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

a method to estimate the phase velocities of microtremors using a time frequency analysis and its applications the phase velocities of rayleigh waves provide basic information for estimating the shear wave velocity structure of the ground many methods have been proposed for this purpose however it is difficult to estimate phase velocities directly from the data found in microtremor records on the differences in phase angles between two sites the reason for this difficulty is that the sources of microtremors are not stable in either time or space in order to counteract this problem therefore we consider the nonstationary characteristic of microtremors in short time range and propose a method that can find the instantaneously corresponding portions of microtremor records at two different sites and that can estimate the apparent phase velocities between the two sites we use the technique of a time frequency analysis for which the hilbert huang transform is adopted after we confirm the applicability of the proposed method based on some numerical calculations the method is applied to some actual data on microtremors and reasonable results are obtained

larger earthquakes recur more periodically new insights in the megathrust earthquake cycle from lacustrine turbidite records in south central chile historical and paleoseismic records in south central chile indicate that giant earthquakes on the subduction megathrust such as in ad1960 mw9 5 reoccur on average every 300 yr based on geodetic calculations of the interseismic moment accumulation since ad1960 it was postulated that the area already has the potential for a mw8 earthquake however to estimate the probability of such a great earthquake to take place in the short term one needs to frame this hypothesis within the long term recurrence pattern of megathrust earthquakes in south central chile here we present two long lacustrine records comprising up to 35 earthquake triggered turbidites over the last 4800 yr calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold vii1 2 vs vi1 2 for the generation of turbidites at the coring sites the strongest earthquakes vii1 2 have longer recurrence intervals 292 93 yrs than earthquakes with intensity of vi1 2 139 69yr moreover distribution fitting and the coefficient of variation cov of inter event times indicate that the stronger earthquakes recur in a more periodic way cov 0 32 vs 0 5 regional correlation of our multi threshold shaking records with coastal paleoseismic data of complementary nature tsunami coseismic subsidence suggests that the intensity vii1 2 events repeatedly ruptured the same part of the megathrust over a distance of at least 300 km and can be assigned to mw 8 6 we hypothesize that a zone of high plate locking identified by geodetic studies and large slip in ad 1960 acts as a dominant regional asperity on which elastic strain builds up over several centuries and mostly gets released in quasi periodic great and giant earthquakes our paleo records indicate that poissonian recurrence models are inadequate to describe large megathrust earthquake recurrence in south central chile moreover they show an enhanced probability for a mw 7 7 8 5 earthquake during the next 110 years whereas the probability for a mw 8 6 ad1960 like earthquake remains low in this period

turbiditic trench deposits at the south chilean active margin a pleistocene holocene record of climate and tectonics the active plate margin of south america is characterized by a frequent occurrence of large and devastating subduction earthquakes here we focus on marine sedimentary records off southern chile that are archiving the regional paleoseismic history over the holocene and late pleistocene the investigated records ocean drilling program odp site 1232 and sonne core 50sl are located at 40 s and 38 s within the peru chile trench and are characterized by frequent interbedded strata of turbiditic and hemipelagic origin on the basis of the sedimentological characteristics and the association with the active margin of southern chile we assume that the turbidites are mainly seismically triggered and may be considered as paleo megaearthquake indicators however the long term changes in turbidite recurrence times appear to be strongly influenced by climate and sea level changes as well during sea level highstands in the holocene and marine isotope stage mis 5 recurrence times of turbiditic layers are substantially higher primarily reflecting a climate induced reduction of sediment availability and enhanced slope stability in addition segmented tectonic uplift changes and related drainage inversions likely influenced the postglacial decrease in turbidite frequencies glacial turbidite recurrence times including mis 2 mis 3 cold substages of mis 5 and mis 6 on the other hand are within the same order of magnitude as earthquake recurrence times derived from the historical record and other terrestrial paleoseismic archives of the region only during these cold stages sediment availability and slope instability were high enough to enable recording of the complete sequence of large earthquakes in southern chile our data thus suggest that earthquake recurrence times on the order of 100 to 200 years are a persistent feature at least during the last glacial period 2008 elsevier b v all rights reserved

