the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

a study of mantle layering beneath the western pacific the reverberative interval of the seismogram defined as the portion following the surface wave train propagating along the minor arc and ending with the first body wave arrivals from the major arc provides an excellent window in which to observe subcritical reflections from mantle discontinuities on an sh polarized seismogram the intervals between scsn and sscsn wave groups zeroth order reverberations are approximately 15 min long and consist almost entirely of waves reflected one or more times from mantle discontinuities first and higher order reverberations we have developed signal enhancement and waveform inversion schemes to progressively extract information pertaining to mantle layering from the waveforms of zeroth and first order reverberations and have applied them to a data set of long period digital seismograms drawn from a number of tectonic regions in and around the western pacific the results place important constraints on the nature of the transition zone discontinuities measurements of the two way vertical shear wave travel time from the free surface to the 400 km and 650 km discontinuities 400 and 650 respectively yield estimates of transition zone travel time tz largely uncontaminated by outside heterogeneity variations in the path averaged estimates of tz are of the order of 5 4 s indicating significant lateral heterogeneity in the transition zone correlations of tz with 400 and lm travel time through the lower mantle are consistent with but do not require the thermal deflection of an exothermic phase transition near 400 km and an endothermic transition at 650 km with 12 km of long wavelength 500 5000 km topography on each the amount of topography estimated for the 650 km discontinuity is significantly less than predicted for a rigorously stratified mantle 100 km in a search for other mantle discontinuities we find evidence for a strong reflector possibly associated with the onset of partial melting in the upper mantle average depth of 86 km due to ambiguity inherent to the method this feature can also be interpreted as an impedance increase in the d region of the lower mantle 70 170 km above the core mantle boundary no evidence is found for a 220 km discontinuity or the d discontinuity proposed by lay and helmberger 1983 suggesting that if such features are present in the western pacific they are either small normal incidence sh reflection coefficient r 1 5 or intermittent or have lateral depth variations well in excess of 50 km

tracking slabs beneath northwestern pacific subduction zones article i nfo article history this study uses the amplitudes of bottom side reflected shear waves to constrain the morphology and dynam ics of subducted oceanic lithosphere beneath northwestern pacific subduction zones across honshu arc the 410 and 660 km seismic discontinuities are detected at the respective depths of 395 5 and 685 5 km within the wadati benioff zone their topographies are negatively correlated along slab dip showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone the base of the upper mantle shows broad depressions as well as localized zones of shallow average depths be neath korea and northeast china the 15 km peak to peak topography west of the wadati benioff zones suggests that the stagnant part of the subducted pacific plate is not as flat as previously suggested eastward slab pile up is also possible at the base of the upper mantle across southern kuril arc the shear wave reflec tion coefficients of major olivine phase boundaries fall below 5 within the wadati benioff zone the appar ent reflection gaps and the spatial connection between a strong reflector at 900 km depth may imply 1 possible compositional variations at the top and bottom of the transition zone and 2 substantial mass heat flux across the 660 km seismic discontinuity we also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths the depths and strengths of these reflectors are highly variable be tween honshu and southern kuril islands

deep upper mantle melting beneath the tasman and coral seas detected with multiple scs reverberations abstract multiple scs reverberations are used to search for mantle reflectors beneath the tasman and coral seas with a hierarchical waveform inversion migration method in addition to the major transition zone discontinuities a low velocity layer above the 410 km discontinuity is detected the top of the low velocity layer lies at an average depth of 352 km indicating that the layer could be more than 70 km thick if it persists to the 410 km discontinuity which occurs at an average depth of 420 km along paths containing the low velocity layer we attribute the low velocities to partial melt resulting from volatile induced melting the considerable thickness of the partial melt layer may require thin films of a hydrous melt with a zero degree dihedral angle surrounding grains or the combined effect on melting of the addition of both water and carbon to the deep upper mantle via subduction although the depths of the transition zone discontinuities do not indicate that the transition zone itself is rich in water the impedance contrasts do contain a subtle signature that could be related to transition zone water namely a decrease in the impedance contrast across the 410 km discontinuity and a relatively strong 520 km discontinuity

early miocene change in direction of least principal stress southwestern united states conflicting inferences from dikes and metamorphic core detachment fault terranes previous investigations have suggested that the direction of least principal stress in the western united states has shifted from northerly to easterly between 50 to 30 ma an effort is made to more tightly constrain the time of this shift using igneous dike host rock systems in which the isotopic age of both host and dike is known and differs by less than 10 ma in such systems the possibility that magma intruded along old fractures unrelated to the state of stress at the time of intrusion is minimized and the axis of least principal stress is considered to be normal to the strike of the subvertical dike during the time interval between the ages of the dike and host rock these systems indicate that a northerly least principal stress orientation persisted more recently than previously believed until probably after 30 ma possibly about 26 ma and conceivably as recently as 18 ma in some areas the data are insufficient and too loosely bracketed in time to decide how fast the change in state of stress occurred in any one place and if by systematic rotation or abrupt shift however the change could be diachronous earlier in the southeast and later in the northwest major easterly trending magmatic and tectonic elements of tertiary age in the great basin of utah and nevada are compatible with the dike data however numerous metamorphic core complexes and detachment fault terranes seem to indicate more or less easterly extension throughout the time period represented by the dikes this inconsistency is not clearly resolvable but may reflect differences between the regional plate stress field and gravitational stresses in a crust overthickened by mesozoic compression

seismic observations of splitting of the mid transition zone discontinuity in earth s mantle the transition zone of earth9s mantle is delineated by globally observed discontinuities in seismic properties at depths of about 410 and 660 kilometers here we investigate the detailed structure between 410 and 660 kilometers depth by making use of regional stacks of precursors to the ss phase the previously observed discontinuity at about 520 kilometers depth is confirmed in many regions but is found to be absent in others there are a number of regions in which we find two discontinuities at about 500 and 560 kilometers depth an effect which can be interpreted as a splitting of the 520 kilometer discontinuity these observations provide seismic constraints on the sharpness and observability of mineralogical phase transitions in the mantle transition zone

retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

a complex 660 km discontinuity beneath northeast china abstract we present a detailed seismic study of the 660 km discontinuity beneath northeast china using the receiver function technique we use seismic data collected from 24 broadband stations in northeast china analysis of these data shows that the 660 km discontinuity is locally depressed in the region from longitude 128 0 e to 130 5 e and latitude 40 0 n to 44 0 n and then it splits into multiple discontinuities in the surrounding regions the complexity of the 660 km discontinuity beneath the subduction zones is probably attributable to the interaction between the upper mantle and subducted slab we speculate that the flattening of the subducted lithosphere near the bottom of the upper mantle causes the multiple discontinuity structure and that the slab penetrating the 660 km discontinuity into the lower mantle causes the narrow 660 km depression area

bayesian estimation of the spatially varying completeness magnitude of earthquake catalogs assessing the completeness magnitude mc of earthquake catalogs is an essential prerequisite for any seismicity analysis we employ a simple model to com putemc inspacebasedontheproximitytoseismicstationsinanetwork weshowthata relationship of the form m predd ad bc with d the distance to the kth nearest seismic station fits the observations well k depending on the minimum number of stations being required to trigger an event declaration in a catalog we then propose anewmc mappingapproach thebayesianmagnitude ofcompleteness bmc method based on a two step procedure 1 a spatial resolution optimization to minimize spatial heterogeneities and uncertainties in mc estimates and 2 a bayesian approach that merges prior information about mc based on the proximity to seismic stations with locally observed values weighted by their respective uncertainties contrary to the cur rentmc mappingprocedures theradiusthatdefineswhichearthquakestoincludeinthe local magnitude distribution is chosen according to an objective criterion and there are no gaps in the spatial estimation of mc the method solely requires the coordinates of seismic stations here we investigate the taiwan central weather bureau cwb seismic network and earthquake catalog over the period 1994 2010

