stress and earthquakes in southern california 1850 2004 1 we compute the stress tensor in the upper crust of southern california as a function of time and compare observed seismicity with the estimated stress at the time of each earthquake several recent developments make it possible to do this much more realistically than before 1 a wealth of new geodetic and geologic data for southern california and 2 a catalog of moment tensors for all earthquakes with magnitudes larger than 6 since 1850 and larger than 5 since 1910 we model crustal deformation using both updated geodetic data and geologically determined fault slip rates we subdivide the crust into elastic blocks delineated by faults which move freely at a constant rate below a locking depth with a rate determined by the relative block motion we compute normal and shear stresses on nodal planes for each earthquake in the catalog we consider stress increments from previous earthquakes seismic stress and aseismic tectonic stress both separately and in combination the locations and mechanisms of earthquakes are best correlated with the aseismic shear stress including the cumulative coseismic effects from past earthquakes does not significantly improve the correlation correlations between normal stress and earthquakes are always very sensitive to the start date of the catalog whether we exclude earthquakes very close to others and whether we evaluate stress at the hypocenter or throughout the rupture surface of an earthquake although the correlation of tectonic stress with earthquake triggering is robust other results are unstable apparently because the catalog has so few earthquakes

shallow seismic source parameter determination using intermediate period surface wave amplitude spectra summary estimating reliable depths for shallow seismic sources is important in both seismo tectonic studies and in seismic discrimination studies surface wave excitation is sensitive to source depth especially at intermediate and short periods owing to the approximate exponential decay of surface wave displacements with depth a new method is presented here to retrieve earthquake source parameters from regional and teleseismic intermediate period 100 15s fundamental mode surface wave recordings this method makes use of advances in mapping globaldispersiontoallowhigherfrequencysurfacewaverecordingsatregionalandteleseismic distances to be used with more confidence than in previous studies and hence improve the resolution of depth estimates synthetic amplitude spectra are generated using surface wave theory combined with a great circle path approximation and a grid of double couple sources are compared with the data source parameters producing the best fitting amplitude spectra are identified by minimizing the least squares misfit in logarithmic amplitude space the f test is used to search the solution space for statistically acceptable parameters and the ranges of these variables are used to place constraints on the best fitting source estimates of focal mechanism depth and scalar seismic moment are determined for 20 small to moderate sized 4 3 mw 6 4 earthquakes these earthquakes are situated across a wide range of geographic and tectonic locations and describe a range of faulting styles over the depth range 4 29km for the larger earthquakes comparisons with other studies are favourable however existing source determination procedures such as the cmt technique cannot be performed for the smaller events by reducing the magnitude threshold at which robust source parameters can be determined the accuracy especially at shallow depths of seismo tectonic studies seismic hazard assessments and seismic discrimination investigations can be improved by the application of this methodology

source effects on regional seismic discriminant measurements source effects on high frequency regional seismic discriminant measurements involving p s type ratios pn lg pg lg are isolated for earthquakes in southern california and southern nevada the scatter in earthquake population discriminant measurements for fixed propagation paths is statistically analyzed to assess the spatial and frequency dependent contributions from source radiation pattern and source depth variations along with variable near source scattering this is useful because procedures for reducing the variance caused by propagation effects must be constrained by knowledge of the intrinsic scatter resulting from independent source effects for which corrections are not available without a priori knowledge of the source type and depth broadband waveforms for earthquakes near the nevada test site nts and in southern california recorded at stations of the livermore nts network lnn the caltech terrascope network and the berkeley digital seismic network bdsn are used to obtain pg lg and pn lg measurements and to assess source depth and mechanism contributions to measurement variance pn lg and pg lg spectral amplitude ratios for several frequency bands between 0 5 and 10 hz from vertical velocity waveforms are computed for a total of 18 tightly located clusters of earthquakes for each cluster we examine the correlations between observed pn lg and pg lg ratios and estimated source depths or predictions based on previously determined source mechanisms focal mechanism predictions do not match the observations well likely due to strong near source scattering and directivity effects that overwhelm the point source radiation pattern however the data do show significant scatter even for sources only a few kilometers apart source depth produces some coherent trends which can be emphasized by averaging results from multiple stations these trends vary from region to region presumably due to specific local crustal layering but most of the variance is not deterministically predictable and appears to arise from strong variations in near source scattering variance estimates for logarithmic amplitude ratios normalized by mean amplitude ratios vary from 0 01 to 0 05 for different phase pairs frequency dependent variations of the mean variance minimum and maximum amplitude ratio parameters show strong distance dependence out to about 300 km and then appear to become independent of event station distance these variance parameters appear to be suitable for use in spatial interpolations of observed p s type ratios for a specific unidentified event path as needed for nuclear test monitoring

multiobjective optimization of regional and teleseismic data to constrain the source of the 12 september 2016 mw 5 4 earthquake in south korea

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

rapid source mechanism determination of large mw 5 earthquakes in the western united states inversion of complete long period ground motions is used for rapid determination of source mechanisms of mw 5 earthquakes in the western united states the first few minutes of ground motions on local and regional distance waveforms are inverted for point source centroid moment tensors waveforms recorded at regional distances 300 1500 km can be adequately modeled at periods longer than 50 s using the laterally homogeneous prem model dziewonski and anderson 1981 at closer distances 300 km waves with periods as short as 35 s can be analyzed using prem best double couple focal mechanisms for 18 recent large western u s earthquakes compare very well with those obtained by other methods our procedure interfaced with automated data retrieval and source location methods is a viable tool for reliable determination of seismic moment and fault mechanism within 30 minutes after an earthquake

rapid full wave centroid moment tensor cmt inversion in a three dimensional earth structure model for earthquakes in southern california summary a central problem of seismology is the inversion of regional waveform data for models of earthquake sources in regions such as southern california preliminary 3 d earth structure models are already available and efficient numerical methods have been developed for 3 d anelastic wave propagation simulations we describe an automated procedure that utilizes these capabilities to derive centroid moment tensors cmts the procedure relies on the use of receiver side green s tensors rgts which comprise the spatial temporal displacements produced by the three orthogonal unit impulsive point forces acting at the receivers we have constructed a rgt database for 219 broad band stations in southern california using a tomographically improved version of the 3 d scec community velocity model version 4 0 cvm4 and a staggered grid finite difference code finite difference synthetic seismograms for any earthquake in our modelling volume can be simply calculated by extracting a small source centred volume from the rgt database and applying the reciprocity principle the partial derivatives needed for the cmt inversion can be generated in the same way we have developed an automated algorithm that combines a grid search for suitable focal mechanisms and hypocentre locations with a gauss newton optimization that further refines the grid search results using this algorithm we have determined cmt solutions for 165 small to medium sized earthquakes in southern california preliminary comparison with the cmt solutions provided by the southern california seismic network scsn shows that our solutions generally provide better fit to the observed waveforms when applied to a large number of earthquakes our algorithm may provide a more robust cmt catalogue for earthquakes in southern california

