Sensitivity of stress inversion of focal mechanisms to. Paper in jgr on improved stress tensor inversion from focal. A new method of seismotectonic stress inversion especially designed for sets of focal mechanisms of earthquakes was described in angelier j. The results of this control study show that focal mechanisms can be inverted to find the best stress tensor, but the resolution is.
Stressinverse is a matlab or python software package for an iterative joint inversion for stress and fault orientations from focal mechanisms. The estimate for hr is more robust and produces a bias toward the stress rate of approximately 40%. To perform stress tensor inversion, a number of focal mechanisms with. Hybrid focal mechanism determination of induced seismicity. A userfriendly interface is provided by the faultkin software, while.
Folding a highamplitude folding simulations program for dos written by kenneth cruikshank at portland state university in oregon journal of structural geology 15. Stress field characterisation in nickel rim south mine. Pore pressure and retrieved r are negatively correlated when r is. An example of the improvement and increased stability of stacked solutions compared to one stress.
The use of the combined sets of information places a better constraint on focal mechanisms than can be obtained from either of the individual datasets. When cff exceeds a critical value, failure occurs on the plane. Software to download usgs earthquake hazard program. Satsi spatial and temporal stress inversion is a modified version of michaels. A methodology for unstructured damped stress inversion of. 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. Working on a large catalog of focal mechanisms determined by the icelandic meteorological office imo, we used a damped regionalscale stress inversion method to obtain an insight of kilometric variations of the stress field.
Frontiers volcanotectonic interactions revealed by. Spatiotemporal changes in the local stress field have been reported at many volcanoes through stress inversion andor by examining the p and t axes of focal mechanism solutions 12,14,15,16. The focal mechanism is based on the first motion of. The software that was used for this purpose was an updated version of simulps12. Introduction the active deformation of iranian plateau is. Aug 24, 2012 focal mechanisms are released after an earthquake to show what type of earth movement produced the earthquake. Fmcearthquake focal mechanisms data management, cluster and. To address this issue, we modified the algorithm to solve for stresses on an irregular. In this analysis, we used regional stress data and wellhead pressure during stimulation. To determine the relationships of the focal mechanism solutions to the regional stress field, we estimated the regional stress pattern around mt.
A refined methodology for stress inversions of earthquake focal mechanisms. 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. Focal mechanisms and stress field in the nobi fault area. Determining the stress field in active volcanoes using focal. 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. We develop an improved methodology for reliable highresolution inversions of focal mechanisms to background stress field orientation and stress ratio r. The method used in this study is satsi spatial and temporal stress inversion developed by hardebeck and michael 2006, which is a modified version of michaels code. Abstract stress inversions from focal mechanisms require knowledge of which nodal plane is the fault. Community stress model csm southern california earthquake.
In theory, four independent focal mechanisms are sufficient to determine the four unknowns of a reduced stress tensor, as discussed in section 7. Current methodologies for stress inversion from microseismic focal mechanisms require the assignment of events to a regular grid and then solving for the stress state at each grid node. Besides its capacities for data storage and management. Resolving the tectonic stress by the inversion of earthquake focal. Current crustal deformation of the taiwan orogen reassessed by cgps strainrate estimation and focal mechanism stress inversion sean kuanhsiang chen. Moment tensor and stress inversion for an active fault. We used the msatsi software package to apply a damped inversion of the stress field. Iterative joint inversion for stress and fault orientations. Department of geosciences, national taiwan university, no. Stress field in tunisia from focal mechanisms 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. The focal mechanism of an earthquake is represented by a beachball diagram.
We study internal deformation of the taiwan orogen, a young arccontinental. Source positions were created by using a singlesource inversion and a gridsearch method computed to optimize the waveform match. In the best case, 80% of the focal mechanisms that are consistent with the first motion data were removed because they were inconsistent with the stress data. The focal mechanism is based on the first motion of the pwave arrival. We investigate the sensitivity of stress inversion from focal mechanisms to pore pressure changes. Simulated focal mechanisms are made from slickenside data and used to provide a control study for the focal mechanism inversion algorithms. This difficult concept is carefully explained using strikeslip, normal, and thrust faults.
