seismic evidence for reactivation of a buried hydrated fault in the pacific slab by the 2011 m9 0 tohoku earthquake 1 we employ seismic tomography to estimate detailed 3d seismic velocity structures in the focal area of an intraslab earthquake m7 1 which occurred on april 7 1 month after the 2011 tohoku earthquake m9 0 near its source area the results show a low velocity zone around the focal area of the m7 1 event and that the aftershock activity is limited to the upper 15 km of the oceanic mantle the lateral extent of the low velocity zone is comparable to the distribution of aftershocks suggesting a concentration of fluids in the aftershock area the angle between the aftershock alignment and the dip of the slab surface is estimated to be 60 which is consistent with the dip of an oceanward dipping normal fault observed at the outer trench slope these observations suggest that the m7 1 intraslab event occurred as a result of reactivation of a buried hydrated fault that formed prior to subduction the upper 15 km of the oceanic mantle may be locally hydrated by bending related tensional faulting at the outer trench slope

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

characterization of the natural fracture system of the eagle ford formation val verde county texas the eagle ford formation has attracted considerable industry attention as a self sourced unconventional shale reservoir the productive interval in the eagle ford formation is the transgressive systems tract which contains parasequences whose lithologic content varies upward with increasing proportions of limestones optimum success in both exploration and production depends on the adequate characterization of fracture systems as a function of lithology the outcrops present along us highway 90 in val verde and terrell counties texas provide considerable insight into the regional natural fracture system of the eagle ford formation fracture orientation analysis reveals two sets of conjugate hybrid shear fractures and two sets of regional fractures abutting relationships suggest that hybrid shear fractures formed first followed by the thoroughgoing northeast striking fracture set and finally by a northwest striking set which tends to be confined to individual mechanical units the orientation of these fractures suggests that they formed during post laramide stress relaxation and progressive exhumation spacing frequency distribution analysis of the fracture population reveals a mature hypersaturated fracture system that likely formed at depth by overburden load and or fluid pressure near maximum burial our results indicate that the eagle ford formation displays a well developed fracture network regionally distributed in the val verde basin and likely present in the productive eagle ford play these observations provide evidence for pathways and vertical connectivity for potential fluid pathways throughout the eagle ford formation

normal faulting earthquakes beneath the outer slope of the japan trench after the 2011 tohoku earthquake implications for the stress regime in the incoming pacific plate 1 after the 2011 mw 9 1 tohoku earthquake numerous intraplate earthquakes occurred beneath the outer slope of the japan trench based on ocean bottom seismograph observations these earthquakes occurred in the oceanic crust and uppermost mantle of the pacific plate at depths shallower than about 40 km and had normal faulting focal mechanisms at all depths before the 2011 earthquake normal faulting earthquakes beneath the outer trench slope occurred only at depths shallower than 20 km whereas those at depths of around 40 km had reverse faulting mechanisms these observations suggest that the stress regime in the pacific plate was changed by the 2011 earthquake the tensional stresses that now extend to depths of about 40 km may play an important role not only in the occurrence of large normal faulting earthquakes but also in hydration of the uppermost mantle of the incoming pacific plate prior to the subduction

geomechanical modeling of hydraulic fracturing why mechanical stratigraphy stress state and pre existing structure matter the increasing exploration and production in unconventional resource plays in the past decade has been accompanied by a greater need for understanding the effectiveness of multistage hydraulic fracturing programs particularly in long 1500 m or 5000 ft subhorizontal boreholes laterals traditional analytical analysis techniques for estimating the size and orientation of fractures induced by fluid injection typically result in predictions of relatively long and planar extension mode i bi wing fractures which may not be representative of natural systems although these traditional approaches offer the advantage of rapid analysis neglect of key features of the natural system e g realistic mechanical stratigraphy pre existing natural faults and fractures and heterogeneity of in situ stresses may render results unrealistic for planning executing and interpreting multimillion dollar hydraulic stimulation programs numerical geomechanical modeling provides a means of including key aspects of natural complexity in simulations of hydraulic fracturing in this study we present the results of two dimensional finite element modeling of fluid injection induced rock deformation that combines a coupled stress pore pressure analysis with a continuum damage mechanics based constitutive relationship the models include both the natural mechanical stratigraphic variability as well as the in situ stress state anisotropy and permit tracking of the temporal and spatial development of shear and tensile permanent strains that develop in response to fluid injection our results show that simple long planar fractures are unlikely to be induced in most mechanically layered natural systems under typical in situ stress conditions analyses that assume this type of fracture geometry may significantly overestimate the reach of hydraulically induced fractures and or effectively stimulated rock volume

