source finiteness of large earthquakes measured from long period rayleigh waves the source finiteness parameters of 11 large shallow earthquakes were determined from long period rayleigh waves recorded by the global digital seismograph network and international deployment of accelerometers networks the basic data sets are the seismic spectra of periods from 150 to 300 s in the determination of source process times we used furumoto s phase method and a linear inversion method in which we simultaneously inverted the spectra and determined the source process time that minimizes the error in the inversion these two methods yielded consistent results the source process times of the sumbawa indonesia colombia ecuador valparaiso chile and michoacan mexico earthquakes were estimated to be 79 118 69 and 77 s respectively from the linear inversion method the source process times determined from long period surface waves were in general longer than those obtained from body waves source finiteness of large shallow earthquakes with rupture on a fault plane with a large aspect ratio was modeled with the source finiteness function introduced by ben menahem the spectra were inverted to find the extent and direction of the rupture of the earthquake that minimize the error in the inversion for a rupture velocity of 2 5 km s 1 the estimated rupture was unilateral 100 km long and along the strike n26 w for the may 26 1983 akita oki japan earthquake 165 km and s57 e for the september 19 1985 michoacan mexico earthquake 256 km and n31 e for the december 12 1979 colombia ecuador earthquake and 149 km and s15 w for the march 3 1985 valparaiso chile earthquake the results for the august 19 1977 sumbawa indonesia earthquake showed that the rupture was bilateral and in the direction n60 e these results are in general consistent with the rupture extent inferred from the aftershock area of these earthquakes

segmentation of the nazca and south american plates along the ecuador subduction zone from wide angle seismic profiles we describe the deep structure of the south colombian northern ecuador convergent margin using travel time inversion of wide angle seismic data recently collected offshore the margin appears segmented into three contrasting zones in the north zone affected by four great subduction earthquakes during the 20th century normal oceanic crust subducts beneath the oceanic cretaceous substratum of the margin underlined by seismic velocities as high as 6 0 6 5 km s in the central zone the subducting oceanic crust is over thickened beneath the carnegie ridge a steeper slope and a well developed high velocity cretaceous oceanic basement characterizes the margin wedge this area coincides with a gap in significant subduction earthquake activity in the south zone the subducting oceanic crust is normal the fore arc is characterized by large sedimentary basins suggesting significant subsidence velocities in the margin wedge are significantly lower and denote a different nature or a higher degree of fracturing even if the distance between the three profiles exceeds 150 km the structural segmentation obtained along the ecuadorian margin correlates well with the distribution of seismic activity and the neotectonic zonation

long period seismic radiation from the may 23 1989 macquarie ridge earthquake evidence for coseismic slip in the mantle long period seismic source parameters of the may 23 1989 macquarie ridge earthquake are determined using a surface wave inversion procedure that incorporates detailed source time functions obtained from shorter period body waves the seismic source model obtained using this method is consistent with observations of both body waves and long period rayleigh waves from the earthquake the macquarie ridge earthquake rupture has a centroid time 28 s and a right lateral strike slip fault mechanism with a rake of 175 on a vertical fault plane striking n38 e this mechanism is consistent with p wave first motions of the event inversions performed for various earth models demonstrate that the choice of surface wave attenuation model in particular affects the estimates of centroid depth and seismic moment significantly allowing for uncertainty in attenuation the long period rayleigh waves periods from 150 to 300 s indicate that the macquarie ridge earthquake had a seismic moment of 1 9 0 2 1021 n m and a corresponding centroid depth of 21 6 km the static stress drop calculated using the depth and seismic moment is 0 7 0 5 107 pa 70 50 bars the centroid depth combined with the lack of resolvable directivity of the earthquake rupture suggests that significant slip occurred beneath the moho which has a maximum depth of about 16 km in the epicentral region the mantle slip component may have preferentially radiated long period seismic energy given the shallow centroid depths and low moments determined for the event from the shorter period body wave observations

mass transport deposits in the northern ecuador subduction trench result of frontal erosion over multiple seismic cycles article i nfo investigations of mass transport deposits mtds and turbidite deposition in the confined north ecuador subduction trench provide access to paleoseismic information and insights into long term mechanisms for frontal tectonic erosion at a convergent margin the studied trench has been the site of four great subduction earthquakes 7 7 mw 8 8 during the 20th century the trench is isolated from major continental sediment input so that investigated mtds and turbidites are considered of local origin swath bathymetry seismic reflection and chirp data together with sedimentary cores and 14 c dating revealed that seven mtds were emplaced in distinct trench sub basins since 23 kyr and 27 turbidites deposited in the southernmost trench sub basin since 4 9 kyr our analysis shows that six mtds were derived from the margin while a single one stemmed from the outer trench wall temporal correlations between mtds emplaced within trench sub basins separated by a structural saddle indicate that the seven mtds were emplaced during five main events three were triggered locally and tentatively dated 5 8 1 6 kyr and recent whereas four were emplaced in distinct trench sub basins as a result of two regional events at 22 6 and 15 4 kyr none of the mtds occurred during the fast stage of the last sea level rise 13 to 8 kyr however dissociation of gas hydrates during the last 8 kyr stage of slow sea level rise might have contributed to trigger the three youngest mtds the large 1 5 13 5 kyr return time of the mtds contrasts with that of 189 yr of the turbidites the later is consistent with the 73 yr return time of two local mw 8 2 earthquakes implying that turbidites might have been triggered by large earthquakes the very large mtds return time is attributed to long term deformation processes and mechanical weakening of the margin outer wedge in response to repeated variations in basal friction pore pressure and margin extensional contraction strain over multiple earthquake cycles this process contributes to short term frontal erosion the rate of which is estimated to be 8 6 10 3 km 3 kyr km since at least 15 4 kyr

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

teleseismic time functions for large shallow subduction zone earthquakes broadband vertical p wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum pacific in the last 45 yr most of the records studied come from a common instrument the pasadena california benioff 1 90 seismometer propagation and instrument effects are deconvolved from the p wave records using a damped least squares inversion to obtain the teleseismic source time function the inversion has the additional constraint that the time function be positive everywhere the period band over which the time functions are considered reliable is from 2 5 to 50 sec fourier displacement amplitude spectra computed for each of the 1 90 p wave trains indicate spectral slopes measured between 2 and 50 sec of 1 0 to 2 25 with an average value of 1 5 these values assume an average attenuation of t 1 0 the seismic moments derived from the p wave time functions compare well with other published values for earthquakes having moments smaller than 2 5 10 28 dyne cm m w 8 2 because the 1 90 seismometer has little response at very long periods this technique underestimates the moments of the very largest events the time functions are characterized using five parameters 1 spectral slope between 2 and 50 sec 2 roughness of the time function 3 multiplicity of sources 4 pulse widths of individual sources and 5 overall signal duration the 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere convergence rates and maximum size of earthquakes comparing the time function parameters with age rate and m w of the subduction zone does not yield obvious global trends however most of the subduction zones do behave characteristically and can be grouped accordingly

source characteristics of the 12 november 1996 m w 7 7 peru subduction zone earthquake the 12 november 1996 m w 7 7 peru subduction zone earthquake occurred off the coast of southern peru near the intersection of the south american trench and the highest topographical point of the subducting nazca ridge we model the broadband teleseismic p waveforms from stations in the global seismic network to constrain the source characteristics of this subduction zone earthquake we have analyzed the vertical component p waves for this earthquake to constrain the depth source complexity seismic moment and rupture characteristics the seismic moment determined from the nondiffracted p waves is 3 5 1020n m corresponding to a moment magnitude m w of 7 6 7 7 the source time function for the 1996 peru event has three pulses of seismic moment release with a total duration of approximately 45 50 seconds the largest moment release occurs at approximately 35 40 seconds and is located 90km southeast of the rupture initiation approximately 70 of the seismic moment was released in the third pulse

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

new insights on the interseismic active deformation along the north ecuadorian south colombian nesc margin 1 the north ecuadorian south colombian subduction zone was the site of the 1906 mw 8 8 megathrust earthquake this main shock was followed by three large events in 1942 1958 and 1979 whose rupture zones were located within the 500 km long 1906 rupture area acombined onshore andoffshore temporary seismic network covering from thetrench to the andes was deployed during 3 months in the area of large earthquakes in order to obtain a detailed knowledge of the seismic background activity resulting earthquakes location and mechanisms bring new insights on interseismic active deformation distribution in the three main tectonic units of the margin namely the interplate seismogenic zone the fore arc region which is part of the north andean block and the downgoing oceanic nazca plate the interplate seismic activity presents along strike variations suggesting that the seismicity and the associated stress buildup along the plate interface depend on the time elapsed since the last large earthquakes according to our results the updip and downdip limits of the seismogenic zone appear to be located at 12 and 30 km depth respectively shallow to intermediate depth seismicity indicates a slab dip angle of 25 north of the carnegie ridge the wadati benioff plane is defined beneath the fore arc down to 100 km depth facing the ridge the wadati benioff plane extends beneath the andes down to 140kmdepth thisobservationconflictswiththehypothesisofthepresenceofaflatslabat a depth of 100 km facing the ridge in the overlying fore arc region the crustal seismicity occurs down to 40 km depth and is mainly concentrated in a roughly nw se 100 km wide stripe stretching from the coast at about 1 n to the andes the location of this active deformation stripe coincides with observed tectonic segmentation of the coastal domain as evidenced by the presence of an uplifting segment to the south and a subsiding segment to the north of the stripe it also corresponds to a 30 change in the trend of the andes suggesting that the curvature of the volcanic arc might play an important role in the deformation of the fore arc region

