seismic imaging of arc magma and fluids under the central part of northeastern japan abstract a dense seismic network was temporarily deployed during 1997 1999 in the central part of northeastern japan by japanese university research groups using the local earthquake arrival time data recorded by the network we have determined high resolution three dimensional images of p wave velocity vp s wave velocity vs and vp vs ratio in this area our results show that low vp low vs and high vp vs areas are extensively distributed in the uppermost mantle along the volcanic front in the lower crust low vp low vs and high vp vs areas are visible but they are confined to the individual volcanic areas in contrast the upper crust of volcanic areas shows low vp low vs and low vp vs rather than high vp vs these observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas low vp low vs and low vp vs in the upper crust of the volcanic areas suggest the presence of h2o rather than melt there deep low frequency microearthquakes perhaps caused by the rapid movement of fluids are located mostly at the edge of partial melting zones particularly at their upper surface distinct s wave reflectors bright spots with large reflection coefficients are distributed in the midcrust with slightly low vp vs suggesting that most of them are filled with h2o

complex slab structure and arc magmatism beneath the japanese islands abstract a dense nationwide seismic network recently constructed in japan has resulted in the production of a large amount of high quality data that have enabled the high resolution imaging of deep seismic structures in the japanese subduction zone seismic tomography precise locations of earthquakes and focal mechanism research have allowed the identification of the complex structure of subducting slabs beneath japan revealing that the subducting philippine sea slab underneath southwestern japan has an undulatory configuration down to a depth of 60 200 km and is continuous from kanto to kyushu without disruption or splitting even within areas north of the izu peninsula analysis of the geometry of the pacific and philippine sea slabs identified a broad contact zone beneath the kanto plain that causes anomalously deep interplate and intraslab earthquake activity seismic tomographic inversions using both teleseismic and local events provide a clear image of the deep aseismic portion of the philippine sea slab beneath the japan sea north of chugoku and kyushu and beneath the east china sea west of kyushu down to a depth of 450 km seismic tomography also allowed the identification of an inclined sheet like seismic low velocity zone in the mantle wedge beneath tohoku a recent seismic tomography work further revealed clear images of similar inclined low velocity zones in the mantle wedge for almost all other areas of japan the presence of the inclined low velocity zones in the mantle wedge across the entirety of japan suggests that it is a common feature to all subduction zones these low velocity zones may correspond to the upwelling flow portion of subduction induced convection systems these upwelling flows reach the moho directly beneath active volcanic areas suggesting a link between volcanism and upwelling

cenozoic history of the himalayan bengal system sand composition in the bengal basin bangladesh stratigraphic sequences preserved in the bengal basin provide detrital information that documents a significantly older history of the eastern himalaya than that available from ocean drilling program and deep sea drilling project cores recovered from the bengal fan the bengal basin formed as a result of the himalayan collision is located at the juncture of the indian craton to the west the shillong massif and the himalayan belt to the north and the indo burman ranges to the east modal analyses of eocene and oligocene sandstones of the cherra kopili and barail formations document compositions that are dominated by subangular monocrystalline quartz grains with scarce to no feldspar grains and few lithic fragments cherra and kopili qt 99 f 1 l 0 barail qt 90 f 3 l 7 qt total quartz f feldspar l lithic fragments these compositions are similar to sands derived from the indian craton suggesting that they underwent intense chemical weathering likely in a source with low relief and considerable transport himalayan tectonism during this time was probably significantly more distant from the bengal basin than at present sandstones of the miocene surma group bhuban and boka bil formations are rich in feldspar grains argillite and very low grade metamorphic lithic fragments bhuban qt 66 f 15 l 19 boka bil qt 57 f 23 l 20 relative to older sandstones suggesting onset of uplift and erosional unroofing in the eastern himalaya and initiation of stream systems supplying orogenic detritus to the bengal basin sands of the upper miocene to pliocene tipam group and the pliocene pleistocene dupi tila sandstone contain abundant argillitic and low to medium grade metamorphic lithic fragments and feldspar grains tipam qt 61 f 19 l 19 dupi tila qt 70 f 13 l 17 suggesting continued orogenic unroofing these younger sands are rich in potassium feldspar p f 0 30 0 20 relative to plagioclase p rich bhuban and boka bil sandstones p f 0 66 and 0 48 suggesting a granitic source probably the miocene leucogranites of the high himalayan crystalline terrane these results document for the first time contrasts in orogenic history recorded in the bengal system vs western himalayan foreland basins sands deposited in the bengal basin are generally more quartzose and less lithic than those from the western himalayan foreland basins and pre miocene strata in the bengal system show little to no evidence of orogenic activity in part this probably reflects west to east progression of the himalayan collision but it probably also results from sedimentary systems propagating southward ahead of the advancing mountain belt as it has been consuming the remnant ocean basin trapped between the indian craton and the burmese block