moment tensor inversion of regional phases application to a mine collapse the aim of our study consists of analyzing potentially non double couple seismic events recorded at regional distances in order to define the nature of the seismic source a moment tensor inversion is carried out as this method is general enough not to initially constrain the source mechanism in this paper we present an application to a seismic event induced by a mine collapse which occurred near the town of halle in germany because of its induced nature many parameters such as the location and geometry of this seismic source are known this information allows us to test the influence of inadequate propagation modeling on the moment tensor obtained from the inversion green s functions have been computed with the reflectivity method in a flat layered medium using the european model eurid du et al 1998 dufumier et al 1997 from the inversion of p wave seismograms recorded by the german regional seismic network will we obtained a source time function which can be decomposed into two subevents the first one has a large isotropic part and a deviatoric mechanism with near vertical nodal planes no volume change is observed for the second subevent but a deviatoric component opposite of the first one the addition of s waves does not change the results of the inversion which are stable surface waves were not used because of their poor dispersion curves based on the moment tensor obtained from these inversions the physical process at the source is compatible with a large cavity collapse

the influence of rock fabric on excavation damage in the lac du bonnett granite this paper documents the contribution of rock fabric on excavation damage development in the granite of the lac du bonnet batholith ldbb it is concluded that the ldbb contains structural elements and distinct textural varieties which differ significantly in their response to rock properties testing and to excavation data collected in this study demonstrate the highly heterogeneous internal structure characteristic of apparently homogenous batholiths and the influence of this heterogeneity on rock mass response evidence for anisotropy of the rock mass is demonstrated to have occurred on the geological time scale and its influence is still present in recent excavations this anisotropy exists at a wide range of scales from the localization of fault zones along low dipping layering at the kilometre scale to the localization of failure around tunnels by separation along this and other weakness directions

in situ measured current structures of the eddy field in the mozambique channel abstract circulation and the related biological production have been studied during five cruises conducted in the mozambique channel mzc between 2005 and 2010 the circulation in the mzc is known to be highly turbulent favouring enhanced primary production as a result of mesoscale eddy dynamics and connectivity throughout the channel due to the variable currents associated with migrating eddies this paper presents the results of in situ measurements that characterize the horizontal and vertical currents in the surface and subsurface layers 0 500 m the in situ data were analysed together with the geostrophic eddy field observed from satellite altimeter measurements different circulation regimes were investigated including the classical anticyclonic eddy generated at the channel narrows 16 s the enhancement of southward migrating eddies by merging with structures both cyclonic and anticyclonic formed in the east of the channel and the presence of a fully developed cyclonic eddy at the channel narrows comparison between in situ measurements s adcp and velocities derived from surface drifters and the geostrophic current derived from sea surface height measurements indicated that the latter can provide a reliable quantitative description of eddy driven circulation in the mzc with the exception that these currents are weaker by as much 30 it is also suggested from in situ observation drifters that the departure from geostrophy of the surface circulation might be linked to strong wind conditions finally our observations highlight that a geostrophic currents need to be considered in future research to facilitate a more comprehensive description of the circulation in this area

local magnitude determinations for intermountain seismic belt earthquakes from broadband digital data the university of utah seismograph stations uuss earthquake catalogs for the utah and yellowstone national park regions contain two types of size measurements local magnitude m l and coda magnitude m c which is calibrated against m l from 1962 through 1993 uuss calculated m l values for southern and central intermountain seismic belt earthquakes using maximum peak to peak p p amplitudes on paper records from one to five wood anderson w a seismographs in utah for m l determinations of earthquakes since 1994 uuss has utilized synthetic w a seismograms from u s national seismic network and uuss broadband digital telemetry stations in the region which numbered 23 by the end of our study period on 30 june 2002 this change has greatly increased the percentage of earthquakes for which m l can be determined it is now possible to determine m l for all m 3 earthquakes in the utah and yellowstone regions and earthquakes as small as m to maintain continuity in the magnitudes in the uuss earthquake catalogs we determined empirical m l station corrections that minimize differences between m l s calculated from paper and synthetic w a records application of these station corrections in combination with distance corrections from richter 1958 which have been in use at uuss since 1962 produces m l values that do not show any significant distance dependence m l determinations for the utah and yellowstone regions for 1981 2002 using our station corrections and richter s distance corrections have provided a reliable data set for recalibrating the m c scales for these regions our revised m l values are consistent with available moment magnitude determinations for intermountain seismic belt earthquakes to facilitate automatic m l measurements we analyzed the distribution of the times of maximum p p amplitudes in synthetic w a records a 30 sec time window for maximum amplitudes beginning 5 sec before the predicted sg time encompasses 95 of the maximum p p amplitudes in our judgment this time window represents a good compromise between maximizing the chances of capturing the maximum amplitude and minimizing the risk of including other seismic events

deformation and strength anisotropy of asan gneiss boryeong shale and yeoncheon schist results of deformability and strength anisotropy on three rock types found in korea are reported the experiments were conducted on rock specimen obtained from the directional coring system the anisotropy ratios of elastic modulus were from 1 7 to 4 0 for rock types in this study the applicability of transversely isotropic model was quantitatively investigated

