interseismic strain accumulation in south central chile from gps measurements 1996 1999 1 two campaigns of global positioning system gps measurements were carried out in the concepcion constitucion area of chile in 1996 and 1999 it is very likely that this area is a mature seismic gap since no subduction earthquake has occurred there since 1835 in 1996 32 sites were occupied in the range 35 s 37 s between the pacific coast of chile and the andes near the chile argentina border in 1999 the network was extended by the installation of 9 new points in the arauco region whereas 13 points among the 1996 stations were reoccupied the analysis of this campaign data set together with the data recorded at eight continuous gps sites mostly igs stations in south america and surrounding regions indicates a velocity of about 40 10 mm yr in the direction n80 90 s for the coastal sites with respect to stable cratonic south america this velocity decreases to about 20 25 mm yr towards the andes we interpret this result as reflecting interseismic strain accumulation above the nazca south america subduction zone due to a locked thrust zone extending down to about 60 km depth

three dimensional distribution of ionospheric anomalies prior to three large earthquakes in chile using regional global positioning system gps networks we studied three dimensional spatial structure of ionospheric total electron content tec anomalies preceding three recent large earthquakes in chile south america i e the 2010 maule mw8 8 the 2014 iquique mw8 2 and the 2015 illapel mw8 3 earthquakes both positive and negative tec anomalies with areal extent dependent on the earthquake magnitudes appeared simultaneously 20 40 minutes before the earthquakes for the two mid latitude earthquakes 2010 maule and 2015 illapel positive anomalies occurred to the north of the epicenters at altitudes 150 250 km the negative anomalies occurred further to the north at higher altitudes 200 500 km this lets the epicenter the positive and negative anomalies align parallel with the local geomagnetic field which is a typical structure of ionospheric anomalies occurring in response to positive surface electric charges

great earthquakes in the 21st century and geodynamics of the tibetan plateau abstract what are the geodynamic processes that caused these deadly earthquakes why have these earthquakes caused so much damage what are the key lessons that we have learned from these devastating earthquakes answers to these questions will significantly enhance not only our understanding of earthquake occurrence but also our ability to reduce seismic hazard under the framework of bi lateral cooperation on earthquake sciences between china and usa the second bi lateral workshop on earthquake sciences was held in chengdu sichuan province china from april 22 to 25 2011 among the goals of this workshop was a review of recent advances in the study of great earthquakes and the exchange of ideas on earthquake disaster reduction the principle theme of the workshop was great earthquakes in the 21st century and geodynamics this special issue contains a total of 24 papers presented during the workshop the contributions cover a wide range of topics associated with the theme this preface summarizes the main points of the papers presented in this issue

coseismic gravity changes of the 2010 earthquake in central chile from satellite gravimetry 1 the first map of coseismic changes in gravity and geoid height has been drawn using the data from the gravity recovery and climate experiment grace satellites for the 2004 sumatra andaman earthquake here we present the second case of coseismic gravity change observation by satellite gravimetry i e the change caused by an interplate thrust earthquake that occurred on 27 february 2010 in central chile mw 8 8 gravity showed a negative jump with the largest drop of 5 gal on the back arc side the observed changes agree with those calculated assuming the realistic earth and fault parameters inferred from coseismic displacements of global positioning system gps stations gravity in this area shows large seasonal and inter annual variability and postseismic gravity changes could be isolated only by carefully removing hydrological signals

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

interseismic strain accumulation measured by gps in the seismic gap between constitucion and concepcion in chile the concepcion constitucion area 35 37 s in south central chile is very likely a mature seismic gap since no large subduction earthquake has occurred there since 1835 three campaigns of global positioning system gps measurements were carried out in this area in 1996 1999 and 2002 we observed a network of about 40 sites including two east west transects ranging from the coastal area to the argentina border and one north south profile along the coast our measurements are consistent with the nazca south america relative angular velocity 55 9 n 95 2 w 0 610 ma discussed by vigny et al 2008 this issue which predicts a convergence of 68 mm year oriented 79 n at the chilean trench near

slip distribution and seismic moment of the 2010 and 1960 chilean earthquakes inferred from tsunami waveforms and coastal geodetic data the slip distribution and seismic moment of the 2010 and 1960 chilean earthquakes were estimated from tsunami and coastal geodetic data these two earthquakes generated transoceanic tsunamis and the waveforms were recorded around the pacific ocean in addition coseismic coastal uplift and subsidence were measured around the source areas for the 27 february 2010 maule earthquake inversion of the tsunami waveforms recorded at nearby coastal tide gauge and deep ocean assessment and reporting of tsunamis dart stations combined with coastal geodetic data suggest two asperities a northern one beneath the coast of constitucion and a southern one around the arauco peninsula the total fault length is approximately 400 km with seismic moment of 1 7 1022 nm mw 8 8 the offshore dart tsunami waveforms require fault slips beneath the coasts but the exact locations are better estimated by coastal geodetic data the 22 may 1960 earthquake produced very large 30 m slip off valdivia joint inversion of tsunami waveforms at tide gauge stations in south america with coastal geodetic and leveling data shows total fault length of 800 km and seismic moment of 7 2 1022 nm mw 9 2 the seismic moment estimated from tsunami or joint inversion is similar to previous estimates from geodetic data but much smaller than the results from seismic data analysis

a review of palaeo tsunamis for the christchurch region new zealand abstract recent earthquake activity in and around the christchurch region new zealand has raised concerns about tsunamis inundating the coastline while the occurrence of historical tsunamis is well documented information about palaeo tsunamis is poorly understood this review draws together data from numerous sources to outline our current understanding of palaeo tsunamis for the region six probable and one possible holocene palaeo tsunamis are identified and proxy data are summarised with reference to all potential near contemporaneous sites throughout new zealand the events cover a period of around 6500 years occurring around 6250 6500 yr bp 4800 5350 yr bp 4050 4450 yr bp 3400 3700 yr bp 2200 2300 yr bp 1250 1350ad and in 1604ad the relative exposure of christchurch city to tsunamis has however fluctuated over time this is most notable over the past 2000 years or so since the brighton spit extended south to close off the bay then retreated and formed again causing the avon heathcote estuary ihutai to change from open to closed bay and then from open bay to estuary the relative extent of the tsunami hazard is therefore controlled to a certain extent by the presence or absence of the spit which is in turn governed by interactions between seismic activity and fluvial processes potential palaeo sources vary from local subduction fault rupture nearshore submarine landslide gas hydrate release seamount flank collapse to distant subduction fault ruptures in central and south america candidates in most cases more than one potential source was identified for each palaeo tsunami however it appears that the most likely sources for most if not all of the palaeo tsunamis were from central and south america as opposed to more local alternatives the identification of palaeo sources was largely based upon historically documented events and palaeoseismic research and as such was almost entirely limited to known local and distant fault ruptures a review of other potential palaeo sources with tsunamigenic potential reveals numerous additional candidates that need to be investigated in more detail