origin of the trachyte quartz trachyte peralkalic rhyolite suite of the oligocene paisano volcano trans pecos texas volcanic rocks of the paisano volcano include trachyte quartz trachyte and peralkalic rhyolite mafic rocks hawaiite and mugearite occur within units that stratigraphically underlie and overlie rocks of the volcano quartz trachyte trachyte and nephe line trachyte occur as discordant plugs and dikes intruded into strata of the volcano central eruptions from dike swarms led to the formation of the shield complex of the volcano 35 m y ago the central dike complex a generalized eruptive sequence of rhyolite quartz trachyte trachyte within the eruptive products of the volcano and the development of a 5 km diameter caldera suggest the presence beneath the volcano of one or more shallow plutonic bodies in which differentiation may have occurred fractionation calculations using whole rock analyses to represent liquid compositions and electron probe microanalyses of phenocryst minerals to represent compositions of fractionating phases indicate plagioclase plus olivine control in the evolution of trachyte from mugearite and anorthoclase control in the evolution of rhyolite from trachyte the feldspar fractionation model is supported by strong enrichment of rb and zr and strong depletion of sr in the series and by a striking eu anomaly in ree plots a compositional gap between mugearite and trachyte analogous to the daly gap of oceanic islands disappears when oxides of major elements are plotted versus zr zr however cannot be used as a strict index of fractionation because zr concentrations were buffered by the crystallization of zircon with feldspar in the crucial trachyte stage of magmatic evolution in more advanced quartz trachyte and rhyolite stages the melts greatly increased in peralkalinity and zircon did not crystallize this effect produced zr concentrations as high as 2 500 ppm in highly fractionated rhyolite glomeroporphyritic clusters of feldspar zoned from andesine to calcic anorthoclase along with augite opaques and in some samples olivine are ubiquitous in mafic trachyte these clusters have textures indicative of crystallization in intrusions they suggest a genetic relationship between mugearite and trachyte where residual trachytic liquids are segregated by filter pressing from crystallizing magma of over all mugearitic composition in subvolcanic chambers paisano igneous rocks closely resemble suites of volcanic rocks from afro arabian central volcanoes associated with intracontinental rifting and suites from some oceanic islands alkalic rocks of the paisano volcano may be related to mantle diapirism triggered by subduction processes

the unusual 3d interplay of basement fault reactivation and fault propagation fold development a case study of the laramide age stillwell anticline west texas usa abstract subsurface fault geometries have a systematic influence on folds formed above those faults we use the extraordinarily well exposed fold geometries of the laramide age stillwell anticline in west texas usa to develop a strain predictive model of fault propagation fold formation the anticline is a 10 km long nw trending ne vergent asymmetric fold system with an axis that displays a map view left stepping en echelon pattern we integrated field observations geologic and structural data cross sections and 2d kinematic modeling to establish an unusual 3d two stage model of contractional fold formation including 1 reverse reactivation of a pre existing nw striking sw dipping left stepping en echelon normal fault system in paleozoic basement rocks to generate monoclinal flexures in overlying layered cretaceous carbonate rocks and 2 the formation of a subsequent flat ramp fault system that propagated horizontally along a mechanically weak clay rich cretaceous unit before ramping up at the hinge of the pre existing monocline system strain is focused within the forelimb of the system in front of the propagating fault tip and is accommodated by a combination of interlayer slip flat ramp faulting and fracturing proximal to planes of slip this strain predictive model can be applied to similar less well exposed contractional systems worldwide and provides a new unusual example of laramide age contractional deformation

integrating high resolution refraction data into near surface seismic reflection data processing and interpretation shallow seismic reflection surveys commonly suffer from poor data quality in the upper 100 to 150 ms of the stacked seismic record because of shot associated noise surface waves and direct arrivals that obscure the reflected energy nevertheless insight into lateral changes in shallow structure and stratigraphy can still be obtained from these data by using first arrival picks in a refraction analysis to derive a near surface velocity model we have used turning ray tomography to model near surface velocities from seismic reflection profiles recorded in the hueco bolson of west texas and southern new mexico the results of this analysis are interval velocity models for the upper 150 to 300 m of the seismic profiles which delineate geologic features that were not interpretable from the stacked records alone in addition the interval velocity models lead to improved time to depth conversion when converted to stacking velocities they may provide a better estimate of stacking velocities at early travelt

transition zone thickness beneath indonesia as inferred using the receiver function method for data from the jisnet regional broadband seismic network 1 we analyzed broadband waveforms recorded by the newly deployed japan indonesia seismic network to determine the depths of the 410 km and 660 km discontinuities and thickness of the mantle transition zone beneath indonesia by the receiver function method the discontinuities have an undulation with a maximum difference of 40 km with respect to the iasp91 model the thickness of the transition zone is well correlated with seismicity and seismic velocity anomalies suggesting that the topography is caused by temperature anomalies associated with the subducted slabs beneath indonesia

structural analysis of the velardena mining district mexico a faulted au ag rich hydrothermal system epithermal au ag veins of the velardena mining district north central mexico correspond to narrow fault controlled high grade structures that are continuous along strike for several kilometres the veins converge toward the guardarraya intrusion where carbonate hosted deposits are found at the contact with surrounding limestones the mineralized structures are cut by basin and range normal faults showing apparent vertical displacement up to 320 m paleostress reconstructions in the velardena mining district suggest that mineralized structures formed during a nne directed extensional event that predated the basin and range faulting event ene directed basin and range normal faulting is responsible for surface exposures of various au ag mineralizations formed at different crustal depths thus enabling studies of the entire hydrothermal system from low grade breccia zones in the volcanic cover rocks to deeper base metal rich deposits

coseismic deformation of the destructive april 6 2009 l aquila earthquake central italy from gps data 1 on april 6 2009 01 32 39 gmt the city of l aquila was struck by a mw 6 3 earthquake that killed 307 people causing severe destruction and ground cracks in a wide area around the epicenter four days before the main shock we augmented the existing permanent gps network with five gps stations of the central apennine geodetic network cageonet bordering the l aquila basin the maximum horizontal and vertical coseismic surface displacements detected at these stations was 10 39 0 45 cm and 15 64 1 55 cm respectively fixing the strike direction according to focal mechanism estimates we estimated the source geometry with a non linear inversion of the geodetic data our best fitting fault model is a 13 15 7 km2 rectangular fault sw dipping at 55 3 1 8 consistent with the position of observed surface ruptures the estimated slip 495 29 mm corresponds to a 6 3 moment magnitude in excellent agreement with seismological data

seismicity precursors to large earthquakes unified in a stress accumulation framework 1 various seismicity patterns before large earthquakes have been reported in the literature they include foreshocks medium term acceleration and short term activation quiescence doughnut patterns and event migration the existence of these precursory patterns is however debated here we develop an approach based on the concept of stress accumulation to unify and categorize all claimed seismic precursors in a same physical framework we first extend the non critical precursory accelerating seismicity theory n c past which already explains most precursors to additionally include short term activation theoretical results are then compared to the time series observed prior to the 2009mw 6 3 l aquila italy earthquake we finally show that different precursory paths are possible before large earthquakes with possible coupling of different patterns or non occurrence of any this is described by a logic tree defined from the combined probabilities of occurrence of the mainshock at a given stress state and of precursory silent slip on the fault in the case of the l aquila earthquake the observed precursory path is coupling of quiescence and accelerating seismic release followed by activation these results provide guidelines for future research on earthquake predictability

