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

stability of earthquake moment tensor inversions effect of the double couple constraint abstract we show that spurious large non double couple components can be obtained in inversions for the full deviatoric moment tensor for shallow crustal earthquakes due to inaccurate earth models the traditional best double couple solution does not in general provide an optimal estimate of a double couple mechanism and is only reliable when the non double couple component of the full deviatoric solution is small the inverse problem for the moment tensors of the 1998 antarctic plate and 2000 wharton basin strike slip earthquakes is shown in each case to have two well fitting minima in the misfit function of pure double couple solutions such pairs of solutions are most likely to exist for earthquakes which are close either to vertical strike slip or to dip slip on a fault plane dipping at 45 it is shown theoretically that these pairs of solutions arise from the combination of the pure double couple constraint and the instability of two elements of the moment tensor no significant non double couple component is found for the shallow thrusting 1996 biak indonesia earthquake

the 2003 boumerdes algeria earthquake regional moment tensor analysis 1 we used regional broadband seismograms to determine seismic moment tensors for the destructive may 21 2003 boumerdes algeria mw 7 0 earthquake and its larger aftershocks fully automatic inversions using near real time data provided solutions for seven mw 4 7 events within 90 minutes after event occurrence after adding off line data we manually obtained 30 solutions mw 3 8 from may 2003 to january 2004 all have shallow source depths 6 21 km the median p axis orientation 338 of 24 thrust and four strike slip events is consistent with africa eurasia plate motion 330 the main shock hypocenter at 8 10 km depth at the coastline and its shallow southward dip 25 5 puts the fault surface trace 15 20 km offshore consistent with documented seafloor deformation at the base of the continental slope a main shock rupture length of about 50 km is deduced from first day aftershocks and location of strike slip events the strike slip events probably define the western rupture end and indicate a left step of main convergence fault strike variability of thrust events suggests fault orientation changes and possibly fault segmentation

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

observations and origin of rayleigh wave amplitude anomalies summary this is a report of observations of amplitude anomalies of fundamental mode rayleigh waves r1 between periods of 17 and 100 s the anomalies are with respect to amplitudes predicted by rayleigh wave excitation for a reference earth model and catalogued centroid earthquake source parameters such as are used in large scale waveform inversions the observations indicate that the amplitude anomalies are consistent for nearby recordings of the same event while there is no obvious relation between the observed anomalies and the paths travelled by the waves this is in contrast to rayleigh wave phase anomalies which are consistent for similar propagation paths and hence form the input in many inversions for along path structure the observations in this paper show that a similar inversion of intermediate period amplitude anomalies for along and near path structure is not warranted without eliminating source evects since the amplitude anomalies are dominated by scattering ov near source earth structure and by possible uncertainties in the source parameters sensitivity kernels that take the coupling between the moment tensor and displacement field into account demonstrate that rayleigh wave amplitude sensitivity is largest near the source this report argues that the interaction between source radiated rayleigh waves and near source earth structure may not be ignored in amplitude inversion procedures

source mechanism of mining induced seismic events resolution of double couple and non double couple models abstract traditional assumption about a seismic source as a double couple dc can represent a serious limitation for describing mechanisms of mining induced seismic events in mining conditions more general process than a shear slip can occur due to stress concentration on mined out areas we assume both non dc components within the dipole description of the source the moment tensor and a single force we processed five seismic events recorded at driefontein gold mine in south africa to demonstrate that waveform modeling is not successful enough due to poor information about the medium inversion of amplitudes of direct p and s waves is more prospective due to their smaller sensitivity to detail of the medium and possibility to correct them for ray bending and shear wave splitting prior to the inversion moreover we are able to estimate the error of the resulting mechanism due to neglect of ray bending all five events processed display non dc mechanisms which are significant at 95 considering the mismodelling of the rock mass by a homogeneous isotropic medium the source mechanisms are in agreement with the underground mining and geological structures one event has a sub vertical pressure single dipole complemented by an implosion which is the body force equivalent of a collapsing horizontal crack or a burst of a pillar supporting the hangingwall of a mined out area two events have mechanisms close to a pressure single couple all three events are located on pillars two out of these three events can be assigned with a downward single force as an alternative mechanism which matches the amplitude data successfully it is the force equivalent of a mined out area collapse when a rock mass falls from the hangingwall to the footwall the events are however rather strong which would require too large rock mass fallen one of the remaining events is a nearly horizontal tensile single couple corresponding to a vertical tensional fault it could be originated by a break of the hangingwall of a mined out area however the hypocenter of this event is deep into the footwall were there is no mining taking place the last event is mostly dc accompanied by a compensated compressive dipole which may be associated to nearly vertical dip slip along a fault in the hangingwall this event is located on the margin of a wide pillar which supports the interpretation

