rupture process of the 1990 luzon philippines mw 7 7 earthquake the rupture process of the destructive july 16 1990 luzon philippines earthquake is analyzed using a long period surface wave spectral inversion technique to estimate the average source properties and a broadband body wave and surface wave empirical green function technique to investigate the slip distribution the average source model has a seismic moment of 4 2 0 1 1020 n m mw 7 7 a total duration of 30 to 35 s a left lateral strike slip focal mechanism with strike 153 dip 89 and rake 16 and a north northwestward directivity these results are consistent with previous work on the luzon earthquake however the broadband analysis indicates that for periods longer than about 20 s the teleseismic source time function is characterized by a single relatively smooth pulse of energy release with azimuthal variations in duration of 24 to 60 s this contrasts with previous body wave results that inferred two discrete pulses of energy release the simpler source process is inferred as a result of using empirical green functions rather than standard theoretical green functions for a layered crustal model and by considering only the seismic energy with periods longer than 20 s the luzon earthquake began rupturing bilaterally but evolved into a predominantly northwest directed rupture that extended for 75 to 100 km the largest slip 10 15 m occurred about 25 km northwest of the epicenter beyond which the slip decreased gradually as the rupture propagated into a restraining bend the peak slip at depth appears to exceed the surface rupture by a factor of 2 to 3 there is little evidence for significant energy release later than 50 s after the rupture initiated

the 2006 2007 kuril islands great earthquake sequence the southwestern half of a 500 km long seismic gap in the central kuril island arc subduction zone experienced two great earthquakes with extensive preshock and aftershock sequences in late 2006 to early 2007 the nature of seismic coupling in the gap had been uncertain due to the limited historical record of prior large events and the presence of distinctive upper plate trench and outer rise structures relative to adjacent regions along the arc that have experienced repeated great interplate earthquakes in the last few centuries the intraplate region seaward of the seismic gap had several shallow compressional events during the preceding decades notably an m s 7 2 event on 16 march 1963 leading to speculation that the interplate fault was seismically coupled this issue was partly resolved by failure of the shallow portion of the interplate megathrust in an m w 8 3 thrust event on 15 november 2006 this event ruptured 250 km along the seismic gap just northeast of the great 1963 kuril island m w 8 5 earthquake rupture zone within minutes of the thrust event intense earthquake activity commenced beneath the outer wall of the trench seaward of the interplate rupture with the larger events having normal faulting mechanisms an unusual double band of interplate and intraplate aftershocks developed on 13 january 2007 an m w 8 1 extensional earthquake ruptured within the pacific plate beneath the seaward edge of the kuril trench this event is the third largest normal faulting earthquake seaward of a subduction zone on record and its rupture zone extended to at least 33 km depth and paralleled most of the length of the 2006 rupture the 13 january 2007 event produced stronger shaking in japan than the larger thrust event as a consequence of higher short period energy radiation from the source the great event aftershock sequences were dominated by the expected faulting geometries thrust faulting for the 2006 rupture zone and normal faulting for the 2007 rupture zone a large intraplate compressional event occurred on 15 january 2009 m w 7 4 near 45 km depth below the rupture zone of the 2007 event and in the vicinity of the 16 march 1963 compressional event the fault geometry rupture process and slip distributions of the two great events are estimated using very broadband teleseismic body and surface wave observations the occurrence of the thrust event in the shallowest portion of the interplate fault in a region with a paucity of large thrust events at greater depths suggests that the event removed most of the slip deficit on this portion of the interplate fault this great earthquake doublet demonstrates the heightened seismic hazard posed by induced intraplate faulting following large interplate thrust events future seismic failure of the remainder of the seismic gap appears viable with the northeastern region that has also experienced compressional activity seaward of the megathrust warranting particular attention

seismic guided waves trapped in the fault zone of the landers california earthquake of 1992 a mobile seismic array of seven stations was deployed at 11 sites along the fault trace of the m7 4 landers earthquake of june 28 1992 with a maximum offset of 1 km from the trace we found a distinct wave train with a relatively long period following the s waves that shows up only when both the stations and the events are close to the fault trace this wave train is interpreted as a seismic guided wave trapped in a low velocity fault zone to study the distribution of amplitude of the guided waves with distance from the fault trace and also their attenuation with travel distance along the fault zone we eliminated source and recording site effects by the coda normalization method the normalized amplitudes of guided waves show a spectral peak at 3 4 hz which decays sharply with distance from the fault trace spectral amplitudes at high frequencies 8 15 hz show an opposite trend increasing with distance from the fault trace the normalized amplitudes of guided waves at 3 4 hz also show a systematic decrease with hypocentral distance along the fault zone from which we infer an apparent q of 50 in order to confirm the existence of the guided waves a dense array of 31 stations was deployed at one of the 11 sites the resultant records revealed unequivocal evidence for the existence of guided waves associated with the fault zone by modeling the waveforms as s waves trapped in a low velocity waveguide sandwiched between two homogeneous half spaces with velocity vs 3 0 km s we infer a waveguide width of about 180 m a shear velocity of 2 0 2 2 km s and a q of 50 hypocenters of aftershocks with clear guided waves show a systematic distribution both laterally and with depth delineating the extent of the low velocity fault zone in three dimensions we find that the zone extends to a depth of at least 10 km this zone apparently continues to the south across the pinto mountain fault because guided waves are observed at stations north of the pinto mountain fault for earthquakes with epicenters south of it on the other hand the zone appears to be discontinuous at the fault bend located about 20 km north of the mainshock epicenter guided waves were observed for stations and epicenters which are located on the same sides of the fault bend but not for those on the opposite sides

source investigation of a small event using empirical green s functions and simulated annealing we propose a two step inversion of three component seismograms that 1 recovers the far field source time function at each station and 2 estimates the distribution of co seismic slip on the fault plane for small earthquakes magnitude 3 to 4 the empirical green s function egf method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path site and instrumental effects from the main event signal the deconvolution between the two earthquakes is an unstable procedure we have therefore developed a simulated annealing technique to recover a stable and positive source time function stf in the time domain at each station with an estimation of uncertainties given a good azimuthal coverage we can obtain information on the directivity effect as well as on the rupture process we propose an inversion method by simulated annealing using the stf to recover the distribution of slip on the fault plane with a constant rupture velocity model this method permits estimation of physical quantities on the fault plane as well as possible identification of the real fault plane we apply this two step procedure for an event of magnitude 3 recorded in the gulf of corinth in august 1991 a nearby event of magnitude 2 provides us with empirical green s functions for each station we estimate an active fault area of 0 02 to 0 15 km2 and deduce a stress drop value of 1 to 30 bar and an average slip of 0 1 to 1 6 cm the selected fault of the main event is in good agreement with the existence of a detachment surface inferred from the tectonics of this half graben

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

rupture process of the 2002 mw 7 9 denali earthquake alaska using a newly devised hybrid blind deconvolution method this paper investigates the kinematics of the rupture process of the main event of the mw 7 9 denali alaska earthquake of 3 november 2002 a newly devised hybrid blind deconvolution method is applied to deconvolve teleseismic broadband s wave displacement recordings of the earthquake so as to determine the apparent source time functions astfs at 10 stations located around the epicenter the derived azimuthal angle of slip strongly indicates that the event ruptured unilaterally in an east southeasterly direction as determined by the calculated astfs the total duration of the rupture process was about 74 sec based on the images of the static slip dis tribution three slip concentrated areas were located at depths of less than 10 km maximum slip was about 13 4 m centered at 170 km east of the hypocenter and the average slip on the observed rupture area reached 4 1 m one concentrated rupture velocity area located at 160 180 km east of the hypocenter coincided with a slip concentrated area of maximum slip amplitude strongly suggesting that seismic energy was released rapidly a region of the fault along the strike direction with high rupture velocity 80 120 km also had very low levels of slip indicating that this portion of the fault may well have been relatively weak maximum and minimum rupture velo cities were respectively 3 32 and 2 64 km sec while the average rupture velocity was about 2 95 km sec based on the average rupture velocity and the source duration it is suggested that the principal rupture length of the denali fault must have been greater than 210 km