paleomagnetism and 40ar 39ar geochronology of gabbro sills at mariscal mountain anticline southern big bend national park texas implications for the timing of laramide tectonism and vertical axis rotations in the southern cordilleran orogenic belt mariscal mountain anticline is a major laramide asymmetric fold located along the frontal margin of the cordilleran orogenic belt in the trans pecos region of southwest texas exposed within the limbs and nose of the anticline are concordant mafic and felsic intrusions whose emplacement based largely on their arcuate outcrop geometry has been interpreted to predate folding paleomagnetic fold tests on samples from large 30 m thick and thin l m thick gabbro sills are negative at the 99 confidence level baked sandstones adjacent to the thick sill give sample directions identical to those of the gabbro whereas sample directions from a site well removed from thermal effects of the gabbro are scattered results of the contact tests are consistent with a thermoremanent origin for the gabbro sill magnetization the negative fold test indicates that sill intrusion at mariscal mountain anticline postdated laramide folding two 40ar 39ar analyses of plagioclase from the gabbro give discordant age spectra but yield an inverse correlation age of 37 0 1 3 ma 2 this date is similar to those from rocks of similar composition elsewhere in trans pecos texas but significantly younger than whole rock and pyroxene k ar dates of late cretaceous and early eocene age commonly cited for the mariscal mountain gabbro the paleomagnetic and geochronologic data indicate that laramide deformation had clearly ceased by late eocene early oligocene time consistent with absence of contractional deformation in middle eocene to lower oligocene volcanic and sedimentary rocks elsewhere in the region although paleomagnetic data from the gabbro sills may not adequately average secular variation the in situ group mean direction d 348 6 i 50 9 k 65 1 95 4 3 n 18 sites is indistinguishable from expected mid tertiary reference directions this indicates no evidence of significant vertical axis rotation in the mariscal mountain area analysis of paleomagnetic data from studies elsewhere in the big bend region indicates that significant problems exist with most data sets used to argue for the existence of local vertical axis rotations thus we conclude that existing paleomagnetic evidence regarding the timing and magnitude of rotations associated with basin and range extension is equivocal

endorheic exorheic transitions of the rio grande and east african rifts this research was supported by nsf ear 1516680 and spanish government project mite cgl2014 59516

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

non critical precursory accelerating seismicity theory nc past and limits of the power law fit methodology abstract the hypothesis that accelerating moment release amr is a precursor to large earthquakes is still debated on one hand amr has been claimed to be observed in many cases and on the other hand it has been proposed that apparent amr is only due to data fitting the debate is in general focused on the validity of the c value curvature parameter which permits to quantify amr i e cumulative benioff strain through time or more generally precursory accelerating seismicity pas i e cumulative number of events through time contrary to previous studies which compare c value optimization in real seismicity catalogues and in random synthetic catalogues i test c value optimization in theoretical synthetic catalogues in that particular case i assume that pas exists and that it can be explained by the non critical precursory accelerating seismicity theory nc past this theory demonstrates that pas can emerge from the background seismicity because of the decrease due to loading of the size of a stress shadow due to a previous earthquake i improve the nc past by integrating the following characteristics of the background seismicity 1 the density of random events outside the stress shadow b0 and 2 the noise ratio b b0 with b being the density of random events inside the stress shadow then i perform a spatiotemporal search of pas using the power law fit methodology i e c value and compare the optimal signal to the expected spatiotemporal extent of the theoretical signal first i show that the optimal starting time and spatial extent of pas are poorly controlled due in part to the intrinsic properties of the c value but also to the random behavior of background seismicity second i show that theoretical pas is identified by an optimal c value clear acceleration only if the regional seismic activity b0 is high and the noise ratio b b0 is low otherwise the signal tends to disappear and the c value becomes unstable as a consequence even if the power law fit methodology is a simple approach to test the presence of pas and can help provide a better understanding of the process engaged it seems inadequate for robust systematic prospective forecasts

evidence for a thick mantle transition zone beneath the philippine sea from multiple scs waves recorded by jisnet 1 we deployed the jisnet broadband seismic network in west and central indonesia using data from jisnet and other broadband stations we estimate the thickness of the mantle transition zone beneath east and southeast asia and the philippine sea using the scs reverberation method the thickness is about 240 km beneath east and southeast asia 280 290 km beneath the western edge of the philippine sea 260 280 km beneath the central part of the philippine sea and 260 km beneath the izu bonin arc these results imply that the temperature is about 300 k lower than the global average beneath the western edge of philippine sea 200 k lower beneath the mid part of the philippine sea 130 k lower beneath the izu bonin arc and almost equal to the average beneath east and southeast asia

the foreshock sequence of the february 4 1975 haicheng earthquake m 7 3 we have examined the locations and radiation patterns of the foreshocks of the february 4 1975 haicheng earthquake m 7 3 using arrival times from six local seismic stations the foreshocks and mainshock were located relative to a master event the foreshocks occurred in a tight cluster that elongated with time before the largest foreshock the activity was located within a small approximately equidimensional volume with a diameter of about 2 km after the largest foreshock the activity spread northwest and southeast forming a 6 km long northwest trending zone first motions and ratios of p to s amplitudes indicate that two different faulting mechanisms occurred during the foreshock sequence the two radiation patterns can tentatively be correlated with different parts of the zone the hypocenter of the mainshock was not located on the same fault as that defined by the foreshocks hypocenters but rather was located 6 km south of and several kilometers shallower than the foreshock cluster we think this large separation between foreshocks and mainshock in a direction perpendicular both to the plane of rupture of the mainshock and to the trend of the foreshocks might be the result of an en echelon step in the fault that slipped during the mainshock an analysis of the change in stress due to slip during the foreshocks shows that the increase in shear stress on the mainshock fault caused by the foreshocks is very small and that direct triggering of the mainshock by the foreshocks is unlikely

tectonic implications of mid tertiary dikes in west central new mexico the n30 35 w trend of three long basaltic andesite dikes in west central new mexico indicates a least principal horizontal stress direction of n55 60 e at the time the dikes were emplaced 28 m y ago this stress direction agrees with recently proposed tectonic models for the region suggesting that northeast southwest extension was pervasive over both the early basin and range and colorado plateau provinces and the southern rocky mountains at this time

reflectivity of the 410 km discontinuity from pp and ss precursors a number of studies have confirmed the global existence of a transition zone discontinuity at 410 km depth by aligning large numbers of long period seismograms on a surface reflection phase before stacking in particular ss and pp precursors from the 410 km discontinuity termed p410p and s410s have revealed long wavelength topography of this discontinuity here we extend these techniques to examine the reflection coefficient of the 410 km discontinuity using our measurements of p410p and s410s amplitudes we constrain the impedance contrasts across the 410 km discontinuity we also show lateral variations in the p wave impedance contrast at 410 km which is typically low under north america and china and higher beneath the north pacific the s wave impedance contrast shows less variability on the regional scale however analysis of p410p and s410s amplitudes over smaller areas by binning traces into spherical caps shows that the s wave reflection coefficient varies over much shorter scale lengths than that for p waves the different patterns of variation for p410p and s410s reflection amplitudes could be due to the presence of melt water or other chemical heterogeneities in the transition zone other factors such as temperature or mantle olivine content variations could also influence precursor amplitudes but they would be expected to lead to correlated variations and so they cannot explain all the variation that we observe

ss wave sensitivity to upper mantle structure implications for the mapping of transition zone discontinuity topographies 1 studies of the depths of the upper mantle discontinuities have relied on the differential travel times between the ss wave and its precursors we examine the effect of velocity heterogeneities on these differential travel time data ray theory which is used to correct these data for the effect of velocity heterogeneities is shown to be inaccurate if the characteristic heterogeneity length scales are similar to those seen in regional models or if the station is near the ss wave radiation nodal plane

compositional changes in trans pecos texas magmatism coincident with cenozoic stress realignment the composition and inferred sources of cenozoic magmas in trans pecos texas changed abruptly between 32 and 28 ma coincident with a fundamental change in stress regime magmas emplaced between 48 and 32 ma comprise extended differentiation suites beginning with relatively evolved basaltic magmas these rocks have low nb and ta compared to zr hf la ba and k characteristics typical of continental volcanic arcs however the texas rocks are more alkalic have higher concentrations of incompatible elements and have higher ratios of nb and ta to zr hf la ba and k than is typical of rocks from arcs near trenches these differences reflect relative position within the cordilleran arc trace element models involving partial melting in the mantle wedge combined with fractional crystallization and assimilation of upper and lower crust can account for most of the observed trace element concentrations and ratios trans pecos magmatism may have involved smaller degrees of partial melting than is typical of arcs located closer to the subduction zone magmas emplaced after 31 ma were either bimodal alkali basalt rhyolite or exclusively basaltic they have high absolute abundances of incompatible trace elements and high ratios of nb and ta to zr hf la ba and k the mafic rocks are typical of continental rift or ocean island basalts trace element models using nb ta y yb hf and zr reproduce the range of concentrations and ratios observed in these rocks and require very small degrees of partial melting variable amounts of fractional crystallization but little or no assimilation the change in magma compositions and sources is best illustrated by a drop in zr nb from between 18 and 6 25 in the earlier arc rocks to between 6 25 and 2 in the later rift related rocks stress regime appears to play an important role in the process of magma generation and evolution the change in trace element compositions indicative of tectonic setting supports interpretations of paleostress data that activity up to 31 ma occurred in a continental volcanic arc whereas later activity occurred in a setting of intraplate extension the magmatic change may have been simultaneous with the change in stress regime or may have lagged by as much as 3 4 m y