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

what are the spratly islands abstract seismic records combined with dredged samples and a core indicate that the spratly islands of the dangerous ground province are constructed of presently active carbonate build ups known to extend back continuously at least to the pleistocene and presumed to have initiated in the miocene most likely upon the crests of sea floor cuestas that trend north east south west parallel to the sea floor spreading magnetic anomalies of the contiguous abyssal plain of the southern part of the south china sea the cuestas range from spectacular to subdued constructed of triassic and cretaceous strata and no older rocks have been identified from dredges the cuesta axes plunge towards the south west away from the islands suggesting that the reefs began colonising their more elevated parts but the timing is uncertain the highest seismically recorded cuesta crest is in 440 m of water and the islands and reefs are generally closely surrounded by water deeper than 1500 m since the so called mid miocene unconformity mmu the region has been undergoing post rift thermal subsidence however the nearby seismic lines show no evidence of drowned carbonate reefs it is suggested that the coral algal reefs colonised the crests of the most elevated cuestas that have maintained stability as shown by the 165 m core of one reef indicating periodic exposure with caliche horizons deepening water has protected the build ups from extinction by post rift draping strata in contrast to the central luconia province and the build ups have been able to keep up with regional thermal subsidence the dredged mesozoic strata indicate that the dangerous ground is not exotic and should be interpreted as an integral part of the pre rift sundaland continent that included south china vietnam peninsular malaysia western sarawak and possibly part of sabah igneous and metamorphic samples have been dredged although individual spot k ar dates cannot be accepted at face value such rocks can also be interpreted as an integral part of sundaland post mmu dredged samples are predominantly deep water calcareous mudstones typified by the draping strata of the ocean drilling program odp site 1143 cored from recent to late miocene

intense foreshocks and a slow slip event preceded the 2014 iquique mw 8 1 earthquake the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 the moment magnitude mw 8 1 iquique earthquake of 1 april 2014 broke a highly coupled portion of this gap to understand the seismicity preceding this event we studied the location and mechanisms of the foreshocks and computed global positioning system gps time series at stations located on shore seismicity off the coast of iquique started to increase in january 2014 after 16 march several mw 6 events occurred near the low coupled zone these events migrated northward for 50 kilometers until the 1 april earthquake occurred on 16 march on shore continuous gps stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred

impact of topography on earthquake static slip estimates abstract our understanding of earthquakes is limited by our knowledge and our description of the physics of the earth when solving for subsurface fault slip it is common practice to assume minimum complexity for characteristics such as topography fault geometry and elastic properties these characteristics are rarely accounted for because our knowledge of them is often partial and they can be difficult to include in simulations however topography and bathymetry are known all over the earth s surface and recently developed software packages such as specfem x have simplified the process of including them in calculations here we explore the impact of topography on static slip estimates we also investigate whether the influence of topography can be accounted for with a zeroth order correction which accounts for variations in distance between subfaults and the surface of the domain to this end we analyze the 2015 mw 7 5 gorkha nepal and the 2010 mw 8 8 maule chile earthquakes within a bayesian framework the regions affected by these events represent different types of topography chile which contains both a deep trench and a major orogen the andes has a greater overall elevation range and steeper gradients than nepal where the primary topographic feature is the himalayan mountain range additionally the slip of the continental nepal event is well constrained whereas observations are less informative in a subduction context we show that topography has a non negligible impact on inferred slip models our results suggest that the effect of topography on slip estimates increases with limited observational constraints and high elevation gradients in particular we find that accounting for topography improves slip estimates where topographic gradients are large when topography has a significant impact on slip the zeroth order correction is not sufficient

the temporal and spatial distribution of volcanism in the south china sea region cenozoic magmatism in the south china sea the associated continental margins coastal south china and indochina is reviewed volcanism contemporaneous with rifting and sea floor spreading in the south china sea was very weak in the margins and adjacent areas there was only very limited magmatic activity most probably after the cessation of sea floor spreading the south china sea has non volcanic margins large basement relief caused by extension formed major basins and a continental oceanic transitional zone in the northern margin reflects high crustal rigidity during rifting and drifting the paucity of a magma supply and presence of rigid fault blocks are unfavorable to the mantle flow model previously proposed to account for the opening of the south china sea which was supposedly linked to the escape of indochina induced by indo eurasia collision c 2005 published by elsevier ltd

high resolution relocation and mechanism of aftershocks of the 2007 tocopilla chile earthquake summary we study the distribution of the aftershocks of tocopillamw 7 7 earthquake of 2007 november 14 in northern chile in detail this earthquake broke the lower part of the seismogenic zone at the southern end of the northern chile gap a region that had its last megathrust earthquake in 1877 the aftershocks of tocopilla occurred in several steps the first day they were located along the coast inside the co seismic rupture zone after the second day they extended ocean wards near the mejillones peninsula finally in december they concentrated in the south near the future rupture zone of the michilla intermediate depth earthquake of 2007 december 16 the aftershock sequence was recorded by the permanent ipoc integrated plate boundary observatory in chile network and the temporary task force network installed 2 weeks after the main event a total of 1238 events were identified and the seismic arrival times were directly read from seismograms initially we located these events using a single event procedure and then we relocated them using the double difference method and a crosscorrelation technique to measure time differences for clusters of aftershocks we tested a 1 d velocity model and a 2 d one that takes into account the presence of the subducted nazca plate relocation significantly reduced the width of the aftershock distribution in the inland area the plate interface imaged by the aftershocks is thinner than 2km the two velocity models give similar results for earthquakes under the coast and a larger difference for events closer to the trench the surface imaged by the aftershocks had a length of 160km it extends from 30 to 50km depth in the northern part of the rupture zone and between 5 and 55km depth near the mejillones peninsula we observed a change in the dip angle of the subduction interface from 18 to 24 at a depth of 30km we propose that this change in dip is closely associated with the upper limit of the rupture zone of the main event we also studied the focal mechanisms of the aftershocks most of them were thrust events like the mainshock as the aftershock activity was significantly reduced on 2007 december 13 an ml 6 1 event occurred offshore of the mejillones peninsula reactivating the seismicity three days later the michilla intraslab earthquake of mw 6 8 ruptured an almost vertical fault with slab push mechanism the aftershocks locations of this event define a planar zone about 11km in depth situated right bellow the subduction interface

mesozoic and cainozoic rocks dredged from the south china sea reed bank area and sulu sea and their significance for plate tectonic reconstructions abstract outcrops of pre quaternary rocks were sampled by dredging and coring during two cruises of rv sonne in the south china sea and sulu sea 1982 1983 late triassic deltaic sandstones wih plant remains are the oldest sediments recovered late jurassic early cretaceous regional metamorphism is indicated by gneiss and garnet mica schists exposed in the northwestern flanks of reed bank these rocks and occurrences of gabbro diorite dacite rhyolite and siliceous shale prove that the dangerous grounds and reed bank are underlain by a continental fragment during the period of seafloor spreading in the south china see a late oligocene to early miocene carbonate platform developed on this southwards drifting continental fragment which subsided in the middle miocene middle miocene andesite and early to middle miocene reefal carbonates were recovered from the cagayan ridge in the sulu sea the new data are in accord with the plate tectonic history developed by taylor and hayes 1980 1983 and holloway 1981