seismic structure of the northeastern japan convergent margin a synthesis many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern japan arc and its relationship to seismic and volcanic activity spatial distributions of the depths to the conrad and the moho discontinuities estimated from shallow earthquake data and seismic explosion data show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the japan sea and the pacific ocean the pn velocity has a lateral variation it is as low as 7 5 km s beneath the land area while that beneath the japan sea and the pacific ocean is 8 0 8 2 km s it changes abruptly at the transition zones which are located along the coastlines precise structure and location of the subducted pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate the pacific plate is composed of a thin 5 km low velocity upper layer and a thick high velocity lower layer its total thickness being 80 90 km the upper plane seismicity of the double seismic zone is confined to the thin low velocity upper layer which probably corresponds to the subducted former oceanic crust the lower plane seismicity lies at the middle of the high velocity lower layer and the lower half of the plate below it is incapable of generating earthquakes the shallower portion of the upper surface of the plate beneath the pacific ocean along which major seismicity with low angle thrust faultings is actually occurring is also located by seismic observations on land and in the sea the pacific plate subducts at an extremely low angle of 5 for the first 25 km depth and then the dip steepens rather abruptly to 30 normal fault type events at the top of the plate have not been detected in the portion where the downward bending is the largest but have been ditected near the trench axis where it is rather small tomographic inversions for seismic velocity structure clearly delineate the inclined high velocity pacific plate with a thickness of 80 90 km and low velocity zones in the crust and the mantle wedge beneath active volcanoes seismic attenuation tomography also shows similar zones of low q value beneath active volcanoes although its spatial resolution is much lower the low velocity zones with 2 6 velocity lows are continuously distributed from the upper crust just beneath active volcanoes to a depth of 100 150 km in the mantle wedge and are approximately parallel to the dip of the underlying pacific plate these low velocity zones probably reflect the pathway of magma ascent from a depth in the mantle wedge to the earth s surface corresponding to a portion of the subduction induced secondary mantle wedge flow

shumagin seismic gap alaska peninsula history of great earthquakes tectonic setting and evidence for high seismic potential the shumagin seismic gap a segment of the plate boundary along the eastern aleutian arc has not ruptured during a great earthquake since at least 1899 1903 because at least 77 years have elapsed since the shumagin gap last ruptured in a great earthquake and repeat times for the 1938 rupture zone and part of the shumagin gap are estimated to be 50 to 90 years a high probability exists for a great earthquake to occur within the shumagin gap during the next one to two decades reconsideration of the rupture zones of the aleutian earthquakes of 1938 1946 and 1948 suggests that those events did not break the interplate boundary beneath the shumagin islands thus the shumagin seismic gap extends from the western end of the 1938 rupture zone to the eastern end of that of 1946 these boundaries also coincide with transverse structural features at least the eastern half of the shumagin gap broke in great earthquakes in 1788 and 1847 and possibly in 1898 1903 the shumagin gap is probably not the result of aseismic slip rather plate motion is accommodated there seismically and episodically and can be expected to produce large earthquakes in the future although there is no definitive evidence of long term precursors of a possible future earthquake several observations suggest that the shumagin gap is in an advanced stage of the earthquake cycle both teleseismic and local network data indicate a near absence of seismic activity m 2 above a depth of 30 km along the main thrust zone within the gap this is in strong contrast to adjacent portions of the arc where seismic activity is scattered across most of the main thrust zone two earthquakes with high stress drops 600 900 bars which occurred at the base of the main thrust zone may indicate the accumulation of a considerable amount of strain energy within the gap a possible seismic gap at the eastern end of the aftershock zone of the aleutian earthquake of 1957 has been identified near unalaska island an earthquake that nucleates in the shumagin gap could also rupture the possible unalaska gap to the west the 1938 aftershock zone to the east or both with resultant magnitude up to mw 9 0 alternatively the shumagin gap alone or in one of the above combinations could rupture in a series of very large earthquakes instead of a single great shock past alaska aleutian earthquakes including those of 1788 1938 1946 1957 1964 and 1965 have generated very large tsunamis future large earthquakes in the shumagin islands region could generate wave heights of several tens of meters along shorelines near the rupture areas the shumagin gap is one of two major gaps along the united states portion of the alaska aleutian plate boundary and is one of the few areas in the united states where processes leading to a great earthquake are likely to be observed within a reasonable span of time

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

impact of local recharge on arsenic concentrations in shallow aquifers inferred from the electromagnetic conductivity of soils in araihazar bangladesh 1 the high degree of spatial variability of dissolved as levels in shallow aquifers of the bengal basin has been well documented but the underlying mechanisms remain poorly understood we compare here as concentrations measured in groundwater pumped from 4700 wells 22 m 75 ft deep across a 25 km2 area of bangladesh with variations in the nature of surface soils inferred from 18 500 measurements of frequency domain electromagnetic induction a set of 14 hand auger cores recovered from the same area indicate that a combination of grain size and the conductivity of soil water dominate the electromagnetic signal the relationship between pairs of individual em conductivity and dissolved as measurements within a distance of 50 m is significant but highly scattered r2 0 12 n 614 concentrations of as tend to be lower in shallow aquifers underlying sandy soils and higher below finer grained and high conductivity soils variations in em conductivity account for nearly half the variance of the rate of increase of as concentration with depth however when the data are averaged over a distance of 50 m r2 0 50 n 145 the association is interpreted as an indication that groundwater recharge through permeable sandy soils prevents as concentrations from rising in shallow reducing groundwater