coastal lake sediments reveal 5500 years of tsunami history in south central chile abstract we present an exceptionally long and continuous coastal lacustrine record of 5500 years from lake huelde on the west coast of chiloe island in south central chile the study area is located within the rupture zone of the giant 1960 ce great chilean earthquake mw 9 5 the subsequent earthquake induced tsunami inundated lake huelde and deposited mud rip up clasts massive sand and a mud cap in the lake long sediment cores from 8 core sites within lake huelde reveal 16 additional sandy layers in the 5500 year long record the sandy layers share sedimentological similarities with the deposit of the 1960 ce tsunami and other coastal lake tsunami deposits elsewhere on the basis of general and site specific criteria we interpret the sandy layers as tsunami deposits age control is provided by four different methods 1 210pb dating 2 the identification of the 137cs peak 3 an infrared stimulated luminescence irsl date and 4 22 radiocarbon dates the ages of each tsunami deposit are modelled using the bayesian statistic tools of oxcal and bacon the record from lake huelde matches the 8 regionally known tsunami deposits from documented history and geological evidence from the last 2000 years without over or underrepresentation we extend the existing tsunami history by 9 tsunami deposits we discuss the advantages and disadvantages of various sedimentary environments for tsunami deposition and preservation e g we find that lake huelde is 2 3 times less sensitive to relative sea level change in comparison to coastal marshes in the same region

mapping the 3d lithofacies architecture of a vms ore system on a curvilinear faulted grid a case study from the flin flon mining camp canada abstract the 3d lithofacies architecture of the thrust imbricated paleoproterozoic 85 5 mt flin flon volcanogenic massive sulfide vms ore system trans hudson orogen canada has been mapped in 3d using a numerical grid modeling methodology this methodology is based on the structural knowledge universal approach skua modeling work flow developed for modeling hydrocarbon reservoirs one of the major advantages of applying this methodology to mineral exploration is that it allows exploiting knowledge on the structural setting of the ore deposit without the need to determine all kinematic constraints that would be required for a full 3d balanced restoration the work flow proceeds by modeling the volume of the thrust repeated mine horizon on a curvilinear faulted grid that is conformable to the enveloping geological structure and that includes discontinuities to model fault offsets it then uses a coordinate transformation to partly remove the influence of geological structure on euclidean distance based geostatistical estimations it subsequently applies the inverse of this coordinate transformation to represent the interpolated or simulated lithofacies distribution in the finite deformed state randomized validation experiments show that the geostatistical analysis resulted in an estimated overall 74 accuracy of the predicted lithofacies classes over the grid the lithofacies grid models provide insight into the post depositional deformation history of the ore system and the rifted volcanic arc setting in which the flin flon massive sulfide ore was deposited the lithofacies grid models also serve as stratified containers for generating lithochemical property models that can be used for spatially characterizing ore forming processes such as hydrothermal alteration and ore metal zoning

the chiloe mw 7 6 earthquake of 25 december 2016in southern chile and its relation tothe mw 9 5 1960 valdivia earthquake on 25 december 2016 a mw 7 6 earthquake broke a portion of the southern chilean subduction zone south of chiloe island located in the central part of the mw 9 5 1960 valdivia earthquake this region is characterized by repeated earthquakes in 1960 and historical times with very sparse interseismic activity due to the subduction of a young 15 ma and therefore hot oceanic plate we estimate the co seismic slip distribution based on a kinematic finite fault source model and through joint inversion of teleseismic body waves and strong motion data the coseismic slip model yields a total seismic moment of 3 94 1020 nm that occurred over 30 s with the rupture propagating mainly downdip reaching a peak slip of 4 2 m regional moment tensor inversion of stronger aftershocks reveals thrust type faulting at depths of the plate interface the fore and aftershock seismicity is mostly related to the subduction interface with sparse seismicity in the overriding crust the 2016 chiloe event broke a region with increased locking and most likely broke an asperity of the 1960 earthquake the updip limit of the main event aftershocks foreshocks and interseismic activity are spatially similar located 15 km offshore and parallel to chiloe islands west coast the coseismic slip model of the 2016 chiloe earthquake suggests a peak slip of 4 2 m that locally exceeds the 3 38 m slip deficit that has accumulated since 1960 therefore the 2016 chiloe earthquake possibly released strain that has built up prior to the 1960 valdivia earthquake

pleistocene glaciation in the southern lake district of chile relative age criteria permit deposits of successive andean glacier advances in the southern lake district of chile to be divided into four mappable drift sheets the oldest two of which overlie tertiary bedrock along the eastern flank of the cordillera de la costa only the youngest drift llanquihue is datable by radiocarbon during the most extensive ice advance of the last glaciation the lago llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m km successive ice advances in the lago llanquihue basin which resulted in construction of end moraines and associated outwash plains beyond the lake margin culminated sometime before about 20 000 yr ago and between 20 000 and 19 000 yr ago a later readvance inferred from the sedimentary record of lake level fluctuations in the basin had begun by about 15 000 yr ago and culminated shortly after 13 000 yr ago a comparable but less closely dated record of ice advances is found northwest of seno reloncavi and on isla chiloe deglaciation following the latest advance is likely to have been rapid for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving

liquefaction as an important source of the a d 2011 tohoku oki tsunami deposits at sendai plain japan this paper describes the topographic change and the recovery process as well as the sediment sources for tsunami deposits based on field surveys and analysis of digital elevation model data before and after the a d 2011 tohoku oki tsunami at the sendai plain japan we found that the amount of sediment deposited on land was approximately four times greater than the eroded volume of sediment at the beach large amounts of the sediments deposited at the studied transect probably originated from liquefaction this result suggests that the vented sediments might have been an important source of the tsunami deposits if liquefaction is generated by the strong ground motion of a near field earthquake in contrast minor erosion was observed at the beach and the beach berm was rebuilt within three months after the tsunami moreover the erosional channel that had cut into the beach had been filled by sand within 13 days after the tsunami therefore it is not expected that a sedimentary record of the tsunami will be preserved in the nearshore zone along the sendai coast although remnants of small scours on land might remain long after the tsunami

reawakening of large earthquakes in south central chile the 2016 mw 7 6 chiloe event on 25 december 2016 the mw 7 6 chiloe earthquake broke a plate boundary asperity in south central chile near the center of the rupture zone of the mw 9 5 valdivia earthquake of 1960 to gain insight on decadal scale deformation trends and their relation with the chiloe earthquake we combine geodetic teleseismic and regional seismological data gps velocities increased at continental scale after the 2010 maule earthquake probably due to a readjustment in the mantle flow and an apparently abrupt end of the viscoelastic mantle relaxation following the 1960 valdivia earthquake it also produced an increase in the degree of plate locking the chiloe earthquake occurred within the region of increased locking breaking a circular patch of 15 km radius at 30 km depth located near the bottom of the seismogenic zone we propose that the chiloe earthquake is a first sign of the seismic reawakening of the valdivia segment in response to the interaction between postseismic viscoelastic relaxation and changes of interseismic locking between nazca and south america

the tsunami phenomenon abstract with human activity increasingly concentrating on coasts tsunamis from japanese tsu harbour nami wave are a major natural hazard to today s society stimulated by disastrous tsunami impacts in recent years for instance in south east asia 2004 or in japan 2011 tsunami science has significantly flourished which has brought great advances in hazard assessment and mitigation plans based on tsunami research of the last decades this paper provides a thorough treatise on the tsunami phenomenon from a geoscientific point of view starting with the wave features tsunamis are introduced as long shallow water waves or wave trains crossing entire oceans without major energy loss at the coast tsunamis typically show wave shoaling funnelling and resonance effects as well as a significant run up and backflow tsunami waves are caused by a sudden displacement of the water column due to a number of various trigger mechanisms such are earthquakes as the main trigger submarine and subaerial mass wastings volcanic activity atmospheric disturbances meteotsunamis and cosmic impacts as is demonstrated by giving corresponding examples from the past tsunamis are known to have a significant sedimentary and geomorphological off and onshore response so called tsunamites form allochthonous high energy deposits that are left at the coast during tsunami landfall tsunami deposits show typical sedimentary features as basal erosional unconformities fining upward and landward a high content of marine fossils rip up clasts from underlying units and mud caps all reflecting the hydrodynamic processes during inundation the on and offshore behaviour of tsunamis and related sedimentary processes can be simulated using hydro and morphodynamic numerical models the paper provides an overview of the basic tsunami modelling techniques including discretisation guidelines for appropriate temporal and spatial resolution as well as the nesting method furthermore the boussinesq approximation a simplification of the three dimensional navier stokes equations is presented as a basic theory behind numerical tsunami models which adequately reflects the non linear dispersive wave behaviour of tsunamis the fully non linear boussinesq equations allow the simulation of tsunamis e g in the form of n waves based on the various subtopics presented recommendations for future multidisciplinary tsunami research are made it is especially discussed how the combination of sedimentary and geomorphological tsunami field traces and numerical modelling techniques can contribute to derive locally relevant tsunami sources and to improve the assessment of tsunami hazards considering the individual pre history and physiogeographical setting of a specific region