strong vertical mixing of deep water of a stratified reservoir during the maule earthquake central chile mw 8 8 1 vertical profiles of water temperature in rapel reservoir central chile 34 2 23 s 71 35 23 w 110 m a s l recorded the hydrodynamic response of the stratified water column of the reservoir produced by the 8 8 magnitude maule earthquake epicentre located in 36 15 36 s 73 14 20 w showing an intense vertical mixing of deep water the vertical mixing was characterized by changes in the potential energy of the water column and the eddy diffusivity of the mixing and these values were used to estimate the mixing efficiency of the event it is hypothesized that the turbulent flow that mixed the water column was mainly induced by the oscillation of the bed although surface gravitational waves could also have contributed to the vertical mixing so far this is the first time that the hydrodynamic response of a reservoir during a mega earthquake is measured and described

tectonic stratigraphic division and blind fold structures in nansha waters south china sea extensive multiple channel reflection seismic data have been collected in the nansha spratley islands waters the southern margin of the south china sea stratigraphic correlation is shown with focus on a comprehensive geophysixcal survey line run front offshore nw sabah to offshore se vietnam according to the varying tectono stratigraphy from southeast to northwest five tectonic belts can be determined i e the palawan borneo nappe nansha trough nanwei liyue compressive belt zheng he extensional belt and the circum southwest subbasin belt in the palawan borneo nappe neogene quaternary deposits were highly upthrust northwestwards resulting in a series of moderately to tightly folded anticlines separated by open synclines the nansha trough was a narrow deep water belt filled with thick undisturbed neogene quaternary deposits the nanwei liyue compressive bell was dominated by strongly folded paleo anticlines overlain by an undeformed sedimentary cap with a pronounced hiatus of paleogene sediments the zheng he extensional belt consisted of a rugged topography and paleogene half grabens bounded by listic faults the major extensional faults were reactivated to cut through the overlying neogene quaternary deposits over the circum southwest subbasin belt neogene quaternary deposits draped on the largely subsided fault blocks related to the late oligocene mid miocene seafloor spreading based on the regional stratigraphic correlation the prominent paleo anticlines found within the nanwei liyue compressive belt are deduced to consist of mainly mesozoic marine sediments that were compressed in the late mesozoic era therefore the nansha microcontinent block is shown to be a collision complex assembled during late mesozoic era c 2004 elsevier ltd all rights reserved

upper plate deformation measured by gps in the coquimbo gap chile abstract since the mw 7 3 punitaqui earthquake in 1997 the area between 30 s and 32 s coquimbo illapel section of the chilean subduction has been the locus of a decennial seismic swarm a dense network of 30 benchmarks have been installed in this area and surveyed six times with high precision gps over the last 3 years surface deformation here is compatible with elastic loading due to partial locking on the subduction interface at depth here we show that in this area only 40 45 of the total convergence rate between nazca and south america plates gives way to accumulation of elastic deformation in the upper plate the remaining 60 55 being dissipated by free or aseismic slip the cumulative slip due to the seismic swarm explaining no more than 1 3rd to 1 4th of it we also find that the accumulation decreases northward to reach almost zero around 30 s la serena tongoy whether this is a steady state or only a transient pattern a steady decrease of coupling is not clear since our measurements span only 3 years and since early measurements 10 years ago were sparse and differ only marginally from ours

the 2007 m7 7 tocopilla northern chile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behavior 1 in 2007 a m7 7 earthquake occurred near the town of tocopilla within the northern chile seismic gap main shock slip derived from coseismic surface deformation was confined to the depth range between 30 and 55 km we relocated 1100 events during six months before and one week after the main shock aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of mejillones peninsula mp waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock however a few events appear to occur in the upper plate some with extensional mechanisms juxtaposing the tocopilla aftershocks with those following the neighboring 1995 antofagasta earthquake produces a striking symmetry across an ew axis in the center of mp events seem to skirt around mp probably due to a shallower moho there we suggest that the seismogenic coupling zone in northern chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable for both earthquake sequences aftershocks agglomerate in the conditionally stable region whereas maximum inter seismic slip deficit and co seismic slip occurs in the unstable region the boundary between the unstable and conditionally stable zones parallels the coastline we identify a similar segmentation for other earthquakes in chile and peru where the offshore segments break in great m 8 earthquakes and the onshore segments in smaller m 8 earthquakes using critical taper analysis we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate dependency of friction

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

marginal basin evolution the southern south china sea abstract the southern south china sea is divided into contrasting morphology by the west baram line to the west is the sundaland extinct passive margin in which rifting began in the eocene 46 ma and ceased at 19 21 ma anomaly 6 where sea floor spreading began much later than along the shelf of china the break up hiatus lasted 3 5 ma marked by the mid miocene unconformity also preserved on land sarawak the post rift strata date from 16 ma and drape over the rifted topography to the east is a convergent margin that became a collision zone in the middle miocene the sunda shelf is of uniform 30 km thickness except in localised deep basins and extends to a water depth of 200 m the continental slope is narrow the continental rise dangerous grounds is covered by water ranging from 500 m to 3 5 km depth at the continent ocean transition its width ranges from 170 to 330 km the rajang delta extends over the shelf and continental slope its post rift sediments drape over the rifted proximal topography of the dangerous grounds to the east the drape is thinner and has not completely buried the rifted topography the cuestas appear to have supported the carbonate build up infrastructures of the spratly islands whose slopes rise abruptly from a sea floor of 2 3 km depth the sabah and brunei margin is a collision zone that was formerly convergent the on land geology indicates a mesozoic ophiolitic basement the main collision feature is the western cordillera constructed mainly of sandy eocene to lower miocene turbidites predominantly oligocene to lower miocene in the west crocker 32 18 ma uplifted episodically throughout the upper miocene and pliocene 14 8 ma the 2 km deep northwest borneo trough may be a relict of the convergence phase but could also be a collisional foredeep the oil prolific baram delta resulting from uplift and erosion of the western cordillera has built out as far as the northwest borneo trough it is suggested that the passive margin continental rise dangerous grounds has been underthrust beneath sabah to cause uplift of the western cordillera the west baram line accordingly abruptly separates the collision zone from the western extinct passive margin and is a now extinct major right lateral transform fault

earthquake cycle dominates contemporary crustal deformation in central and southern andes with the advent of global positioning system gps technology and its applications to high precision geodesy earth scientists have gained an unprecedented opportunity to study the kinematics and dynamics of present day deformation processes along plate boundary zones however until now our knowledge of the deformation processes associated with the andean subduction along the western coast of south america has been limited here we present first estimates of present day crustal deformation rates in the central and southern sections of the andes between latitudes 22 s and 42 s we find that the deformation in the central section of our study area is dominated by the interseismic phase of an earthquake deformation cycle caused by 100 coupling of the thrust interface between the subducting nazca and the overriding south america plates the estimated depth of coupling is not uniform along strike north of 30 s it is v33 km deep while south of 35 s it reaches 50 km depth in addition we observed postseismic relaxation effects in the northern part of our network in the area of the 1995 mw8 0 antofagasta earthquake south of 38 s we detected a similar deformation pattern as in the antofagasta area which we attribute to postseismic relaxation effects of the 1960 mw9 5 valdivia earthquake fl 2001 elsevier science b v all rights reserved