orbicular oxides in carbonatitic kimberlites a renewed interest in mineral spheres that exhibit oscillatory layering is assured with the spectacular discovery of hematite beads in meridiani planum mars the martian blueberries are variously interpreted as sedimentary concretions impact spherules or accretionary lapilli we draw attention to a possible alternative that the spheres of oxides are of igneous origin in carbonate rich upper mantle systems two spherical oxide assemblages from cabonatitic kimberlites in the central namibia formerly south west africa volcanic field show similarities and contrasts to orbicular structures in carbonatites from uganda south africa germany finland and russia structures have rapakivi appearances that bear upon the controversial issue of a relation between kimberlites and carbonatites the first example is from a carbonatitic kimberlite adjacent to the mukorob kimberlite sesu stricto oblate spheroidal nuggets 2 1 5 0 5 cm have olivine now serpentine calcite cores with concentrically layered bands of ilmenite calcite and pedestals of ilmenite ilm 55 geik 40 hem 5 with intergranular calcite the spheres are matrix supported in massive ferroan calcite serpentine with minor apatite f 1 5 wt and barite the matrix contains xenocrystic mg al chromite 55 wt cr 2 o 3 mantled by ilmenite ilm 51 geik 43 hem 6 but the dominant groundmass oxide mineral is mg al ti mat magnetite the second example is from the carbonatite facies of the hatzium kimberlite and is also in a dike mat magnetite pellets 2 3 cm have alternating wide 1 mm and thin 0 25 mm bands of magnetite nucleated on a complex mixture of calcite feo 0 1 wt and serpentine 4 wt feo 0 5 1 wt al 2 o 3 the matrix assemblage of serpentine calcite mat magnetite has mineral compositions similar to the spheroids but is distinguished by abundant ba phlogopite and lesser apatite f 2 wt phlogopite is strongly zoned in patches and bands is kink banded and contains inclusions of mat magnetite calcite the assemblage is typical of phoscorites also known as camaforites in other carbonatites but the ilmenite spheroids appear to be restricted to mukorob our interpretation is that both types result from the nucleation of immiscible liquids a high density and high viscosity ore carbonate silicate component in a low viscosity phosphoric carbonatite melt on olivine or olivine magnetite assisted by frothing and slow degassing on decompression and dike intrusion

evaluation of tsunami risk from regional earthquakes at pisco peru we evaluate tsunami risk for the port city of pisco peru where major liquefied natural gas facilities are planned we use a compilation of instrumental and historical seismicity data to quantify the sources of six earthquakes that generated tsunamis resulting in minor inundation 1974 to catastrophic destruction 1687 1746 1868 in pisco for each of these case scenarios the seismic models are validated through hydrodynamic simulations using the most code which compute both flow depth on virtual offshore gauges located in pisco harbor and the distribution of runup in the port and along the nearby beach space time histories of major earthquakes along central and southern peru are used to estimate recurrence times of tsunamigenic earthquakes we conclude that pisco can expect a metric tsunami capable of inflicting substantial damage every 53 years and a dekametric tsunami resulting in catastrophic destruction of infrastructures every 140 years the last such event occurred 138 years ago an important result of our study is that total destruction of the city of pisco during the famous 1868 arica tsunami requires an earthquake rupture straddling the nazca ridge which thus constitutes at best an imperfect barrier for the propagation of rupture during megathrust events this gives a truly gigantic size to the 1868 arica earthquake with a probable seismic moment reaching 1030 dyne cm

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

pre and post seismic slow slip on the plate boundary off sanriku ne japan associated with three interplate earthquakes as estimated from small repeating earthquake data abstract the spatio temporal variation of quasi static slow slip on the plate boundary before and after three major earthquakes mj 7 1 in 1989 mj 6 9 in 1992 and mj 7 6 in 1994 off sanriku northeastern japan is estimated using small repeating earthquake data the small repeating earthquake sequence employed is considered to correspond to repeated rupture of a small isolated asperity surrounded by a quasi static slipping area and the activity of the source reflects the quasi static slip rate small repeating earthquakes accompanying moderate sized events appear to have been activated prior to the major events under investigation with activity starting 6 days 2 days and 8 months before the occurrence of the 1989 1992 and 1994 events these results indicate that the quasi static slip near the hypocenters of these major earthquakes was accelerated prior to the main shocks causing stress concentration at the asperities responsible for the main shocks this idea is supported by the fact that both the epicenters locations of initial breaks and areas where quasi static slip was accelerated were located on the same side of the main shock asperities migration of quasi static slip acceleration in the off sanriku region was also identified apparent in the aftershock activity of the 1994 event and the earthquake swarms including the 1989 mj 7 1 and 1992 mj 6 9 events the present results reveal that quasi static slip may have played a crucial role in the occurrence of these large earthquakes as well as contributing to aftershock and swarm activity on the plate boundary

sediment effect on tsunami generation of the 1896 sanriku tsunami earthquake the 1896 sanriku earthquake was one of the most devastating tsunami earthquakes which generated an anomalously larger tsunami than expected from its seismic waves previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis it was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift in this paper the effect of the additional uplift to tsunami generation of the 1896 sanriku tsunami earthquake is quantified we estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges the estimated slip for the model without the additional uplift is 10 4 m and those with the additional uplift are 5 9 6 7 m this indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation

thermal state under the tohoko arc with consideration of crustal heat generation abstract the thermal structure beneath subduction zones plays a key role in aiding understanding of tectonic activities such as seismicity volcanism arc formation and genesis of back arc basins around subduction zones many simulations have been made to estimate the thermal process in the mantle wedge which causes the surface activities in the tohoku arc many heat flow measurements have been made and the heat flow profile from the trench to the back arc has been constructed in this study the thermal structure in the crust of northeast japan is investigated to account for the surface heat flow data to estimate the contribution of the heat generation in the crust to the surface heat flow the heat production rate was obtained on granitic and metamorphic rocks collected from the hidaka metamorphic zone hokkaido japan where the vertical crustal section of an island arc is understood to be exposed at the surface instrumentation neutron activation analysis and gamma ray spectrometry were adopted to analyze the concentration of heat producing elements the obtained rate of heat generation and its decrease with increasing depth for the upper part of the crust were found to be similar to those estimated for stable continental areas but the heat generation rate was almost constant in the lower part of the crust the vertical distribution of the heat production rate in the crust of the northeastern japan arc was estimated from the present results and previous estimates of heat production rates in various rocks using the crustal structure determined by explosion seismology the total heat generation in the crust thus estimated is about 30 mw m 2 with the surface heat flow data and estimated heat generation distribution in the crust the thermal structure in the crust was simulated numerically modeling calculations were made on a cross section along the line from the japan trench to the japan sea a direction parallel to the direction of convergence of the pacific and eurasian plates the models were two dimensional and included frictional heating at the upper surface of the slab the calculated thermal structure in the crust shows that the temperature at the moho is about 850 c and almost about 250 c lower than previous estimates the magnitude of the interplate stress was derived by considering the rate of frictional heating at the interface between the plates in order to explain the surface heat flow between the trench and aseismic front the interplate stress should be less than 20 mpa at depth in the crust

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

a seismicity gap beneath the inner wall of the japan trench as derived by ocean bottom seismograph measurement abstract an ocean bottom seismograph obs array covered the area of the japan trench about 40 n off the tohoku district of northeastern honshu japan the obs array was operated for two weeks in june 1981 arrival time data of 8 obss were used to study a spatial distribution of microearthquakes around the trench during the observation period 400 500 events with a signal to noise ratio greater than 2 were detected by each obs the arrival times of 223 of these events could be picked 38 earthquakes were located in the area of the japan trench within the latitude range of 38 5 41 0 n and the longitude range of 142 0 146 0 e and about a hundred events were located beneath or near honshu island s p time distribution recorded by each obs showed seismic activities to exist on both sides of the trench axis while the seismic level was low beneath the inner wall of the trench epicentral distribution showed a seismicity gap beneath the inner wall of the trench the area of the landward activity continued eastward up to the position where the water depth is about 4000 m seismic activity existed beneath the trench axis and the seaward wall of the trench the seismicity gap suggested from the 1980 obs observations in the vicinity of the present study area was clearly confirmed by the present observations the obs array enabled us to determine the focal depth of microearthquake activity with better resolution than was possible from land observations the obs data showed that the landward activity beneath the continental slope was concentrated in the very shallow part of the lithosphere at a depth less than 30 km foci started to deepen westward with a very low dip angle of less than 10 which was the most shallow part of the upper plane of the double seismic zone the focal depth distribution showed that events just beneath the trench axis occurred to depths slightly greater than 50 km while the foci of the seaward activity were concentrated in the uppermost lithosphere at depths less than 30 km seismic cross sections clearly show that the activity beneath the trench axis and seaward wall of the trench is separated from the landward activity which is a shallow extension of the double seismic zone by the seismicity gap

aftershocks near the updip end of the 2011 tohoku oki earthquake abstract the march 2011 m w 9 0 tohoku oki earthquake activated shallow aftershocks with normal faulting focal mechanisms near the trench axis to investigate stress state in the shallow subduction zone near the trench axis we used ocean bottom seismographs obss to record earthquakes from august to october 2011 we estimated hypocenter locations and focal mechanisms of the recorded earthquakes by using a grid search method in a 2 d velocity model based on an active seismic survey the results show that most of the earthquakes occurred within both the overriding and subducting plates with very few on the plate interface and none in the most seaward 45 km of the overriding plate aseismic wedge the low seismicity along the plate interface is consistent with the nearly complete stress drop on the megathrust fault in the m w 9 0 earthquake focal mechanisms indicate that trench normal tension is pre dominant in both plates and extends to a depth of about 30 km at least on the other hand several trench normal compressional earthquakes were located at the landward end of the aseismic wedge these earthquakes suggest horizontal compression of the overriding prism that may be caused by a strengthening of the shallowest part of the megathrust

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

characterization and tectonic evolution of a mesoproterozoic island arc in the southern grenville orogen llano uplift central texas abstract integrated field and u pb geochronologic data document the presence and tectonic evolution of a distinct lithotectonic terrane in the southeastern llano uplift here termed the coal creek domain ccd the ccd consists of tonalitic and amphibolitic gneisses foliated gabbroic tonalitic and granodioritic intrusions and the structurally emplaced coal creek serpentinite the oldest rocks in the ccd consist of tonalitic gneisses with protolith crystallization ages of 1326 ma and 1301 ma and pre 1292 ma amphibolitic gneisses all ages are u pb zircon they were intruded by dominantly mafic and intermediate with subordinate amounts of felsic low k plutonic rocks between 1286 ma and 1275 ma high temperature metamorphism and local anatexis that resulted in the formation of gneisses and migmatites occurred between 1301 ma and 1286 ma and is suggested to have occurred at 1292 ma metamorphism at 1256 ma resulted in the growth of zircons in mafic rocks the regional significance of this metamorphic event is unclear but it may be related to dynamothermal metamorphism of the ccd the contemporaneous emplacement of low k gabbro tonalite and granodiorite and their spatial association with serpentinite combined with published geochemical data strongly suggest that the ccd represents an ensimatic arc the coal creek serpentinite is interpreted as a fragment of oceanic crust that formed either basement to the arc or in a related back arc or intra arc setting combined field u pb geochronologic isotopic and geochemical data indicate that the magmatic metamorphic and structural history of the ccd differs from that of coeval rocks elsewhere in the llano uplift the boundary between the ccd and deformed and metamorphosed granitic and supracrustal rocks to the north is a zone of intense mylonitization and polyphase deformation this zone is interpreted as the structural boundary between the arc terrane and units to the north