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

the 1946 nankai earthquake and segmentation of the nankai trough abstract we perform a simple subevent analysis of seismic p waveforms from historical records of the 1946 nankai earthquake the results of this analysis establish that the earthquake rupture consisted of two main subevents one lying within the 1 day aftershock area off the kii peninsula while the other lies much farther to the west in the area of pronounced crustal deformation of western shikoku these conform to two segments of the nankai trough which have long been referred to in studies of historical earthquakes and geology of the nankai trough but to our knowledge have not previously been established as having distinct megathrust rupture behavior we show that these two subevents are bounded by pronounced features in the geometry of the subducting philippine sea plate psp a tear in the plate to the east beneath the kii peninsula and a subducting seamount farther to the west we speculate that these features may be associated with low strength parts of the upper and or lower plates that may be susceptible to permanent anelastic deformation which prevents the accumulation of the elastic strain energy necessary to sustain seismic rupture

structural control on megathrust rupture and slip behavior insights from the 2016 mw 7 8 pedernales ecuador earthquake the heterogeneous seafloor topography of the nazca plate as it enters the ecuador subduction zone provides an opportunity to document the influence of seafloor roughness on slip behavior and megathrust rupture the 2016 m w 7 8 pedernales ecuador earthquake was followed by a rich and active postseismic sequence an internationally coordinated rapid response effort installed a temporary seismic network to densify coastal stations of the permanent ecuadorian national seismic network a combination of 82 onshore short and intermediate period and broadband seismic stations and six ocean bottom seismometers recorded the postseismic pedernales sequence for over a year after the mainshock a robust earthquake catalog combined with calibrated relocations for a subset of magnitude 4 earthquakes shows pronounced spatial and temporal clustering a range of slip behavior accommodates postseismic deformation including earthquakes slow slip events and earthquake swarms models of plate coupling and the consistency of earthquake clustering and slip behavior through multiple seismic cycles reveal a segmented subduction zone primarily controlled by subducted seafloor topography accreted terranes and inherited structure the 2016 pedernales mainshock triggered moderate to strong earthquakes 5 m 7 and earthquake swarms north of the mainshock rupture close to the epicenter of the 1906m w 8 8 earthquake and in the segment of the subduction zone that ruptured in 1958 in a m w 7 7 earthquake

the 16 april 2016 mw 7 8 ms 7 5 ecuador earthquake a quasi repeat of the 1942 ms 7 5 earthquake and partial re rupture of the 1906 ms 8 6 colombia ecuador earthquake the 2016 ecuador m w 7 8 earthquake ruptured the subduction zone boundary between the nazca and south american plates joint modeling of seismic and tsunami observations indicates an 120 km long rupture area beneath the coastline north of the 1998 m w 7 2 rupture the slip distribution reveals two discrete asperities near the hypocenter and around the equator their locations and the patchy pattern are consistent with the prior interseismic geodetic strain which showed highly locked patches also beneath the coastline aftershocks cluster along two streaks one aligned nearly parallel to the plate convergence direction up dip of the main slip patches and the other on a trench perpendicular lineation south of the 1958 rupture zone comparisons of seismic waveforms and magnitudes show that the 2016 event and 1942 earthquakes have similar surface wave magnitude m s 7 5 overlapping rupture areas and similar main pulses of moment rate the same area ruptured as the southernmost portion of the larger earthquake of 1906 m w 8 6 m s 8 6 the seismic behavior reflects persistent heterogeneous frictional properties of the colombia ecuador megathrust

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

rupture of a seismic gap in southeastern alaska the 1972 sitka earthquake ms 7 6 abstract the sitka alaska earthquake of july 30 1972 m s 7 6 is one of the largest strike slip events since 1963 this earthquake is thought to have ruptured the pacific north america plate boundary segment between the large strike slip events in 1949 and 1958 and the sitka earthquake was heralded as one of the first successful forecasts of an earthquake based on the seismic gap hypothesis another motivation to study this event is the availability of a strong ground motion recording 50 km from the epicenter which is near the middle of the 180 km long plate boundary segment the teleseismically located aftershocks occur only in the southern half of this segment we have analyzed rayleigh waves and p waves recorded by wwssn long period vertical instruments a total of 25 very long period rayleigh phases r2 r5 define a symmetric four lobed radiation pattern from which we can infer a nearly pure right lateral strike slip fault striking 340 n20 w and a bilateral rupture comparison of synthetic and observed rayleigh waves yields a seismic moment of 3 10 27 dyn cm m w 7 6 the p waves are characterized by a dominant complex pulse in the first 40 s and a succession of smaller pulses after that the source time functions are deconvolved from 32 p waves with good azimuthal distribution to obtain the moment depth extent and rupture history the mean moment of the source time functions is 5 0 2 4 10 27 dyn cm and the depth extent is 0 10 km tomographic inversion of the source time functions produces an image of the earthquake rupture process this procedure maps the moment release of the complex pulse into two high displacement regions i e asperities 1 the epicentral area to 40 km north and 2 between 60 and 90 km south of the epicenter the main asperity just north of the epicenter coincides with a quiescent zone of microaftershocks while the overall average seismic displacement is 6 m the displacement at the main asperity is 7 m the same value as the tectonic displacement accumulated since the previous earthquake in 1848 the fault averaged stress drop is 100 bars while the asperity stress drop is 130 bars tomographic imaging of the source time functions thus resolves several features of the rupture process notably the bilateral propagation and rupture initiation at the largest asperity this is in contrast to the large 1976 guatemala strike slip earthquake where the largest displacements occurred away from rupture initiation

earthquake source processes and subduction regime in the santa cruz islands region abstract the source process of two large earthquakes that occurred in the santa cruz islands subduction zone has been studied one with a surface wave magnitude m s 7 9 in 1966 and the other with m s 7 7 in 1980 the seismic moment of the 1980 event estimated from long period surface waves of global digital seismograph network gdsn and international deployment of accelerographs ida records is 5 6 10 27 dyn cm both of these events occurred at a shallow depth i e between 20 and 40 km with a similar thrust type focal mechanism with a strike 347 parallel to the local trench axis and they are located within 100 km in distance the 1966 event is a break of a single asperity which ruptured unilaterally to the north along the local trench strike and was truncated sharply at the northern boundary this rupture pattern and the aftershock area expansion to the north indicate that there was a distinct barrier on the south of the 1966 source area the major moment release of the 1980 event represents the rupture of this barrier however inversion of p waves with an assumption of a constant focal mechanism failed to constrain the source process thereafter in particular the deconvolved source time functions of the 1980 event do not show such a clear truncation as is observed in the 1966 source process indicating that some unresolved features followed the peak of the moment release nevertheless the 1 day aftershock area suggests that the rupture propagated to the north into the source area of the 1966 event we conclude that both earthquakes are subduction events between the pacific and indo australian plates the 1966 event is a break of a single asperity and the 1980 event is a break of the remnant asperity which acted as a barrier for the 1966 source rupture the subduction segmentation inferred from the intermediate depth seismicity seems to control the mechanical condition of the subduction interface at shallow depths where the two large events took place this interface created a barrier between the two source areas

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

the tsunami signature on a submerged promontory the case study of the atacames promontory ecuador shelf promontories exhibit very specific bathymetric features with regards to tsunamis because of their submerged cape morphology a potential tsunami generated seawards of the promontory will exhibit a specific mode of propagation and coastal impact to identify this peculiar tsunami signature the atacames promontory ecuador was chosen as a case study another example is the shelf of the nile delta egypt the area is tectonically very active hosts earthquakes among the most powerful recorded as well as areas of slope instabilities that have triggered significant submarine landslides in the past several cubic kilometres of volume both types of events are likely to be tsunamigenic to examine the tsunami behaviour at the coastal area of the promontory and at its vicinity we have considered two examples of tsunamigenic landslides of which scars were identified near the base of the continental slope we also took into consideration two earthquake scenarios that are likely to represent most classes of earthquakes possibly occurring in this area depending on their locations and subsequent tsunami directivity that is a sensitivity test investigation we took two distinct earthquake scenarios which are based on the 1942 and 1958 events that stroke the area then we computed their derived tsunamis and analysed their coastal impact we found that significant tsunamis can be generated by either landslides or earthquakes however the maxima of wave amplitude occur offshore but still above the underwater promontory the concave type shape of the bathymetric field often yields a refraction focusing area that is located on the shelf promontory and not at the coast area of the promontory the wave propagates first through the focusing area before striking the considered coast this area may be considered as a sheltered zone besides in the vicinity of the promontory not exactly concerned by the study the city of esmeraldas is relatively sheltered due to the presence of the underwater canyon at its termination and due to diverging waves

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

variable rupture mode of the subduction zone along the ecuador colombia coast three large earthquakes occurred within the rupture zone of the 1906 colombia ecuador earthquake m w 8 8 in 1942 m s 7 9 1958 ms 7 8 and 1979 m s 7 7 we compared the size and mechanism of these earthquakes by using long period surface waves tsunami data and macroseismic data the 1979 event is a thrust event with a seismic moment of 2 9 10 28 dyne cm and represents subduction of the nazca plate beneath south america the rupture length and direction are 230 km and n40 e respectively examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction the seismic moment estimated from the tsunami data and the size of the rupture zone is 2 10 29 dyne cm the 1942 and 1958 events are much smaller about 1 5 to 1 10 of the 1979 event in the seismic moment than the 1979 event we conclude that the sum of the seismic moments of the 1942 1958 and 1979 events is only formula of that of the 1906 event despite the fact that the sequence of the 1942 1958 and 1979 events ruptured approximately the same segment as the 1906 event this difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between the weak zone normally behaves aseismically but slips abruptly only when it is driven by failure of the asperities a small earthquake represents failure of one asperity and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small a great earthquake represents failure of more than one asperity and consequently involves much larger width and slip

interpretation of earthquake epicenter and cmt centroid locations in terms of rupture length and direction abstract a comparison is made between hypocenter and centroid estimates of shallow earthquakes to investigate whether the difference between these two quantities contains useful information on fault rupture length and direction an initial comparison of international seismological centre isc and harvard centroid moment tensor cmt catalog locations suggests that for earthquakes below mw 6 5 the difference in location is dominated by location errors whilst larger earthquakes appear to show the effect of increasing spatial rupture however for this data set combined location errors greater than 25 km are observed for a majority of earthquakes imposing a limit on interpretation we use these constraints to investigate this approach using a consistent earth model in the re analysis of eight previously well studied events new hypocenter estimates based on teleseismic p wave arrivals from the isc bulletin and a 3 d velocity model of the mantle s p12 wm13 are compared with new centroid locations obtained using the same 3 d model and waveform data from international deployment of accelerometers ida global digital seismic network gdsn and re calibrated high gain long period hglp stations the distance between our new hypocenter and centroid locations is shown to provide reliable information on both the rupture length and direction the rupture lengths and azimuths generally agree with the most recent previous results from other methods and provide an absolute estimate of the location of the rupture