active faulting and heterogeneous deformation across a megathrust segment boundary from gps data south central chile 36 39 s 1 this study focuses on the present day deformation mechanisms of the south central chile margin at the transition zone between two megathrust earthquake segments defined from historical data the valdivia and concepcion sectors new gps data and finite element models with complex geometries constrained by geophysical data are presented to gain insight into forearc kinematics and to address the role of upper plate faults on contemporary deformation gps vectors are heterogeneously distributed in two domains that follow these two earthquake segments we find that models which simulate only interseismic locking on the plate interface fail to reproduce surface deformation in the entire study area in the concepcion domain models that include a crustal scale fault in the upper plate better reproduce the gps observations in the valdivia domain gps data show regional scale vertical axis rotations which could reflect postseismic deformation processes at the edge of the mw 9 5 earthquake that ruptured in 1960 and or activity of another crustal fault related to motion of a forearc sliver our study suggests that upper plate faults in addition to earthquake cycle transients may exert an important control on the surface velocity of subduction zone forearcs

heterogeneous plate locking in the south central chile subduction zone building up the next great earthquake abstract we use global positioning system gps velocities and kinematic finite element models fe models to infer the state of locking between the converging nazca and south america plates in south central chile 36 s 46 s and to evaluate its spatial and temporal variability gps velocities provide information on earthquake cycle deformation over the last decade in areas affected by the megathrust events of 1960 m w 9 5 and 2010 m w 8 8 our data confirm that a change in surface velocity patterns of these two seismotectonic segments can be related to their different stages in the seismic cycle accordingly the northern 2010 segment was in a final stage of interseismic loading whereas the southern 1960 segment is still in a postseismic stage and undergoes a prolonged viscoelastic mantle relaxation after correcting the signals for mantle relaxation the residual gps velocity pattern suggests that the plate interface accumulates slip deficit in a spatially and presumably temporally variable way towards the next great event though some similarity exist between locking and 1960 coseismic slip extrapolating the current decadal scale slip deficit accumulation towards the 300 yr recurrence times of giant events here does neither yield the slip distribution nor the moment magnitude of the 1960 earthquake this suggests that either the locking pattern is evolving in time to reconcile a slip deficit distribution similar to the 1960 earthquake or that some asperities are not persistent over multiple events the accumulated moment deficit since 1960 suggests that highly locked patches in the 1960 segment are already capable of producing a m 8 event if triggered to fail by stress transfer from the 2010 event

paleoceanography of the south china sea since the middle miocene evidence from planktonic foraminifera late middle miocene to pleistocene planktonic foraminifera pf in fairly continuous hemipelagic sediments recovered at ocean drilling program odp site 1143 from the southern south china sea scs were studied with sampling intervals of 10 to 150 cm a total of 16 pf events are revised for the 516 m long section providing an age model for the last 12 ma at this site on the basis of benthic foraminiferal d 18 o stratigraphy and the smoothed planktonic age model new ages are assigned to three pf events last occurrence lo globorotalia multicamerata sensu lato s l at 2 18 ma first occurrence fo sphaeroidinella dehiscens sensu stricto s s at 3 6 ma and fo globigerinoides conglobatus at 6 6 ma in the south china sea distinct pf faunal transition from globorotalia siakensis g mayeri group to mixed layer species occurred during the early late miocene 9 6 ma the transition reflects a deepened upper water thermocline possibly corresponding to the closure of the indonesian seaway and intensification of equatorial pacific warm currents abundance variations of neogloboquadrina spp indicate a marked shoaling of the thermocline in the northern south china sea after 3 2 5 ma affected possibly by a strengthened asian winter monsoon while a deeper thermocline existed in the southern south china sea since the late miocene characterizing the west pacific bwarm poolq wpwp a deepening thermocline influenced by consistently warm surface water since the late miocene in the southern south china sea is also evidenced by a two stepwise increase of pulleniatina group by a gradually decreasing sphaeroidinella sphaeroidinellopsis spp and abundant globorotalia menardii and related species the fo globigerinoides ruber pink at approximately 1 ma and an abrupt increase in the pink to all ratio of g ruber at 0 4 ma at site 1143 provide two additional pf events for deciphering pleistocene biostratigraphy and paleoceanography d 2004 elsevier b v all rights reserved

analysis of submarine landsliding in the rupture area of the 27 february 2010 maule earthquake central chile the comparison of bathymetric datasets compiled before and after the mw 8 8 maule earthquake of the 27 february 2010 offshore central chile proves that no new submarine landslides on a size scale detectable with hull mounted bathymetric echosounders features of a horizontal size of 1 km formed as a direct consequence of the ground shaking gravity coring around a pre existing slide feature offshore concepcion biobio slide however documents that 1 a number of events occurred as retrogressive failures of the biobio slide wall the youngest of which is 700 1000 years old and that 2 a very recent small scale slide structure resulted from non destructive imbricate stacking of a thin sediment layer pore water geochemical data show that this event post dates the maule earthquake suggesting that it was triggered by one of the numerous aftershocks the absence of larger failures and the presence of a small slide let us propose that in contrast to apparent logic frequent violent earthquakes at convergent margins do not necessarily pose a particular tsunami risk by landslides the frequent shaking might even limit the slide volume and therefore their tsunami hazard as instead of rare and large slides frequent smaller slides are induced

slip rate of trench parallel normal faulting along the mejillones fault atacama fault system relationships with the northern chile subduction and implications for seismic hazards the recent tectonics of the arid northern chile andean western forearc is characterized by trench parallel normal faults within the atacama fault system afs since the 1995 mw8 1 antofagasta earthquake the mechanism driving this recent and localized extension is considered to be associated with the seismic cycle within the subduction zone analyzing morphotectonic patterns along these faults allows examining the seismic potential associated with the subduction zone using field digital elevation models and in situ produced cosmogenic 10be we determined a 0 2 mm yr 1 long term vertical slip rate along the mejillones fault one of the most prominent structures within the afs this result suggests that the afs corresponds to slow slip rate faults despite the rapid subduction context however the size of coseismic slips observed along the afs faults suggests that larger subduction earthquakes mw 8 1 may occur episodically in the area

potential slab deformation and plunge prior to the tohoku iquique and maule earthquakes megathrust earthquakes rupture the shallow plate boundary in subduction zones analysis of seismic activity preceding megathrust quakes in japan and chile reveals deep seismicity that may mark plunging of the slabs prior to main fault rupture