the effectiveness of a distant accelerometer array to compute seismic source parameters the april 2009 l aquila earthquake case history the 6 april 2009 mw 6 3 l aquila earthquake central italy has been recorded by the irpinia seismic network isnet about 250 km southeast of the epicenter up to 19 three component accelerometer stations could be used to infer the main source parameters with different seismological methods we obtained an approximate location of the event from arrival times and array based back azimuth measurements and estimated the local magnitude 6 1 from an at tenuation relation for southern italy assuming an omega square spectral model we inverted s wave displacement spectra for moment magnitude 6 3 corner frequency 0 33 hz stress drop 2 5 mpa and apparent stress 1 6 mpa waveform modeling using a point source and an extended source model provided consistent moment tensors with a centroid depth around 6 km and a prevalently normal fault plane solution with a dominant directivity toward the southeast the relatively high corner frequency and an overestimated moment magnitude of 6 4 from moment tensor inversions are attributed to the rupture directivity effect to image the rupture geometry we implemented a beamforming technique that back projects the recorded direct p wave amplitudes into the earthquake source region a northwest southeast striking rupture of 17 km length is imaged propagat ing with an average velocity up to 3 km s this value is significantly higher than our estimate of 2 2 km s from s wave spectra our case study demonstrates that the use of array techniques and a dense accelerometer network can provide quick and robust estimates of source parameters of moderate sized earthquakes located outside the network

risk and return evaluating reverse tracing of precursors earthquake predictions summary in 2003 the reverse tracing of precursors rtp algorithm attracted the attention of seismologists and international news agencies when researchers claimed two successful predictions of large earthquakes these researchers had begun applying rtp to seismicity in japan california the eastern mediterranean and italy they have since applied it to seismicity in the northern pacific oregon and nevada rtp is a pattern recognition algorithm that uses earthquake catalogue data to declare alarms and these alarms indicate that rtp expects a moderate to large earthquake in the following months the spatial extent of alarms is highly variable and each alarm typically lasts 9 months although the algorithm may extend alarms in time and space we examined the record of alarms and outcomes since the prospective application of rtp began and in this paper we report on the performance of rtp to date to analyse these predictions we used a recently developed approach based on a gambling score and we used a simple reference model to estimate the prior probability of target earthquakes for each alarm formally we believe that rtp investigators did not rigorously specify the first two successful predictions in advance of the relevant earthquakes because this issue is contentious we consider analyses with and without these alarms when we included contentious alarms rtp predictions demonstrate statistically significant skill under a stricter interpretation the predictions are marginally unsuccessful

geology structure and tectonics of the pajarito fault zone in the espanola basin of the rio grande rift new mexico the pajarito fault zone forms the western border of the velarde graben the presently active central subbasin of the espanola basin section of the rio grande rift in north central new mexico the fault zone is a north northeast trending zone of predominantly down to the east faults that cut miocene to pliocene volcanic rocks along the eastern flank of the jemez mountains where the fault zone cuts the 1 1 m y old tshirege member of the bandelier tuff it has produced a steep 50 to 100 m high fault scarp the total displacement across the fault zone during its 5 m y history is between 200 and 600 m rates of displacement for the time periods 0 5 0 1 1 and 1 1 5 m y ago range from 0 02 to 0 136 mm yr abrupt facies changes between older volcanics and volcaniclastic sediments of the jemez mountains appear to have controlled the local position trend and character of the pajarito fault zone the fault zone bows and or steps eastward where two large volcanic complexes are present but is found farther west in between and at either end of the volcanic complexes one complex was sufficiently massive to interfere with the development of the velarde graben slickensides on mesoscopic faults in the tshirege member of the bandelier tuff indicate that the pajarito fault zone has undergone extension in two directions during the past 1 1 m y approximately parallel and perpendicular to the local trend of the fault zone these directions indicate that the pajarito fault zone has reoriented the regional minimum and intermediate stress directions to perpendicular and parallel respectively to the local trend of the fault zone and that both minimum and intermediate stress directions are tensional a tectonic history for the pajarito fault zone area of the espanola basin begins with relatively stable accumulation of prerift and synrift sediments from eocene to oligocene time sedimentation concomitant with faulting unrelated to the pajarito fault zone filled deep central depressions within the espanola basin this faulting ceased prior to the end of the filling of the basin around 10 m y ago in the local area jemez mountain volcanism began about this time before movement along the western margin border faults of the espanola basin caused west tilting of old volcanics and sediments about 7 5 m y ago volcanism continued under relatively stable conditions until 5 m y ago at this time the pajarito fault zone and velarde graben formed faulting has continued to the present localized along this central subbasin

an analysis of ss precursors using spectral element method seismograms summary the traveltimes of underside shear wave reflections i e ss precursors are widely used data for mapping the topography of mantle discontinuities in the upper mantle here we examine the accuracy of ray theory in estimating the contribution of shear velocity heterogeneity in the mantle to ss s400s ss s670s and s400s s670s traveltimes we analyse stacks of spectral element method waveforms computed for 34 shallow earthquakes and 16 020 globally distributed virtual seismometers the waveforms are computed for three versions of shear velocity model s20rts with variable strengths of the volumetric shear velocity perturbations within the layered structure of the preliminary reference earth model we find that ray theoretical corrections account for only 50 per cent of the traveltime variation due to large scale velocity heterogeneity for current tomographic models as represented by s20rts this translates into unpredictable long and short wavelength errors in maps of mantle discontinuity depths of about 5 km this amounts to roughly 10 per cent of published variations in mantle discontinuity depths however relative errors will be significantly larger if ray theoretical traveltime corrections are based on forthcoming models of shear velocity with much stronger heterogeneity at the smallest scales

relationship between accelerating seismicity and quiescence two precursors to large earthquakes 1 the non critical precursory accelerating seismicity theory past has been proposed recently to explain the formation of accelerating seismicity increase of the a value observed before large earthquakes in particular it predicts that precursory accelerating seismicity should occur in the same spatiotemporal window as quiescence in this first combined study we start by determining the spatiotemporal extent of quiescence observed prior to the 1997 mw 6 umbria marche earthquake italy using the rtl region time length algorithm we then show that background events located in that spatiotemporal window form a clear acceleration as expected by the non critical past this result is a step forward in the understanding of precursory seismicity by relating two of the principal patterns that can precede large earthquakes

statistics between mainshocks and foreshocks in italy and southern california 1 the most used and accepted models for daily forecasts are based on short term space and time earthquake clustering for occurrence rates and on the gutenberg richter law for the frequency magnitude these models have been demonstrated to produce reliable prospective space time magnitude forecasts during an aftershock sequence but their skill in forecasting mainshocks is still under discussion this paper studies the foreshock statistics of the italian and californian seismicity in two ways i we compare the foreshock activity observed in real seismic catalogs and in synthetic catalogs derived from a pure epidemic type aftershock sequence etas model ii we analyze the triggering capability of earthquakes using different etas parameterizations in order to check whether large events are triggered in the same way as regular earthquakes the results indicate that the foreshock activity observed in the real catalogs is compatible with what is expected by the etas model moreover we find that the empirical foreshock rates have an intrinsic variability due to limited sampling that may explain most of the differences found so far in different seismic catalogs

