late pleistocene sea level change in the bahamas from mass spectrometric u series dating of submerged speleothem abstract the dating of sea level events by a method independent of orbital tuning techniques and the marine foraminiferal isotopic record provides a test of both the dating of the marine record and the strength and nature of the relationship between climatic change sea level change and milankovitch cycles dating of fossil corals and submerged speleothem provides such independent information results of thermal ionization mass spectrometric u series dating on layers of flowstone speleothem from lucayan caverns grand bahama island indicate that multiple sea level events have passed through a depth of 10 to 15 m below modern sea level during the last 300 000 years these data are used to constrain the magnitude and timing of sea level fluctuations during the late pleistocene the new sea level curve constructed from these data correlates closely with the marine isotopic record sea level peaks occurred at around 233 215 125 and 100 ka bp there is no evidence at the depth from which this speleothem was retrieved of any high sea stands at 195 or 80 ka corresponding to the foraminiferal 7a and 5a oxygen isotope peaks there is also no evidence of a double rise around the 125 ka 5e peak although such an oscillation could have occurred above 10 m leaving no record in the lucayan caverns speleothem

response of seismicity to static and dynamic stress changes induced by the 2011 m9 0 tohoku oki earthquake 1 a growing body of evidence indicates that many earthquakes are triggered by static and dynamic stress changes following large earthquakes however it has been difficult to differentiate the roles of static and dynamic stress transfer on earthquake triggering here we focus on two adjacent seismic clusters aligned e w beneath the hida mountain range central japan where spatially uniform static and dynamic stress changes resulted from the tohoku oki earthquake the rate of seismicity in the western cluster detected by the matched filter technique showed a slight increase after the mainshock which can be explained by static stress transfer in contrast seismicity in the eastern cluster showed a marked increase due to dynamic stress change the difference in the number of triggered events between these clusters indicates that dynamic stress change is more important than the static one in terms of remote triggering provided that large sized potential earthquake nucleation patches are close to failure

the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

aftershock sequence and statistics of the 2017 mw 5 5 pohang south korea earthquake implications of fault heterogeneity and postseismic relaxation

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

early last glacial intra interstadial climate variability recorded in a sardinian speleothem chemical and physical proxy data from a precisely dated early last glacial 113 110 ka mis5d sardinian stalagmite reveal a sub millennial scale cool dry climate event centered at 112 0 0 52 0 59 ka followed by a rapid return to warm wet conditions at 111 76 0 43 0 45 ka comparison with regional speleothem records and the palaeotemperature proxy record from the ngrip ice core greenland suggests that this event corresponds to greenland interstadial gi 25b and 25a an intra interstadial climate oscillation within gi 25 according to the recent greenland stratigraphic framework the speleothem age is in reasonable agreement within 0 8 kyr with that of the corresponding event in greenland based on the gicc05modelext ice chronology but is older by about 3 7 kyr than the greenland age based on the aicc2012 chronology

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

updip and along strike aftershock migration model driven by afterslip application to the 2011 tohoku oki aftershock sequence

constraining holocene sea levels using u th ages of phreatic overgrowths on speleothems from coastal caves in mallorca western mediterranean phreatic overgrowths on speleothems pos are carbonate formations deposited at the water table of caves in unique karstic coastal settings having morphologies that can be directly related to sea level at the time of formation the u th ages of calcite and aragonite overgrowths collected from the modern water table in coastal caves on mallorca cova de cala varques a and cova des pas de vallgornera were determined using high precision mc icpms techniques u th ages indicate that phreatic carbonate deposition occurred between ca 2 8 and at least 0 6 ka bp and are in accord with an archeologically estimated age of 3 7 3 0 ka bp for a drowned prehistoric construction at a depth of 1 m below current sea level in a cave from the same area speleothem 13c and 18o and chemical composition of cave pools provide supportive evidence that pos reflect mixing between seawater and brackish water table copyright 2010 john wiley sons ltd

tidal notches in mediterranean sea a comprehensive analysis abstract recent works evelpidou et al 2012 suggest that the modern tidal notch is disappearing worldwide due sea level rise over the last century in order to assess this hypothesis we measured modern tidal notches in several of sites along the mediterranean coasts we report observations on tidal notches cut along carbonate coasts from 73 sites from italy france croatia montenegro greece malta and spain plus additional observations carried outside the mediterranean at each site we measured notch width and depth and we described the characteristics of the biological rim at the base of the notch we correlated these parameters with wave energy tide gauge datasets and rock lithology our results suggest that considering the development of tidal notches the consequence of midlittoral bioerosion as done in evelpidou et al 2012 is a simplification that can lead to misleading results such as stating that notches are disappearing important roles in notch formation can be also played by wave action rate of karst dissolution salt weathering and wetting and drying cycles of course notch formation can be augmented and favoured also by bioerosion which can in particular cases be the main process of notch formation and development our dataset shows that notches are carved by an ensemble rather than by a single process both today and in the past and that it is difficult if not impossible to disentangle them and establish which one is prevailing we therefore show that tidal notches are still forming challenging the hypothesis that sea level rise has drowned them

