the rupture history of the mw 8 0 jalisco mexico earthquake of 1995 october 9 summary finite fault broad band teleseismic p waveform inversion was applied to the large mw 8 0 jalisco mexico earthquake of 1995 october 9 the earthquake hypocentre was located at shallow depths just near the boundary zone between two lithospheric plates rivera and cocos and was felt with a maximum intensity of 9 mm on the pacific coast it was the first earthquake of magnitude greater than 6 to occur in this region since the two great jalisco earthquakes ms 8 0 and 7 6 of 1932 for inversion we used vertical records from 14 digital stations situated 30d to 90d from the epicentre we used the fixed rake of the thrust type focal mechanism given by the preliminary harvard cmt the low angle dipping fault plane was taken as a 180 90 km2 rectangle divided into 162 subfaults of 10 10 km2 each subfault had five intermediate point sources along strike and five intermediate point sources downdip the size of the fault plane was changed from an initial size of 110 60 km2 estimated by resco as an aftershock area to the final size of 180 90 km2 which included all significant displacements along the fault the hypocentre was embedded 40 km from the left edge of the 180 km long fault 40 km down dip from the top of the fault which was situated practically along the trench axis a boxcar source time function of width 2 0 s was used for each discrete rupture interval of each subfault the rupture velocity was taken to be 2 8 km s 1 which is approximately 80 per cent of the shear wave speed in the layer containing the hypocentre the following results on the rupture history were obtained 1 the rupture duration was about 55 s and slip occurred within an area of about 180 90 km2 along the middle american trench in the depth interval from 9 to 33 km 2 there were two main stages in the rupture history during the first 18 s two main asperities at a distance of about 30 km from the earthquake hypocentre were ruptured with maximum slip up to 610 cm at a depth of 12 15 km then during the next 37 s rupturing was observed to the north along the trench the slip distribution obtained shows that the faulting originating near the boundary between the rivera and cocos plates went mainly along the rivera north american plate boundary and is consistent with the subduction of the rivera plate beneath north america

the macroseismic field generated by the mw 8 0 jalisco mexico earthquake of 9 october 1995 abstract the mw 8 0 earthquake of 9 october 1995 occurred within the jalisco block that represents the northern part of the mexican subduction zone where the rivera plate subducts beneath the north america plate along the middle american trench the source rupture of the 1995 low angle thrust type event was complicated the studies of rupture history had shown that the slip occurred within an area of about 180 90 km 2 along the middle american trench at the depth interval from 9 to 33 km the rupture duration was estimated in interval from 55 to 62 sec at least three main asperities ruptured along the fault plane the earthquake was felt along the 600 km coast of the mexican states of colima jalisco and michoacan and in the continental part of mexico the macroseismic study presented in this article was carried out in march through july 1997 more than one year after the earthquake we had about 300 interviews with people who felt the earthquake in their houses located in 56 cities and towns of the states of colima jalisco and michoacan all our estimates of the earthquake intensity were referred to the intermediate type of masonry situated on the intermediate type of soils for this purpose corrections were introduced for type of soil and masonry the study of macroseismic effects related to the 1995 jalisco earthquake allows description of some properties of the macroseismic field generated by the earthquake 1 three zones of intensity 4 5 and 6 to 7 grades of mm modified mercalli scale were distinguished 2 the zone of maximum intensity of 6 to 7 mm was heterogeneous this heterogeneity was in accordance with the rupture asperities distribution 3 the study of intensity attenuation along the coast had demonstrated the asymmetry in intensity distribution according to the epicenter the maximum intensities were observed for the sites that were situated to the northwest of the epicenter 4 a good correlation was observed between the observed intensities and the values of gps displacements

a geodetic study of the 2003 january 22 tecoman colima mexico earthquake we use coseismic displacements and aftershock information from global positioning system gps measurements at 27 sites in western mexico and a 12 station local seismic network to determine the characteristics of the 2003 january 22 m w 7 2 subduction thrust earthquake near tecoman colima mexico estimates of the earthquake moment slip direction and best fitting slip distribution are derived by optimizing the fit to the gps displacements for a 3 d finite element mesh that simulates the study area the calculated moment release is 9 1 10 19 n m m w 7 2 with maximum slip of 2 m at a depth of 24 km and a maximum rupture depth of 35 40 km the inversion indicates that coseismic rupture extended downdip from depths of 9 to 40 km along a 80 km along strike region that is bounded by the edges of the manzanillo trough the optimal solution is robust with respect to plausible changes in the subduction interface geometry and differing subsets of the data a comparison of the cumulative post seismic slip that can be inferred separately from earthquake aftershocks and gps measurements within a year of the earthquake indicates that 95 per cent or more of the post seismic deformation was aseismic near term post seismic measurements indicate that slip propagated downdip to areas of the subduction interface beneath the coastline within days following the earthquake as also occurred after the nearby m w 8 0 colima jalisco subduction earthquake in 1995 the similar behaviours and locations of the 1995 2003 earthquake sequence to two earthquakes in june of 1932 suggests that thrust earthquakes along the subduction interface northwest of the manzanillo trough may trigger earthquakes in the vicinity of the manzanillo trough however our modelling of coulomb stress changes caused by the 1995 earthquake indicate that it induced only modest unclamping of the subduction interface in the vicinity of the tecoman rupture in addition gps measurements indicate that elastic shortening characterized areas onshore from the tecoman rupture from mid 1997 up until the time of the rupture consistent with progressively stronger clamping of the subduction interface during this period this precludes any obvious triggering relationship with the 1995 earthquake the apparent coincidence of the edge of both the 1932 and 1995 2003 rupture sequences with the edge of the manzanillo trough may indicate that the trough is a mechanical barrier to along strike rupture propagation this implies a limit to the area of potential slip and hence rupture magnitude during future large earthquakes in this region