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

initial investigation of the landers california earthquake of 28 june 1992 using terrascope the 1992 landers earthquake m s 7 5 m w 7 3 was recorded at six terrascope stations in southern california peak accelerations ranged from 0 16 g at svd 63 km to 0 0092 g at isa 245 km decreasing with distance away from the fault zone the peak velocity showed a different pattern reflecting the rupture directivity from south to north the largest peak velocity 19 cm sec was observed at gsc 125 km moment tensor inversion of long period surface waves yielded a mechanism with m 0 1 1 10 27 dyne cm m w 7 3 dip 74 rake 176 and strike 340 inversion of teleseismic p and s waves revealed two distinct sub events of 6 and 8 sec duration and about 10 sec apart the source parameters for the first and second events are m 0 1 9 10 26 dyne cm dip 83 rake 179 strike 359 and m 0 6 1 10 26 dyne cm dip 87 rake 178 strike 333 respectively the radiated wave energy e s was estimated as 4 3 10 23 ergs the ratio e s m 0 3 9 10 4 corresponds to a stress drop of 280 bars and suggests that the landers earthquake belongs to the group of high stress drop earthquakes and occurred on a fault with a long recurrence time the rupture directivity can be seen clearly in the records from pfo 68 km located to the south and gsc located to the north of the epicenter the maximum displacement at pfo is only 13 of that at gsc despite the shorter epicentral distance to pfo than to gsc the slip distribution determined with the empirical green s function method indicates that the landers earthquake consists of two distinct sub events about 30 km apart with the second sub event to the north being about twice as large as the first one this slip distribution is consistent with the teleseismic data and the surface offsets mapped in the field

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

effect of layer orientation on the failure of layered sandstone under brazilian test conditions abstract the experimental research in this paper focuses at macro scale on the effect of the layer orientation on failure strength and fractures induced by the brazilian tensile test for one particular sandstone sandstone from modave in the south of belgium the variation in the strength the applied energy and the failure pattern are examined as a function of the inclination angle between the layer plane and the loading direction for each sample the length of fractures parallel to the layers as well as corresponding to other directions is measured for the layered sandstone in this study the transition angle range is determined whereby the relative importance of both types of fractures switches

analysis of broadband records from the 28 june 1992 big bear earthquake evidence of a multiple event source the 28 june 1992 big bear earthquake occurred at 15 05 21 gmt and is considered to be an aftershock of the earlier m w 7 3 landers earthquake from overall aftershock locations and long period focal studies rupture is generally assumed to have propagated northeast no surface rupture was found however and the mainshock locations determined from both strong motion and terrascope data are mutually consistent and do not lie on the assumed fault plane further directivity analysis of records from the terrascope array suggests significant short and long period energy propagating northwest along the presumed antithetic fault plane this observation is supported by significant early aftershocks distributed along both the presumed rupture plane and the antithetic plane to the northwest an empirical green s function egf approach using both the m w 5 2 28 june 1992 14 43 gmt foreshock and the m w 5 0 17 august 1992 aftershock produces consistent results and suggests that the big bear event comprised at least two substantial subevents from the egf results we infer that the second and possibly a third subevent occurred on the presumed northeast striking mainshock rupture surface but that significant moment release occurred on the antithetic northwest striking surface we present results from line source fault modeling of broadband displacement recordings of the big bear mainshock which indicate that a two fault event is necessary to produce the observed waveforms the limitations imposed by the mainshock location and directivity analysis require that the initial rupture be towards the northwest striking 320 this was followed approximately 4 sec later by bilateral rupture along a northeast southwest fault that strikes 50 east of north

calibration of the regional crustal waveguide and the retrieval of source parameters using waveform modeling regional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller m 4 8 seismic events this path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration or master events this information can be difficult to obtain especially for smaller events generally explosion or quarry blast generated travel time data with known locations and origin times are useful for developing the path calibration parameters but in many regions such data sets are scanty or do not exist we present a method which is useful for regional path calibration independent of such data i e with earthquakes which is applicable for events down to m w 4 and which has successfully been applied in india central asia western mediterranean north africa tibet and the former soviet union these studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events we find that the error in source depth does not necessarily trade off only with the origin time for events with poor azimuthal coverage but with the horizontal location as well thus resulting in poor epicentral locations for example hypocenters for some events in central asia were found to move from their fixed depth locations by about 20 km such errors in location and depth will propagate into path calibration parameters particularly with respect to travel times the modeling of teleseismic depth phases pp sp yields accurate depths for earthquakes down to magnitude m w 4 7 this m w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth with the relative amplitude of the p nl waves to the surface waves and the interaction of regional spmp and ppmp phases being good indicators of event depths we also found that for deep events a seismic phase which follows an s wave path to the surface and becomes critical developing a head wave by s to p conversion is also indicative of depth the detailed characteristic of this phase is controlled by the crustal waveguide the key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms the regionalization scheme can also incorporate mixed path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures we also demonstrate that once depths are established we need only two stations travel time data to obtain reliable epicentral locations using a new adaptive grid search technique which yields locations similar to those determined using travel time data from local seismic networks with better azimuthal coverage

the 18 june 2002 caborn indiana earthquake reactivation of ancient rift in the wabash valley seismic zone the 18 june 2002 caborn indiana earthquake m w 4 6 occurred on a steeply dipping fault at a depth of about 18 km regional and teleseismic waveform data were used to obtain an accurate hypocenter with uncertainties better than about 2 km in both vertical and horizontal directions the source mechanism determined from regional waveform analysis is predominantly strike slip along near vertical nodal planes dips 82 and 84 striking 28 and 297 the nearly horizontal p axis trends 252 and plunges 10 the close proximity of the epicenter to the trace of the compound caborn fault and good agreement between the strike and dip of that fault and the source mechanism of the 2002 event suggests that the earthquake may have occurred on that fault most of the wabash valley faults as mapped from the shallow subsurface data extend into the precambrian basement to at least 7 km depth without significantly changing their orientation the june 2002 event at 18 km depth and the south central illinois earthquake on 9 november 1968 m w 5 3 which occurred at 25 km depth suggest that the seismogenic depth in the wabash valley seismic zone extends down to at least 18 km depth this earthquake is unique because it is the largest instrumented event to date that is clearly located within the area spanned by the wabash valley fault system its focal mechanism vertical strike slip faulting at depth may suggest that buried faults associated with a possible precambrian rift system are being reactivated by the contemporary east east northeast trending regional horizontal compressive stress