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

recent advances in modeling swash zone dynamics influence of surf swash interaction on nearshore hydrodynamics and morphodynamics the role of the swash zone in influencing the whole nearshore dynamics is reviewed with a focus on the interaction between surf and swash zone processes local and global hydromorphodynamic phenomena are discussed in detail and a description of the overall swash zone operation is given the effects of swash zone boundary conditions are highlighted together with the importance of surf zone boundary conditions major emphasis is placed on illustrating the interactions of various hydrodynamic modes which in turn control the swash and surf zone morphology finally methods to account for swash zone processes in coastal models with different temporal and spatial resolutions are proposed

230th u dating of last interglacial brain corals from bonaire southern caribbean using bulk and theca wall material abstract we compared the suitability of two skeletal materials of the atlantic brain coral diploria strigosa for 230th u dating the commonly used bulk material comprising all skeletal elements and the denser theca wall material eight fossil corals of presumably last interglacial age from bonaire southern caribbean sea were investigated and several sub samples were dated from each coral for four corals both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232th content and 230th 238u ratios the bulk material samples of another coral show younger ages and lower 230th 238u ratios than the corresponding theca wall samples this coral also contains a considerable amount of 232th the application of the available open system models developed to account for post depositional diagenetic effects in corals shows that none of the models can successfully be applied to the bonaire corals the most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set comparison of the theca wall and bulk material data enables us to obtain information about the open system processes that affected the corals the corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary detrital phase the most likely source of the detrital material is carbonate sand the higher 230th 232th ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk earth 230th 232th ratio and that the threshold for the commonly applied 232th reliability criterion would be much lower than the generally used value of 1 ng g 1 the coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process a potential scenario is a combination of detrital contamination and u addition by secondary pore infillings our results show that the dense theca wall material of d strigosa is generally less affected by post depositional open system behaviour and better suited for 230th u dating than the bulk material this is also obvious from the fact that all ages of theca wall material reflect a last interglacial origin 125 ka whereas the bulk material samples are either substantially older or younger however for some corals the 230th u ages and activity ratios of the bulk material and the theca wall samples are similar this shows that strictly reliable 230th u ages can also be obtained from bulk material samples of exceptionally well preserved corals however the bulk material samples more frequently show elevated activity ratios and ages than the corresponding theca wall samples our findings should be generally applicable to brain corals mussidae that are found in tropical oceans worldwide and may enable reliable 230th u dating of fossil corals with similar skeletal architecture even if their bulk skeleton is altered by diagenesis the 230th u ages we consider reliable 120 130 ka along with a recently published age of 118 ka provide the first comprehensive dating of the elevated lower reef terrace at bonaire 118 130 ka which is in agreement in timing and duration with other last interglacial records

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

anomalous depth dependency of the stress field in the 2007 noto hanto japan earthquake potential involvement of a deep fluid reservoir 1 we have elucidated depth variations in the stress field associated with the 2007 noto hanto japan earthquake by stress tensor inversion using high quality aftershock data obtained by a dense seismic network aftershocks that occurred above 4 km in depth indicated a strike slip stress regime by contrast aftershocks in deeper parts indicated a thrust faulting stress regime this depth variation in the stress regime correlates well with that in the slip direction derived from a finite source model using geodetic data furthermore the maximum principal stress 1 axis was stably oriented approximately w20 n down to the depth of the mainshock hypocenter largely in agreement with the regional stress field but below that depth the 1 axis had no definite orientation indicating horizontally isotropic stress one likely cause of these drastic changes in the stress regime with depth is the buoyant force of a fluid reservoir localized beneath the seismogenic zone

coastal uplift rate at matanzas cuba inferred from mis5e phreatic overgrowths on speleothems many morphological elements in cuba s landscape e g marine terraces tidal notches demonstrate that coastal uplift has taken place but the rate at which this occurs is not known carbonate phreatic overgrowths on speleothems have been found in a cave in central north cuba 1 km from the present coastline at 16 m asl they form exceptional and unique mushroom shaped speleothems and balconies decorating the walls of the rooms these phreatic overgrowths on speleothems pos formed at the oscillating air water interface in sea level controlled anchialine lakes u th dating of these overgrowths suggests ages that are compatible with the marine isotope stage 5e i e 130 115 ka these pos have fixed this sea level highstand and demonstrate that this part of cuba has been subjected to a much lower uplift rate than previously reported i e less than 0 1 mm a 1 since the last interglacial this article is protected by copyright all rights reserved

foreshock migration preceding the 2016 mw 7 0 kumamoto earthquake japan we investigated the spatiotemporal evolution of an earthquake sequence following a series of large shallow intraplate earthquakes including a mw 6 2 foreshock and mw 7 0 main shock in the kumamoto area of kyushu sw japan to more precisely characterize the evolution of the earthquake sequences we applied a matched filter technique to continuous waveform data using template events obtained via a double difference relocation algorithm migrations of seismicity fronts along the directions of fault strike and dip are clearly seen starting immediately after the mw 6 2 foreshock these migrations are interpreted to result from aseismic slip triggered by the foreshock propagating toward the nucleation point of the subsequent mw 7 0 main shock rupture when combined with static stress changes induced by the mw 6 2 foreshock it is likely that stress transfer from both aseismic and seismic slip during the foreshock sequence loaded stress onto the main shock rupture faults bringing them closer to failure