local earthquake tomography of the jalisco mexico region abstract the states of jalisco colima and michoacan in western mexico overlie the boundary of the subducting rivera and cocos plates presenting an ideal target for seismological inquiry to better understand the resulting mantle flow and regional volcanism the different dips between the two subducting plates are thought to provide a mantle conduit that has contributed to the colima volcanic complex cvc but there is considerable debate on the depth of the rivera plate and width of the resulting conduit with data from the mapping the rivera subduction zone mars and colima deep seismic experiment codex networks two temporary broadband arrays deployed in the region between 2006 and 2008 we inverted for three dimensional p and s wave velocity as well as vp vs structure of the upper 70 km of the crust and mantle in the jalisco region using a newly developed automatic p and s wave picker we increased p picks by 74 and s picks by more than a factor of four compared to a database of manual picks for the 803 earthquakes used in the inversion additional relocated earthquakes extending to the trench are consistent with previous interpretations of the rivera and cocos plate interfaces areas of high vp vs above both subducting slabs suggest the presence of fluids resulting from dehydration of subducted material extensive crustal seismicity occurs near these anomalies a zone of high vp vs is also present under the cvc we also compare the results of different methods for obtaining vp vs a direct inversion for vp vs from s minus p times versus simply dividing the vp model by the vs model we find direct inversions of s minus p times to be more reliable

far field simulation of tsunami propagation in the pacific ocean impact on the marquesas islands french polynesia the islands in the marquesas archipelago are most exposed to far field tsunamis in french polynesia four recent earthquakes located at the pacific rim kurile 1994 chile 1995 mexico 1995 and peru 1996 earthquakes generated trans pacific tsunamis and caused contrasting inundations in several inhabited marquesian bays the aim of this study is to better understand the amplification phenomena observed in the marquesas islands and to improve the risk assessment we present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales the water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method these numerical results allow us to determine 1 which propagation azimuths are dangerous for the whole marquesas archipelago and 2 the behavior of each studied bay amplitude frequency in response to tsunami waves we observe that the seismogenic subduction zone along south america is likely to define one of the most dangerous tsunami generation areas for the marquesas archipelago owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern pacific ocean fracture zones seamount chains

finite element model predictions of static deformation from dislocation sources in a subduction zone sensitivities to homogeneous isotropic poisson solid and half space assumptions 1 dislocation models can simulate static deformation caused by slip along a fault these models usually take the form of a dislocation embedded in a homogeneous isotropic poisson solid half space hipshs however the widely accepted hipshs assumptions poorly approximate subduction zone systems of converging oceanic and continental crust this study uses three dimensional finite element models fems that allow for any combination including none of the hipshs assumptions to compute synthetic green s functions for displacement using the1995 mw 8 0 jalisco colima mexico subduction zone earthquake and associated measurements from a nearby gps array as an example fem generated synthetic green s functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface loading a forward hipshs model with dislocation distributions estimated from fems that sequentially relax the hipshs assumptions yields the sensitivity of predicted displacements to each of the hipshs assumptions for the subduction zone models tested and the specific field situation considered sensitivities to the individual poisson solid isotropy and homogeneity assumptions can be substantially greater than gps measurement uncertainties forward modeling quantifies stress coupling between the mw 8 0 earthquake and a nearby mw 6 3 earthquake that occurred 63 days later coulomb stress changes predicted from static hipshs models cannot account for the 63 day lag time between events alternatively an fem that includes a poroelastic oceanic crust which allows for postseismic pore fluid pressure recovery can account for the lag time the pore fluid pressure recovery rate puts an upper limit of 10 17 m2 on the bulk permeability of the oceanic crust

the october 9 1995 colima jalisco mexico earthquake mw8 an aftershock study and a comparison of this earthquake with those of 1932 data from portable seismographs and a permanent local network called resco are used to locate the aftershocks of the october 9 1995 colima jalisco earthquake mw 8 0 the maximum dimension of the aftershock area which is rectangular in shape is 170 km 70 km our study shows that the mainshock nucleated 24 km south of manzanillo near the foreshock of october 6 1995 mw 5 8 and propagated 130 km to the nw and 40 km to se the aftershock area lies offshore and is oriented parallel to the coast the observed subsidence of the coast is a consequence of this offshore rupture area the aftershocks reach unusually close to the trench within 20 km this may be due to lack of sediments with high pore pressure at shallow depth there are some similarities between this earthquake and the two great earthquakes of 1932 3 june ms 8 1 18 june ms 7 8 which occurred in this region in both cases the aftershocks were located offshore and the coastline subsided the sum of seismic moments and the rupture lengths of the 1932 events 1 8 1021 n m and 280 km respectively however were greater than the 1995 earthquake also a comparison of seismograms of 1932 and 1995 earthquakes show great differences it seems that the 1995 event is not a repeat of either june 3 or june 18 1932 earthquakes

geology of the northern colima and zacoalco grabens southwest mexico late cenozoic rifting in the mexican volcanic belt the south trending northern colima graben intersects two other grabens the northwest trending zacoalco graben and the east trending chapala graben to form a rift rift rift triple junction 50 km south southwest of guadalajara in southwest mexico the northern colima graben represents the northernmost extension of the 190 km long 20 to 65 km wide colima rift which overlies the projection of the subducting boundary of the rivera and cocos plates and represents a rift of probable pliocene pleistocene age of the east trending mexican volcanic belt mvb associated with the northernmost 90 km of the rift there are 4 6 m y old to holocene alkaline volcanic rocks rarely found in continental volcanic arc environments and which are more typically associated with either continental intraplate rifting or oceanic islands these alkaline lavas have erupted side by side with 10 m y old to holocene calc alkaline lavas that represent typical arc volcanism it is proposed that the grabens are associated with the initiation of a rifting of a portion of southwest mexico away from the mexican mainland similar to the rifting of baja california away from the mexican mainland the calc alkaline k ar dates are consistent with post mid miocene development of east trending mvb volcanism