an experimental study of the mechanical properties of granite after high temperature exposure based on mineral characteristics abstract the macroscopic mechanical properties of granite collected from the fujian province china were measured using uniaxial compression and three point bending after the granite was exposed to high temperatures the stress strain relationship was measured and mechanical properties including the young s modulus uniaxial compressive strength ucs and fracture toughness were calculated in general the uniaxial compressive strength ucs young s modulus and fracture toughness of the granite specimens decrease with an increase in heat treatment temperature up to 800 c above which there is no obvious change the microstructure of the failed specimens was explored using scanning electron microscopy sem and stereomicroscopy after heat treatment the minerals within the granite were analysed using x ray diffraction the failure mechanisms and the mechanical characteristics of the granite are explained in terms of the microstructure and the minerals present the results of the experiments indicate that the crystal structure of the phlogopite in granite transforms to a more stable structure between 400 c and 600 c with an associated increase in volume a dehydroxylation reaction also occurs in the phlogopite at 400 c after which the uniaxial compressive strength ucs decreases and the ductility increases using sem and stereomicroscopy it was observed that the connection between the minerals within the granite becomes weaker with increasing heat treatment temperature intercrystalline cracking is the main failure mode for samples exposed to temperatures below 800 c whereas transcrystalline cracking can be observed in samples exposed to 1000 c

long period regional wave moment tensor inversion for earthquakes in the western united states source parameters of moderate to large size mw 4 5 earthquakes in the western united states from 1992 to 1994 are determined by point source moment tensor inversion of complete long period t 35 50 s ground motions recorded at regional distances 1 12 stable long period signals are obtained by low pass filtering records from the very broadband seismometers recently deployed in several networks in the western united states these signals are dominated by fundamental mode rayleigh and love waves which have very simple waveforms due to the limited dispersion on the short paths to regional stations since long period motions are relatively insensitive to the attenuation model and crustal structure used in the inversion they provide robust constraints on the seismic moment and faulting geometry as long as adequate azimuthal coverage is available comparisons of solutions for 21 events with results of other regional and teleseismic wave inversions are made to assess the model dependence and uncertainties of our regional centroid moment tensor rcmt solutions rcmt inversion has limited source depth resolution for shallow crustal events but the focal mechanism and seismic moment determinations prove quite stable over a range of source depths in the crust as well as over a range of crustal propagation models simultaneous waveform inversion of shorter period body wave signals can improve the source depth resolution by applying path corrections for heterogeneous crustal structure shorter period surface wave energy can also be inverted allowing the methodology to be extended to lower magnitude regional events as well the rcmt procedure requires minimal signal processing only a sparse broadband network and a simple laterally homogeneous propagation model thus it can readily be automated and applied in near real time to events in the magnitude range from 4 5 to 7 5 distributed over an area as large as the western united states

control of seafloor roughness on earthquake rupture behavior earthquake rupture complexity is described for three recent large underthrusting earthquakes along the costa rican subduction zone the 1983 osa 1990 nicoya gulf and 1999 quepos events these earthquakes occurred in regions characterized by distinctly different morphologic features on the subducting plate the 1990 and 1999 events occurred along linear projections of subducting seamount chains and had fairly simple earthquake rupture histories both events are interpreted as failure of the basal contact of closely spaced isolated seamounts acting as asperities in contrast the 1983 event occurred along the subducting cocos ridge and had a complex rupture history comparison of rupture characteristics of these large underthrusting earthquakes with size and location of subducting features provides evidence that seamounts can be subducted to seismogenic depths and that variations in seafloor bathymetry of the subducting plate strongly influence the earthquake rupture process

revisiting the 1956 anjar earthquake in western india empirical green s function approach we estimated ground motions at 12 selected sites in the kachchh rift basin of gujarat in the western peninsular shield area of india where the damaging 1956 anjar earthquake m w 6 0 was experienced the ground motions are estimated by applying the empirical green s function approach using an earthquake of m w 4 5 which occurred on the inferred rupture plane of the anjar earthquake with a nearly similar fault mechanism the estimated peak ground acceleration pga varies between 114 and 22 cm s2 at these sites located at distances of 21 127 km from the epicenter respectively the maximum accelerations are correlated with the modified mercalli intensity reported for the anjar earthquake using the empirical relationship between the pga and intensity at most of the sites the level of acceleration could explain the reported damage at a few sites the instrumental intensity estimated using the acceleration values obtained from the synthesis is larger than the felt intensity the ground motion prediction equation gmpe developed for the region estimates the maximum pga near the epicenter area in the 250 300 cm s2 range and the acceleration obtained by our analysis is found to be closer to the predicted acceleration obtained by gmpe our analysis assesses the level of ground motion that was experienced during the 1956 anjar earthquake fairly well and corroborates that reasonable prediction of the ground motion of a historical earthquake is achievable if strong motion recordings are available from the rupture plane of the historical earthquake

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

rupture process of the 2012 mw 7 8 haida gwaii earthquake from an empirical green s function method abstract this article examines rupture processes of the 28 october 2012 m w 7 8 haida gwaii earthquake off the coast of british columbia canada using an empirical green s function egf technique the haida gwaii earthquake was the largest event along the canadian portion of the pacific north american plate boundary since the m s 8 1 queen charlotte earthquake of 1949 it occurred along a potentially blind thrust fault dipping gently to the northeast rather than the main subvertical queen charlotte fault surface waveforms from a 2001 m w 6 3 event located only 15 km from the 2012 epicenter and with similar mechanism are used as an egf and deconvolved from those of the 2012 mainshock the resulting source time functions contain minimal path effects focal mechanism effects and instrument response so the waveforms display only properties of the 2012 mainshock rupture itself by examining azimuthal variations in these source time functions we constrain parameters such as average rupture velocity extent and directivity in addition information is obtained about the possible existence of major subevents and their relative locations results indicate two subevents within this rupture the first 12 km south and updip of the epicenter and the second approximately 28 km from the first along a heading parallel to the queen charlotte terrace 323 overall the rupture front propagated roughly 50 km at an azimuth of 308 5 this evidence for directivity to the northwest is important given that earthquakes with strong directivity such as the 2002 m w 7 9 denali earthquake have been shown to be capable of triggering earthquakes thousands of kilometers away in this case we suggest that northwest directivity of this earthquake is responsible for amplification of surface waves observed at seismic stations in alaska gomberg 2013 and may provide a potential link between this 2012 event and the 2013 craig alaska earthquake online material figure of all relative source time functions used in directivity analysis

rupture directivity of the 3 november 2002 denali fault earthquake determined from surface waves the m w 7 9 earthquake that struck central alaska on 3 november 2002 was preceded 11 days earlier by an mw 6 7 strike slip foreshock on 23 october 2002 both events were predominantly strike slip and ruptured structures associated with the denali fault system previous studies have shown that the mainshock began with failure on a relatively small northeast striking reverse fault before breaking out for 300 km of right lateral strike slip rupture aftershock patterns suggest that the fore shock ruptured a region west of the mainshock which began near the eastern extent of the foreshock sequence and proceeded east southeast to constrain and to quantify source duration and directivity effects we examine surface wave displacement seis mograms and use an empirical green s function egf to isolate and explore main shock rupture kinematics our particular interest lies in large amplitude focussing caused by directivity we observe love and rayleigh wave amplification of two orders of magnitude in the period range from 10 to 33 sec these remarkable directivity enhanced surface waves triggered small earthquakes more than 3000 km from the mainshock rupture

routine estimation of earthquake source complexity the 18 october 1992 colombian earthquake we describe two methods suitable for routine application to tele seismic recordings that characterize the time history of seismic events stacking short period signals from large regional arrays provides stable estimates of high frequency radiation from the source and an empirical green s function decon volution procedure extracts reliable broadband time functions suitable for anal ysis of faulting complexity and the spatio temporal extent of rupture combined these procedures characterize the source radiation of large events ms 7 be tween 200 and 0 5 sec periods

