s wave attenuation in the coastal region of jalisco colima mexico abstract aftershock data from the october 9 1995 m 7 6 earthquake that occurred in the coastal subduction region of colima jalisco mexico are used to obtain estimates of the frequency independent quality factor q s and spectral decay parameter in the approximate frequency range 3 hz f 40 hz as functions of hypocentral distance r a regression analysis results in the relations for s waves q s 261 397 3 198r 15 536 0 009651 0 000462r 0 0012 the observed distance dependence of q s and is similar to that reported for the mexican regions of oaxaca and guerrero our q s values agree with those reported for oaxaca and northern baja ca for frequencies around 8 hz and are somewhat lower a factor of 0 8 to 0 5 for higher frequencies around 20 hz however they are significantly lower than all but the lowest values reported for the guerrero region attaining factors 0 25 and 0 13 for frequency ranges around 8 and 20 hz respectively it thus appears that the guerrero region has an anomalously low attenuation compared with the flanking coastal regions of oaxaca chiapas to the se and jalisco colima to the nw

source spectra and spectral attenuation of seismic waves from mexican earthquakes and evidence of amplification in the hill zone of mexico city it is well known that seismic waves are enormously amplified at lake bed sites with respect to hill zone sites in mexico city it has been suggested that even hill zone sites suffer amplification in this paper we use eight recent well recorded earthquakes to determine spectral attenuation of seismic waves and to quantify the suggested amplification in the hill zone results show that indeed spectral amplitudes at these sites are roughly 10 times greater than expected for sites outside mexico city at similar hypocentral distances this implies that lake bed sites are amplified by a factor of 100 to 500 at some frequencies between 0 2 to 0 7 hz the source spectra retrieved from the regression analysis agree well with those obtained from epicentral recordings alone for two of the largest earthquakes ms 8 1 and 7 6 whose seismic moments are well determined and whose source spectra can be patched in a very broad band of frequencies 0 015 to 20 hz we observe clear deviation from an 2 model the spectra at intermediate frequencies from about 0 05 to 2 hz show a sag whether the observed spectra deviate from an 2 model for events with ms 6 depends on the reliability of the reported long period seismic moments if they are considered reliable then these events also deviate from the model if however the reported seismic moments of smaller events are ignored then the observed spectra can be fitted well with the 2 model

locating spatial changes of seismic scattering property by sparse modeling of seismic ambient noise cross correlation functions application to the 2008 iwate miyagi nairiku mw 6 9 japan earthquake

high frequency source radiation during the 2011 tohoku oki earthquake japan inferred from kik net strong motion seismograms 1 to investigate source processes of the 2011 tohoku oki earthquake we utilized a source location method using high frequency 5 10 hz seismic amplitudes in this method we assumed far field isotropic radiation of s waves and conducted a spatial grid search to find the best fitting source locations along the subducted slab in each successive time window our application of the method to the tohoku oki earthquake resulted in artifact source locations at shallow depths near the trench caused by limited station coverage and noise effects we then assumed various source node distributions along the plate and found that the observed seismograms were most reasonably explained when assuming deep source nodes this result suggests that the high frequency seismic waves were radiated at deeper depths during the earthquake a feature which is consistent with results obtained from teleseismic back projection and strong motion source model studies we identified three high frequency subevents and compared them with the moment rate function estimated from low frequency seismograms our comparison indicated that no significant moment release occurred during the first high frequency subevent and the largest moment release pulse occurred almost simultaneously with the second high frequency subevent we speculated that the initial slow rupture propagated bilaterally from the hypocenter toward the land and trench the landward subshear rupture propagation consisted of three successive high frequency subevents the trenchward propagation ruptured the strong asperity and released the largest moment near the trench

ground motion scaling in eastern sicily italy we describe the characteristics of crustal wave propagation in eastern sicily by using the background seismicity of the area we follow the approach de scribed by malagnini hermann and di bona 2000 and malagnini et al 2002 our data set consists of 106 earthquakes recorded by nine three component digital seismic stations between 1994 and 2001 we used only crustal events depths shal lower than 25 km with local magnitudes ranging from 1 0 to 4 3 and hypocentral distances from 10 to 130 km peak ground velocities from 1311 narrow bandpass filtered waveforms are mea sured in thefrequency range 1 0 16 0 hz and regressedtodefinecrustalpropagation excitation and site characteristics with respect to a reference station a subsequent modeling effort is carried out through the use of random vibration theory rvt for obtaining a quantitative evaluation of the apparent geometrical spreading g r and of the crustal quality factor q f an attenuation parameter j0 is also evaluated relative to a reference rock site the attenuation and source parameters estimated in this study are used through the rvt in order to predict the peak horizontal ground acceleration pga and the 5 damping pseudoacceleration spectra psa

piecewise linear model for large strain radial consolidation a piecewise linear model for radial consolidation called rcs1 is presented rcs1 accounts for vertical strain soil self weight hydraulic conductivity anisotropy radial and vertical flows soil

coseismic radiation and stress drop during the 2015 mw 8 3 illapel chile megathrust earthquake on 16 september 2015 an mw 8 3 earthquake struck middle chile due to the subduction of the nazca plate beneath the south america plate this earthquake is the consequence of 72 years of strain accumulation in the region since the 1943 m 8 3 event in this study we apply the compressive sensing method cs to invert for the spatiotemporal distribution of the coseismic radiation at different frequencies of this event the results show clear frequency dependent feature of earthquake rupture with low frequency lf radiation located in the updip region while high frequency hf radiation concentrated in the downdip region of the megathrust we also compare the cs results with three coseismic slip models as well as the stress drop distributions inferred from these slip models the comparison confirms our understanding of coseismic radiation that energy sources are mostly located in the margin of large coseismic slip regions furthermore we find that the lf radiation sources are mainly within the stress decreasing releasing regions while the hf radiation sources are mainly located in the stress increasing loading regions due to rupturing of relatively large asperities nearby stress decreasing and releasing these results help to better understand the physics of the rupture process during megathrust earthquakes moreover our results do not show radiation sources south of the epicenter suggesting that the subducting juan fernandez ridge probably stopped the rupture of this earthquake toward the south

smooth and rapid slip near the japan trench during the 2011 tohoku oki earthquake revealed by a hybrid back projection method abstract we developed a new back projection method that uses teleseismic p waveforms to integrate the direct p phase with reflected phases from structural discontinuities near the source and used it to estimate the spatiotemporal distribution of the seismic energy release of the 2011 tohoku oki earthquake we projected a normalized cross correlation of observed waveforms with corresponding green s functions onto the seismic source region to obtain a high resolution image of the seismic energy release applying this method to teleseismic p waveform data of the 2011 tohoku oki earthquake we obtained spatiotemporal distributions of seismic energy release for two frequency bands a low frequency dataset and a high frequency dataset we showed that the energy radiated in the dip direction was strongly frequency dependent the area of major high frequency seismic radiation extended only downdip from the hypocenter whereas the area of major low frequency seismic radiation propagated both downdip and updip from the hypocenter we detected a large release of seismic energy near the japan trench in the area of maximum slip which was also the source area of the gigantic tsunami when we used only the low frequency dataset the timing of this large seismic energy release corresponded to an episode of smooth and rapid slip near the japan trench and reflects the strong dependence of the seismic energy distribution obtained on the frequency band of the input waveform dataset the episode of smooth and rapid slip may have been the trigger for a release of roughly all of the accumulated elastic strain in the seismic source region of the 2011 tohoku oki earthquake

a new strategy of finite fault inversion using multiscale waveforms and its application to the 2015 gorkha nepal earthquakefinite fault inversion using multiscale waveforms and its application to the 2015 gorkha earthquake