present day kinematics of the rivera plate and implications for tectonics in southwestern mexico we model the present day motion of the rivera plate relative to the pacific north america and cocos plates and combine the results with the nuvel i model for cocos north america motion to examine present day deformation in southwestern mexico the pacific rivera data which include 25 three m y average spreading rates determined from original surface ship magnetic data and 22 azimuthal data along the rivera transform are systematically misfit by the nuvel i pacific north america and pacifie cocos euler vectors indicating that the rivera plate is kinematically distinct from north america and cocos an f test shows that the improvement in fit to the pacific rivera data from a model with a distinct rivera plate exceeds that expected solely from adding three model parameters the rivera north america euler vector derived from closure of the rivera pacific north america plate circuit predicts slower and more trenchnormal convergence along the acapulco trench than prior models in addition the model predicts convergence normal to the eastern tamayo fracture zone at a rate 60 slower than the right lateral strike slip predicted by prior models an observed systematic misfit of the pacific rivera euler vector to azimuths from the western rivera transform fault may have several causes there may be a time averaging problem between the 3 0 m y average rates and the shorter time average transform fault azimuths and earthquake slip vectors alternatively rivera transform trends may be biased by deformation within lithosphere adjacent to the transform valley or future detailed mapping of the transform may reveal the misfit to be an artifact of the presently available bathymetry along the entire pacific rivera rise spreading rates averaged over the past 0 7 m y are systematically faster than 3 0 m y average rates with the difference increasing southward along the rise the post 3 ma change in the rate gradient has caused a southward migration of the pacific rivera euler pole since 3 ma possibly in response to the 3 ma completion of a spreading reorganization that doubled the length of the rivera transform fault and halved the area of the rivera plate we hypothesize that deformation in southwestern mexico including opening along the colima rift is related to oblique subduction of the cocos plate along the northern middle america trench three unes of evidence support this hypothesis first the sense of oblique subduction predicted by nuvel i along the middle america trench is consistent with a model in which part of western mexico located southeast of the colima rift moves to the southeast relative to north america second field geologic data and landsat imagery suggest that in the past few million years the chapala oaxaco fault zone has accommodated several kilometers of sinistral motion and sinistral transtension has occurred along the trans mexican volcanic belt either or both of these fault zones could accommodate any southeastward coastal block motion that might result from oblique subduction third the observation that earthquake slip vectors from the northern middle america trench trend systematically counterclockwise from the predicted cocos north america convergence direction is also consistent with southeastward motion the discrepancy between the observed and predicted slip directions along the middle america trench suggests sinistral slip is 0 10 mm yr 1 if oblique subduction is driving southeastward transport of a coastal sliver the colima rift is a passive pull apart zone at the northwestern end of this sliver rather than an incipient spreading ridge that will replace the pacific rivera rise

morphotectonic zones along the coast of the pacific continental margin southern mexico geomorphic analysis employing topographic morphologic geologic and bathymetric maps and field studies show that the morphology of the southern coast of mexico can be linked to lateral variations in the geometry and tectonism of the subduction zone a reconnaissance study based on the regional morphological characteristics and correlation with seismotectonic segments regional tectonics and major bathymetric features allows identification of several morphotectonic zones along the coast of southern mexico 1 jalisco zone 2 colima zone 3 michoacan zone 4 guerrero zone 5 oaxaca zone and 6 tehuantepec zone a range of geomorphological evidence including marine terraces river terraces uplifted notches and elevated wave cut platforms indicates local and regional uplift along the coast of the jalisco michoacan guerrero and oaxaca zones coasts of the colima and tehuantepec zones show morphological evidence of subsidence

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

refined insight into 40ar 39ar progressive crushing technique from k cl ar correlations in fluid inclusions abstract hydrothermal fluid activity associated with geological processes can now be dated by 40ar 39ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry however methods of data analysis and interpretation for these high resolution measurements still need to be refined in this study we report further insights into using k cl ar diagrams as tools for interpreting ages of secondary and primary fluids from 40ar 39ar stepwise crushing experiments three paragenetic mineral pairs of muscovite and wolframites from a southern china tungsten deposit were investigated using the 40ar 39ar technique through laser incremental heating and progressive crushing of single minerals incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156 153 ma progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40ar however the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156 153 ma without excess 40ar the plateau age steps interpreted as ages of gases derived from primary fluid inclusions pfis yield well defined isochrons with ages ranging from 157 to 153 ma and initial 40ar 36ar values that are indistinguishable from the modern atmospheric value digitally created 2d and 3d diagrams of k cl ar correlations can easily reveal distribution trends and correlation planes from the crushing steps interpretations of these diagrams further reveal the ages of secondary fluid inclusions sfis 87 to 83 ma and primary fluid inclusions pfis 159 to 150 ma raw data from sfis degassed during the initial crushing steps form scatters on inverse isochron plots however 2d and 3d k cl ar diagrams yield sfi ages that agree with 40ar 39ar ages of k feldspar veins cutting the tungsten ore bodies

seismotectonic constraints on the convergence rate between the rivera and north american plates there are two significantly different types of models for the convergence rate between the rivera and north american plates the first type the high rate model bandy 1992 predicts convergence rates of approximately 5 0 cm yr near the southern end of the rivera north america subduction zone and between 2 0 and 3 0 cm yr at its northern end in contrast the second type the low rate model e g demets and stein 1990 predicts convergence rates of between 2 0 and 3 3 cm yr near the southern end of the rivera north america subduction zone and between 0 6 and 1 7 cm yr at its northern end seismotectonic relationships which relate seismic characteristics of subduction zones maximum magnitudes maximum seismic depths etc to plate tectonic parameters convergence rates age of the oceanic lithosphere etc provide a means of distinguishing between the two different models three such relationships suggest that the rivera north american and cocos north american convergence rates should be roughly equal across the rivera cocos plate boundary favoring the high rate model employing the high rate model one can evaluate the magnitude and distribution of the strike slip component of forearc motion vss produced by oblique convergence between the rivera and north american plates the analysis indicates both a progressive increase and clockwise reorientation of vss northwestward along the plate contact zone of the rivera north america subduction zone such a distribution in vss should produce a northwestward movement of and nw se oriented extension within the interior of the jalisco block consistent with previous proposals of jalisco block motions also such a distribution in vss should produce a slight clockwise rotation of the jalisco block in the vicinity of bahia de banderas consistent with paleomagnetic data