foreshock patterns preceding great earthquakes in the subduction zone of chile foreshock activity is considered as one of the most promising precursory changes for the main shock prediction in the short term averaging over several foreshock sequences has shown that foreshocks are characterized by distinct 3d patterns their epicenters move towards the main shock epicenter event count accelerates and b value drops however these space time size patterns were verified so far only in a very few individual cases mainly due to inadequate seismicity catalogue data we have investigated 3d foreshock patterns before the mw 8 8 maule in 27 february 2010 mw 8 1 iquique in 1 april 2014 and mw 8 4 illapel in 16 september 2015 great earthquakes in the chile subduction zone to avoid biased results no a priori spatiotemporal definitions of foreshocks were inserted the procedure was based on pattern recognition from statistically significant seismicity changes in the three domains the pattern recognition in one domain was independent of the pattern recognition in another domain we found and verified with two independent catalogue data sets csn ipoc that within a critical area of ca 65 km from the main shock epicenter the 2014 event was preceded by distinct foreshock 3d patterns a nearly weak foreshock stage 20 january 14 march 2014 was followed by a main strong stage 15 march 1 april 2014 highly significant in all domains although foreshock activity slightly decreased in about the last 5 days seismic moment release also accelerated in the last stage due to the occurrence of a cluster of very strong foreshock events foreshock activity very likely occurred in the hanging wall fault domain on the south american plate overriding nazca plate the 2014 foreshock activity was quite similar to the one preceding the 6 apr 2009 l aquila italy mw 6 3 earthquake associated with normal faulting using the 2014 earthquake as a reference event we observed that similar foreshock 3d patterns preceded the 2010 and 2015 earthquakes within critical distances of about 170 and 50 km respectively however the foreshock activities were only weak in both the cases likely because of poor catalogue completeness

past and potential tsunami sources in the south china sea a brief synthesis abstract extending across some 3 5 million square km and with coastlines populated by in excess of 80 million people the south china sea scs is bordered by seven independent states understanding the risk of tsunamis in the scs is therefore an imperative especially given the new priorities for the science community following the endorsement by the un general assembly of the sendai framework for disaster risk reduction 2015 2030 our review presents a synthesis of existing literature on the current state of knowledge concerning known tsunamigenic threats but also highlights a number of other potential sources that have so far received less attention or gone largely un or under recognised an overview of the geological evolution of the scs is presented in order to appreciate how the existing structural configuration of the ocean basin is responsible for the presence of a variety of potential tsunamigenic mechanisms traditional thinking places the generation of a large magnitude earthquake at the manila trench subduction zone at the top of the spectrum for tsunami potential with several simulations already available in the literature illustrating wave characteristics resulting from the worst case rupture in addition to the manila trench and other possible earthquake sources however volcanic activity and submarine landsliding of sediment burden on continental shelves on the scs margins represent hitherto fundamentally unquantified tsunami threats although revealed nonetheless by for example the existence of the giant brunei and baiyun submarine slides furthermore in the central scs previously considered essentially devoid of tsunami sources numerous near surface carbonate platforms and coral atolls show evidence of arcuate bight like structures in their planform geometry likewise suggesting their propensity for possible tsunamigenic lateral flank collapse in the current absence of well constrained tsunami probability estimates and scenarios of wave size and propagation features for non earthquake tsunami sources future research priorities lie in two main areas these are 1 improvement of modelling for tsunamigenic submarine failures as well as for earthquakes and 2 a greater focus on geomorphic investigation to identify palaeotsunami deposits on coastlines considered likely to have been impacted in the past and where good preservation potential exists this is needed to establish the magnitude timing frequency of events on holocene timescales the last 10 000 years well beyond historical records thereby improving our capabilities for understanding and forecasting the likelihood and severity of future tsunami risk in the south china sea

deep crustal structure of the conjugate margins of the sw south china sea from wide angle refraction seismic data abstract the south china sea is the largest marginal basin of se asia yet its mechanism of formation is still debated a 1000 km long wide angle refraction seismic profile was recently acquired along the conjugate margins of the sw sub basin of the south china sea over the longest extended continental crust a joint reflection and refraction seismic travel time inversion is performed to derive a 2 d velocity model of the crustal structure and upper mantle based on this new tomographic model northern and southern margins are genetically linked since they share common structural characteristics most of the continental crust deforms in a brittle manner two scales of deformation are imaged and correlate well with seismic reflection observations small scale normal faults grabens horsts and rotated faults blocks are often associated with a tilt of the velocity isocontours affecting the upper crust the mid crust shows high lateral velocity variation defining low velocity bodies bounded by large scale normal faults recognized in seismic reflection profiles major sedimentary basins are located above low velocity bodies interpreted as hanging wall blocks along the northern margin spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the continent ocean transition the continent ocean transitions are narrow and slightly asymmetric 60 km on the northern side and no more than 30 km on the southern side indicating little space for significant hyper stretched crust although we have no direct indication for mantle exhumation shallow high velocities are observed at the continent ocean transition the moho interface remains rather flat over the extended domain and remains undisturbed by the large scale normal faults the main decollement is thus within the ductile lower crust

megathrust friction determined from mechanical analysis of the forearc in the maule earthquake area the seismogenic potential of a given fault depends essentially on its frictional properties and on the mechanical properties of the medium determining the spatio temporal variations of frictional properties is therefore a key issue in seismotectonics this study aims to characterize the friction on the south america megathrust in the 2010 mw 8 8 maule earthquake area from mechanical analysis of the forearc structure and morphology based on the critical taper theory we first show that the rupture area of the maule earthquake also shown to be locked in the interseismic period coincides with the stable part of the wedge in the surrounding area the wedge is critical a finding consistent with various evidence for active deformation there this is in particular true for the arauco peninsula area which seems to have arrested the maule earthquake s rupture to the south this observation lends support to the view that the seismic rupture is inhibited when propagating beneath a critical area the geometry of the critical portion of the wedge suggests a standard internal friction int 0 7 0 13 and a hydrostatic pore pressure within the wedge the effective friction beneath the critical outer wedge is estimated to be eff b 0 27 0 03 this could be related to intrinsically low friction minerals clay or high pore pressure along the megathrust we next use the limit analysis approach to constrain the variation of the effective friction along the megathrust based on the location and geometry of internal faulting within the forearc a low effective friction is found within the rupture area eff b 0 14 to explain the reactivation of thrust fault such as the santa maria updip of the coseismic rupture or the activation of normal splay faults downdip of the rupture area the low effective friction found there could reflect strong dynamic weakening

criteria for identifying bone modification by termites in the fossil record three geographically dispersed middle and later stone age cave sites in south africa and a middle stone age cave site in ethiopia share a similar taphonomic signature that includes destruction of bones associated with variable forms of star shaped features clusters of microscopically visible sub parallel striations edge gnawing pits and etching of the bone surface similar traces preserved on plio pleistocene fauna are interpreted by different authors as the possible work of termites or ants considering that ambiguity exists in the interpretation of these traces and that there are no modern examples available for comparison we set out to create a reference collection of bones modified by southern african termites here we present the results of an actualistic experiment conducted with the harvester termite trinervitermes trinervoides sjostedt isoptera termitidae in the sterkfontein valley south africa results show that within six months all bones were approximately half covered with a dark surface residue had an etched surface appearance and recorded boreholes and destruction particularly of less dense elements and epiphyses star shaped marks edge gnawing and clusters of sub parallel striations on the periosteal surface were faint after six months but became clearly visible and more plentiful after 12 months a finding attributed to the termites being more active in austral autumn and spring this result demonstrates the pertinence of insect modification studies to our understanding of regional palaeoenvironment palaeoecology and palaeoclimate this experiment has demonstrated that t trinervoides can destroy bone in all stages of preservation favouring fresh thin cortical and spongy bone with meat and marrow the presence of appreciable quantities of calcium carbonate in termite mounds suggests that termites may be drawn to dolomitic cave sites and the calcium rich bones they contain to satisfy their mineral requirements they therefore have the potential to bias taxonomic and element representation minimum number of individuals and age profiles in a faunal assemblage and may account in part for the patchy preservation of faunal remains including hominins in fossil deposits and or the lack of bone artefacts at some middle stone age cave sites preserving long sequences of occupation