shear wave attenuation and site response in guerrero mexico spectra from moderate earthquakes are used to investigate shear wave attenuation and site response for accelerographs located on rock outcrops in guerrero mexico a least squares method is used to model the strong motion spectra assuming an 2 source and an exponential decay term e f to describe the high frequency spectral shape the spectral decay variable associated with attenuation is parameterized as the sum of a distance dependent component r and a site term s which takes a different value for each site s frequency dependent site response is determined by comparing observed spectra to model event spectra corrected for and geometrical spreading averaging these residuals over several earthquakes results in an estimate of site response that is generally free of source and path effects the distance dependence of the spectral decay parameter as expressed by r is very weak in the guerrero region in contrast to that in southern california anderson 1991b this difference may be due to greater shear strength of the top 20 km of crust in the guerrero subduction zone near site attenuation represented by s is greater in guerrero compared to the stations in the anza array of southern california no obvious correlation with site geology was found a combination of a deeper weathered layer of crystalline rock and varying subsurface lithology may be responsible for the greater mean values of s in guerrero the frequency dependent site functions show significant amplification and deamplification effects for the hard rock sites no direct correlation with local topography is observed to explain these effects the site functions obtained here by constraining the source shape and geometrical spreading closely resemble those derived for guerrero stations by castro et al 1990 using much less restrictive assumptions about the source and propagation effects

initiation of the great mw 9 0 tohoku oki earthquake abstract we determined the location size mechanism and the frequency content of the first 4 0 s of the 2011 tohoku oki earthquake since the beginning of this earthquake is very small we develop a comparative approach against a near by reference earthquake the master event we first determined the water depth near the master event using the differential timing between the water phase pwp reflected from the air water interface and the depth phase pp reflected from the water crust interface then we located the master event using the well known ocean bathymetry in the area after calibrating teleseismic arrays 30 to 90 at short periods for timing and amplitude with respect to the master event we were able to determine the initiation of the main event it began as a small m w 4 9 thrust event located at 38 19 n 142 68 e at a depth of 21 km and a few seconds later evolved into a slower extremely large slip event up dip

p wave velocity tomography from local earthquakes in western mexico in western mexico the subduction of the rivera and cocos plates beneath the north america plate has deformed and fragmented the overriding plate forming several structural rifts and crustal blocks to obtain a reliable subsurface image of the continental crust and uppermost mantle in this complex area we used p wave arrivals of local earthquakes along with the fast marching method tomography technique we followed an inversion scheme consisting of 1 the use of a high quality earthquake catalog and corrected phase picks 2 the selection of earthquakes using a maximum location error threshold 3 the estimation of an improved 1 d reference velocity model and 4 the use of checkerboard testing to determine the optimum configuration of the velocity nodes and inversion parameters surprisingly the tomography results show a very simple vp distribution that can be described as being controlled by geologic structures formed during two stages of the separation of the rivera and cocos plates the earlier period represents the initial stages of the separation of the rivera and cocos plates beneath western mexico the later period represents the more advanced stage of rifting where the rivera and cocos plates had separated sufficiently to allow melt to accumulate below the colima volcanic complex during the earlier period 14 or 10 1 6 ma ne sw oriented structures lineaments such as the southern colima rift were formed as the two plates separated during the second period 1 6 ma to the present the deformation is attributed to magma generated within and above the tear zone between the rivera and cocos plates rising beneath the region of the colima volcanic complex the rising magma fractured the overlying crust forming a classic triple rift junction geometry this triple rift system is confined to the mid to lower crust perhaps indicating that this rifting process is still in an early stage this fracturing along with fluid circulation and associated heat advection within the fractures can easily explain the observed distribution of vp as well as many of the results of previous seismological studies also surprisingly we find no evidence at deep crustal depths to support either a trenchward migration of the volcanic arc or toroidal asthenospheric flow through the slab tears bounding the jalisco block to the nw and se

back projection imaging of earthquakes back projection analysis of earthquakes is a type of array processing that images the source of seismic waves coherently recorded at stations throughout the seismic network the method was developed following the magnitude 9 2 sumatra andaman earthquake in 2004 although properties of earthquakes have been investigated using array data prior to the introduction of the back projection method this technique differs from other approaches because it makes limited assumptions and allows detailed and complex rupture propagation to be examined these advantages have led several researchers to apply the method to many of the largest earthquakes to occur this century the method has also been effective for the detection of smaller events a critical component of the success of back projection has been the development of large scale dense seismic arrays further improvements and future applications of the method will depend greatly on the continued maintenance and development of these networks

coda waves a review the analysis and interpretation of coda waves have received increasing attention since the early seventies in the past few years interest in this subject has spread worldwide and the study of high frequency seismic coda waves has become a very important seismological topic as a conclusion of the studies accomplished in this time coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves p ands waves play a particularly important role in this interaction the process introduces an attenuation which added to the intrinsic absorption gives the observed apparent attenuation therefore coda waves constitute a thumbprint left by the heterogeneities on the seismograms coda waves offer decisive information about the mechanism of how scattering and attenuation take place this review describes coda waves in detail and summarizes the work done in this subject to 1986 the relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed particular attention has been given to the application of coda waves to estimate source and medium parameters the state of the art of the temporal variations of coda wave shape and the possible use of these variations as an earthquake precursor also are presented care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering

a frequency dependent relation of coda q c for koyna warna region india attenuation properties of the lithosphere around the koyna warna seismic zone is studied by estimating the coda q c from 30 local earthquakes of magnitude varying from 1 5 to 3 8 an average lapse time of 65 sec used in the single scattering model sampled a circular area with an average radius of 114 km the estimated q c values show a frequency dependent relation q c 169 f0 77 and range from 169 at i hz to 1565 at 18 hz a comparison of worldwide q studies reveals that for a large frequency range the q for active regions is low as compared to that for stable regions however south carolina and norway are exceptions in that their q is low in the low frequency range while new england and north iberia are exceptions as they have a q value similar to that for active regions like spain turkey italy and garhwal himalaya stih in the higher frequency range in contrast to this the q for the koyna warna area which belongs to a stable region is low in the entire frequency range as compared to the stable regions and similar to the active stih regions

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

attenuation of high frequency p and s waves in the gujarat region india the local earthquake waveforms recorded on broadband seismograph network of institute of seismological research in gujarat india have been analyzed to understand the attenuation of high frequency 2 25 hz p and s waves in the region the frequency dependent relationships for quality factors for p qp and s qs waves have been obtained using the spectral ratio method for three regions namely kachchh saurashtra and mainland gujarat the earthquakes recorded at nine stations of kachchh five stations of saurashtra and one station in mainland gujarat have been used for this analysis the estimated relations for average qp and qs are qp 105 2 f0 82 0 01 qs 74 2 f1 06 0 01 for kachchh region qp 148 2 f0 92 0 01 qs 149 14 f1 43 0 05 for saurashtra region and qp 163 7 f0 77 0 03 qs 118 34 f0 65 0 14 for mainland gujarat region the low q 0 5 as obtained from present analysis indicate the predominant seismic activities in the region the lowest q values obtained for the kachchh region implies that the area is relatively more attenuative and heterogeneous than other two regions a comparison between qs estimated in this study and coda q qc previously reported by others for kachchh region shows that qc qs for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to the attenuation of s waves in the kachchh region infested with faults and fractures the qs qp ratio is found to be less than 1 for kachchh and mainland gujarat regions and close to unity for saurashtra region this reflects the difference in the geological composition of rocks in the regions the frequency dependent relations developed in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake ground motions in the region

direct body wave q estimates in northern baja california mexico abstract we used direct arrivals of p and s waves recorded by the seismic network of northern baja california resnom to estimate the quality factor q in the peninsular ranges of baja california mexico spectral amplitudes from 34 earthquakes with magnitudes between 2 2 and 4 0 were analyzed to determine attenuation functions at 17 frequencies 0 3 1 r r being the hypocentral distance for r 80r 1 2 for r 80 km q for both p and s increases with frequency taking the form qp 14 4f0 9 for p waves and qs 28 3f1 0 for s waves the ratio of q p q s 0 5 obtained in northern baja california is similar to that obtained by hough et al 1988 attenuation near anza california bull seism soc am 78 672 691 q p q s 0 54 for the southern california batholith near anza and the ratio reported by taylor et al 1986 attenuation and scattering of broadband p and s waves across noth america j geophys res 91 7309 7325 for the crust and upper mantle in the basin and range region for high frequencies f 2 hz this result suggests that scattering effects are an important factor affecting the decay of the attenuation functions in the peninsular ranges of baja california