the rupture process of the 1976 mindanao earthquake the large mindanao earthquake mw 8 1 of august 16 1976 presents a complex rupture history the epicenter of this earthquake is located at the southern end of the 160 80 km2 aftershock area and the thrust mechanism with a shallow ne dipping plane indicates the subduction of the north celebes sea beneath mindanao we have characterized both temporally and spatially the rupture process of this event by deconvolving the source time functions from long period p wave seismograms at 20 azimuthally well distributed stations the seismic moment is released in a jagged fashion in two main pulses the observable directivity associated with these two pulses of moment release defines three segments on the fault 1 from 0 to 54 km n nw of the epicenter with of the moment release and an apparent rupture velocity of 2 0 km s 2 from 54 to 72 km n nw of the epicenter with low to no resolvable moment release and an apparent rupture velocity of 0 8 km s and 3 from 72 to 157 km n nw of the epicenter with of the moment release and a rupture velocity of 3 3 km s although the overall moment release is comparable in the first and second pulses the second pulse has a substantially higher rupture velocity and a higher level of short period radiation the sharp truncation of the second pulse generates the largest amplitudes in the p wave seismograms and is interpreted as the abrupt termination of the rupture front against mindanao island 160 km n nw of the epicenter an additional third pulse of moment release after the dominant truncation is identified at stations to the nw and se this additional moment release is located on a separate fault to the west which is probably strike slip in nature and related to a large strike slip aftershock along the coast of mindanao the jagged multiple event moment release of the mindanao earthquake is in sharp contrast to the smooth rupture of the 1979 colombia subduction zone earthquake mw 8 2 which resulted from the rupture of a single large asperity 60 km although these two earthquakes are both underthrusting events they occur in very different tectonic settings the mindanao earthquake occurred at a relatively young subduction zone in a region with rapidly evolving plate boundaries whereas the colombia earthquake occurred at a well established plate boundary

historical 1942 ecuador and 1942 peru subduction earthquakes and earthquake cycles along colombia ecuador and peru subduction segments two large shallow earthquakes occurred in 1942 along the south american subduction zone inclose proximity to subducting oceanic ridges the 14 may event occurred near the subducting carnegie ridge off the coast of ecuador and the 24 august event occurred off the coast of southwestern peru near the southern flank of the subducting nazca ridge source parameters for these for these two historic events have been determined using long periodp waveforms p wave first motions intensities and local tsunami data we have analyzed thep waves for these two earthquakes to constrain the focal mechanism depth source complexity and seismic moment modeling of thep waveform for both events yields a range of acceptable focal mechanisms and depths all of which are consistent with underthrusting of the nazca plate beneath the south american plate the source time function for the 1942 ecuador event has one simple pulse of moment release with a duration of 22 suconds suggesting that most of the moment release occurred near the epicenter the seismic moment determined from thep waves is 6 8 1020n m corresponding ot a moment magnitude of 7 8 7 9 the reported location of the maximum intensities ix for this event is south of the main shock epicenter the relocated aftershcks are in an area that is approximately 200 km by 90 km elongated parallel to the trench with the majority of aftershocks north of the epicenter in contrast the 1942 peru event has a much longer duration and higher degree of complexity than the ecuador earthquake suggesting a heterogeneous rupture seismic moment is released in three distinct pulses over approximately 74 seconds the largest moment release occurs 32 seconds after rupture initiation the seismic moment as determined from thep waves for the 1942 peru event is 10 25 1020n m corresponding to a moment magnitude of 7 9 8 2 aftershock locations reported by the iss occur over a broad area surrounding the main shock the reported locations of the maximum intensities ix are concentrated south of the epicenter suggesting that at least part of the rupture was to the south we have also examined great historic earthquakes along the colombia ecuador and peru segments of the south american subduction zone we find that the size and rupture length of the underthrusting earthquakes vary between successive earthquake cycles this suggests that the segmentation of the plate boundary as defined by earthquakes this century is not constant

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

fault size and depth extent of the ecuador earthquake m w 7 8 of 16 april 2016 from teleseismic and tsunami data the april 2016 ecuador mw 7 8 earthquake was the first megathrust tsunamigenic earthquake along the ecuador colombia subduction zone since 1979 mw 8 2 with 200 deaths from tsunami while there was no tsunami damage from the 2016 earthquake small tsunamis were recorded at deep ocean assessment and reporting of tsunami and tide gauges here we designed various fault models with and without shallow slip area and compared the computed teleseismic and tsunami waveforms with the observations while teleseismic inversions were indifferent about inclusion or exclusion of the shallow slip tsunami waveforms strongly favored the slip model without shallow slip our final slip model has a depth range of 15 44 km and its western shallowest limit is located at the distance of 60 km from the trench maximum and average slips were 2 5 and 0 7 m respectively the large slip area was 80 km along strike 60 km along dip in the depth range of 15 35 km

directivity analysis of the deep bolivian earthquake of june 9 1994 the june 9 1994 deep bolivian earthquake m w 8 3 d 636 km occurred on a nearly horizontal rupture plane with an approximate area of 2000 km 2 the rupture plane is constrained by directivity analysis of the p wave displacement pulses recorded at local regional and teleseismic distances the fact that there are local recordings of the displacement provides a strong constraint on the vertical extent of faulting which is less than 10 km the moment release had at least four distinct episodes or subevents the best overall explanation for the subevents is rupture which initiates on the western margin of the fault plane propagates to the east and then continues bilaterally along a 350 azimuth with most of the moment release occurring to the north the apparent rupture velocity between subevents is very low approximately 1 2 km s

a new gps velocity field for the pacific plate part 1 constraints on plate motion intraplate deformation and the viscosity of pacific basin asthenosphere

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

rupture process of an extended earthquake sequence teleseismic analysis of the chilean earthquake of march 3 1985 broadband displacement and velocity records of p waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the chilean earthquake of march 3 1985 ms 7 8 and seven large mb 5 6 aftershocks besides the usual parameters of depth moment and focal mechanism the analysis provides estimates of radiated energy associated stresses and source dimension for seven of the eight modeled earthquakes to insure that the parameters are describing the same physical aspect of the rupture process the parameters for each shock are computed from the time window in which most of the seismic energy is radiated the hypocenters of an additional 149 small foreshocks and aftershocks of 4 5 mb 5 6 are computed with the method of joint hypocenter determination the spatial and temporal variation of source parameters and earthquake locations are used to infer a description of the rupture process before during and after the main shock the main shock and modeled aftershocks occurred as thrust faulting on the interface between the nazca and south american plates a cluster of foreshocks in the 10 days preceding the main shock also involved thrust faulting on the plate interface the main shock itself was a complex rupture consisting of three events the first two events denoted as ms1 and ms2 released minor amounts of energy and they occurred on the periphery of the small zone defined by the foreshocks the major release of energy occurred with the third event denoted by ms which nucleated downdip of ms1 and ms2 within the time window of major energy release rupture extended approximately 90 km to the south from the point at which ms nucleated the size of the early aftershock zone which far exceeds our inferred dimensions for the major shock and the strong frequency dependence of scalar moment imply that substantial slow slip occurred on the plate interface that was not associated with major energy release the dip of the seismically active interface increases landward from about 15 at 20 km depth to about 35 at 40 km depth where the seismogenic interface reaches its maximum observed depth the vast majority of small and moderate aftershocks occurred in the shallower part of the interface as did the foreshocks ms1 and ms2 it appears however that the asperities that control the rupture of the largest earthquakes are the asperities on the deeper interface ms and the largest 1985 aftershock that of april 9 ms 7 2 occurred on the deeper interface the chilean earthquake of july 9 1971 ms 7 5 which occurred just north of the 1985 earthquake also involved main shock rupture on the deeper interface and was followed by aftershocks on the shallower interface asperities on the deeper interface appear on average to be stronger larger and more uniform in size than asperities on the shallow interface a greater average strength for deeper asperities is suggested by the observation that stress drops and apparent stresses of the main shock and the after shock of april 9 ms 7 2 are higher than those of the large shallow aftershocks and is consistent with arguments that the maximum friction on a fault zone should be near the base of the seismogenic zone one deep interface aftershock with low stress drop and apparent stress may have been situated below the point of maximum friction on the interface the inferred larger and more uniform sizes of the deeper asperities are suggested by the higher proportion of large to small shocks on the deeper interface the downdip change in the asperity size distribution may reflect increased friction on the plate interace or the coalescence of small asperities into large asperities with increased subduction the radiated energies of the main shock and large aftershocks that are computed directly from the broad bandwidth data are smaller than those predicted by standard empirical formulas by factors ranging from 4 to 20

recurrent slow slip events as a barrier to the northward rupture propagation of the 2016 pedernales earthquake central ecuador the northern ecuador segment of the nazca south america subduction zone shows spatially heterogeneous interseismic coupling two highly coupled zones 0 4 s 0 35 n and 0 8 n 4 0 n are separated by a low coupled area hereafter referred to as the punta galera mompiche zone pgmz large interplate earthquakes repeatedly occurred within the coupled zones in 1958 mw 7 7 and 1979 mw 8 1 for the northern patch and in 1942 mw 7 8 and 2016 mw 7 8 for the southern patch while the whole segment is thought to have rupture during the 1906 mw 8 4 8 8 great earthquake we find that during the last decade the pgmz has experienced regular and frequent seismic swarms for the best documented sequence december 2013 january 2014 a joint seismological and geodetic analysis reveals a six week long slow slip event sse associated with a seismic swarm during this period the microseismicity is organized into families of similar earthquakes spatially and temporally correlated with the evolution of the aseismic slip the moment release 3 4 1018 nm mw 6 3 over a 60 40 km area is considerably larger than the moment released by earthquakes 5 8 1015 nm mw 4 4 during the same time period in 2007 2008 a similar seismic aseismic episode occurred with higher magnitudes both for the seismic and aseismic processes cross correlation analyses of the seismic waveforms over a 15 years long period further suggest a 2 year repeat time for seismic swarms which also implies that sses recurrently affect this area such sses contribute to release the accumulated stress likely explaining why the 2016 pedernales earthquake did not propagate northward into the pgmz