the endocast of mh1 australopithecus sediba the virtual endocast of mh1 australopithecus sediba obtained from high quality synchrotron scanning reveals generally australopith like convolutional patterns on the frontal lobes but also some foreshadowing of features of the human frontal lobes such as posterior repositioning of the olfactory bulbs principal component analysis of orbitofrontal dimensions on australopith endocasts mh1 sts 5 and sts 60 indicates that among these mh1 orbitofrontal shape and organization align most closely with human endocasts these results are consistent with gradual neural reorganization of the orbitofrontal region in the transition from australopithecus to homo but given the small volume of the mh1 endocast they are not consistent with gradual brain enlargement before the transition

insights from geochemistry and diatoms to characterise a tsunami s deposit and maximum inundation limit abstract geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 february 2010 maule tsunami at las canas maule region chile but also to trace the maximum inundation limit of the event the sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60 of the total tsunami inundation distance of 380 m which was marked by organic debris pumice clasts and wooden logs it consisted of coarse to medium sand that thinned and fined inland at the most seaward point the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening fining upward units suggesting deposition by at least two waves while farther inland the fining upward deposit was probably left behind by only one wave chemical proxies ca ti vs sr ba allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and or dune area with diatom assemblages confirming the marine origin of the deposit saltwater indicators e g cl s provide evidence for the maximum inundation limit beyond the extent of the sandy deposit despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami marine and marine brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond suggesting the effect of diatom bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind while the latter might result in a slight over estimation of the inundation distance they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis thus allowing for a better estimation of the magnitude of past events post depositional processes were found to have affected the thinner sandy deposits

termites and necrophagous insects associated with early pleistocene gelasian australopithecus sediba at malapa south africa abstract this study focuses on two early pleistocene australopithecus sediba hominin specimens and associated fauna from malapa south africa these specimens have been interpreted as having fallen through a shaft opening into a cave where they died and likely mummified before being washed into a lower chamber in order to better understand the taphonomy of the fossils and to identify the invertebrate agent s responsible for damage we examined the fossils using high resolution imagery and studied the site and associated breccia blocks in the laboratory for traces of invertebrate activity we also conducted bone modification experiments with termites and hide beetles results show the presence of blowfly puparia within the cranium of the juvenile male mh1 indicating that flies visited the facial orifices of the freshly decomposing corpse blowflies which have a requirement to oviposit in daylight imply that the body was exposed to sunlight for part of the day a shaft opening that admitted sunlight is supported by the presence of a fossil fungus garden associated with mh2 fungus gardens occur subsurface and sprout mushrooms in areas with dappled light analysis of the fossil surfaces revealed a pattern comprising 14 damage types that were made on relatively fresh bone a bone modification experiment conducted with resident termites at the site showed that they created the same suite of microscopic surface features as those observed on the fossils the features are mostly the result of harvesting symbiotic fungi from fresh bones and mineral rich coatings from fossils damage resulting from the activity of hide beetles is similar to that of termites apart from invasive edge gnawing produced by the beetles this research highlights the importance of insect activity in the modification of fossils in the cradle of humankind world heritage site area and calls for consideration of this agent at other fossil sites in the region

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

australopithecus sediba at 1 977 ma and implications for the origins of the genus homo newly exposed cave sediments at the malapa site include a flowstone layer capping the sedimentary unit containing the australopithecus sediba fossils uranium lead dating of the flowstone combined with paleomagnetic and stratigraphic analysis of the flowstone and underlying sediments provides a tightly constrained date of 1 977 0 002 million years ago ma for these fossils this refined dating suggests that au sediba from malapa predates the earliest uncontested evidence for homo in africa

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

a seismological study of the 1835 seismic gap in south central chile we study the possible seismic gap in the concepcion constitucion region of south central chile and the nature of the m 7 8 earthquake of january 1939 from 1 march to 31 may 1996 a seismic network of 26 short period digital instruments was deployed in this area we located 379 hypocenters with rms travel time residuals of less than 0 50 s using an approximate velocity distribution using the velest program we improved the velocity model and located 240 high precision hypocenters with residuals less than 0 2 s the large majority of earthquakes occurred along the wadati benioff zone along the upper part of the downgoing slab under central chile a few shallow events were recorded near the chain of active volcanos on the andes these events are similar to those of las melozas near santiago a few events took place at the boundary between the coastal ranges and the central valley well constrained fault plane solutions could be computed for 32 of the 240 well located events most of the earthquakes located on the wadati benioff zone had slab pull fault mechanism due to tensional stresses sub parallel to the downgoing slab this slab pull mechanism is the same as that of eight earthquakes of magnitude around 6 that are listed in the cmt catalog of harvard university for the period 1980 1998 this is also the mechanism inferred for the large 1939 chilean earthquake a very small number of events in the benioff zone had slab push mechanisms that is events whose pressureaxis is aligned with the slab these events are found in double layered wadati benioff zones such as in northern chile or japan our spatial resolution is not good enough to detect the presence of a double layer but we suspect there may be one 2002 elsevier science b v all rights reserved

the structure and stratigraphy of deepwater sarawak malaysia implications for tectonic evolution abstract the structural stratigraphic history of the north luconia province sarawak deepwater area is related to the tectonic history of the south china sea the sarawak basin initiated as a foreland basin as a result of the collision of the luconia continental block with sarawak sarawak orogeny the foreland basin was later overridden by and buried under the prograding oligocene recent shelf slope system the basin had evolved through a deep foreland basin flysch phase during late eocene oligocene times followed by post oligocene molasse phase of shallow marine shelf progradation to present day seismic interpretation reveals a regional early miocene unconformity emu separating pre oligocene to miocene rifted basement from overlying undeformed upper miocene pliocene bathyal sediments seismic well data and subsidence analysis indicate that the emu was caused by relative uplift and predominantly submarine erosion between 19 and 17 ma ago the subsidence history suggests a rift like subsidence pattern probably with a foreland basin overprint during the last 10 ma modelling results indicate that the emu represents a major hiatus in the sedimentation history with an estimated 500 2600 m of missing section equivalent to a time gap of 8 10 ma the emu is known to extend over the entire nw borneo margin and is probably related to the sabah orogeny which marks the cessation of sea floor spreading in the south china sea and collision of dangerous grounds block with sabah gravity modelling indicates a thinned continental crust underneath the sarawak shelf and slope and supports the seismic and well data interpretation there is a probable presence of an overthrust wedge beneath the sarawak shelf which could be interpreted as a sliver of the rajang group accretionary prism alternatively magmatic underplating beneath the sarawak shelf could equally explain the free air gravity anomaly the sarawak basin was part of a remnant ocean basin that was closed by oblique collision along the nw borneo margin the closure started in the late eocene in sarawak and moved progressively northeastwards into sabah until the middle miocene the present day nw sabah margin may be a useful analogue for the oligocene miocene sarawak foreland basin