the 14 september 1995 m 7 3 copala mexico earthquake a source study using teleseismic regional and local data we analyze source characteristics of the 14 september 1995 copala mexico earthquake m 7 3 using teleseismic regional and local seismograms in the analysis of the teleseismic and the regional seismic waves we apply the empirical green s function egf technique the recording of an appropriate aftershock is taken as the egf and is used to deconvolve the mainshock seismogram thus obtaining an apparent far field source time function at each station the deconvolution has been done using surface waves for teleseismic data we apply a spectral deconvolution method that enables us to obtain 37 apparent source time functions astfs at 29 stations in the analysis of the regional broadband seismograms we use two different aftershocks as egf and the deconvolution is performed in the time domain with a nonlinear method imposing a positivity constraint and the best azimuth for the directivity vector is obtained through a grid search approach we also analyze two near source accelerograms the traces are inverted for the slip distribution over the fault plane by applying a linear inversion technique with the aid of a time window analysis we obtain an independent estimation of the source time function and a more detailed description of the source process the analysis of the three datasets permits us to deduce the main characteristics of the source process the rupture initiated at a depth of 16 km and propagated in two directions updip along the plate interface toward 165 n and toward 70 n the source duration was between 12 and 14 sec with the maximum of energy release occurring 8 sec after the initiation of the rupture the estimated rupture dimension of 35 45 km is about one fourth of the aftershock area the average dislocation over the fault was 1 4 m with a maximum dislocation of 4 1 m located 10 km south of the hypocenter which gives roughly 1 mpa as the average static stress drop

the cape mendocino california earthquakes of april 1992 subduction at the triple junction the 25 april 1992 magnitude 7 1 cape mendocino thrust earthquake demonstrated that the north america gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the cascadia region the shock occurred just north of the mendocino triple junction and caused strong ground motion and moderate damage in the immediate area rupture initiated onshore at a depth of 10 5 kilometers and propagated up dip and seaward slip on steep faults in the gorda plate generated two magnitude 6 6 aftershocks on 26 april the main shock did not produce surface rupture on land but caused coastal uplift and a tsunami the emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity

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

empirical green s function analysis of loma prieta aftershocks abstract following the 18 october 1989 loma prieta earthquake an array of 22 three component iris passcal instruments was deployed in the santa cruz mountains we use an empirical green9s function method to study source properties of aftershocks as well as attenuation in the epicentral area using pairs of closely spaced events we show that the largest aftershocks are well modelled by an 2 source spectrum and we obtain estimates of the p wave corner frequency for a total of 15 events brune stress drops are observed to have no systematic variation over the range of moments spanned by the data set down to 10 19 dyne cm there is a suggestion that aftershocks that occurred outside the mainshock rupture have higher stress drops than those that occurred within the mainshock rupture a m l 3 4 foreshock in the subsequence associated with the 18 april 1990 m l 5 4 watsonville earthquake yields a stress drop estimate of 820 bars this value is well outside the stress drops obtained for all other events 6 to 266 bars site specific attenuation parameters suggest large lateral and vertical heterogeneity in p wave q structure station holy in a valley near the surface trace of the san andreas fault is characterized by low q values while stations to the north of the aftershock zone are characterized by the highest q values

earthquakes casting stress shadows earthquakes may trigger or retard quakes on nearby faults but such relationships are difficult to verify observations showing that the landers earthquake in california shut down aftershocks from a preceding event validate such relationships

rapid estimation of rupture directivity application to the 1992 landers ms 7 4 and cape mendocino ms 7 2 california earthquakes using empirical green functions with regional and teleseismic surface waves it is possible to resolve fault finiteness effects in many cases uniquely defining the fault plane for relatively large earthquakes the technique requires very little data processing and can be applied in near real time with the current distribution of seismic stations the landers strike slip earthquake was dominated by two sub events with predominantly north northwestward rupture the second sub event was 1 5 times larger and rotated in strike by 12 counterclockwise relative to the first the cape mendocino thrust event had a relatively smooth rupture that propagated to the southwest on a shallow dipping fault

the 1992 cape mendocino earthquake broadband determination of source parameters the april 25 1992 cape mendocino earthquake ms 7 1 has renewed speculation about the nature of subduction along the cascadia subduction zone and the associated seismic hazard this event may represent the first large m 6 thrust event along the entire cascadia subduction zone in historic times last 200 years we analyze long period surface waves and broadband body waves in order to estimate the mainshock source parameters we also examine broadband body waves from the nearby 1991 honeydew earthquake m 6 in order to assess the contributions of both rupture complexity and unmodeled source and receiver structure in the cape mendocino waveforms from both body and surface wave inversions as well as forward modeling of body waves we estimate a best double couple mechanism for the cape mendocino earthquake strike 330 10 dip 12 2 rake 75 15 seismic moment 1 93 1019 n m and mw 6 8 this mechanism contains a significant component of slip in the estimated direction of gorda north america plate convergence although this earthquake had suitable geometry for relieving strain accumulated by gorda north america plate convergence we cannot resolve whether it occurred on the interplate megathrust or on a fault within the overriding accretionary prism we find evidence for southwest offshore rupture toward an azimuth of 240 in addition we find evidence for early aftershocks in both the teleseismically recorded body waves and in locally recorded strong motions we model one aftershock delayed 13 s from the mainshock with a mechanism that is different from the mainshock mechanism but is consistent with the north south trending horizontal compression found offshore within the gorda plate we postulate that this aftershock and two additional large strike slip aftershocks that ruptured the gorda plate within 24 hours of the mainshock were caused by the transfer of stress accumulated across the cascadia subduction zone and accretionary prism far offshore to the gorda plate where it reduced the normal stress across nw se oriented faults triggering failure the complexity of fault interactions near the mendocino triple junction needs to be understood before potential seismic hazards of the southern cascadia subduction zone can be quantified

recent large earthquakes near cape mendocino and in the gorda plate broadband source time functions fault orientations and rupture complexities the northward migration of the mendocino triple junction is associated with complex faulting within the gorda plate and in the convergent zone between the gorda and north american plates this region has experienced substantial recent large earthquake activity and quantification of these faulting processes is essential for understanding the evolution of the triple junction using an empirical green function deconvolution method for teleseismic and regional surface waves and body waves we obtain relative source time functions for the april 25 1992 cape mendocino thrust earthquake m w 7 2 its two large strike slip aftershocks on april 26 1992 m w 6 5 6 6 and two large strike slip events in the gorda plate that occurred july 13 1991 m w 6 8 and august 17 1991 m w 7 1 the removal of propagation effects using empirical green functions provides unusually detailed source rupture information and indicates that all the ruptures are less than 16 s in duration analyzing the directivity effects observed in the source time functions we resolve rupture directions and corresponding fault orientations for the four largest events and place some constraints on the smaller aftershock significant differences in the rupture duration and stress drop are observed between the cape mendocino mainshock and its two largest aftershocks the mainshock which ruptured westward on a shallow dipping plane either on or paralleling the interplate contact between the gorda and north american plates had a smooth 9 s long rupture with a 0 9 4 6 mpa static stress drop the two largest aftershocks occurred within the uppermost mantle of the gorda plate and have more complex ruptures with total durations of 14 15 s and static stress drops of less than 0 3 mpa perhaps reflecting a difference between mantle and crustal earthquakes in this region the aftershocks appear to have ruptured conjugate strike slip faults accounting for differences in their damage patterns the august 17 1991 gorda plate event ruptured a southwest striking fault while the july 13 1991 event ruptured a southeast striking fault with both events relieving north south compression within the deforming gorda plate the existence of multiple active faults in the region constitutes a significant earthquake hazard associated with the complex stress environment of the migrating triple junction

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

redshift of earthquakes via focused blind deconvolution of teleseisms we thank the editor prof huajian yao and reviewers jiuxun yin and anonymous for providing their valuable feedback we thank our colleagues nafi toks oz matt li aurelien mordret tom herring hongjian fang and michael floyd for providing insight and expertise that greatly assisted this research we thank martin mai from king abdullah university of science and technology for his informative commentary of a draft version the material is based upon work assisted by a grant from equinor any opinions findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of equinor ld is also supported by afosr grant fa9550 17 1 0316

study of the source process of the 1992 colombia ms 7 3 earthquake with the empirical green s function method the source time function stf of the october 18 1992 colombia ms 7 3 earthquake has been determined using long period teleseismic surface and body waveform data and the empirical green s function egf method love and sh waveforms of a ms 6 7 foreshock were treated as the egfs and deconvolved from the mainshock waveforms to obtain the relative stf this indicated that the ms 7 3 mainshock was a double event followed 100 seconds later by a large aftershock not previously reported the source durations for the mainshock and the aftershock are about 45 and 25 seconds respectively based on the source radiation directivity the rupture directions for the mainshock and aftershock are about s50 w the total length of the fault for the mainshock and aftershock is about 140 km which agrees with the fault dimension estimated using the aftershock distribution the seismic moment releases for the three asperities on the rupture surface are 1 0 1019 6 9 1019 and 2 3 1019 nm with respect to time