the application of diatoms to reconstruct the history of subduction zone earthquakes and tsunamis abstract earthquake and tsunami records on centennial and millennial temporal scales are necessary to understanding long term subduction zone behavior and the occurrences of large but infrequent events microfossils such as diatoms incorporated into coastal stratigraphy provide some of the most detailed reconstructions of the history of earthquakes and tsunamis we explore qualitative and quantitative techniques that employ the relation between diatoms and salinity tidal elevation and life form to 1 reconstruct records of vertical land level change associated with large earthquakes and 2 identify anomalous sand and silt beds deposited by tsunamis a global database shows that diatoms have been successfully employed in the reconstruction of earthquake and tsunami histories in chile the indian ocean japan new zealand the north sea the pacific northwest of north america and the south pacific we use case studies from some of these locations to highlight advancements in the field and new capabilities that diatoms have enabled examples from the pacific northwest of north america illustrate the evolution of quantitative diatom based reconstructions of earthquake related land level change in alaska and japan diatoms have documented land level changes throughout the earthquake deformation cycle including possible preseismic land level change signals and postseismic deformation diatoms helped identify coseismic uplift along the central chile subduction zone coast and uplift and subsidence along the alaska aleutian megathrust expanding our knowledge of the variability of slip in megathrust ruptures in tsunami studies diatoms help determine the provenance of anomalous sands and silts found in low energy coastal stratigraphic sequences in japan allochthonous marine and brackish diatoms within sand deposits signaled repeated marine incursions into a coastal lake helping identify a possible predecessor to the 2011 tohoku tsunami in the pacific northwest of north america and chile diatoms were used to estimate tsunami run up beyond the landward limit of tsunami sedimentation examples from the north sea thailand and japan show how the fragmentation and sorting of diatom valves may provide evidence of high energy transport during the rapid turbulent flow of a tsunami to conclude we emphasize the importance of studying the modern diatom response to changes in land level and or tsunami inundation to improve diatom based records of prehistoric earthquakes and tsunamis

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

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

diatoms as an aid in identifying late holocene tsunami deposits diatoms bacillariophyta help identify the onshore deposits of tsunamis from earthquakes on the cascadia subduction zone along the pacific coast of oregon washington and british columbia and on faults high in the north american plate in the puget sound area of washington at the copalis river washington diatom analyses suggest that a tsunami deposit about 300 calendric years old 300 yr bp originated from sandy shoals of the lower estuary rather than nearby beaches or coastal dunes at cultus bay and west point washington well preserved benthic estuarine diatoms in sand sheets overlying tidal marsh peat indicate that the deposits came from intertidal or nearshore areas of puget sound on an abruptly uplifted mudflat at the landward end of hood canal at lynch cove washington tidal flat diatoms refute the possibility of a terrestrial source for the sand diatoms in 300 yr bp tsunami deposits on the niawiakum river washington confirm that the sand in these deposits had a marine source and help

historical nankai suruga megathrust earthquakes recorded by tsunami and terrestrial mass movement deposits on the shirasuka coastal lowlands shizuoka prefecture japan geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records in this paper we present a multi proxy investigation of a coastal lowland site facing the nankai suruga megathrust and appraise evidence for tsunamis and earthquake triggered terrestrial mass movements occurring over the last 800 years combining a high resolution chronology with x ray computed tomography and analyses of particle size diatoms pollen non pollen palynomorphs and aerial photographs we present the most compelling geological evidence of the 1361 ce koan also known as shohei tsunami reported to date from any site along the megathrust this finding is consistent with either of two recent hypotheses a single larger rupture of both the nankai and tnankai regions or two smaller ruptures separated by a few days enhancing the site chronology using bayesian age modelling we verify evidence for inundation during the 1498 ce mei tsunami while previous investigations identified evidence for historically recorded tsunamis in 1605 1707 and 1854 ce and a storm surge in 1680 or 1699 ce we encountered a thick sand layer rather than discrete extreme wave deposits in this interval the overprinting of evidence highlights the potential for geological records to underestimate the frequency of these events a terrestrial mass movement also deposited a sand layer at the site radionuclide dating and aerial photographs provide independent confirmation that this may have been triggered by intense shaking in 1944 ce during the most recent great nankai suruga megathrust earthquake

variable rupture mode of the subduction zone along the ecuador colombia coast three large earthquakes occurred within the rupture zone of the 1906 colombia ecuador earthquake m w 8 8 in 1942 m s 7 9 1958 ms 7 8 and 1979 m s 7 7 we compared the size and mechanism of these earthquakes by using long period surface waves tsunami data and macroseismic data the 1979 event is a thrust event with a seismic moment of 2 9 10 28 dyne cm and represents subduction of the nazca plate beneath south america the rupture length and direction are 230 km and n40 e respectively examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction the seismic moment estimated from the tsunami data and the size of the rupture zone is 2 10 29 dyne cm the 1942 and 1958 events are much smaller about 1 5 to 1 10 of the 1979 event in the seismic moment than the 1979 event we conclude that the sum of the seismic moments of the 1942 1958 and 1979 events is only formula of that of the 1906 event despite the fact that the sequence of the 1942 1958 and 1979 events ruptured approximately the same segment as the 1906 event this difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between the weak zone normally behaves aseismically but slips abruptly only when it is driven by failure of the asperities a small earthquake represents failure of one asperity and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small a great earthquake represents failure of more than one asperity and consequently involves much larger width and slip