order and diversity in the modes of circum pacific earthquake recurrence recurrence characteristics of great circum pacific earthquakes and determinations of spatial distribution of seismic moment release are surveyed in order to delineate their general features and relate earthquake slip distribution to models of recurrent rupture as noted by others the pattern of moment release is typically very irregular with strong concentrations in a few isolated regions of a much larger aftershock zone despite this complexity rupture nucleation is notably systematic with mainshock epicenter showing a strong tendency to locate in or immediately adjacent to identified regions of high moment release this generalization suggests that earthquake recurrence is more likely to be controlled by maximum rather than average fault slip well documented case histories from twelve plate boundary regions demonstrate that seismic strain release tends to be temporally well ordered while source dimensions slip and cumulative moment release vary considerably from cycle to cycle on none of the segments studied do earthquakes consistently recur in nearly identical events instead individual great earthquakes differ significantly from cycle to cycle or rerupture takes place in a sequence of two or more smaller events despite these differences the duration of the seismic cycle is approximately uniform furthermore when strain release occurs in a sequence of large earthquakes these events take place towards the end of the cycle and occur with increasing rupture length and magnitude these ordered and irregular features of earthquake recurrence argue for the existence of corresponding elements on plate boundary faults the ordered characteristics are identified with zones of concentrated moment release that slip comparable amounts in each cycle and have high shear strength the irregular features are associated with intervening weaker regions that move in response to the stress concentration of dynamic rupture and slip by differing amounts in each event although these mechanistic associations are indirect and tentative the features of recurrent behavior documented here have implications for long term earthquake hazard assessment that are not dependent on the models proposed to explain them chief among these are the cycle to cycle differences among gap filling events and the absence of shocks that fill major slip deficient regions early in the seismic cycle

high resolution 3 d seismic survey over a coal mine reserve area in the u s a case study a high resolution three dimensional 3 d seismic survey was conducted in advance of coal mine development in the illinois basin in may 1989 to better define a geologic structure with the potential to adversely affect longwall mining conditions the 3 d seismic data indicate that an abrupt change in seam elevation or roll encountered near the northern property line trends south into the reserve area and then turns southeast a personal computer based workstation was used to integrate borehole and seismic data for modeling in which 3 d block diagrams of the calculated seam elevations were generated the block diagrams show a steep slope on the west flank of the roll that gradually decreases as the roll turns to the southeast the survey also reveals a geologic structure beneath the roll at an estimated depth of 46 62 m horizontal time slice sections of this feature suggest the presence of a paleochannel that meanders on a similar course as the roll which apparently was connected to a larger paleochannel system a conoco high frequency vibroseis unit was successfully used as the seismic source to generate the high frequencies necessary to detect and resolve the thin coal beds

seismic rupture associated with subduction of the cocos ridge the april 3 1983 costa rica earthquake mw 7 4 ms 7 3 occurred where the aseismic cocos ridge has been partially subducting beneath the caribbean plate the epicenter is at the eastern edge of the 70 110 km initial aftershock area which later shows considerable expansion p wave directivity analysis indicates that the rupture front propagated westward 63 km from the epicenter to where the major moment release was truncated the source time history of the 1941 event ms 7 5 which occurred in the same epicentral area appears to be similar to the 1983 event but with more complexity and a slower initiation of moment release the low stress drop of the 1983 event 2 3 bar and low ratio of seismic slip to tectonic slip 0 15 for the 1983 event suggest that the coupling between the descending slab and the overlying plate is weak yet a recurrence time for large events mag 7 0 in this zone of about 40 years is implied by the 1904 1941 and 1983 events suggesting that the cocos ridge causes increased partial coupling compared with that in the adjacent subduction zone the slow source rupture process may reflect the nature of the contact area between the costa rica arc and the subducting plate in the vicinity of the bouyant cocos ridge the normal faulting event of july 1 1979 mb 5 3 is consistent with present day uplift of the burica peninsula which previous studies suggest is related to the subduction of the cocos ridge the burica and osa peninsulas may behave as detached blocks which influence the distribution of partial coupling reflected in the aftershock expansion pattern

great earthquakes and subduction along the peru trench subduction along the peru trench between 9 and 15 s involves both large interplate underthrusting earthquakes and intraplate normal fault earthquakes the four largest earthquakes along the peru trench are from north to south the 1970 m 7 9 intraplate normal fault earthquake and the interplate underthrusting earthquakes in 1966 m 8 0 1940 m 8 and 1974 m 8 0 we have studied the rupture process of these earthquakes and can locate spatial concentrations of moment release through directivity analysis of source time functions deconvolved from long period p wave seismograms the 1966 earthquake has a source duration of 45 s with most of the moment release concentrated near the epicenter two intraplate normal fault events occurred in 1963 m 6 7 and 7 0 at the down dip edge of the 1966 dominant asperity the 1940 earthquake is an underthrusting event with a simple source time function of 30 s duration that represents the rupture of a single asperity near the epicenter the 1974 earthquake has a source duration of 45 50s and two pulses of moment release this earthquake has a bilateral rupture with the first pulse of moment release located northwest of the epicenter and the second pulse of moment release located southeast of the epicenter both pulses of moment release occur on the northern half of the aftershock area the 1970 earthquake is one of the largest intraplate normal fault earthquakes to occur in a subduction zone and has a moment release comparable with many large underthrusting events the aftershocks for the 1970 earthquake form two distinct clusters the smaller cluster near the epicenter has focal mechanisms characterized by down dip tension but the second aftershock cluster located 80 km southeast of the epicenter has focal mechanisms characterized by down dip compression the p waves for the main shock can be modeled as two sources with different focal mechanisms and depths similar to the two clusters of aftershocks the first event has a down dip tensional focal mechanism and is followed 40 s later by a distinct second event located 80 km southeast of the epicenter with a down dip compressional focal mechanism and a somewhat shallower depth than the first event the observable directivity indicates that the second source is located at the second cluster of aftershocks that have down dip compressional focal mechanisms the occurrence of both down dip tensional and compressional focal mechanisms may be explained by extreme unbending stresses associated with the anomalous slab geometry the unusually large size of the 1970 earthquake may also be related to the subduction of the mendana fracture zone the historic earthquake record along the peru trench indicates that the previous event in 1746 was much larger than any of the three underthrusting earthquakes this century the 1746 earthquake may have ruptured the entire segment in a multiple asperity earthquake thus the mode of rupture along the peru coast has changed between successive earthquake cycles

late quaternary geomorphologic evolution of submarine canyons as a marker of active deformation on convergent margins the example of the south colombian margin abstract the morphology of patia and mira canyons on the south colombian convergent margin reflects an interplay between tectonic deformation sea level variation and canyon evolution and provides new insight into the age and location of margin deformation over the last 150 ka multibeam bathymetry seismic and sedimentary data reveal that tectonically active structural highs control canyon incision and the canyon s course the canyons developed across the margin in five major stages first the upper slope was incised by headward and downward erosion during the pleistocene infilling a structurally bounded slope basin the basin periodically spilled over and breached the accretionary prism at 150 ka leading to the development of isolated sediment lobes in the trench the prism was efficiently breached leading to a well developed trench channel levee system at 53 67 ka today the system shows limited activity antecedent streams convex up axial incision profiles and increasing height width ratio indicate an active uplift of the structural highs since at least 150 ka and support localized shortening through the margin accommodated by out of sequence structures thrusts and folds an 80 m high scarp where the canyon crosses a fault on the middle slope further supports active uplift related to a major thrust previous seismostratigraphic studies of the margin have demonstrated that active uplift occurred during the early pliocene here we demonstrate that uplift continued throughout the late pleistocene comparisons with canyons on other convergent margins reveal that features relating to margin deformation and canyon age tortuous path convex up profiles abandoned canyon paths overincision abrupt canyon turns are generally restricted to accretionary margins because of their complex morphology accretionary margins appear more favorable for the occurrence of such features than margins undergoing tectonic erosion with more simple morphology

source mechanisms of colombia aftershocks using digital surface wave data love and rayleigh wave signals recorded at stations of the global digital seismograph network were used to retrieve focal mechanism information for moderate magnitude mb 5 0 aftershocks that followed the large m s 7 7 colombia earthquake of 12 december 1979 source mechanisms compatible with the observed love rayleigh spectral amplitude ratios were identified following a comparison against theoretical values calculated for a suite of source models p wave first motions observed at worldwide stations were then used to remove ambiguities in the sense of slip and strike orientation for most of the events examined the focal depths of the events were fixed at values determined from depth phase arrival times in the surface wave comparison a reference earthquake with known focal mechanism and depth was used to calibrate the procedure and to minimize the path and size effects aftershocks whose epicenters lie within the asperity region from which most of the moment release originated during the large colombia earthquake denote thrust faulting similar to that of the main shock consistent with occurrence along the interplate zone the few near trench events in the vicinity of the asperity may have resulted from secondary deformation away from the major plane of rupture rather than from a propagation of interplate rupture seaward to the trench axis these near trench aftershocks which are seaward of the region of maximum energy release do not provide strong evidence for seismogenic failure of the plate interface at least one of the events is a normal faulting earthquake that occurred either above the interplate boundary or in the subducting nazca plate source mechanisms computed for aftershocks located northeast of the asperity but within the length of the rupture reported for the main shock are also consistent with interplate slip the aftershock activity observed north of this distance is associated with a separate and perhaps offset segment of the nazca south america plate boundary

seismicity associated with the great colombia ecuador earthquakes of 1942 1958 and 1979 implications for barrier models of earthquake rupture abstract we have relocated earthquakes along the colombia ecuador coast with the method of joint hypocenter determination in order to examine the nature of fault heterogeneities that controlled northward propagation of plate boundary rupture from the source region of the earthquake of 14 may 1942 to the source region of the 19 january 1958 earthquake and eventually to the source region of the earthquake of 12 december 1979 the entire region of the 1942 1958 and 1979 shocks had previously ruptured in the single great earthquake of 31 january 1906 the relocated hypocenters lie on the same plane to within the approximately 20 km uncertainty of the focal depths also the main shocks nucleated at nearly the same distance from the colombia trench these observations suggest that the heterogeneities between the 1942 and 1958 ruptures and between the 1958 and 1979 ruptures do not correspond to a major distortion of the downgoing slab but rather to either minor distortions of the slab or to regions of high friction or low available strain energy on a continuous fault surface in particular the heterogeneity between the 1958 and 1979 rupture zones seems to have been a high strength barrier with dimensions much smaller than the dimensions of either of the rupture zones the 1942 and 1958 earthquakes had source dimensions no larger than the 1979 main shock but they had stronger aftershock sequences than the 1979 earthquake this observation suggests that the arrest of earthquake rupture in 1979 left the plate boundary segment that had ruptured in 1906 in a state of lower stress than it had been following the 1942 and 1958 earthquakes long term seismicity in the decades preceding the 1979 earthquake occurred mostly outside or on the boundaries of the rupture area defined by the distribution of 1979 aftershocks the intense aftershock activity that followed the 1958 main shock within tens of kilometers of the eventual 1979 hypocenter may correspond to a long term precursory seismic swarm for the 1979 earthquake

