wadati method to travel times derived at the base of the surface layer yields a Vp/Vs ratio in deeper layers of 1.73. Relocating earthquakes using this more appropriate velocity structure for direct and converted shear waves alters hypocentral parameters such that epicenters diverge and depths converge. It is inferred that these relocated earthquakes are not exclusively associated with a single seismogenic fault.

Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes

1991 ◽  
Vol 81 (2) ◽  
pp. 508-523
Author(s):  
Jim Mori
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
P Wave ◽  
Sediment Layer ◽  
Source Depth ◽  
Imperial Valley ◽  
P Waves ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Event Record

Abstract Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley, California. The relative timing of these arrivals is used to estimate the strength of the P-wave velocity gradient within the upper 5 km of the sediment layer. Consistent with previous studies, a velocity model with a value of 1.8 km/sec at the surface increasing linearly to 5.8 km/sec at a depth of 5.5 km fits the data well. The relative amplitudes of the P and PP arrivals are used to estimate the source depth for the aftershock distributions of the Elmore Ranch and Superstition Hills main shocks. Although the depth determination has large uncertainties, both the Elmore Ranch and Superstition Hills aftershock sequences appear to have similar depth distribution in the range of 4 to 10 km.

scholarly journals Characteristics of local earthquake seismograms of varying dislocation sources in a stratified upper crust and modeling for P and S velocity structure: comparison with observations in the Koyna-Warna region, India

2016 ◽  
Vol 58 (6) ◽  
Author(s):  
V. G. Krishna
Keyword(s):  
Velocity Structure ◽  
Source Parameters ◽  
Velocity Model ◽  
Strike Slip ◽  
Synthetic Seismograms ◽  
Structure Comparison ◽  
Earthquake Sources ◽  
Crustal Velocity ◽  
Source Mechanisms ◽  
Local Earthquake

<p>Vertical component record sections of local earthquake seismograms from a state-of-the-art Koyna-Warna digital seismograph network are assembled in the reduced time versus epicentral distance frame, similar to those obtained in seismic refraction profiling. The record sections obtained for an average source depth display the processed seismograms from nearly equal source depths with similar source mechanisms and recorded in a narrow azimuth range, illuminating the upper crustal P and S velocity structure in the region. Further, the seismogram characteristics of the local earthquake sources are found to vary significantly for different source mechanisms and the amplitude variations exceed those due to velocity model stratification. In the present study a large number of reflectivity synthetic seismograms are obtained in near offset ranges for a stratified upper crustal model having sharp discontinuities with 7%-10% velocity contrasts. The synthetics are obtained for different source regimes (e.g., strike-slip, normal, reverse) and different sets of source parameters (strike, dip, and rake) within each regime. Seismogram sections with dominantly strike-slip mechanism are found to be clearly favorable in revealing the velocity stratification for both P and S waves. In contrast the seismogram sections for earthquakes of other source mechanisms seem to display the upper crustal P phases poorly with low amplitudes even in presence of sharp discontinuities of high velocity contrasts. The observed seismogram sections illustrated here for the earthquake sources with strike-slip and normal mechanisms from the Koyna-Warna seismic region substantiate these findings. Travel times and reflectivity synthetic seismograms are used for 1-D modeling of the observed virtual source local earthquake seismogram sections and inferring the upper crustal velocity structure in the Koyna-Warna region. Significantly, the inferred upper crustal velocity model in the region reproduces the synthetic seismograms comparable to the observed sections for earthquake sources with differing mechanisms in the Koyna and Warna regions.</p>

scholarly journals Travel Time Tomography to Delineate 3-D Regional Seismic Velocity Structure in the Banyumas Basin, Central Java, Indonesia, Using Dense Borehole Seismographic Stations

2021 ◽  
Vol 9 ◽  
Author(s):  
Hidayat Hidayat ◽  
Andri Dian Nugraha ◽  
Awali Priyono ◽  
Marjiyono Marjiyono ◽  
Januar H. Setiawan ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Crustal Layer ◽  
Central Java ◽  
Resolution Element ◽  
Passive Seismic ◽  
Dextral Strike Slip Fault ◽  
Southern Central ◽  
Well Data