thermal models of the mexico subduction zone implications for the megathrust seismogenic zone 1 it has been proposed that the seismogenic zone of subduction thrust faults is primarily controlled by temperature or rock composition changes we have developed numerical models of the thermal structure of the mexico subduction zone to examine the factors that affect the temperature of the subduction thrust fault although the oceanic plates subducting beneath mexico are young the top of the oceanic plate at the trench is cool because of the lack of a thick cover of insulating sediments marine heat flow observations suggest that hydrothermal circulation may further cool the oceanic plate this results in a cool subduction thrust fault where the brittle part of the fault extends to depths of over 40 km at these depths even slight frictional heating may have significant effects on temperature along the thrust fault particularly for regions with a high convergence rate and shallow plate dip with the addition of a small amount of frictional heating the temperatures of the deep 30 40 km thrust fault are increased by over 200 c as the observed downdip limit of rupture in recent well constrained megathrust earthquakes is confined to depths above the intersection of the thrust fault and the continental moho a temperature of 350 c may control the downdip extent of the seismogenic zone thus in order to be consistent with the observed shallow rupture areas it is necessary to include a small amount of frictional heating corresponding to an average shear stress of 15 mpa

fault slip distribution of the 1995 colima jalisco mexico earthquake abstract broadband teleseismic p waves have been analyzed to recover the rupture history of the large m s 7 4 colima jalisco mexico shallow interplate thrust earthquake of 9 october 1995 ground displacement records in the period range of 1 60 sec are inverted using a linear finite fault waveform inversion procedure that allows a variable dislocation duration on a prescribed fault the method is applied using both a narrow fault that simulates a line source with a dislocation window of 50 sec and a wide fault with a possible rise time of up to 20 sec that additionally allows slip updip and downdip from the hypocenter the line source analysis provides a spatio temporal image of the slip distribution consisting of several large sources located northwest of the hypocenter and spanning a range of rupture velocities the two dimensional finite fault inversion allows slip over this rupture velocity range and indicates that the greatest coseismic displacement 3 4 m is located between 70 and 130 km from the hypocenter at depths shallower than about 15 km slip in this shallow region consists of two major sources one of which is delayed by about 10 sec relative to a coherent propagation of rupture along the plate interface these two slip sources account for about one third of the total p wave seismic moment of 8 3 10 27 dyne cm m w 7 9 and may have been responsible for the local tsunami observed along the coast following the earthquake

homogeneous vs heterogeneous subduction zone models coseismic and postseismic deformation a finite element model fem incorporating geologic properties characteristic of a subduction zone is compared with fems approximating homogeneous elastic half spaces hehs s to investigate the effect of heterogeneity on coseismic and postseismic deformation predictions for the 1995 colima jalisco m w 8 0 earthquake the fems are used to compute a coefficient matrix relating displacements at observation points due to unit dislocations of contact node pairs on the fault surface the green s function responses are used to solve the inverse problem of estimating dislocation distributions from coseismic gps displacements predictions from the fem with heterogeneous material properties loaded with either of the hehs dislocation distributions significantly overestimate coseismic displacements postseismic deformation predictions are also sensitive to the coseismic dislocation distribution which drives poroelastic and viscoelastic relaxation fem generated green s functions which allow for spatial variations in material properties are thus preferable to those that assume a simple hehs because the latter leads to dislocation distributions unsuitable for predicting the postseismic response

overview of recent coastal tectonic deformation in the mexican subduction zone holocene and pleistocene tectonic deformation of the coast in the mexico subudction margin is recorded by geomorphic and stratigraphic markers we document the spatial and temporal variability of active deformation on the coastal mexican subduction margin pleistocene uplift rates are estimated using wave cut platforms at ca 0 7 0 9 m ka on the jalisco block coast rivera north america tectonic plate boundary we examine reported measurements from marine notches and shoreline angle elevations in conjunction with their radiocarbon ages that indicate surface uplift rates increasing during the holocene up to ca 3 0 5 m ka in contrast steady rates of uplift ca 0 5 1 0 m ka in the pleistocene and holocene characterize the michoacan coastal sector south of el gordo graben and north of the orozco fracture zone ofz incorporated within the cocos north america plate boundary significantly higher rates of surface uplift ca 7 m ka across the ofz subduction may reflect the roughness of subducting plate absence of preserved marine terraces on the coastal sector across el gordo graben likely reflects slow uplift or coastal subsidence stratigraphic markers and their radiocarbon ages show late holocene ca last 6 ka bp coastal subsidence on the guerrero gap sector in agreement with a landscape barren of marine terraces and with archeological evidence of coastal subsidence temporal and spatial variability in recent deformation rates on the mexican pacific coast may be due to differences in tectonic regimes and to localized processes related to subduction such as crustal faults subduction erosion and underplating of subducted materials under the southern mexico continental margin