the north west borneo trough abstract the north west borneo trough is bordered along its south east margin by a melange wedge that has been the subject of disagreement with insufficient discussion offshore palawan it has been interpreted as an accretionary prism that has been preserved in place when subduction ceased in the middle miocene it is unconformably overlain by undeformed upper miocene to holocene draping strata farther south west along the trough the seismically identical melange wedge has been named a major thrust sheet system which was assumed to have been thrust as a nappe north westwards over the autochthonous dangerous grounds terrane of attenuated continental crust of the south china sea passive margin the accretionary prism model is the simplest resulting in interpretation of the north west borneo trough as a fossil trench subduction was halted by the rifted and attenuated continental crust arriving at the benioff zone choking subduction and causing isostatic uplift of the western cordillera of sabah the subduction system therefore became a collision zone resulting in the term foredeep in which case the actual trench position remains obscure and somewhere towards the south east but shown in unrestrained geological cartoons enigmas remain in the palawan area of the philippines the trough position is bathymetrically obscure in places and its given position makes it impossible to derive the calamian micro continent from continental asia as required from its stratigraphy in the south west the trough terminates abruptly at the west baram line the trough contains several spectacular edifices formerly suggested to be volcanoes or mud volcanoes but herein shown to be carbonate build ups that were drowned indicating that the trough subsided too fast for build up continuation whereas post rift thermal subsidence of the dangerous grounds was slower allowing the spratly islands build ups to continue active

seismic sequence stratigraphic analysis of the carbonate platform north offshore taiping island dangerous grounds south china sea abstract taiping island also known as itu aba is the largest natural terrestrial landmass in the south china sea and is centrally located using bathymetry and marine multi channel seismic data we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of taiping island the western flank of the carbonate platform is characterized by an intercalation between high amplitude and low amplitude reflections showing the landward and seaward migration of the platform foreslope deposits in addition there are two offshore carbonate build ups that are underlain by normal faults six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart although the evolution of the seismic sequences is partly controlled by local tectonics the overall stacking pattern of the sedimentary strata in our study area reveals five third order cycles and one second order cycle which is in accordance with the eustatic sea level chart additionally the formations of the western taiping seamount group and the zhenghe daoming trough are preliminarily analyzed based on seismic data

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

post earthquake coastal evolution and recovery of an embayed beach in central southern chile abstract earthquakes and tsunamis are significant factors for change along active margin shores and influence coastal evolution the chilean coast was affected in 2010 by a subduction earthquake with a magnitude of mw 8 8 and also by a trans pacific tsunami which generated violent geomorphologic changes and damaged homes following these events the magnitude of the changes which affect chile s central southern coast 37 s and the role of subduction earthquakes in coastal evolution on a historical scale were investigated at lebu bay an embayed beach data were generated for variations in time and space along the shoreline topographical and bathymetric changes in the bay and for morphodynamic littoral processes logarithmic and parabolic models were applied to the shoreline along with map overlays in order to determine changes the shoreline processes were analyzed based on statistics for waves tides and sediment transport for pre and post tsunami conditions an average accretion rate of 2 80 m year 1984 2010 was established for the shoreline with a strong trend towards accretion in the last 30 years a parabolic function best represented the general form of the shoreline although the presence of a river in the concave zone affected the fit in this sector two factors controlled historical changes on the beach one of anthropic origin in addition to the earthquake and tsunami on february 27th 2010 the post earthquake recovery was fast and currently the beach is in a stable condition despite the inter seismic subsidence process previous to the event this coastal system showed a high resilience in the face of coastal geomorphological changes induced by high impact natural disturbances however the opposite occurred in relation to changes induced by anthropogenic disturbances

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

estimates of stress drop and crustal tectonic stress from the 27 february 2010 maule chile earthquake implications for fault strength 1 the great 27 february 2010 mw 8 8 earthquake off the coast of southern chile ruptured a 600 km length of subduction zone in this paper we make two independent estimates of shear stress in the crust in the region of the chile earthquake first we use a coseismic slip model constrained by geodetic observations from interferometric synthetic aperture radar insar and gps to derive a spatially variable estimate of the change in static shear stress along the ruptured fault second we use a static force balance model to constrain the crustal shear stress required to simultaneously support observed fore arc topography and the stress orientation indicated by the earthquake focal mechanism this includes the derivation of a semianalytic solution for the stress field exerted by surface and moho topography loading the crust we find that the deviatoric stress exerted by topography is minimized in the limit when the crust is considered an incompressible elastic solid with a poisson ratio of 0 5 and is independent of young s modulus this places a strict lower bound on the critical stress state maintained by the crust supporting plastically deformed accretionary wedge topography we estimate the coseismic shear stress change from the maule event ranged from 6 mpa stress increase to 17 mpa stress drop with a maximum depth averaged crustal shear stress drop of 4 mpa we separately estimate that the plate driving forces acting in the region regardless of their exact mechanism must contribute at least 27 mpa trench perpendicular compression and 15 mpa trench parallel compression this corresponds to a depth averaged shear stress of at least 7 mpa the comparable magnitude of these two independent shear stress estimates is consistent with the interpretation that the section of the megathrust fault ruptured in the maule earthquake is weak with the seismic cycle relieving much of the total sustained shear stress in the crust

outer rise seismicity boosted by the maule 2010 mw 8 8 megathrust earthquake abstract the maule 2010 megathrust earthquake mw 8 8 has been characterized by two coseismic high slip patches asperities north and south of the epicenter separated by a region of lower slip here we invert full broadband waveforms to obtain regional moment tensors yielding precise centroid depth and source parameters of outer rise events mw 4 5 including a large mw 7 4 event that occurred just 1 5 h after the maule mainshock outer rise seismicity occurred mainly in two clusters 1 a large number of outer rise events in the subducting plate located just seaward of the northern asperity of the maule earthquake and 2 a second cluster with fewer events seaward of the southern edge of the maule rupture area thus the outer rise seismicity is correlated with the coseismic rupture of the maule earthquake reflecting the stress state of the interplate coupled zone the moment tensor results indicate similar extensional focal mechanisms for all outer rise events in the northern zone in the southern region most of the outer rise events are also extensional except for one strike slip event located near the oceanic mocha fracture zone the centroid depths vary from 5 to 20 km depth and present similar magnitudes many of the outer rise events nucleated near the mocha fracture zone including the mw 7 4 event and one strike slip event the calculated yield strength envelope for the oceanic nazca lithosphere suggests that the centroid depths of intraplate tensional events span almost the entire upper brittle part of the oceanic lithosphere

a review of source models of the 2015 illapel chile earthquake and insights from tsunami data the 16 september 2015 illapel chile earthquake and associated tsunami have been studied by many researchers from various aspects this paper reviews studies on the source model of the earthquake and examines tsunami data the illapel earthquake occurred in the source region of previous earthquakes in 1943 and 1880 the earthquake source was studied using various geophysical data such as near field seismograms teleseismic waveform and backprojection gps and insar data and tsunami waveforms most seismological analyses show a duration of 100 s with a peak at 50 s the spatial distribution has some variety but they all have the largest slip varying from 5 to 16 m located at 31 s 72 w which is 70 km nw of the epicenter the shallow slip seems to be extended to the trench axis a deeper slip patch was proposed from high frequency seismic data a tsunami earthquake model with a total duration of 250 s and a third asperity south of the epicenter is also proposed but we show that the tsunami data do not support this model

