differential cratering of synchronously rotating satellites by ecliptic comets abstract we use monte carlo methods to simulate impacts of ecliptic comets on the synchronously rotating satellites of giant planets we reconfirm the long standing prediction that the cratering rate should be much higher on the leading hemispheres than on the trailing hemisphere indeed we find that previously published analytical formulations modestly underestimate the degree of apex antapex asymmetry to be expected we then compare our results to new mapping of impact craters on ganymede callisto and triton ganymede reveals a pronounced apex antapex asymmetry that is nonetheless much less than predicted all of triton s confirmed impact craters are clustered toward the apex of motion far exceeding the predicted asymmetry no asymmetry is observed on callisto in each case at least one of our basic assumptions must be wrong likely candidates include the following i the surfaces of all but the most sparsely cratered satellites are saturated or nearly saturated with impact craters ii these satellites have rotated nonsynchronously over geological time iii most of the craters are made not by heliocentric sun orbiting comets and asteroids but rather by planetocentric planet orbiting debris of indeterminate origin or iv pathological endogenic resurfacing has created illusions of structure callisto s surface is readily classified as nearly saturated ganymede s bright terrains although less heavily cratered than those of callisto can also be explained by crater densities approaching saturation on a world where endogenic processes were active the leading alternative is nonsynchronous rotation an explanation supported by the distribution of catenae crater chains produced by impact of tidally disrupted comets triton s craters can be explained by planetocentric debris or by capricious resurfacing but both hypotheses are inherently improbable

forearc collapse plate flexure and seismicity within the downgoing plate along the sunda arc west of sumatra deformation within the downgoing oceanic lithosphere seawards of subduction zones is typically characterised by regimes of shallow extension and deeper compression due to the bending of the oceanic plate as it dips into the subduction zone however offshore sumatra there are shallow compressional earthquakes within the downgoing oceanic plate outboard of the region of high slip in the 2004 aceh andaman earthquake occurring at the same depth as extensional faulting further seaward from the trench a clear separation is seen in the location of intraplate earthquakes with extensional earthquakes occurring further seawards than compressional earthquakes at the same depth within the plate the adjacent section of the forearc prism west of aceh is also anomalous in its morphology characterised by a wide prism with a steep bathymetric front and broad gradually sloping top this shape is in contrast to the narrower and more smoothly sloping prism to the south and along other subduction zones the anomalous near trench intraplate earthquakes and prism morphology are likely to be the result of the geologically rapid gravitational collapse of the forearc which leads to induced bending within the subducting plate and the distinctive plateau like morphology of the forearc such collapse of the forearc could be caused by changes through time of the material properties of the forearc rocks or of the thickness of the sediments entering the subduction zone

estimation of strong ground motions from hypothetical earthquakes on the cascadia subduction zone pacific northwest strong ground motions are estimated for the pacific northwest assuming that large shallow earthquakes similar to those experienced in southern chile southwestern japan and colombia may also occur on the cascadia subduction zone fifty six strong motion recordings for twenty five subduction earthquakes ofms 7 0 are used to estimate the response spectra that may result from earthquakesmw 81 4 large variations in observed ground motion levels are noted for a given site distance and earthquake magnitude when compared with motions that have been observed in the western united states large subduction zone earthquakes produce relatively large ground motions at surprisingly large distances an earthquake similar to the 22 may 1960 chilean earthquake mw 9 5 is the largest event that is considered to be plausible for the cascadia subduction zone this event has a moment which is two orders of magnitude larger than the largest earthquake for which we have strong motion records the empirical green s function technique is used to synthesize strong ground motions for such giant earthquakes observed teleseismicp waveforms from giant earthquakes are also modeled using the empirical green s function technique in order to constrain model parameters the teleseismic modeling in the period range of 1 0 to 50 sec strongly suggests that fewer green s functions should be randomly summed than is required to match the long period moments of giant earthquakes it appears that a large portion of the moment associated with giant earthquakes occurs at very long periods that are outside the frequency band of interest for strong ground motions nevertheless the occurrence of a giant earthquake in the pacific northwest may produce quite strong shaking over a very large region