seismicity and state of stress in guerrero segment of the mexican subduction zone 1 we take advantage of a relatively dense network of seismic stations in the guerrero segment of the mexican subduction zone to study seismicity and state of stress in the region we combine our results with recent observations on the geometry of the subducted cocos plate imaged from receiver function rf analysis an ultraslow velocity layer mapped in the upper crust of the subducted slab and episodic slow slip events sses and nonvolcanic tremors nvts reported in the region to obtain a comprehensive view of the subduction process seismicity and focal mechanisms confirm subduction of the cocos plate below mexico at a shallow angle reaching a depth of 25 km at a distance of 65 km from the trench the plate begins to unbend at this distance and becomes horizontal at a distance of 120 km at a depth of 40 km some of the highlights of the inslab seismicity are as follows 1 a cluster of earthquakes in the depth range of 25 45 km immediately downdip from the strongly coupled part of the plate interface revealing both downdip compressional and extensional events this seismicity extends from 80 to 105 km from the trench and may be attributed to the unbending of the slab 2 the slab devoid of seismicity in the distance range of 105 160 km 3 sparse inslab seismicity revealing downdip extension in the distance range of 160 240 km the nvts are also confined to this distance range the episodic sses occur on the horizontal segment in the distance range of 105 240 km where an ultraslow velocity layer in the upper crust of the slab has been mapped from waveform modeling of converted sp phases thus in the distance range of 105 160 km sses occur but nvts and inslab earthquakes are absent this suggests that metamorphic dehydration reactions in the subducting oceanic crust and upper mantle begin at a distance of 160 km giving rise to both the inslab earthquakes and nvts no inslab earthquake occurs beyond 240 km the receiver function images and p wave tomography suggest that the slab begins a steep plunge at a distance of 310 km reaching a depth of 500 km around 340 km from the trench the negative buoyancy of such a slab should give rise to large extensional stress in the slab yet inslab seismicity is remarkably low which may be explained by a slab that is not continuous up to a depth of 500 km but is broken at a shallower depth the resulting slab window may permit subslab material to flow through the gap this may provide an explanation for the recent rift related basalts found near mexico city the fore arc upper plate seismicity which during the period of study 1995 2007 consisted of a moderate earthquake mw5 8 near the coast h 12 km its numerous aftershocks and two shallow events farther inland demonstrates a trench normal extension in the upper plate near this convergent margin a state of stress that may be explained by tectonic erosion and or seaward retreat of the trench seismicity location of the mantle wedge and rupture areas of mexican earthquakes suggest that the downdip limit of rupture during large great earthquakes in guerrero may be 105 15 km shallow dipping interplate thrust earthquakes are not the only type of events that affect the seismic hazard in the region the magnitudes of inslab downdip compressional and extensional earthquakes that occur within 20 km inland from the coast in the depth range of 25 45 km may reach 6 5 and 7 5 respectively in addition we now identify normal faulting earthquakes in the upper plate these sources need to be taken into account in the hazard estimation

rapid postseismic transients in subduction zones from continuous gps 1 continuous gps time series from three of four recently measured large subduction earthquakes document triggered rapid postseismic fault creep representing an additional moment release upward of 25 over the weeks following their main shocks data from two mw 8 0 and mw 8 4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep time series for another mw 7 7 event show 30 postseismic energy release but here we cannot differentiate between afterslip and triggered deeper creep a fourth mw 8 1 event which occurred in the broad chilean seismogenic zone shows no postseismic deformation despite coseismic offsets in excess of 1 m for the three events which are followed by postseismic deformation stress transferred to the inferred centroids at 34 60 and 36 km depths by their respective main shock asperities increased reverse shear stress by 0 5 0 8 and 0 2 bar with a comparatively small decrease in normal stress 0 01 bar constraining the coulomb stress increase required to force slip along the metastable plate interface deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins these events captured by some of the first permanent gps networks show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes index terms 7209 seismology earthquake dynamics and mechanics 3040 marine geology and geophysics plate tectonics 8150 8155 8157 8158 8150 tectonophysics plate boundary general 3040 7230 seismology seismicity and seismotectonics keywords subduction zone earthquake postseismic moment release

rupture length of the october 9 1995 colima jalisco earthquake mw8 estimated from tsunami data we analyze tsunami data of the great 1995 colima jalisco mexico earthquake recorded in cabo san lucas baja california sur to estimate its rupture length l to model the tsunami arrival time we assume a rectangular source area oriented parallel to the trench whose se limit is fixed at the point of rupture initiation the nw limit of the source area i e l is varied between 120 and 200 km the comparison between synthetic and observed data strongly suggests that l of the earthquake was 160 20 km this length agrees with those reported in various other studies of the earthquake it however disagrees with a previous study based on the same tsunami data which suggested that the rupture may have extended 250 km nw from the epicenter tanioka and ruff 1996 the cause of this discrepancy is most likely an error in the timing of the records used by tanioka and ruff 1996 we conclude that the earthquake only partially ruptured the rivera north america plate interface a 120 km long segment in the nw extreme of this interface which apparently ruptured in 1932 remains presently unbroken

holocene emerged notches and tectonic uplift along the jalisco coast southwest mexico this paper presents the preliminary results from a study of holocene emerged shorelines marine notches and their tectonic implications along the jalisco coast the pacific coast of jalisco sw mexico is an active tectonic margin this coast has been the site of two of the largest earthquakes to occur in mexico this century the 1932 mw 8 2 jalisco earthquake and the 1995 mw 8 0 colima earthquake measurement and preliminary radiocarbon dating of emergent paleoshorelines along the jalisco coast provide the first constraints upon the timing for tectonic uplift along this coastline uplifted holocene marine notches and wave cut platforms occur at elevations ranging from ca 1 to 4 5 m amsl in situ intertidal organisms dated with radiocarbon the first ever reported for the jalisco area provide preliminary results that record tectonic uplift during at least the past 1300 years bp at an average rate of about 3 mm year we propose a model in which coseismic subsidence produced by offshore earthquakes is rapidly recovered during the postseismic and interseismic periods the long term period is characterized by slow tectonic uplift of the jalisco coast we found no evidence of coastal interseismic and long term subsidence along the jalisco coast