low coda qc in the epicentral region of the 2001 bhuj earthquake of mw 7 7 on 26 january 2001 03 46 55 ut a devastating intraplate earthquake of m w 7 7 occurred in a region about 5 km nw of bhachau gujarat 23 42 n 70 23 e the epicentral distribution of aftershocks defines a marked concentration along an e w trending and southerly dipping 45 zone covering an area of 60 40 km2 the presence of high seismicity including two earthquakes of magnitudes exceeding 7 7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the kutch area a site lying in the seismic zone v zone of the highest seismicity for potentially m8 earthquakes on the seismic zoning map of india attenuation property of the medium around the epicentral area of the bhuj earthquake covering a circular area of 61 500 km2 with a radius of 140 km is studied by estimating the coda q c from 200 local earthquakes of magnitudes varying from 3 0 4 6 the estimated q 0 values at locations in the aftershock zone high seismicity are found to be low in comparison to areas at a distance from it this can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone distribution of q 0 values suggests that the local variation in q 0 values is probably controlled by local geology the estimated q 0 values at different stations suggest a low value of q 102 0 80 f 0 98 0 02 indicating an attenuative crust beneath the entire region the frequency dependent relation indicates a relatively low q c at lower frequencies 1 3 hz that can be attributed to the loss of energy due to scattering attenuation associated with heterogeneities and or intrinsic attenuation due to fluid movement in the fault zone and fluid filled cracks the large q c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneity is expected based on the attenuation curve estimated for q 0 102 the ground acceleration at 240 km distance is 13 of 1 g i e 0 13 g agreeing well with the ground acceleration recorded by an accelerograph at ahmedabad 0 11 g hence it is inferred that the q 0 value obtained from this study seems to be apt for prediction of ground motion for the region

multiple branching rupture of the 2009 tonga samoa earthquake several source models have been proposed to explain the enigmatic 2009 tonga samoa earthquake the long period data require a composite source model and can be fit with a normal faulting subevent followed by one or more reverse faulting subevents the short period data in contrast indicate a more compact rupture pattern around the epicenter the lack of a unified source model reflects the complexity of the event we analyze the spatiotemporal evolution of this earthquake with p wave back projection from globally distributed stations in different frequency bands low frequency 0 05 0 2 hz high frequency 0 2 2 hz and a multiple moment tensor inversion the rupture propagation revealed by back projection exhibits frequency dependent behavior with two branches of high frequency enriched bilateral rupture around the epicenter and a high frequency deficient rupture branch at the subduction interface a composite source model with one mw 8 0 normal faulting earthquake east of the trench axis seaward followed by one mw 8 1 reverse faulting earthquake along the subduction interface west of the trench axis landward can explain the very long period data 200 500 s combined with high resolution swath bathymetry data the back projection images show that the azimuth of rupture branches east of the trench axis were controlled by the geometry of bending related faults on the pacific plate and that the rupture branch west of the trench axis may correlate with the along strike fore arc segmentation the rupture along the subduction interface was triggered by the seaward rupture and a partially subducted normal fault may have played a key role in facilitating the triggering the apparent normal reverse faulting interactions pose a higher seismic risk to this region than their individual strands at the northernmost corner of the tonga subduction zone

benchmark problems for large strain consolidation abstractmodeling of the one dimensional consolidation process for soil and other compressible porous media is important for a variety of engineering applications this paper presents solutions for two benchmark problems for large strain consolidation of a saturated soil layer that can be used to check other analytical and numerical analysis methods the solutions include effects of vertical strain soil self weight nonlinear constitutive relationships and changing material properties during the consolidation process high accuracy data are presented for each problem and include changes of settlement void ratio and excess pore pressure with time

s wave coda q from 3 to 20 hz and p wave q for foreshocks and aftershocks of the petatlan earthquake in order to understand better the variations of mechanical properties close to the source and the failure process in the upper portion of the crust in a geologically very young subduction zone the seismic s wave coda qc from 3 to 20 hz and p wave half pulse width qp from 6 to 12 hz were determined for selected foreshocks and aftershocks of the 1979 petatlan mexico ms 7 6 earthquake to limit the region being sampled the quality factor of s coda qc was obtained from the first 10 s following the s onset qc exhibited a strong spatial temporal and frequency dependence and in the small foreshock portion of the aftershock area qc and to a lesser extent qp were significantly lower before the mainshock than afterward the frequency dependence n in qc qo n was practically constant for aftershocks in four different regions n 1 32 0 03 and for foreshocks n 1 43 0 07 only in one peripheral region station pair did we find a significantly different n n 0 97 0 09 our observations indicate that qc and perhaps the frequency dependence n are sensitive to the physical property changes in the source region and might be useful as predictors of large earthquakes in a shallow subduction zone environment

evidence of spatial variations of attenuation in the western pyrenean range summary spectral attenuation of coda waves has been studied in the range 2 40 hz from local events recorded in the western pyrenean range from 1980 to 1982 q was obtained using a single scattering model ol s waves for different segments of the coda an increase of q with lapse time was found and attributed to a rapid increase of qp with depth three groups of events were selected from distinct focal areas two data sets are mainly composed of aftershocks of moderate earthquakes of magnitude 5 1 and 4 8 respectively no moderate earthquake occurred in the third area in the few years preceding or following the selected events use of stations close to epicentres allowed sampling of the coda at very short lapse times and then study of small distinct scattering volumes noticeable differences were found between the three studied areas and attributed to spatial rather than temporal variations the q frequency dependence was studied according to q qfa y is found to range from 0 7 to 1 1 and q from 30 to 140 these values are in agreement with those found inother tectonic areas it is shown that scattering is the dominant attenuation process below 10 hz

estimates of shallow attenuation and apparent stresses from aftershocks of the oaxaca earthquake of 1978 acceleration spectra at high frequencies were analyzed to make an estimation of the spectral decay parameter in the aftershock area of the 1978 oaxaca earthquake it was found that follows a linear behavior given by r r increasing with source to station distance r in the frequency band from 8 to 25 hz values range from 15 7 to 33 9 msec and do not show a strong variation from station to station on different types of crystalline terrain estimates of d r dr do not indicate a strong lateral variation of the frequency independent quality factor q in the crust of the oaxaca region apparent stresses were also calculated for a subset of aftershocks and no clear scaling with seismic moment or is observed apparent stresses lie between 3 6 to 256 bars

spatio temporal distribution of fault slip and high frequency radiation of the 2010 el mayor cucapah mexico earthquake 1 earthquake slip history and moment release are best resolved using long period seismic waves but details in the rupture process such as sharp changes in rupture velocity or direction can be imaged more clearly using higher frequency waves here we investigate the slip and the high frequency radiation histories of the 2010 el mayor cucapah baja california mexico earthquake mw 7 2 the slip distribution inferred from inversion of strong motion data between 0 02 and 0 25 hz indicates northwest propagating rupture followed by bilateral rupture for 40 s the sources of high frequency radiation between 0 3 and 2 hz inferred from back projection analysis using teleseismic data are adjacent to but not within the high slip patches from the finite slip model in time and space this implies relatively smooth rupture during the times and regions of maximum moment release as theoretical models have predicted high frequency radiation seems mostly associated with changes in rupture velocity or slip magnitude strong high frequency radiation is also found where the rupture propagated to a branch fault 50 km northwest of the hypocenter complementary constraints on both fault slip and high frequency radiation provide increased understanding of earthquake rupture mechanics and may help improve strong motion evaluation at high frequencies

dual megathrust slip behaviors of the 2014 iquique earthquake sequence the transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes a mw 8 2 earthquake occurred on april 1st 2014 in the iquique seismic gap of northern chile this event was preceded by a long foreshock sequence including a 2 week long migration of seismicity initiated by a mw 6 7 earthquake repeating earthquakes were found among the foreshock sequence that migrated towards the mainshock hypocenter suggesting a large scale slow slip event on the megathrust preceding the mainshock the variations of the recurrence times of the repeating earthquakes highlight the diverse seismic and aseismic slip behaviors on different megathrust segments the repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip while repeaters that occurred both before and after the mainshock were in the area complementary to the mainshock rupture the spatiotemporal distribution of the repeating earthquakes illustrates the essential role of propagating aseismic slip leading up to the mainshock and illuminates the distribution of postseismic afterslip various finite fault models indicate that the largest coseismic slip generally occurred down dip from the foreshock activity and the mainshock hypocenter source imaging by teleseismic back projection indicates an initial down dip propagation stage followed by a rupture expansion stage in the first stage the finite fault models show an emergent onset of moment rate at low frequency 0 5 hz 0 5 hz this indicates frequency dependent manifestations of seismic radiation in the low stress foreshock region in the second stage the rupture expands in rich bursts along the rim of a semi elliptical region with episodes of re ruptures suggesting delayed failure of asperities the high frequency rupture remains within an area of local high trench parallel gravity anomaly tpga suggesting the presence of subducting seamounts that promote high frequency generation our results highlight the complexity of the interactions between large scale aseismic slow slip and dynamic ruptures of megathrust earthquakes