characteristics of focal mechanisms and the stress field in the southeastern margin of the tibetan plateau crustal earthquake focal mechanisms are investigated in the southeastern margin of the tibetan plateau where the tibetan plateau and stable south china block merge an updated database of focal mechanisms has been compiled by selecting 132 global centroid moment tensor solutions and by adding the 173 new solutions 3 5 ms 7 4 estimated by waveform inversion in this study a total of 305 mechanisms are included in this database these solutions show regionally specific distributions with dominant strike slip faulting and some normal and reverse faulting focal mechanism solutions have also been inverted for the stress tensor orientation to obtain the principal stress axes over the study region results show that the horizontal maximum principal 1 axes rotate clockwise with a wider range than the geodetically measured surface motion in the east which is not limited to the xianshuihe xiaojiang fault but has some overlap with the zhaotong lianfeng fault localized normal faulting stress regimes are observed in the jinshajiang litang fault areas and the baoshan sub block the minimum principal axes are oriented with a gradually changing trend from north south to northwest southeast from north to south indicating diverse compression stress patterns significant changes in the crustal stress field after the wenchuan earthquake are preliminarily observed in the baoshan sub block where orientations of two principal axes have changed and in the jinggu ximeng sub block areas where the strike slip faulting stress pattern has transformed to normal faulting

relationship between the deformation characteristics and microscopic properties of sandstone explored by the bonded particle model abstract previous research shows that the mechanical properties of sandstone are strongly influenced by porosity and grain area ratio gar this study explores how these microscopic factors affect the elasto plastic deformation of sandstone and adopts a modified bonded particle model to study the deformation behavior of sandstone under biaxial loading compared with the natural sandstone the analysis model can effectively capture the elasto plastic behavior of sandstone including non linear elasticity and the variations of plastic flow furthermore the simulated results of biaxial compressive tests show that the mechanical behavior of sandstone with different porosities and gars possesses the following characteristics the cohesion is significantly influenced by both gar and porosity greater gar and porosity values lead to a lesser cohesion however the influence of gar on the friction angle is insignificant and a lower porosity leads to a higher friction angle for elastic deformation the elastic shear and bulk modulus increase with decreasing porosity and increasing gar for plastic deformation the influence of porosity and gar on the variations of plastic angle under different shear stress ratios seems insignificant on the other hand the plastic strain trajectory increases with increasing porosity but the influence of gar is insignificant

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

source complexity of the 1994 northridge earthquake and its relation to aftershock mechanisms we determined the source process of the 1994 northridge earthquake in relation to the aftershock mechanisms to study the source complexity of the mainshock we inverted the p and sh waveforms recorded by the iris and ida iris networks using the method of kikuchi and kanamori 1991 in which the rupture is represented by a series of discrete subevents with varying mechanisms the waveforms show that the rupture consisted of several subevents with about 2 sec in between our solution consists of three subevents with essentially the same mechanism viz strike dip and slip of 130 42 and 116 respectively the first subevent occurred at a depth of about 19 km followed after 2 sec by the second and largest subevent at a depth of 17 km and the third subevent again 2 sec after the second at a depth of about 13 km the total moment from the body waves of this sequence is about 1 1 10 26 dyne cm m w 6 6 with a source duration of 7 sec the large depths of these subevents explain the lack of any surface rupture furthermore the upward propagation of the subevents is consistent with the depth of the hypocenter and the distribution of the aftershocks which are shallower and more northerly than the mainshock hypocenter the aftershocks were analyzed using data from the terrascope network we inverted short period surface waves to determine the moment tensor for 70 events with m w 3 5 the aftershocks can be grouped into three regions based on the mechanisms the eastern part of the aftershock zone where we find thrust events with mechanisms very similar to the main event a central area with predominantly strike slip events and an area to the west where we find oblique thrust events but with more northerly p axes than in the eastern region this distribution suggests that the fault system on which the northridge earthquake occurred is segmented and that the extent of the northridge rupture is controlled by a change in geometry of the fault we find a high stress drop 270 bar for the mainshock we propose that the changes in the fault geometry prevented a slip pulse from propagating thereby causing a high ratio of slip to rupture length

modelling progressive failure in fractured rock masses using a 3d discrete element method instabilities in rock structures involve coupled mechanisms related to both deformations along existing discontinuities and brittle fracture of intact rock conventional kinematic and limit equilibrium techniques used to study rock slope stability suffer from oversimplifications mass strength degradation and progressive failure mechanisms in rock bridges cannot be ignored and must be considered to predict the overall slope behaviour a 3d numerical model based on the discrete element method has been developed to overcome these limitations pre existing discontinuities as a discrete fracture network dfn can be initially plugged into a set of discrete elements combined with the use of a modified contact logic which provides an explicit representation of joints both fracturing of intact material and yielding within discontinuities can therefore be reproduced depending on the loading conditions and material strength simulations of referenced experimental tests are presented here to show the capabilities of the model in tackling the failure mechanisms of intact rock in the presence of pre existing discrete fractures with an emphasis on the initiation and propagation processes this model proves to be a promising tool in understanding and predicting instabilities that could lead to the failure of fractured rock slopes

source parameters of the june 29 1992 little skull mountain earthquake from complete regional waveforms at a single station the june 29 1992 m sub b 5 5 little skull mountain earthquake occurred 20 km southeast of yucca mountain within the boundaries of the nevada test site this event was recorded at a very broadband station located about 310 km to the east at kanab utah both body and surface waves from this single station were used in a grid search technique for the best fitting double couple moment tensor the technique minimizes the misfit between reflectivity generated complete synthetic seismograms and the three component displacement data via a search over the strike dip and rake of the source in the passband of 50 15 s period the grid search results in a well defined nearly pure normal mechanism with a strike of 35 degrees a dip of 54 degrees a rake of minus 87 degrees and a seismic moment of 4 1 x 10 sup 17 n m applying the same technique to the large aftershock on july 5 1992 the authors obtain a somewhat less well defined minimum with a strike of 358 degrees a dip of 36 degrees a rake of minus 177 degrees and a moment of 4 3 x 10 sup 15 n m the minimum compression axes of these mechanisms are consistent with northwest southeast extension in the basin and range 14more refs 7 figs less

locating and modeling regional earthquakes with two stations 1 we developed a new technique caploc to retrieve full source parameters of small seismic events from regional seismograms which include origin time epicenter location depth focal mechanism and moment magnitude despite rather complicated propagation effects at short periods a simple localized one dimensional model can well explain signals of periods 3 10 s if we break the three component records into different segments and allow differential time shifts among them these differential time shifts once established from a calibration process or a well determined tomographic map can be used together with p wave travel times to refine an event s location in this study we tested whether our new method could produce satisfactory results with as few as two stations so that we can improve source estimates of poorly monitored events with sparse waveform data we conducted the test on 28 events in the tibetan plateau the focal mechanisms and locations determined from only two stations agree well with those determined from a whole passcal array in particular our new method produces better locations than international seismological centre with the average mislocation error reduced from 16 to 5 km we also tested whether an event s depth and mechanism can be determined separately from its epicenter relocation in a two step approach we find that the two step approach does not always give the correct solution but the reliability of a solution can be evaluated using a reduced chi square value