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

constraining the boundary between the sunda and andaman subduction systems evidence from the 2002 mw 7 3 northern sumatra earthquake and aftershock relocations of the 2004 and 2005 great earthquakes the 2004 m w 9 0 sumatra andaman earthquake initiated along the andaman subduction zone north of the last great sumatra earthquake along the sunda trench in 1861 during the 2005 m w 8 7 banyak islands earthquake a portion of the 1861 rupture subsequently failed the boundary between the 2004 and 2005 ruptures broadly coincides with local trench rotation and the southern edge of the andaman microplate which suggests structural control on fault segmentation aftershock relocations of the 2004 and 2005 earthquakes show little overlap and the sharp boundary between the series locates near the 2002 m w 7 3 northern sumatra earthquake we posit that these features represent the southern extent of the stable andaman microplate 50 100 km northwest of what was previously reported broadband analyses of the 2002 earthquake yield a bilateral rupture pattern that is used to model coulomb stress changes near the 2004 hypocenter to assess stress interactions along adjacent fault segments

slip distribution of the mw 5 9 1999 athens earthquake inverted from regional seismological data 1 we studied the kinematic rupture process of the moderate magnitude mw 5 9 1999 athens earthquake using broadband seismic recordings at regional distances the apparent source time functions astf obtained by retrieving the wave propagation and site effects from the seismic recordings using an empirical green s function method indicate a rather complex rupture with a source directivity primarily pointing towards athens to further characterize the faulting we inverted the astfs for the kinematic history of the rupture using a damped least square inversion scheme with inequality constraints the rupture extent is delimited by a 10 km along strike 20 km along dip zone the mean slip amplitude on the observed rupture area is equal to 25 cm the slip concentrates in two elongated zones with amplitudes reaching locally 60 cm the total rupture lasted between 5 and 6 s

source parameters and rupture velocity of small m 2 1 reservoir induced earthquakes summary we calculate stress drop and rupture speed for ml 2 1 shallow reservoir induced earthquakes and find them to be similar to those of large natural earthquakes previous studies have suggested that hydrofractures mining and reservoir induced earthquakes have lower average stress drop than natural tectonic earthquakes this difference might result from the different tectonic setting or the shallower hypocentral depths of induced earthquakes alternatively difficulties in correcting for attenuation and site effects in earlier studies may lead to underestimation of stress drop in addition most studies assume the rupture velocity of small reservoir induced earthquakes to be the same as for the large earthquakes we analyse a set of 101 ml 2 1 earthquakes induced by changing water level in the acu reservoir ne brazil the earthquakes are shallow depth 5 km and the region has negligible natural seismicity we use three different approaches to calculate the source parameters of the six largest 1 9 ml 2 1 earthquakes we model the individual spectra to find corner frequency frequency independent q and long period amplitude we use collocated small earthquakes as empirical green s functions to calculate the spectral ratios and determine the relative source time functions estimates of the source duration and corner frequency imply stress drops in the range of 26 179 mpa these are similar to or higher than tectonic earthquakes suggesting that the shallow hypocentral depth and the presence of water do not affect stress drop we observe clear directivity for one of the earthquakes and use the azimuthal variation in pulse width to estimate a rupture velocity of 0 6

three dimensional crustal structure of the mendocino triple junction region from local earthquake travel times the large scale three dimensional geometry of the mendocino triple junction at cape mendocino california was investigated by inverting nearly 19 000 p wave arrival times from over 1400 local earthquakes to estimate the three dimensional velocity structure and hypocentral parameters a velocity grid 175 km n s by 125 km e w centered near garberville california was constructed with 25 km horizontal and 5 fan vertical node spacing the model was well resolved near cape mendocino where the earthquakes and stations are concentrated at about 40 6 n latitude a high velocity gradient between 6 5 and 7 5 km s dips gently to the south and east from about 15 km depth near the coast relocated hypocenters concentrate below this high gradient which we interpret as the oceanic crust of the subducted gorda plate therefore the depth to the top of the gorda plate near cape mendocino is interpreted to be 15 km the gorda plate appears intact and dipping 8 eastward due to subduction and flexing downward 6 12 to the south both hypocenters and velocity structure suggest that the southern edge of the plate intersects the coastline at 40 3 n latitude and maintains a linear trend 15 south of east to at least 123 w longitude the top of a large low velocity region at 20 30 km depth extends about 50 km n s and 75 km e w roughly between garberville and covelo and is located above and south of the southern edge of the gorda plate we interpret this low velocity area to be locally thickened crust 8 10 km due to either local compressional forces associated with north south compression caused by the northward impingement of the rigid pacific plate or by underthrusting of the base of the accretionary subduction complex at the southern terminous of the cascadia subduction zone south of cape mendocino and southwest of the garberville fault high velocities indicative of oceanic crust are detected at 15 km depth we interpret this evidence as tectonic underplating of the pacific oceanic crust beneath the coastal franciscan complex similar to the situation seismically imaged in central coastal california page and brocher 1994 this geometry indicates that the westernmost portion of the slab window has been filled by tectonic underplating and crustal thickening while deep seated mantle upwelling is confined to an area centered about 75 km north of clear lake benz et al 1992 zandt et al 1992

the march 9 1994 m w 7 6 deep tonga earthquake rupture outside the seismically active slab we investigate the rupture process of the march 9 1994 m w 7 6 deep tonga earthquake and its relationship to the background seismicity of the subducted tonga slab variations in observed p and s wave pulse duration indicate that the rupture propagated to the nne and extended well beyond the background seismicity we inverted 47 p and sh waveforms including regional broadband waveforms from the southwest pacific seismic experiment using a method that solves for the focal mechanism change during the rupture and the distribution of moment release along the fault plane the results indicate that significant moment release occurred in previously aseismic regions outside the active seismic zone and that the rupture terminated 10 20 km beyond the bounds of the previous seismic activity a significant change in focal mechanism occurred when the rupture propagated into the previously aseismic region rupture along the near vertical nne striking nodal plane provides a somewhat better fit to the body waveforms than rupture along the near horizontal nodal plane this result combined with the planar alignment of aftershocks and the general nne directivity of the waveforms provides strong evidence that the rupture occurred on the near vertical plane thermal modeling of the tonga slab indicates that the rupture terminated in material about 200 c warmer than the temperature that normally limits the occurrence of smaller earthquakes additionally aftershocks seem to be suppressed in the outer regions of the rupture which contain about half of the moment release but only 1 of the 15 well located aftershocks we suggest that slabs may be composed of an inner cold core where seismic rupture initiates and small earthquakes occur and a thermal halo of warmer material which can sustain rupture and only a few aftershocks the mechanism by which rupture propagates through the warmer material need not be similar to the process governing rupture nucleation in the cold slab core nucleation may occur through a process limited to the cold core such as transformational faulting and propagation through the warmer material may occur through ductile faulting or plastic instabilities isolated deep earthquakes in other subduction zones such as the 1994 bolivia event may occur almost completely within the warmer zone accounting for the lack of background seismicity and the dearth of aftershocks

seismic attenuation normal moveout stretch and low frequency shadows underlying bottom simulating reflector events abstract in many cases the seismic response of bottom simulating reflectors is characterised by low frequencies called low frequency shadow generally this phenomenon is interpreted as attenuation due to partial saturation with free gas actually this frequency loss may have multiple causes with a normal moveout stretch as a possible candidate to analyse this phenomenon we compute synthetic seismograms by assuming a lossy bottom simulating layer with varying quality factor and thickness bounded by the upper hydrate brine gas brine and lower gas brine brine interfaces first we estimate the shift of the centroid frequency of the power spectrum as a function of the travelled distance of the seismic pulse then we perform one dimensional numerical experiments to quantify the loss of frequency of the seismic event below the bottom simulating reflector as a function of the quality factor of the bottom simulating layer and its thickness due to wave interference then we compute shot gathers to obtain the stacked section with and without the normal moveout stretch correction and with and without the presence of wave attenuation in the bottom simulating layer the results indicate that the low frequency shadow due to the normal moveout stretch is stronger than that due to attenuation and may constitute a false indicator of the presence of gas in fact often the low frequency shadow overlies events with higher frequencies in contradiction with the physics of wave propagation this is particularly evident when the low frequency shadow is so extensive that the presence of high frequencies below cannot be justified by the acquisition geometry