tidal notches a sea level indicator of uncertain archival trustworthiness abstract in this paper after a short summary on the processes and rates of bioerosion that contribute to the deepening of a tidal notch profile some mediterranean case studies are presented where a tidal notch is prevented either from forming or from being preserved furthermore as shown also in a complementary paper the recent global sea level rise is preventing the development of new tidal notches in the present mid littoral zone this very useful sea level indicator of past temporary standstills of the relative sea level in carbonate rock areas is of great value in assisting interpretations of relative sea level change in locations where it is preserved the possibilities of absence of formation or of preservation however imply that it should be interpreted carefully before reconstructing local relative sea level histories in particular the lack of fossil tidal notches cannot be relied upon to interpret the absence of past periods of relative sea level stabilization

solution conduits as indicators of late quaternary sea level position abstract solution conduits or caves can provide a measure of glacio eustatic sea level position for the quaternary in high latitudes cave deposits contain artifacts fossils and sediments that reflect surface conditions with respect to climate secondary calcite deposits most notably stalagmites record growth episodes during ice minima and non growth during ice maxima they provide an indirect estimate of areal ice cover at high latitudes and are an indirect measure of sea level in low latitudes stable carbonate platforms contain caves that provide a direct measure of past sea level position solution conduits developing in a fresh water lens will record the position of the lens and therefore sea level as sea level fluctuates fresh water lens horizons and conduit development horizons will shift preserving a record of past sea level position cave wall rock and cave deposits can produce a chronology for given conduit positions secondary calcite deposits notably stalagmites record growth periods during sea level low stands or ice maxima and record growth hiatuses during flooding by sea level high stands or ice minima the inverse of high latitude stalagmites lighthouse cave san salvador island bahamas records a sea level high stand at 1 to 6 m for some time period between 85 000 and 70 000 years ago based on position and timing of conduit development and records sea level at present elevation for some time period between 49 000 and 37 000 years ago based on a stalagmite with a marine overgrowth

genesis of folia in a non thermal epigenic cave matanzas cuba abstract folia are an unusual speleothem type resembling inverted cups or bracket fungi the mechanism of folia formation is not fully understood and is the subject of an ongoing debate this study focuses on an occurrence of folia present in santa catalina cave a non thermal epigenic cave located close to matanzas cuba the sedimentology morphology petrology permeability and geochemistry of these folia have been studied to gain new insight on the processes leading to their development it is concluded that folia in santa catalina cave formed at the top of a fluctuating water body through co2 degassing or evaporation which may have been enhanced by the proximity to cave entrances two observations strongly support our conclusions 1 when compared to other subaqueous speleothems e g cave clouds present in the same rooms folia occur exclusively within a limited vertical interval that likely represents an ancient water level folia occur together with calcite rafts and tower cones that developed respectively on top of and below the water level this suggests that a fluctuating interface is required for folia formation 2 the measured permeability of the folia is too high to trap gas bubbles thus in contrast to what has been proposed in other studies trapped bubbles of co2 cannot be invoked as the key factor determining the genesis and morphology of folia in this subaqueous environment

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

sea level oscillations during the last interglacial highstand recorded by bahamas corals whether sea level was stable during the last interglacial remains a subject of debate an analysis of the u th ages of coral reefs in the bahamas corrected for open system behaviour confirms the presence of at least one oscillation within the sea level highstand

late quaternary sea level position evidence from bahamian carbonate deposition and dissolution cycles abstract the bahama islands offer a unique opportunity to examine late quaternary sea level position as the island group places significant constraints on the time and space boundary conditions for climatic events recorded there the bahamian archipelago extends as a series of large and small islands on shallow carbonate banks of various sizes for 1400 km across a climatic gradient wet in the northwest to dry in the southeast the entire island group is tectonically stable and consists solely of quaternary carbonate sediments with interspersed paleosols the islands reflect glacioeustatic sea level highstand positions in their eolian and subtidal suite of limestones a depositional record of platform flooding and carbonate sediment production a coeval record of phreatic cave development in the island s fresh water lenses also documents sea level highstand positions absolute dating of late pleistocene fossil corals and cave stalagmites by u th methods has produced an excellent record of the last interglacial marine isotope substage mis 5e holocene eolianites have been dated by 14 c to reveal platform flooding at 5000 ybp and sea level stabilization at 3000 ybp pleistocene eolianites have been dated by amino acid racemization analysis but subdivisons of the eolianites into separate mis 5a 5c and 5e deposits are controversial paleosols representing integrated aerosol dust deposition of 100 ka long platform exposure events during glaciations have been differentiated by paleomagnetic secular variation measurements previous interpretations of a beach unit to indicate a 20 m mis stage 11 sea level highstand and of large boulders to represent a mega tsunami appear to be incorrect phreatic caves in today s subaerial environment have been ascribed to mis 5e but some may have formed earlier carbonate deposition and dissolution cycles create a mass flux of co 2 sufficient to explain the atmospheric co 2 excursions of the quaternary

