broadband waveform inversion of moderate earthquakes in the messina straits southern italy abstract we report the first application of the cut and paste cap method to compute earthquake focal mechanisms in the messina straits area by waveform inversion of pnl and surface wave segments this application of cap has furnished new knowledge about low magnitude earthquake mechanics that will be useful for improved understanding of the local geodynamics this is possible because the cap inversion technique can be applied to small earthquakes for which traditional moment tensor inversion methods are not appropriate and p onset focal mechanisms in the study area fail because of a lack of sufficient observations we estimate the focal mechanisms of 23 earthquakes with local magnitudes in the range of 3 4 occurring in the 2004 2008 time period and recorded by the broadband stations of the italian national seismic network and the mediterranean very broadband seismographic network mednet run by the istituto nazionale di geofisica e vulcanologia ingv the solutions show that normal faulting is the prevailing style of seismic deformation in the northern part of the study area while co existence of normal faulting and strike slip has been detected in the southern part in the whole area of investigation the t axes of focal mechanisms display a preferential northwest southeast direction of extension combined with the findings of previous investigations this improved database of focal mechanisms allows us to better detail the transitional area between the extensional domain related to subduction trench retreat southern calabria and the compressional one associated with continental collision western central sicily the observed spatial change of seismic deformation regime offers new data to current seismotectonic and seismic hazard investigations in the area of messina straits where a magnitude 7 2 earthquake caused more than 60 000 casualties on 28 december 1908

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

inversion of source parameters for moderate earthquakes using short period teleseismic p waves in this paper we introduce a new method for estimating the source parameters of moderate earthquakes mw 5 0 by modeling short period teleseismic waveforms this method uses a grid search algorithm to minimize misfits between observed data and synthetic seismograms in depth magnitude and mechanism domain in a relative high frequency range of 0 8 2 0 hz similar to the traditional cut and paste method used in regional modeling zhu and helmberger bull sesimol soc am 86 1634 1641 1996 in this frequency range a significant challenge is determining the initial p wave polarity because of a low signal to noise ratio snr therefore we first determine source properties for a master earthquake with a relative strong snr both the travel time and amplitude corrections are developed relative to the reference 1d model along each path used in inverting the master event we then applied these corrections to other earthquakes clustered in the same area to constrain the initial p polarities thus the focal mechanisms can be determined reasonably well we inverted focal mechanisms for a small set of events beneath qeshm island in southern iran and demonstrate the importance of radiation pattern at short periods

the ionian and alfeo etna fault zones new segments of an evolving plate boundary in the central mediterranean sea highlights plate boundary re organization in the central mediterranean sea segmentation of the subduction complex along lithospheric transverse faults step faults in the ionian sea pleistocene active faulting and mt etna formation abstract the calabrian arc is a narrow subduction rollback system resulting from africa eurasia plate convergence while crustal shortening is taken up in the accretionary wedge transtensive deformation accounts for margin segmentation along transverse lithospheric faults one of these structures is the nnw sse transtensive fault system connecting the alfeo seamount and the etna volcano alfeo etna fault aef a second nw se crustal discontinuity the ionian fault if separates two lobes of the ca subduction complex western and eastern lobes and impinges on the sicilian coasts south of the messina straits analysis of multichannel seismic reflection profiles shows that 1 the if and the aef are transfer crustal tectonic features bounding a complex deformation zone which produces the downthrown of the western lobe along a set of transtensive fault strands 2 during pleistocene times transtensive faulting reactivated structural boundaries inherited from the mesozoic tethyan domain which acted as thrust faults during the messinian and pliocene 3 the if and the aef and locally the malta escarpment accommodate a recent tectonic event coeval and possibly linked to the mt etna formation regional geodynamic models show that whereas aef and if are neighboring fault systems their individual roles are different faulting primarily resulting from the ese retreat of the ionian slab is expressed in the northwestern part of the if the aef on the other hand is part of the overall dextral shear deformation resulting from differences in africa eurasia motion between the western and eastern sectors of the tyrrhenian margin of northern sicily and accommodating diverging motions in the adjacent compartments which results in rifting processes within the western lobe of the calabrian arc accretionary wedge as such it is primarily associated with africa eurasia relative motion