groundwater dynamics and arsenic contamination in bangladesh although arsenic contaminated groundwater in bangladesh is a serious health issue little is known about the complex transient patterns of groundwater flow that flush solutes from aquifers and carry solutes into the subsurface hydrologic modeling results for our field site in the munshiganj district indicate that groundwater flow is vigorous flushing the aquifer over time scales of decades to a century and also transporting solute loads into the aquifer with recharge from ponds rivers and rice fields the combined hydrologic and biogeochemical results from our field site imply that the biogeochemistry of the aquifer system may not be in steady state and that the net effect of competing processes could either increase or decrease arsenic concentrations over the next decades modeling results suggest that irrigation has greatly changed the location timing and chemical content of recharge to the aquifer flushing water through the system more quickly and also cycling large fluxes of water through rice fields during the dry season that could mobilize arsenic from oxides in near surface sediments furthermore the hydrologic model reveals that ponds many of which have been excavated over the last 50 years now provide much of the groundwater recharge these ponds receive most of the waste from the villages and thus provide another potential source of organic carbon to the groundwater system

redox control of arsenic mobilization in bangladesh groundwater abstract detailed hydrochemical measurements 34sso4 and 3h analyses were performed on 37 groundwater samples collected during february 1999 january and march 2000 from 6 locations in eastern and southeastern bangladesh to examine redox processes that lead to as mobilization in groundwater the study sites were chosen based on available nation wide as surveys to span the entire spectrum of as concentrations in bangladesh groundwater and to represent 3 of 5 major geological units of the ganges brahmaputra delta uplifted pleistocene terrace fluvial flood plain and delta plain arsenic was found to be mobilized under fe reducing conditions in shallow aquifers 50 g l or 0 7 m were always accompanied by high dissolved hco3 4 mm and were close to saturation with respect to calcite groundwater enriched in as 200 800 g l or 2 7 10 7 m and phosphate 30 100 m but relatively low in dissolved fe 5 40 m probably resulted from re oxidation of reducing as and fe enriched water this history was deduced from isotopic signatures of 34sso4 and 3h2o 3h to delineate the nature of redox changes for some of the reducing groundwaters in contrast as is not mobilized in presumed pleistocene aquifers both shallow 30 60 m and deep 150 270 m because conditions were not reducing enough due to lack of sufficient o2 demand

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

three dimensional structure of vp vs and vp vs beneath northeastern japan implications for arc magmatism and fluids we estimated both p v p and s wave velocity v s structures beneath northeastern japan by applying a tomographic method to 169 712 p and 103 993 s wave arrival time data from 4338 local events the average value of v p v s ratio is 1 69 in the upper crust 1 75 in the lower crust and 1 77 in the uppermost mantle these differences in v p v s ratio may mainly reflect the lithological variations with depth low v p low v s and high v p v s zones are extensively distributed along the volcanic front in the uppermost mantle and are downward to the back arc side in the mantle wedge here the low v p low v s and high v p v s values are interpreted because of partial melting materials which imply the presence of a vast amount of melt in the uppermost mantle in the lower crust low v p low v s and high v p v s zones are not continuously visible along the volcanic front but are confined to individual volcanic areas which suggests that melting of lower crustal materials occurs just beneath each active volcano in contrast the upper crust beneath active volcanoes exhibits low v p low v s and low v p v s these results suggest that the partial melting zones under northeastern japan spread out from the uppermost mantle along the volcanic front up to the midcrust right beneath active volcanoes the low v p low v s and low v p v s features in the upper crust suggest the existence of h 2 o rather than melt right beneath active volcanoes

stress before and after the 2002 denali fault earthquake 1 spatially averaged absolute deviatoric stress tensors along the faults ruptured during the 2002 denali fault earthquake both before and after the event are derived using a new method from estimates of the orientations of the principal stresses and the stress change associated with the earthquake stresses are estimated in three regions along the denali fault one of which also includes the susitna glacier fault and one region along the totschunda fault estimates of the spatially averaged shear stress before the earthquake resolved onto the faults that ruptured during the event range from near 1 mpa to near 4 mpa shear stresses estimated along the faults in all these regions after the event are near zero 0 1 mpa these results suggest that deviatoric stresses averaged over a few tens of km along strike are low and that the stress drop during the earthquake was complete or nearly so

mineralogical profiling of alluvial sediments from arsenic affected ganges brahmaputra floodplain in central bangladesh abstract mineral assemblages heavy and light fractions and sedimentological characteristics of the quaternary alluvial aquifers were examined in the central bengal basin where as concentrations in groundwater are highly variable in space but generally decrease downward chemical compositions of sediment samples from two vertical core profiles 2 150 m below ground level bgl were analyzed along with groundwater in moderately as enriched aquifers in central bangladesh manikganj district and the as mobilization process in the alluvial aquifer is described heavy minerals such as biotite magnetite amphibole apatite and authigenic goethite are abundant at shallow 4 reduction mediated by so 4 reducing bacteria in manikganj groundwater is limited in contrast to the southeastern bengal basin where precipitation of arsenian pyrite is thought to sequester as from groundwater