precise relative earthquake location using surface waves 1 earthquake locations provide a fundamental tool for seismological investigations while dense seismic networks can provide robust locations accuracy and precision of these locations suffer outside dense networks this is particularly true in offshore areas where location analysis relies heavily on distant seismic observations we present a method for estimating precise relative seismic source epicentroid locations using surface waves several reasons including lower velocities and strength of the signal at distance make use of surface waves for event location appealing we focus on the panama fracture zone region and relocate 81 strike slip earthquakes to produce tectonically consistent epicentroid locations the resulting pattern of earthquakes more clearly delineates recently active regional structures than original body wave locations the mean shift between the us geological survey national earthquake information center epicenter and our epicentroids is about 14 km the median is about 11 km and typical origin time changes are generally less than 2 s we find that north of 6 5 n the plate boundary motion is split across two roughly north south striking structures the panama and balboa fracture zones for the last 36 years slip along these two structures roughly matches slip along the panama fracture zone to the south from 4 5 n to 6 25 n but the balboa fracture zone has roughly three times the moment than the northern panama fracture zone our analyses show that observed rayleigh wave signal to noise ratios for moderate to large shallow earthquakes are suitable for applying the procedure and that rayleigh wave observations form a self consistent set of constraints on the relative location of earthquake centroids

real time seismology at uc berkeley the rapid earthquake data integration project the rapid earthquake data integration project is a system for the fast determination of earthquake parameters in northern and central california based on data from the berkeley digital seismic network and the usgs northern california seismic network program development started in 1993 and a prototype system began providing automatic information on earthquake location and magnitude in november of 1993 via commercial pagers and the internet recent enhancements include the exchange of phase data with neighboring networks and the inauguration of processing for the determination of strong motion parameters and seismic moment tensors

tikhonov s regularization for deconvolution in the empirical green function method and vertical directivity effect abstract application of tikhonov s technique using input errors for the parameter of regularization estimation enhances the accuracy and stability of the reconstruction of a source time function stf by the empirical green function egf method that gives us an opportunity to use simultaneously for analysis body and surface waves data and to estimate the horizontal and vertical directivity effects knowledge of the last is particularly useful for the choice of an active nodal plane of earthquakes with the dip slip fault orientation that allows us to classify these earthquakes to the interplate or intraplate types and thereby to reach the better understanding of tectonic processes in the region of interest by way of illustration an attempt to estimate average parameters of faulting in a first approximation is made herein for two russian far east large events with opposite types of focal mechanism orientation strike slip and dip slip the former is not a matter of interest in the context of vertical directivity effect but enables us to test the method the directivity analysis of pulse durations and inverse amplitudes of the relative source time functions rstfs restored at eight globally distributed stations iris indicates that the destruction in the source of the neftegorsk earthquake 05 27 1995 m w 7 1 propagated roughly horizontally in the direction 8 11 during 19 2 0 4 s along the rupture extending 35 5 4 9 km the calculated slip distribution along the rupture coincides within the error with the results of field geological measurements on the causal surface fault that proves that the neftegorsk earthquake source is well described by the model of the linear unilateral fault and gives a good assessment of the method applied the average parameters of faulting in the kamchatka earthquake 03 08 1999 m w 6 9 have been determined from data of 13 station iris it was shown that the destruction in its source propagated downward at an angle of about 60 with horizon in the direction about s156 e during 13 4 0 2 s along the rupture totaling 25 5 2 3 km in length therefore the nodal plane steeply dipped to the se was active and this event can be regarded as an intraplate type two asperities can be selected the first with the maximum slip 3 3 m located at a distance of about 7 km from the onset of rupture and the second with the maximum slip about 0 9 m centered at approximately 19 km from that

the 1995 colima jalisco mexico earthquake mw 8 a study of the rupture process in this study we map rupture characteristics of the great shallow thrust earthquake of october 9 1995 which caused extensive damage to the coastal towns of colima and jalisco to isolate the earthquake rupture details we deconvolve surface waves with two empirical green s functions the aftershock of october 12 1995 mw 5 9 and the foreshock of october 6 1995 mw 5 8 from the corresponding mainshock records specifically we use a spectral water level deconvolution to obtain 80 apparent source time functions astf at 62 stations rayleigh and love waves durations of the astf as a function of azimuth indicate that the rupture propagated toward n70 w the duration of the source time function stf is around 62 s with a large pulse at 45 s to map the main characteristics of the rupture we use an inverse radon transform of the astfs assuming a ribbon fault model aligned in the direction of the rupture propagation our analysis indicates that the rupture initiated about 20 km offshore of manzanillo and propagated almost unilaterally for 150 km towards n70 w with an average rupture velocity of approximately 2 8 km s the earthquake was a composite of three significant subevents the largest occurred 45 s after the initiation of the rupture and was located about 100 km away this result is in good agreement with the inversion of deformation data measured with gps melbourne et al 1997

investigation of the rupture process of the 28 june 1992 landers earthquake utilizing terrascope abstract displacement seismograms recorded by terrascope for the 28 june 1992 landers earthquake m w 7 3 are deterministically modeled using a forward point source summation technique although the data set is sparse it was possible to robustly determine important rupture parameters such as gross slip distribution rupture velocity rise time and total source duration the relatively simple approach lends itself to rapid application following large earthquakes provided that a catalog of green9s functions appropriate for the region is available the fault used in the modeling of the landers mainshock has a length of 70 km along strike and a width of 15 km along dip a model was found in which the distribution and amplitude of slip at the surface matches the observed surface slip and provides a very good level of fit to the seismic data seismically the landers earthquake is characterized as two subevents the peak slip of the first subevent is 10 km north of the epicenter and the second is 40 km northwest along strike from the epicenter the seismic moment is distributed as 2 10 26 dyne cm to the first and 6 10 26 to the second subevent respectively it was assumed in our modeling that the distribution of seismic moment along strike was the same at all depths this assumption implies that slip at depth is 69 of that at the surface as a result of differences in the material properties in the velocity model the sensitivities of the source model to rupture velocity and dislocation rise time were examined a rupture velocity of 2 9 km sec 80 of the shear wave velocity and a rise time of 1 to 3 sec were found to satisfy the data the rise time is only a fraction of the total source process time of 24 sec and implies that slip on the fault occurred within a narrow band 3 to 10 km at any instant during the rupture

source time functions of nuclear explosions and earthquakes in central asia determined using empirical green s functions relative source time functions rstf have been estimated for four underground nuclear explosions and seven earthquakes in central asia using broadband p waveforms of nearby smaller events as empirical green s functions egf rstfs of the four explosions m sub b 5 3 to 6 5 are each dominated by a simple pulse with a source duration of 0 4 to 0 8 s rstfs for two of the explosions show a significant secondary pulse with a pulse width similar to that of the first pulse the authors conclude that the secondary phases are most likely associated with the spall slapdown phenomenon seismic moment releases by the spall phases are less than one third of those by the first explosion pulses elastic radii of the explosions are estimated to be about 0 25 to 0 5 km and stress drops of the explosion range from 13 to 52 mpa in contrast rstfs of earthquakes studied m sub b 5 5 to 6 6 typically comprise multiple source pulses with a total source duration from a few to several tens of seconds indication that the complex source process involves a fault dimension of several tens of kilometers stress drops of the earthquakes are much smaller than those of the nuclearmore explosions ranging from 0 5 to 3 5 mpa the authors study demonstrates the power of the egf method for retrieving rstfs and reveals that differences in rstfs and source parameters can be used to distinguish large nuclear explosions from moderate to large earthquakes m sub b 5 5 80 refs 11 figs 6 tabs less

rupture process of the 1995 antofagasta subduction earthquake mw 8 1 a finite source rupture model of the july 30 1995 m w 8 1 antofagasta northern chile subduction earthquake is developed using body and surface waves that span periods from 20 to 290 s a long period 150 290 s surface wave spectral inversion technique is applied to estimate the average finite fault source properties deconvolutions of broadband body waves using theoretical green s functions and deconvolutions of broadband fundamental mode surface waves using empirical green s functions provided by a large aftershock yield effective source time functions containing periods from 20 to 200 s for many directivity parameters the source time functions are used in an inverse radon transform to image a one dimensional spatial model of the moment rate history the event produced a predominantly unilateral southward rupture yielding strong directivity effects on all seismic waves with periods less than a few hundred seconds the aftershock information spectral analysis and moment rate distribution indicate a rupture length of 180 200 km with the largest slip concentrated in the first 120 km a rupture azimuth of 205 10 along the chilean coastline and a rupture duration of 60 68 s with a corresponding average rupture velocity of 3 0 3 2 km s the overall rupture character is quite smooth accentuating the directivity effects and reducing the shaking intensity however there are three regions with enhanced moment rate distributed along the rupture zone near the epicenter 50 to 80 km south of the epicenter and 110 to 140 km south of the epicenter