locating seismic events in the ctbt context the verification of the comprehensive nuclear test ban treaty ctbt requires the determination of accurate location of seismic events from a fixed network of seismic stations across the globe the requirements of possible on site inspections mean that the goal is to place the location estimate in a zone smaller than 1000 km2that includes the true location because a defined set of stations will be used corrections can be refined to represent the influence of departures from the global reference model iaspei91 the primary stations in the international monitoring scheme ims are mostly seismic arrays and therefore the present location scheme is based on minimisation of a misfit function built from arrival time azimuth and array slowness residuals the effective network will change markedly with the magnitude of the event and as a result regional information has to be integrated into the location process

seismic location calibration of the european arctic a crustal velocity model has been developed for fennoscandia the baltic shield and adjacent areas this model represents a simplified average of various models developed for parts of this region we show that p wave travel times calculated with this model provide an excellent fit to observations at the fennoscandian krsc and iris station networks for a set of seismic events with known or very well constrained locations the station event paths cover large parts of western russia and the barents sea thus indicating that this model which we denote the barents model is appropriate for this entire region we show by examples that significant improvements in event location precision can be achieved compared to using the 1aspei model we finally use the barents model to calculate locations of recent small seismic events in the novaya zemlya region of interest in a ctbt monitoring context

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

an intense earthquake swarm in the southernmost apennines fault architecture from high resolution hypocenters and focal mechanisms abstract between 2010 and 2013 the pollino mountains region south italy already proposed as a seismic gap was affected by a seismic crisis of more than 5000 small to moderate earthquakes maximum magnitude m l 5 0 preliminary analyses performed in a previous work highlighted that this activity can be ascribed to normal faulting on north northwest trending west dipping dislocation surfaces consistent with the general seismotectonic frame of the southern apennines this work contributes additional data and a more sophisticated analyses that highlight new features of the seismic swarm and support a new interpretation for the study area we obtained high precision locations and focal mechanisms using the double difference method and the cut and paste waveform inversion method respectively the 3d patterns of hypocenters and focal mechanisms consistently image an 10 km long north northwest striking and west dipping fault zone between 5 and 10 km depth with predominantly extensional kinematics the high resolution data show that this zone broadens from north to south as a result of secondary faulting the depicted geometry with preliminary geological observation leads to the hypothesis of multiple seismogenic normal faults rooted into more regional shallow dipping detachments inherited from the pre existing apennine thrust tectonics online material table of estimated focal mechanism parameters

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

seismicity of central tibet from project indepth iii seismic recordings as part of project international deep profiling of tibet and the himalaya iii a 400 km long densely spaced array of 57 broadband and short period seismic stations was deployed in central tibet from august 1998 through may 1999 although originally designed to image the lithosphere with teleseismic events the array also recorded numerous local and regional seismic events more than 900 local and regional events were detected on at least 10 stations during the 1 year deployment and we were able to locate 267 local earthquakes a substantial number of the events were found to cluster in or near large grabens and along known strike slip faults while other events show no obvious correlation with known structures in addition to spatial clustering at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust the average v p and v s are estimated to be 5 85 and 3 35 km sec for the upper crust and 7 0 and 3 9 km sec for the lower crust respectively the 50 focal mechanisms computed from this set of events are consistent with north south shortening and east west extension there are no clear indications of significant local perturbations in the regional stress field induced by the collision between india and eurasia the majority of the focal mechanisms indicate normal and strike slip faulting at least six of the newly computed focal mechanisms however indicate thrust faulting which is a phenomenon not well documented previously ninety nine percent of the local earthquakes have focal depths shallower than 25 km and the locations of the few deeper events are poorly constrained the shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central tibet figure 6 1 figure 6 a earthquake locations computed from this study shown on shaded topographic data triangles are indepth iii seismic stations circles are events and are scaled by magnitude graphic 2 a color version of this figure is available online at the ssa web site b earthquake locations shown with major geologic structures from taylor et al 2003 3 reproduced with permission m h taylor personal comm 2002 triangles are indepth iii seismic stations geologic structures are as in figure 2 4 1 pending yes 2 f1 embed inline graphic 1 gif 3 ref 46 4 f3