geodetic teleseismic and strong motion constraints on slip from recent southern peru subduction zone earthquakes we use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 november 1996 m w 7 7 and 23 june 2001 m w 8 5 southern peru subduction zone earthquakes as well as two large aftershocks following the 2001 earthquake on 26 june and 7 july 2001 we use all available data in our inversions gps interferometric synthetic aperture radar insar from the ers 1 ers 2 jers and radarsat 1 satellites and seismic data from teleseismic and strong motion stations our two dimensional slip models derived from only teleseismic body waves from south american subduction zone earthquakes with m w 7 5 do not reliably predict available geodetic data in particular we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic teleseismic and two strong motion stations or geodetic insar and gps data the differences might be related to postseismic deformation or more likely the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties the earthquakes studied here follow the pattern of earthquake directivity along the coast of western south america north of 5 s earthquakes rupture to the north south of about 12 s directivity is southerly and in between earthquakes are bilateral the predicted deformation at the arequipa gps station from the seismic only slip model for the 7 july 2001 aftershock is not consistent with significant preseismic motion

are rupture zone limits of great subduction earthquakes controlled by upper plate structures evidence from multichannel seismic reflection data acquired across the northern ecuador southwest colombia margin 1 subduction of the nazca plate beneath the ecuador colombia margin has produced four megathrust earthquakes during the last century the 500 km long rupture zone of the 1906 mw 8 8 event was partially reactivated by three thrust events in 1942 mw 7 8 1958 mw 7 7 and 1979 mw 8 2 whose rupture zones abut one another multichannel seismic reflection and bathymetric data acquired during the sisteur cruise show evidence that the margin wedge is segmented by transverse crustal faults that potentially correlate with the limits of the earthquake coseismic slip zones the paleogene neogene jama quininde and esmeraldas crustal faults define a 200 km long margin crustal block that coincides with the 1942 earthquake rupture zone subduction of the buoyant carnegie ridge is inferred to partially lock the plate interface along central ecuador however coseismic slip during the 1942 and 1906 earthquakes may have terminated against the subducted northern flank of the ridge we report on a newly identified manglares crustal fault that cuts transversally through the margin wedge and correlates with the limit between the 1958 and 1979 rupture zones during the earthquake cycle the fault is associated with high stress concentration on the plate interface an outer basement high which bounds the margin seaward of the 1958 rupture zone may act as a deformable buttress to seaward propagation of coseismic slip along a megathrust splay fault coseismic uplift of the basement high is interpreted as the cause for the 1958 tsunami we propose a model of weak transverse faults which reduce coupling between adjacent margin segments together with a splay fault and an asperity along the plate interface as controlling the seismogenic rupture of the 1958 earthquake

strain budget of the ecuador colombia subduction zone a stochastic view the 2016 pedernales earthquake m w 7 8 ruptured a portion of the colombia ecuador subduction interface where several large historical earthquakes have been documented since the great 1906 earthquake m 8 6 considering all significant ruptures that occurred in the region it has been suggested that the cumulative moment generated co seismically along this part of the subduction over the last century exceeds the moment deficit accumulated inter seismically since 1906 such an excess challenges simple models with earthquakes resetting the elastic strain accumulated inter seismically in locked asperities these inferences are however associated with large uncertainties that are generally unknown the impact of spatial smoothing constraints on co seismic and inter seismic models also prevents any robust assessment of the strain budget we propose a bayesian kinematic slip model of the 2016 pedernales earthquake using the most comprehensive dataset to date including insar and gps offsets tsunami waveforms and kinematic records from high rate gps and strong motions in addition we use inter seismic geodetic velocities to produce a probabilistic inter seismic coupling model of the subduction interface our stochastic co seismic and inter seismic solutions include the ensemble of all plausible models consistent with our prior information and that fit the observations within uncertainties the analysis of these model ensembles indicates that an excess of co seismic moment during the 1906 2016 period is likely in central ecuador only if we assume that 1942 and 2016 earthquakes are colocated if this assumption is relaxed we show that this conclusion no longer holds given uncertainties in co and inter seismic processes the comparison of 1942 and 2016 teleseismic records reveals large uncertainties in the location of the 1942 event hampering our ability to draw strong conclusions on the unbalanced moment budget in the region our results also show a heterogeneous coupling of the subduction interface that coincides with two slip asperities in our co seismic model for the 2016 pedernales earthquake and with the location of historical ruptures in 1958 1979 and 1998 the spatial variability in coupling and complexity in earthquake history suggest strong heterogeneities in frictional properties of the subduction megathrust

thermal regime from bottom simulating reflectors along the north ecuador south colombia margin relation to margin segmentation and great subduction earthquakes 1 the north ecuador south colombia nesc margin has three transverse morphotectonic segments the manglares tumaco and patia segments each with different tectonic and structural patterns following the 1906 subduction earthquake the nesc margin has been the site of three megathrust events in 1942 1958 and 1979 for which the rupture zones abut one another we first investigated variations in heat flow derived from bottom simulating reflectors bsr observed along multichannel seismic lines sampling the three morphotectonic segments strong along strike variations of the bsr derived heat flow just landward of the deformation front suggest that each morphotectonic segment has a specific thermal regime finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling we then examined the relationship between seismogenesis and thermal structure along the plate boundary the updip limits of the 1942 and 1979 seismogenic zones estimated from the aftershock area and rupture zone reach the trench where the temperature at the top of the subducting plate appears to be 50 60 c between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100 120 c we propose that on the nesc margin the updip limit of the seismogenic zone is primarily controlled by low temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate

hypocenter depths of large interplate earthquakes and their relation to seismic coupling we examine locations of hypocenters of large interplate earthquakes mv 7 5 at subduction zones relative to their rupture areas to obtain a relation between the hypocentral depth and the seismic coupling coefficient which is the ratio of the long term slip rate estimated from cumulative seismic moment of large earthquakes to the relative plate motion we find 1 that the hypocentral depth is close to the bottom of the depth extent of the rupture area when the seismic coupling coefficient is nearly equal to 1 0 and 2 that the hypocentral depth relative to the depth extent of the rupture area shows a large scatter from shallow to deep when the seismic coupling coefficient is smaller than about 0 5 to interpret these observations we conduct a numerical simulation of seismic cycles of interplate earthquakes where the frictional stress on the plate boundary is assumed to obey a laboratory derived rate and statedependent friction law the observed result 1 is reproduced in the simulation when the critical fault length which is the size of the fault where the slip nucleation process takes place is much shorter than the seismogenic zone of the plate boundary in this case the plate boundary is strongly locked during an interseismic period and accordingly the calculated seismic coupling coefficient is close to 1 0 seismic slip starts near the bottom of the seismogenic zone because the maximum shear stress concentration is generated near the bottom of the seismogenic zone due to deeper steady plate motion on the other hand when the critical fault length is large appreciable aseismic sliding occurs in the seismogenic zone and therefore the calculated seismic coupling coefficient becomes significantly smaller than 1 0 the hypocentral depths of simulated large earthquakes tend to be shallow for large critical fault lengths heterogeneous frictional properties on the plate boundary may produce non uniform aseismic sliding during an interseismic period in this case the seismic coupling is small and seismic slip starts in various portions of the seismogenic zone this can explain the observed result 2 2 2003 elsevier science b v all rights reserved

three dimensional velocity structure of the outer fore arc of the colombia ecuador subduction zone and implications for the 1958 megathrust earthquake rupture zone in 2005 an onshore offshore 3 d refraction and wide angle reflection seismic experiment was conducted along the convergent margin at the border between colombia and ecuador over the rupture zone of the 1958 mw 7 6 subduction earthquake a well defined vp velocity model of the plate boundary and upper and lower plates was constructed down to 25 km depth using first arrival traveltimes inversion the model reveals a several kilometers thick low velocity zone in the upper plate located immediately above the interplate contact this low velocity zone might be related to alteration and fracturing of the mafic and ultramafic rocks which composed the upper plate in this area by fluids released by the lower plate with possible contributions from sediment underplating near the toe of the margin the model shows a low velocity gradient in the outer wedge which is interpreted as highly faulted and fractured rocks this low velocity low gradient region appears to limit the oceanward extension of the rupture zones of the 1958 and 1979 earthquakes possibly because coseismic deformation and uplift of the outer margin wedge dissipates most of the seismic energy

global survey of aftershock area expansion patterns we developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock the definition is based upon the amount of energy released by aftershocks the spatial distribution of the energy release is first determined and is contoured the 1 day aftershock area is defined by a contour line corresponding to the energy release level of 10 15 6 ergs 100 km 2 day the 10 day 100 day and 1 y aftershock areas are similarly defined by contour lines corresponding to 10 14 8 10 14 0 and 10 13 5 ergs 100 km 2 day respectively we also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day using this method we study the aftershock area expansion patterns of 44 large m s 7 5 and five moderate shallow earthquakes which occurred from 1963 to 1980 each aftershock sequence is examined at four different times i e 1 day 10 days 100 days and 1 y after the main event we define the aftershock area expansion ratios and e by s 100 s 1 and l 100 l 1 respectively here s t and l t are the area and the length of the aftershock area respectively at time t our study suggests that a distinct regional variation of aftershock area expansion patterns is present it is strongly correlated with the tectonic environment in general the subduction zones of the mariana type have large expansion ratios and those of the chilean type have small expansion ratios some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios these results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots called the asperities and weak zones surrounding the asperities the rupture immediately after the main shock mostly involves asperities after the main rupture is completed the stress change caused by the main shock gradually propagates outward into the surrounding weak zones this stress propagation manifests itself as expansion of aftershock activity in this simple picture if the fault zone is represented by relatively large asperities separated by small weak zones chilean type then little expansion of aftershock activity would be expected on the other hand if relatively small asperities are sparsely distributed mariana type significant expansion occurs the actual distribution of asperities is likely to be more complex than the two cases described above however we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area