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

european mediterranean regional centroid moment tensors 1997 2000 the mediterranean region is seismically very active and undergoing rapid deformation earthquakes as strong as m 6 are present but relatively rare on the other hand moderate magnitude seismicity 4 5 m 5 5 is widespread and often damaging an improved knowedge of moderate magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region harvard centroid moment tensors cmt today represent the most widely used reference for reliable source mechanisms but modelling seismic sources with the cmt technique for earthquakes with magnitude less than m 5 5 5 is quite difficult since 1997 we are using an extension of the standard cmt algorithm to compute regional centroid moment tensors rcmt for moderate magnitude earthquakes mw as low as 4 0 analyzing intermediate period surface waves from regional and teleseismic seismograms we routinely apply the algorithm to european mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4 5 and 5 5 which generally are not included in the harvard cmt catalog in this paper we show the results for earthquakes that occurred between 1997 and 2000 consisting of 252 solutions and we discuss the characteristics of the catalog and the areas where these new data are most relevant

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

automated procedure for point and kinematic source inversion at regional distances 1 the development of fast automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades providing an increasing number of focal mechanism solutions original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets the majority of these methods are based on the fit of low passed time traces we present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances assuming the recently proposed eikonal model to describe the extended source in our approach we use a larger set of information to better constrain the source parameters including the fit of amplitude spectra and displacements at different phases and frequency ranges the time consumption of the inversion process is significantly improved thanks to the implementation of green s functions databases we adopt a multistep inversion approach finally providing the focal mechanism magnitude and centroid location of the point source for events with magnitude higher than a threshold of mw 5 5 source geometry rupture extension and average slip may be additionally retrieved we discuss the methodology and the inversion stability showing applications to significant earthquakes in two case areas we focus on germany and greece and their neighboring areas considering major shallow earthquakes in the last 5 years the proposed method is currently implemented for automatic data processing at the seismological observatory of the federal institute for geosciences and natural resources in germany

seismotectonics of the armutlu peninsula marmara sea nw turkey from geological field observation and regional moment tensor inversion abstract the armutlu peninsula located in the eastern marmara sea coincides with the western end of the rupture of the 17 august 1999 izmit mw 7 6 earthquake which is the penultimate event of an apparently westward migrating series of strong and disastrous earthquakes along the nafz during the past century we present new seismotectonic data of this key region in order to evaluate previous seismotectonic models and their implications for seismic hazard assessment in the eastern marmara sea long term kinematics were investigated by performing paleo strain reconstruction from geological field investigations by morphotectonic and kinematic analysis of exposed brittle faults short term kinematics were investigated by inverting for the moment tensor of 13 small to moderate recent earthquakes using surface wave amplitude spectra our results confirm previous models interpreting the eastern marmara sea region as an active transtensional pull apart environment associated with significant nne ssw extension and vertical displacement at the northern peninsula long term deformation pattern did not change significantly since pliocene times contradicting regional tectonic models which postulate a newly formed single dextral strike slip fault in the marmara sea region this area is interpreted as a horsetail splay fault structure associated with a major normal fault segment that we call the waterfall fault apart from the waterfall fault the stress strain relation appears complex associated with a complicated internal fault geometry strain partitioning and reactivation of pre existing plane structures at the southern peninsula recent deformation indicates active pull apart tectonics constituted by ne sw trending dextral strike slip faults earthquakes generated by stress release along large rupture zones seem to be less probable at the northern but more probable at the southern peninsula additionally regional seismicity appears predominantly driven by plate boundary stresses as transtensional faulting is consistent with the southwest directed far field deformation of the anatolian plate