triple junction instability as cause for late cenozoic extension and fragmentation of the western united states regional extension in the western united states began soon after 30 m y b p the time of first interaction between the pacific and north american plates previous explanations for extension include lithospheric active processes and asthenospheric active processes the former are favored because of coincidence of timing with lithospheric interactions relative timing of volcanism and deformation and coincidence with pre existing structures although extension has occurred in part in a back arc setting it cannot be attributed to age of subducted crust or azimuth of subduction because both attributes favor back arc contraction characteristic behavior before 40 m y b p the mendocino triple junction has been unstable since its inception the continental margin was relatively straight before 30 m y b p and it has become more convex westward as the triple junction has migrated northward the continental margin and arc have been anchored to the subducting slab farallon juan de fuca whereas the triple junction must move parallel to the san andreas transform the combined result has been the northwestward and clockwise movement of coastal blocks relative to the continental interior and the eastward stepping of the san andreas transform relative to the coast these effects result from the unstable geometry of the mendocino triple junction lack of a subducted slab slab window beneath the extended lithosphere enables asthenospheric rise but does not cause extension

seismicity and geodetic anomalies in a wide area preceding the niigata ken chuetsu earthquake of 23 october 2004 central japan 1 the ordinary short term occurrence rate of earthquakes in a region is predicted using the epidemic type aftershock sequence etas model of triggering seismicity any anomalous seismic activity such as quiescence and activation can be quantified by identifying significant deviation from the predicted rate such anomalies are revealed to have occurred during the three year period leading up to the 2004 chuetsu earthquake of m6 8 mw6 6 central japan the quiescence and activation which took place in the zone of negative and positive increments of the coulomb failure stress respectively were possibly caused by aseismic slip on or near the focal fault plane such slip is further supported by transient crustal movement around the rupture source time series records of the baseline distances between permanent gps stations deviated from the predicted trends with the deviations mostly consistent with the coseismic horizontal displacements of the stations due to the chuetsu earthquake the cumulated preceding slip is estimated to be roughly equivalent to mw6

a mathematical formulation of accelerating moment release based on the stress accumulation model large earthquakes can be preceded by a period of accelerating seismic activity of moderate sized earthquakes this phenomenon usually termed accelerating moment release has yet to be clearly understood a new mathematical formulation of accelerating moment release is obtained from simple stress transfer considerations following the recently proposed stress accumulation model this model based on the concept of elastic rebound simulates accelerating seismicity from theoretical stress changes during an idealized seismic cycle in this view accelerating moment release is simply the consequence of the decrease due to loading of the size of a stress shadow due to a previous earthquake we show that a power law time to failure equation can be expressed as a function of the loading rate on the fault that is going to rupture we also show that the m value which is the power law exponent can be defined as m d 3 with d a parameter that takes into account the geometrical shape of the stress lobes and the distribution of active faults in the stress accumulation model the power law is not due to critical processes

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

the effect of topography of upper mantle discontinuities on ss precursors using the spectral element method we explored the effect of topography of upper mantle discontinuities on the traveltimes of ss precursors recorded on transverse component seismograms the latter are routinely used to infer the topography of mantle transition zone discontinuities the step from precursory traveltimes to topographic changes is mainly done using linearised ray theory or sometimes using finite frequency kernels we simulated exact seismograms in 1 d and 3 d elastic models of the mantle in a second simulation we added topography to the discontinuities we compared the waveforms obtained with and without topography by cross correlation of the ss precursors since we did not add noise the precursors are visible in individual seismograms without the need of stacking the resulting time anomalies were then converted into topographic variations and compared to the original topographic models based on the correlation between initial and inferred models and provided that ray coverage is good we found that linearised ray theory gives a relatively good idea on the location of the uplifts and depressions of the discontinuities it seriously underestimates the amplitude of the topographic variations by a factor ranging between 2 and 7 real data depend on the 3 d elastic structure and the topography all studies to date correct for the 3 d elastic effects assuming that the traveltimes can be linearly decomposed into a structure and a discontinuity part we found a strong non linearity in this decomposition which cannot be modelled without a fully non linear inversion for elastic structure and discontinuities simultaneously

mid cenozoic stress evolution and magmatism in the southern cordillera texas and mexico transition from continental arc to intraplate extension orientations of dikes veins faults and slickenlines reveal the evolution of stress during eocene to miocene magmatism in the southern cordillera where most thoroughly studied by us in trans pecos texas magmatism began at about 48 ma shortly after the cessation of laramide folding dikes and veins that formed from then until about 32 ma strike dominantly east northeast this indicates that the least principal stress 3 was north northwest additional data suggest that the maximum principal stress 1 was east northeast the stress field changed to 1 vertical and 3 east northeast i e east northeast extension at least by 28 ma and probably by 31 ma dikes and veins that formed between 31 and 17 ma when all magmatism ceased in texas strike north northwest this change marks the beginning of regional basin and range extension however major normal faulting exclusively of high angle type did not begin until about 24 ma a similar stress change marked by a similar change in dike and vein orientations occurred throughout the southwestern united states and northern mexico the time of change is not well constrained in texas but available information allows it to have occurred at the same time thoughout the southern cordillera we suggest the earlier stress field is related to east northeast convergence between the farallon and north american plates the change in stress is approximately coincident with collision of the east pacific rise and paleotrench extension may be related to the change from a convergent to a transform margin along the western edge of north america the changes in the stress field are accompanied by changes in the sources and compositions of magmas erupted in texas contemporaneity of the changes in stress and magmatism indicates that they are related combined with regional age patterns paleostress and geochemical data indicate that pre 31 ma magmatism in the southern cordillera occurred in a subduction related continental volcanic arc subsequent magmatism occurred in an environment of intraplate extension of the basin and range province

plate interactions control middle late miocene proto gulf and basin and range extension in the southern basin and range middle late miocene proto gulf 12 6 ma extension around the gulf of california gulf extensional province is commonly interpreted as resulting from partitioning of oblique pacific north american plate motion into strike slip displacement along the margin and east northeast extension perpendicular to the margin within the north american plate we propose that this mechanism also applies to kinematically similar predominantly east northeast extension that occurred at the same time throughout the southern basin and range province from southern arizona and new mexico to the trans mexican volcanic belt new field and 40ar 39ar data in sinaloa and durango confirm that this episode of extension occurred on the mainland side of the gulf and in the basin and range east of the sierra madre occidental which is generally considered the eastern margin of the gulf extensional province published data indicate the middle late miocene episode also occurred across the northern and southern ends of the sierra madre where the gulf extensional province connects with the basin and range 1 from central sonora into southern arizona and new mexico and 2 from nayarit into central mexico north of the trans mexican volcanic belt this episode appears to have avected an area that continues to the eastern edge of the basin and range province in texas and san luis potosi recognition that this episode of extension avected the entire southern basin and range resolves the discrepancy between the amount of extension calculated based on plate reconstructions and that based on field data within the gulf extensional province alone published plate reconstructions require 160 to 110 km of east northeast extension between 12 and 6 ma if taken up solely within the gulf extensional province this would have generated 66 to 78 extension which is much greater than observed spread across the entire southern basin and range it requires only 20 total extension which is more consistent with observations of cumulative extension between 12 and 6 ma extension was partitioned into the gulf extensional province because 1 it lies between two stable batholith belts mesozoic peninsular ranges on the west and mid tertiary sierra madre occidental on the east that resisted extension and 2 the gulf was thermally weakened by immediately preceding arc magmatism extension in the main basin and range province in part probably avoided the relatively strong batholithic crust of the sierra madre occidental 2000 elsevier science b v all rights reserved

