A refined methodology for stress inversions of earthquake focal mechanisms. The softwares straightforward interactive and intuitive approach to stress analysis makes it especially useful in the classroom. The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. Iterative joint inversion for stress and fault orientations from focal mechanisms.
Cisternasthe inverse problem in microtectonics and the separation of tectonic phases. Spatial distribution and focal mechanisms of aftershocks. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. It uses an adaptive smoothing method that discriminates between variations that are or arent. A high amplitude folding simulations program for dos written by kenneth cruikshank at portland state university in oregon journal of structural geology. New insights into structural interpretation and modelling d. A new paradigm for interpreting stress inversions from. Interseismic crustal deformation in the taiwan plate. However, the development of the program is finished and the application is not support. Tector tectonic analysis and stress inversion of fault slips, brittle structures and earthquake mechanisms. An updated database of focal mechanisms has been compiled by selecting 2 global centroid moment tensor solutions and by adding the 173 new solutions 3. Satsi spatial and temporal stress inversion is a modified version of. Earthquakes focal mechanism and stress field pattern in. Faultkin, a computer program for the analysis of fault slip data marret and.
A fortran program for inverting faultslickenside and. Inversion of earthquake focal mechanisms to obtain the. Requests for stress maps will be sent to our server for further processing. As outlined in the introduction, many studies about the stress state of the lmsfz have been done by using in situ stress data and focal mechanism solution data, based on which various segmentation schemes were proposed e. The resolution can also be increased by including constraints on the magnitude of.
Origin and main features of the tector software system. Inversion of a mechanism is obtained by fixing different links of the mechanism, one at a time. An analysis of a moderate earthquake, eastern flank of the. A refined methodology for stress inversions of earthquake focal. Two new seismographs coleyville cvj and negril nej were installed in central and westernmost jamaica in 2001 and 2002. A new method of seismotectonic stress inversion especially designed for sets of focal mechanisms of earthquakes was described in angelier j. Spatialtemporal analysis of the stress field derived from seismological datasets associated to a continuous recording of ground. Abstract stress inversions from focal mechanisms require knowledge of which nodal plane is the fault. The results of this control study show that focal mechanisms can be inverted to find the best stress tensor, but the resolution is decreased unless the fault planes can be picked a priori. Spatiotemporal changes in the local stress field have been reported at many volcanoes through stress inversion andor by examining the p and t.
The aftershock decay was very fast, and the focal mechanism of the strongest event with magnitude of 4. The inversion results show that the average misfit is small enough to satisfy the assumption of homogeneity in the focal mechanism data and that the 95% confidence regions of. Software to download usgs earthquake hazard program. The jamaica seismograph network jsn consists of 12 shortperiod seismograph stations and is fully described in wigginsgrandison 2001. It allows kinematic separation of faultslip and focal mechanism data together with progressive stress tensor optimisation. Numerical tests show that the new iterative stress inversion is fast and accurate and performs.
This method is based on the slip shear stress component sssc criterion. Seismic moment tensor is powerful tool which provides. Corresponding python code requires matplotlib, numpy, scipy and os modules. The inversion computes a mean bestfitting deviatoric stress tensor from a set of fault slip vectors by minimizing the angular deviation between a predicted slip vector maximum shear. The program requires as input a gis point dataset of earthquake. The inversion technique scheme is used also in the present study for determining the regional stress. Fitting waveform envelopes to derive focal mechanisms of. For calculation of focal mechanisms, i recommend to have a look into the foci software package. Unpack downloaded version of msatsi to some directory.
This site is intended to provide online support for the dissemination of the tensor software for fault kinematic analysis and stress tensor inversion in structural geology and tectonophysics. Stress tensor inversion from fault kinematic indicators and focal mechanism data. The stress estimates obtained by the focal mechanism. In the case of a faultrelated event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a faultplane solution. Current stress studies often utilize stress inversions of earthquake focal mechanisms to estimate four parameters of the spatially uniform stress tensor, three principal stress orientations, and a ratio of the principal stresses. The results of this control study show that focal mechanisms can be inverted to find the best stress tensor, but the resolution is. The role of stress transfer in earthquake occurrence. Stress inversion of earthquake focal mechanism solutions from. This method may be of interest to seismologists who need to compute focal mechanisms for stress. Multiple inverse method software package november 3, 2011 atsushi yamaji, katsushi sato. Pdf resolving the tectonic stress by the inversion of earthquake. Crustal earthquake focal mechanisms are investigated in the southeastern margin of the tibetan plateau, where the tibetan plateau and stable south china block merge.