the 1993 klamath falls oregon earthquake sequence source mechanisms from regional data we use regional broadband seismograms to obtain seismic moment tensor solutions of the two september 20 1993 mw 6 klamath falls oregon earthquakes their foreshock and largest aftershocks my 3 5 several sub groups with internally consistent solutions indicate activity on several fault segments and faults from the estimated moment tensors and depths of the main shocks and from the aftershock distribution we deduce that both main shocks occurred on an east dipping normal fault pos sibly related to the lake of the woods fault system rotation of t axes between the two main shocks is consistent with the two dominant trends of the aftershocks and mapped faults we pro pose that a change in fault strike acted as temporary barrier sepa rating the rupture of the main shocks empirical green s function analysis shows that the first main event had a longer rupture du ration half duration 1 7 s than the second 1 2 s in december vigorous shallow activity commenced near klamath lake s west ern shore 5 10 km east of the primary aftershock zone it ap pears a mw 5 5 aftershock occurring the day before though within the primary aftershock zone triggered the activity

significance of non double couple components of deep and intermediate depth earthquakes implications from moment tensor inversions of long period seismic waves abstract analysis of long period seismic waves suggests that non double couple components in source moment tensors of intermediate depth and deep earthquakes are significant and appear to respond to the state of predominant strain release within slabs the strain regime is partially or fully induced by the sources themselves or by slab structures near the sources we observe consistency in the non double couple components from three different seismic wave inversions among 21 earthquakes studied 17 events have the same sign in the three non double couple components and the signs show a correlation with the state of strain release within the slabs the effects of unmodeled propagation structure and instability of the inversion procedure are unlikely to be responsible for the consistent non double couple components because the suites of seismic waves traverse different paths and the various inversion schemes have the different resolvabilities of the moment tensors

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

a preliminary catalog of moment tensors for the pyrenees abstract using waveform data gathered from the different organizations that operate seismological networks in the pyrenees we have obtained a complete moment tensor catalog of pyrenean earthquakes with magnitude larger than 3 covering the time period 2001 2011 our moment tensor solutions are in good agreement with those previously reported by other institutions we find absolutely no evidence for inverse faulting in the pyrenees on the opposite almost all the events have extensional focal mechanisms while only one event has a clear strike slip mechanism the t axes are consistently oriented along a nne ssw direction giving further support for a currently active extensional regime of deformation in the pyrenees the scaling relation between moment magnitude and local magnitude has a slope close to unity in contrast the scaling between our moment magnitudes obtained by waveform inversion and the moment magnitudes determined by inversion of shear wave spectra from drouet et al 2010 has a slope of 1 31 further work is thus required to identify the source of this discrepancy and to define a robust magnitude scale for the quantification of earthquakes in the pyrenees

frequency sensitive moment tensor inversion for light to moderate magnitude earthquakes in eastern africa 1 we provide a procedure for the routine determination of moment tensors from earthquakes with magnitudes as low as mw 4 4 using data recorded by only a few permanent seismic stations at regional to teleseismic distances waveforms are inverted for automatically determined frequency pass bands that depend on source receiver locations as well as the earthquake magnitude inversion results are stable against small variations in the frequency band and provide low data variances i e a good fit between observed and modelled waveform traces the total frequency band used for our procedure ranges from 10 mhz to 29 mhz periods of 35 s to 100 s this enables us to determine focal mechanisms for earthquakes that were not derived previously by routine procedures of cmt or other agencies as a case study we determine focal mechanism solutions of 38 light to moderate magnitude earthquakes in eastern africa between 1995 and 2002

automated near realtime cmt inversion the earthquake research institute eri of the university of tokyo has completely automated the process of determining source mechanisms of earthquakes using waveform data the solutions are automatically distributed using the internet without being checked the process is initiated by receipt of e mail giving the origin time and location of an earthquake to determine the source mechanism we apply the harvard centroid moment tensor cmt inversion method to long period body wave data the portion of the seismogram from the first arrival to the initial surface wave the method has been successfully applied since october 1993 to all of the major earthquakes in the world for which we received event e mail 108 of the 242 cmt solutions in 1994 were determined within 6 hours of the event with an average delay of 3 8 hours for local events e g events around japan it is also possible to determine cmt solutions within 30 minutes from the occurrence of the earthquakes using an efficient dialup data retrieval system operated by eri