orientational data on the state of stress in northeastern mexico as inferred from stress induced borehole elongations preferential elongation directions are presented from 46 subvertical wells in northeastern mexico from depth intervals ranging from 161 to 4 912 m the measurements document a remarkably consistent west east to northwest southeast direction of the contemporary least horizontal stress in the upper crust of this intraplate region in the regional neotectonic framework the data suggest that mexico north of the trans mexican volcanic belt is being stretched in west east to northwest southeast direction the measurements from the area of the laramide chihuahua and coahuila fold thrust belts define the southern extend of the basin and range rio grande rift stress province of the southwestern united states into northern mexico the least horizontal in situ stress directions recorded in the gulf coastal plain burgos and tampico misantla basins are oblique to the continental margin of the gulf of mexico but subparallel to the direction measured in the area of the basin and range rio grande rift stress province this suggests that the stress distribution in these basins is not mainly the result of gravitational loading as in the gulf coast stress province of the united states but is controlled by the same lithospheric stress system that characterizes the basin and range rio grande rift stress province this is also supported by the north south trending zone of oligocene quaternary alkaline volcanism that crosses the tampico misantla basin furthermore the data indicate that the active deformation of the mexican ridges fold belt east of the study area in the gulf of mexico cannot be caused by a compressional external tectonic load the direction of the least horizontal in situ stress measured in the area of the laramide sierra madre oriental fold thrust belt in hidalgo and san luis potosi states is consistent with that of the other zones however wellbore elongations were recorded less frequently and show a rather large circular variance which suggests that the minimum and maximum horizontal far field stresses are about equal in this area

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

the impact of inter bed cohesion on fold related fracture development stillwell anticline west texas usa abstract the interpretation of fracture networks in contractional folds is challenging due to the range of factors that control fracture formation we use outcrop based analysis of fractures in plan view pavements and in a 9 bed cross sectional exposure to evaluate the fracture system within cretaceous limestone layers of a laramide fold in west texas the stillwell anticline opening mode extension fractures veins at high angles to bedding dominate the fracture population although shear fractures and faults cut bedding at low angles within the forelimb analysis of extension fractures reveals nw striking axial parallel and ne striking axial perpendicular fracture sets interpreted to have formed during contractional folding a third n striking fracture set formed during subsequent basin and range extension and a fourth ese striking fracture formed due to unloading during exhumation fracture fill textures suggest that many fracture apertures increased during exhumation the relative abundances of the four fracture sets and the intensity of each set vary from bed to bed in cross section because beds display no significant differences in mechanical strength and there is no correlation between bed thickness and fracture intensity we attribute this bed to bed variability to differences in cohesion between beds bed decoupling when combined with low extensional

upper mantle discontinuity topography from thermal and chemical heterogeneity using high resolution stacks of precursors to the seismic phase ss we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers km deep within earth beneath south america and the surrounding oceans detailed maps of phase boundary topography revealed deep 410 and 660 km discontinuities in the down dip direction of subduction inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature in some regions multiple reflections from the discontinuities were detected consistent with partial melt near 410 km depth and or additional phase changes near 660 km depth thus the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

uplift unbuckling and collapse flexural history and isostasy of the wind river range and granite mountains wyoming two dimensional gravity and flexural models constrain the structure and isostatic compensation of the wind river range and granite mountains wyoming these ranges are asymmetric basement cored laramide uplifts their large positive isostatic gravity anomalies imply that the topography of the uplifts is not locally compensated for the wind river range gravity data are consistent with thrusting along a listric fault which flattens and soles out at 30 km depth with no detectable offset on the moho we model the large bouguer gravity high over the range with high density lower crustal rocks emplaced over lower density middle crustal rocks along the wind river thrust the high positive gravity anomaly over the granite mountains can be modeled as an extension of the south pass greenstone belt from the southern wind river range eastward beneath the emigrant trail thrust a crustal root as required in local airy compensation for either range requires unreasonably high density material in the upper crust to obtain the observed anomaly combined gravity and flexural models show that a flexural rigidity at least 2 55 1022 n m maximum deflection of 2 km of the moho is required to satisfy the gravity data our results are consistent with models of uplift due to horizontal compression and support of the resulting topography by lithospheric strength an otherwise puzzling episode of oligocene uplift of the wind river range can be explained as unbuckling decrease of deflection of lithosphere accompanying release of laramide compressional stresses flexurally supported uplifts will collapse if the lithosphere is weakened a number of laramide uplifts have collapsed primarily east west trending structures such as the granite mountains the southern end of the wind river range and the uinta mountains we propose that collapse has occurred along zones of established weakness in the crust in response to north south extension

early basin and range development in trans pecos texas and adjacent chihuahua magmatism and orientation timing and style of extension magmatism during early basin and range extension in trans pecos texas consisted of widespread but volumetrically minor alkali basalts 24 17 ma an alkalic mafic to intermediate composition stratovolcano 28 27 ma and a dominantly rhyolitic possibly bimodal caldera complex in adjacent chihuahua 31 28 ma this magmatism contrasted sharply with the much more voluminous and compositionally more diverse eocene oligocene magmatism the age and orientation of dikes emplaced during this magmatic episode have been used to determine the orientation of least principal stress 3 an ene orientation of 3 similar to early extension throughout the basin and range province can be well documented by 28 ma and possibly as early as 31 ma faulting consisting almost exclusively of movement along high angle normal faults was underway by 23 ma some initial extension was taken up along preexisting wnw trending structures oblique to ene oriented 3 the least principal stress probably changed to wnw as it did elsewhere in the basin and range province but the timing of this change is not well constrained in texas ene and ne striking silver copper lead veins in precambrian and cretaceous red beds may have formed during the later basin and range extension the present basin and range topography of this region is the result of movement along high angle and dominantly nnw trending faults established early under 3 oriented ene and reactivated after 3 changed to wnw

sensitivity analysis of seismic waveforms to upper mantle discontinuities using the adjoint method using spectral element simulations of wave propagation we investigated the sensitivity of seismic waveforms recorded on transverse components to upper mantle discontinuities in 1 d and 3 d background models these sensitivity kernels or frechet derivatives illustrate the spatial sensitivity to model parameters of which those for shear wave speed and the surface topography of internal boundaries are discussed in this paper we focus on the boundaries at 400 and 670 km depth of the mantle transition zone ss precursors have frequently been used to infer the topography of upper mantle discontinuities these seismic phases are underside reflections off these boundaries and are usually analysed in the distance range of 110 160 this distance range is chosen to minimize the interference from other waves we show sensitivity kernels for consecutive time windows at three characteristic epicentral distances within the 110 160 range the sensitivity kernels are computed with the adjoint method using synthetic data from our simulations we can draw three main conclusions i the exact frechet derivatives show that in all time windows and also in those centred on the ss precursors there is interference from other waves this explains the difficulty reported in the literature to correct for 3 d shear wave speed perturbations even if the 3 d structure is perfectly known ii all studies attempting to map the topography of the 400 and 670 km discontinuities to date assume that the traveltimes of ss precursors can be linearly decomposed into a 3 d elastic structure and a topography part we recently showed that such a linear decomposition is not possible for ss precursors and the sensitivity kernels presented in this paper explain why iii in agreement with previous work we show that other parts of the seismograms have greater sensitivity to upper mantle discontinuities than ss precursors especially multiply bouncing s waves exploiting the s wave triplications due to the mantle transition zone these phases can potentially improve the inference of global topographic variations of the upper mantle discontinuities in the context of full waveform inversion in a joint inversion for an elastic parameters and topography

stress orientations during oligocene volcanism in trans pecos texas timing the transition from laramide compression to basin and range tension orientations of dikes and hydrothermal veins indicate that east northeast compression occurred during the main pulse of volcanism in west texas 39 to 32 m y ago direction of compression was essentially the same as that during eocene laramide deformation the observations support a continental arc tectonic setting the beginning of extension between 32 and 30 m y ago coincides with a regional change in style of magmatism from intrusions and eruptions spanning a wide range in chemical composition to basaltic volcanism in texas and to bimodal but dominantly rhyolitic volcanism in northern mexico