channel incision in the rio atenguillo jalisco mexico defined by 36cl measurements of bedrock abstract the jalisco block of western mexico has undergone uplift in the tertiary in response to subduction tectonics the atenguillo river interior to the jalisco block has incised the bedrock units of the jalisco block including cretaceous ash flow tuff granite as well as younger volcanic lava flows to study incision rates knickpoint propagation and the uplift rate of the region samples from nine different points along the atenguillo channel were collected for 36 cl exposure age dating exposure ages along the length of the channel are high near the head of the basin where the river meanders in a broad plain ages are younger at the knickpoints and downstream where the river cuts deeply and forms a canyon incision rates measured at different points along the channel also correlate with channel slope and age low incision rates are measured in the oldest part of the channel near the head station b 2 5 mm year and just above the knickpoints station c 0 6 mm year and station g 1 4 mm year the incision rates are highest just below the knickpoints station f 2 4 mm year and farther downstream stations h and i 5 6 and 2 9 mm year respectively the high incision rates can be attributed to subduction related uplift of the jalisco block other features attributable to uplift are emergent paleoshorelines and uplifted marine sediments along the coast and relatively lower incision rates were measured north of the jalisco block

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

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

implications of the october 1995 colima jalisco mexico earthquakes on the rivera north america euler vector rivera north america euler vectors fall into three groups based on the predicted motion of the rivera plate relative to the north america plate along the middle america trench north of 18 5 n namely those that predict 1 a slow more easterly directed motion 2 a slow more northerly directed motion and 3 a faster more northerly directed motion the focal mechanism solution rupture area and seismic moment of the great m w 8 0 colima jalisco mexico earthquake of october 9 1995 and its foreshocks and aftershocks provide additional constraints on the rivera north america euler vector the slip direction n30 e of the main event clearly favors those euler poles which predict a more northerly direction of motion this direction lies within 5 of those predicted by these poles whereas it differs by between 9 and 18 from those poles which predict a more easterly motion the amount of slip which occurred during the main event suggests a minimum convergence rate of between 4 3 and 6 5 cm yr this favors euler vectors which predict higher convergence rates however a firm conclusion cannot be made due to the uncertainty in the recurrence time estimation a new rivera north america euler pole calculated incorporating the information provided by the 1995 events lies at 21 87 n 109 58 w it predicts a n30 3 e directed motion of the rivera plate relative to north america at the location of the main event a difference of only 0 3 from the slip direction of the main event

the geodetic signature of the m8 0 oct 9 1995 jalisco subduction earthquake the october 1995 mw 8 0 jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process an 11 station regional gps network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest directed extension with measured displacements reaching 1 meter unusually shallow and non uniform faulting is required to explain the displacements we determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km and that slip was likely distributed in two main patches the paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting

teleseismic body wave analysis of the 9 october 1995 mw 8 0 colima jalisco mexico earthquake and its largest foreshock and aftershock the source process of the october 9 1995 colima jalisco mexico earthquake mw 8 0 and its largest foreshock and aftershock were determined from teleseismic body waves using a least squares inversion scheme the three events are shallow dipping thrust fault earthquakes in agreement with the relative plate motions for rivera north america and cocos north america plate boundaries neither the foreshock nor the largest aftershock show significant differences in focal mechanism nor centroidal depth with respect to the average mechanism of the mainshock the rupture of the mainshock began near the foreshock hypocenter and propagated with a variable rupture velocity towards the nw the source time function for this event shows four distinct episodes of energy release about 50 of the moment was released at the northern end of the rupture between 90 and 110 km from the epicenter this rupture geometry is in agreement with crustal deformation observed inland using gps measurements however the scalar seismic moment of the main shock obtained in this study mo 1 84 1020 is smaller with respect to the lower frequency cmt results reported by harvard mo 1 15 1021

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

deformation of mexico from continuous gps from 1993 to 2008 1 we combine the velocities of 13 continuous global positioning system stations from mexico and 448 north american plate stations to better understand deformation and earthquake cycle effects in mexico velocities estimated at the mexican sites from high quality gps data collected since 2003 show no evidence for a previously reported eastward bias at sites in and near the yucatan peninsula the new velocities are compared to the predictions of two models one in which all motion in mexico is attributed to north american plate motion and the second of which attributes site motions to a combination of plate motion and the elastic effects of frictional coupling along the mexican subduction zone and faults in the gulf of california the second model fits the velocities within their estimated uncertainties mainland mexico thus moves with the north american plate to within 1 mm per year and undergoes elastic interseismic deformation far into its interior two stations inland from the guerrero and oaxaca segments of the mexican subduction zone have alternated between several year long periods of landward motion and several month long periods of trenchward motion frequently since 1993 consistent with previously described repeating transient slip events along the subduction interface the motions of two stations inland from the rivera plate subduction zone are dominated by the coseismic and postseismic effects of the m 8 0 9 october 1995 colima jalisco earthquake and m 7 5 22 january 2003 tecoman earthquake offshore from western mexico

late holocene vegetation change in the sierra madre oriental of central mexico abstract past vegetation and climate changes reconstructed from a sediment core from laguna atezca molango mexico provide new insights into the environmental and cultural histories of the sierra madre oriental during the last 1700 yr pollen microscopic charcoal sediment chemistry loss on ignition and magnetic susceptibility indicate that three phases of human occupation deforestation and erosion ca a d 280 890 ca a d 1030 1420 and ca a d 1680 present alternate with two phases of abandonment ca a d 890 1030 and ca a d 1420 1680 forest composition of the two abandonment phases differed with cloud forest taxa liquidambar ostrya carpinus ulmus etc dominating the pollen record during the first phase and quercus and pinus pollen characterizing phase two these differences may reflect a climate change in which the second phase was drier than the first alternatively the increase in pinus and quercus may have been caused by a human induced decline in soil fertility the laguna atezca record also differs from several other mesoamerican paleoenvironmental records in that it shows no evidence of drought at the end of the classic period ca a d 900