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

fault parameters of the 1896 sanriku tsunami earthquake estimated from tsunami numerical modeling the june 15 1896 sanriku earthquake generated devastating tsunamis with the maximum run up of 25 m and caused the worst tsunami disaster in the history of japan despite its moderate surface wave magnitude ms 7 2 and weak seismic intensity this is a typical tsunami earthquake which generates anomalously larger tsunamis than expected from its seismic waves previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments in this paper we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in japan the result indicates that the tsunami source is very close to the japan trench and the fault strike is parallel to the trench axis the fault width is about 50 km suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge

faulting and fracturing in shale and self sourced reservoirs introduction production from self sourced reservoirs relies on natural and induced fracturing for permeability and conductance of hydrocarbons to the producing wellbores thus natural or induced fracturing is often a key to success in unconventional reservoir plays on the other hand fractures may compromise seals and large or well connected fractures or faults may cause undesirable complications for unconventional reservoirs natural and induced fractures are influenced by 1 mechanical stratigraphy 2 pre existing natural deformation such as faults fractures and folds and 3 in situ stress conditions both natural and as modified by stimulation and pressure depletion this special issue of the aapg bulletin elucidates some of these structural geologic and geomechanical controls understanding the occurrence and controls on natural and induced faulting and fracturing in self sourced reservoirs is a key component for developing effective approaches for exploiting self sourced reservoirs

high resolution seismic imaging in the japan trench axis area off miyagi northeastern japan 1 newly obtained high resolution seismic data reveal the detailed structure of the japan trench axis off miyagi japan in the region of large shallow slip during the 11 march 2011 m9 tohoku earthquake correlation of seismic images with previous drilling results identifies a possible basal chert rich layer and hemipelagic pelagic mudstones overlying igneous pacific crust mapping of acoustic basement depicts the subduction of horst and graben topography the basement and basal chert are subducted beneath a seismically chaotic frontal prism but the majority of overlying hemipelagic mudstones is offscraped and imbricated at the trench axis as a result of plate boundary compression a possible decollement is imaged as a seaward dipping reflection at landward part of the trench graben and was likely generated by loading and failure of underthrust sediments collectively these analyses provide a structural framework for understanding sedimentary inputs and the localization of shallow plate boundary slip at the japan trench

interplate seismic activity near the northern japan trench deduced from ocean bottom and land based seismic observations the off sanriku area the landward slope area of the northern japan trench is characterized by its active seismicity which is directly related to the subduction process of the pacific plate in july august 1992 a seismic swarm activity was observed near the trench five earthquakes of m 6 occurred successively within 2 weeks at the beginning of the activity we deployed an ocean bottom seismograph obs array in the epicentral region to make an in situ observation of the spatial distribution of these events and to study the characteristics of the swarm activity in detail we relocated 357 events from 23 july to 26 august with focal depth errors less than 5 km by using both the obs and the land network data the swarm events are not distributed homogeneously over the plate boundary but form several clusters a remarkable concentration of the earthquakes was found in the vicinity of the hypocenter of the largest event during the obs observation m 6 2 29 july this formed the most active cluster almost all the earthquakes including the m 6 2 event occurred at depths of about 15 km and were concentrated along a thin plane dipping to the west at 5 the location of the plane coincides well with that of the plate boundary derived from previous seismic explorations we also relocated epicenters of the off sanriku events by introducing station corrections to the land network data during the period when the obs array was absent the corrections were estimated from the travel time residuals of the hypocenter relocation using the obs and the land network data the result of the epicenter relocation strongly indicates the existence of a zone of extremely low seismic activity beneath the inner trench wall where low seismic velocity mechanically weak unconsolidated sediments overly the subducting pacific plate

a reassessment of outer rise seismicity and its implications for the mechanics of oceanic lithosphere we use body waveform modelling to constrain the source parameters of earthquakes occurring globally in oceanic lithosphere beneath the subduction zone outer rise and outer trench slope these data are then used to map the stress state in the lithosphere of the downgoing plate as it bends into the subduction zone our results provide new constraints on the faulting of oceanic lithosphere at the outer rise which is important for understanding the transmission of plate driving forces through the subduction system in all cases shallow normal faulting earthquakes are observed at the top of the plate and are separated in depth from any deeper thrust faulting earthquakes no temporal variation associated with large thrust faulting earthquakes on the subduction interface is seen in the depth extent of each type of faulting at the outer rise the transition depth from trench normal extension to compression is found to vary in agreement with models in which deformation is driven by the combination of in plane stresses and bending stresses resulting principally from slab pull combining the seismologically derived constraints on the thickness of the elastic core of the plate with estimates of the plate curvature we place upper bounds on the strength of the lithosphere at the outer rise which is required to be 300 mpa for a constant yield stress model or governed by an effective coefficient of friction of 0 3