the 1985 central chile earthquake a repeat of previous great earthquakes in the region a great earthquake surface wave magnitude 7 8 occurred along the coast of central chile on 3 march 1985 causing heavy damage to coastal towns intense foreshock activity near the epicenter of the main shock occurred for 11 days before the earthquake the aftershocks of the 1985 earthquake define a rupture area of 170 by 110 square kilometers the earthquake was forecast on the basis of the nearly constant repeat time 83 9 years of great earthquakes in this region an analysis of previous earthquakes suggests that the rupture lengths of great shocks in the region vary by a factor of about 3 the nearly constant repeat time and variable rupture lengths cannot be reconciled with time or slip predictable models of earthquake recurrence the great earthquakes in the region seem to involve a variable rupture mode and yet for unknown reasons remain periodic historical data suggest that the region south of the 1985 rupture zone should now be considered a gap of high seismic potential that may rupture in a great earthquake in the next few tens of years

heterogeneities in stress and strength in tohoku and its relationship with earthquake sequences triggered by the 2011 m9 tohoku oki earthquake inland tohoku has been recognized as under the wnw ese compressional stress state before the 2011 m9 tohoku oki earthquake earthquakes that occurred there were characterized by reverse faulting with the compressional axis oriented in almost the wnw ese direction the tohoku oki earthquake reduced this wnw ese compressional stress and therefore should have suppressed the earthquake occurrence however several intensive earthquake sequences were triggered in inland tohoku in this study we investigated the triggering mechanism of these remote earthquake sequences in the stress shadow based on the detailed distribution of stress orientations newly determined from pre mainshock focal mechanism data the spatial distribution of stress orientations shows that there exist some regions with anomalous stress fields even before the tohoku oki earthquake on the spatial scale of a few tens of kilometers this spatial heterogeneity in the stress field suggests that the differential stress magnitude in inland tohoku is low a few tens of mpa locations of the earthquake clusters tend to correspond to regions where the principal stress axis orientations of the pre mainshock period are similar to those of the static stress change by the tohoku oki earthquake this observation suggests that these earthquake sequences were triggered by a local increase in differential stress due to the static stress change however a few swarm sequences occurred in central tohoku with delays ranging from a few days to few weeks after the tohoku oki earthquake despite the reduction in differential stress these sequences have notable characteristics including upward migration of hypocenters such features are similar to the fluid injection induced seismicity the source regions of these swarms are located near the ancient caldera structures and major geological boundaries the swarm activities were probably triggered by the upward fluid movement along such pre existing structures these observations demonstrate that information about the temporal evolutions of both stress and frictional strength is necessary to understand the triggering mechanism of earthquakes

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

inversion of long period p waves from great earthquakes along subduction zones abstract long period p waves from subduction zone earthquakes in the moment range from 7 1027to 8 1029dyn cm are analyzed using an iterative deconvolution method in addition to discrete subevents which effectively contribute to the observed seismograms the long period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long period surface waves it is shown that great earthquakes can be described by several subevents with a duration of about 10 s which changes little from earthquake to earthquake in the above moment range the long period component of the moment rate function becomes larger for a greater earthquake the greatest earthquakes of mw 9 additionally involve subevents with another duration scale much longer than 10 s it is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane the constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes these observations suggest an essential similarity in the mode of dislocation distribution

change in stress directions along the central denali fault alaska after the 2002 earthquake sequence 1 on the basis of earthquake focal mechanisms the state of stress along the central denali fault alaska system changed after the 2002 earthquake sequence before the earthquake sequence the maximum stress 1 was at a 60 angle with the denali fault west of the point of its maximum curvature fault normal between the fault apex and the totschunda strand and at 50 with respect to the totschunda fault in the epicentral region the post event 1 has rotated counter clockwise along the rest of the rupture zone the sense of rotation is clockwise the 1 direction became nearly fault normal along the totschunda strand along the central part of the rupture 1 is over rotated with 3 being nearly vertical promoting reverse aftershocks this could be an indication of dynamic overshoot

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

spatial heterogeneity of tectonic stress and friction in the crust the complex geometry of faults seismicity and diversity of earthquake mechanisms suggest that the stress and strength in earth s crust are spatially heterogeneous we investigated the degree of heterogeneity using the following two end member models in one end member model we assumed that the orientation of stress is uniform in the crust as is assumed in many stress inversion studies in this model the variability of earthquake mechanisms means that friction during faulting must vary for each event we computed friction from the ratio of the resolved shear stress to the effective normal stress on the fault plane with the assumption of hydrostatic pore pressure the values of vary over a large range from 0 to 1 5 in the other extreme model we assumed optimally oriented slip and a constant 0 6 as is suggested by byerlee s law for all the earthquakes and determined the local stress orientation for each earthquake the orientation of the stress changes drastically from one earthquake to another and the assumption of uniform stress field commonly used in stress inversion is not warranted an important conclusion is that a regionally uniform stress field and constant friction on optimally oriented faults are mutually exclusive the actual situation in the crust is most likely to be intermediate between these two end member models from the existing data alone we cannot determine the degree of heterogeneity uniquely but both and the local stress field near earthquake faults are likely to vary substantially and studies on earthquake rupture dynamics must take these heterogeneities into consideration

stress before and after the 2011 great tohoku oki earthquake and induced earthquakes in inland areas of eastern japan 1 stress fields in inland areas of eastern japan before and after the tohoku oki earthquake were estimated by inverting focal mechanism data before the earthquake s1 axis was oriented ew in tohoku but nw se in kanto chubu the stress fields changed after the earthquake in northern tohoku and in southeastern tohoku near iwaki city where the orientations of the principal stresses became approximately the same as the orientations of the static stress change associated with the earthquake this indicates that differential stress magnitudes in these areas before the earthquake were smaller than 1 mpa the stress field did not change in central tohoku even though the stresses loaded after the earthquake had nearly reversed orientations which indicates that the differential stress magnitudes there were significantly larger than 1 mpa in kanto chubu stresses having nearly the same orientations as the background stresses were loaded after the earthquake and the stress fields did not change as expected this may have caused very high induced seismicities in kanto chubu citation yoshida k a hasegawa t okada t iinuma y ito and y asano 2012 stress before and after the 2011 great tohoku oki earthquake and induced earthquakes in inland areas of eastern japan geophys res lett 39 l03302

spatial variation of stress orientations in ne japan revealed by dense seismic observations abstract in order to investigate the spatial distribution of the crustal stress state across ne japan we determined 1370 focal mechanisms by picking p wave polarities from seismograms observed by temporary and permanent seismic networks densely deployed in this area we applied stress tensor inversions to these data plus to those routinely determined the results show that the stress state in ne japan is heterogeneous in space which is different from previous results that showed that the ne japan arc is characterized by margin normal compression the orientations of the maximum compressional stress 1 axes are significantly different with 95 confidence limits between the arc backarc region and the forearc region the arc backarc region is characterized by spatially uniform margin normal compression however the north and south parts of the forearc region have the 1 axis oriented nearly n s and vertical respectively the region in between has a similar stress orientation to the arc backarc region moreover the stress regime in the arc backarc region varies spatially in response to change in the surface altitude beneath regions of relatively low altitudes a reverse faulting stress regime is dominant however regions of higher altitudes are characterized by a strike slip faulting stress regime numerical model calculations in which gravitational and buoyancy forces caused by topography are incorporated show that differential stresses of about 15 25 mpa are needed to explain the lateral variation of the stress regime observed in the arc backarc region this suggests that the background deviatoric stress magnitude in ne japan is very low

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

state of stress from focal mechanisms before and after the 1992 landers earthquake sequence the state of stress in the eastern california shear zone ecsz changed significantly because of the occurrence of the 1992 m w 6 1 joshua tree and the m w 7 3 landers earthquakes to quantify this change focal mechanisms from the 1975 galway lake sequence the 1979 homestead valley sequence background seismicity from 1981 to 1991 and the 1992 landers sequence are inverted for the state of stress in all cases the intermediate principal stress axis s2 remained vertical and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes s 1 and s 3 and small variations in the value of the relative stress magnitudes in general the stress state in the ecsz has s 1 trending east of north and 0 43 to 0 65 suggesting that the ecsz is a moderate stress refractor and the style of faulting is transtensional south of the pinto mountain fault in the region of the 1992 joshua tree earthquake the stress state determined from the 1981 to 1991 background seismicity changed on 23 april and again on 28 june 1992 in the central zone s 1 rotated from n14 5 e to n28 5 e on 23 april and back again to n16 5 e on 28 june thus the landers mainshock in effect recharged some of the shear stress in the region of the m w 6 1 joshua tree earthquake comparison of the state of stress before and after 28 june 1992 along the landers mainshock rupture zone showed that the mainshock changed the stress orientation the s1 trend rotated 7 to 20 clockwise and became progressively more fault normal from south to north along the emerson camp rock faults the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor the complex distribution of p and t axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock the san bernardino mountains region of the m w 6 2 big bear earthquake has a distinctively different state of stress as compared to the landers region with s 1 trending n3 5 w this region did not show any significant change in the state of stress following the 1992 m w 6 2 big bear sequence

spatial relationship of groundwater arsenic distribution with regional topography and water table fluctuations in the shallow aquifers in bangladesh the present study has examined the relationship of groundwater arsenic as levels in alluvial aquifers with topographic elevation slope and groundwater level on a large basinal scale using high resolution 90 m 90 m shuttle radar topography mission srtm digital elevation model and water table data in bangladesh results show that high as 50 g l tubewells are located in low lying areas where mean surface elevation is approximately 10 m similarly high as concentrations are found within extremely low slopes 0 7 in the country groundwater elevation weekly measured by bangladesh water development board was mapped using water table data from 950 shallow depth 100 m piezometers distributed over the entire country the minimum maximum and mean groundwater elevation maps for 2003 were generated using universal kriging interpolation method high as tubewells are located mainly in the ganges brahmaputra meghna delta sylhet trough and recent floodplains where groundwater elevation in shallow aquifers is low with a mean value of 4 5 m above the public works datum pwd level extremely low groundwater gradients 0 01 0 001 m km within the gbm delta complex hinder groundwater flow and cause slow flushing of aquifers low elevation and gentle slope favor accumulation of finer sediments as carrying iron oxyhydroxide minerals and abundant organic matter within floodplains and alluvial deposits at low horizontal hydraulic gradients and under reducing conditions as is released in groundwater by microbial activity causing widespread contamination in the low lying deltaic and floodplain areas where as is being recycled with time due to complex biogeochemical processes

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

aseismic deep subduction of the philippine sea plate and slab window abstract we have made great efforts to collect and combine a large number of high quality data from local earthquakes and teleseismic events recorded by the dense seismic networks in both south korea and west japan this is the first time that a large number of korean and japanese seismic data sets are analyzed jointly as a result a high resolution 3 d p wave velocity model down to 700 km depth is determined which clearly shows that the philippine sea phs plate has subducted aseismically down to 460 km depth under the japan sea tsushima strait and east china sea the aseismic phs slab is visible in two areas one is under the japan sea off western honshu and the other is under east china sea off western kyushu however the aseismic phs slab is not visible between the two areas where a slab window has formed the slab window is located beneath the center of the present study region where many teleseismic rays crisscross detailed synthetic tests were conducted which indicate that both the aseismic phs slab and the slab window are robust features using the teleseismic data recorded by the japanese stations alone the aseismic phs slab and the slab window were also revealed zhao et al 2012 though the ray paths in the japanese data set crisscross less well offshore the slab window may be caused by the subducted kyushu palau ridge and kinan seamount chain where the phs slab may be segmented hot mantle upwelling is revealed in the big mantle wedge above the pacific slab under the present study region which may have facilitated the formation of the phs slab window these novel findings may shed new light on the subduction history of the phs plate and the dynamic evolution of the japan subduction zone

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

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

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

integration of aquifer geology groundwater flow and arsenic distribution in deltaic aquifers a unifying concept groundwater arsenic as presents a public health risk of great magnitude in densely populated asian delta regions most acutely in the bengal basin west bengal india and bangladesh research has focused on the sources mobilisation and heterogeneity of groundwater as but a consistent explanation of as distribution from local to basin scale remains elusive we show for the bengal aquifer system that the numerous discontinuous silt clay layers together with surface topography impose a hierarchical pattern of groundwater flow which constrains as penetration into the aquifer and controls its redistribution towards discharge zones where it is re sequestered to solid phases this is particularly so for the discrete periods of as release to groundwater in the shallow subsurface associated with sea level high stand conditions of quaternary inter glacial periods we propose a hypothesis concerning groundwater flow silt clay layers impose hierarchical groundwater flow patterns constraining arsenic progression siha which links consensus views on the as source and history of sedimentation in the basin to the variety of spatial and depth distributions of groundwater as reported in the literature siha reconciles apparent inconsistencies between independent in some cases contrasting field observations we infer that lithological and topographic controls on groundwater flow inherent to siha apply more generally to deltaic aquifers elsewhere the analysis suggests that groundwater as may persist in the aquifers of asian deltas over thousands of years but in certain regions particularly at deeper levels as will not exceed low background concentrations unless groundwater flow systems are short circuited by excessive pumping

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

a generalized regression model of arsenic variations in the shallow groundwater of bangladesh localized studies of arsenic as in bangladesh have reached disparate conclusions regarding the impact of irrigation induced recharge on as concentrations in shallow 50 m below ground level groundwater we construct generalized regression models grms to describe observed spatial variations in as concentrations in shallow groundwater both i nationally and ii regionally within holocene deposits where as concentrations in groundwater are generally high 10 g l 1 at these scales the grms reveal statistically significant inverse associations between observed as concentrations and two covariates 1 hydraulic conductivity of the shallow aquifer and 2 net increase in mean recharge between predeveloped and developed groundwater fed irrigation periods further the grms show that the spatial variation of groundwater as concentrations is well explained by not only surface geology but also statistical interactions i e combined effects between surface geology and mean groundwater recharge thickness of surficial silt and clay and well depth net increases in recharge result from intensive groundwater abstraction for irrigation which induces additional recharge where it is enabled by a permeable surface geology collectively these statistical associations indicate that irrigation induced recharge serves to flush mobile as from shallow groundwater

temporal changes in stress drop frictional strength and earthquake size distribution in the 2011 yamagata fukushima ne japan earthquake swarm caused by fluid migration

delineating low arsenic groundwater environments in the bengal aquifer system bangladesh studies within the as affected bengal basin have indicated that low as groundwater can be found in a variety of geological and geomorphological settings the hydrogeological environments that host lowas groundwater may be interpreted within a geological framework determined by the quaternary evolution of the bengal aquifer system bas this provides the basis for delineating the position and extent of shallow low as groundwater low as groundwater in oxidised red bed sediments and deep low as groundwater data available on a national scale allow a preliminary delineation of these low as groundwater environments across bangladesh based on empirical associations of low as groundwater occurrences with topography water table elevation surface sediment lithology geology and the screen depth of deep wells in low as zones