grid mt grid based real time determination of moment tensors monitoring the long period seismic wavefield we have developed and implemented a new grid based earthquake analysis system that continuously monitors long period seismic wavefield of 20 50 s recorded by broadband seismometers the new analysis system automatically and simultaneously determines the origin time location and seismic moment tensor of seismic events within 3 min of their occurrence this system has been in operation since 2003 at the earthquake research institute http wwweic eri u tokyo ac jp grid mt and the locations and origin times are usually obtained within 3 s and 20 km away from the earthquake catalog values determined by the japan meteorological agency jma in addition moment tensor solutions are comparable to the network solutions manually obtained this new system should enable us to monitor long period seismic wavefield continuously further to help identifying long period or low frequency events which are undetectable by the conventional monitoring of short period seismic wavefields

the spatially extended 2006 april zakynthos ionian islands greece seismic sequence and evidence for stress transfer summary the seismic sequence at the southern part of zakynthos island ionian sea western greece during april and may of 2006 is investigated it consists of four moderate earthquakes 5 3 mw 5 7 that were followed by significant seismic activity source parameters of the significant events were determined using two different techniques teleseismic body wave modelling was employed for the major events of the sequence mw 5 6 although for the moderate ones the frequency wavenumber integration method was used the calculated fault plane solutions of the 2006 april seismic sequence revealed compressional regime in all cases more than 3500 microearthquakes were recorded and located using a local temporary network their spatial distribution indicated high concentration of seismic activity within an expanded area taking into account the magnitudes of the major events within this expanded area approximately 10 30 km 2 the focal depths varied between 10 and 25 km two main clusters were revealed the major events occurred in an area of low seismic activity that separates the two clusters seismic cross sections indicated a complex pattern of the hypocentre distribution with the activation of two nearly antithetical faults consistent with the determined focal mechanisms the northern cluster can be associated with a fault plane trending nnw sse and dipping towards sw although the southern cluster with a fault plane striking nw se and dipping towards ene finally coulomb stress analysis was performed to calculate the stress transfer and correlate it with the activated area positive lobes with stress more than 0 3 bars were obtained indicating that these values are large enough to increase the seismicity towards the observed nnw sse direction

moment tensor inversions using strong motion waveforms of taiwan tsmip data 1993 2009 abstract earthquake source parameters are important for earthquake studies and seismic hazard assessment moment tensors are among the most important earthquake source parameters and are now routinely derived using modern broadband seismic networks around the world similar waveform inversion techniques can also apply to other available data including strong motion seismograms strong motion waveforms are also broadband and recorded in many regions since the 1980s thus strong motion data can be used to augment moment tensor catalogs with a much larger dataset than that available from the high gain broadband seismic networks however a systematic comparison between the moment tensors derived from strong motion waveforms and high gain broadband waveforms has not been available in this study we inverted the source mechanisms of taiwan earthquakes between 1993 and 2009 by using the regional moment tensor inversion method using digital data from several hundred stations in the taiwan strong motion instrumentation program tsmip by testing different velocity models and filter passbands we were able to successfully derive moment tensor solutions for 107 earthquakes of m w 4 8 the solutions for large events agree well with other available moment tensor catalogs derived from local and global broadband networks however for m w 5 0 or smaller events we consistently over estimated the moment magnitudes by 0 5 to 1 0 we have tested accelerograms and velocity waveforms integrated from accelerograms for the inversions and found the results are similar in addition we used part of the catalogs to study important seismogenic structures in the area near meishan taiwan which was the site of a very damaging earthquake a century ago and found that the structures were dominated by events with complex right lateral strike slip faulting during the recent decade the procedures developed from this study may be applied to other strong motion datasets to compliment or fill gaps in catalogs from regional broadband networks and teleseismic networks

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

surface displacement of the 17 may 1993 eureka valley california earthquake observed by sar interferometry satellite synthetic aperture radar sar interferometry shows that the magnitude 6 1 eureka valley earthquake of 17 may 1993 produced an elongated subsidence basin oriented north northwest parallel to the trend defined by the aftershock distribution whereas the source mechanism of the earthquake implies a north northeast striking normal fault the 3 millimeter accuracy of the radar observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event these observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west dipping north northeast fault plane reactivating the largest escarpment in the saline range

moment tensor inversion for offshore earthquakes east of taiwan and their implications to regional collision reliable determination of source parameters for offshore earthquakes east of taiwan with mb 5 5 was a difficult task because of the poor azimuthal coverage by local network and the lack of signals at teleseismic distances we take advantage of the recently established broadband array in taiwan for seismology bats to invert seismic moment tensors for 7 such events occurred in 1996 to cope with different patterns of background noise and unknown structural details we utilize variable frequency bands in the inversion and adapt a two step procedure to select best velocity models for individual epicenter station paths our results are consistent with the overall patterns of regional collision and indicate that the resulting compressive stress has caused significant intraplate deformation within the philippine sea plate simulation of the region s geological evolution and orogenic processes should take this factor into account and allow the philippine sea plate to deform internally

regional magnitude scaling transportability and ms mb discrimination at small magnitudes data sets of mb pn and mb lg measurements are presented for three continental regions in order to investigate scaling relationships with moment magnitude w and event discrimination at small magnitudes compilations of published measurements are provided for eastern north american and central asian earthquakes and new measurements are reported for earthquakes located in western united states statistical tests on w mb relationships show that the mb lg scale of nurru 1973 is transportable between tectonic regions and a single unified w mb lg relationship satisfies observations for m 6 5 in all regions a unified relationship is also developed for nuclear explosions detonated at the nevada test site and test sites of the former soviet union regional mb for explosions scale at higher rates than for earthquakes and of significance is the finding that mb pn for explosions scales at a higher rate than mb lg a model is proposed where differences in scaling rates are related to effects of spectral overshoot and near field rg scattering on the generation of pn and lg waves by explosions for earthquakes mb pn and mb lg scale similarly showing rates near 1 0 or 2 3 log1omo seismic moment