sensitivity of probabilistic tsunami hazard assessment to far field earthquake slip complexity and rigidity depth dependence case study of australia probabilistic tsunami hazard assessment ptha often proceeds by constructing a suite of hypothetical earthquake scenarios and modelling their tsunamis and occurrence rates both tsunami and occurrence rate models are affected by the representation of earthquake slip and rigidity but the overall importance of these factors for far field ptha is unclear we study the sensitivity of an australia wide ptha to six different far field earthquake scenario representations including two rigidity models constant and depth varying combined with three slip models fixed area uniform slip with rupture area deterministically related to magnitude variable area uniform slip and spatially heterogeneous slip earthquake tsunami scenarios are tested by comparison with dart buoy tsunami observations demonstrating biases in some slip models scenario occurrence rates are modelled using bayesian techniques to account for uncertainties in seismic coupling maximum magnitudes and gutenberg richter b values the approach maintains reasonable consistency with the historical earthquake record and spatially variable plate convergence rates for all slip rigidity model combinations and facilitates partial correction of model specific biases identified via dart buoy testing the modelled magnitude exceedance rates are tested by comparison with rates derived from long term historical and paleoseismic data and alternative moment conservation techniques demonstrating the robustness of our approach the tsunami hazard offshore of australia is found to be insensitive to the choice of rigidity model but significantly affected by the choice of slip model the fixed area uniform slip model produces lower hazard than the other slip models bias adjustment of the variable area uniform slip model produces a strong preference for compact scenarios which compensates for a lack of slip heterogeneity thus both heterogeneous slip and variable area uniform slip models induce similar far field tsunami hazard

five centuries of tsunamis and land level changes in the overlapping rupture area of the 1960 and 2010 chilean earthquakes a combination of geological and historical records from south central chile provides a means to address general questions about the stability of megathrust rupture patches and the range of variation expected among earthquakes and tsunamis along a particular stretch of a subduction zone the tirua river estuary 38 3 s records four large tsunamis and coseismic land level changes over the past 450 years within the overlapping rupture zones of the great subduction zone earthquakes of a d 1960 mw 9 5 and 2010 mw 8 8 sand layers 2 km up the tirua river represent the 2010 and 1960 tsunamis and two historical tsunamis most likely in a d 1751 and 1575 differing land level changes during these earthquakes likely denote differences in the spatial distribution of slip on the megathrust in both the strike and dip directions within the overlapping rupture zone with the uplift at tirua in 1751 and 2010 probably caused by slip extending farther landward and to greater depth than in 1575 and 1960 which showed subsidence or little change

estimating coseismic coastal uplift with an intertidal mussel calibration for the 2010 maule chile earthquake mw 8 8 abstract coseismic coastal uplift has been quantified using sessile intertidal organisms after several great earthquakes following fitzroy s pioneer measurements in 1835 a dense survey of such markers may complement space geodetic data to obtain an accurate distribution of fault slip and earthquake segmentation however uplift estimates based on diverse intertidal organisms tend to differ because of few methodological and comparative studies here we calibrate and estimate coastal uplift in the southern segment of the 2010 maule chile earthquake m w 8 8 using 1100 post earthquake elevation measurements of the sessile mussel perumytilus purpuratus this mussel is the predominant competitor for rocky shores all along the pacific coast of south america where it forms fringes or belts distinctively in the middle intertidal zone these belts are centered at mean sea level and their width should equal one third of the tidal range we measured belt widths close to this value at 40 of the sites but overall widths are highly variable due to the unevenness in belt tops belt bases in turn are rather regular belt top unevenness apparently results from locally enhanced wave splash whereas belt base evenness is controlled by predation according to our measurements made beyond the earthquake rupture the belt base is at the bottom of the middle intertidal zone and thus we propose to estimate coastal uplift using the belt base mean elevation plus one sixth of the tidal range to reach mean sea level within errors our estimates agree with gps displacements but differ from other methods comparisons of joint inversions for megathrust slip suggest combining space geodetic data with estimates from intertidal organisms may locally increase the detail of slip distributions