constraints on sustainable development of arsenic bearing aquifers in southern bangladesh part 1 a conceptual model of arsenic in the aquifer arsenic is widespread in groundwater of the holocene alluvial aquifers in southern bangladesh yet its concentration is highly variable spatially and with depth a conceptual model of arsenic in the aquifer is proposed as a basis for addressing questions concerning sustainability of groundwater development patterns and profiles of arsenic distribution in the aquifer have been determined at meherpur in western bangladesh over an area of 15 km 2 and a depth range of 15 225 m the hydrochemical and hydraulic environments of arsenic occurrence have been established the conceptual model incorporates the conditions of arsenic release to groundwater the depth distribution of the arsenic source likely sedimentological controls on the lateral discontinuity of the arsenic source and the hydraulic regime imposed by pumping from the hydrogeologically leaky multi layered aquifer reducing conditions conducive to arsenic release from sedimentary iron oxyhydroxides are widespread the arsenic source occurs at a distinct horizon at a depth of about 20m but is laterally discontinuous the catchments of shallow hand pumped tubewells htws are limited in extent by vertical leakage arsenic concentration in water pumped from tubewells depends on the depth separation between the htw screen and the arsenic source the overlap between the htw catchment and the arsenic source layer and the duration of pumping implications are drawn for treatment tubewell location and design monitoring and predictive modelling

stress rotations due to the m6 5 foreshock and m7 3 main shock in the 2016 kumamoto sw japan earthquake sequence a shallow m7 3 event with a m6 5 foreshock occurred along the futagawa hinagu fault zone in kyushu sw japan we investigated the spatiotemporal variation of the stress orientations in and around the source area of this 2016 kumamoto earthquake sequence by inverting 1 218 focal mechanisms the results show that the 3 axis in the vicinity of the fault plane significantly rotated counterclockwise after the m6 5 foreshock and rotated clockwise after the m7 3 mainshock in the hinagu fault segment this observation indicates that a significant portion of the shear stress was released both by the m6 5 foreshock and m7 3 mainshock it is estimated that the stress release by the m6 5 foreshock occurred in the shallower part of the hinagu fault segment which brought the stress concentration in its deeper part this might have caused the m7 3 mainshock rupture mainly along the deeper part of the hinagu fault segment after 28 hours

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

near surface lithology and spatial variation of arsenic in the shallow groundwater southeastern bangladesh this study investigated the relationship between near surface lithology and the spatial variability of as concentrations using sediment grain size analysis and electromagnetic induction survey in the southeast bangladesh it has been observed that the aquifers overlain by finer sediments have higher concentrations of as in groundwater whereas as concentrations are remarkably low in aquifers having permeable sandy materials or thinner silt clay layer at the surface the near surface lithology acts as a controlling factor for spatial distributions of groundwater as within the very shallow depths 15 m shallow alluvial aquifers can provide low as drinking water in many areas of the country when tube wells are properly installed after investigation of the overlying near surface sediment attributes and hydraulic properties

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

natural arsenic contamination of holocene alluvial aquifers by linked tectonic weathering and microbial processes 1 linked tectonic geochemical and biologic processes lead to natural arsenic contamination of groundwater in holocene alluvial aquifers which are the main threat to human health around the world these groundwaters are commonly found a long distance from their ultimate source of arsenic where chemical weathering of as bearing minerals occurs we propose a gbh as model that ties together all of the important tectonic biologic and hydrologic processes that cause natural as release in groundwater in holocene terrestrial deposits processes highlighted by the gbh as model can explain the movement of arsenic from lithosphere to hydrosphere however we propose a factor that has increased dissolved as concentrations in holocene aquifers to levels where human health is threatened mechanical weathering associated with pleistocene glaciation our model invokes erosion of mountain belts aided by glaciers transport of arsenic by surface waters adsorption of as by stream sediments and deposition of stream sediments and organic matter in alluvial deposits subsequently fe iii reducing bacteria present in alluvial aquifers cause the release of sorbed as to groundwater under moderately reducing conditions

imaging the subducting slabs and mantle upwelling under the japan islands summary a high resolution p wave tomography of the crust and mantle down to 700 km depth beneath the japan islands is determined using a large number of high quality arrival time data from local earthquakes and teleseismic events simultaneously the tomography shows that the philippine sea slab is subducting aseismically down to 430 km depth under southwest japan though the seismicity within the slab ends at 180 km depth a low velocity low v zone in the mantle wedge under tohoku and kyushu is found to extend westward from the volcanic front to the backarc under the japan sea and east china sea significant low v anomalies are revealed in the deep portion of the mantle wedge 400 500 km depth above the pacific slab under southwest japan which may reflect hot mantle upwelling associated with fluids from the deep dehydration of the pacific slab low v anomalies appear at 420 700 km depths beneath the pacific slab under eastern japan which may reflect hot mantle upwelling associated with the deep subduction of the pacific slab and its collapsing down to the lower mantle