teleseismic slowness azimuth station corrections for the international monitoring system seismic network abstract the prototype international data center pidc in arlington virginia has been developing and testing software and procedures for use in the verification of the comprehensive test ban treaty after three years of operation with a global network of array and three component stations it has been possible to characterize various systematic biases of those stations that are designated in the treaty as part of the international monitoring system ims these biases include deviations of azimuth and slowness measurements from predicted values caused largely by lateral heterogeneity for events recorded by few stations azimuth and slowness are used in addition to arrival time data for location by the pidc corrections to teleseismic azimuth and slowness observations have been empirically determined for most ims stations providing data to the pidc application of these corrections is shown to improve signal association and event location at some stations an overall systematic bias can be ascribed to local crustal structure or to unreported instrumental problems the corrections have been applied in routine operation of the pidc since february 1998

passcal instrument performance during the tibetan plateau passive seismic experiment summary the passcal instrumentation performed very well in the tibetan plateau seismic experiment this experiment has demonstrated the viability of recording high quality broadband data at temporary sites in extreme environments it also highlights some areas where further development is needed primarily more effort is needed to develop more versatile triggering options for the passcal instruments such developments could both increase the instrument9s success at recording low magnitude teleseismic events for travel time studies and save disk space when recording local events thus further increasing the feasibility of long deployments in remote regions although the use of the passcal instrument9s calibration circuitry for sensor recentering is a valuable technique more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter this may also lead to improved low frequency noise levels although signals with periods greater than 200 sec can be recovered from these sites the most exciting aspect of the data we have collected is its broad frequency content and spatial density we anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep earth structure this data was delivered to the iris data management center in early september 1993 and is available to the community two other broadband passive seismic experiments the baikal rift experiment gao et al 1992 and the rocky mountain front experiment sheehan et al 1992 should be delivered to the iris dmc in the fall of 1993 as well temporary broadband seismic experiments represent an extension of the permanent global seismic network gsn we encourage the seismological community to incorporate these data into any research using gsn data in order to maximize the potential utility of this new mode of seismic recording

calibration of the tibetan plateau using regional seismic waveforms we use the recordings from 51 earthquakes produced by a passcal deployment in tibet to develop a two layer crustal model for the region starting with their isc locations we iteratively fit the p arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters an average crustal p velocity of 6 2 6 3 km s is obtained for a crustal thickness of 65 km while the p velocity of the uppermost mantle is 8 1 km s the upper layer of the model is further fine tuned by obtaining the best synthetic sh waveform match to an observed waveform for a well located event green s functions from this model are then used to estimate the source parameters for those events using a grid search procedure average event relocation relative to the isc locations excluding two poorly located earthquakes is 16 km all but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km this is 15 km shallower on average than depths reported by the isc the shallow seismicity cut off depth and low crustal velocities suggest high temperatures in the lower crust thrust faulting source mechanisms dominate at the margins of the plateau within the plateau at locations with surface elevations less than 5 km source mechanisms are a mixture of strike slip and thrust most events occurring in the high plateau where elevations are above 5 km show normal faulting this indicates that a large portion of the plateau is under ew extension

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

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

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

5hz gps seismology of the el mayor cucapah earthquake estimating the earthquake focal mechanism summary high rate 5hz gps records observed in the near field following the magnitude 7 2 el mayor cucapah earthquake that occurred in northern mexico on 2010 april 4 are compared with broad band seismograms the high rate gps displacement records are consistent with the twice integrated strong motion seismic records in the near field where broad band seismograms are clipped due to strong shaking agreement degrades at distances greater than about 150 km from the epicentre where displacement amplitudes approach the noise level of gps seismograms using high rate gps data the focal mechanism of the main shock is estimated and is shown to be consistent with teleseismic estimates the result is seen as confirmation that high rate gps observed at near field stations can be applied together with teleseismic seismometers to yield better information about earthquake rupture properties and parameters

locating earthquakes with surface waves and centroid moment tensor estimation traditionally p wave arrival times have been used to locate regional earthquakes in contrast the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently thus surface wave path delays need to be known before such data can be used for location these delays can be estimated from previous earthquakes using the cut and paste technique ambient seismic noise tomography and from 3d models taking the chino hills event as an example we show consistency of path corrections for 10 s love and rayleigh waves to within about 1 s obtained from these methods we then use these empirically derived delay maps to determine centroid locations of 138 southern california moderate sized 3 5 m w 5 7 earthquakes using surface waves alone it appears that these methods are capable of locating the main zone of rupture within a few 3 km accuracy relative to southern california seismic network locations with 5 stations that are well distributed in azimuth we also address the timing accuracy required to resolve non double couple source parameters which trades off with location with less than a km error required for a 10 compensated linear vector dipole resolution