a surface wave dispersion study of the middle east and north africa for monitoring the comprehensive nuclear test ban treaty we present results from a large scale study of surface wave group velocity dispersion across the middle east north africa southern eurasia and the mediterranean our database for the region is populated with seismic data from regional events recorded at permanent and portable broadband three component digital stations we have measured the group velocity using a multiple narrow band filter on deconvolved displacement data overall we have examined more than 13 500 seismograms and made good quality dispersion measurements for 6817 rayleigh and 3806 love wave paths we use a conjugate gradient method to perform a group velocity tomography our current results include both love and rayleigh wave inversions across the region for periods from 10 to 60 seconds our findings indicate that short period structure is sensitive to slow velocities associated with large sedimentary features such as the mediterranean sea and persian gulf we find our long period rayleigh wave inversion is sensitive to crustal thickness such as fast velocities under the oceans and slow along the relatively thick zagros mts and turkish iranian plateau we also find slow upper mantle velocities along known rift systems accurate group velocity maps can be used to construct phase matched filters along any given path the filters can improve weak surface wave signals by compressing the dispersed signal the signals can then be used to calculate regionally determined m s measurements which we hope can be used to extend the threshold of m b m s discriminants down to lower magnitude levels other applications include using the group velocities in the creation of a suitable background model for forming station calibration maps and using the group velocities to model the velocity structure of the crust and upper mantle

detailed waveform inversion for moment tensors of m 4 events examples from the corinth gulf greece moment tensors mts of weak events are often calculated by a single agency network thus lacking independent validation this article investigates how to increase reliability of the single agency solutions through various multiple checks it deals with the inversion of complete waveforms for six representative events mw 3 4 4 6 in the range of 0 08 0 15 hz several three station sets at near regional distances 8 103 km are used the mts are repeatedly calculated for two independent locations from a regional and local network the source depth is held fixed at the hypocenter and also grid searched to optimize the waveform match initially large variations instability of the mt solution with the approach we used were found for some events later the difficulties were understood and the solutions stabilized it led to practical recommendations on how to detect or even avoid problematic mt solutions first avoid mt solutions for a single fixed depth hypocenter second optimize mt solutions by the depth grid search below epicenter or better for at least two alternative epicenters third carefully analyze i any rapid variation of the so lution ii major misfit of the first motion polarities iii low double couple percen tage often correlating with ii iv low values of the min max eigenvalue ratio and v departures of the mt preferred depth from the location derived depth the mt preferred depths hence also the focal mechanism may be misleading due to data problems e g long period disturbances clipping hidden in the band pass wave forms the location derived depth may be especially wrong for very shallow earth quakes if the crustal model is inadequate in its shallow part and or near stations are lacking on the other hand near stations 20 km should not be used in the wave form inversion together with distant stations because of their large amplitudes the inversion can be easily biased due to instrumental data errors and small location errors online material color figures and waveform match

on the origin and consequences of crustal scale extension between africa and sicily since late miocene insights from the kaboudia area western pelagian sea abstract the eastern tunisian shelf is located between the gulf of hammamet and the gulf of gabes and belongs to the pelagian domain which underwent a continuous ne directed extension and crustal thinning since late miocene this geodynamic process induced the formation of nw striking normal faults and associated grabens both in the tunisian atlas and the pelagian domain including the sicily channel rifting zone scrz in this study we combine regional stratigraphy from seismic reflection profiles focal mechanisms space geodetic measurements gnss and thermal indicators from well data to propose a backward tectonic reconstitution of the pelagian domain the thinning of the continental crust is demonstrated by gravity inversion integrating published seismic refraction profiles by completing the interpretation of tectono stratigraphic records we highlight a northeastward propagation of extension prevailing within the pelagian shelf from messinian to plio quaternary times we suggest that extensional tectonics is explained by 1 eastward slab tearing between the african continental lithosphere and the tethyan oceanic slab allowing asthenospheric upwelling and 2 forces arising from relative motions between nubia and the hyblean malta block the decoupling of these domains since late miocene likely results from a combination of the nw directed plate convergence inherited rheological contrasts within the continental crust and weakening arising from mantle flow induced by the tethyan slab rollback and tearing