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

the 3 d tectonic stress fields in and around japan inverted from centroid moment tensor data of seismic events 1 we can regard the occurrence of earthquakes as the partial release of tectonic stress by sudden brittle rupture in the framework of linear elasticity any indigenous source including earthquake rupture is represented by a moment tensor the moment tensor is mathematically equivalent to the volume integral of stress release over the whole elastic region surrounding the source and so we can quantitatively relate the centroid moment tensor cmt of seismic events with an unknown tectonic stress field on the basis of such an idea and bayesian statistical inference theory we developed an inversion method to estimate the 3 d pattern of tectonic stress from cmt data applying the cmt data inversion method to 12 500 seismic events in and around japan we obtained precise 3 d tectonic stress patterns that illuminate the present day quaternary complex tectonic motion of japanese islands the stress pattern of the kuril japan nankai arc is basically e w compression but the direction of intermediate principal stress changes from n s reverse faulting type in northeast japan to vertical strike slip faulting type in southwest japan on the other hand the stress pattern of the ryukyu and izu bonin back arc regions is basically trench perpendicular tension normal faulting type in addition to these basic stress patterns governed by mechanical interaction between the eurasian north american pacific and philippine sea plates we can recognize several characteristic local stress patterns corresponding to the horizontal motion of the kuril fore arc sliver the collision of the izu peninsula with the mainland of japan and the opening of the beppu shimabara rift zone

rupture process of the 2011 tohoku oki earthquake and absolute elastic strain release 1 on 11 march 2011 the tohoku oki earthquake in eastern japan and the devastating tsunami that followed it caused severe damage and numerous deaths to clarify the rupture process of the earthquake we inverted teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 5 7 1022 nm mw 9 1 associated with a fault rupture 440 km long and 180 km wide along the plate interface the source process is characterized by asymmetric bilateral rupture propagation but we also found continuous slips up dip from the hypocenter which led to a large maximum slip 50 m long slip duration 90 s and a large stress drop 20 mpa the long slip duration large stress drop extensional normal faulting aftershocks in a previously compressional stress regime and low angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault the stress accumulated on the plate interface was about 20 mpa near the trench and 0 10 mpa in the down dip source region

aperiodic recurrence of geologically recorded tsunamis during the past 5500 years in eastern hokkaido japan 1 along hokkaido s pacific coast near the town of kiritappu sandy deposits in a muddy lagoon and on a nearby beach ridge plain provide evidence for 15 tsunamis between 200 and 6000 years ago additional sand beds at the lagoon probably represent the historical tsunamis of a d 1843 and 1894 we observed the sequences of sandy deposits in continuous slices 2 to 4 m deep some of the deposits consist of just a single sand bed whereas others contain multiple units of sand muddy sand or sandy mud and mud caps including plant detritus we also found at the lagoon a 17th century tsunami deposit that thickens and thins regardless of elevation or distance inland we bracketed the ages of most of the inferred tsunamis by radiocarbon dating of detritus mainly seeds and leaves at the lagoon and charcoal at the beach ridge plain from pretsunami and posttsunami beds tsunami dates computed from the bracketing ages commonly have uncertainties spanning 2 to 4 centuries within these uncertainties the inferred sequence of 15 prehistoric tsunamis at the lagoon beginning almost 6000 years ago can be matched tsunami by tsunami with the inferred history at the beach ridge plain 15 km away the sand sheet extents suggest that most of these tsunamis were larger than any generated at hokkaido in the last 200 years the intervals between these inferred outsized tsunamis average nearly 400 years but range widely from about 100 to about 800 years

control of mechanical stratigraphy on bed restricted jointing and normal faulting eagle ford formation south central texas outcrops of the middle eagle ford formation in south central texas reveal well developed joint networks in subhorizontal competent carbonate chalk beds and less well developed networks in interlayered incompetent calcareous mudrock beds northeast striking bed perpendicular joints in competent beds have the longest trace lengths and are abutted by northwest striking joints all observed joints terminate vertically in incompetent beds normal faults are common but less abundant than joints dominantly dip north northwest or southeast and are abutted by the joint sets and thus predated jointing the faults cut multiple competent and incompetent beds providing vertical connectivity across mechanical layering products of hybrid and shear failure the dip of these faults is steep through competent beds and moderate through incompetent beds resulting in refracted fault profiles with dilation and calcite precipitation along steep segments fluid inclusions in fault zone calcite commonly contain liquid hydrocarbons rare two phase fluid inclusions homogenized between about 1 40 and 58 c and 2 90 and 100 c suggesting trapping of aqueous fluids at elevated temperatures and depths on the order of 2 km 6562 ft fluid inclusion and stable isotope geochemistry analyses suggest that faults transmitted externally derived fluids these faults likely formed at depths equivalent to portions of the present day oil and gas production from the eagle ford play in south texas faults connect across layering and provide pathways for vertical fluid movement within the eagle ford formation in contrast to vertically restricted joints that produce bed parallel fracture permeability these observations elucidate natural fractures and induced hydraulic fracturing within the eagle ford formation