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

source specific station corrections for regional phases at fennoscandian stations the iaspei91 global travel time curves are used as the default for event location at the prototype international data center pidc in order to improve event location a 1 d baltic travel time model was implemented at the pidc in 1997 for locating events using regional phases from fennoscandian stations where a single model is insufficient for characterizing the regional geology path dependent corrections or source specific station corrections ssscs are more appropriate for event locations we have developed ssscs for regional phases at the fennoscandian stations by interpolating travel times through different 1 d models ssscs for stations nris and spits are also derived given the fact that paths from both stations to high latitude events are within the fennoscandia regionalization as baltic

evidence of complex faulting near the huangcheng shuangta fault gansu china from the 11 may 2012 mw 4 8 sunan earthquake we determined the mainshock source parameters relocated aftershocks and modeled broadband waveforms from 14 stations within 300 km of the 11 may 2012 m w 4 8 sunan earthquake the focal mechanism determined by the cut and paste method is predominantly strike slip with a component of thrust and occurred at a depth of 5 1 km the shallow focal depth likely contributed to the strong shaking in the epicentral area the strike and dip of nodal plane i are consistent with the strike and dip of the huangcheng shuangta fault which may have hosted the devastating 1927 m s 8 0 gulang earthquake and the surface trace for which is 2 km northeast of the sunan epicenter we used the double difference location method to relocate aftershocks and found that they occurred at depths from 4 to 7 km on a well defined plane dipping to the northwest this plane closely corresponds with nodal plane ii of our focal mechanism the dip of the relocated aftershocks is consistent with the dip of nodal plane ii therefore this earthquake likely occurred on a secondary fault in a region undergoing transpression which indicates that deformation is not restricted to the huangcheng shuangta fault

seismogenic stress field estimation in the calabrian arc region south italy from a bayesian approach a new high quality waveform inversion focal mechanism database of the calabrian arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions the new database has then been used for computation of posterior density distributions of stress tensor components by a bayesian method never applied in south italy before the present study the application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated our results well constrain the extensional domain of calabrian arc and the compressional one of the southernmost tyrrhenian sea in addition previously undetected transcurrent regimes have been identified in the ionian offshore the new information released here will furnish useful tools and constraints for future geodynamic investigations

earthquake centroid locations using calibration from ambient seismic noise earthquakes occur in complex geology making it difficult to determine their source parameters and locations because of uncertainty in path effects we can avoid some of these problems by applying the cut and paste cap method which allows for timing shifts between phases assuming a 1d model and determines source parameters if the travel times or lags of the phases due to path effects are known relative to a reference model we can locate the events centroid with surface waves without knowledge of the 3d velocity structure here we use ambient seismic noise for such a calibration we cross correlate the seismic stations near the earthquake with stations 100 300 km away to obtain the 10 100 s surface wave green s functions the new method is tested in southern california to locate the 2008 chino hills earthquake which proves consistent with the epicenter location from p waves it appears possible to use the location offset between the high frequency p wave onset relative to the centroid to provide a fast estimate of directivity

the determination of source parameters for small earthquakes from a single very broadband seismic station the installation of very broadband seismic stations makes it possible to recover the source parameters of small earthquakes 2 5 ml 5 0 which occur at local and regional distances if the gross crustal structure along the travel path is known it is possible to use the p sv and sh displacement waveforms from a single station to determine the seismic moment tensor although the details of the crustal structure strongly affect the body waveforms at regional distances the signature of the seismic source orientation on the waveform is robust at frequencies less than 1 3 hz we explore the trade offs between crustal model hypocentral depth and filtering for a linear moment tensor inversion procedure the procedure is tested on two small earthquakes which occurred in the rio grande rift and were recorded at the iris usgs station anmo the agreement between the single station moment tensor inversion fault plane parameters and those determined from local first motions is excellent