data dependent non double couple components of shallow earthquake source mechanisms effects of waveform inversion instability seismic moment tensors are routinely determined for global earthquakes using waveform inversions and the resulting double couple and non double couple characteristics are extensively used in tectonic analyses for shallow events several moment tensor components are intrinsically poorly resolved especially for surface wave inversions which can lead to artificial non double couple components or can obscure actual non double couple components in the source representations the relatively greater instability of surface wave inversions can cause differences between inversions based on only body waves and joint inversions of body and surface waves the harvard cmt catalog exhibits systematic variations in non double couple components with seismic moment which can be attributed to use of only body waves in inversions for small events and combined body and surface waves for large events systematic behavior of non double couple components with regional strain environment is significantly less dependent on seismic moment when solutions influenced by less stable surface waves are omitted

global compilation of interferometric synthetic aperture radar earthquake source models 2 effects of 3 d earth structure 1 we carry out long period surface wave centroid moment tensor cmt inversions using various global tomographic models and two different forward modeling techniques for 32 large earthquakes previously studied using interferometric synthetic aperture radar insar data since insar methods provide an alternative and independent way of locating and characterizing shallow continental earthquakes comparisons of our source parameters with those from insar are a novel way to assess limitations in the insar models as well as the effects of inaccurate wave propagation formulations and or 3 d earth structure on earthquake source determinations we show that comparing insar results with our seismic solutions is valuable to identify inaccuracies in the earthquake slip distribution retrieved using insar moreover we find that using more accurate formulations together with the best fitting earth models substantially reduces biases and differences between moment magnitude and fault strike determined using insar and seismic data as expected for long period surface wave source inversions for shallow earthquakes the fault dip and rake angles are difficult to constrain but we show that when using the best fitting earth models differences to insar estimates are reduced moreover spurious deviations from a pure double couple earthquake mechanism are on average smaller for the best fitting earth models and the more accurate formulation of wave propagation there are large differences between insar epicentral locations and those obtained in this study and on average no clear improvements to the global cmt locations are achieved this suggests that higher resolution earth models are necessary to further refine long period cmt epicentral locations

source analysis of the mw 6 3 2004 al hoceima earthquake morocco using regional apparent source time functions 1 we use small and moderate aftershocks of the 24 february 2004 al hoceima earthquake as empirical greens functions egfs to retrieve the rupture history of the main event the magnitude depth and geometry of faulting were estimated for the main shock and 20 small and moderate aftershocks mw between 3 9 and 5 2 computing moment tensor solutions for the main shock we obtain a moment magnitude of mw 6 3 and a nearly pure double couple source 4 compensated linear vector dipole with predominately strike slip faulting the preferred fault plane has a strike of n11 e a dip of 72 and a rake of 17 fourteen aftershocks having depths 4 km and faulting geometries 11 for the strike of the preferred plane similar to the ones found for the main event were used as egfs apparent source time functions astfs of the al hoceima event were retrieved at twelve regional stations using an iterative time domain deconvolution on the p waveforms at each station time functions are enhanced by stacking of the deconvolved waveforms for different egfs astfs show total durations of 5 to 6 s two consecutive subevents separated by about 3 s and only a weak effect of directivity we further investigate the source history by inverting the set of astfs for the distribution of fault slip and rupture propagation two different source models were selected for presentation one involving one single fault plane and the other involving two parallel fault planes the two fault model fits more accurately the observations and leads to a more plausible slip distribution we estimate rupture dimensions of about 10 10 km2 and 8 8 km2 and moment magnitudes of mw 6 2 and 6 0 for the first and second subevent respectively