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

fault structure stress or pressure control of the seismicity in shale insights from a controlled experiment of fluid induced fault reactivation clay formations are present in reservoirs and earthquake faults but questions remain on their mechanical behavior as they can vary from ductile aseismic to brittle seismic an experiment at a scale of 10 m aims to reactivate a natural fault by fluid pressure in shale materials the injection area was surrounded by a dense monitoring network comprising pressure deformation and seismicity sensors in a well characterized geological setting thirty two microseismic events were recorded during several injection phases in five different locations within the fault zone their computed magnitude ranged between 4 3 and 3 7 their spatiotemporal distribution compared with the measured displacement at the injection points shows that most of the deformation induced by the injection is aseismic whether the seismicity is controlled by the fault architecture mineralogy of fracture filling fluid and or stress state is then discussed the fault damage zone architecture and mineralogy are of crucial importance as seismic slip mainly localizes on the sealed with calcite fractures which predominate in the fault damage zone as no seismicity is observed in the close vicinity of the injection areas the presence of fluid seems to prevent seismic slips the fault core acts as an impermeable hydraulic barrier that favors fluid confinement and pressurization therefore the seismic behavior seems to be strongly sensitive to the structural heterogeneity including permeability of the fault zone which leads to a heterogeneous stress response to the pressurized volume

interplate seismogenic zones along the kuril japan trench inferred from gps data inversion stress accumulation between earthquakes results from slip that is insufficient to fully accommodate plate movement an inverse analysis of gps data from the kuril japan trench reveals a trench parallel belt of stress accumulation with six peaks in the depth range of 10 40 km suggesting potential source regions for future earthquakes in the subduction zones around japan where four plates interact with one another large earthquakes have occurred repeatedly1 these interplate earthquakes are part of the process of tectonic stress accumulation and release that is driven by relative plate motion2 3 4 stress accumulation between earthquakes results from slip deficit slip that is insufficient to fully accommodate plate movement for the prediction of large earthquakes it is therefore important to monitor the distribution of slip deficit on plate interfaces here we apply an inversion method based on bayesian modelling using direct and indirect prior information on the magnitude and distribution of fault slip5 to horizontal and vertical velocities from global positioning system data for the seismically calm period between 1996 and 2000 we obtain a precise distribution of slip deficit rates on the interface between the north american and pacific plates around japan which reveals a trench parallel belt of slip deficit with six peaks in the depth range of 10 40 km these peaks agree with the source regions of past large interplate earthquakes along the kuril japan trench we conclude that the slip deficit zones identified with our method are potential source regions of large earthquakes

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

fault zone processes and fluid history in austin chalk southwest texas faults are commonly the largest fractures in a fracture network forming the backbone of the permeability system in low permeability rocks faults in outcrops of the austin chalk an important oil and gas reservoir in south texas louisiana and westernmost mississippi exemplify deformation and fluid histories of subseismic scale faults in mechanically layered chalk dominated strata exposures of near horizontal austin chalk in southwest texas contain northwest and southeast dipping normal faults with exposed heights of meters to tens of meters and displacements of centimeters to decimeters local fault dips are steep to vertical through chalk and limestone beds and moderate through marl mud rock and clay rich ash beds producing refracted fault profiles failure surface characteristics indicate various failure modes including tensile hybrid shear and locally compactive shear behavior depending on the host lithology dilational zones associated with steep fault segments host calcite veins crack seal textures in fault zone veins record repeated reactivation of refracted fault profiles fluid inclusion and stable isotope geochemistry analyses of fault veins indicate formation at depths of 1 4 to 2 9 km 4593 to 9514 ft and possibly of 4 2 km 13 780 ft fluids include locally sourced saline waters and externally sourced waters and oil in rocks that did not reach oil maturation conditions inclusions of 30 api to greater than 50 api oil are found in veins 30 km 19 mi updip from the eagle ford formation oil zone these results illustrate the migration of oil and other fluids within subseismic scale austin chalk faults and fundamental control of lithology on fault zone architecture

earthquake distribution in the subduction zone off eastern hokkaido japan deduced from ocean bottom seismographic and land observations summary in 1986 observations of microearthquakes were conducted with the use of five ocean bottom seismometers obss on the continental slope east of the kushiro submarine canyon ksc off hokkaido island japan the observation area is located about 50 100 km landward of the southern kuril trench beneath which the pacific plate is subducted toward hokkaido island the obs data were analysed together with land data on hokkaido island to determine the precise earthquake distribution and the geometry of the subducted plate the obs data revealed for the first time the seaward seismicity east of ksc high and shallow seismicity is concentrated in an area between the coast line of hokkaido island and the 2000 m isobath a region between the 2000 and 4000 m isobaths corresponds to the source area of an interplate earthquake occurring in 1973 the nemuro hanto oki earthquake m 7 4 the obs array detected more than 10 events in this region most of them however are classified as earthquakes occurring within the subducted plate and the remarkable aftershock activity of the 1973 event is not recognized the seismic activity is extremely low between the 4000 and 6000 m isobaths as is commonly seen in subduction zones the seismicity is also very low beneath the trench in contrast with the adjacent trench areas in a vertical section taken perpendicular to the trench axis most of the located events form a seismic plane dipping landward the dip angle of the plane is 20d 25d beneath the continental slope while 35d 40d under hokkaido island the change in dip angle occurs 150 km landward of the trench axis this seismic plane is located 30 40 km below the plate boundary defined from the aftershock distribution of the nemuro hanto oki event the seismicity on the plate boundary is correlated with the geometry of the subducted plate the high activity occurs in a restricted region where the subducted plate shows a remarkable bend the seismic activity obtained is different from those in the adjacent regions along the southern kuril trench in particular the regional difference in seismicity is remarkable between the western and eastern sides of ksc our result suggests that the subduction zone along the kuril trench is divided into several tectonic blocks and ksc is one of their boundaries