seismic energy attenuation in the region between the coast of guerrero and mexico city differences between paths along and perpendicular to the coast attenuation of seismic energy in central mexico from earthquakes generated along the south coast has been discussed in several works the attenuation interpretations falls broadly in two categories the first lower attenuation in paths going inland relative to paths going along the coast the second attenuation follows the same model regardless of the path in this paper we analyze data from a seismic refraction experiment between the coast of guerrero and the valley of mexico as well as data from an earthquake with its epicenter in the coast of guerrero in order to study seismic wave attenuation along the two paths we found a lower attenuation of s waves going toward the continent than along the coast this fact is clear from refraction data and can be concluded from our earthquake data and by reinterpreting information from previous works we find q values that indicate the attenuation relations based mainly in anelastic dissipation currently used for the region between the coast and the valley of mexico are not adequate other factors should be considered to explain the inland observations this regional effect should also be considered in the study of the large amplification of seismic signals in the valley of mexico and also for other cities in mexico

active rifting in southwestern mexico manifestations of an incipient eastward spreading ridge jump a major ongoing episode of continental rifting has formed a system of three intersecting grabens in the western mexican volcanic belt these structures may mark the initial stage of an eastward spreading ridge jump beneath continental crust eastward ridge segment jumps have been propagating northward along this part of the east pacific rise for the past 12 m y but this is the first plate boundary reorganization event to involve continental crust since the separation of baja california in the miocene since pliocene time small volumes of unusual alkaline magmas have erupted in the graben areas in close association with the more abundant subduction related calc alkaline magmas erupted from andesitic stratovolcanoes the alkaline magmas are varieties found in zones of active rifting elsewhere in the world

application of seismic array processing to earthquake early warning earthquake early warning eew systems that issue warnings prior to the arrival of strong shaking are essential in mitigating earthquake hazard currently operating eew systems work on point source assumptions and are of limited effectiveness for large events for which ignoring finite source effects result in magnitude underestimation here we explore the concept of characterizing rupture dimensions in real time for eew using small aperture seismic arrays located near active faults back tracing array waveforms allow estimation of the extent of the rupture front as a proxy of the rupture size and directivity in real time providing complementary eew capabilities for m 7 earthquakes to existing eew systems we implement it in a simulated real time environment and analyze the 2004 m 6 parkfield california earthquake recordings by the u s geological survey parkfield dense seismograph array upsar array and the 2010 m 7 2 el mayor cucapah earthquake recordings by strong motion sensors in san diego california we find it important to correct for the bias in back azimuth induced by dipping structures beneath the upsar array based on data from smaller events our estimated rupture length is 30 shorter than those inferred from other studies but still reasonable for eew purposes we attribute this difference to rupture directivity effects and the limited field of view of a single array the accuracy of the approach may be improved with a network of arrays with overlapping fields of view we demonstrate this by tracking the 2011 tohoku earthquake rupture with two clusters of hi net stations in kyushu and northern hokkaido the obtained results are consistent with teleseismic back projection results and yield reasonable estimates of rupture length and directivity compared with other proposed finite fault eew approaches the array method is less affected by the coarseness of a global positioning system or seismic network and provides a high frequency characterization of the rupture that yields more suitable predictors of ground shaking for certain structures

geodetic imaging of coseismic slip and postseismic afterslip sparsity promoting methods applied to the great tohoku earthquake 1 geodetic observations of surface displacements during and following earthquakes such as the march 11 2011 great tohoku earthquake can be used to constrain the spatial extent of coseismic slip and postseismic afterslip and characterize the spectrum of earthquake cycle behaviors slip models are often regularized by assuming that slip on the fault varies smoothly in space which may result in the artificial smearing of fault slip beyond physical boundaries alternatively it may be desirable to estimate a slip distribution that is spatially compact and varies sharply here we show that sparsity promoting state vector regularization methods can be used to recover slip distributions with sharp boundaries representing an alternative end member result to very smooth slip distributions using onshore gps observations at 298 stations during and in the 2 weeks following the tohoku earthquake we estimate a band of coseismic slip between 30 and 50 km depth extending 500 km along strike with a maximum slip of 64 m corresponding to a minimum magnitude estimate of mw 8 8 our estimate of afterslip is located almost exclusively down dip of the coseismic rupture with a transition between 40 and 50 km depth and an equivalent moment magnitude mw 8 2 this depth may be interpreted as coincident with the transition from velocity strengthening to velocity weakening frictional behavior consistent with the upper limit of cold subduction estimates of the thermal structure of the japan trench

a catalog of shallow earthquakes of mexico from 1900 to 1981 a catalog of shallow earthquakes depth 65 km of mexico 15 to 20 n 94 5 to 105 5 w covering the period 1900 to 1981 is presented the catalog includes only those events whose magnitudes m ms or magnitude from pasadena are 5 9 it is most likely complete for shocks with ms 6 5 from july 1906 to december 1981 for many shocks ms has been determined from uppsala bulletins and or uppsala and gottingen wiechert seismograms the statistics of incremental frequency n ms shows a peak at ms 7 7 reinforcing a previous observation by singh et al 1981 in the range 6 4 ms 7 5 the observed n ms deviates significantly from an exponential distribution the catalog provides a basis for further statistical analysis of earthquakes in mexico

fast rupture propagation for large strike slip earthquakes abstract studying rupture speeds of shallow earthquakes is of broad interest because it has a large effect on the strong near field shaking that causes damage during earthquakes and it is an important parameter that reflects stress levels and energy on a slipping fault however resolving rupture speed is difficult in standard waveform inversion methods due to limited near field observations and the tradeoff between rupture speed and fault size for teleseismic observations here we applied back projection methods to estimate the rupture speeds of 15 m w 7 8 dip slip and 8 m w 7 5 strike slip earthquakes for which direct p waves are well recorded in japan on hi net or in north america on usarray we found that all strike slip events had very fast average rupture speeds of 3 0 5 0 km s which are near or greater than the local shear wave velocity supershear these values are faster than for thrust and normal faulting earthquakes that generally rupture with speeds of 1 0 3 0 km s

cs3 large strain consolidation model for layered soils abstracta numerical model called cs3 is presented for one dimensional large strain consolidation of layered soils the algorithm accounts for vertical strain soil self weight conventional constitutive relationships changing material properties during consolidation unload reload time dependent loading and boundary conditions an externally applied hydraulic gradient and multiple soil layers with different material properties cs3 can accommodate equilibrium and nonequilibrium profiles for the initial void ratio as well as variable profiles for preconsolidation stress and applied stress increment verification checks show excellent agreement with available analytical and numerical solutions several numeric examples are used to illustrate the capabilities of cs3 and highlight errors that may occur when multilayer systems are modeled as a single layer with average properties finally settlement estimates obtained using cs3 are in good agreement with field measurements for the gloucester test fill

lapse time and frequency dependent attenuation characteristics of kumaun himalaya abstract we have analyzed local earthquake data set consists of 84 well located events recorded by a digital seismic network in the kumaun himalaya region during 2004 2007 to study seismic attenuation characteristics of the region single back scattering assumption is used to estimate coda q q c values of the region at frequency range of 1 5 3 6 8 12 and 18 hz for different lapse time window length the values of q c show a ubiquitous observation of frequency dependence and follow a substantially similar trend as observed in other tectonically active parts of the himalaya the lapse time dependencies of coda waves are investigated which reveal that by increasing lapse time window from 20 to 50 s q 0 q c at 1 hz increases from 64 2 to 230 19 while frequency dependent parameter n decreases from 1 08 to 0 81 increase in q c with lapse time indicates decrease in heterogeneity with depth the observed values of q 0 and n infer that the medium beneath the study area is highly heterogeneous and tectonically very active the variation of q c with lapse time at 1 5 hz follow a similar pattern with the theoretically predicted values of gusev 1995 although the frequency parameter n does not match with the model it may suggest that the turbidity decays rapidly with depth for the kumaun himalaya our results are comparable with those obtained from tectonically active regions in the world