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

effects of centroid location on determination of earthquake mechanisms using long period surface waves determination of shallow earthquake source mechanisms by inversion of longperiod 150 to 300 sec rayleigh waves requires epicentral locations with greater accuracy than that provided by routine source locations of the national earthquake information center neic and international seismological centre isc the effects of epicentral mislocation on such inversions are examined using synthetic calculations as well as actual data for three large mexican earthquakes for rayleigh waves of 150 sec period an epicentral mislocation of 30 km introduces observed source spectra phase errors of 0 6 radian for stations at opposing azimuths along the source mislocation vector this is larger than the 0 5 radian azimuthal variation of the phase spectra at the same period for a thrust fault with 15 dip and 24 km depth the typical landward mislocation of routinely determined epicenters of shallow subduction zone earthquakes causes source moment tensor inversions of long period rayleigh waves to predict larger fault dip than indicated by teleseismic p wave first motion data for dip slip earthquakes inversions of long period rayleigh waves that use an erroneous source location in the down dip or along strike directions of a nodal plane overestimate the strike dip and slip of that nodal plane inversions of strike slip earthquakes that utilize an erroneous location along the strike of a nodal plane overestimate the slip of that nodal plane causing the second nodal plane to dip incorrectly in the direction opposite to the mislocation vector the effects of epicentral mislocation for earthquakes with 45 dip slip fault mechanisms are more severe than for events with other fault mechanisms existing earth model propagation corrections do not appear to be sufficiently accurate to routinely determine the optimal surface wave source location without constraints from body wave information unless extensive direct path r1 data are available or empirical path calibrations are performed however independent surface wave and body wave solutions can be remarkably consistent when the effects of epicentral mislocation are accounted for this will allow simultaneous unconstrained body wave and surface wave inversions to be performed despite the well known difficulties of extracting the complete moment tensor of shallow sources from fundamental modes

disputable non double couple mechanisms of several strong earthquakes second degree moment approach the earthquake source mechanism description of the geometry of the source and its strength in terms of forces equivalent to rupturing of the rock mass is routinely modeled as a moment tensor mt describing the earthquake focus as a point however sometimes this approximation is not satisfied and seismic radiation keeps the directivity due to the finite extent of the source inversion into the mt then may yield a biased mechanism synthetic study in the adamova and silen 2010 demonstrated the appearance of spurious non double couple components in the mechanism even for a pure double couple dc source their method was designed to reduce the spurious source components by using the second degree moments to evaluate their contribution into the records and subtract it from the data here we applied the procedure to five moderate to large regional events with large nonshear components they are mostly located on large tectonic faults where predominantly pure shear slip is expected we studied one event on the prominent north anatolian fault three events in the pacific area and one event in bolivia in most cases the non dc components essentially were reduced and the geometry of the mechanism remained largely unchanged this confirms the hypothesis that part of the non dc components in regional mt solutions may be spurious due to the neglect of the source finiteness in the routine procedure of the mt retrieval in addition the geometrical and kinematical characteristics of the foci provided by the second degree moments the source ellipsoid and rupture velocity vector are mostly consistent with the fault geometry aftershock distribution and estimates of rupture speed from available previous studies

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

moment tensor inversion from mednet data 1 large worldwide earthquakes of 1990 we develop a method for the rapid determination of the moment tensor of large worldwide earthquakes by inversion of long period data recorded by the mednet regional network and we apply it to the most significant events of 1990 march 3 fiji and 25 costa rica may 12 sakhalin 20 sudan and 30 romania june 20 iran july 16 luzon and december 30 new britain the comparison with cmts and moment tensors by usgs shows that an advanced regional seismic network is capable of providing reliable and rapid control of the seismic source for worldwide seismicity

broadband analysis of the 21 september 1993 klamath falls earthquake sequence the source characteristics of the klamath falls earthquake sequence were estimated from broadband seismograms recorded by the berkeley digital seismic network bdsn terrascope and western united states iris stations solutions were obtained for events ranging in size from mw 3 8 to mw 6 0 an empirical green s function inverse approach was used to estimate kinematic source parameters of the two mw 6 0 mainshocks both events were found to have ruptured northwest on adjacent segments of the lake of the woods system of normal faults the two main shocks abut where there is a pronounced 10 to 20 clockwise rotation of strike which may have initially acted as a barrier to a through going mw 6 2 event