path dependent regional phase travel time corrections for the international monitoring system in north america the software developed for the comprehensive nuclear test ban treaty ctbt international data centre idc in vienna austria uses the iaspei91 seismic travel time tables as default however in reality travel times as a function of source location are different for each station especially at regional distances this is not modeled by a global one dimensional model such as iaspei91 the software therefore allows the application of a suite of travel time corrections for improved travel time prediction and consequently more accurate hypocentral locations to account for path dependency we have developed gridded source specific station corrections ssscs for pn sn pg and lg phases for 22 international monitoring system ims stations in north america in deriving the ssscs and associated modeling errors we used a methodology that had been successfully applied previously for fennoscandia we first compiled regionalized one dimensional travel times for north america then we assigned travel times as weighted sums of the travel times in each region to calculate ssscs validation testing of the ssscs was conducted using two separate sets of north american ground truth gt events with location accuracies within 10 km gt0 gt10 these events were recorded at ims stations between 1995 and 1999 and distributed throughout north america test event location results with ssscs applied show reductions in both mislocations and error ellipses for gt events with location accuracies better than 2 km the median change in location was a 5 km improvement and the median area of the 90th percentile error ellipses was reduced from 2550 km 2 to 910 km 2 using ssscs for both data sets the median improvement is less than 5 km the testing emphasized that gt events with accuracies 5 km or better are crucial for validating ssscs using ssscs for all 51 gt0 gt10 events used in the validation testing the median area of the error ellipses was reduced to less than 1000 km 2 and the error ellipse reductions were achieved without significant degradation of coverage the modeling errors used in this study may be somewhat underestimated however leaving the target goal of error ellipses less than 1000 km 2 still somewhat in question we expect the ssscs event locations and uncertainties can be improved by future refinement of travel times and modeling errors these corrections were implemented in the operational prototype idc system located in arlington virginia in march 2000 and have been delivered to the vienna idc in january 2001

the seismic interactions and spatiotemporal evolution of seismicity following the october 23 2011 m w 7 1 van eastern anatolia earthquake abstract we studied the mechanisms and spatiotemporal distribution of aftershocks of the mw 7 1 van earthquake in eastern turkey the van earthquake occurred on an e w trending thrust fault in a region under n s compression due to the convergence of the arabian plate toward eurasia we relocated the seismicity by combining catalogs from two agencies and studied the source mechanisms of the mw 3 5 5 6 aftershocks using regional body and surface waves in addition to the aftershocks with thrust mechanism on the mainshock fault we identified three clusters with strike slip activity two of the clusters are on the left lateral faults perpendicular to the mainshock fault and are located at the lateral termination of the co seismic rupture in each direction both western and eastern strike slip clusters were triggered within the first few hours following the mainshock they were initiated very close to the mainshock rupture plane and propagated away toward the south and north respectively these two dominantly strike slip zones are connected to the mainshock fault at a depth of 15 km and possibly determined the lateral extent of the 2011 rupture this system of two bounding left lateral faults with a thrust fault in between is overall consistent with the n s convergent tectonic regime in the region the complex geometry explains unexpected post seismic motion at a gps site and can be used to improve the post seismic slip estimate of the earthquake the third strike slip cluster with 17 days delay occurred on an e w trending right lateral fault and 40 km on the south of the mainshock the three activated faults have experienced coulomb stress increase due to co seismic rupture in addition most of the seismicity has occurred in regions that experienced coulomb stress increase

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

best practice in earthquake location using broadband three component seismic waveform data we present an earthquake location algorithm the broadband waveform regional earthquake location program bw relp which utilizes phase onset times and wave azimuths recorded by three component broadband seismic stations and an adaptive migrating grid search algorithm to find the global minimum in an arbitrary normed misfit parameter the performance ofbw relpis demonstrated using regional 300 800 km distant broadband recordings to locate events in the 1995 ridgecrest california earthquake sequence the purpose of this study is to introduce thebw relpalgorithm in detail and to expand on the previous paper by dregeret al bssa 88 1353 1362 1998 using one berkeley digital seismic network bdsn station ybh and two usnsn stations elk and mnv which span 300 800 km in distance and 55 degrees in azimuth to further investigate the capability of a sparse broadband network of three component stations at monitoring a region located outside of the network as will be the case in the monitoring of the comprehensive test ban treaty ctbt for low magnitude seismic events we assess the capability of this sparse three station broadband network and we compare locations estimated from phase onset time and wave azimuth measurements to a ground truth catalog of high quality earthquake locations derived from data recorded by the southern california seismic network scsn the results indicate that in the regional distance range it is possible when an appropriate calibration event is available to obtain absolute event locations to within 18 km as is prescribed by the ctbt