hydrological control of as concentrations in bangladesh groundwater 1 the elevated arsenic as content of groundwater from wells across bangladesh and several other south asian countries is estimated to slowly poison at least 100 million people the heterogeneous distribution of dissolved arsenic in the subsurface complicates understanding of its release from the sediment matrix into the groundwater as well as the design of mitigation strategies using the tritium helium 3h 3he groundwater dating technique we show that there is a linear correlation between groundwater age at depths 20 m and dissolved as concentration with an average slope of 19 g l 1 yr 1 monitoring wells only we propose that either the kinetics of as mobilization or the removal of as by groundwater flushing is the mechanism underlying this relationship in either case the spatial variability of as concentrations in the top 20 m of the shallow aquifers can to a large extent be attributed to groundwater age controlled by the hydrogeological heterogeneity in the local groundwater flow system

deep structure of the northeastern japan arc and its implications for crustal deformation and shallow seismic activity abstract seismic tomography studies in the northeastern japan arc have revealed the existence of an inclined sheet like seismic low velocity and high attenuation zone in the mantle wedge at depths shallower than about 150 km this sheet like low velocity high attenuation zone is oriented sub parallel to the subducted slab and is considered to correspond to the upwelling flow portion of the subduction induced convection the low velocity high attenuation zone reaches the moho immediately beneath the volcanic front or the ou backbone range running through the middle of the arc nearly parallel to the trench axis which suggests that the volcanic front is formed by this hot upwelling flow aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the backbone range where they are expelled from solidified magma and migrate further upward the existence of aqueous fluids may weaken the surrounding crustal rocks resulting in local contractive deformation and uplift along the backbone range under the compressional stress field of the volcanic arc a strain rate distribution map generated from gps data reveals a notable concentration of east west contraction along the backbone range consistent with this interpretation shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone based on these observations a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern japan arc

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

quaternary shoreline shifting and hydrogeologic influence on the distribution of groundwater arsenic in aquifers of the bengal basin abstract naturally occurring high arsenic concentration in groundwater of most alluvial aquifers in the bengal basin has been causing serious health problems in millions of people elevated dissolved arsenic concentrations are mostly confined within a shallow depth

coseismic and postseismic stress rotations due to great subduction zone earthquakes 1 the three largest recent great subduction zone earthquakes 2011 m9 0 tohoku japan 2010 m8 8 maule chile and 2004 m9 2 sumatra andaman exhibit similar coseismic rotations of the principal stress axes prior to each mainshock the maximum compressive stress axis was shallowly plunging while immediately after the mainshock both the maximum and minimum compressive stress axes plunge at 45 dipping faults can be oriented for either reverse or normal faulting in this post mainshock stress field depending on their dip explaining the observed normal faulting aftershocks without requiring a complete reversal of the stress field the significant stress rotations imply near complete stress drop in the mainshocks with 80 of the pre mainshock stress relieved in the tohoku and maule earthquakes and in the northern part of the sumatra andaman rupture the southern part of the sumatra andaman rupture relieved 60 of the pre mainshock stress the stress axes rotated back rapidly in the months following the tohoku and maule mainshocks and similarly in the southern part of the sumatra andaman rupture a rapid postseismic rotation is possible because the near complete stress drop leaves very little background stress at the beginning of the postseismic reloading in contrast there has been little or no postseismic rotation in the northern part of the sumatra andaman rupture over the 7 years since the mainshock all m 8 0 subduction earthquakes since 1990 with an adequate number of pre and post mainshock events were evaluated and not all show similar coseismic stress rotations deeper earthquakes exhibit smaller coseismic stress rotations likely due to increasing deviatoric stress with depth

arsenic iron and organic matter in sediments and groundwater in the pannonian basin hungary in the central part of the pannonian basin factors controlling the distribution of as in sediments and groundwater of the upper 500 m were studied in core samples the amounts of as fe and mn extractable with hydroxylamine hydrochloride nh2oh hcl in 25 acetic acid the proportion of the 0 063 mm size fraction and the sediment organic c corg contents were measured in the groundwaters concentrations of as humic substances and selected major chemical components were determined in most core samples extractable fe as feooh and corg are correlated but some samples have excess fe or organic matter in cases where either excess fe or excess organic matter is found the amount of as is also elevated the spatial distribution of as in the groundwater and the lack of a consistent correlation of as with a single component indicate that there is no single factor controlling the concentration of dissolved as over the entire study area the only consistent feature is enrichment of as relative to fe in the groundwater compared to the sediments this suggests that the dissolution of fe minerals which primarily adsorb as is not congruent in reducing conditions fe iii oxyhydroxides together with adsorbed as dissolve and siderite with little or no as precipitates when sub regions are separated and studied individually it can be shown that hydrogeological features of the sediments the proportions of fe minerals and sedimentary organic matter and the concentration of dissolved humic materials all influence the accumulation and mobilization of as the significance of the different mobilizing processes however and the mean concentration of as is different in the recharge through flow and discharge areas

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con