fragmentary evidence of great earthquake subsidence during holocene emergence valdivia estuary south central chile a reconnaissance of holocene stratigraphy beneath fringing marshes of the valdivia estuary where an m 9 5 earthquake caused 1 2 m of regional coseismic subsidence in 1960 shows only fragmentary evidence of prehistoric coseismic sub sidence in most of the 150 hand driven cores that were examined a distinct uncon formity separates 0 5 1 5 m of late holocene tidal and floodplain mud peat and sand from underlying middle holocene subtidal mud and sand at the las coloradas site where stratigraphy is best preserved two a horizons of marsh and meadow soils abruptly overlain by sand and mud probably record coseismic subsidence shortly fol lowed by tsunamis the amount of subsidence during the earthquakes proved difficult to reconstruct with a diatom transfer function because of differences between modern and fossil diatom assemblages maximum 14 c ages on macrofossils from the two a horizons at the las coloradas site of 1 7 1 3 ka and 2 7 1 7 ka allow correlation of the younger horizon with either of two of six 14 c dated a horizons buried by tsunami sand or post tsunami tidal sand 200 km to the south at maullin and with a lake wide mass wasting event in lago puyehue 100 km to the southeast tidal records of prehistoric coseismic subsidence at valdivia are scarce because of a sea level fall of 3 8 m over the past 6000 years erosion of marsh and meadow soils during subsidence induced flooding of the estuary and largely complete land level recovery during cycles of coseismic subsidence and postseismic uplift online material diatom species data from the las coloradas site valdivia estuary

a 600 year long stratigraphic record of tsunamis in south central chile the stratigraphy within coastal river valleys in south central chile clarifies and extends the region s history of large earthquakes and accompanying tsunamis our site at quidico 38 1 s 73 3 w

evidence for a large strike slip component during the 1960 chilean earthquake the strainmeter record observed at isabella isa california for the 1960 chilean earthquake m w 9 5 is one of the most important historical records in seismology because it was one of the three records that provided the opportunity for the first definitive observations of free oscillations of the earth because of the orientation of the strainmeter rod with respect to the back azimuth to chile the isa strainmeter is relatively insensitive to g love waves and higher order order 6 toroidal modes yet long period g waves and toroidal modes were recorded with large amplitude on this record this observation cannot be explained with the conventional low angle thrust mechanism typical of great subduction zone earthquakes and requires an oblique mechanism with half strike slip and half thrust the strain record at ogdenburg new jersey the press ewing seismograms at berkeley california and the ultra long period displacement record at pasadena california also support the oblique mechanism we tested the performance of the isa strainmeter using other events including the 1964 alaskan earthquake and found no instrumental problems thus the isa observation of large g r and toroidal spheroidal ratios most likely reflects the real characteristics of the 1960 chilean earthquake rather than an observational artefact the interpretation of the large strike slip component is not unique but it may represent release of the strike slip strain that has accumulated along the plate boundary as a result of oblique convergence at the nazca south american plate boundary the slip direction of the 2010 chilean maule earthquake m w 8 8 is rotated by about 10 clockwise from the plate convergence direction suggesting that right lateral strain comparable to that of an m w 8 3 earthquake remained unreleased and accumulates near the plate boundary one possible scenario is that the strike slip strain accumulated over several great earthquakes like the 2010 maule earthquake was released during the 1960 chilean earthquake if this is the case we cannot always expect a similar behaviour for all the great earthquakes occurring in the same subduction zone and such variability needs to be considered in long term hazard assessment of subduction zone earthquakes

late holocene paleoseismology of shuyak island alaska we report stratigraphic evidence of land level changes along the eastern portion of the alaska aleutian megathrust four marshes on shuyak island record variable amounts of coseismic deformation during four pre 20th century earthquakes we combine these data with paleoseismic evidence from across the kodiak kenai and prince william sound segments of the megathrust these indicate that in the last 2000 years ad 1964 was the only one to rupture all three segments simultaneously and generate a mw 9 2 earthquake the kodiak segment ruptured independently on four further occasions with magnitudes mw 8 0 in ad 1788 and c 400 440 320 bp and independently but around the times of great earthquakes in the prince william sound segment c 850 and c 1500 bp

long term perspectives on giant earthquakes and tsunamis at subduction histories of earthquakes and tsunamis inferred from geological evidence aid in anticipating future catastrophes this natural warning system now influences building codes and tsunami planning in the united states canada and japan particularly where geology demonstrates the past occurrence of earthquakes and tsunamis larger than those known from written and instrumental records under favorable circumstances paleoseismology can thus provide long term advisories of unusually large tsunamis the extraordinary indian ocean tsunami of 2004 resulted from a fault rupture more than 1000 km in length that included and dwarfed fault patches that had broken historically during lesser shocks such variation in rupture mode known from written history at a few subduction zones is also characteristic of earthquake histories inferred from geology on the pacific rim