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

rupture directivity of the major shocks in the 1997 umbria marche central italy sequence from regional broadband waveforms we derive the relative moment rate function for the main shocks in the fall 1997 central italy seismic sequence mw 5 7 6 0 5 6 by applying an empirical green function method by using three conveniently placed broad band mednet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one taking a simple source model forward modeling is utilized for determining fault parameters such as length rupture propagation velocity and direction and slip distribution

very broadband seismic analysis of the 1992 flores indonesia earthquake mw 7 9 the december 12 1992 flores island earthquake m w 7 9 which caused a destructive tsunami is located in the back arc of the transition zone between the sunda and banda arcs a region in active collision with the australian continental margin we study the earthquake using four seismological techniques spanning a period range of 1 1000 s and infer that the flores event may be characterized as a shallow back arc thrust with fault plane strike 70 30 dip 28 10 and rake 80 to 140 linear trade off with strike a rupture consisting of three discrete pulses with a total duration of 70 s centroid time 26 3 s and an estimated moment release between 7 5x10 20 and 8 0x10 20 n m from the slip vector we infer that compressional forces play an important role in the deformation mechanism of the back arc north of flores island body waves constrain the hypocentral depth to be 16 km with rupture mainly propagating updip to shallow depth and bilaterally along strike with most subevents located toward the northeast evidence for rupture directivity from surface wave deconvolutions is inconclusive but the overall source function is consistent with body wave results our body wave finite fault model is in rough agreement with two models proposed to explain tsunami run up observations normal mode modeling of w phase observations at periods longer than 70 s shows that slow slip is negligible from this and the slip distribution determined from the body wave analysis we infer that the seismic source is an unlikely candidate to explain anomalously high tsunami run ups measured on northeastern flores island

relative source time function studies and stress drop of earthquakes in southeastern alaska northwestern canada abstract we use the relative source time function rstf method to estimate the source properties of earthquakes within southeastern alaska northwestern canada in an effort to determine if there are systematic variations in the source parameters of these earthquakes e g stress drop rupture complexity and rupture directivity with the tectonic setting in the rstf technique we deconvolve the p arrival signal of a smaller event from that of a larger event by the following process select arrivals with a tapered cosine window fast fourier transform to obtain the spectrum apply a water level to the spectrum of the smaller event and apply a band pass filter before inverse transforming the result to obtain the rstf our results show self similarity over earthquakes of magnitude less than five and stress drop dependence on focal mechanism strike slip events appear to have larger stress drops with the highest stress drops for events within the queen charlotte fault system we find evidence for rupture directivity consistent with previous studies for three earthquakes that had adequate azimuthal station coverage

broadband source modeling of the november 8 1997 tibet mw 7 5 earthquake and its tectonic implications we studied the source process of a large ms 7 9 intraplate earthquake that occurred on november 8 1997 at 1002 ut in a remote region of northern tibet we used four distinct methods to investigate the broadband source process and thereby better understand the tectonic implications of this event we relocated aftershocks using a master event technique and found that the distribution of aftershocks covers a region of 200 km in lateral extent we also employed a surface wave spectral inversion technique to estimate the mainshock moment depth centroid location and centroid time and utilized an empirical green s function technique to extract rupture directivity information and a detailed source time function from observed seismograms we also inverted body waves to estimate the moment release along the fault and the source time function the 1997 earthquake ruptured a strike slip fault that appears to be an extension or splay of the kun lun fault system this fault is one of the most seismically active strike slip faults within the tibetan plateau and has had events with surface wave magnitudes of 6 1 7 4 and 7 9 in this region since 1973 the rupture released most of the energy within the first 20 s and propagated bilaterally initially with the later rupture propagating westward for 20 30 s the absence of large aftershocks suggests that the earthquake efficiently released the stored strain comparing mainshock to the largest aftershock energy ratios for this event and other large strike slip events shows that faulting within the plateau has the characteristics of weak faults e g fracture zone faulting

source time function complexity of the great 1989 macquarie ridge earthquake the rupture process of the great 1989 macquarie ridge mw 8 1 strike slip faulting earthquake is examined using an empirical green function deconvolution method which provides broadband source time functions from both body and surface waves recordings from a nearby much smaller mw 6 4 strike slip event provide accurate broadband green functions for pp s ss rayleigh and love waves spanning the period range 20 150 s body wave deconvolutions indicate that the principle short period 30 s moment release occurred in the first 25 s of rupture with no resolvable directivity only minor short period energy release occurred over the next 30 s surface wave deconvolutions for the usually neglected 20 150 s period range produce source time functions with slightly larger total moment than the body wave deconvolutions and no resolvable directivity from the onset to the peak of moment release in the first 20 s however azimuthally dependent broadening of the surface wave source functions which extend to more than 50 s duration indicates a component of northeastward unilateral rupture extension requiring about 30 50 km asymmetry in the overall rupture compatible with the northeastward asymmetry of the 1 day aftershock zone spectral inversions of long period love and rayleigh waves indicate a centroid time shift of approximately 25 3 s 50 7s duration trapezoid source in the period range of 150 280 s compatible with the deconvolved surface wave source time functions deconvolutions using both empirical and theoretical green functions are optimized to detect any long period precursory radiation for periods up to about 250 s but no convincing evidence for precursory radiation in the passband is found the long period surface wave phase data also do not require a precursor

rupture directivity and slip distribution for the ms 6 8 earthquake of 6 april 1992 offshore british columbia an application of the empirical green s function method using surface waves on 6 april 1992 at 13 55 ut an earthquake of ms 6 8 occurred along the revere dellwood wilson rdw fault in the triple junction region at the northern end of the cascadia subduction zone this was the first significant event in this region recorded by modern digital broadband seismic networks thus providing the first opportunity to examine the rupture process of a major earthquake along this young oceanic transform fault in this article an empirical green s function technique is applied to regional and teleseismic surface waves to estimate the rupture directivity the extent of rupture and the slip distribution along the revere dellwood wilson fault associated with this earthquake the 20 sec low pass filtered relative source time functions rstf s are single pulses with an azimuthal variation in the pulse width this suggests that the rupture propagated to the nw 315 20 along the revere dellwood wilson fault striking 326 higher frequency rstf s reveal two discrete subevents the clear azimuthal variation in the time separation of these subevents requires that relative to the first subevent the second is located 13 to 20 km in the direction 345 20 using the rstf at hrv perpendicular to the rupture direction a total rupture length of 35 km is estimated with the bulk of the slip concentrated in a 20 km long segment of the rdw fault to the northwest of the epicenter two peaks are observed in the estimated slip distribution with maximum values of 1 8 and 1 1 m respectively the rupture model derived from this analysis is similar to that obtained from the analysis of body waves and is consistent with the results of aftershock studies the latter indicate a paucity of aftershock activity and low moment release in the 20 km long segment of the rdw fault to the nw of the epicenter a distinct peak in aftershock activity 30 to 40 km to the nw of the epicenter likely represents the termination of rupture the good agreement between the results of this study the rupture model estimated from body wave analysis and the aftershock distribution bode well for the application of the empirical green s function method using surface waves it suggests that this method could be applied to large historic earthquakes in this region for which regional and teleseismic surface waves are often the most reliable data set