The Banyumas Basin is a tertiary sedimentary basin located in southern Central Java, Indonesia. Due to the presence of volcanic deposits, 2-D seismic reflection methods cannot provide a good estimation of the sediment thickness and the subsurface geology structure in this area. In this study, the passive seismic tomography (PST) method was applied to image the 3-D subsurface Vp, Vs, and Vp/Vs ratio. We used 70 seismograph borehole stations with a recording duration of 177 days. A total of 354 events with 9, 370 P and 9, 368 S phases were used as input for tomographic inversion. The checkshot data of a 4, 400-meter deep exploration well (Jati-1) located within the seismic network were used to constrain the shallow crustal layer of the initial 1-D velocity model. The model resolution of the tomographic inversions was assessed using the checkerboard resolution test (CRT), the diagonal resolution element (DRE), and the derivative weight sum (DWS). Using the obtained Vp, Vs, and Vp/Vs ratio, we were able to sharpen details of the geological structures within the basin from previous geological studies, and a fault could be well-imaged at a depth of 4 km. We interpreted this as the main dextral strike-slip fault that controls the pull apart process of the Banyumas Basin. The thickness of the sediment layers, as well as its layering, were also could be well determined. We found prominent features of the velocity contrast that aligned very well with the boundary between the Halang and Rambatan formations as observed in the Jati-1 well data. Furthermore, an anticline structure, which is a potential structural trap for the petroleum system in the Banyumas Basin, was also well imaged. This was made possible due to the dense borehole seismographic stations which were deployed in the study area.

scholarly journals APPLICATION OF 3-D VELOCITY MODELS AND RAY TRACING IN DOUBLE DIFFERENCE EARTHQUAKE LOCATION ALGORITHMS: APPLICATION TO THE MYGDONIA BASIN (NORTHERN GREECE)

2004 ◽  
Vol 36 (3) ◽  
pp. 1396 ◽  
Author(s):  
O. C. Galanis ◽  
C. B. Papazachos ◽  
P. M. Hatzidimitriou ◽  
E. M. Scordilis
Keyword(s):  
Ray Tracing ◽  
Velocity Structure ◽  
Test Site ◽  
Earthquake Location ◽  
Double Difference ◽  
Northern Greece ◽  
Local Networks ◽  
Velocity Models ◽  
Earthquake Locations

In the past years there has been a growing demand for precise earthquake locations for seismotectonic and seismic hazard studies. Recently this has become possible because of the development of sophisticated location algorithms, as well as hardware resources. This is expected to lead to a better insight of seismicity in the near future. A well-known technique, which has been recently used for relocating earthquake data sets is the double difference algorithm. In its original implementation it makes use of a one-dimensional ray tracing routine to calculate seismic wave travel times. We have modified the implementation of the algorithm by incorporating a three-dimensional velocity model and ray tracing in order to relocate a set of earthquakes in the area of the Mygdonia Basin (Northern Greece). This area is covered by a permanent regional network and occasionally by temporary local networks. The velocity structure is very well known, as the Mygdonia Basin has been used as an international test site for seismological studies since 1993, which makes it an appropriate location for evaluating earthquake location algorithms, with the quality of the results depending only on the quality of the data and the algorithm itself. The new earthquake locations reveal details of the area's seismotectonic structure, which are blurred, if not misleading, when resolved by standard (routine) location algorithms.