unusual geologic evidence of coeval seismic shaking and tsunamis shows variability in earthquake size and recurrence in the area of the giant 1960 chile earthquake an uncommon coastal sedimentary record combines evidence for seismic shaking and coincident tsunami inundation since ad 1000 in the region of the largest earthquake recorded instrumentally the giant 1960 southern chile earthquake mw 9 5 the record reveals significant variability in the size and recurrence of megathrust earthquakes and ensuing tsunamis along this part of the nazca south american plate boundary a 500 m long coastal outcrop on isla chiloe midway along the 1960 rupture provides continuous exposure of soil horizons buried locally by debris flow diamicts and extensively by tsunami sand sheets the diamicts flattened plants that yield geologically precise ages to correlate with well dated evidence elsewhere the 1960 event was preceded by three earthquakes that probably resembled it in their effects in ad 898 1128 1300 1398 and 1575 and by five relatively smaller intervening earthquakes earthquakes and tsunamis recurred exceptionally often between ad 1300 and 1575 their average recurrence interval of 85 years only slightly exceeds the time already elapsed since 1960 this inference is of serious concern because no earthquake has been anticipated in the region so soon after the 1960 event and current plate locking suggests that some segments of the boundary are already capable of producing large earthquakes this long term earthquake and tsunami history of one of the world s most seismically active subduction zones provides an example of variable rupture mode in which earthquake size and recurrence interval vary from one earthquake to the next

lacustrine turbidites as a tool for quantitative earthquake reconstruction new evidence for a variable rupture mode in south central chile understanding the long term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions south central chilean lakes are typically characterized by laminated sediments providing a quasi annual resolution our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes among others the 2010 and 1960 events furthermore we found that a turbidite s spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo intensities consequently our multilake turbidite record aids in pinpointing magnitudes rupture locations and extent of past subduction earthquakes in south central chile comparison of the lacustrine turbidite records with historical reports a paleotsunami subsidence record and a marine megaturbidite record demonstrates that the valdivia segment is characterized by a variable rupture mode over the last 900 years including i full ruptures mw 9 5 1960 1575 1319 9 1127 44 ii ruptures covering half of the valdivia segment mw 9 1837 and iii partial ruptures of much smaller coseismic slip and extent mw 7 5 8 1737 1466 4 also distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values for instance the 2010 event at the maule segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near concepci n

reconstructing paleoseismic deformation 2 1000 years of great earthquakes at chucalen south central chile in this paper we adopt a quantitative biostratigraphic approach to establish a 1000 year long coastal record of megathrust earthquake and tsunami occurrence in south central chile our investigations focus on a site in the centre of the rupture segment of the largest instrumentally recorded earthquake the ad 1960 magnitude 9 5 chile earthquake at chucalen coseismic subsidence in 1960 is recorded in the lithostratigraphy and biostratigraphy of coastal marshes with peat overlain by minerogenic sediment and changes in the assemblages of diatoms unicellular algae indicating an abrupt increase in relative sea level in addition to the 1960 earthquake the stratigraphy at chucalen records three earlier earthquakes the historically documented earthquake of 1575 and two prehistoric earthquakes radiocarbon dated to ad 1270 1450 and 1070 1220 laterally extensive sand sheets containing marine or brackish diatom assemblages suggest tsunami deposition associated with at least two of the three pre 1960 earthquakes the record presented here suggests a longer earthquake recurrence interval averaging 270 years than the historical recurrence interval which averages 128 years the lack of geologic evidence at chucalen of two historically documented earthquakes in 1737 and 1837 supports the previously suggested hypothesis of variability in historical earthquake characteristics our estimates of coseismic land level change for the four earthquakes range from meter scale subsidence to no subsidence or slight uplift suggesting earthquakes completing each 270 year cycle may not share a common characteristic slip distribution the presence of buried soils at elevations below their modern equivalents implies net relative sea level rise over the course of the chucalen paleoseismic record in contrast to relative sea level fall over preceding millennia inferred from sites on the mainland sea level rise may contribute to the preservation of evidence for multiple earthquakes during the last millennium while net relative sea level fall over the last 2000 5000 years may explain the lack of evidence for older earthquakes

the 1960 chilean earthquakes an unusual foreshock sequence that began with an earthquake of moment 2 0 1021 n m and rupture length of about 150 km preceded the great 1960 chilean earthquake earthquake relocations of the sequence show a progression of seismic activity toward the initiation of the main shock the rupture length of the great 1960 chilean earthquake is estimated from the distribution of aftershocks and crustal deformation to be 920 100 km the source mechanisms of a foreshock and two aftershocks are determined and used to constrain the source mechanism of the main shock the first event in the sequence ruptured the segment of the peru chile trench between 37 03 s and 38 74 s whereas the great 1960 chilean main shock ruptured the adjoining segment to the south the great 1960 chilean main shock initiated within the rupture area of the first event and terminated near the intersection of the chile ridge with the peru chile trench 46 5 s