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

reconciling pp and p p precursor observations of a complex 660 km seismic discontinuity high frequency precursors to p p almost invariably observe a narrow 660 km discontinuity whereas pp precursor studies at long periods struggle to detect a reflection from the 660 despite its apparent sharpness to p p to investigate these contradictory observations we compare pp and p p precursors in the same region using short period p p precursors we observe a sharp 660 km discontinuity which appears to vary in depth substantially the apparent topography on the 660 is too large to originate solely from thermal variations regardless of its cause therefore indicating chemical variations at the base of the mantle transition zone long period p p precursors show no 660 as they are sensitive to a larger area and thus average out the apparent topography in agreement with long period pp precursors instead we see some evidence in both long period data types for a reflection from 720 km depth which is likely to correspond to a phase change in the garnet system

waveform inversion of ss precursors an investigation of the northwestern pacific subduction zones and intraplate volcanoes in china abstract the arrival time and amplitude of underside reflections from mantle seismic discontinuities ss precursors have made major contributions to the understanding of mantle composition and dynamics in this study we introduce a nonlinear waveform inversion technique to simultaneously constrain shear velocities and discontinuity depths beneath the northwestern pacific subduction system based exclusively on a large ss precursor waveform dataset we are able to clearly delineate the morphology of the descending pacific plate which flattens at the base of the upper mantle and extends westward by 1500 km toward northern central china our grid search yields the maximum correlation between shear velocity and transition zone thickness at an angle of 30 consistent with the reported average slab dip beneath the study region the strongly positive correlation suggests predominantly thermal rather than compositional variations along the descending pacific plate the joint depth velocity solution also shows a 5 10 km depression of the 410 km discontinuity and an average decrease of 1 2 in upper mantle shear velocity beneath the intraplate volcanic fields in northeastern china this anomaly which reaches the middle of the upper mantle transition zone beneath the changbai hotspot initiates at a significantly shallower 320 km depth beneath the wudalianchi region high amplitude reflections at depths greater than 410 km suggest a water poor melt layer in possible association with 1 decompression melting from passive upwelling and or 2 active upwelling through a slab window

the volcanic section at nazas durango mexico and the possibility of widespread eocene volcanism within the sierra madre occidental descriptions of volcanic rocks in the sierra madre occidental of western mexico have thus far emphasized the widespread and nearly continuous cover of ash flow tuffs and other units attributed to the oligocene ignimbrite flare up however much less attention has been given to the pre oligocene volcanic sequence beneath this ash flow blanket at nazas durango on the eastern flank of the sierra madre occidental a well exposed section includes voluminous felsic volcanic rocks of both eocene and oligocene age the oldest igneous rocks at nazas include a small exposure of intermediate volcanic breccias and lava flows that overlie cretaceous limestones and apparently were deformed with them during laramide tectonism more commonly the limestones are overlain by tertiary volcanic rocks and continental clastic deposits the tertiary volcanic section is about 800 m thick not including intercalated fanglomerates the section records three distinct magmatic episodes from 51 to 40 ma comprising felsic ash flow tuffs and intermediate lava flows and domes a pulse at about 30 ma comprising voluminous felsic ash flow tuffs with an aggregate thickness of about 500 m and from 24 to 20 ma comprising alkalic basalts the ahuichila formation a molasse type conglomerate up to 200 m thick that underlies the tertiary volcanic section was deposited during or just after the laramide deformation the santa ines formation is a widespread fanglomerate up to 110 m thick that underlies the basalts and apparently accumulated during normal faulting eocene volcanism in the nazas area is characterized by interfingering felsic ash flow tuffs and intermediate lava flows and domes a similar sequence of eocene volcanic rocks has been mapped in central chihuahua state about 350 km to the northwest of nazas felsic tuffs interbedded with intermediate volcanic rocks older than 40 ma are also exposed at tayoltita durango about 200 km southwest of nazas these occurrences suggest that a wider spectrum of compositions and volcanic styles existed during the eocene than during the oligocene in the sierra madre occidental eocene volcanism was more typical of orogenic magmatic belts developed at continental margins whereas the oligocene activity was dominated by voluminous felsic ash flow tuffs erupted during a transition of tectonic setting from subduction along a continental margin to intraplate extension in addition to these three areas there are several other localities in western mexico having volcanic rocks with reported ages between 40 and 53 ma it is possible that the volcanic field during the eocene in mexico was comparable in extent to that of the oligocene the eocene volcanism in western mexico was in part contemporaneous with the challis volcanic episode of northwestern united states and its extension into western canada however eocene magmatism in the pacific northwest apparently developed in an extensional tectonic setting whereas in mexico no evidence for eocene extensional deformation is known

structural and biological control of the cenozoic epithermal uranium concentrations from the sierra pena blanca mexico epithermal uranium deposits of the sierra pena blanca are classic examples of volcanic hosted deposits and have been used as natural analogs for radionuclide migra tion in volcanic settings we present a new genetic model that incorporates both geochemical and tectonic features of these deposits including one of the few documented cases of a geochemical signature of biogenic reducing conditions favoring uranium mineralization in an epithermal deposit four tectono magmatic faulting events affected the volcanic pile uranium occurrences are associated with breccia zones at the intersection of fault systems periodic reactivation of these structures associated with basin and range and rio grande tectonic events resulted in the mobilization of u and other elements by meteoric fluids heated by geothermal activity focused along breccia zones these fluids precipi tated under reducing conditions several generations of pyrite and uraninite together with kaolinite oxygen isotopic data indicate a low formation temperature of uraninite 45 55 c for the uraninite from the ore body and 20 c for late uraninite hosted by the underlying conglomerate there is geochemical evidence for biological activity being at the origin of these reducing conditions as shown by low 34 s values 24 5 in pyrites and the presence of low 13 c 24 values in microbial patches intimately associated with uraninite these data show that tectonic activity cou pled with microbial activity can play a major role in the formation of epithermal uranium deposits in unusual near surface environments

topography of the 410 km and 660 km discontinuities beneath the japan sea and adjacent regions by analysis of multiple scs waves the northwest pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities due to the sparse distribution of seismic stations in the sea previous studies mostly focus on mantle transition zone mtz structures beneath continents or island arcs leaving the vast area of the japan sea and okhotsk sea untouched in this study we analyzed multiple scs reverberation waves and a common reflection point stacking technique was applied to enhance consistent signals beneath reflection points a topographic image of the 410 km and 660 km discontinuities is obtained beneath the japan sea and adjacent regions one dimensional and 3 d velocity models are adapted to obtain the apparent and true depth we observe a systematic pattern of depression 10 20 km and elevation 5 10 km of the 660 with the topography being roughly consistent with the shift of the olivine phase transition boundary caused by the subducting pacific plate the behavior of the 410 is more complex it is generally 5 15 km shallower at the location where the slab penetrates and deepened by 5 10 km oceanward of the slab where a low velocity anomaly is observed in tomography images moreover we observe a wide distribution of depressed 410 beneath the southern okhotsk sea and western japan sea the hydrous wadsleyite boundary caused by the high water content at the top of the mtz could explain the depression the long history trench rollback motion of pacific slab might be responsible for the widely distributed depression of the 410 ranging upward and landward from the slab

seismic shear wave reflectivity structure of the mantle beneath northeast china and the northwest pacific 1 using multiple scs reverberations we examine the mantle reflectivity structure beneath northeast china and the northwest pacific we find several upper mantle discontinuities including a melt layer with a mean thickness of 64 km atop the 410 km discontinuity present on both sides of the subducting slab near the nankai trench the transition zone contains a split 520 km discontinuity in several paths and tomographic images show stagnant slabs at this depth we believe that this may be slab related based on experimental work a negative reflector is found in one path beneath the northeast china craton at a depth of 598 km mid mantle reflectors are found in all of our paths and are present throughout a wide depth range 750 1600 km