rapid estimation of first order rupture characteristics for large earthquakes using surface waves 2004 sumatra andaman earthquake 1 broadband surface waves from large earthquakes can be rapidly processed to estimate seismic moment faulting duration and general slip distribution supplying important information for hazard response efforts including tsunami warnings deconvolution of surface wave green s functions removes propagation effects yielding azimuthally varying effective source time functions even a single faultperpendicular time function can provide robust first order estimates of the temporal history of seismic radiation and associated slip distribution simplified two dimensional finite fault modeling using a few surface wave time functions can reliably characterize the smooth component of the overall rupture process these procedures are demonstrated using 13 rayleigh wave observations for the 26 december 2004 sumatra andaman earthquake yielding satisfactory agreement with models based on more complete seismic data sets depending on source and station locations stable slip estimates can be obtained within 15 60 minutes of the onset of a large earthquake citation ammon c j a a velasco and t lay 2006 rapid estimation of first order rupture characteristics for large earthquakes using surface waves 2004 sumatra andaman earthquake geophys res lett 33 l14314 doi 10 1029 2006gl026303

a faulting model for the 1992 petrolia earthquake can extreme ground acceleration be a source effect the 1992 petrolia earthquake m 7 0 was quite remarkable in that an accelerometer at cape mendocino cap recorded a high frequency pulse of almost 2 g whereas the nearby roughly 6 km away petrolia station pet recorded a maximum of only 0 6 g in our model for this event we have investigated the possibility that extreme ground acceleration with high spatial variability can be caused by a source effect specifically the rupture of a barrier asperity this type of rupture feature can produce extreme ground acceleration provided that certain geometrical constraints are met in the present study we derive a combined high and low frequency faulting model for the 1992 petrolia earthquake that is consistent with the slip distribution on the fault and that produces the high frequency pulse at cap our model consists of four parts 1 a low frequency 0 1 0 6 hz inversion that determines the slip rupture time and risetime distributions on the fault 2 an interpolation and perturbation of the above distributions that produces synthetic accelerograms between 0 6 and 3 0 hz 3 random phase signal that is scaled to the spectral amplitude level of the data between 3 0 and 12 5 hz and 4 the rupture of a barrier like asperity that produces greatly amplified radiation at cap but not at other stations we find that our model produces a good fit to the near source records of the 1992 petrolia event the results emphasize the interaction between fault geometry and rupture propagation to produce ground motion as well as the hazard associated with locations above the hanging walls of dipping faults where the geometry permits the production of extreme ground acceleration

the 1989 ms 6 3 ungava quebec earthquake a complex intraplate event on 25 december 1989 the largest earthquake ms 6 3 in northern quebec in at least 60 yr occurred in the ungava peninsula this earthquake was unique in that it marked the first time surface faulting could be confirmed for a historical eastern north american earthquake field observations indicated a combination of thrust and strike slip motion waveforms modeled in this study show that the earthquake consisted of two subevents a thrust subevent on a ne sw striking plane followed by a larger strike slip subevent on a nne ssw striking plane the surface waves give an equivalent double couple moment of 1 3 1025 dyne cm the sum of the subevent moments is greater than the simple source moment by almost a factor of 2 both subevents occurred at a depth of 3 km they were separated by 0 9 sec in time with the second subevent occurring 5 2 km southwest of the first the source parameters determined by modeling and those inferred from the ground observations generally agree but there are some differences with respect to the subevent offset these may be reconciled if the strike slip motion was distributed among the several small faults at the southwestern end of the rupture or if the complete surface rupture was not found the stress orientation nw compression inferred from the fault plane solution is consistent with the focal mechanisms of many other recent northeastern canadian events the ungava earthquake and many intraplate events from several continents share a number of characteristics including shallow hypocenters source complexity and occurrence on faults that showed no evidence for previous ruptures

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

rupture dimensions and rupture processes of fluid induced microcracks in salt rock abstract we developed and applied a simple empirical green function method to study induced microcracks observed during hydraulic fracturing experiments in salt rock either unidirectional ruptures on rectangular faults or allround ruptures on elliptical faults are tested to explain the observed directivity effects in body wave amplitude spectra mostly the rectangular rupture model and horizontal fault planes are favored the average rupture lengths are between 15 and 27 mm the average rupture durations between 14 and 26 s small average rupture velocities of 30 of the s wave velocity of the rock are indicated the dispersive low frequency coda waves present in the data look similar to coda waves observed during other hydraulic fracturing experiments and to long period events from some volcanoes which have been explained by the resonance of a fluid filled crack the radiation pattern of first motion amplitudes of most events is dominated by a dip slip double couple indicating slip on horizontal or vertical planes we cannot distinguish whether the observed low frequency coda waves are influenced by a source effect or by a possible sensor borehole coupling however a simple method using gauss filter at different center frequencies and relocation is tested to analyze the low frequency coda waves in terms of source models

spatial slip distribution of the september 20 1999 chi chi taiwan earthquake mw7 6 inverted from teleseismic data the teleseismic waveforms of the mw7 6 september 20 1999 chi chi earthquake were examined to obtain the quick information on the fault rupture process the deconvolution results show the fault ruptured from south to the north and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane the spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km 15km the maximum slip was about 8 m located at about 45 km to the north of the epicenter the slip distributions obtained in this study have a good agreement with the observed surface breaks the comparable static and the dynamic stress drops of about 11 mpa in the large slip region indicate that the melting fluid pressurization might have taken place in this earthquake it reduces the dynamic friction and results in the large slip observed

rupture properties of the giant sumatra earthquake imaged by empirical green s function analysis empirical green s function egf analysis has remained little used to image the rupture properties of the giant 26 december 2004 sumatra earthquake the 2 november 2002 foreshock m w 7 2 close to the mainshock epicenter gives us the opportunity to use its waveforms to empirically simulate the rayleigh wave propagation of the sumatra earthquake we first show that the exceptional size of the sumatra earthquake does not prevent use of the egf technique four aftershocks m w 5 9 6 1 distributed along the sumatra andaman trench are shown to have consistent rayleigh waves for periods between 100 and 200 sec at a lower frequency we present two large earthquakes of the mexican subduction zone m w 7 2 7 3 close to the selected egf magnitude for which long period green s functions 100 2000 sec remain very similar even if event epicenters are separated by about 650 km this justifies the possibility of using the 2002 foreshock as an egf for the whole rupture process of the sumatra earthquake and shows more generally the very broad range of application of egf technique then a specific analysis reveals that seismic moment magnitude is close to 9 1 seismic moment equal to 5 6 10 22 n m moment release analysis along the sumatra andaman trench shows two main slip episodes one next to the northern extremity of sumatra 20 m slip and the other one along the nicobar islands 10 m slip with a global extent of 1150 1200 km rupture velocity varies between values around 2 5 km sec in the first half of the rupture and values closer to 2 km sec in the second half total duration imaged by rayleigh waves is 580 sec 20 sec and no activity of the fault is found in the time scale between 600 and 2000 sec in the hypothesis of even longer timescale slip this phenomenon would be of the order of 10 20 of the global moment and likely restricted to the andaman islands

the 1968 tokachi oki and the 1969 kurile islands earthquakes variability in the rupture process the may 16 1968 tokachi oki mw 8 2 and the august 11 1969 kurile islands mw 8 2 shallow thrust earthquakes occurred along the japan kurile arc about 500 km apart and possess similar static fault parameters their dynamic source processes were investigated using the observable directivity in the source time functions deconvolved from long period p waves the rupture processes of both earthquakes can be understood in terms of a combination of the end member asperity and barrier models of earthquake rupture the 1969 kurile islands earthquake ruptured in the sense of the asperity model one region of the fault plane radiated most of the seismic moment i e the asperity and is surrounded by the rupture zones of large precursor events the rupture process of the 1968 tokachi oki earthquake contains elements of both end member rupture models a dominant asperity is bounded to the south by a region of the fault plane ruptured by a large precursor event and is bounded to the north by a geometric barrier where the plate margin changes direction this geometric feature is responsible for the abrupt termination of the rupture front it appears that the tectonic setting plays a vital role in determining the rupture mode earthquakes that occur along linear trenches where no geometric or topographic complications exist seem to rupture in the sense of the asperity model whereas earthquakes that occur in the vicinity of such complications are more likely to possess rupture processes intermediate between the two end member models