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

effects of historical land use on sediment yield from a lacustrine watershed in central chile sediment yield in the san pedro lake watershed inferred from sedimentation in the lake can be related to land use changes shown on aerial photographs taken during the period 1943 1994 in this watershed which covers 4 5 km2 of mountainous terrain in san pedro county central chile the area of native forest species decreased from 70 per cent in 1943 to 13 per cent in 1994 during this same period the area of pine plantations increased from 4 to 46 per cent to study effects of these changes we took a core from the centre of the lake and estimated sedimentation rates by 210pb dating which we checked with 137cs and pine pollen the results show that sedimentation rate ranged from 5 mg cm 2 a 1 in the late 1800s to 60 mg cm 2 a 1 in the late 1960s these rates together with assumptions about the production and delivery of the sediment give corresponding figures for sediment yields with maximum values close to 1 t ha 1 a 1 sediment yield between 1955 and 1994 closely tracks the total land use change that can be detected irrespective of land use type on sets of aerial photographs taken four to 18 years apart however this measure of land use change while convenient and successful as a predictor of historical erosion may be unreliable because it probably excludes many changes that occurred in long intervals between successive photographs copyright 2001 john wiley sons ltd

net late holocene emergence despite earthquake induced submergence south central chile abstract intertidal deposits show net late holocene emergence at three sites along the pacific coast near maullin and carelmapu chile latitude 41 6 41 7 s the maximum amount of net emergence is ca 1 m in the past 1500 years and ca 2 1 2 m in the past 4000 years emergence probably would have prevailed at a fourth site near maullin were the site not underlain by easily compacted deposits this site shows slight

giant earthquakes in south central chile revealed by holocene mass wasting events in lake puyehue abstract very high resolution reflection seismic profiling 3 5 khz revealed nine holocene mass wasting events in lake puyehue south central chile these events are made up of numerous coeval mass wasting deposits and some homogenites which are radiocarbon dated the two youngest mass wasting events could be attributed to the giant ad 1960 and ad 1575 valdivia earthquakes the most extensive event took place around 1660 cal yr bp evaluation of all possible slope failure processes led us to infer that giant earthquakes roughly comparable to the ad 1960 valdivia earthquake mw 9 5 are the most likely trigger mechanisms of all mass wasting events in lake puyehue these occurred with a mean recurrence rate of 1000 yr although relatively aperiodically ranging between 500 and 2000 yr quantitative comparison of mass wasting events related to historically reported earthquakes ad 1960 and ad 1575 showed significant differences although these earthquakes are assumed to have had a comparable strength a lowered background sedimentation rate could be responsible for this variable earthquake recording which highlights the importance of a thorough assessment of the depositional history before using lacustrine records for quantitative paleoseismic analysis

turbidite paleoseismology along the active continental margin of chile feasible or not abstract much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial lacustrine and marine paleoseismic archives recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events turbidite paleoseismic archives may potentially extend past earthquake records to the pleistocene and can thus complement commonly shorter term terrestrial archives however in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents synchronous deposition of turbidites in widely spaced isolated depocenters has to be ascertained furthermore characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account here we analyze 8 marine sediment cores along 950 km of the chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites our results suggest that the deposition of areally widespread synchronous turbidites triggered by seismicity is largely controlled by sediment supply and hence the climatic and geomorphic conditions of the adjacent subaerial setting the feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high resolution radiocarbon dating we conclude that offshore northern central chile 29 32 5 s holocene turbidite paleoseismology is not feasible because sediment supply from the semi arid mainland is low and almost no holocene turbidity current deposits are found in the cores in contrast in the humid region between 36 and 38 s frequent holocene turbidite deposition may generally correspond to paleoseismic events however high terrigenous sedimentation rates prevent high resolution radiocarbon dating the climatic transition region between 32 5 and 36 s appears to be best suited for turbidite paleoseismology

diatom biostratigraphy of tsunami deposits examples from the 1998 papua new guinea tsunami abstract distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment sediments associated with the 1998 tsunami that destroyed much of the sissano lagoon area in northern papua new guinea have been investigated surface sediments from three transects across the sediment spit near warapu have been examined for diatom content and preservation the preservation is variable and the data show an often chaotic assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash the diatoms identified within the warapu sediments indicate an origin from within the inter tidal and offshore area rather than from the beach sand spit complex the sand deposits disclose a high percentage in excess of 75 of broken diatom valves and a predominance of centric circular species due to preferential preservation the study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo tsunami deposits