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

dry climate near the western pacific warm pool pleistocene caliches of the nansha islands south china sea abstract the nansha spratly islands are located in the middle of the south china sea at about 10 n near the northwestern margin of the western pacific warm pool wpwp a borehole was drilled at an atoll at nansha and cores were taken the upper 165 4 m of the borehole consists entirely of limestone of reef facies and lagoon facies which had been influenced by extensive meteoric diagenesis petrographic and geochemical studies have identified at least four subaerial exposure surfaces ses in the pleistocene carbonate sequence these ses are thought to have resulted from global sea level changes and characterized by caliche formation when developed in limestone caliches typically form in areas where annual precipitation ranges from 500 mm up to about 1200 mm compared with 1800 2200 mm of annual rainfall of the present day nansha islands the nansha caliche therefore indicates the existence of several dry climate episodes during pleistocene sea level lowstands lower rainfall and higher evaporation during such dry conditions may explain the higher sea surface salinities reported elsewhere in the south china sea the nansha caliche may also indicate reduced extent of the wpwp and southerly shift of the intertropical convergence zone during major sea level lowstands

spatial and temporal forecasting of large earthquakes in a spring block model of a fault summary we study a recently proposed statistical physics model of earthquake dynamics that includes stress relaxation in the plates as a fundamental ingredient the model is known to reproduce manyrealisticfeaturesofseismicphenomena suchas thegutenberg richterlawfortheevent size distribution the omori law for aftershocks and an overall velocity weakening dependence of the average friction force here we analyse the dynamics of the model in detail in order to investigate to what extent the occurrence of large events in the model can be anticipated we systematically find that large events occur in fault patches where strain accumulation has exceeded some threshold value the spatial extent of these patches which correlate with the magnitude offorthcoming events canbe calculated ifthe strainstateofthe systemissupposed tobe known inaddition wefind that some large events are preceded by well defined precursor activity thisallows inafractionofcases tocomplementtheforecastofmagnitudeandspatial location with a sensible prediction of time of occurrence although our work is exclusively limited to the numerical model analysed we argue that it gives new breath to earthquake forecast techniques that combine the historical analysis of seismic activity with a search of appropriate precursor activity

origin of atoll lagoons a database of 301 atolls from the pacific indian and atlantic oceans has been analyzed with respect to factors governing maximum atoll lagoon depth statistically significant correlations between maximum atoll lagoon depth and both atoll area and present day rainfall are viewed as the combined effect of paleorainfall precipitation and catchment area in contributing to overall atoll morphology this interpretation is supported by the gross saucer shaped morphology of several of the lau group of the fiji islands and the subsurface cretaceous golden lane atoll of mexico where evidence of reef rim construction is lacking but evidence for significant solution relief is compelling the contribution of reefs to atoll rim construction appears to be limited generally to 10 m leaving more than 20 m of relief to be explained at most atolls at a number of these the last interglacial highstand surface is 15 20 m beneath holocene rim sediments subsidence rates of even 5 cm k y do not suffice to explain the subsea depth of this unconformity suggesting the dominating influence of solution on relief expression calculations of solution rates relative to the residence time of sea level below given depths during the past 700 k y suggest that the observed atoll relief is in part inherited from more than one pleistocene or perhaps earlier glacial stage whatever the precise time of origin the data available strongly suggest that atoll morphology is solution determined rather than growth predicated

an alternative stratigraphic scheme for the sarawak basin abstract the present stratigraphic scheme for the tertiary of sarawak ho k f 1978 stratigraphic framework for oil exploration in sarawak bulletin of the geological society of malaysia 10 1 14 which subdivides the entire sedimentary succession into eight sedimentary cycles is based on the genetic sedimentary cycle concept each cycle starts with a transgressive basal part followed by a regressive unit which is in turn overlain by the basal transgressive unit of the next cycle the limitation of the present scheme is however in its general applicability for instance when one tries to identify the equivalents of marine surfaces within non marine sediments this is critical for some areas in sarawak where the sediments were deposited predominantly within lower coastal plain to upper coastal plain environments normally barren of foraminifera among other inadequacies of the scheme is the lack of basin wide association between the cycle boundaries and seismic reflectors in practice cycle boundaries picked on the composite well logs often do not agree with the seismic pick the scheme is however well accepted and continues to be used the alternative stratigraphic scheme for the sarawak basin which will be discussed in this paper is based on sequence stratigraphic concepts with the utilisation of unconformity or its correlative conformity as the stratigraphic boundary this scheme has been generated as the result of a programme of basin wide seismic mapping of the sarawak basin seven regional unconformities within the tertiary sedimentary sequences have been mapped the sedimentary units between the unconformities can be recognised as sequences the oldest unconformity is that between the basement belaga formation and the overlying tertiary sediments mainly of late oligocene age since the sediments in the basin are mainly of tertiary age the oldest unit of the succession is referred to as the tertiary one sequence t1 s the next younger sequence is called tertiary two sequence t2 s and so on the proposed scheme which is based on a more conventional and multi disciplinary approach can be understood and appreciated not only by palaeontologists but by all members of exploration and production teams the scheme should be able to facilitate prediction of stratigraphic levels not only after the well has been drilled but also prior to drilling

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

strain rate relaxation of normal and thrust faults in italy summary we find that geodetic strain rate sr integrated with the knowledge of active faults points out that hazardous seismic areas are those with lower sr where active faults are possibly approaching the end of seismic cycle sr values estimated from gps velocities at epicentral areas of large historical earthquakes in italy decrease with increasing elapsed time thus highlighting faults more prone to reactivation we have modelled an exponential decrease relationship between sr and the time elapsed since the last largest earthquake differencing historical earthquakes according to their fault rupture style then we have estimated the characteristic times of relaxation by a non linear inversion showing that events with thrust mechanism exhibit a characteristic time 990yr about three times larger than those with normal mechanism assuming standard rigidity and viscosity values we can infer an average recurrence time of about 600yr for normal faults and about 2000yr for thrust faults

central chile finally breaks chile is the site of some of the largest earthquakes in the world on average a magnitude 8 earthquake occurs there every 10 years or so these earthquakes take place in the subduction zone either as interplate ruptures at the interface between the south american and nazca plates or as intraplate events within the subducted nazca plate a few times in every century massive plate interface earthquakes break several hundred kilometers in a single shock this is what happened on 27 february 2010 when a major earthquake magnitude 8 8 occurred in the maule and biobio regions in central chile see the first figure this region had last experienced a major subduction earthquake in 1835 when darwin 1 visited the area as part of his voyage on the beagle his description of the earthquake inspired many seismologists and historians of chilean earthquakes 2 3

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally