paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

migration of shallow and deep slow earthquakes toward the locked segment of the nankai megathrust abstract the nankai megathrust is located offshore shikoku and kyushu japan and is characterized by various kinds of slow earthquakes whose relative motions across the plate boundary faults are slower than regular earthquakes in the area the interplate locking is stronger in the northern area offshore shikoku than in the southern area offshore kyushu and mw 8 earthquakes nankai earthquakes have occurred repeatedly in the northern area in this paper the spatio temporal distributions of slow earthquakes very low frequency earthquakes tremors and slow slip events are examined based on the analyses of repeating earthquakes and slow earthquakes with special focus on the interaction between different activities a comprehensive analysis of the seismic and geodetic data from 2003 to 2016 indicates complementary distribution of various types of slow earthquakes down to 35 50 km depth outside the nankai main locking area we also found interactions between different kinds of activities the interactions between the repeating earthquakes and slow earthquakes suggest that the area of the repeating earthquakes activity can be divided into deeper depth 20 km and shallower depth

sedimentary organic matter preservation a test for selective degradation under oxic conditions the authors report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water sediment interface oxygen penetration depths organic element compositions and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the washington continental shelf slope and adjacent cascadia basin individual amino acid sugar and pollen distributions were analyzed for a 11 to 12 cm horizon from each core and sup 14 c based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites sediment accumulation rates decreased and dissolved o sub 2 penetration depths increased offshore along the sampling transect as a result oxygen exposure times oet increased seaward from decades mid shelf and upper slope to more than a thousand years outer cascadia basin organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location in particular organic carbon surface area ratios decreased progressively offshore and with increasing oet three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded both concentrationmore and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible oxic effect oet helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere less

imaging of the subducted kyushu palau ridge in the hyuga nada region western nankai trough subduction zone abstract we performed 3d seismic tomography of the hyuga nada region western nankai subduction zone to investigate the relationship of the subducted part of kyushu palau ridge kpr to coseismic rupture propagation seismicity and shallow very low frequency earthquakes combining active source and passive source data recorded both onshore and offshore we imaged the deep slab from near the trough axis to the coastal area our results show the subducted kpr as a low velocity belt oriented nw se extending down the plate boundary to around 30 km depth at this depth we suggest that the subducted kpr detaches from the slab and becomes underplated on the overriding continental plate as the coseismic slip areas of past large earthquakes do not extend into the subducted kpr we suggest that it may inhibit rupture propagation the interior of the subducted kpr shows active intraslab seismicity with a wide depth distribution shallow very low frequency earthquakes are continuously active above the location of the subducted kpr whereas they are intermittent to the northeast of the subducted kpr thus the subducted kpr appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

interannual and interdecadal variability of the south atlantic convergence zone interannual variations of the summertime january march atmospheric circulation over subtropical south america are examined during the period 1958 97 using the national centers for environmental prediction national center for atmospheric research reanalysis data it is found from an empirical orthogonal function analysis that an anomalous upper tropospheric large scale stationary eddy in the lee of the andes tends to accompany a dipole in anomalous vertical motion an anomalous cyclonic anticyclonic eddy accompanies an intensified diffuse south atlantic convergence zone sacz with anomalous descent ascent to the southwest the cold core equivalent barotropic vertical structure of the anomalous cyclonic eddy and the 200 hpa vorticity balance are both characteristic of a stationary rossby wave the tendency for the eddy to be advected downstream by the mean westerlies is compensated by meridional advection of planetary vorticity and stretching associated with vertical motion the anomalous cyclonic flow at low levels reinforces the thermally direct circulation associated with the sacz a weak funneling of submonthly rossby wave activity into this descent region is also identified the interannual time series of the eddy is significantly correlated with north south dipolar sea surface temperature sst anomalies over the southwest atlantic one standard deviation 200 hpa wind speed anomalies of up to 5 m s21 are accompanied by sst anomalies of up to 0 38c a near cyclic 15 yr component is identified which the authors corroborate from independent analyses of southwest atlantic ssts and river flows both are