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

imaging coseismic rupture in far field by slip patches summary since the end of the 1970s teleseismic waves are used routinely to infer the first order characteristics of the event location depth duration focal mechanism but finding the second order kinematic parameters spatial distribution of slip rupture velocity and more basically the discrimination between the fault plane and the other nodal plane of distant events remains a difficult task classically these events are studied by two different methods either they are seen as a succession of subevents each of which is considered as a point source or like in near field as extended sources where the kinematic parameters are retrieved on a grid the first approach is not physically satisfactory and can lead to erroneous interpretations of the

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

shape of the subducted rivera and cocos plates in southern mexico seismic and tectonic implications the geometry of the subducted rivera and cocos plates beneath the north american plate in southern mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes the hypocenters of the teleseisms were relocated and the focal depths of 21 events were constrained using a body wave inversion scheme the suduction in southern mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the cocos plate beneath the caribbean plate to the east and of the rivera plate beneath north america to the west the dip of the interplate contact geometry is constant to a depth of 30 km and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate on the basis of the seismicity the focal mechanisms and the geometry of the downgoing slab southern mexico may be segmented into four regions 1 the jalisco region to the west where the rivera plate subducts at a steep angle that resembles the geometry of the cocos plate beneath the caribbean plate in central america 2 the michoacan region where the dip angle of the cocos plate decreases gradually toward the southeast 3 the guerrero oaxaca region bounded approximately by the onshore projection of the orozco and o gorman fracture zones where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km and 4 the southern oaxaca and chiapas region in southeastern mexico where the dip of the subduction gradually increases to a steeper subduction in central america these drastic changes in dip do not appear to take place on tear faults suggesting that smooth contortions accommodate these changes in geometry the inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the trans mexican volcanic belt suggesting it is directly related to the subduction thus the observed nonparallelism with the middle american trench is apparently due to the changing geometry of the rivera and cocos plates beneath the north american plate in southern mexico and not to zones of weakness in the crust of the north american plate as some authors have suggested

regional and stress drop effects on aftershock productivity of large megathrust earthquakes the total number of aftershocks increases with mainshock magnitude resulting in an overall well defined relationship observed variations from this trend prompt questions regarding influences of regional environment and individual mainshock rupture characteristics we investigate how aftershock productivity varies regionally and with mainshock source parameters for large mw 7 0 circum pacific megathrust earthquakes within the past 25 years drawing on extant finite fault rupture models aftershock productivity is found to be higher for subduction zones of the western circum pacific than for subduction zones in the eastern circum pacific this appears to be a manifestation of differences in faulting susceptibility between island arcs and continental arcs surprisingly events with relatively large static stress drop tend to produce fewer aftershocks than comparable magnitude events with lower stress drop however for events with similar co seismic rupture area aftershock productivity increases with stress drop and radiated energy indicating a significant impact of source rupture process on productivity

shallow depth of seismogenic coupling in southern mexico implications for the maximum size of earthquakes in the subduction zone abstract studies of locally recorded microearthquakes and the centroidal depths of the largest earthquakes analyzed using teleseismic data show that the maximum depth of thrust faulting along the mexican subduction zone is anomalously shallow this observed maximum depth of about 25 5 km is about half of that observed in most subduction zones of the world a leveling line that crosses the rupture zone of the 19 september 1985 michoacan event was revisited after the earthquake and it shows anomalously low deformation during the earthquake the comparison between the observed coseismic uplift and dislocation models of the seismogenic interplate contact that extend to depths ranging from 20 to 40 km shows that the maximum depth at which seismic slip took place is about 20 km this unusually shallow and narrow zone of seismogenic coupling apparently results in the occurrence of thrust events along the mexican subduction zone that are smaller than would be expected for a trench where a relatively young slab subducts at a rapid rate of relative motion a comparison with the chilean subduction zone shows that the plate interface in mexico is half that in chile not only in the down dip extent of the seismogenic zone of plate contact but also in the distance of the trench from the coast and in the thickness of the upper continental plate it appears that the narrow plate contact produced by this particular plate geometry in mexico is the controlling variable defining the size of the largest characteristic earthquakes in the mexican subduction zone

strong interseismic coupling fault afterslip and viscoelastic flow before and after the oct 9 1995 colima jalisco earthquake continuous gps measurements from colima mexico 1 continuous gps measurements from colima mexico during 4 93 6 01 bracketing the oct 9 1995 m 8 0 colima jalisco earthquake provide new constraints on rivera plate subduction mechanics modeling of margin normal strain accumulation before the earthquake suggests the rivera north america subduction interface was fully locked transient postseismic motion from 10 95 6 97 is well fit by a model that includes logarithmically decaying fault afterslip elastic strain from shallow fault relocking and possibly a minor viscoelastic response but is fit poorly by models that assume a dominant maxwell viscoelastic response of the lower crust and upper mantle independent of the assumed viscosities landward margin normal motion since mid 1997 is parallel to but 75 slower than the pre seismic velocity afterslip alone fails to account for this slowdown the viscoelastic response predicted by a fem correctly resolves the remaining velocity difference within the uncertainties both processes thus offset elastic strain accumulating from the relocked subduction interface