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

how precise are u series coral ages abstract u series dating of fossil reef corals is a well established and widely applied technique in paleoclimate research many fossil corals however show evidence for post depositional diagenetic alteration and it is generally accepted that the accuracy of u series coral ages is more limited due to coral diagenesis than analytical precision in recent years three models have been published that try to correct the effects of diagenesis and allow the calculation of model ages thompson w g spiegelmann m w goldstein s l and speed r c 2003 an open system model for u series age determinations of fossil corals earth and planetary science letters 210 365 381 villemant b and feuillet n 2003 dating open systems by the 238u 234u 230th method application to quaternary reef terraces earth and planetary science letters 210 105 118 scholz d mangini a and felis t 2004 u series dating of diagenetically altered fossil reef corals earth and planetary science letters 218 163 178 here we assess the age variability of both conventional 230th u dating and the three models by application to different sub samples of individual coral specimens the age variability estimated as the 2 standard deviation on the individual ages is compared with the errors quoted by the different methods our results show that the errors of conventional 230th u dating as well as those of the method of thompson et al 2003 do not account for the true age variability the age variability of both methods is in the range of the errors given by the models of villemant and feuillet 2003 and scholz et al 2004 furthermore we show that the widely used reliability criteria are not sufficient to identify all diagenetically altered corals in contrast analysis of different sub samples of one coral specimen allows i to estimate the real age variability ii to test if the assumptions of the models are fulfilled and iii to investigate the diagenetic processes in more detail thus this method should generally be applied to obtain more reliable u series coral ages and errors

esr and u th dating results for last interglacial coral reef terraces at the northern coast of cuba abstract fossil coral reef terraces at the northern coast of cuba in the vicinity of the bay of matanzas are forming a prominent flight of terraces these terraces were already studied by several investigators but a chronological classification based on numerical dating is still missing in this study we focus on the lowest unit the seboruco terrace which is assumed to be of mis 5e age the morphology of the seboruco terrace and associated sea level markers reef crests and notches were mapped and their altitude was measured over the whole study area in the field and by using remote sensing the fossil corals building up the terrace were surveyed in numerous natural outcrops the species of the fossil coral reefs were determined and subdivided in different facies zones fossil corals were taken for numerical dating by electron spin resonance esr and uranium series u th to establish a chronology of the mis 5e coral reef formation both dating techniques yielded age results in good agreement with each other and the stratigraphic context corresponding to the field evidence the age data indicates one mis 5e sea level highstand around 126 ka some younger esr ages may be explained by the recrystallization of aragonitic corals and or by u leaching at one locality east of matanzas the radiometric results for an underlying coral reef body suggest an mis 7 age the sea level markers for the mis 5e highstand range from 5 5 m a s l reef crest to a maximum of 7 m notches west of the bay of matanzas resulting in relatively low uplift rates of 0 003 m ka and 0 036 m ka when applying early mis 5e sea level estimates from tectonically stable coasts in the caribbean between 2 5 m and 6 6 m inside the bay of matanzas itself the elevation of sea level markers increases to more than 10 m a s l indicating a stronger uplift rate of 0 027 m ka to 0 060 m ka here

loading rate variations along a midcrustal shear zone preceding the m w 6 0 earthquake of 24 august 2016 in central italy

abundant aftershock sequence of the 2015 mw7 5 hindu kush intermediate depth earthquake the 2015 m w7 5 hindu kush earthquake occurred at a depth of 213 km beneath the hindu kush region of afghanistan while many early aftershocks were missing from the global earthquake catalogues this sequence was recorded continuously by eight broad band stations within 500 km here we use a waveform matching technique to systematically detect earthquakes around the main shock more than 3000 events are detected within 35 d after the main shock as compared with 42 listed in the advanced national seismic system catalogue or 196 in the international seismological centre catalogue the aftershock sequence generally follows the omori s law with a decay constant p 0 92 we also apply the recently developed double pair double difference technique to relocate all detected aftershocks most of them are located to the west of the hypocentre of the main shock consistent with the westward propagation of the main shock rupture the aftershocks outline a nearly vertical southward dipping plane which matches well with one of the nodal planes of the main shock we conclude that the aftershock sequence of this intermediate depth earthquake shares many similarities with those for shallow earthquakes and infer that there are some common mechanisms responsible for shallow and intermediate depth earthquakes

early aftershocks and afterslip surrounding the 2015 mw 8 4 illapel rupture abstract on 16 september 2015 the mw 8 4 illapel earthquake ruptured a section of the subduction thrust on the west coast of central chile the mainshock was followed by numerous aftershocks including some normal faulting events near the trench we apply a template matching approach to improve the completeness of early aftershocks within one month of the mainshock to constrain the distribution of afterslip we utilize repeating earthquakes among the aftershocks and perform a joint slip inversion of postseismic gps and insar data the results show that the aftershock zone abruptly expands to the south 14 h after the mainshock while growing relatively continuously to the north within the first day the repeating earthquakes accompanying the early expansion suggest that aseismic afterslip on the subduction thrust surrounding the coseismic rupture is an important triggering mechanism of aftershocks in addition to stress transfer or poroelastic effects an energetic earthquake sequence near the trench initiated with a m 4 6 event 3 5 h after the mainshock suggesting delayed triggering by the static or dynamic stress changes induced by the mainshock the spatial distribution of repeating earthquakes and the geodetic inverted afterslip are consistent and appear to wrap around the large coseismic slip patch both data sets suggest that the largest cumulative afterslip is located at 30 5 s to the north of the mainshock rupture zone the estimated postseismic moment released in the first 24 days of afterslip is equivalent to an earthquake of mw 7 5 the afterslip illuminates the velocity strengthening sections of the plate interface that surround the mainshock rupture consistent with plate coupling models inferred from interseismic gps velocities