attenuation of coda waves in northern greece the single scattering model has been applied for the estimation of codaq values for local earthquakes that occurred in northern greece during the period 1983 1989 and recorded by the telemetered network of the geophysical laboratory of the university of thessaloniki codaq estimations were made for four frequency bands centered at 1 5 hz 3 0 hz 6 0 hz and 12 0 hz and for the lapse time windows 10 20 sec 15 30 sec 20 45 sec 30 60 sec and 50 100 sec the codaq values obtained show a clear frequency dependence of the formq c q 0 f n whileq 0 andn depend on the lapse time window q 0 was found equal to 33 andn equal to 1 01 for the time window of 10 to 20 sec while for the other windowsq 0 increased from 60 to 129 withn being stable close to 0 75 this lapse time dependence is interpreted as due to a depth dependent attenuation the high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity in agreement with studies in other seismic regions

time space variation of seismic s wave coda attenuation qc 1 and magnitude distribution b values for the petatlan earthquake average s wave coda q qc at 6 hz and to about 10 sec after the s wave arrival shows 1 temporal variation positively correlated with the magnitude distribution parameter b for foreshocks and aftershocks of the 1979 petatlan mexico earthquake 2 spatial variation through the aftershock area positively correlated with b high qc b values at the two activity centers intermediate values in between and landward and low values toward the middle america trench which remain low for two weeks after the main shock and 3 five foreshock average qc 135 1 6 and eleven aftershock average qc 175 1 3 for the eastern asperity the b values and possibly qc values seem to correlate with the level of aftershock activity

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

attenuation characteristics of coda waves in mainland gujarat india abstract the attenuation characteristics based on coda waves of mainland gujarat india have been investigated in the present study the broadband waveforms of 53 local earthquakes mw 1 1 3 3 having focal depths in the 6 0 33 6 km range recorded at five stations of mainland gujarat region has been used for the analysis the frequency dependent relationships q q0fn for coda q qc and dependency of coda q on lapse time windows have been determined for the said region the average lapse time dependent coda q relations estimated for the region are qc 87 13 f 1 01 0 06 lapse time 30 s qc 112 20 f 0 94 0 08 lapse time 40 s and qc 120 22 f 0 76 0 07 lapse time 50 s the increase in qc values with lapse time shows the depth dependence of qc as longer lapse time windows will sample larger area the observed quality factor is strongly dependent on frequency and lapse time which indicates that the upper lithosphere is more heterogeneous and seismotectonically active while the lower lithosphere is homogeneous and relatively less active a comparison of the coda q estimated for mainland gujarat region with those of nearby kachchh and saurashtra regions shows that mainland gujarat region is more heterogeneous the rate of decay of attenuation q 1 with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ the obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the mainland gujarat region where no such relations were available earlier these relations are also important for the simulation of earthquake strong ground motions in the region

influence of subduction zone structure on coastal and inland attenuation in mexico summary although it has been suggested in the past that the attenuation of seismic waves along the pacific coast of mexico and towards the continent differs the subject has been controversial and as yet unresolved here we re examine this issue using more extensive and higher quality data now available our analysis of more than 450 local and regional r 400 km records from interplate earthquakes 5 0 m w 8 0 10 h 30 km shows that the fourier spectral amplitudes at inland sites exceed those at coastal ones especially in the frequency range of 0 3 2 hz we find that site or source effects are not the cause of this difference the observed disparity of amplitudes is in fact a consequence of the efficient propagation of lg and sms phases along the convergence direction as it is confirmed by numerical modelling the simulations show that the energy radiated by interplate earthquakes is efficiently guided towards the continent by the wedge shape geometry and the structure of the subduction zone thus enhancing the inland wavefield beyond 100 150 km on the contrary for coastal paths there is a rapid drop of amplitude due to lateral heterogeneity and low crustal thickness corresponding to geometrical spreading terms of

seismicity in subduction zones from local and regional network observations the data provided by local and regional seismograph networks are essential for the solution of many problems of subduction zone seismology the capabilities of such networks are limited by the instrumentation currently in common use and the unfavorable source station geometry often imposed by the regional geography nevertheless important contributions have come from the data gathered in many of the earth s subduction zones the accuracy of hypocenter locations based on regional data is affected by the complex velocity structures characteristic of subduction zones but the problems are now well understood examples of numerous studies of the spatial configurations of the seismicity in subduction zones and consequent interpretations of seismogenesis and subduction processes are reviewed studies of the distributions of earthquakes in time and with magnitude for events down to the microearthquake level have the potential for clarifying the earthquake generating processes and possibly a basis for earthquake prediction other uses of local and regional network data have been for investigations of coda s and the identification of asperities in subduction zones

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

source spectra and rms acceleration of mexican subduction zone earthquakes strong motion sm data of six mexican subduction zone earthquakes 6 4 ms 8 1 recorded near the epicentral zone are analyzed to estimate their far field source acceleration spectra at higher frequencies f 0 3 hz apart from the usual corrections such as geometrical spreading 1 r average radiation pattern 0 6 free surface amplification a factor of 2 and equal partitioning of the energy into two orthogonal horizontal components a factor of 1 sqrt 2 the observed spectra are corrected for a frequency dependentq q 100f a site dependent filter e kf and amplification ofs waves near the surface a factor of about 2 atf 2hz we taker as the average distance from the rupture area to the site if we model the high frequency plateau f 1 hz of the source spectra by a point source 2 model and interpret them in terms of brune s model we obtain between 50 and 100 bars for all earthquakes the low frequency broadband teleseismicp wave spectra corrected witht 1 0 s agrees within a factor of two with sm source spectra near 1 hz the 2 model is inadequate to explain the observed source spectra in a broad frequency range these resemble spectra given bygusev 1983 with some differences

site response attenuation and source spectra of s waves along the guerrero mexico subduction zone acceleration spectra from nine earthquakes and up to 11 stations per earthquake are inverted to find the source spectra the site response and the quality factor q of s waves this method is applied to moderate earthquakes 4 0 0 8 hz does not follow a simple linear relation as observed in previous studies of attenuation in other regions when the source spectra are interpreted in terms of brune s model the stress drops obtained are less than 20 bars for the four larger events analyzed the site functions obtained indicate that although all the stations used are on rock the effect of the near surface geology caused important amplifications at some stations

automatic imaging of earthquake rupture processes by iterative deconvolution and stacking of high rate gps and strong motion seismograms by combining the complementary advantages of conventional network inversion and backprojection methods we have developed an iterative deconvolution and stacking ids approach for imaging earthquake rupture processes with near field complete waveform data this new approach does not need any manual adjustment of the physical empirical constraints such as restricting the rupture time and duration and smoothing the spatiotemporal slip distribution therefore it has the ability to image complex multiple ruptures automatically the advantages of the ids method over traditional linear or nonlinear optimization algorithms are demonstrated by the case studies of the 2008 wenchuan and 2011 tohoku earthquakes for such large earthquakes the ids method is considerably more stable and efficient than previous inversion methods additionally the robustness of this method is demonstrated by comprehensive synthetic tests indicating its potential contribution to tsunami and earthquake early warning and rapid response systems it is also shown that the ids method can be used for teleseismic waveform inversions for the two major earthquakes discussed here the ids method can provide without tuning any physical or empirical constraints teleseismic rupture models consistent with those derived from the near field gps and strong motion data

the transition of dynamic rupture styles in elastic media under velocity weakening friction although kinematic earthquake source inversions show dominantly pulse like subshear rupture behavior seismological observations laboratory experiments and theoretical models indicate that earthquakes can operate with different rupture styles either as pulses or cracks that propagate at subshear or supershear speeds the determination of rupture style and speed has important implications for ground motions and may inform about the state of stress and strength of active fault zones we conduct 2d in plane dynamic rupture simulations with a spectral element method to investigate the diversity of rupture styles on faults governed by velocity and state dependent friction with dramatic velocity weakening at high slip rate our rupture models are governed by uniform initial stresses and are artificially initiated we identify the conditions that lead to different rupture styles by investigating the transitions between decaying steady state and growing pulses cracks sub shear and super shear ruptures as a function of background stress nucleation size and characteristic velocity at the onset of severe weakening our models show that small changes of background stress or nucleation size may lead to dramatic changes of rupture style we characterize the asymptotic properties of steady state and self similar pulses as a function of background stress we show that an earthquake may not be restricted to a single rupture style but that complex rupture patterns may emerge that consist of multiple rupture fronts possibly involving different styles and back propagating fronts we also demonstrate the possibility of a super shear transition for pulse like ruptures finally we draw connections between our findings and recent seismological observations

a broadband seismological investigation of the 1989 loma prieta california earthquake evidence for deep slow slip analysis of regional and teleseismic broadband body waves and long period surface waves from the 1989 loma prieta earthquake demonstrates that a fairly simple average fault model explains most characteristics of seismic wave radiation over a broad period range 1 to 300 sec but there are some systematic period dependent characteristics that are not yet understood determinations of the preferred point source focal mechanism are consistent for different seismic waves as long as optimal source time functions and depths are chosen for each wavetype the major double couple orientation compatible with the entire period range has a strike 128 3 dip 67 5 and rake 133 8 while this source mechanism consistency is encouraging and indicates that the average source process is quite simple there are some systematic discrepancies in the source parameter estimates from different period waves the source duration estimated from the principal body wave ground motions is 8 2 sec compatible with the duration of near field strong motion vibrations but the surface waves indicate total durations of 18 to 30 sec depending on the earth model selected for computing propagation corrections the model dependence of the surface wave results suggests that it may be possible to reconcile the duration estimates with improved earth models but the discrepancy is quite large there is some complexity in the source time function comprised of three subevents at different depths but this complexity is only manifested in short period signals and does not explain the duration discrepancy changes of fault geometry or slip direction during rupture as suggested by recent finite fault inversions are unlikely to cause a bias in source duration estimates the centroid depth determined from our body wave analysis is 10 to 12 km consistent with the finite fault models which indicate rupture extending from 5 to 18 km surface wave centroid depth estimates 15 to 30 km vary substantially for different choices of global q model and lithospheric structure in the source region but they do tend to be deeper than the body wave results it is again not clear whether this depth discrepancy is due to the source process or inadequate earth models the body wave and surface wave seismic moment estimates are also not fully consistent the moment from our body wave inversions is 2 4 0 3 x 1019 n m while our surface wave analysis gives 3 2 0 5 x 1019 n m it is not known whether reasonable changes of the earth models can bring the moment estimates into full agreement the systematic discrepancies in source duration centroid depth and seismic moment despite the consistency in source orientation raise the possibility of a deep relatively slow co seismic slip component but trade offs with modeling assumptions preclude us from confirming this hypothesis at present

coseismic radiation of the 2008 m w 7 9 wenchuan earthquake and its relationship to fault complexities the long rupture length and complex fault geometries of the 2008 mw 7 9 wenchuan earthquake offer a great opportunity to investigate the relationship between coseismic radiation and fault complexities in this study we first improved the compressive sensing back projection method cs bp with window time adjustment and parallel computation to enhance its spatial temporal resolution and computational efficiency then we applied the cs bp to invert for the coseismic radiation of the wenchuan earthquake in multiple frequency bands our results show that the coseismic radiation of the wenchuan earthquake is frequency dependent and strongly associated with the fault geometries low frequency radiation sources are concentrated on smooth fault segments with large coseismic slip while higher frequency sources are mainly related to fault complexities e g xiaoyudong fault gaochuan fault bend leigu fault bend and nanba fault step over an acceleration of rupture speed from 1 5 to 3 0 km s is also observed the near xiaoyudong fault where strong high frequency energies were radiated finally we discuss the role of rupture speed in mediating the relationship between coseismic radiation and fault complexities on one hand sudden changes of rupture speeds contribute to strong high frequency radiation on the other hand fault complexities can also strongly affect the rupture speed a sudden break of a large asperity is able to propel the acceleration while rupture front may decelerate when it jumps across geometric barriers

compressive sensing of frequency dependent seismic radiation from subduction zone megathrust ruptures megathrust earthquakes rupture a broad zone of the subducting plate interface in both along strike and along dip directions the along dip rupture characteristics of megathrust events e g their slip and energy radiation distribution reflect depth varying frictional properties of the slab interface here we report high resolution frequency dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive sensing sparse source recovery technique resolving generally low frequency radiation closer to the trench at shallower depths and high frequency radiation farther from the trench at greater depths together with coseismic slip models and early aftershock locations our results suggest depth varying frictional properties at the subducting plate interfaces the shallower portion of the slab interface above 15 km is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip deficient high frequency radiation and few early aftershocks the slab interface at intermediate depths 15 35 km is the main unstable seismogenic zone for the nucleation of megathrust quakes typically with large coseismic slip abundant early aftershocks and intermediate to high frequency radiation the deeper portion of the slab interface 35 45 km is seismically unstable however with small coseismic slip dominant high frequency radiation and relatively fewer aftershocks

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

automated determination of magnitude and source length of large earthquakes using backprojection and p wave amplitudes fast estimates of magnitude and source extent of large earthquakes are fundamental for disaster mitigation however resolving these estimates within 10 20 min after origin time remains challenging here we propose a robust algorithm to resolve magnitude and source length of large earthquakes using seismic data recorded by regional arrays and global stations we estimate source length and source duration by back projecting seismic array data then the source duration and the maximum amplitude of the teleseismic p wave displacement waveforms are used jointly to estimate magnitude we apply this method to 74 shallow earthquakes that occurred within epicentral distances of 30 85 degrees to hi net 2004 2014 the estimated magnitudes are similar to moment magnitudes estimated from w phase inversions usgs with standard deviations of 0 14 0 19 depending on the global station distributions application of this method to multiple regional seismic arrays could benefit tsunami warning systems and emergency response to large global earthquakes

a window into the complexity of the dynamic rupture of the 2011 mw 9 tohoku oki earthquake the 2011 mw 9 tohoku oki earthquake recorded by over 1000 near field stations and multiple large aperture arrays is by far the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in earthquake source dynamics here we conduct a high resolution array analysis based on recordings from the usarray and the european network the mutually consistent results from both arrays reveal rupture complexity with unprecedented resolution involving phases of diverse rupture speed and intermittent high frequency bursts within slow speed phases which suggests spatially heterogeneous material properties the earthquake initially propagates down dip with a slow initiation phase followed by sustained propagation at speeds of 3 km s the rupture then slows down to 1 5 km s for 60 seconds a rich sequence of bursts is generated along the down dip rim of this slow and roughly circular rupture front before the end of the slow phase an extremely fast rupture front detaches at about 5 km s towards the north finally a rupture front propagates towards the south running at about 2 5 km s for over 100 km key features of the rupture process are confirmed by the strong motion data recorded by k net and kik net the energetic high frequency radiation episodes within a slow rupture phase suggests a patchy image of the brittle ductile transition zone composed of discrete brittle asperities within a ductile matrix the high frequency is generated mainly at the down dip edge of the principal slip regions constrained by geodesy suggesting a variation along dip of the mechanical properties of the mega thrust fault or their spatial heterogeneity that affects rise time

understanding the physics of kappa κ insights from a downhole array at high frequencies the acceleration spectral amplitude decreases rapidly this has been modelled with the spectral decay factor its site component 0 is used widely today in ground motion prediction and simulation and numerous approaches have been proposed to compute it in this study we estimate for the euroseistest valley a geologically complex and seismically active region with a permanent strong motion array consisting of 14 surface and 6 downhole stations site conditions range from soft sediments to hard rock first we use the classical approach to separate local and regional attenuation and measure 0 second we take advantage of the existing knowledge of the geological profile and material properties to examine the correlation of 0 with different site characterization parameters 0 correlates well with vs30 as expected indicating a strong effect from the geological structure in the upper 30 m but it correlates equally well with the resonant frequency and depth to bedrock of the stations which indicates strong effects from the entire sedimentary column down to 400 m third we use our results to improve our physical understanding of 0 we propose a conceptual model of 0 with vs comprising two new notions on the one hand and contrary to existing correlations we observe that 0 stabilizes for high vs values this may indicate the existence of regional values for hard rock 0 if so we propose that borehole measurements almost never used up to now for 0 may be useful in determining these values on the other hand we find that material damping as expressed through travel times may not suffice to account for the total 0 measured at the surface we propose that apart from material damping additional site attenuation may be caused by scattering from small scale variability in the profile if this is so then geotechnical damping measurements may not suffice to infer the overall crustal attenuation under a site but starting with a regional value possibly from a borehole and adding damping we might define a lower bound for site specific 0 more precise estimates would necessitate seismological site instrumentation

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

a bayesian source model for the 2004 great sumatra andaman earthquake the 2004 m w 9 1 9 3 sumatra andaman earthquake is one of the largest earthquakes of the modern instrumental era despite considerable efforts to analyze this event the different available observations have proven difficult to reconcile in a single finite fault slip model in particular the critical near field geodetic records contain variable and significant postseismic signal between 2 weeks and 2 months worth while the satellite altimetry records of the associated tsunami are affected by various sources of uncertainties e g source rupture velocity and mesoscale oceanic currents in this study we investigate the quasi static slip distribution of the sumatra andaman earthquake by carefully accounting for the different sources of uncertainties in the joint inversion of available geodetic and tsunami data to this end we use nondiagonal covariance matrices reflecting both observational and modeling uncertainties in a fully bayesian inversion framework modeling errors can be particularly large for great earthquakes here we consider a layered spherical earth for the static displacement field nonhydrostatic equations for the tsunami and a 3 d megathrust interface geometry to alleviate some of the potential epistemic uncertainties the bayesian framework then enables us to derive families of possible models compatible with the unevenly distributed and sometimes ambiguous measurements we infer two regions of high fault slip at 3 n 4 n and 7 n 8 n with amplitudes that likely reach values as large as 40 m and possibly larger these values are a factor of 2 larger than typically found in previous studies potentially an outcome of commonly assumed forms of regularization finally we find that fault rupture very likely involved shallow slip within the resolution provided by the existing data we cannot rule out the possibility that fault rupture reached the trench

spatial and temporal correlation between coda q and seismicity in china a map of coda q at 1 hz q was constructed for china by analyzing more than 1000 seismograms from 80 seismic stations distributed throughout china the resultant contour map of q shows a strong correlation with the epicenters of historic great earthquakes in china the high q regions are devoid of the epicenters and the low q regions are full of them a remarkably linear relation was found between the logarithm of coda q and the maximum earthquake within the area sampled by coda waves radius of about 150 km from each station when we consider earthquakes which occurred from 1700 to present roughly speaking if q is 1000 m max is about 4 and if q is 100 m max is about 8 this relation will be very useful for siting critical facilities such as nuclear power plants and waste disposal sites we also found evidence in support of the migration of low q region coincident with the well known migration of high seismicity region over the distance of several hundred kilometers during the period of several hundred years if the migration is due to a diffusion process the diffusion constant is of the order of 100 km2 yr which agrees very well with those associated with the aftershock migration fluid injection and vp vs anomaly comparison of coda q with q1 estimated from the intensity data shows that they agree very well for q1 150 supporting the validity of the s to s single backscattering model for coda waves for q1 150 however coda q becomes constant independent of q1 this behavior is qualitatively consistent with numerical experiments of frankel and clayton and suggests that coda q may be measuring the intrinsic q of about 150 for these regions where q1 150 this limiting coda q value may depend on regions because coda q lower than 100 has been observed in some active regions in this study and also coda q as low as 30 to 40 has been reported in california mexico and italy

experimental study and numerical reproduction of self weight consolidation behavior of thickened tailings abstractthickened tailings defined as mineral wastes that behave as a non newtonian fluid show a small yield stress and release a small amount of water following deposition thickening has become an increasingly used option in tailings management this paper presents a detailed examination of gold mine thickened tailings undergoing self weight consolidation which is an important mechanism affecting soft soils immediately after deposition self weight consolidation was evaluated using a column equipped with water pressure transmitters whereas a slurry consolidometer was employed to obtain the compressibility relationship under low vertical effective stresses the piecewise linear model cs2 was used to model the experimental self weight consolidation test this model proved very accurate in reproducing the observed behavior both the test results and the model results also confirmed the absence of sedimentation in the thickened tailings which is in agreement with values reported in the literature relate

frequency dependent energy radiation and fault coupling for the 2010 mw8 8 maule chile and 2011 mw9 0 tohoku japan earthquakes 1 we carried out back projections of teleseismic data filtered in different frequency bands for the 2010 maule chile and the 2011 tohoku japan earthquakes for the maule earthquake there were differences along strike of the fault with the high frequency energy mainly originating from an area 200 km northeast of the epicenter whereas low frequency energy came from a location closer to the epicenter the tohoku earthquake shows strong frequency dependence in the dip direction high frequency sources were located about 100 km west of the epicenter while low frequency sources were around epicenter near the japan trench we compare the spatial distributions of energy with estimates of seismic coupling before the earthquakes areas of high frequency radiation seem correlated with regions that were strongly coupled before the earthquakes areas of high coupling may be associated with fault properties that are more heterogeneous and or have overall higher stress producing higher frequency seismic waves

regional variations of seismic attenuation from coda and l g waves in northern baja california attenuation of coda and lg waves was estimated from events recorded by the seismic network of northern baja california red sismica del noroeste de mexico resnom in the frequency band 1 to 12 hz in order to find a regional variation of qc crustal quality factor for s waves in northern baja california mexico we used the single scattering model of sato 1977 in the time domain to estimate quality factor qc and a spectral approach to relate acceleration spectra with distance to estimate the anelastic attenuation coefficient of lg waves we calculated qc for short 10 s and long lapse times 70 s using local events and the events that originated at the main tectonic features of the area assuming a frequency dependence of qc of the form qc qc we observed for short lapse times a regional variation of q0 with low values from about 53 in the inner continental borderland icb province to about 115 in the peninsular ranges pr and 144 in the gulf of california depression gcd province the values range from 0 70 and 0 85 for events in the icb and pr to 0 44 in the gcd region for long lapse times and for events located in the pr we found q0 values from 49 at stations within the icb to 101 at stations within the gcd attenuation coefficient of lg waves between 1 and 6 hz was also estimated using events located in southern california with source station distances up to 420 km we found that frequency dependence of was higher for source receiver paths going from a typical continental structure to a pull apart basin the gcd province than for paths within the pr using all data in a linear inversion process and assuming a group velocity vlg of 3 4 km s we obtained a power law dependence of the form qlg 288 20 0 32 02

along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake 1 the short period 0 5 2 s seismic radiation properties of the august 15 23 40 57 utc 2007 mw 8 0 pisco peru earthquake are imaged by back projecting p waves recorded at 374 elements of usarray deployed in western north america at distances of 54 74 from the source region the coherent short period seismic energy release has two main intervals similar to moment rate functions determined by inversion of longer period teleseismic body waves however the spatial locations of the coherent bursts of short period energyrelease are located northanddown dip of the region of major slip the contrast between short and long period seismic radiation properties of the pisco earthquake is more subtle than for the 2011 mw 9 0 tohoku earthquake but provides further support for the idea of depth dependent changes in sliding behavior during megathrust ruptures citation sufri o k d koper and t lay 2012 along dip seismic radiation segmentation during the 2007 mw 8 0 pisco peru earthquake geophys res lett 39 l08311 doi 10 1029 2012gl051316

stress drop estimates for some aftershocks of the ometepec guerrero mexico earthquake of june 7 1982 brune s stress drop apparent stress and arms stress drop are estimated at a single station for 25 aftershocks of the ometepec earthquakes ms 6 9 and ms 7 0 the arms stress drops and apparent stresses are systematically smaller than brune s stress drops stress drops from the root mean square of acceleration and apparent stress range from 0 01 to 10 2 bars 1 bar 100 kpa except for two values 21 4 and 33 0 bars on the other hand brune s stress drops range from 0 6 to 239 bars seismic moments ranging from 0 5 1019 to 289 1019 dyn cm 1 dyn cm 10 n cm were estimated for events with coda magnitudes between 0 6 and 2 2 values of radiated seismic energy calculated by integration of the displacement spectra range from 2 5 1012 to 2 3 1016 dyn cm the fmax values lie between 16 and 30 hz seismic coda wave attenuation measured on narrow band pass filtered seismograms show a linear dependence of the seismic quality factor of the form in the range of frequencies from 3 to 24 hz