The focal mechanisms were binned in 3d, in cubes of 2, 4, 8, 16, or 32 km on a side, depending on the spatial density of the data. The inversion finds the least complex stress field model that is consistent with the data. Spatially andor temporally varying stress field from focal mechanisms. Investigate coulomb stress changes on mapped faults and earthquake nodal planes. Fmsithe focal mechanism stress inversion program for the macintosh written by john gephart at the institute for the study of the continents instoc in ithaca, new york. I claim that the downloaded software will be used for noncommercial purposes. Msatsi is a matlab software package that allows performing the stress inversion using. For focal mechanism solutions of double couple type without any choice between nodal planes, the fastest analytical method resembles the former invgli program of tector 2000 absent in tector 1994. Monitoring eruption activity using temporal stress changes. The common method to obtain reliable focal mechanisms of observed microseismic events is decomposing of the full moment tensor.
Some sources of focal mechanism data in progress a focal mechanism plottercalculator. Extensive filtering has been applied to the seismic data to improve the quality, and for the stress inversion process the first motion stress inversion motsi software is used. To obtain a detailed in situ stress field, we use the msatsi software package martinezgarzon et al. We created a new tool, 3d focal mechanisms 3dfm, for viewing earthquake focal mechanism symbols three dimensionally. Satsi spatial and temporal stress inversion is a modified version of michaels jgr 1984, 1987 code that inverts focal mechanism data for a spatially andor temporally varying stress field. A comprehensive compilation of 112 earthquake focal mechanism solutions in norway and. Full version of the application is available for download using the link below. Geological society, london, special publications, 212. Use of the remaining stations fails to provide the true mechanism through waveform inversion, but a correct estimate of the solution is found using envelopes.
Pdf resolving the tectonic stress by the inversion of. To perform stress tensor inversion, a number of focal mechanisms with. Paper in jgr on improved stress tensor inversion from. As there is no need to store the data in memory, the space required by the program is small. Mech application works under 32bit versions of microsoft windows 2000xpvista.
A refined methodology for stress inversions of earthquake. Pdf sensitivity of stress inversion of focal mechanisms. Characteristics of focal mechanisms and the stress field. Analyses of the stress field in southeastern france from. They revealed that aftershocks with similar focal mechanisms to that of the mainshock were distributed to the northeast of the mainshock and this aftershock area did not overlap with the coseismic. This combination of sensors results in a large catalogue of events with good focal sphere coverage that permits source mechanism analyses to be performed. Earthquake focal mechanism gps we use gpsderived surface velocities, seismicity, as well as estimates of earthquake focal mechanisms from the time period before the 1999 chichi earthquake to evaluate spatial variations of surface strain rate and crustal stress regime in the taiwan plate boundary zone. Subsurface structure and spatial segmentation of the. Folding a highamplitude folding simulations program for dos written by kenneth cruikshank at portland state university in oregon journal of structural geology 15. After downloading executable tector 1994 programs, the user can enter his. Presentday tectonic regime and stress patterns from the. An implicit assumption in these studies is that earthquakes are good random samplers of stress. The satsi spatial and temporal stress inversion method of hardebeck and michael jgr, 2006 was used to invert the focal mechanism dataset of yang, hauksson, and shearer bssa, 2012 for stress orietation.
Comparison of solutions for microseismic focal mechanism. In tector xxi like in tector 2000, tensor include two approaches for stress inversion. The focal mechanism stress inversion program for the macintosh written by john gephart at the institute for the study of the continents instoc in ithaca, new york. A fortran program for inverting faultslickenside and earthquake focal mechanism data to obtain the regional stress tensor. Simulated focal mechanisms are made from slickenside data and used to provide a control study for the focal mechanism inversion algorithms. Crustal stress field in southern california and its. In particular, aftershocks are strongly influenced by the stress transfer from. If such information is missing, and faults and auxiliary nodal planes are interchanged, the stress inversions can produce inaccurate results.
The deviatoric moment tensor inversion was used for focal mechanism calculations. The global cmt catalog appears to be available from. The number of inversions for a mechanism is equal to the number of links in the mechanism. We develop an improved methodology for reliable highresolution inversions of focal mechanisms to. Online copy the first reference to the tensor program is an abstract presented at the egu in 1993. Casmo creates maps with the available stress orientations of any geographical region. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an. The joint inversion of ground deformation and focal mechanism is more efficient than the mere comparison of the results obtained by the separate inversion segall, 20. The focal mechanisms were retrieved from the regional momenttensor inversion for the mainshock and using the pwave polarities for the corresponding aftershocks of mw.
However, in most cases either the wenchuan or the lushan earthquake sequence was. Introduction casmo is a webbased html form that allows the user to create own stress maps using the data of the wsm database. Matlab package for stress inversion from focal mechanisms. The results of the stress tensor using focal mechanisms of recent. Source positions were created by using a singlesource inversion and a gridsearch method computed to optimize the waveform match. Full moment tensor inversion software, 1, 10312018, publicly accessible.
1095 713 779 1180 1025 1008 35 1038 1170 34 425 790 635 788 283 1145 986 1484 87 117 890 881 1366 704 592 811 1078 600 1275 252 840 1206 1494 995 1388 708 1428 338 56 60 1395