Results of the downhole microseismic monitoring at a pilot hydraulic fracturing site in Poland — Part 1: Event location and stimulation performance

2018 ◽  
Vol 6 (3) ◽  
pp. SH39-SH48 ◽  
Author(s):  
Wojciech Gajek ◽  
Jacek Trojanowski ◽  
Michał Malinowski ◽  
Marek Jarosiński ◽  
Marko Riedel
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Anisotropy ◽  
Transverse Isotropy ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Baltic Basin ◽  
Hydraulic Stimulation ◽  
Lower Paleozoic ◽  
Event Location ◽  
Microseismic Events

A precise velocity model is necessary to obtain reliable locations of microseismic events, which provide information about the effectiveness of the hydraulic stimulation. Seismic anisotropy plays an important role in microseismic event location by imposing the dependency between wave velocities and its propagation direction. Building an anisotropic velocity model that accounts for that effect allows for more accurate location of microseismic events. We have used downhole microseismic records from a pilot hydraulic fracturing experiment in Lower-Paleozoic shale gas play in the Baltic Basin, Northern Poland, to obtain accurate microseismic events locations. We have developed a workflow for a vertical transverse isotropy velocity model construction when facing a challenging absence of horizontally polarized S-waves in perforation shot data, which carry information about Thomsen’s [Formula: see text] parameter and provide valuable constraints for locating microseismic events. We extract effective [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] for each layer from the P- and SV-wave arrivals of perforation shots, whereas the unresolved [Formula: see text] is retrieved afterward from the SH-SV-wave delay time of selected microseismic events. An inverted velocity model provides more reliable location of microseismic events, which then becomes an essential input for evaluating the hydraulic stimulation job effectiveness in the geomechanical context. We evaluate the influence of the preexisting fracture sets and obliquity between the borehole trajectory and principal horizontal stress direction on the hydraulic treatment performance. The fracturing fluid migrates to previously fractured zones, while the growth of the microseismic volume in consecutive stages is caused by increased penetration of the above-lying lithologic formations.

Velocity models for routine earthquake monitoring at volcanoes: from deterministic to Bayesian

2021 ◽  
Author(s):  
Jeremy Pesicek ◽  
Trond Ryberg ◽  
Roger Machacca ◽  
Jaime Raigosa
Keyword(s):  
Velocity Structure ◽  
Full Range ◽  
Earthquake Location ◽  
Monitoring Networks ◽  
Unknown Parameters ◽  
Widespread Application ◽  
Starting Values ◽  
Velocity Models ◽  
Earthquake Locations ◽  
Station Corrections

&lt;p&gt;Earthquake location is a primary function of volcano observatories worldwide and the resulting catalogs of seismicity are integral to interpretations and forecasts of volcanic activity.&amp;#160; Ensuring earthquake location accuracy is therefore of critical importance.&amp;#160; However, accurate earthquake locations require accurate velocity models, which are not always available.&amp;#160; In addition, difficulties involved in applying traditional velocity modeling methods often mean that earthquake locations are computed at volcanoes using velocity models not specific to the local volcano.&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;Traditional linearized methods that jointly invert for earthquake locations, velocity structure, and station corrections depend critically on having reasonable starting values for the unknown parameters, which are then iteratively updated to minimize the data misfit.&amp;#160; However, these deterministic methods are susceptible to local minima and divergence, issues exacerbated by sparse seismic networks and/or poor data quality common at volcanoes.&amp;#160; In cases where independent prior constraints on local velocity structure are not available, these methods may result in systematic errors in velocity models and hypocenters, especially if the full range of possible starting values is not explored.&amp;#160; Furthermore, such solutions depend on subjective choices for model regularization and parameterization.&lt;/p&gt;&lt;p&gt;In contrast, Bayesian methods promise to avoid all these pitfalls.&amp;#160; Although these methods traditionally have been difficult to implement due to additional computational burdens, the increasing use and availability of High-Performance Computing resources mean widespread application of these methods is no longer prohibitively expensive.&amp;#160; In this presentation, we apply a Bayesian, hierarchical, trans-dimensional Markov chain Monte Carlo method to jointly solve for hypocentral parameters, 1D velocity structure, and station corrections using data from monitoring networks of varying quality at several volcanoes in the U.S. and South America.&amp;#160; We compare the results with those from a more traditional deterministic approach and show that the resulting velocity models produce more accurate earthquake locations.&amp;#160; Finally, we chart a path forward for more widespread adoption of the Bayesian approach, which may improve catalogs of volcanic seismicity at observatories worldwide.&amp;#160;&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document