Adaptation of the multiple inverse method to focal mechanism data is explained as follows. The focal mechanisms were retrieved from the regional momenttensor inversion for the mainshock and using the pwave polarities for the corresponding aftershocks of mw. A refined methodology for stress inversions of earthquake focal. Depending on the distribution and quality of firstmotion data, more than one focal mechanism solution may fit the data equally well. The matlab code needs just the matlab kernel and no toolboxes are required. Stress tensor inversion inversion of earthquake focal mechanisms to determine the stress orientation and the stress ratio is a wellestablished technique e. The program requires as input a gis point dataset of earthquake locations containing strike, dip. The clustering analysis of focal mechanism populations has also been explored, but again, no specific software has been developed. Tector tectonic analysis and stress inversion of 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. Our model to create heterogeneous focalmechanism orientations contrasts with the stress model used by many previous studies of focalmechanism statistics. Abou elenean and others published focal mechanism and stress tensor inversion of earthquakes at and around nasser lake, egypt find, read and cite all the research you. The tector xxi softwares, including dedicated analyses of focal mechanisms. Spatialtemporal analysis of the stress field derived from seismological datasets associated to a continuous recording of ground. Pdf sensitivity of stress inversion of focal mechanisms to. 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. A refined methodology for stress inversions of earthquake.
This file contains focal mechanism data divided arbitrarily into 27 temporal divisions in the formal documentation of msatsi package presented in this documentation the term division is referred as grid point containing 70 seismic focal mechanisms. In contrast to usual standard procedures, this paper aims to justify the focal mechanism results as much as possible using various qualityassessments applied both to input data and output. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. Monitoring eruption activity using temporal stress changes. Focal mechanism, isola, moment tensor inversion, stress inversion, strikeslip faulting. A crucial aspect in the inversion of fault slip data or earthquake focal mechanisms is the number of data required in the inversion. A matlab package for stress inversion combining solid classic methodology, a new simplified user handling, and a visualization tool by patricia martinezgarzon, grzegorz kwiatek, michele ickrath, and marco bohnhoff online material. For each earthquake sequence, the principal stress orientations are combined with. This approach can lead to irregularities in the solution because some nodes may contain few or even no events. Focal mechanisms are derived from a solution of the moment tensor for the earthquake, which itself is estimated by an analysis of observed seismic waveforms.
If the numbers of focal mechanism are still below the threshold, the grid nodes will be excluded from the 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. Corresponding python code requires matplotlib, numpy, scipy and os modules. Paper in jgr on improved stress tensor inversion from focal mechanism grzegorz 18 february 2017 publications another article related to stress tensor inversion has been published in jgr.
It uses an adaptive smoothing method that discriminates between variations that are or arent. Jun 17, 2010 in order to produce a regional scale model of stress orientation, we applied a stress tensor inversion method to the focal mechanism solutions obtained by the hash technique. Determination of stresses from heterogeneous focal mechanism. A new paradigm for interpreting stress inversions from. A new method is proposed to separate stresses from earthquake focal mechanism data double couple component of focal mechanisms from spatially or temporarily varying state of stress.
May 23, 2014 volcanotectonic processes in the central part of iceland, covered by the vatnajokull glacier, are investigated by inversion of focal mechanisms. Stress orientations in the fort worth basin, texas. Multiple inverse method software package november 3, 2011 atsushi yamaji, katsushi sato. In these previous studies, stress is assumed to be approximately homo. The deviatoric moment tensor inversion was used for focal mechanism calculations. The software and synthetic focal mechanism catalogs used in this. The aftershock decay was very fast, and the focal mechanism of the strongest event with magnitude of 4. Pdf focal mechanism and stress tensor inversion of.