dike swarms on seward peninsula alaska and their implications for the kinematics of cretaceous extension in the bering strait region late cretaceous dike swarms on seward peninsula northwestern alaska represent the youngest local manifestation of a 115 75 ma magmatic event in the bering strait region magmatism accompanied and followed high grade metamorphism and ductile deformation a late cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic reflection characteristics of the crust regional basin development formation of high strain tectonites with subhorizontal foliations bimodal magmatism and dike swarms the orientation of the dike swarms is used to address the kinematics of extension a diabase dike swarm in the kigluaik mountains consists of dikes that strike northeast 040 and dip steeply phenocrysts include plagioclase clinopyroxene orthopyroxene and hornblende geochemical data indicate that sio2 ranges from 48 to 56 and k2o from 1 2 to 4 0 the dikes are geochemically similar to the mafic to intermediate root of the 90 ma kigluaik pluton sr and nd isotope data show that initial 87 sr 86 sr ranges from 0 7070 to 0 7077 and initial end ranges from 0 85 to 2 90 field relations and 40 ar 39 ar geochronology bracket the dike ages between 90 and 84 ma diabase dikes in the york mountains are associated with normal faults that strike east west to east northeast dikes in the bendeleben mountains are both mafic and felsic but their orientations are unknown alkalic dikes in the darby mountains strike 030 050 similar to those in the kigluaik mountains regional relationships including the orientation of dikes normal faults mineral stretching lineations and other shear sense indicators suggest that between 110 and 90 ma extension on seward peninsula was generally oriented north south to north northwest south southeast

faulting within the eastern baikal rift as characterized by earthquake studies earthquake relocations focal mechanism determinations waveform modeling and stress analyses using focal mechanism information are used to examine the faulting processes within the western baikal rift 95 to 108 5 results of the study show that high angle dip 70 faulting is most likely to occur in the more youthful parts of the rift and is most likely to be associated with m 4 5 events like the eastern rift nearly all earthquakes occurred on faults dipping 30 suggesting that in no part of the rift is significant deformation occurring on low angle structures focal mechanism information does not indicate there is a sharp boundary to the western rift as observed in the eastern rift less normal faulting rakes 60 to 120 occurs in the western rift than the eastern rift waveform modeling of the two largest earthquakes 1950 mondy and 1959 srednebaikal in the western rift gives focal depths of 10 to 15 km the 1959 event appears to have occurred along the eastern boundary fault on lake baikal just to the north of proval bay a feature created a m 7 1 earthquake in 1862 the 1950 event may have occurred along the southern boundary fault of the tunka depression stress orientation information indicates a near horizontal nw se to wnw ese striking 3 in the eastern part of the western rift

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

receiver functions in northeast china implications for slab penetration into the lower mantle in northwest pacific subduction zone abstract seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest pacific subduction zone beneath japan and northeast china have suggested contrary subduction scenarios there was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660 km discontinuity over several hundred kilometers we calculate receiver functions from a recent seismic broadband station network located in northeast china and find topographic variations of the upper mantle discontinuities a deeper than normal 660 km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography the 660 km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab these observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle

the magnitude distribution of earthquakes near southern california faults we investigate seismicity near faults in the southern california earthquake center community fault model we search for anomalously large events that might be signs of a characteristic earthquake distribution we find that seismicity near major fault zones in southern california is well modeled by a gutenberg richter distribution with no evidence of characteristic earthquakes within the resolution limits of the modern instrumental catalog however the b value of the locally observed magnitude distribution is found to depend on distance to the nearest mapped fault segment which suggests that earthquakes nucleating near major faults are likely to have larger magnitudes relative to earthquakes nucleating far from major faults

lithospheric stress and deformation the study of the mechanisms magnitudes and modes of lithospheric stress and deformation occupies a central position in the discipline of tectonophysics it is therefore difficult in assembling a comprehensive review to place limits on what should be included for example one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors once admitting to the importance of rheological considerations in discussing stress and deformation one is then compelled to include information relating to the thermal state of the lithosphere since temperature is one of the foremost environmental variables controlling rheology furthermore lithospheric processes cannot be considered in isolation from those affecting the asthenosphere since surely there exists some coupling between the motion of the lithosphere and convection in the earth s interior in fact an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth the topic of this report cannot even be cleanly separated from reviews in other disciplines such as seismology and geodesy the magnitude and orientation of lithospheric stress is often indicated by earthquakes while lithospheric strain can be observed geodetically the philosophy i have adopted here is that some overlap with other review papers in this series is unavoidable and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere s state of stress and mechanisms of deformation i have however resisted the temptation to include extraterrestrial studies presumably covered in the planetary section despite the similar causes for deviatoric stress and deformational mechanisms operating on other terrestrial planets certainly ideas of how silicate materials behave and how lithosphere responds to internal forces benefit from the perspective of omparative planetology finally in defining the scope of this portion of the u s national report to the iugg i did not consciously exclude papers by non u s citizens work done at non u s institutions projects not funded by the u s government or however else foreign might be defined topics in geophysical research cannot be divided along political boundaries however i did not attempt to seek out articles written in languages other than english or published in journals not readily available in the united states and i apologise for this obvious shortcoming

dead horse graben a west texas accommodation zone the cretaceous rocks of the dead horse graben area underwent two superposed deformations laramide latest cretaceous to early tertiary left transpression structures are overprinted by a basin and range miocene to recent accommodation zone during laramide shortening two northwest trending sets of monoclines developed an en echelon set over a left slip basement fault and a single monocline draped over the uplifted edge of a rotated basement block basin and range extension caused northerly trending half grabens that have opposing asymmetry downthrown to the east north of the study area and downthrown to the west south of the area these half grabens are separated by an accommodation zone expressed as a northwest trending right lateral pull apart graben the normal faults of the pull apart graben flatten at a shallower depth than those of the half grabens this suggests not only that accommodation zones can be mechanically layered but that this layering can occur on a scale different from the adjacent half grabens the northwest trend and superposition of both sets of structures implies a tectonic control by the preexisting structural fabric of the texas lineament

gross errors in upper mantle discontinuity topography from underside reflection data summary currnet models of upper mantle discontinuity topography derived from traveltime variations of long period underside reflections pdp or sds waves may contain gross errors due to the use of geometrical optics in relating observed traveltimes to depth variations of the discontinuity near the reflection point the use of geometrical optics is not valid if variations in the depth of the discontinuities exist on a lateral scale smaller than the size of the fresnel zone in the data geometrical optics does not take into account the large size and the complex structure of the traveltime surface of underside reflections and may introduce spurious structure when used in inversions examples of synthetic long period pdp waveforms for reflections near subducting lithosphere show that scattering from expected small scale depth variations of the discontinuities inside slabs causes complex waveform variations for a 15 20s pdp wave these small scale depth variations with a scale length of 4 are smaller than the fresnel zone roughly 20 but larger than the pdp wavelength at 420 km depth about 150 200 km the synthetic waveforms are processed to obtain pdp traveltimes which are in turn converted to apparent discontinuity depth at the reflection point using geometrical optics the apparent discontinuity depth variations are not only of the same order of magnitude as those obtained from real data but also exhibit artefacts that closely resemble features observed in current models it is shown that large scale wavelengths of the order of 1000 km downwarping of the 670 km discontinuity near subduction zones derived from underside reflection data can be explained as the long wavelength manifestation of a single small scale wavelengths of several hundreds of kilometres deflection of the discontinuity inside and near subducting slabs

synchronous seismicity changes in and around the northern japan preceding the 2003 tokachi oki earthquake of m8 0 1 the epidemic type aftershock sequence etas model predicts the normal seismic rate that superposes the empirical laws of decreasing aftershock activity anomalies lowering and enhancement of the seismic rate from the rate predicted by the etas model are found to have occurred concurrently during 1996 in three interplate aftershock sequences and in inland intraplate seismicity in and around northern japan each anomaly is explained by change in coulomb failure stress caused by aseismic slip that is assumed to have occurred on the plate interface of the 2003 tokachi oki rupture of m8 0 the slip is also supported by a significant change in the distribution of fault mechanisms of moderate earthquakes before and after 1996 in northern japan using the occurrence data of strong earthquakes of m5 0 or larger for the long period 1926 2003 a similar relative quiescence lasting about 10 years is indicated not only preceding the recent 2003 earthquake but also preceding the 1952 and 1968 great tokachi oki earthquakes