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

source area and rupture parameters of the 31 december 1881 mw 7 9 car nicobar earthquake estimated from tsunamis recorded in the bay of bengal 1 on the morning of 31 december 1881 a submarine earthquake beneath the andaman islands generated a tsunami with a maximum crest height of 0 8 m that was recorded by eight tide gauges surrounding the bay of bengal since the earthquake occurred 8 years before the construction of the world s first teleseismic recording seismometer little has been known about its rupture parameters or location waveform and amplitude modeling of the tsunami indicate that it was generated by a mw 7 9 0 1 rupture on the india andaman plate boundary resulting in 10 60 cm of uplift of the island of car nicobar the rupture consisted of two segments the northern 40 km long segment is separated from the southern 150 km long segment by a 100 km region corresponding to the westward projection of the west andaman spreading center the main rupture occurred between 8 5 n and 10 n with a total area of 150 km 60 km dipping 20 e with a mean slip of 2 7 m the recurrence time for 1881 type events is estimated to be 114 200 years on the basis of inferred gps convergence rates and inferred plate closure vectors although slip partitioning in the region may extend this estimate by as much as 30

constraints on jalisco block motion and tectonics of the guadalajara triple junction from 1998 2001 campaign gps data a gps campaign network in the state of jalisco was occupied for 36 h per station most years between 1995 and 2005 we use data from 1998 2001 to investigate tectonic motion and interseismic deformation in the jalisco area with respect to the north america plate the twelve stations used in this analysis provide coverage of the jalisco block and adjacent north america plate and show a pattern of motion that implies some contribution to jalisco block boundary deformation from both tectonic motion and interseismic deformation due to the offshore 1995 earthquake the consistent direction and magnitude of station motion on the jalisco block with respect to the north america reference frame 2 mm year to the southwest 95 confidence level perhaps can be attributed to tectonic motion however some station velocities within and across the boundaries of the jalisco block are also non zero 95 confidence level and the overall pattern of station velocities indicates both viscoelastic response to the 1995 earthquake and partial coupling of the subduction interface together termed interseismic deformation our results show motion across the northern colima rift the eastern boundary of the jalisco block which is likely to be sinistral oblique extension rather than pure extension we constrain extension across both the colima rift and the northeastern boundary of the jalisco block the tepic zacoalco rift to 8 mm year 95 confidence level slow compared to relative rates of motion at nearby plate boundaries

crustal deformation at the nankai subduction zone southwest japan derived from gps measurements the interseismic strain accumulation process at the nankai subduction zone the plate boundary region between the philippine sea and the eurasian plates off southwest japan has been revealed by gps measurements spanning five years large strains characterized by a contraction of 2 2 3 4 10 7 yr have accumulated in a narrow region extending parallel to the strike of the plate boundary the contraction axes lie in a northwest southeast direction nearly parallel to the direction of relative motion of the philippine sea plate with respect to the eurasian plate gps derived deformation data including both rate and direction are consistent with the expected earthquake deformation cycle at the nankai subduction zone current interplate coupling in this zone is strong much of the relative plate motion has been taken up by deformation of the marginal parts of the eurasian plate

nitrogen isotopes in thermal fluids of a forearc region jalisco block mexico evidence for heavy nitrogen from continental crust 1 the jalisco block jb is a geologically and tectonically complex part of northwestern mexico characterized by active subduction type volcanism rifting and old stable structures thermal springs and groups of springs are widely distributed over jb bubbling gas from seven thermal springs located within different tectonic environments of the jb was analyzed for he 20ne and n2 concentrations and 15n ratios all gases are n2 dominant 84 with the exception of one sample rio purificacion which has a significant ch4 content about 50 all collected gas samples are relatively high in he up to 1500 ppm vol and with 3he 4he values ranging from 0 6 to 4 5 ra all measured nitrogen isotope ratios are heavier than air with 15n values ranging from 0 5 to 5 0 the relative n2 excess with respect to air saturated water computed on the basis of n2 and 20ne contents indicates the contribution of a nonatmospheric n2 source all the samples show a good correlation between 15n and the relative excess of n2 with 15n 5 3 for the maximum n2 excess of 100 due to a presumed lack of seafloor sediment involved in the subduction process such a 15n positive value seems to reflect the addition to the fluids of a heavy nitrogen originating from metamorphism processes of rocks occurring within the overlying continental crust

slip kinematics and dynamics during and after the 1995 october 9 mw 8 0 colima jalisco earthquake mexico from gps geodetic constraints we use horizontal and vertical crustal displacements derived from gps measurements at 26 sites in western mexico to study the coseismic and post seismic kinematics and dynamics of the 1995 october 9 m w 8 0 colima jalisco earthquake along the middle america trench the measurements bracket the entire landward edge of the approximately 150 km long rupture zone and span a 4 yr period for most sites we solve for the temporal evolution of slip along the subduction interface by inverting gps displacements for the coseismic and four post seismic intervals march 1995 march 1999 subject to the assumption that the crust responds elastically to slip along a shallow dipping curved subduction interface coseismic rupture of up to 5 m was largely focused above depths of 20 km and was limited to a 120 140 km long segment of the subduction zone within one week of the earthquake post seismic slip migrated downdip to depths of 16 35 km where it has since decayed logarithmically we also find evidence for shallow aseismic slip during 1996 or early 1997 northwest of the coseismic rupture zone and increasingly widespread relocking of shallow regions of the subduction interface after early 1997 the relative lack of afterslip in shallow regions of the subduction interface suggests that the interface lies in the unstable frictional regime and hence is strongly coupled between earthquakes by 1999 the cumulative slip moment associated with post seismic slip equaled 70 per cent of the coseismic moment with nearly all of this slip occurring downdip from the coseismic rupture zone the migration of slip after the earthquake to a deeper and presumably velocity strengthening area of the subduction interface and the logarithmic decay of afterslip conform to the qualitative and quantitative predictions of a model in which the fault kinematics are prescribed by rate and state variable frictional laws however misfits to the geodetic displacements exceed the average displacement uncertainties for all epochs implying one or more of the following 1 the elastic response is heterogeneous due to slip along unmodelled upper crustal faults or variations in the elastic properties of the crust 2 other post seismic mechanisms such as viscoelastic or poroelastic effects contribute to or possibly dominate the post seismic response 3 we have underestimated the uncertainties in the gps displacements