Source positions were created by using a singlesource inversion and a gridsearch method computed to optimize the waveform match. 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. The jamaica seismograph network jsn consists of 12 shortperiod seismograph stations and is fully described in wigginsgrandison 2001. Online copy the first reference to the tensor program is an abstract presented at the egu in 1993. To perform stress tensor inversion, a number of focal mechanisms with. Origin and main features of the tector software system. The softwares straightforward interactive and intuitive approach to stress analysis makes it especially useful in the classroom. As there is no need to store the data in memory, the space required by the program is small. 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. Simulated focal mechanisms are made from slickenside data and used to provide a control study for the focal mechanism inversion algorithms. The resolution can also be increased by including constraints on the magnitude of.
Interseismic crustal deformation in the taiwan plate. Stress inversion of earthquake focal mechanism solutions from. 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. Some sources of focal mechanism data in progress a focal mechanism plottercalculator. Monitoring eruption activity using temporal stress changes. The inversion finds the least complex stress field model that is consistent with the data. Spatial distribution and focal mechanisms of aftershocks.
Subsurface structure and spatial segmentation of the. Tector tectonic analysis and stress inversion of fault slips, brittle structures and earthquake mechanisms. Iterative joint inversion for stress and fault orientations from focal mechanisms. Pdf resolving the tectonic stress by the inversion of. It uses an adaptive smoothing method that discriminates between variations that are or arent. The aftershock decay was very fast, and the focal mechanism of the strongest event with magnitude of 4. Inversion of a mechanism is obtained by fixing different links of the mechanism, one at a time. Analyses of the stress field in southeastern france from. 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 results of the stress tensor using focal mechanisms of recent. Two new seismographs coleyville cvj and negril nej were installed in central and westernmost jamaica in 2001 and 2002. If such information is missing, and faults and auxiliary nodal planes are interchanged, the stress inversions can produce inaccurate results.
Presentday tectonic regime and stress patterns from the. 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. 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. A comprehensive compilation of 112 earthquake focal mechanism solutions in norway and. This method may be of interest to seismologists who need to compute focal mechanisms for stress. This method is based on the slip shear stress component sssc criterion.
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 deviatoric moment tensor inversion was used for focal mechanism calculations. Unpack downloaded version of msatsi to some directory. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an. Pdf resolving the tectonic stress by the inversion of earthquake. A fortran program for inverting faultslickenside and. Inversion of earthquake focal mechanisms to obtain the. Full version of the application is available for download using the link below. Satsi spatial and temporal stress inversion is a modified version of. In particular, aftershocks are strongly influenced by the stress transfer from. A high amplitude folding simulations program for dos written by kenneth cruikshank at portland state university in oregon journal of structural geology.
Casmo creates maps with the available stress orientations of any geographical region. Spatiotemporal changes in the local stress field have been reported at many volcanoes through stress inversion andor by examining the p and t. The pattern of presentday tectonic stress in nceib is controlled by the dynamics of the collision between the arabian and eurasian plates. After downloading executable tector 1994 programs, the user can enter his.
Investigate coulomb stress changes on mapped faults and earthquake nodal planes. Comparison of solutions for microseismic focal mechanism. Folding a highamplitude folding simulations program for dos written by kenneth cruikshank at portland state university in oregon journal of structural geology 15. I claim that the downloaded software will be used for noncommercial purposes. 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. 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. The number of inversions for a mechanism is equal to the number of links in the mechanism. 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. We develop an improved methodology for reliable highresolution inversions of focal mechanisms to. The role of stress transfer in earthquake occurrence. Spatially andor temporally varying stress field from focal mechanisms. The stress estimates obtained by the focal mechanism.
Geological society, london, special publications, 212. This combination of sensors results in a large catalogue of events with good focal sphere coverage that permits source mechanism analyses to be performed. 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 common method to obtain reliable focal mechanisms of observed microseismic events is decomposing of the full moment tensor. 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. 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. Seismic moment tensor is powerful tool which provides.
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. For calculation of focal mechanisms, i recommend to have a look into the foci software package. The global cmt catalog appears to be available from. The results of this control study show that focal mechanisms can be inverted to find the best stress tensor, but the resolution is. Full moment tensor inversion software, 1, 10312018, publicly accessible. 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. A refined methodology for stress inversions of earthquake focal mechanisms. 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 refined methodology for stress inversions of earthquake focal. Crustal stress field in southern california and its. Corresponding python code requires matplotlib, numpy, scipy and os modules. A refined methodology for stress inversions of earthquake. Software to download usgs earthquake hazard program. Paper in jgr on improved stress tensor inversion from. Matlab package for stress inversion from focal mechanisms.
Pdf sensitivity of stress inversion of focal mechanisms. New insights into structural interpretation and modelling d. An analysis of a moderate earthquake, eastern flank of the. Numerical tests show that the new iterative stress inversion is fast and accurate and performs. Requests for stress maps will be sent to our server for further processing. Characteristics of focal mechanisms and the stress field. Stress tensor inversion from fault kinematic indicators and focal mechanism data. Mech application works under 32bit versions of microsoft windows 2000xpvista. The focal mechanisms were retrieved from the regional momenttensor inversion for the mainshock and using the pwave polarities for the corresponding aftershocks of mw. The inversion technique scheme is used also in the present study for determining the regional stress. A new paradigm for interpreting stress inversions from. The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. 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. An implicit assumption in these studies is that earthquakes are good random samplers of stress.
However, in most cases either the wenchuan or the lushan earthquake sequence was. Abstract stress inversions from focal mechanisms require knowledge of which nodal plane is the fault. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. The matlab code needs just the matlab kernel and no toolboxes are required. The software and synthetic focal mechanism catalogs used in this work. To obtain a detailed in situ stress field, we use the msatsi software package martinezgarzon et al. Cisternasthe inverse problem in microtectonics and the separation of tectonic phases. 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. Stressinverse is a matlab or python software package for an iterative joint inversion for stress and fault orientations from focal mechanisms.
Introduction casmo is a webbased html form that allows the user to create own stress maps using the data of the wsm database. Multiple inverse method software package november 3, 2011 atsushi yamaji, katsushi sato. The program requires as input a gis point dataset of earthquake. Faultkin, a computer program for the analysis of fault slip data marret and. 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. We created a new tool, 3d focal mechanisms 3dfm, for viewing earthquake focal mechanism symbols three dimensionally.906 146 206 361 1413 823 392 1104 1215 1072 927 1217 1291 416 557 57 891 198 1198 244 449 570 939 346 79 474 1304 515 1094 100 16 644 992 571 65 889 232 784