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

diagenesis of speleothems and its effect on the accuracy of 230th u ages abstract speleothems can be precisely dated by u series disequilibrium methods one basic assumption of the 230th u dating method is that the system remains closed and u and th isotopes are neither lost nor added after deposition for stalagmites this requirement is usually fulfilled due to their protected environment in caves however undersaturated drip water may lead to diagenesis of speleothem caco3 and altered 230th u ages here we present a detailed petrographic investigation using thin sections and 230th u ages of a stalagmite from the riesenberghohle northern germany which grew during marine isotope stages 5e c and a the occurrence of a mosaic fabric in large parts of the stalagmite in combination with several age inversions is a clear indication for diagenetic alteration we discuss the potential diagenetic processes and quantitatively model their influence on the 230th u ages post depositional u loss leads to increasing 230th 238u activity ratios and thus apparently older ages in contrast post depositional addition of u results in decreased 230th 238u activity ratios and apparently younger ages comparison with our modelling results suggests that diagenesis occurred early after deposition initial and post depositional detrital contamination probably played a minor role for the observed age inversions

step like migration of early aftershocks following the 2007 mw 6 7 noto hanto earthquake japan seismic data reveal that the aftershock zone expands with time after a main shock event here we examine the aftershock sequence recorded during the first 32 days following the 2007 noto hanto earthquake japan by applying a matched filter technique to the data we detected about 10 times more events than those listed in the routinely constructed earthquake catalog the aftershock area expanded along the fault strike as a logarithmic function of time beginning immediately after the main shock aftershock expansion toward the sw was especially extensive and developed more rapidly than toward the ne interestingly the aftershock area expanded in a step like manner by the activation of a series of spatially clustered seismic bursts spatial correlation between the aftershock extension and the afterslip distribution suggests that the expansion of the aftershock area could be mainly driven by aseismic afterslip the aftershock area continues to expand even though 7 years have now passed since the main shock

detailed spatiotemporal evolution of microseismicity and repeating earthquakes following the 2012 mw 7 6 nicoya earthquake we apply a waveform matching technique to obtain a detailed earthquake catalog around the rupture zone of the 5 september 2012 moment magnitude 7 6 nicoya earthquake with emphasis on its aftershock sequence starting from a preliminary catalog we relocate 7900 events using tomodd to better quantify their spatiotemporal behavior relocated aftershocks are mostly clustered in two groups the first is immediately above the major coseismic slip patch partially overlapping with shallow afterslip the second one is 50 km se to the main shock nucleation point and near the terminus of coseismic rupture in a zone that exhibited little resolvable afterslip using the relocated events as templates we scan through the continuous recording from 29 june 2012 to 30 december 2012 detecting approximately 17 times more than template events we find 190 aftershocks in the first half hour following the main shock mostly along the plate interface later events become more scattered in location showing moderate expansion in both along trench and downdip directions from the detected catalog we identify 53 repeating aftershock clusters with mean cross correlation values larger than 0 9 and indistinguishably intracluster event locations suggesting slip on the same fault patch most repeating clusters occurred within the first major aftershock group very few repeating clusters were found in the aftershock grouping along the southern edge of the peninsula which is not associated with substantial afterslip our observations suggest that loading from nearby afterslip along the plate interface drives spatiotemporal evolution of aftershocks just above the main shock rupture patch while aftershocks in the se group are to the se of the observed updip afterslip and poorly constrained

omori utsu law c values associated with recent moderate earthquakes in japan we investigate the early aftershock activity associated with four moderate earthquakes m w 6 6 6 7 that occurred recently in japan for each aftershock sequence we examine continuous high pass filtered seismograms recorded at seismic stations nearby the main fault to identify as many early events as possible the magnitude of these events is calibrated using aftershocks that are listed in the earthquake catalog of japan meteorological agency jma the analysis of the aftershock decay rates reveals a power law time dependence with a scaling exponent close to 1 0 that starts from about one minute from the mainshock our results demonstrate that the c value of the omori utsu law is very small although a lower bound is not established due to completeness problems in the first minute after the mainshock and statistical fluctuations

ice volume and sea level during the last interglacial during the last interglacial period 125 000 years ago sea level was at least several meters higher than at present with substantial variability observed for peak sea level at geographically diverse sites speculation that the west antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice sheet dynamics during this time interval we provide an internally consistent database of coral u th ages to assess last interglacial sea level observations in the context of isostatic modeling and stratigraphic evidence these data indicate that global eustatic sea level peaked 5 5 to 9 meters above present sea level requiring smaller ice sheets in both greenland and antarctica relative to today and indicating strong sea level sensitivity to small changes in radiative forcing