variability of fault slip behavior along the san andreas fault in the san juan bautista region an improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process using a waveform cross correlation approach we document spatially and temporally varying fault slip along the northernmost creeping section of the san andreas fault near san juan bautista sjb california by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes cres the spatial distribution of pre 1998 sjb earthquake 1984 1998 fault slip rate inferred from the cres reveals a 15 km long low creep or partially locked section located near the 1998 mw 5 1 sjb earthquake rupture a finite fault slip inversion reveals that the rupture of the 1998 sjb earthquake is characterized by the failure of a compact 4 km2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 mpa whereas the mean stress drop is about 15 mpa following the 1998 earthquake the cre activity was significantly increased in a 5 10 km deep zone extending 2 7 km northwest of the main shock which indicates triggering of substantial aseismic slip the postseismic slip inferred from the cre activity primarily propagated to the northwest and released a maximum slip of 9 cm in this 5 10 km depth range the estimated postseismic moment release is 8 6 1016 n m which is equivalent to mw 5 22 the aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress driven afterslip but represents a triggered long lasting slow earthquake

a model with rigid rotations and slip deficits for the gps derived velocity field in southwest japan abstract we interpret the gps derived velocity field in southwest japan by a superposition of the elastic deformation caused by fault interactions slips or slip deficits on the rigid motion of tectonic blocks or plates based on the strain rate field and crustal seismicity we apply a model with three blocks inner arc outer arc and the northern ryukyu block and slip deficits along the block boundaries several characteristics of the synthesized contributions are found 1 westward motion of the outer arc relative to the amurian plate and the inner arc 2 southeastward motion of the northern ryukyu block relative to the amurian plate 3 2 4 mm yr deficits of left lateral slip rates along the boundary at 32 n in southern kyushu 4 0 8 mm yr deficits of right lateral slip rates along the median tectonic line and the beppu shimabara graben 5 slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions 6 clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration

the long recurrence intervals of small repeating earthquakes may be due to the slow slip rates of small fault strands observations since 1998 have revealed that repeating earthquakes and particularly small repeating earthquakes occur less often than expected given their seismically derived slip and the regional fault slip rate here we test the hypothesis that small repeaters occur infrequently because they occur on fault segments or strands with low slip rates we analyze the recurrence interval moment scaling of earthquake sequences near parkfield california we find that closely spaced sequences which likely occur on the same fault strand and respond to the same slip rate follow a scaling consistent with seismic slip rates while widely spaced sequences which likely occur on different strands follow a scaling consistent with the previous counter intuitive observations these results suggest that spatially varying slip rates could create the recurrence interval scaling though we cannot exclude other explanations

repeating volcano tectonic earthquakes at mt etna volcano sicily italy during 1999 2009 abstract repeating volcano tectonic vt earthquakes taking place at mt etna during 1999 2009 were detected and analyzed to investigate their behavior we found 735 families amounting to 2479 vt earthquakes representing 38 of all the analyzed vt earthquakes the number of vt earthquakes making up the families ranges from 2 to 23 over 70 of the families comprise 2 or 3 vt earthquakes and only 20 families by more than 10 events the occurrence lifetime is also highly variable ranging from some minutes to ten years in particular more than half of the families have a lifetime shorter than 0 5 day and only 10 longer than 1 year on the basis of these results most of the detected families were considered burst type i e show swarm like occurrence and hence their origin cannot be explained by a temporally constant tectonic loading indeed since the analyzed earthquakes take place in a volcanic area the rocks are affected not only by tectonic stresses related to the fairly steady regional stress field but also by local stresses caused by the volcano such as magma batch intrusions movements and gravitational loading we focused on the five groups of families characterized by the longest repeatability over time namely high number of events and long lifetime located in the north eastern eastern and southern flanks of the volcano unlike the first four groups which similarly to most of the detected families show swarm like vt occurrences group v located in the north eastern sector exhibits a more tectonic behavior with the events making up such a group spread over almost the entire analyzed period it is clear how both occurrence and slip rates do not remain constant but vary over time and such changes are time related to the occurrence of the 2002 2003 eruption finally by fpfit algorithm a good agreement between directions identified by nodal planes and the earthquake epicentral distribution was generally found

small repeating earthquake activity interplate quasi static slip and interplate coupling in the hyuga nada southwestern japan subduction zone 1 small repeating earthquake re analysis is a useful method for estimating interplate quasi static slip which is a good indicator of interplate coupling we detected 170 continual type interplate re groups and then estimated the spatial variation in quasi static slip in the hyuga nada over the past 17 years the re activity in this region has different characteristics compared with that in the northeast japan subduction zone presumably reflecting differences in the subduction properties our results revealed that interplate coupling spatially changes along the trench axis and dip direction a phenomenon that cannot be resolved by land based global positioning system gps analysis by comparing seismicity the low slip rate areas correspond with the location of hypocenters and asperities for large and moderate sized interplate earthquakes suggesting strong interplate coupling at these sites these results indicate that the slip rate distribution estimated from re activity is reliable and useful for assessing the potential of future large earthquakes

plate geometry model and seismicity in the northern ryukyu subduction zone japan deduced from amphibious seismic observations abstract in this study the geometry of the subducted philippine sea plate interface beneath the northern ryukyu trench subduction zone was estimated based on seismic tomography and focal mechanism estimations using passive data obtained from a temporary amphibious seismic network and permanent land stations using relocated low angle thrust type earthquakes and information obtained from previous studies we constrained the plate geometry from the trench axis to a depth of 60 km with uncertainties of

enigmatic highly active left lateral shear zone in southwest japan explained by aseismic ridge collision global positioning system gps site velocities and earthquake focal mechanisms reveal an active left lateral shear zone cutting across kyushu in southwest japan surprisingly no active faults have been identified in association with this zone of rapid contemporary deformation to explain the existence of this shear zone we propose a model comprising subduction of an aseismic ridge kyushu palau ridge at the southwest end of the nankai trough because of rapid 40 mm yr along strike migration of the ridge we suggest that the ridge subduction point and resulting left lateral shear zone is never in one place long enough to enable the development of a through going fault zone that can be identified at the ground surface reconciling the mismatch between the gps seismological and geological data in this region our conceptual model is supported by numerical modeling results we also suggest that the along strike change in subducting plate buoyancy explains the recent counterclockwise rotation of the kyushu forearc documented in paleomagnetic studies as is found in many other western pacific subduction margins

triggering of repeating earthquakes in central california dynamic stresses carried by transient seismic waves have been found capable of triggering earthquakes instantly in various tectonic settings delayed triggering may be even more common but the mechanisms are not well understood catalogs of repeating earthquakes earthquakes that recur repeatedly at the same location provide ideal data sets to test the effects of transient dynamic perturbations on the timing of earthquake occurrence here we employ a catalog of 165 families containing 2500 total repeating earthquakes to test whether dynamic perturbations from local regional and teleseismic earthquakes change recurrence intervals the distance to the earthquake generating the perturbing waves is a proxy for the relative potential contributions of static and dynamic deformations because static deformations decay more rapidly with distance clear changes followed the nearby 2004 mw6 parkfield earthquake so we study only repeaters prior to its origin time we apply a monte carlo approach to compare the observed number of shortened recurrence intervals following dynamic perturbations with the distribution of this number estimated for randomized perturbation times we examine the comparison for a series of dynamic stress peak amplitude and distance thresholds the results suggest a weak correlation between dynamic perturbations in excess of 20 kpa and shortened recurrence intervals for both nearby and remote perturbations

terrestrial plant biopolymers in marine sediments the vascular land plant biopolymers lignin and cutin were surveyed in the surface sediments of coastal and open ocean waters by controlled alkaline cuo oxidation reaction two contrasting oceanic regimes were studied the northwest mediterranean nwm sea which receives significant particulate terrigenous debris through riverine discharge and the northeast atlantic nea ocean with poorly characterised terrestrial carbon inputs in the nwm products of lignin and cutin co occurred at all stations elevated levels ca 0 5 3 0 mg lignin phenols 100 mg organic carbon ca 0 01 0 09 mg cutin acids 100 mg organic carbon were observed for near shore deltaic and shelf sediments the influence of terrestrial land plant inputs extended across the shelf and through the slope to the abyssal plain providing molecular evidence for advective offshore transfer of terrestrial carbon mass balance estimates for the basin suggest riverine inputs account for the majority of surface sedimentary lignin cutin most of which 90 is deposited on the shelf products of cuo oxidation of lignin and cutin were also detected in nea surface sediments at levels comparable to those observed for the nwm continental slope and were detectable at low concentrations ca 0 5 gg 1 in the sediments of the abyssal plains 4 000 m depth while atmospheric deposition of lignin cutin derived material cannot be discounted in this open ocean system lateral advective transfer of enriched shelf sediments is inferred as a possible transport process a progressive enrichment in cutin derived material relative to lignin was observed offshore with evidence of an increase in the degree of oxidative alteration of lignin residues to account for these observations preferential offshore transport of finer and more degraded material is proposed nonspecific oxidation products dominated the gas chromatograms of nea sediments which appear to originate from marine sources of sedimentary organic carbon preliminary mass balance calculations applied to the global ocean margin suggest riverine sources of both particulate lignin and cutin are important and that most 95 deposition of recognisable land plant biopolymers occurs in shelf seas

quasi periodic slow slip events in the afterslip area of the 1996 hyuga nada earthquakes japan 1 the time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay the global positioning system network in japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6 8 and 6 7 in the hyuga nada area southwest japan in 1996 the spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7 3 however quasi periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two year recurrence interval the moment magnitudes of the three slow slip events since january 2005 range from 6 7 to 6 8 this differs greatly from the expected behavior of logarithmic decay over time both velocity strengthening and velocity weakening rate and state modes have been implicated as the cause of afterslip whose location is complementary to the main shock area of velocity weakening while a slow slip event occurs in the velocity weakening area with different frictional properties from those of an afterslip area in light of the seemingly different frictional properties the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving the monitoring of these slow slip events should give the clues to understanding the coexistence of long term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas

comparison of the coseismic rupture with the aftershock distribution in the hyuga nada earthquakes of 1996 on october 19 1996 a large underthrusting earthquake ms 6 7 the hyuga nada japan earthquake occurred along the southern end of nankai trough about two months later a second large earthquake ms 6 7 occurred in the adjacent region we study the source process of the two large earthquakes in the hyuga nada region and compare the coseismic rupture area with aftershock distribution the main source parameters obtained for the first mainshock are strike dip rake 210 12 81 the seismic moment mo 2 3 1019 nm mw 6 8 the rupture area s 20 15 km and the source duration t 17 s for the second main shock strike dip rake 210 12 87 the seismic moment mo 1 5 1019 nm mw 6 7 the rupture area s 18 18 km and the source duration t 15 s the coseismic rupture areas do not overlap the aftershock area while the aftershock areas of the two main shocks mutually overlap this implies that the common aftershock region takes a role of barriers to dynamic rupture it is also seen that the aftershock area expanded during the first one day

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

numerical simulation of afterslips and slow slip events that occurred in the same area in hyuga nada of southwest japan summary we propose a model of numerical simulation for the coexistence of afterslip for m7 earthquake and slow slip events in the hyuga nada region of japan that incorporates 3 d geometry of the philippine sea plate coseismic slip events recurrence of slow slip events and afterslip are qualitatively reproduced using the composite law which is a type of rate and state dependent friction law with higher cut off velocity in addition characteristic slip distances in the area are larger than those in other seismic source areas in our simulation afterslip which occurred at the velocity weakening regime triggered an aseismic transient event after the termination of this event spontaneous slow slip events repeatedly occurred in the same area after a similar event sequence was repeated another afterslip occurrence triggered a larger coseismic slip in a wide area including that of the slow slip events following this coseismic slip the aseismic slip area was locked until the next afterslip propagation which triggered an aseismic transient event these results suggest that detailed observation of spatial and temporal distribution within the area of aseismic slip may indicate the potential of recurring slow slip events and future large earthquakes

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

spatial changes of inter plate coupling inferred from sequences of small repeating earthquakes in japan 1 we extract sequences of small repeating earthquakes to clarify inter plate coupling of subducting plates over a large area of the japanese islands as a result many sequences arc detected at the philippine sea plate subducting from the ryukyu trench and pacific plate subducting from the kuril japan trench the average slip rates and standard deviations estimated from the sequences show substantial spatial changes of inter plate coupling the large deviations of slip rates correspond to the occurrence of episodic slips such as after slips following large earthquakes constant slip rates approaching the relative plate motion indicate weak coupling areas slip deficits and sparse distributions of repeating groups suggest locked areas in the nankai trough deep low frequency earthquakes in the transition zone and burst type repeating sequences within plates have not been located in the downdip direction of groups with slow slip rates this suggests that the space time characteristics of inter plate coupling affected these seismic events

possible slip history scenarios for the hyuga nada region and bungo channel and their relationship with nankai earthquakes in southwest japan based on numerical simulations the nankai earthquakes are great interplate earthquakes with recurrence intervals of 100 200 years occurring along the nankai trough southwestern japan new geological evidences suggest that the rupture area of the 1707 earthquake one of the largest extended farther westward than previously thought and similar magnitude events may have recurrence intervals of several hundred years west of the nankai earthquake segments in the bungo channel region slow slip events sses have occurred with recurrence intervals of several years since 1980 farther westward no m 7 5 interplate earthquakes have occurred except for one in 1968 in the northern hyuga nada region near the bungo channel we numerically simulated the generation cycles of nankai earthquakes hyuga nada earthquakes and bungo channel sses to obtain possible slip histories in these regions particularly during 1707 1980 we showed that the nankai and hyuga nada earthquakes occur mostly independently with average recurrence intervals of 151 and 117 years respectively an sse patch slipped coseismically during both the nankai and hyuga nada earthquakes the rupture of the nankai earthquakes extended to the hyuga nada region every 500 600 years and was followed by quiescence of sses for more than 200 years subsequently sses occurred repeatedly every 8 years current observational findings are generally consistent with the characteristics obtained from our scenarios except regarding the recurrence intervals of hyuga nada earthquakes for which few observations are available further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

migrating tremor off southern kyushu as evidence for slow slip of a shallow subduction interface detection of shallow slow earthquakes offers insight into the near trench part of the subduction interface an important region in the development of great earthquake ruptures and tsunami generation ocean bottom monitoring of offshore seismicity off southern kyushu japan recorded a complete episode of low frequency tremor lasting for 1 month that was associated with very low frequency earthquake vlfe activity in the shallow plate interface the shallow tremor episode exhibited two migration modes reminiscent of deep tremor down dip of the seismogenic zone in some other subduction zones a large scale slower propagation mode and a rapid reversal mode these similarities in migration properties and the association with vlfes strongly suggest that both the shallow and deep tremor and vlfe may be triggered by the migration of episodic slow slip events

centroid moment tensor inversions of offshore earthquakes using a three dimensional velocity structure model slip distributions on the plate boundary along the nankai trough due to complex three dimensional 3d heterogeneous structures conventional one dimensional 1d analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters especially dip angles and centroid depths of offshore earthquakes combining long term onshore seismic observations and numerical simulations of seismic wave propagation in a 3d model we conducted centroid moment tensor cmt inversions of earthquakes along the nankai trough between april 2004 and august 2019 to evaluate decade scale seismicity green s functions for cmt inversions of earthquakes with moment magnitudes of 4 3 6 5 were evaluated using finite difference method simulations of seismic wave propagation in the regional 3d velocity structure model significant differences of focal mechanisms and centroid depths between previous 1d and our 3d catalogues were found in the solutions of offshore earthquakes by introducing the 3d structures of the low velocity accretionary prism and the philippine sea plate dip angles and centroid depths for offshore earthquakes were well constrained teleseismic cmt also provides robust solutions but our regional 3d cmt could provide better constraints of dip angles our 3d cmt catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the nankai trough the regular and slow interplate earthquakes were separately distributed with these distributions reflecting the heterogeneous distribution of effective strengths along the nankai trough plate boundary by comparing the spatial distribution of seismic slip on the plate boundary with the slip deficit rate distribution regions with strong coupling were clearly identified

the geochemistry of river particulates from the continental usa major elements river particulates have been collected from twenty three rivers from throughout the continental usa the rivers drain mostly large basins basin areas range from 2 1 x 10 3 to 2970 x 10 3 km2 composed of mixed lithologies and spanning a wide range of climatic conditions as evidenced by a large variation in air and ground water temperatures precipitation and runoff suspended particulates have been analyzed for organic and inorganic carbon as well as the major elements al fe mn k si ca mg and na also determined were suspended sediment loads at the time of sampling particle surface areas and grain size distributions five year average river water chemistry and suspended sediment concentrations obtained from usgs water supply reports are also included as supporting information particle chemistry systematically varies with rates of runoff with high runoff rivers transporting the most heavily altered particulates and low runoff rivers carrying the least altered degrees of alteration are indicated by the extent to which the refractory nonmobile elements al and fe are concentrated into the particulates and the extent to which the most easily weathered elements na ca and mg have been leached overall the susceptibility of elements towards leaching is consistent with numerous previous descriptions of element mobility on weathering a simple predictive model has been developed to explore and explain the observed trends between particle composition and river runoff thus the elemental composition of riverine particulates may be given by the expression pcoi propi tm dcoi ss where pcoi is the concentration of element i as the oxide in a riverine particulate propi is the proportion of i as the oxide in unweathered rock dcoi is the dissolved concentration of i as the equivalent oxide tm is the total rock derived mass dissolved in river water and ss is suspended sediment concentration to utilize this equation a model was first developed to predict the concentration of river solutes with the input of temperature precipitation and a limited number of weathering parameters combining this solute model with the above predictive equation for particle composition it was discovered that the observed trends between particle composition and runoff require the special circumstance of decreasing ss with increasing runoff hence the composition of river particulates depends both on the climate parameters of runoff and temperature as they control dissolved river chemistry and the nonclimate parameters including elevation relief tectonics and basin area that control the ss load of rivers

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

sources and transport of land derived particulate and dissolved organic matter in the gulf of mexico texas shelf slope the use of ligninphenols and loliolides as biomarkers the fate and transport of terrestrial organic matter across the continental margin in the gulf of mexico was studied in 1992 and 1993 using chemical biomarkers lignin phenols were utilized as biomarkers for terrestrial inputs and indicated that much of the terrestrial organic matter inputs were deposited on the shelf break and slope the lignin phenol concentrations normalized to carbon in poc hmw doc and sediments in slope waters were considerably higher than at other open ocean sites studied previously the dominant mechanism for transport of terrestrially derived poc and hmw doc across the shelf and slope was hypothesized to be advection of riverine and estuarine discharges through benthic nepheloid layers based on loliolide concentrations in the water column we believe that lateral transport of these materials at the shelf break through extensions of benthic nepheloid layers may have been an important mechanism for the injection of terrestrially derived organic matter into deep slope waters