lateral variations of lg coda q in southern mexico broad band digital three component data recorded at unm a geoscope station were used to estimate lg coda q for 34 medium size 3 9 m b 6 3 earthquakes with travel paths laying in different geological provinces of southern mexico in an effort to establish the possible existence of geological structures acting as wave guides and or travel paths of low attenuation between the pacific coast and the valley of mexico the stacked spectral ratio method proposed by xie and nuttli 1988 was chosen for computing the coda q the variation range of q 0 q at 1 hz and the frequency dependence parameter estimates averaged on the frequency interval of 0 5 to 2 hz for the regions and the three components considered are i guerrero region 173 q 0 182 and 0 6 q 0 0 7 ii oaxaca region 183 q 0 198 and 0 6 q 0 0 8 iii michoacan jalisco region 187 q 0 204 and 0 7 q 0 0 8 and iv eastern portion of the transmexican volcanic belt tmvb 313 q 0 335 and 0 9 the results show a very high coda q for the tmvb as compared to other regions of southern mexico this unexpected result is difficult to reconcile with the geophysical characteristics of the tmvb e g low seismicity high volcanic activity and high heat flow typical of a highly attenuating low q region visual inspection of seismograms indicates that for earthquakes with seismic waves traveling along the tmvb the amplitude decay of lg coda is anomalously slow as compared to other earthquakes in southern mexico thus it seems that the high q value found does not entirely reflect the attenuation characteristics of the tmvb but it is probably contaminated by a wave guide effect this phenomenon produces an enhancement in the time duration of the lg wave trains travelling along this geological structure this result is important to establish the role played by the transmission medium in the extremely long duration of ground motion observed during the september 19 1985 michoacan earthquake the overall spatial distribution of coda q values indicates that events with focus in the michoacan jalisco and oaxaca regions yield slightly higher values than those from guerrero this feature is more pronounced for the horizontal component of coda q a slight dependence of average coda q 1 on earthquake focal depth is observed in the frequency range of 0 2 to 1 0 hz approximately on the horizontal component deeper h 50 km events yield lower values of q 1 than shallower events for frequencies higher than 1 0 hz no clear dependence of q 1 on focal depth is observed however due to the estimates uncertainties this result is not clearly established

subevent location and rupture imaging using iterative backprojection for the 2011 tohoku mw 9 0 earthquake summary knowledge of the rupture speed and spatial temporal distribution of energy radiation of earthquakes is important for earthquake physics backprojection of teleseismic waves is commonly used to image the rupture process of large events the conventional backprojection method typically performs temporal and spatial averaging to obtain reliable rupture features we present an iterative backprojection method with subevent signal stripping to determine the distribution of subevents large energy bursts during the earthquake rupture we also relocate the subevents initially determined by iterative backprojection using the traveltime shifts from subevent waveform cross correlation which provides more accurate subevent locations and source times a bootstrap approach is used to assess the reliability of the identified subevents we apply this method to the mw 9 0 tohoku earthquake in japan using array data in the united states we identify 16 reliable subevents in the frequency band 0 2 1 hz which mostly occurred around or west of the hypocentre in the downdip region analysis of tohoku aftershocks shows that depth phases can often produce artefacts in the backprojection image but the position and timing of our main shock subevents are inconsistent with depth phase artefacts our results suggest a complicated rupture with a component of bilateral rupture along strike the dominant energy radiation between 0 2 and 1 hz is confined to a region close to the hypocentre during the first 90 s a number of subevents occurred around the hypocentre in the first 90 s suggesting a low initial rupture speed and repeated rupture or slip near thehypocentre therupturereachedthecoastalregionabout106kmnorthwestofthehypocentreat43sandtheregionabout110kmnorthofthehypocentreat105swithanorthwardrupture speed 2 0 kms 1 at 60 110 s after 110 s a series of subevents occurred about 120 220 km southwest of the hypocentre consistent wit ha3k ms 1 along strike rupture speed the abundant high frequency radiation in the downdip region close to the coast suggests intermittent rupture probably in the brittle ductile transition zone the lack of high frequency radiation in the updip region suggests the rupture near the trench was more continuous probably due to more homogeneous frictional properties of the shallow slab interface the lack of early aftershocks in the updip region indicates that most of the accumulated slip in the updip region during the interseismic period was probably released during the main shock

regional variations of seismic attenuation of lg waves in southern mexico attenuation of lg waves is estimated using 61 events located in the subduction zone of the middle american trench and recorded by the seismic network of laguna verde veracruz mexico we estimate the anelastic attenuation coefficient of lg waves or equivalently qlg by calculating the rate of acceleration spectra decay with distance we consider paths from two regions guerrero veracruz ne sw direction and oaxaca veracruz north south direction assuming a frequency dependence of of the form 0 we find that 0 175 0 05 for both regions and that 0 was lower for paths from guerrero to veracruz 0 0 0071 0 002 than for paths from oaxaca to veracruz 0 0 0161 0 003 in the frequency range from 2 to 7 hz in terms of the quality factor qlg values of qlg 134 30 0 83 0 2 and qlg 59 10 0 81 0 2 were found for the guerrero veracruz and the oaxaca veracruz paths respectively this difference in attenuation may be due to the state of stresses that prevails in both regions including the density and fluid content of fractures which are attenuation mechanisms also suggested for other regions mitchell 1995

spatiotemporal evolution of a fault shear stress patch due to viscoelastic interseismic fault zone rheology abstract we conducted numerical studies to explore how shear stress anomalies on fault planes shear stress patches evolve spatiotemporally during the interseismic period under the influence of viscoelastic rheology assigned to fault zones of finite thickness 2 d viscoelastic models consisting of a fault zone and host rock were sheared to simulate shear stress accumulation along fault zones due to tectonic loading no fault slip along a distinct fault planes is implied in the model thus all fault shear motion is accommodated by distributed deformation in the viscoelastic fault zone results show that magnitudes of shear stress patches evolve not only temporally but also spatially especially when the stress anomaly is created by a geometrical irregularity asperity along the interface of an elastic host rock and viscoelastic fault zone such shear stress anomalies diffuse spatially so that the spatial dimension of the shear stress patch appears to grow over time models with varying fault zone viscoelastic properties and varying fault zone viscosity both show that such spatial diffusion of shear stress is enhanced by increasing the contribution of the viscous behavior the absolute rate at which shear stress patches grow spatially is generally not influenced by the size of the shear stress patch therefore shear stress patches with smaller dimensions will appear to grow quicker in the relative sense compared to larger stress patches these results suggest that the minimum dimensions of shear stress patches that can exist along a fault could be governed by the effective viscosity of the fault zone therefore patterns of accumulated shear stress could vary along faults when viscous properties are heterogeneous for instance due to depth or material heterogeneity which has implications on how earthquake rupture behavior could vary along faults

multiple resolution seismic attenuation imaging at mt vesuvius abstract a three dimensional s wave attenuation tomography of mt vesuvius has been obtained with multiple measurements of coda normalized s wave spectra of local small magnitude earthquakes we used 6609 waveforms relative to 826 volcano tectonic earthquakes located close to the crater axis in a depth range between 1 and 4 km below the sea level recorded at seven 3 component digital seismic stations we adopted a two point ray tracing rays were traced in an high resolution 3 d velocity model the spatial resolution achieved in the attenuation tomography is comparable with that of the velocity tomography we resolve 300 m side cubic cells we statistically tested that the results are almost independent from the radiation pattern we also applied an improvement of the ordinary spectral slope method to both p and s waves assuming that the differences between the theoretical and the experimental high frequency spectral slope are only due to the attenuation effects consequently we could check the coda normalization method also comparing the s attenuation image with the p attenuation image the images were obtained inverting the spectral data with a multiple resolution approach results have shown the general coincidence of low attenuation with high velocity zones the joint interpretation of velocity and attenuation images allows us to interpret the low attenuation zone intruding toward the surface until a depth of 500 m below the sea level as related to the residual part of solidified magma from the last eruption in the depth range between 700 and 2300 images are consistent with the presence of multiple acquifer layers no evidence of magma patches greater than the minimum cell dimension 300 m has been found a shallow p wave attenuation anomaly beneath the southern flank of the volcano is consitent with the presence of gas saturated rocks the zone characterized by the maximum seismic energy release cohincides with a high attenuation and low velocity volume interpreted as a cracked medium