rupture process of the february 4 1965 rat islands earthquake the great rat islands underthrusting earthquake mw 8 7 of february 4 1965 represents subduction of the pacific plate beneath the north american plate along a 600 km segment of the western end of the aleutian islands body wave inversion techniques are used to determine the spatial and temporal heterogeneities associated with the rat islands earthquake we have deconvolved world wide standard seismograph network long period teleseismic p wave seismograms to obtain source time functions directivity associated with the three major pulses of moment release in the source time functions indicates a total source duration of 160 s unilateral rupture in the direction 300 fault length of 420 km and average rupture velocity of 2 5 km s the three pulses of moment release are located along the fault and these regions of high moment release are interpreted as asperities the first asperity extends from the epicenter to 100 km to the wnw this is the largest asperity and corresponds to a smooth pulse of moment release in the source time function with a duration of 50 s the second pulse of moment release is very jagged is less coherent between stations and is centered 200 km wnw of the epicenter the third pulse of moment release extends from 360 to 420 km wnw of the epicenter although the aftershock area is 600 km in length we can not resolve any moment release from the p waves beyond 420 km wnw of the epicenter the rat islands event was closely followed by a large tensional outer rise event on march 30 1965 ms 7 5 which is located oceanward of the largest moment release associated with the rat islands mainshock rupture detailed analysis of the p waves for this large outer rise event confine the depth extent to the upper 30 5 km of the crust the spatial and temporal association between the february 4 mainshock and the march 30 tensional outer rise event suggests the tensional event may have been triggered by the large displacement near the mainshock epicenter the overriding plate along the western aleutian subduction zone is laterally segmented into a series of rigid tectonic blocks separated by fault controlled canyons and extensional basins geist et al 1988 we suggest that the central undeformed parts of the blocks have the strongest coupling with the down going plate and hence are the sites of the largest moment release during an underthrusting earthquake the three asperities determined from the p waves correspond to the rat buldir and near tectonic blocks respectively hence the p wave seismic moment release of the rat islands earthquake is controlled by the lateral segmentation of the overriding plate

rupture process of the 2016 mw 7 8 ecuador earthquake from joint inversion of insar data and teleseismic p waveforms abstract the 2016 ecuador earthquake ruptured the ecuador colombia subduction interface where several historic megathrust earthquakes had occurred in order to determine a detailed rupture model interferometric synthetic aperture radar insar images and teleseismic data sets were objectively weighted by using a modified akaika s bayesian information criterion abic method to jointly invert for the rupture process of the earthquake in modeling the rupture process a constrained waveform length method unlike the traditional subjective selected waveform length method was used since the lengths of inverted waveforms were strictly constrained by the rupture velocity and rise time the slip duration time the optimal rupture velocity and rise time of the earthquake were estimated from grid search which were determined to be 2 0 km s and 20 s respectively the inverted model shows that the event is dominated by thrust movement and the released moment is 5 75 1020 nm mw 7 77 the slip distribution extends southward along the ecuador coast line in an elongated stripe at a depth between 10 and 25 km the slip model is composed of two asperities and slipped over 4 m the source time function is approximate 80 s that separated into two segments corresponding to the two asperities the small magnitude of the slip occurred in the updip section of the fault plane resulted in small tsunami waves that were verified by observations near the coast we suggest a possible situation that the rupture zone of the 2016 earthquake is likely not overlapped with that of the 1942 earthquake

asperity distribution and earthquake occurrence in the southern kurile islands arc the seismicity in the southern kurile islands arc is characterized by a complex overlapping of aftershock zones of a few great and many large earthquakes ms 7 0 the spatial relationships of these aftershock zones can be explained in terms of a simple pattern of fault plane heterogeneity the four largest earthquakes in this region are from north to south the 1963 kurile islands mw 8 5 the 1958 etorofu mw 8 3 the 1969 kurile islands mw 8 2 and the 1973 nemuro oki mw 7 8 events detailed body wave studies indicate that the moment release associated with each event is concentrated in a small portion of the aftershock area with scale lengths 100 km these regions of high moment release are the largest asperities the areas that surround the large asperities slip in two modes 1 coseismically during the great events and 2 as distinct large ms 7 0 earthquakes both before and after the great events the second mode involves either rupture of relatively weak regions which results in low stress drop events or rupture of smaller asperities the earthquakes produced by failure of small asperities tend to repeatedly rupture the same regions and they have impulsive source time functions indicating rupture of highly stressed regions of the fault surface by analysis of all ms 7 0 events since 1946 in this region we find a segmentation of the southern kurile islands thrust zone into strongly coupled regions with two scale lengths dominant and secondary asperities and weakly coupled regions the surrounding areas generating the low stress drop events the largest earthquakes and the smaller asperity earthquakes occur at the down dip portion of the lithospheric interface while the low stress drop events occur much closer to the trench axis this implies a difference in the degree of mechanical coupling between the subducting and overriding plates with the deeper portions having greater strength than the shallower parts

stopping phases in seismograms and the spatiotemporal extent of earthquakes on the basis of long period wwssn and some broadband seismograms from grafenberg we investigate the following earthquakes view this table p wave seismograms or true ground displacements show clearly the directivity effect of rupture propagation and the multiple event nature of these earthquakes fault plane solutions of individual source shocks and their relative localization by the master event technique yield fixpoints of rupture history the most striking feature is a strong stopping phase which is interpreted kinematically by abrupt termination of rupture expansion at the end of the fault we use the stopping phase to determine total source extent in space and time as well as the mean rupture velocity the results of this first stage of investigation are subsequently used for modeling the rupture according to the dislocation theory of shear faulting wave propagation through the earth s mantle is treated by ray theory this forward modeling approach yields seismic moment source dimensions mean dislocation and stress drop source complexities are related to unbroken fault gaps bending of the fault plane acceleration of rupture propagation in asperities and most impressive in its radiation effect to the sudden termination of rupture in front of a barrier source complexities are also discussed with respect to tectonic implications

shallow seismogenic zone detected from an offshore onshore temporary seismic network in the esmeraldas area northern ecuador for a given site many factors control the seismic risk earthquake magnitude hypocentral distance rupture mechanism site effects and site vulnerability are among the most important this article deals with one of these factors the depth of the seismogenic zone in the northern ecuadorian subduction system beneath a highly vulnerable site the city of esmeraldas and its industrial complex the ecuadorian oil refinery and shipping terminal to address this problem we analyzed data from a three weeks passive seismological experiment conducted in the spring of 1998 using 13 ocean bottom seismometers and 10 portable land stations a preliminary interpretation of wide angle data obtained in the fall of 2000 in the manta area 100 km south of the study area unambiguously indicates the presence of a velocity inversion in the ecuadorian margin velocity structure this velocity inversion is characterized by a shadow zone of 1 s on the record sections and is interpreted as the result of a velocity contrast between the upper plate structure and the sedimentary and basaltic layer ii of the subducted oceanic nazca plate one dimensional velocity models are deduced from these wide angle data and are used for earthquake location in the esmeraldas area this highly improved the hypocentral parameter determinations the updip limit of the seismogenic zone is found at a depth of 12 km 35 km eastward of the trench and the depth of the seismogenic zone below the esmeraldas city is found at 20 km this shallow depth of the seismogenic zone dramatically increases the seismic hazard of the area

recent crustal deformation and the earthquake cycle along the ecuador colombia subduction zone recent results from global positioning system gps measurements show deformation along the coast of ecuador and colombia that can be linked to the rupture zone of the earthquake in 1979 a 3d elastic boundary element model is used to simulate crustal deformation observed by gps campaigns in 1991 1994 1996 and 1998 deformation in ecuador can be explained best by 50 apparent locking on the subduction interface although there have not been any historic large earthquakes mw 7 south of the 1906 earthquake rupture zone 50 apparent elastic locking is necessary to model the deformation observed there in colombia only 30 apparent elastic locking is occurring along the subduction interface in the 1979 earthquake rupture zone mw 8 2 and no elastic locking is necessary to explain the crustal deformation observed at two gps sites north of there there is no evidence from seismicity or plate geometry that plate coupling on the subduction zone is reduced in colombia however simple viscoelastic models suggest that the apparent reduction in elastic locking can be explained entirely by the response of a viscous upper mantle to the 1979 earthquake these results suggest that elastic strain accumulation is occurring evenly throughout the study area but postseismic relaxation masks the true total strain rate

structure of the ecuadorian forearc from the joint inversion of receiver functions and ambient noise surface waves the ecuadorian forearc is a complex region of accreted terranes with a history of largemegathrust earthquakes most recently amw7 8 megathrust earthquake ruptured the plateboundary offshore of pedernales ecuador on 16 april 2016 following this event an inter national collaboration arranged by the instituto geofisico at the escuela polit ecnica nacionalmobilized a rapid deployment of 65 seismic instruments along the ecuadorian forearc wecombine this new seismic data set with 14 permanent stations from the ecuadorian nationalnetwork to better understand how variations in crustal structure relate to regional seismichazards along the margin here we present receiver function adaptive common conversionpoint stacks and a shear velocity model derived from the joint inversion of receiver functionsand surface wave dispersion data obtained through ambient noise cross correlations for theupper 50 km of the forearc beneath the forearc crust we observe an eastward dipping slowvelocity anomaly we interpret as subducting oceanic crust which shallows near the projectedcentre of the subducting carnegie ridge we also observe a strong shallow positive conversionin the ecuadorian forearc near the borbon basin indicating a major discontinuity at a depth of 7 km this conversion is not ubiquitous and may be the top of the accreted terranes we alsoobserve significant north south changes in shear wave velocity the velocity changes indicatevariations in the accreted terranes and may indicate an increased amount of hydration beneaththe manab i basin this change in structure also correlates geographically with the southernrupture limit of multiple high magnitude megathrust earthquakes the earthquake record alongthe ecuadorian trench shows that no event with amw 7 4 has ruptured south of 0 5 sinsouthern ecuador or northern peru our observations along with previous studies suggestthat variations in the forearc crustal structure and subducting oceanic crust may influance theoccurrence and spatial distribution of high magnitude seismicity in the region