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

oceanic island arc stratigraphy in the caribbean region don t take it for granite abstract a popular misconception of island arcs is that they consist mostly of intrusive rocks belonging to the granite family and volcanic rocks study of exhumed caribbean island arcs indicates that they are composed mostly of sedimentary rocks such as epiclastic volcanic materials and true plutonic and volcanic rocks are relatively minor a simple model for the stratigraphic development of oceanic island arcs is proposed based on observations in the caribbean region and intuitive reasoning the lowermost part of the model arc is oceanic crust oceanic arc depositional system 1 or oads i built atop of the oceanic crust is the arc sequence including volcaniclastic strata lava flows with feeder dikes and plutons oceanic arc strata consist of a lower pyroclastic absent volcanic unit oads ii formed by submarine volcanism and an upper unit oads iii bearing volcanic pyroclastic and epiclastic rocks referred to here as the pyroclastic present association or unit both oads ii and iii may contain intercalated pelagic and or biogenic sediments such as limestones and cherts submarine volcanic rocks include pillowed and sheet lava flows lithic and hyaloclastic breccias and resedimented lithic and hyaloclastic debris oads iii can be recognized by the presence of shallow water fossils stream or beach worn volcanic clasts and other epiclastic materials even in deep water environments where such materials are resedimented shallow water materials and epiclastic strata are never found in oads ii thickness of the units vary in accordance with initial water depth of oceanic crust prior to arc formation amount of thermally induced uplift during early arc rifting subsidence due to loading and differential basinal subsidence or rates of volcanic aggradation examples of arc sequences from aruba bonaire curacao grenada martinique the virgin islands and puerto rico show significant variability aruba and curacao show incomplete sequences of arc growth and may reflect arc development on thick oceanic crust for example a plateau submarine volcanic arc facies associations oads ii occur only in the northern virgin islands water island formation and bonaire washikemba formation typically great structural thicknesses 5 10 km of arc related strata are preserved although condensed arc sequences built upon accreted terranes are present locally southwest puerto rico grenada on grenada the active magmatic platform is underlain by overthrust forearc basin strata indicating that magmatic platforms may grow by means other than volcanic aggradation

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

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

segmentation of the blanco transform fault zone from earthquake analysis complex tectonics of an oceanic transform fault 1 the blanco transform fault zone btfz forms the 350 km long pacific juan de fuca plate boundary between the gorda and juan de fuca ridges nearby broadband seismic networks provide a unique framework for a detailed long term seismotectonic study of an entire oceanic transform fault otf system we use regional waveforms to determine 129 earthquake source parameters combined with 28 harvard moment tensors they represent the largest waveform derived otf source parameter data set joint epicenter determination removes the northeasterly routine location bias projecting seismicity onto the btfz we determine along fault seismic slip rate variations earthquake source parameters and morphology indicate several transform segments separated by extensional step overs the eastern segment from gorda ridge to gorda depression is a pull apart basin the longest transform 150 km following blanco ridge from the gorda to cascadia depression is seismically very active seismically fully coupled has a wider seismic zone 9 km than other btfz transform segments and accommodates the largest mw 6 4 6 5 btfz earthquakes interpretation of cascadia depression as spreading ridge is supported by plate motion parallel normal faulting t axes spreading is currently tectonic 9 km deep earthquakes indicate a deep source for intermittent intrusives and rapid postemplacement cooling a short transform connects to the pull apart surveyor depression widely spread seismicity along the western btfz reflects complex morphology indicating ongoing plate boundary reorganization along short narrow width subparallel faults seismic coupling is low in extensional 15 compared to transform areas 35 100 implying different mechanical properties centroid depth variations are consistent with seismic slip cutoff near 600 c