slip distribution of the february 27 2010 mw 8 8 maule earthquake central chile from static and high rate gps insar and broadband teleseismic data 1 the shallow depth underthrust earthquake of february 27 2010 mw 8 8 ruptured the subduction plate interface in central chile between 34 s and 38 s we retrieve the spatial and temporal distribution of slip during this mega earthquake through a joint inversion of teleseismic records insar and high rate gps hrgps data additionally our model is shown to agree with broadband surface waves rupture initiated at about 32 km depth and propagated bilaterally resulting in two main slip zones located ssw and nne of the hypocenter nucleation did not take place within or at the edge of one of these main asperities but in between during the first 30s slip propagated predominantly southwards later on the rupture evolved more slowly and more symmetrically eventually the northern asperity became predominant with maximum slip reaching about 20 m most of the seismic moment was released within 110s a relatively short time explained by the bilateral propagation the overall average rupture velocity is 2 6 km s but propagation occurred initially faster towards the south 3 2 km s large slip did not reach the trench a result consistent with the moderate size of the tsunami down dip rupture stopped at about 50 km depth in agreement with the lower limit of the locked zone inferred by ruegg et al 2009 from pre seismic gps data

seismic structure and seismogenesis off sanriku region northeastern japan summary in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeastern japan nej arc the objectives of this experiment were to clarify seismic structures of the forearc region off sanriku japan using airgun obs data and to understand the nature of the japan trench seismogenic zone fundamental features of the structure are as follows i the subduction angle becomes steeper from east to west from 3 to 8 to 11 with the top of the plate located at depths of 11 km 40 km west from the trench 21 km 120 km west from the trench and 28 km 140 km west from the trench respectively ii the nej moho beneath the forearc is defined at a depth of approximately 20 km iii p wave velocity of the island arc upper mantle is approximately 8 km s 1 iv the p wave velocity of the cretaceous sedimentary layer exhibits significant lateral variability 4 0 5 5 km s 1 i nthe e w direction v the upper crust of nej forearc also has the significant lateral heterogeneity 5 0 6 3 km s 1 i nthe e w direction but not in the n s direction vi the middle crust defined on land extends in some locations 40 km east of the coastline vii lateral variability in the p wave velocity of the lower crust 6 7 7 0 km s 1 i ssmall compared with that of the upper crust according to these results it is suggested that the rupture areas of large earthquakes m7 in this region are limited within the contact zone between the nej arc crust and the subducting oceanic crust although a thin layer with low velocity is probably present within this contact zone the serpentinization of uppermost mantle wedge of the nej arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited this might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km

petrogenesis of orbicular ijolites from the prairie lake complex marathon ontario textural evidence from rare processes of carbonatitic magmatism abstract a unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1 1 ga prairie lake carbonatite complex marathon ontario canada and is the only known occurrence of this textural type in a rock of ijolitic composition this mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites granites diorites and lamprophyres the orbicules occur along distinct densely packed bands in equigranular nepheline rich ijolite and range up to 6 cm in diameter macroscopically the orbicules show variability in the mineralogy of their cores detailed imaging of the cores shows evidence of quench textures radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules the mineralogy of the orbicules consists of nepheline diopside calcite apatite andradite melanite garnet titanite fe rich phlogopite titaniferous magnetite perovskite with secondary natrolite calcite and cancrinite the mineralogy of the host ijolite is similar to that of the orbicules mineral compositions from the orbicular ijolite and the host ijolite are similar within the orbicules anhedral minerals are found occurring in a matrix of garnet throughout the distinct concentric bands the textures within the concentric bands of the orbicules are best described as annealing recrystallization textures the rims of the orbicules form interlocking crystals with the host ijolite resulting in near indistinguishable boundaries the orbicules are interpreted to represent interaction of a partially crystallized quenched ijolitic melt which was in contact with a second pulse of consanguineous ijolite magma immersion in the latter resulted in sub solidus diffusion and annealing recrystallization orbicular textures were produced from previously formed quenched ijolite which was recrystallized producing the monominerallic concentric layers sequentially from the margins toward the center of the orbicule this proposed model for the formation of orbicular ijolite from prairie lake highlights the complexities of these rock types and supports previous models of magma mixing during the later stages of carbonatite emplacement and crystallization

the great 1933 sanriku oki earthquake reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data

detection of gas in sandstone reservoirs using avo analysis a 3 d seismic case history using the geostack technique the geostack technique is a method of analyzing seismic amplitude variation with offset avo information one of the outputs of the analysis is a set of direct hydrocarbon indicator traces called fluid factor traces the fluid factor trace is designed to be low amplitude for all reflectors in a clastic sedimentary sequence except for rocks that lie off the mudrock line the mudrock line is the line on a crossplot of p wave velocity against s wave velocity on which water saturated sandstones shales and siltstones lie some of the rock types that lie off the mudrock line are gas saturated sandstones carbonates and igneous rocks in the absence of carbonates and igneous rocks high amplitude reflections on fluid factor traces would be expected to represent gas saturated sandstones of course this relationship does not apply exactly in nature and the extent to which the mudrock line model applies varies from area to area however it is a useful model in many basins of the world including the one