circum pacific seismic potential 1989 1999 the seismic potential for 96 segments of simple plate boundaries around the circum pacific region is presented in terms of the conditional probability for the occurrence of either large or great interplate earthquakes during the next 5 10 and 20 years i e 1989 1994 1989 1999 and 1989 2009 this study represents the first probabilistic summary of seismic potential on this scale and involves the comparison of plate boundary segments that exhibit varying recurrence times magnitudes and tectonic regimes presenting these data in a probabilistic framework provides a basis for the uniform comparison of seismic hazard between these differing fault segments as well as accounting for individual variations in recurrence time along a specific fault segment and uncertainties in the determination of the average recurrence time

source spectra of great earthquakes teleseismic constraints on rupture process and strong motion short period body waves recorded at teleseismic distances from great earthquakes provide information about source rupture processes and strong motions first we examine mostly wwssn records of 19 earthquakes of moment magnitude m w of 6 5 to 9 5 four parameters are measured from the short period p wave train the maximum amplitude the period at maximum amplitude the time between the first arrival and when the maximum amplitude is attained and coda length an extension m b of the teleseismic magnitude m b is defined using the maximum amplitude of the entire short period p wave rather than the amplitude achieved in the first few p wave cycles a least squares fit to the data yields the following relationship between m b and m w m b 0 53 m w 2 70 for m w 6 5 to 9 5 the time from the first arrival until the maximum amplitude is achieved and the coda length are roughly proportional to m w but are further interpreted by a simple asperity model of the rupture process these data support that short period waves are on average generated preferentially in the same regions of the fault plane as long period waves with periods of 10 to 50 sec we analyze the spectra of short and intermediate period teleseismic gdsn records for seven earthquakes with m w s of 6 4 to 7 8 and hand digitized short period wwssn records of the 1971 san fernando earthquake significant differences exist between the spectra of different events due partly to variations in tectonic setting or seismic coupling using the digital data we also investigate the relationship between time domain amplitude and spectral amplitude for short period p waves from our empirical relation between spectral amplitude and time domain amplitude we estimate the spectral amplitudes implied by the m b data we compare our results to the 2 and gusev spectral models neither model can completely represent the data nevertheless we consider the 2 model a useful reference model for comparing different events the average source spectrum of six large events with m w 7 4 to 7 8 does not have the spectral structure suggested by gusev an application to strong motion modeling is presented in which a 1971 san fernando teleseismic short period record is summed up to simulate teleseismic records produced by five great earthquakes the summation procedure matches the moment of the event to be simulated and includes rupture propagation fault plane roughness and randomness the m b data provide an important constraint on the summation procedures thus constrained this summation procedure can be more confidently used with near field strong motion records as green s functions to predict strong motions from great earthquakes

distribution of discrete seismic asperities and aseismic slip along the ecuadorian megathrust abstract a dense gps network deployed in ecuador reveals a highly heterogeneous pattern of interseismic coupling confined in the first 35 km depth of the contact between the subducting oceanic nazca plate and the north andean sliver interseismic models indicate that the coupling is weak and very shallow 0 15 km in south ecuador and increases northward with maximum found in the rupture areas of large mw 7 0 megathrust earthquakes that occurred during the 20th century since the great 1906 mw 8 8 colombia ecuador earthquake may have involved the simultaneous rupture of three to six asperities only one or two asperities were reactivated during the large seismic sequence of 1942 mw 7 8 1958 mw 7 7 1979 mw 8 2 and 1998 mw 7 1 the axis of the carnegie ridge which is entering the subduction zone south of the equator coincides well with the location of a 50 km wide creeping corridor that may have acted as persistent barrier to large seismic ruptures south of this creeping region a highly locked asperity is found right below la plata island while this asperity may have the potential to generate an mw 7 0 7 5 earthquake and a local tsunami until now it is unknown to have produced any similar events that region is characterized by the presence of slow slip events that may contribute significantly to reduce the long term moment deficit accumulated there and postpone the failure of that asperity at the actual accumulation rate a characteristic recurrence time for events such as those in 1942 1958 and 1979 is 140 30 yr 90 20 yr 153 80 yr respectively for the great 1906 event we find a recurrence time of at least 575 100 yr making the great 1906 earthquake a rare super cycle event

rupture process of the march 3 1985 chilean earthquake the march 3 1985 central chile earthquake ms 7 8 ruptured a well studied seismic gap along the chilean subduction zone the epicenter of this event is located near the center of an approximately 300 km long region which ruptured in a great event in 1906 mw 8 2 the northern portion of the 1906 zone has since ruptured in 1971 ms 7 5 and 1973 ms 6 7 we have determined the rupture history of the 1985 central chile earthquake from the deconvolved source functions of body waves both p and pp the source functions show one major pulse of moment release the onset of which occurs about 16 seconds after an initial small pulse the azimuthal directivity in the p waves indicates that the rupture front propagated from the epicenter southward and that the moment release of the major pulse is concentrated in a region between the epicenter and approximately 75 km south of the epicenter we conclude that the region of high moment release is the dominant asperity and was loaded by slip in the relatively weaker northern region

ridge subduction and afterslip control aftershock distribution of the 2016 mw 7 8 ecuador earthquake we characterise the aftershock sequence following the 2016 mw 7 8 pedernales earthquake more than 10 000 events were detected and located with magnitudes up to 6 9 most of the aftershock seismicity results from interplate thrust faulting but we also observe a few normal and strike slip mechanisms seismicity extends for more than 300 km along strike and is constrained between the trench and the maximum depth of the coseismic rupture the most striking feature is the presence of three seismicity bands perpendicular to the trench which are also observed during the interseismic period additionally we observe a linear dependency between the temporal evolution of afterslip and aftershocks we also find a temporal semi logarithmic expansion of aftershock seismicity along strike and dip directions further indicating that their occurrence is modulated by afterslip lastly we observe that the spatial distribution of seismic and aseismic slip processes is correlated to the distribution of bathymetric anomalies associated with the northern flank of the carnegie ridge suggesting that slip in the area could be influenced by the relief of the subducting seafloor to explain our observations we propose a conceptual model in which the ecuadorian margin is subject to a bimodal slip mode with distributed seismic and aseismic slip mechanically controlled by the subduction of a rough oceanic relief our study sheds new light on the mechanics of subduction relevant for convergent margins with a complex and heterogeneous structure such as the ecuadorian margin

aftershock area expansion and mechanical heterogeneity of fault zone within subduction zones we investigate global variations in the pattern of aftershock area expansion associated with large subduction zone earthquakes the expansion of aftershock areas with time is relatively small in the subduction zones of alaska the aleutians mexico and parts of the kuriles and south america these subduction zones are interpreted to be characterized by moderate to strong interplate coupling in contrast the extent of aftershock expansion is greater for events within the subduction zones of northeast japan and western and south pacific where interplate coupling is inferred to be weak these results are interpreted in terms of an asperity model where a fault zone is represented by a distribution of strong spots asperities and weaker zones the immediate aftershock area is assumed to extend over an area occupied by asperities and the subsequent expansion to occur into the surrounding weaker zones if large asperities abut each other on a fault plane interplate coupling is strong and little expansion of aftershock area occurs smaller and more sparsely distributed asperities cause weak interplate coupling and significant expansion of aftershock area small and densely distributed asperities result in moderate interplate coupling and little aftershock expansion

the rupture process of the great 1979 colombia earthquake evidence for the asperity model we have determined the asperity distribution in the segment of the ecuador colombia subduction zone that was ruptured by the 1979 mw 8 2 and 1958 mw 7 7 earthquakes for the 1979 earthquake we are able to document directivity in the p wave source time functions and consequently have spatially located the moment release by combining results from both p wave and surface wave directivity we have defined three regions 1 from 0 to 56 km northeast of the epicenter with low moment release and a small seismic displacement 2 the asperity from 56 to 116 km northeast of the epicenter with most of the moment release and a displacement of 6 m and 3 a small displacement region from 116 to 180 240 km northeast of the epicenter thus the 1979 rupture zone is composed of an asperity 60 km in length bounded by two weak small displacement regions the displacement at the asperity is equal to the cumulative tectonic displacement between 1979 and 1906 the year of the previous great earthquake in this segment the 1958 earthquake is characterized by the rupture of a small asperity length scale approximately 25 km in the epicentral region the 1958 event continued to rupture past this small epicentral asperity and stopped near the epicenter of the following 1979 event this detailed study of the spatial variation in moment release offers strong support for the asperity model of large earthquake occurrence

depositional trends in siliciclastic deposits of the stone city transgressive systems tract middle eocene texas abstract strata exposed at stone city bluff texas contain shelf sediments deposited during progressive marine deepening from shallow water depths and then capped by a maximum flooding horizon they are part of the early bartonian np16 cook mountain transgressive systems tract exposed in the type section of the stone city member of the crockett formation this locality lies on the inner portion of a shelf transect about 175 km 110 mi shoreward of the late eocene shelf slope margin and probably never farther than 80 km 50 mi from the shoreline sedimentary structures in the sediments change upward reflecting a shift from tidal current dominated to storm dominated deposition in lower intervals tidal control is dominant the transition interval contains isolated storm sands as sheets with lenses 40 cm 15 in thick in mudstones with tidal bedding these storm beds contain teeth bone concentrates and some gravel size clasts at the bases of larger lenses in higher intervals storm deposition is dominant in all units mostly as thin distal layers of very fine sand or silt amalgamated storm deposits form larger units e g the moseley bed local hardground surfaces are developed where storm washing exposed concretionary layers or on condensed winnowed zones glauconite occurrence and siderite concretion formation are most common in the upper intervals storm deposits have dual sediment sources and contain 1 skeletal remains shells fish bone and glauconite pellets concentrated by in place winnowing or 2 fine quartzose sand washed in from shallower water settings alternation of amalgamated storm deposits and mudstone units with thin storm deposits indicate a cyclic record of storm activity