application of 3 d crustal and upper mantle velocity model of north america for location of regional seismic events seismic event locations based on regional 1 d velocity depth sections can have bias errors caused by travel time variations within different tectonic provinces and due to ray paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures seismic event locations based on 3 d velocity models have the potential to overcome these limitations this paper summarizes preliminary results for calibration of ims for north america using 3 d velocity model a 3 d modeling software was used to compute source station specific corrections ssscs 3 d for pn travel times utilizing 3 d crustal and upper mantle velocity model for the region this research was performed within the framework of the united states russian federation joint program of seismic calibration of the international monitoring system ims in northern eurasia and north america an initial 3 d velocity model for north america was derived by combining and interpolating 1 d velocity depth sections for different tectonic units in areas where no information on 1 d velocity depth sections was available tectonic regionalization was used to extrapolate or interpolate a moho depth map was integrated this approach combines the information obtained from refraction profiles with information derived from local and regional network data the initial 3 d velocity model was tested against maps of pn travel time residuals for eight calibration explosions corrections to the 3 d model were made to fit the observed residuals our goal was to find a 3 d crustal and upper mantle velocity model capable predicting pn travel times with an accuracy of 1 0 1 5 seconds r m s the 3 d velocity model for north america that gave the best fit to the observed travel times was used to produce maps of ssscs 3 d for seismic stations the computed ssscs 3 d vary approximately from 5 seconds to 5 seconds for the western usa and the pre cambrian platform respectively these ssscs 3 d along with estimated modeling and measurement errors were used to relocate using regional data an independent set of large chemical explosions with known locations and origin times detonated within various tectonic provinces of north america utilization of the 3 d velocity model through application of the computed ssscs 3 d resulted in a substantial improvement in seismic event location accuracy and in a significant decrease of error ellipse area for all events analyzed in comparison both with locations based on the iaspei91 travel times and locations based on 1 d regional velocity models

one minute after strong motion map effective epicenter and effective magnitude abstract this article reports the recent progress on real time seismic monitoring in taiwan particularly the real time strong motion monitoring by the taiwan central weather bureau9s telemetered seismic network cwbsn which is presently aiming at rapid reporting immediately after a large earthquake occurrence if rapid reporting can be achieved before the arrival of the strong shaking earthquake early warning will become possible cwbsn has achieved the generation of the intensity map epicenter and magnitude within 1 min of the occurrence of a large earthquake both rapid reporting and early warning are principally applied to large m 5 events the requirement of on scale waveform recording prompted cwbsn in 1995 to integrate strong motion sensors e g force balance accelerometers into its telemetered seismic monitoring system time domain recursive processing is applied to the multi channel incoming seismic signals by a group of networked personal computers to generate the intensity map from the isoseismal contours an effective epicenter is immediately identified that resides in the middle of the largest usually the 100 gal contour curve of the intensity map an effective magnitude is also defined that can be derived immediately from the surface area covered by the largest usually the 100 gal contour curve for a large event with a finite rupture surface the epicenter and magnitude so derived are more adequate estimates of the source location and of the strength of destruction the effective epicenter gives the center of the damage area it stands in contrast with the conventional epicenter location which only gives the initial point of rupture nucleation the effective magnitude reflects more closely the earthquake damage potential instead of the classical magnitude definition that emphasizes the total energy release the cwbsn has achieved in obtaining the above crucial source information well within 1 min this time can further be reduced to better than 30 sec as illustrated by the example in this article showing that earthquake early warning is indeed an achievable goal the rapid reporting and early warning information is electronically transmitted to users to allow rapid response actions with or without further human intervention