lack of precursory slip to the 1999 hector mine california earthquake as constrained by insar we looked for evidence of interseismic strain occurring between the 1992 landers earthquake and the 1999 hector mine earthquake near the lavic lake and bullion faults by using interferometric synthetic aperture radar insar interferograms covering the hector mine epicentral region were studied for possible slip along the bullion and lavic lake faults by both visual inspection and a matched filter technique intended to emphasize slip located at the nucleation point some indications of possible deformation associated with the 5 july 1992 m l 5 4 pisgah event was observed but high decorrelation prevented a conclusive determination we have seen no evidence for precursory slip in the epicentral region up to 30 days before the hector mine event we estimated that the slip equivalent to a m w 4 5 event would have been observable in the months before the hector mine event and this places an upper bound on the long term precursory slip had it occurred we have noted that insar is well suited for detecting precursory slip in general due to the high spatial resolution and the lack of ground instrumentation required but that the detection level depends on the depth and orientation of the slip back

rapid identification of earthquake rupture plane using source scanning algorithm summary accurate identification of an earthquake s rupture plane is critical in many aspects ranging from scientific such as seismology and plate tectonics to societal such as emergency rescue planning we modify the recently developed source scanning algorithm ssa to rapidly image the rupture pattern of an earthquake using waveform data recorded at local and regional distances the method calculates the brightness function of a grid point by summing the observed amplitudes of the p wave envelopes at the corresponding predicted arrival times at all stations the composite image consisting of brightness functions of all grid points within a prescribed source volume and time interval illuminates the locations on the rupture plane where significant seismic energy is emitted synthetic tests indicate that the proposed method is robust even under the presence of hypocentral mislocation and origin time errors application of this method to the 2003 san simeon and 2004 parkfield earthquakes both occurred in central california clearly identifies the nw se striking planes as the actual rupture planes a conclusion consistent with all available evidences limited azimuthal distribution of seismic stations will not severely affect the identification result making this method ideal for offshore earthquake studies because the proposed method is able to identify the rupture plane using seismic waveform data only it is perfectly suited for near real time operation and may enable routine report of earthquake rupture planes by local seismic networks in the future

development of a shear zone in brittle rock subjected to direct shear abstract laboratory direct shear tests were carried out on a brittle synthetic rock at various normal loads the observed fracture patterns changes as the normal load increased a discrete element code was used to simulate the direct shear tests the simulation results clearly showed that cracks that developed during the test were predominantly tension cracks these cracks started to grow from the upper edge of the shear box due to the highly non uniform stress distribution along the shear plane the fracture development observed in discrete element simulation models showed that inclined fractures developed parallel to the maximum principal stress direction en echelon type extensile fractures were also generated and assemblies of theses fractures formed shear bands similar to the process observed in conventional triaxial test using brittle rocks the discrete element simulations showed that the macro scale shear band in the direct shear tests resulted from progressive failure of tension induced micro cracks

real time determination of seismic moment tensor for the italian region this work has been funded by the 2005 2007 dpc s4 and 2008 2010 dpc s3 italian civil protection contracts

automatic regional moment tensor inversion in the european mediterranean region summary we produce fast and automatic moment tensor solutions for all moderate to strong earthquakes in the european mediterranean region the procedure automatically screens near real time earthquake alerts provided by a large number of agencies each event with magnitude m 4 7 triggers an automatic request for near real time data at several national and international data centres moment tensor inversion is performed using complete regional long period 50 100 s waveforms initially the data are inverted for a fixed depth to remove traces with a low signal tonoise ratio the remaining data are then inverted for several trial depths to find the best fitting depth solutions are produced within 90 min of an earthquake we analyse the results for the period 2000 april to 2002 april to evaluate the performance of the procedure for quality assessment we compared the results with the independent swiss regional moment tensor catalogue srmt and divided the 87 moment tensor solutions into three groups 38 a quality solutions with well resolved m w depth and focal mechanism 21 b quality solutions with wellresolved m w and 28 unreliable c quality solutions the non homogeneous station and event distributions varying noise level and inaccurate earthquake locations affected solution quality for larger events m w 5 5 we consistently obtained a quality solutions for m w 4 5 5 5 we obtained a and b quality solutions solutions that pass empirical rules mimicking the a posteriori quality for our data set are automatically disseminated

strong motion and broadband teleseismic analysis of the 1991 sierra madre california earthquake short period and broadband teleseismic waveform data and three component strong motion records were analyzed to obtain the source parameters of the 1991 sierra madre earthquake close in strong motion velocity records analyzed from 5 s to 5 hz show two distinct pulses about 0 35 s apart requiring some rupture complexity the near field shear wave displacement pulse from this event has a relatively short duration about 1 s for the magnitude of the event requiring a particularly high average stress drop to further constrain the rupture process the data were used in a finite fault source inversion to determine the temporal and spatial distribution of slip we chose a fault plane orientation striking s 62 w and dipping 50 toward the northwest as required by the distribution of aftershocks the first motion mechanism and the teleseismic bodywave point source inversion in addition to the aftershock locations depth constraints are provided by teleseismic short period and broadband recordings which require a centroid depth of 10 11 km our inverse modeling results indicate that both the teleseismic and strong motion data sets can be fit with a compact rupture area about 12 km2 southwest and up dip from the hypocenter the average slip is approximately 50 cm and the maximum slip is 120 cm the seismic moment obtained from either of the separate data sets or both sets combined is about 2 8 0 3 1024 dyn cm and the potency is 0 01 km3 using the area of significant slip estimated from the finite fault inversion the resulting stress drop is on the order of 150 200 bars

spectral element moment tensor inversions for earthquakes in southern california we have developed and implemented an automated moment tensor inversion procedure to determine source parameters for southern california earthquakes the method is based upon spectral element simulations of regional seismic wave propagation in an integrated 3d southern california velocity model sensitivity to source parameters is determined by numerically calculating the frechet derivatives required for the moment tensor inversion we minimize a waveform misfit function and allow limited time shifts between data and corresponding synthetics to accommodate additional 3d heterogeneity not included in our model the technique is applied to three recent southern california earthquakes the 9 september 2001 m l 4 2 hollywood event the 22 february 2003 m l 5 4 big bear event and the 14 december 2001 m l 4 0 diamond bar event using about half of the available three component data at periods of 6 sec and longer we obtain focal mechanisms depths and moment magnitudes that are generally in good agreement with estimates based upon traditional body wave and surface wave inversions