a new view for the geodynamics of ecuador implication in seismogenic source definition and seismic hazard assessment a new view of ecuador s complex geodynamics has been developed in the course of modeling seismic source zones for probabilistic seismic hazard analysis this study focuses on two aspects of the plates interaction at a continental scale a age related differences in rheology between farallon and nazca plates marked by the grijalva rifted margin and its inland projection as they subduct underneath central ecuador and b the rapidly changing convergence obliquity resulting from the convex shape of the south american northwestern continental margin both conditions satisfactorily explain several characteristics of the observed seismicity and of the interseismic coupling intermediate depth seismicity reveals a severe flexure in the farallon slab as it dips and contorts at depth originating the el puyo seismic cluster the two slabs position and geometry below continental ecuador also correlate with surface expressions observable in the local and regional geology and tectonics the interseismic coupling is weak and shallow south of the grijalva rifted margin and increases northward with a heterogeneous pattern locally associated to the carnegie ridge subduction high convergence obliquity is responsible for the north andean block northeastward movement along localized fault systems the cosanga and pallatanga fault segments of the north andean block south american boundary concentrate most of the seismic moment release in continental ecuador other inner block faults located along the western border of the inter andean depression also show a high rate of moderate size earthquake production finally a total of 19 seismic source zones were modeled in accordance with the proposed geodynamic and neotectonic scheme

subducted oceanic relief locks the shallow megathrust in central ecuador whether subducted oceanic reliefs such as seamounts promote seismic rupture or aseismic slip remains controversial here we use swath bathymetry pre stack depth migrated multichannel seismic reflection lines and wide angle seismic data collected across the central ecuador subduction segment to reveal a broad 55 km x 50 km 1 5 2 0 km high low height to width ratio multi peaked sediment bare shallow subducted oceanic relief owing to la plata island and the coastline being located respectively 35 km and 50 60 km from the trench gps measurements allow us to demonstrate that the subducted oceanic relief spatially correlates to a shallow 80 km x 55 km locked interplate asperity within a dominantly creeping subduction segment the oceanic relief geometrical anomaly together with its highly jagged topography the absence of a subduction channel and a stiff erosive oceanic margin are found to be long term geological characteristics associated with the shallow locking of the megathrust although the size and level of locking observed at the subducted relief scale could produce a mw 7 event no large earthquake are known to have happened for several centuries on the contrary frequent slow slip events sse have been recorded since 2010 within the locked patch and regular seismic swarms have occurred in this area during the last 40 years these transient processes together with the rough subducted oceanic topography suggest that interplate friction might actually be heterogeneous within the locked patch additionally we find that the subducted relief undergoes internal shearing and produces a permanent flexural bulge of the margin which uplifted la plata island

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

do trench sediments affect great earthquake occurrence in subduction zones seismic energy release is dominated by the underthrusting earthquakes in subduction zones and this energy release is further concentrated in a few subduction zones while some subduction zones are characterized by the occurrence of great earthquakes others are relatively aseismic this variation in maximum earthquake size between subduction zones is one of the most important features of global seismicity previous work has shown that the variation in maximum earthquake size is correlated with the variation in two other subduction zone properties age of the subducting lithosphere and convergence rate these two properties do not explain all the variance in maximum earthquake size i propose that a third subduction zone property trench sediments explains part of the remaining variance in maximum earthquake size subduction zones are divided into two groups 1 those with excess trench sediments and 2 those with horst and graben structure at the trench thirteen of the 19 largest subduction zone events including the three largest occur in zones with excess trench sediments about half the zones with excess trench sediments are characterized by great earthquake occurrence most of the other zones with excess trench sediments but without great earthquakes are predicted to have small earthquakes by the age rate correlation two notable exceptions are the oregon washington and middle america zones overall the presence of excess trench sediments appears to enhance great earthquake occurrence one speculative physical mechanism that connects trench sediments and earthquake size is that excess trench sediments are associated with the subduction of a coherent sedimentary layer which at elevated temperature and pressure forms a homogeneous and strong contact zone between the plates

use of the mantle magnitude m m for the reassessment of the moment of historical earthquakes the mantle magnitudemm is used on a dataset of more than 180 wavetrains from 44 large shallow historical earthquakes to reassess their moments which in many cases had been previously estimated only on the basis of the earthquake s rupture area we provide 27 new or revised values ofmo based on the spectral amplitudes of surface waves recorded at a number of stations principally uppsala and pasadena among them and most significantly we document a large low frequency component to the source of the 1923 kanto earthquake the low frequency seismic moment is 2 9 1028 dyn cm in accord with geodetic observations on the other hand we revise downwards the seismic moment of the 1906 ecuador event which did not exceed 6 1028 dyn cm

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

further evidence for the compound nature of slow earthquakes the prince edward island earthquake of april 28 1997 seismograms of the april 28 1997 prince edward island transform fault earthquake mw 6 8 show clear evidence for the superposition of two types of rupture a normal earthquake and a slow component which primarily radiated energy at low frequencies we combined low frequency spectral data with p waveform data to invert for a source time function that satisfied data from 0 001 to 2 5 hz the results show that the earthquake started with a slow event which began 15 s before the fast mainshock and was part of a slow earthquake which lasted over 30 s the smoothness of the initial event is inferred from the low amplitude of high frequency energy at regional stations during the initial portion of the p wave arrival directivity analysis shows that the two components of the rupture occurred on different faults the slow event occurred on the main transform and the fast event occurred on a parallel fault 40 km to the east a similar compound sequence involving both slow and fast components and rupture on multiple faults occurred on the romanche transform in 1994 these and other results for slow earthquakes suggest that many large events on oceanic transform faults are compound events

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

imaging rapid early afterslip of the 2016 pedernales earthquake ecuador abstract high rate hr gps time series following the 2016 mw 7 8 pedernales earthquake suggest significant postseismic deformation occurring in the early postseismic period i e first few hours after the earthquake that is not resolved with daily gps time series to understand the characteristics of early postseismic deformation and its relationship with the mainshock rupture area aftershocks and longer term postseismic deformation we estimate the spatio temporal distribution of early afterslip with hr gps time series that span 2 5 min to 72 hr after the earthquake and compare with afterslip models estimated with daily gps time series spanning a similar postseismic time period and up to 30 days after the earthquake inversion of the hr gps time series enables us to image the initiation of afterslip in the initial hours after the earthquake bringing us closer to the transition between the coseismic and postseismic phases the spatial signature of early afterslip in the region updip of the mainshock rupture area is consistent with longer term afterslip that occurs in the 30 day postseismic period indicating that afterslip initiated updip of and adjacent to peak coseismic slip asperities in two localised areas and subsequently continued to grow in amplitude with time in these specific areas a striking difference however is that inversion of the 72 hour hr gps time series suggests early afterslip within the mainshock rupture area but which may have been short lived finally using the first daily gps position as the origin of the postseismic displacement here at 12 hr after the earthquake biases the postseismic geodetic moment with 60 missing over the first 72 hr that corresponds to 10 over the first 30 days the results of our study demonstrate that imaging the spatio temporal evolution of afterslip using subdaily gps time series is important for evaluating postseismic slip budgets and provides additional insights into the postseismic slip behaviour of faults

two 1993 kamchatka earthquakes two earthquakes occurred in 1993 off southern kamchatka they have similar surface wave magnitudes focal mechanisms and depths but have distinctly different characteristics the november earthquake is a standard or impulsive m7 underthrusting event the june earthquake is a tsunamigenic or low stress drop event with several unusual characteristics including a large diffuse aftershock zone directivity and a long source time function the 1993 earthquakes ruptured a segment of the kamchatka arc which has not ruptured since 1904 the 1993 earthquakes seem to signal the midpoint in the southern kamchatka seismic cycle

earthquakes of the holocene geologic studies of earthquakes involve mapping of coseismic surface faulting and secondary deformation from historical events trenching and geomorphic analysis to define the timing and size of past earthquakes and investigations of fault zone structure and geometry in both unconsolidated sediments and bedrock this research is now being referred to as paleoseismology seismic geology and earthquake geology since the mid 1970s it has led to some of the most exciting and important contributions to the understanding of earthquake behavior in space and time hanks 1985 allen 1986 the present report is the first of what is hoped will become a regularly contributed summary of the geologic aspects of the study of earthquakes

earthquake recurrence and risk assessment in circum pacific seismic gaps the development of the concept of seismic gaps regions of low earthquake activity where large events are expected has been one of the notable achievements of seismology and plate tectonics its application to long term earthquake hazard assessment continues to be an active field of seismological research here i have surveyed well documented case histories of repeated rupture of the same segment of circum pacific plate boundary and characterized their general features i find that variability in fault slip and spatial extent of great earthquakes rupturing the same plate boundary segment is typical rather than exceptional but sequences of major events fill identified seismic gaps with remarkable order earthquakes are concentrated late in the seismic cycle and occur with increasing size and magnitude furthermore earthquake rup ture starts near zones of concentrated moment release suggesting that high slip regions control the timing of recurrent events the absence of major earthquakes early in the seismic cycle indicates a more complex behaviour for lower slip regions which may explain the observed cycle to cycle diversity of gap filling sequences

seamount subduction at the north ecuadorian convergent margin effects on structures inter seismic coupling and seismogenesis at the north ecuadorian convergent margin 1 s 1 5 n the subduction of the rough nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust we used three selected pre stack depth migrated multi channel seismic reflection lines collected during the sisteur cruise to investigate the margin structure and decipher the impact of the subducted atacames seamounts on tectonic erosion interseismic coupling and seismogenesis in the region of the 1942 mw7 8 earthquake this dataset highlights a subducted 30 40 km 30 40 km double peak seamount that belongs to the atacames seamount chain and that is associated with a deep morphologic re entrant containing mass transport deposits the seamount subduction uplifted the margin basement by 1 6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount a process that is likely to weaken considerably the margin in the seamount wake the basement reverse fault system rotated counter clockwise this faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the bsr this superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion in addition to long term regional basal erosion the margin basement has thinned locally by an extra 0 8 1 km in response to the subduction of the atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe this pervasively and deeply fractured margin segment is associated with a seismically quiet and gps modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone we suggest that the deeply buried double peak atacames seamount triggered the 1942 earthquake ahead of its leading flank this result supports previous studies proposing that subducted seamounts provide unfavorable conditions for locking the updip segment of the plate boundary limiting the updip extent of seismogenic zones but may favor large subduction earthquakes at greater depths