use of curved scanlines and boreholes to predict fracture frequencies abstract we advance the method of hudson and priest journal of rock mechanics and mining sciences geomechanics abstracts 20 1983 73 89 to develop a method for a curved scanline to be used to predict the numbers of fractures that would be observed in any direction when sampling along a scanline the probability of intersecting a fracture is influenced by the relative orientations of the fracture and of the scanline at that location this sampling bias can be minimised by the use of the terzaghi correction w cos 1 where is the angle between the scanline and the normal to the fracture these corrected frequencies are used to simulate fracture frequencies for all other orientations by doubly correcting the data modelled fracture frequency is contoured on a graph of simulated scanline plunge against simulated scanline azimuth this method is based upon the assumption that the data collected along the scanline is representative of the fracture population when the terzaghi correction has been applied a graph of cumulative frequency of fractures against distance along a scanline provides a simple method for determining whether the scanline crosses differently fractured areas frequencies are corrected for dip strike and both dip and strike with data from homogeneously fractured areas plotting as straight lines these frequencies can be normalised for ease of comparison

complex rupture of the 2014 m s 6 6 jinggu earthquake sequence in yunnan province inferred from double difference relocation to study the seismogenic structure of the 7 october 2014 ms 6 6 jinggu earthquake we use the cut and paste cap method to obtain the focal mechanisms and depths of the mainshock and the two largest aftershocks with ms 5 then we take advantage of waveform cross correlations to obtain precise time difference data and apply the double difference method to relocate the aftershocks between october 7 and december 31 we relocate 2076 earthquakes approximately 73 6 of the total with an average horizontal accuracy of approximately 150 m and a depth uncertainty of approximately 700 m the ms 6 6 mainshock epicenter originated at 23 378 n 100 475 e at a depth of 15 38 km the jinggu earthquake sequence exhibited a linearly concentrated distribution in the northwest southeast direction with obvious segmentation features and thus it can be divided into four branches spatially and two stages temporally the aftershocks first appeared around the ms 6 6 mainshock and then extended on either side of the mainshock along the nw se direction the nw branch the earthquake rupture direction experienced a slight clockwise deflection at the nw end and rotated clockwise by approximately 90 toward the sw the ne branch at the se end then the rupture propagated a short distance along the sw direction and rotated counterclockwise by approximately 90 into an sse direction the nnw branch there is a small angle between the nw and nnw branches the depths of the whole sequence with vertical dip angles were shallower toward the nw and deeper with two seismogenic layers toward the se according to the distributions of the earthquakes and nearby fractures it is highly possible that the jinggu earthquake sequence occurred along a hidden fracture section of the wuliangshan fault in the nw direction moreover we can confirm that the three large earthquakes all occurred along right lateral strike slip faults

a focused look at the alpine fault new zealand seismicity focal mechanisms and stress observations the alpine fault is the pacific australian plate boundary in the south island of new zealand this study analyzes 195 earthquakes recorded during the 6 month duration of the southern alps passive seismic experiment sapse in 1995 1996 and two mr 5 0 earthquakes and aftershocks in 1997 which occurred close to the central part of the alpine fault precise earthquake locations are derived by simultaneous inversion for hypocenter parameters a one dimensional velocity model and station corrections together with focal mechanisms calculated using a first motion and amplitude ratio method these results provide a picture of the seismotectonics in the central south island over a 6 month period moment tensor inversions of three earthquakes provide an independent means of comparison to the focal mechanisms derived using the amplitude first motion method to validate our observations over time we compare the sapse seismicity with the seismicity recorded by the new zealand national seismic network nznsn and a local network at lake pukaki east of the southern alps 6 months versus 8 years our study indicates that the alpine fault releases elastic strain seismically from the surface down to 10 12 km depth between milford sound in the south and the hope fault in the north the seismicity rate of the alpine fault is low but comparable to locked sections of the san andreas fault with large earthquakes expected seismicity decreases north of bruce bay at the alpine fault and within a triangular region along the alpine fault located between the hope and porters pass fault zones we interpret this as the result of deformation distributed on the alpine fault and the hope and porters pass fault zones the base of the seismogenic zone is fairly uniform at 12 km 2km over large parts of the south island the high alps region has a shallower base of the seismogenic zone indicating localized elevated temperatures east of the alpine fault most of the study region deforms under a uniform stress field with a maximum principal horizontal shortening direction of 110o 120 o similar to geodetic observations and plate motions this confirms that the region is not undergoing strain partitioning the earthquake data show that the deformation away from the alpine fault is distributed on mainly nne trending thrust faults and strike slip transfer faults with a maximum seismogenic depth of 12km