temporal change of interplate coupling in northeastern japan during 1995 2002 estimated from continuous gps observations summary temporal change of deformation in northeastern japan is clarified by continuous global positioning system gps observations from 1995 april to 2002 march the observed gps velocity is approximately parallel to the direction of plate convergence on east and west plate boundaries of northeastern japan and shows post seismic transient deformation around source regions of the mw 7 8 1993 hokkaido nansei oki and the mw 7 7 1994 sanriku haruka oki earthquakes we interpret the source of the observed deformation as contemporary interplate coupling on the east subducting boundary to the pacific plate and the west collision boundary to the amurian plate using elastic dislocation theory we inverted horizontal and vertical velocities of 212 gps stations to estimate interplate coupling on both boundaries the estimated coupling during 1995 2002 is spatially heterogeneous however it is temporally almost constant except for the region around the 1993 and 1994 earthquakes after slip of the 1994 earthquake occurred over the coseismic rupture area and its downdip extension on the plate boundary for 0 3 1 3 yr after the earthquake after slip continued only in the downdip extension for later periods and decayed with time weak coupling was recovered in the eastern part of the coseismic rupture area 3 3 yr after the earthquake interplate coupling on the pacific plate was strong in two regions miyagi oki and tokachi oki the west plate boundary is tightly coupled except for the source areas of three large earthquakes that occurred in 1964 1983 and 1993 the apparent decoupling of the source areas of these earthquakes implies long term post seismic deformation as a result of viscoelastic relaxation in the subseismogenic lithosphere

fault zone deformation controlled by carbonate mechanical stratigraphy balcones fault system texas normal faults in cretaceous carbonates in the balcones fault system provide important analogs for fault zone architecture and deformation in carbonate reservoirs worldwide mechanical layering is a fundamental control on carbonate fault zones relatively planar faults with low displacement gradients develop in massive strong clay poor limestones and dolomites in less competent clay rich strata shale beds impede fault propagation resulting in fault related folding and locally steep bedding dips faults in clay poor massive limestones and dolomites tend to be steep 70 or more whereas weaker clay rich limestones develop faults with shallower dips 60 or less fault zone rocks show evidence of cataclasis cementation deformation of cement by mechanical twinning and pressure solution and multiple generations of cement with differing degrees of deformation indicating contemporaneous cementation and fault slip in stratigraphic sequences consisting of both competent and incompetent strata the ratio of incompetent to competent strata by thickness is a useful guide for inferring the relative rates of fault displacement and propagation low displacement to propagation ratios associated with competent strata generate low displacement gradients inhibiting fault related folding conversely high displacement to propagation ratios associated with incompetent strata promote high displacement gradients and fault related folding

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

the role of seismic attributes in understanding the hydraulically fracturable limits and reservoir performance in shale reservoirs an example from the eagle ford shale south texas as the importance of self sourcing reservoirs continues to increase it is more important than ever to evaluate rock properties that contribute to productive wells it has become increasingly evident that in order to maximize potential returns an integrated approach to shale play characterization is necessary to identify productive areas numerous criteria exist to characterize ultra low permeability shale reservoirs and their associated resource potential these include measures of organic richness thermal maturity lithologic heterogeneity and formation brittleness the latter a descriptor of the geomechanical rock properties can play a significant role in overall well performance and is commonly a key productivity driver thus an understanding of the mechanical properties of the target section is fundamental for high grading prospective areas well placement design and hydraulic stimulation effectiveness observation of geomechanical attributes extracted from seismic data in the eagle ford shale captures changing mechanical properties indicative of strike oriented lithologic facies changes using acoustic logs core and three dimensional seismic data we assess the mechanical contrast between eagle ford facies units and their effect on well performance we use three dimensional seismic data to map the structure and facies distribution in an area where identification of reservoir facies is a major challenge to development drilling in this study we demonstrate how young s modulus and density inverted from three dimensional seismic data prove as effective discriminators for the purpose of identifying and mapping facies changes and establishing the hydraulically fracturable limits in areas where effective stimulation and proppant embedment in the formation during pressure drawdown is a concern the result is an interpretation that identifies and uses the mechanical changes from three dimensional seismic data attributes associated with the brittle carbonate rich eagle ford facies to predict both the reservoirs hydraulically fracturable limits as well as the variability in well performance associated with proppant embedment the changes in mechanical properties of the eagle ford facies are important in high grading productive intervals in these ultra low permeability rocks we believe we can apply this method to other shale reservoirs where rock mechanics may play an important role

mantle wedge water contents estimated from seismic velocities in partially serpentinized peridotites 1 water carried into subduction zones with the down going plate and subsequently released by dehydration reactions at depth affects the composition of the mantle wedge triggers partial melting and affects subduction zone seismicity partially serpentinized peridotite may be a significant reservoir for water in the subducted plate the mantle wedge and the overriding plate here we develop a model that relates the degree of serpentinization and water content of partially serpentinized peridotites to their seismic p wave velocities in partially serpentinized ultramafic rocks a 1 decrease in p wave velocity corresponds to a 2 4 increase in serpentine content and a 0 3 0 18 moles m3 increase in h2o content up to a maximum of 13 where there is evidence of serpentinization mantle serpentine content is typically 15 corresponding to 4 5 wt h2o 6 10 moles m3