aftershock zones of large shallow earthquakes fault dimensions aftershock area expansion and scaling relations summary we determine the aftershock areas from relocated hypocentres for 64 dip slip and eight strike slip earthquakes in the period 1977 1996 together with those for three recent earthquakes the 1998 antarctic plate earthquake the 1999 izmit turkey earthquake and the 2000 wharton basin earthquake we also include the data for 27 strike slip earthquakes from pegler das 1996 we find that the location of the hypocentre is essentially random along strike for both strike slip and dip slip earthquakes subduction zone earthquakes appear to initiate more frequently towards the down dip edge of the fault whereas the non subduction zone dip slip earthquakes do not have any preferred depth of initiation the aftershock zones of subduction zone earthquakes often expand substantially along strike and up dip but far less in the down dip direction whereas those for non subduction zone earthquakes do not expand significantly in either the up or the down dip direction subduction zone thrust earthquakes have larger and more numerous aftershocks than earthquakes in all other tectonic settings for strikeslip earthquakes we find that slip increases at least linearly with length for dip slip earthquakes we find that the ratio of length to width increases systematically with length for lengths 40 km indicating that there is some restriction on fault width slip is found to be proportional to length over the moment range 10 17 nm m0 3r10 21 nm

a sustained 21 m sea level highstand during mis 11 400 ka direct fossil and sedimentary evidence from bermuda abstract a small protected karstic feature exposed in a limestone quarry in bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase still stand and regressive phase of a sea level in excess of 21 3 m above present during marine isotope stage mis 11 400 ka as determined by u th dating and amino acid racemization cobbles and marine sediments deposited during the high energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment this was succeeded stratigraphically by a still stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates probably upogebiid shrimp that could not be produced under any condition other than sustained marine submergence overlying this were pure carbonate beach sands of a low energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates the considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run up waves over a minimum duration of months if not years the maximum duration has yet to be determined but probably did not exceed one or two thousand years the most abundant snails in this fauna are two species indicative of brackish water and high tide line showing that a ghyben herzberg lens must have existed at 20 m the nature of these sediments and fossil accumulation is incompatible with tsunami deposition and given the absence of evidence for tectonic uplift of the bermuda pedestal or platform provide proof that sea level during mis 11 exceeded 20 m a fact that has widespread ramifications for geologists biogeographers and human demographics along the world s coastlines

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

light attenuation as a control for microbiogeomorphic features implications for coastal cave speleogenesis san salvador bahamas is a carbonate island with dozens of flank margin caves formed in the phreatic zone by fresh seawater mixing within the freshwater lens these caves have no direct connection with the sea and form at or close to the tidally influenced fluctuating water table after sea level fall in their subaerial parts caves are enlarged mainly by rock dissolution and by erosion close to the water level condensation corrosion and breakdown processes for understanding the geomorphological features observed in these caves and how they are related to light attenuation we investigated three sampling sites in the tidally influenced zone of lighthouse cave which has been re invaded by seawater during the holocene sea level highstand a freshwater lens no longer exists within or adjacent to the cave rock samples were collected above and below the internal lake shores close to the entrance and in the twilight and dark zones of this cave light and electron microscopy examinations were conducted for detecting microbial cells as well as bioconstruction and bioweathering features in addition a high precision laser scanner was used for characterising sample microtopography our data showed that the microtopography and geomorphology of the lake shore samples cave entrance are dominated by bioweathering whereas the samples of the twilight and dark zones are controlled by a combination of both bioweathering and bioconstructive processes depending on light availability bioconstructive structures such as semi planar lamination at the fluctuating water level of the lighthouse cave show that dissolution due to water mixing of sea and freshwater in the holocene is no longer the most important speleogenetic process we propose that the geomorphological evolution is strongly influenced by the degree of rock diagenesis more than the initial mechanism of speleogenesis

the analysis of last interglacial mis 5e relative sea level indicators reconstructing sea level in a warmer world the last interglacial mis 5e 128 116 ka is among the most studied past periods in earth s history the climate at that time was warmer than today primarily due to different orbital conditions with smaller ice sheets and higher sea level field evidence for mis 5e sea level was reported from thousands of sites but often paleo shorelines were measured with low accuracy techniques and in some cases there are contrasting interpretations about paleo sea level reconstructions for this reason large uncertainties still surround both the maximum sea level attained as well as the pattern of sea level change throughout mis 5e such uncertainties are exacerbated by the lack of a uniform approach to measuring and interpreting the geological evidence of paleo sea levels in this review we discuss the characteristics of mis 5e field observations and we set the basis for a standardized approach to mis 5e paleo sea level reconstructions that is already successfully applied in holocene sea level research application of the standard definitions and methodologies described in this paper will enhance our ability to compare data from different research groups and different areas in order to gain deeper insights into mis 5e sea level changes improving estimates of last interglacial sea level is in turn a key to understanding the behavior of ice sheets in a warmer world