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

geophysical and geotechnical studies of geology and sediment properties at a quick clay landslide site at esp trondheim norway abstract increased urbanisation and development in previous marginal areas have led to the need to protect the population the environment and infrastructure from hazards such as quick clay landslides in this paper the opportunity which was presented following the gathering of a large amount of data in the area of the quick clay landslide at esp trondheim norway in 2012 is explored the data is of particular interest given the availability of frequency domain helicopter borne electromagnetic data fhem and extensive lidar imaging as well as a full range of in situ geophysical and geotechnical soundings and samples the ground conditions in the area are shown to be complex and it is clear that a multi disciplinary type approach combining geophysical geomorphological and geotechnical investigations is necessary in order to understand the hazards posed by potential quick clay landslides the investigation shows that very good overview mapping of the area can be obtained from fhem and that the data obtained from local electrical resistivity tomography ert and resistivity cone rcptu are consistent with each other and with the fhem data use of ert immediately after the landslide was particularly useful in delineating further risk areas and as an aid for assessment of evacuation of the local population lidar data is particularly useful in understanding the landslide trigger mechanisms the depth of the landslide the form of the run out and the nature of the material in the run out geotechnical data collected in the area is characteristic of that of soft sensitive norwegian marine clays and the various geotechnical and geophysical parameters correlate well with one another and also follow well established patterns the data shows that no single investigative method is available to accurately define quick clay layers but that a number of complimentary in situ and laboratory techniques are necessary for that purpose

moment tensor inversion from mednet data 2 regional earthquakes of the mediterranean we present a method for the rapid determination of the moment tensor suitable for application to regional earthquakes up to 3000 km distance the algorithm is based on the inversion of long period waveforms in the time domain and is routinely applied to significant events of the mediterranean from iran to the azores using digital data recorded by the mednet regional network we show results for 20 significant earthquakes of 1990 1992 including the large shocks in romania may 30 1990 iran june 20 1990 caucasus april 29 1991 turkey march 13 1992 and egypt october 12 1992 the damaging italian earthquakes of potenza may 5 1990 and siracusa december 13 1990 unusual events in the southern mediterranean november 11 1990 and holland april 13 1992 and the recent shocks of october 23 1992 in morocco and caucasus the comparison with published focal mechanisms and centroid moment tensors show our results to be consistent with those retrieved using global data and local networks proving that an advanced regional seismic network is capable of providing accurate rapid control of regional seismicity

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

constraints on macquarie ridge tectonics provided by harvard focal mechanisms and teleseismic earthquake locations in this study we evaluate teleseismically determined focal mechanisms and epicenters for earthquakes along the macquarie ridge complex mrc from 45os to 61 os and 155oe to 168oe a region characterized by some previous investigators as undergoing subduction initiation from 65 centroid moment tensors reported by harvard we develop statistical guidelines for choosing 26 which represent better determined more reliable focal mechanisms for tectonic analysis although thrust mechanisms occur in the north near fiordland elsewhere along the mrc the better determined mechanisms virtually all indicate that present day motion along most of the mrc is strike slip this is consistent with sidescan sonar and multichannel reflection data collected between 50os and 57os on 1994 and 1996 cruises the active plate boundar3 zone appears to be quite narrow 5 km wide and no active compressional features can be observed on the seafloor if we determine a rotation pole for plate boundary motion using only slip vectors from better determined harvard mechanisms along the mrc the best fitting instantaneous pole is at 57 4os 179 4oe about 2 5 o north of the nuvel i australian pacific pole which averages motion over the last 3 0 my if the mrc pole was formerly farther south than at present this could explain the existence of relict features associated with crustal shortening such as bathymetric highs and troughs yet the absence of active features such as thrust faults etc suggests ongoing compression or subduction initiation we also carefully read arrival times for p phases for 53 earthquakes at 16 teleseismic stations selected to represent a range of azimuths surrounding the earthquakes we relocated these earthquakes using standard joint epicentral determination jed methods while most of the better quality relocations lie on or very close to the australia pacific boundar3 as determined on the 1994 cruise a few epicenters occur well away from the boundar3 apparently on cenozoic fracture zones thus on the macquarie ridge complex and other major strike slip boundaries e g in california it appears that the very largest earthquakes occur on the principal plate boundar3 fault but that other earthquakes some quite large may occur away from the boundary along zones of preexisting weakness