First, we estimate all possible fpss from pwave first motion observed at ms network fig. 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. Suppose that we have n earthquake focal mechanism data, but we do not know which of the two nodal planes for each focal mechanism is the fault fig. Focal mechanisms are released after an earthquake to show what type of earth movement produced the earthquake. In order to produce a regional scale model of stress orientation, we applied a stress tensor inversion method to the focal mechanism solutions obtained by the hash technique. Gifs for select segments included as optional download. Because focal mechanisms have fault plane ambiguity, an additional criterion is needed to select the fault planes used in the inversion. Next, regional stress data is used to calculate critical pore pressure cpp for arbitrary fpss. A new paradigm for interpreting stress inversions from focal.
Then, the range of possible focal mechanisms estimated from available first motion data is constrained by superposing the range of focal mechanisms that can slip from the insitu stress condition. The averages of the azimuths of the p and taxes were n97 23 e and n6 32 e, and the averages of the dips of the p and taxes were 11 10 and 32 25, respectively. The coulomb stress, also referred to as coulomb failure function, is given by. Synthetic tests reveal that pore pressure variations can cause apparent changes in the retrieved stress ratio r relating the magnitude of the intermediate principal stress with respect to the maximum and minimum principal stresses. In this study, we obtained 728 focal mechanisms of small earthquakes with depths shallower than 20 km that occurred from may 2009 to may 20 in the nobi fault area in central japan.
Focal mechanism known as fault plane solution in the case of fault slip related events and seismic moment tensor inversion are the most frequently used techniques for seismic stress inversion. Keywords, microearthquakes, focal mechanism, stress inversion, seismotectonics. Msatsi is a matlab software package that allows performing the stress inversion using earthquake focal mechanisms. We display the numbers within each grid cell in fig. If the spatial mean stress and the stress rate are not aligned, the average focal mechanism failure mechanism should yield a stress estimate from stress inversions, approximately halfway between the two.
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 program tensor is an interactive software for tectonic stress determination from geological faultslip and earthquake focal mechanisms data in structural geology, neotectonic and seismotectonic investigations. Focal mechanisms pacific northwest seismic network. Iterative joint inversion for stress and fault orientations from focal mechanisms. Schematic picture illustrating the underlying philosophy of the present method based on the multiple. Monitoring eruption activity using temporal stress changes at. Two possible perpendicular fault planes for mechanisms calculated from firstmotion directions as well as some methods that model waveforms, there is an ambiguity in identifying the fault plane on which slip. Determination of stresses from heterogeneous focal. Analyses of the stress field in southeastern france from. An analysis of a moderate earthquake, eastern flank of the.
Calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor, geophys. Jun 25, 2015 in this study, we obtained 728 focal mechanisms of small earthquakes with depths shallower than 20 km that occurred from may 2009 to may 20 in the nobi fault area in central japan. Paper in jgr on improved stress tensor inversion from. Spatiotemporal changes in the local stress field have been reported at many volcanoes through stress inversion andor by examining the p and t. Since the fault plane ambiguity in focal mechanisms may bias the retrieved stress ratio vavrycuk, 2015, the. The focal mechanism can be derived from observing the pattern of first motions, that is, whether the first arriving p waves break up or down. The present method is based on the multiple inverse method, makes use of a resampling technique. Mar 06, 2019 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. If such information is missing, and faults and auxiliary nodal planes are interchanged, the stress inversions can produce inaccurate results.
Sensitivity of stress inversion of focal mechanisms to pore. The inversion finds the least complex stress field model that is consistent with the data. Volcanotectonic interactions revealed by inversion of focal. The main differences between existing stress inversion methods are related to the inversion algorithm and handling the fault plane ambiguity. An implicit assumption in these studies is that earthquakes are good random samplers of stress. We develop an improved methodology for reliable highresolution inversions of focal mechanisms to. Fmcearthquake focal mechanisms data management, cluster. This tool operates within the environmental systems research institute esri gis software arcscene 9. These are released after an earthquake to illustrate the type of faulting produced the earthquake. Current crustal deformation of the taiwan orogen reassessed.