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

a novel method for tracking individual waves in the surf zone a new method to obtain information on individual waves as they travel shoreward is described the wave tracking method involves analysis of synchronous water level records obtained from a shore normal transect of pressure transducers pts the method is illustrated here using data from field deployments inside the surf zone although the method could equally be applied outside the surf zone as a wave travels shoreward along the instrument transect it appears in the pt records at a progressively later time serial cross correlation techniques are used to shift each record in time so that each wave in the first record aligns approximately with the corresponding wave if it exists in subsequent records from along the transect a local minima analysis power et al 2010 is used to delimit individual waves in each record and then parameters of interest can be determined for each wave at each pt location the wave tracking method provides the evolution of these parameters for a single wave as it travels to shore and they can be analysed as a function of distance or local water depth the utility of the method is illustrated with case studies including the evolution of wave height and the evolution of the ratio of wave height to water depth for surf zone waves

maximum sea levels for the last glacial period from u series ages of submerged speleothems pleistocene sea levels reflect changes in the surface distribution of land sea and ice which in turn significantly influence the earth s climate1 the most complete record of sea levels for the last glacial cycle has come from raised coral reef terraces of the huon peninsula papua new guinea2 4 but interpretation of this record is hampered by relatively large age uncertainties and the possibility of variation in the rate of tectonic uplift subaerial speleothems stalagmites stalactites and flowstones from submerged caves in tetonically stable areas provide an alternative source of data5 8 as their growth stops when rising sea levels flood the caves previous studies of speleothems have been limited by dating precision5 6 and sample availability5 7 here we present high precision thermal ionization mass spectrometric 230th ages9 11 for a comprehensive suite of speleothem samples from the bahamas our results provide a record of maximum elevation of sea levels for the period from 80 to 10 kyr before the present for much of which sea levels are poorly known we also find that regional palaeoclimatic change can be an important factor in the termination of speleothem growth

on the role of multiple interactions in remote aftershock triggering the landers and the hector mine case studies the observed seismicity rate increase after large earthquakes in sites that are located several source lengths away from the mainshock centroid poses a major problem this is because the static stress change induced by a mainshock in that region seems to be insignificant and the dynamic stress changes can only en hance the seismicity during the passage of the seismic waves but not at later times in quest for a physically viable triggering mechanism for delayed aftershocks in remote sites we examine earthquake activities in remote sites that were triggered by two california earthquakes the magnitude 7 1 hector mine earthquake and the mag nitude 7 3 landers earthquake we introduce a new method for quantifying the de gree to which the triggering effect of each aftershock is locally more important than the triggering effect of the mainshock we apply this method to the landers and the hector mine remote aftershock sequences we show that multiple stress transfers from early aftershocks to later aftershocks played an important role in the enhance ment of both the landers and the hector mine aftershock activities in remote sites we present a time space diagram of the hector mine remote aftershock sequence in the imperial valley which shows that this sequence is made up of several subse quences and that the onset of activity migrated southward

cryptic diagenesis and its implications for speleothem geochronologies abstract speleothems are usually considered as one of the most amenable palaeoclimate archives for u series dating a number of studies in recent years however report cases of diagenetic alteration which compromises the use of u series systematics in speleothems resulting in inaccurate u th ages here we present the results of a high resolution u th dating study of a stalagmite cc26 from corchia cave in italy where we document a number of departures from an otherwise well defined age depth model and explore potential causes for these outliers unlike examples illustrated in previous studies cc26 contains no visible evidence of neomorphism and appears at least superficially ideally suited to dating good reproducibility obtained between multi aliquot u th analyses removes any possibility of analytical issues contributing to these outliers furthermore replicate analyses of samples from the same stratigraphic layer yielded ages in stratigraphic sequence implying very localized open system behavior uranium loss is suggested as a causative mechanism on account of the fact that all the outliers are older than their assumed true age a limited number of micro voids were observed under micro ct analyses and it is proposed that these were pathways for u loss uranium loss modelling allows us to constrain the possible timing of diagenetic alteration and indicates that the precursor for the outlier with the largest age discrepancy 309 must have been aragonite this study indicates that visibly unaltered speleothems may still contain small domains that have experienced post depositional alteration such cryptic diagenesis as recorded in this stalagmite has implications for the constancy of accuracy of the u series dating technique and suggests a need for careful examination of speleothems prior to dating particularly in low resolution u th studies