empirical green function deconvolution of broadband surface waves rupture directivity of the 1992 landers california mw 7 3 earthquake we present a simple method to determine gross temporal and spatial characteristics of faulting that can uniquely define the fault plane for a relatively large earthquake the technique involves deconvolution of teleseismic and regional broadband surface waves and or body waves of a small event an empirical green function from the corresponding signals at the same stations for a large mainshock this deconvolution corrects each mainshock seismic record for propagation and instrument response and if the focal mechanisms and centroid depths are identical deconvolution provides relative source time functions for the mainshock azimuthal variations of source time function width or subevent interference reveal the mainshock rupture directivity changes in the source mechanism during rupture can be evaluated for some classes of events our empirical green function procedure is novel in its application to surface waves and its use for large m 7 earthquakes we perform synthetic tests to establish intrinsic limitations of the method the procedure requires very little data processing and can be applied in near real time with the current distribution of seismic stations that have dial up data retrieval capability it also provides a straightforward procedure for reducing bias in source duration estimates resulting from aspherical heterogeneity and for detecting anomalous long period radiation we apply the procedure to the 28 june 1992 landers california mw 7 3 earthquake the landers earthquake source duration lasted about 25 sec and was dominated by two subevents with predominantly north northwestward rupture extending 60 to 70 km the subevents show counter clockwise rotations of at least 12 in strike that correlate well with mapped surface rupture

rupture process of the june 28 1992 big bear earthquake the june 28 1992 big bear earthquake in southern california was assumed to have ruptured along a northeast trending plane as suggested by long term aftershock distribution no surface rupture was found however and mainshock locations determined from both strong motion and terrascope data are mutually consistent and do not lie on the assumed fault plane an integrated study involving waveform modeling directivity and seismicity analyses suggests a complex rupture pattern with significant short and long period energy propagating northwest along the presumed conjugate fault plane

relative source time function studies of earthquakes along the denali totschunda fault system abstract we use the relative source time function method to estimate the source properties of aftershocks of the november 2002 denali earthquake sequence to determine if there are systematic variations in scaling relationships of these events that can be related to seismic moment focal mechanism event date time and location along the fault and bedrock type our results show self similarity over earthquakes of magnitude less than five and stress drop dependence on focal mechanism strike slip events appear to have larger stress drops we observed a clear stress drop decrease from west to east that correlates with changes in earthquake focal mechanisms along the denali fault

a rupture model for the 1999 chi chi earthquake from inversion of teleseismic data using the hybrid homomorphic deconvolution method this study investigates the kinematics of the rupture process of the ml 7 3 chi chi taiwan earthquake on september 21 1999 by applying the proposed hybrid homomorphic deconvolution method to deconvolve teleseismic broadband p wave displacement recordings of the earthquake this study derives the apparent source time functions astfs at ten stations located around the epicenter to further characterize the fault the kinematic history of the rupture was inverted from astfs using a genetic algorithm coupled with nonlinear iterative technique the calculated asfts reveal that the total rupture event lasted for approximately 27 s static slip distribution images indicate that most slip occurred at shallower portions of the fault plane especially 20 55 km north of the epicenter the maximum slip reached 20 m at 45 km north of the epicenter and the average slip throughout the observed rupture area was approximately 2 m large asperities on the fault appeared at 25 35 km and 40 50 km north of the hypocenter and coincided with relatively high rupture velocity this suggests that the earthquake s energy may have been released quickly the rupture velocity decreased upon encountering an asperity and increased again after passing the asperity this implies that the rupture required more time to overcome the resistances of the asperities the maximum rupture velocity was 3 8 km s while the average rupture velocity was approximately 2 2 km s the rise time distribution suggests that larger slip amplitudes generally correspond to shorter rise times on the subfaults

self consistent retrieval of source parameters using mantle waves the large number of high quality stations from global networks e g iris geoscope allows for rapid and robust recovery of source parameters of large earthquakes we present a self consistent analysis of surface waves in terms of directivity parameters the boxcar is often used to recover source parameters but is rarely a faithful representation of an event s time function we demonstrate that more reliable estimates of directivity parameters can be obtained when we take into account the source time function stf of the event a low frequency stf is obtained from first r1 and second r2 orbit rayleigh waves in the range 2 to 15 mhz with a spectral synthesis and inversion method we measure the differential amplitudes between data and 3d synthetics we use the r1 r2 ratio of differential amplitudes to invert in a single narrow frequency band for the event s apparent rupture azimuth and velocity for the mw 8 1 chile 1995 event data are consistent with unilateral southward propagation with a velocity of about 2 4 km sec for the mw 7 9 mexico 1995 earthquake the rupture propagated toward the nw at about 2 0 km sec our low frequency estimates agree with broadband studies of both events and can be retrieved rapidly on a routine basis after a large earthquake

radiated energy of great earthquakes from teleseismic empirical green s function deconvolution we expand on the empirical green s function deconvolution method of ide et al 2011 to estimate radiated energy for the six largest earthquakes worldwide over the last 10 years 2011 m w 9 0 tohoku oki 2004 m w 9 1 sumatra 2010 m w 8 8 maule 2005 m w 8 7 nias 2007 m w 8 5 bengkulu and 2012 m w 8 6 off sumatra deconvolution of p sv and sh components gives consistent energy results that are comparable to estimates found independently by other researchers apparent stress for the five great thrust earthquakes is between 0 4 and 0 8 mpa while the 2012 off sumatra strike slip earthquake has a higher apparent stress of 3 mpa which is consistent with other studies that find a tendency for strike slip events to be more energetic our results are within the spread of apparent stress from the wider global earthquake population over a large magnitude range the azimuthal distribution of energy in each case shows signs of directivity and in some cases shows less energy radiated in the trench ward direction which may suggest enhanced tsunami potential we find that egfs as small as m 6 5 can be used for teleseismic deconvolution and that an egf mainshock magnitude difference of 1 5 units yields stable results this implies that m 8 is the minimum mainshock size for which teleseismic egf deconvolution will work well we propose that a database of egf events could be used to calculate radiated energy and apparent stress of great hazardous events in near real time i e promptly enough that it could contribute to rapid response measures

analysis of the 23 june 2001 mw 8 4 peru underthrusting earthquake and its aftershocks on 23 june 2001 a m w 8 4 underthrusting earthquake occurred in the southern peru subduction zone followed by several large aftershocks including 26 june m w 6 7 and 7 july m w 7 5 broadband analyses of seismic data for the largest of these earthquakes show southeastward rupture of 180 km along the portion of the subduction zone previously ruptured in 1868 m w 8 8 9 moment release distributions determined are consistent with aftershock location patterns earthquake rupture mode varies along southern peru from larger multi segment rupture in 1868 to several smaller segment ruptures in 2001 similar to rupture variation observed in northern peru and other subduction zones based on models of subduction zone segment interaction the 2001 earthquake sequence may suggest a shorter recurrence time for future earthquakes along this portion of the peru chile subduction zone

rapid source mechanism analysis of the april 29 1993 cataract creek mw 5 3 northern arizona earthquake abstract the source mechanism of two moderate size normal faulting earthquakes located slightly south of the grand canyon in arizona are studied using several near real time seismic wave analysis procedures the events are found to have source depths near 10 to 15 km and the smaller of the two events m b 4 8 is used to provide empirical green9s functions to analyze the rupture directivity of the larger m w 5 3 mainshock these events indicate complexity in the crustal stress environment on the western margin of the colorado plateau

determination of earthquake source mechanisms using teleseismic 30 140 s waves the january 17 1994 northridge earthquake complete seismic waveforms with periods between 30 and 140 s recorded at teleseismic distances 10 are used to determine the source mechanism of the january 17 1994 northridge earthquake ms 6 8 an algorithm called the earth simplifying transformation est is applied to the mainshock primary event data to calibrate and remove propagation effects of earth s lateral and radial heterogeneities that are not predicted by a reference earth model the procedure involves frequency domain division of each pair of observed and synthetic waveforms for an auxiliary event with a well constrained source mechanism in proximity to the primary event with the synthetics being computed for a reference earth model if the auxiliary event source mechanism is correct the differences between the data and synthetics represent the residual effects of the earth s structure that are not predicted by the earth model the frequency dependent deconvolution filters are convolved with the corresponding observed signals for the primary event the resulting waveforms are then used to determine the source mechanism of the primary event by forward modeling and by centroid moment tensor inversion with excellent fits to the complete waveforms being achieved the resulting solution for the northridge event has a centroid depth of 12 1 km and a mechanism with strike 115 dip 40 and rake 95 with 5 uncertainty for each parameter the est procedure holds promise for reliable source inversion for small earthquakes in a region calibrated by large events with well determined source parameters