regional seismic discriminants using wave train energy ratios we have examined broadband regional waveforms of recent since 1988 nevada test site nts underground explosions and earthquakes throughout the southwestern united states and baja mexico recorded by terrascope and other iris stations in order to characterize seismic sources for the purposes of event identification as expected earthquakes tended to be richer in long period surface wave and short period shear wave energy relative to explosions of comparable p wave strength also explosions in general were found to be richer in 1 to 6 sec surface wave rg energy and other late arriving coda energy than were earthquakes most earthquakes show relatively little long period t 6 sec rg and surface wave coda energy which we attribute to their deeper source depths whereas known shallow earthquakes do exhibit these phases we have developed several seismic discriminants based on our observations the most promising discriminant is the ratio of short period f 1 0 hz vertical component pnl wave train energy esppz to long period 0 05 to 0 167 hz three component surface wave energy e lp 3 for this ratio explosions tend to have a higher value than do earthquakes this discriminant works on the same premise as the teleseismic mb ms ratio for which earthquakes are richer in long period surface wave energy relative to explosions with the same body wave magnitude the long period passband was chosen to limit the effect of longer period noise and to remove the effect of the coda surface waves another potential discriminant examined is the ratio of short period f 1 0 hz vertical component p wave to s wave energy esppz espsz we find that this criterion only yields marginal separation of the source populations but becomes more effective at higher frequency bands f 4 0 hz or when looking at single station observations it does however help to quantify significant short period waveform differences between the three test subsites with pahute mesa shots generating relatively little s wave energy compared to those of yucca flat for which the s wave or lg is often the largest phase while rainier s shots are intermediate in character with distinct but less prominent s waves this s wave generation is thought to be caused by near source scattering to converted phases and appears to be highly dependent on the near source geology these two discriminants are useful in that they are simple and fast to calculate using regional stations for sources 200 to 1300 km away the magnitude threshold for the esppz e lp 3 discriminant is roughly ml 4 0 the limiting factor being the signal level of the airy phase while that for the esppz espsz discriminant is roughly ml 3 0 for the same distance ranges

centroid moment tensor solutions for april june 1992 abstract centroid moment tensor solutions are presented for 245 earthquakes that occurred during the second quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward the solution for an earthquake under mindanao philippines on 9 may represents the 10 000th event in the cmt catalogue

failure of transversely isotropic rock under brazilian test conditions abstract the behavior of transversely isotropic rock material was studied under brazilian test conditions for nine different rocks two sandstones one shale two slates one schist and three gneiss both the variation of the strength and the final fracture patterns induced by testing were examined as a function of the inclination angle of the weak planes the combination of the observations for both parameters illustrated clearly the complexity of the failure of such rocks which was summarized by assuming four different trends the four trends for the variation of the strength as a function of the inclination angles range from little or no variation trend 1 i e isotropic behavior for strength to a sharp decrease of the strength from very small angles onwards followed by a leveling off trend 4 trend 2 is characterized by a constant value between 0 and about 45 followed by a linear decrease while trend 3 corresponds to a decrease of the strength over the entire interval but a rather systematic decrease approximating a linear variation different variations were observed among these four trends in terms of the relative lengths of the respective fractures along the weak planes and in any other direction for the rocks investigated there is a cross over from dominant fractures in directions other than the weak planes to dominant fractures along the weak planes for the four trends there are systematic changes in the position of this cross over point i e on average at about an inclination angle of 75 for trend 1 and at about 15 for trend 4 for inclination angles larger than the cross over point the rock specimens failed primarily by splitting between both loading lines

moment tensor inversions for local earthquakes using surface waves recorded at terrascope we have developed a method to determine moment tensors for local earthquakes using short period 10 to 50 sec surface waves recorded at terrascope stations to correct for the substantial lateral variations in crustal structure we applied phase corrections to the data using a regionalized phase velocity model we have determined moment tensors for over 180 events in the last 3 yr in southern california for magnitudes as small as 3 2 and as large as 6 5 the results are consistent with those obtained from first motion data as well as other waveform inversions when continuous data telemetry from the stations becomes available this method can yield moment tensors for earthquakes in southern california and adjacent regions within minutes after the occurrence of an event our results confirm the relation log m o seismic moment 1 5m l local magnitude obtained by an earlier study

monitoring of strain release in central and northern california using broadband data systematic cataloguing of seismic moment depth and mechanism of regional earthquakes down to magnitude m 4 can now be achieved in close to real time using data from sparse networks of digital broadband stations the procedure we have developed relies on 3 independent methods for the determination of moment tensor providing confidence limits on the results we show the results of application to the seismicity in central and northern california for a one year period starting in march 1992 and illustrate how patterns of stress and strain release can now be monitored systematically and reliably in a timely fashion

an evaluation of the scsn moment tensor solutions robustness of the mw magnitude scale style of faulting and automation of the method we have generated moment tensor solutions and moment magnitudes m w for 1700 earthquakes of local magnitude m l 3 0 that occurred from september 1999 to november 2005 in southern california the method is running as an automated real time component of the southern california seismic network scsn with solutions available within 12 min of event nucleation for local events the method can reliably obtain good quality solutions for m w with m l 3 5 and for the moment tensor for events with m l 4 0 the method uses the 1d time domain inverse code tdmt invc software package dreger 2003 the green s functions have been predetermined for various velocity profiles in southern california which are used in the inversion of observed three component broadband waveforms 10 100 sec using data from at least four stations moment tensor solutions have an assigned quality factor dependent on the number of stations in the inversion and the goodness of fit between synthetic and observed data if a minimum quality factor is attained the m l or m w is 5 0 or greater and if the event is in the southern california reporting regions the m w will be the official scsn cisn magnitude the m w from the high quality solutions determined from our method generally correlate very well with reviewed m l except in regions at the perimeter of the network the m w reported here indicates the scsn m l systematically underestimates the magnitude in the mexicali region of baja california mono lakes area coso region and the brawley seismic zone and overestimates the magnitude in the coastal ranges comparisons of the moment tensors determined using this model are made with harvard centroid moment tensors generated for larger earthquakes in the california region and recent 3d models for events in the los angeles region with excellent correlation most of the earthquakes with good quality solutions exhibit strike slip faulting in particular along the major late quaternary strike slip faults thrust faulting on east west striking planes is observed along the southern edge of the transverse ranges while northwest striking thrust faulting is observed in the coastal ranges normal faulting is most common in baja california and southern sierra nevada including the western basin and range region poor quality solutions with unreliable m w are caused by excessive background noise in the waveforms small events m l 4 0 can be affected by ambient noise or teleseisms but larger events can also have unreliable solutions if they follow a recent large regional event

seismic source and structure estimation in the western mediterranean using a sparse broadband network we present a study of regional earthquakes in the western mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations the results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations the area consists of several contrasting geological provinces with distinct seismic properties which complicates the modeling of seismic wave propagation we started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces we found variations of crustal thickness ranging from 45 km under the atlas and betic mountains and 37 km under the saharan shield to 20 km for the oceanic crust of the western mediterranean sea which is consistent with earlier works throughout most of the region the upper mantle velocities are low which is typical for tectonically active regions the most complex areas in terms of wave propagation are the betic cordillera in southern spain and its north african counterparts the rif and tell atlas mountains as well as the alboran sea between spain and morocco the complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion we used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism we found that this method which is in use in many parts of the world works very well provided that data from several stations are available in order to study the events in the region using very few broadband stations or even a single station we developed a hybrid inversion method which combines p nl waveforms synthesized with the traditional body wave methods with surface waves that are computed using normal modes this procedure facilitates the inclusion of laterally varying structure in the green s functions for the surface waves and allows us to determine source mechanisms for many of the larger earthquakes m 4 throughout the region with just one station we compared our results with those available from other methods and found that they agree quite well the epicentral depths that we have obtained from regional waveforms are consistent with observed teleseismic depth phases as far as they are available we also show that the particular upper mantle structure under the region causes the various p n and s n phases to be impulsive which makes them a useful tool for depth determination as well thus we conclude that with proper calibration of the seismic structure in the region and high quality broadband data it is now possible to characterize and study events in this region both with respect to mechanism and depth with a limited distribution of regional broadband stations

global cmt analysis of moderate earthquakes mw 4 5 using intermediate period surface waves a new method for calculating centroid moment tensor cmt solutions for moderate sized earthquakes is presented and tested in the new algorithm which is a modification to the standard harvard cmt method intermediate period surface waves are included in the inversion for source parameters the dispersion of teleseismic surface waves in the period range 40 to 150 sec is predicted by interpolation of recent global phase velocity maps the method is tested on a set of 20 moderate and large 5 2 mw 7 2 earthquakes with known mechanisms the retrieved mechanisms are similar to the previous results even when noise is added to the seismograms to simulate earthquakes of a smaller magnitude mw 4 5 the inversion algorithm is applied to the 1993 klamath falls mainshock and aftershock sequence and the results compare well with earlier results a catalog of mw 4 5 focal mechanisms for greece and surrounding areas for the first six months of 1995 is derived using the new method of analysis

evolution of stress induced borehole breakout in inherently anisotropic rock insights from discrete element modeling the aim of this study is to better understand the mechanisms controlling the initiation propagation and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings a two dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs both isotropic and anisotropic hollow square shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale the isotropic model is validated by comparing the stress distribution around borehole wall and along x axis direction with analytical solutions effects of different factors including the particle size distribution borehole diameter far field stress anisotropy and rock anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure rock anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress far field stress anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings results from this study can provide fundamental insights on the underlying particle scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic rock

estimates of regional and local strong motions during the great 1923 kanto japan earthquake ms 8 2 part 1 source estimation of a calibration event and modeling of wave propagation paths this article is the first of a pair of articles that estimate regional and local strong motions from the 1923 kanto japan earthquake this ms 8 2 earthquake caused the most devastating damage in the metropolitan area in tokyo history in this article we first calibrate wave propagation path effects with a moderate sized modern event this event the odawara earthquake of 5 august 1990 m 5 1 is the first earthquake larger than m 5 in the last 60 years near the hypocenter of the 1923 kanto earthquake we estimate the source parameters based on a grid search technique using body waveform data bandpass filtered from 1 to 10 sec at four local stations because accurate source parameters are critical for calibrating the propagation effects we find that the odawara earthquake had a depth of 15 3 km a dip of 35 a rake of 40 a strike of 215 a seismic moment of 3 3 10 23 dyne cm a source duration of 0 65 sec and a stress drop of 170 bars next we investigate the effects of the propagation paths to the local and regional stations where seismograms of the 1923 kanto earthquake were recorded by comparing recorded waveforms with synthetic seismograms built with the calibration event path specific flat layered velocity models are estimated along travel paths from the event to stations hongo epicentral distance r 82 km in tokyo gifu r 213 km and sendai r 374 km using forward modeling in constructing the velocity model for the gifu station we use sts 1 broadband seismograms recorded at the nearby inuyama station consequently at periods greater than 3 sec the velocity models for stations hongo and gifu can successfully reproduce both body waves and direct surface waves and the velocity model for sendai station can explain the predominant direct surface waves in the companion article sato et al 1998 these velocity models are used to examine the adequecy of the variable slip rupture models of the 1923 kanto earthquake wald and somerville 1995 takeo and kanamori 1992 to explain recorded seismograms and also to simulate strong motions from that event

source parameters of the sierra madre earthquake from regional and local body waves we inverted the three component long period data recorded by the terrascope array for the june 28 1991 sierra madre california event to determine the seismic moment and source orientation of the mainshock ml 5 8 remarkably four of the six stations were located 159 2 0 7 km from the epicenter variations in absolute traveltime were smaller than 2 and 3 for pn and sn whereas the surface waves displayed greater variation similarities in the waveforms and the small variance in traveltime suggest that a common green s function can be used to invert the data we used the whole waveforms excluding the fundamental surface waves at the more distant stations to invert for source parameters the results of the inversion indicated that this event was predominately a thrust type earthquake where the strike rake and dip were determined to be 235 74 and 50 respectively the seismic moment was determined to be 2 5 1024 dyne cm the source duration was found to be about 1 0 seconds by direct measurement of the s wave recorded at the pasadena station located 21 km from the epicenter considering circular rupture we obtain a stress drop of 460 bars