quaternary tectonic stability of the bahamian archipelago evidence from fossil coral reefs and flank margin caves abstract throughout the islands of the bahamian archipelago fossil coral reefs are found from current sea level up to a maximum elevation of 4 m 234 u 230 th radiometric dates obtained from in situ corals from these reefs by both alpha count and mass spectrometric techniques indicates that they were all formed during oxygen isotope substage 5e ca 125 000 years ago those data are consistent with a maximum sea level highstand of 6 m during substage 5e and either no vertical motion of the bahamas or possible isostatic subsidence of up to 2 m during the past 120 000 years no older in situ fossil corals or other subtidal deposits have been found subaerially exposed anywhere in the bahamas that finding suggests that late quaternary at least the past 300 000 years isostatic subsidence has occurred at a rate of 1 2 m per hundred thousand years and or no pre 5e highstands were above modern sea level an independent corroboration of the conclusions drawn about sea level amplitude and tectonic stability of the bahamas from the coral reef data is available from examination of abundant flank margin caves horizontal phreatic dissolution caves found above modern sea level throughout the bahamas these horizontally extensive air filled caves have dissolutional ceilings with elevations that are restricted to 1 to 7 m which is consistent with formation at the margin of a thin freshwater lens elevated by a past 6 m sea level highstand the restricted cave elevations and the lack of stalagmites in these caves that are older than 100 000 years are also consistent with cave formation during substage 5e and possible subsequent isostatic subsidence of a few metres the subsurface geology of the southeastern bahamas contains a long term record millions of years that has been attributed to past tectonic activity along the north american caribbean plate boundary while that record suggests differential subsidence across the bahamas in the tertiary period the data from fossil coral reefs and subtidal deposits and flank margin caves indicate that all bahamian banks on which there are islands have been tectonically stable and behaving similarly for at least the past several hundred thousand years

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

increasing seismicity in southern tibet following the 2015 mw 7 8 gorkha nepal earthquake abstract we conducted a systematic detection of micro seismicity in southern tibet 1 6 days before and 4 4 days after the 2015 mw 7 8 gorkha nepal earthquake our study employs 368 template events listed in the china earthquake networks center cenc catalog with the waveform based matched filter technique we detected five times more earthquakes than listed in the cenc catalog during our study period the seismicity in southern tibet shows a significant increase immediately following the gorkha nepal earthquake including two normal faulting events the mw 5 8 tingri and mw 5 3 nyalam earthquakes about 3 and 11 h after the mainshock respectively although the static stress changes cfs showed a slightly better correlation with the seismicity rate changes than the peak dynamic stress changes cfs t the absolute value of the static stress change at the epicenter region of the mw 5 8 tingri earthquake is 10 kpa roughly two orders smaller than the peak dynamic stress change of 2 2 mpa although we are unable to identify the primary triggering mechanism it is evident that the 2015 nepal earthquake triggered widespread seismicity in southern tibet our results highlight the potential increase of seismic hazard in southern tibet due to the occurrence of major thrust earthquakes along the himalaya frontal thrust faults

spatial temporal evolutions of early aftershocks following the 2013 mw 6 6 lushan earthquake in sichuan china we perform a comprehensive detection of early aftershocks following the 2013 mw 6 6 lushan earthquake which occurred in the southern longmenshan fault zone in sichuan province china about 5 years after the 2008 mw 7 9 wenchuan earthquake we use events in both standard and relocated catalogs as templates to scan through continuous waveforms 2 days before and 3 days after the main shock we successfully reduce the magnitude of completeness mc by more than 1 order and obtain up to 6 times more events than listed in both catalogs aftershocks in the first hour mostly occur around the main shock slip region and aftershocks at later times show systematic expansions in the along strike perpendicular strike and updip directions although postseismic deformation following the lushan main shock has not been clearly identified we suggest that early aftershock expansions are likely driven by afterslip of the lushan main shock this is consistent with the observations that most aftershocks were in the stress shadow of the lushan main shock and that there was significant slip deficit in the top 10 km of the crust we also find that seismicity on the back thrust fault was activated as soon as 20 min after the main shock earlier than previously reported we are unable to detect any clear foreshocks in the last 2 days before the lushan main shock

global survey of aftershock area expansion patterns we developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock the definition is based upon the amount of energy released by aftershocks the spatial distribution of the energy release is first determined and is contoured the 1 day aftershock area is defined by a contour line corresponding to the energy release level of 10 15 6 ergs 100 km 2 day the 10 day 100 day and 1 y aftershock areas are similarly defined by contour lines corresponding to 10 14 8 10 14 0 and 10 13 5 ergs 100 km 2 day respectively we also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day using this method we study the aftershock area expansion patterns of 44 large m s 7 5 and five moderate shallow earthquakes which occurred from 1963 to 1980 each aftershock sequence is examined at four different times i e 1 day 10 days 100 days and 1 y after the main event we define the aftershock area expansion ratios and e by s 100 s 1 and l 100 l 1 respectively here s t and l t are the area and the length of the aftershock area respectively at time t our study suggests that a distinct regional variation of aftershock area expansion patterns is present it is strongly correlated with the tectonic environment in general the subduction zones of the mariana type have large expansion ratios and those of the chilean type have small expansion ratios some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios these results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots called the asperities and weak zones surrounding the asperities the rupture immediately after the main shock mostly involves asperities after the main rupture is completed the stress change caused by the main shock gradually propagates outward into the surrounding weak zones this stress propagation manifests itself as expansion of aftershock activity in this simple picture if the fault zone is represented by relatively large asperities separated by small weak zones chilean type then little expansion of aftershock activity would be expected on the other hand if relatively small asperities are sparsely distributed mariana type significant expansion occurs the actual distribution of asperities is likely to be more complex than the two cases described above however we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area