wedge geometry mechanical strength and interseismic coupling of the hikurangi subduction thrust new zealand the hikurangi subduction thrust interface east coast north island new zealand exhibits along strike variations in seismic style the southern segment is interseismically locked while the plate boundary thrust slips aseismically in the north the geometry of the offshore accretionary prism is also heterogeneous changing from small to large taper angle fault dip plus surface slope from south to north along strike variations in accretionary prism geometry generally reflect changes in coulomb wedge critical taper angle such variations are controlled by the relative strengths of the subduction megathrust and the wedge material in the southern hikurangi margin the small taper angle indicates a relatively weak subduction thrust interface where strong interseismic locking is inferred in the northern margin high taper angle reflects a strong shallow decollement relative to the south thus based on critical coulomb wedge theory the shallow megathrust appears relatively weak in the locked segment and stronger in weakly coupled regions

chilean megathrust earthquake recurrence linked to frictional contrast at depth fundamental processes of the seismic cycle in subduction zones including those controlling the recurrence and size of great earthquakes are still poorly understood here by studying the 2016 earthquake in southern chile the first large event within the rupture zone of the 1960 earthquake moment magnitude mw 9 5 we show that the frictional zonation of the plate interface fault at depth mechanically controls the timing of more frequent moderate size deep events mw 8 5 we model the evolution of stress build up for a seismogenic zone with heterogeneous friction to examine the link between the 2016 and 1960 earthquakes our results suggest that the deeper segments of the seismogenic megathrust are weaker and interseismically loaded by a more strongly coupled shallower asperity deeper segments fail earlier 60 yr recurrence producing moderate size events that precede the failure of the shallower region which fails in a great earthquake recurrence 110 yr we interpret the contrasting frictional strength and lag time between deeper and shallower earthquakes to be controlled by variations in pore fluid pressure our integrated analysis strengthens understanding of the mechanics and timing of great megathrust earthquakes and therefore could aid in the seismic hazard assessment of other subduction zones the recurrence time of megathrust earthquakes in chile may be controlled by frictional contrasts at depth according to analyses of stress build up and release related to the december 2016 southern chile earthquake

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

crustal structure and seismicity beneath the forearc off northeastern japan marine seismological and other data in the japan trench area north of 38 5 n were used to infer the relation of subducting plate structure seismicity and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates previous crustal models from ocean bottom seismographic refraction obs surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data a wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting pacific plate crust its dip angle increases to about 7 110 km landward of the trench axis a large increase beneath the deep sea terrace is required to reach the well defined angle of 25 beneath the tohoku east coast a large wave speed gradient within layer 2 commonly observed under normal oceans seems to vanish beneath the inner trench slope at about 10 km depth within the overriding plate apparently brittle material with a p wave speed of 6 km s can be found as near as 35 km from the trench axis the upper limit of the seismogenic zone of interplate low angle thrust events is about 15 km depth from obs seismicity and large event analyses both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates

megathrust earthquake swarms indicate frictional changes which delimit large earthquake ruptures abstract using a recently constructed catalog of megathrust earthquake swarms we present results that illustrate how fault slip for m w 8 5 earthquakes with a publicly available finite fault rupture model is delimited along strike by swarm regions we further investigate this relationship for all m w 7 5 subduction zone megathrust earthquakes that have occurred over the last 40 years by estimating the rupture area from early aftershocks this extended comparison shows only 2 out of 42 earthquakes propagate through regions of the megathrust that have documented recurring earthquake swarm activity while about 40 17 out of 42 are terminate on at least one side near regions with swarm activity in japan chile sumatra and alaska earthquake swarms correlate with regions of the plate interface that exhibit low interseismic strain accumulation this suggests earthquake swarms are associated with reduced plate coupling and possibly aseismic moment release however earthquakes in chile and alaska ruptured through regions of weak coupling that do not show swarm activity we propose instead that stress heterogeneity on the megathrust can best explain why large earthquake ruptures terminate in swarm regions but not in regions with weak coupling alone earthquake swarms appear to be a proxy for along strike segmentation of subduction megathrusts at least on the time scale of one seismic cycle

ultralong period seismic study of the december 2004 indian ocean earthquake and implications for regional tectonics and the subduction process analysis of the earth s longest period normal modes shows that the december 2004 sumatra andaman earthquake was much larger mw 9 3 than ini tially inferred from surface wave data and involved slip on a much longer fault than initially inferred from body wave data the seismic moment and relative excitation of the normal modes indicate that the entire aftershock zone ruptured consistent with the large tsunami amplitudes in thailand sri lanka and india an apparent increase in seismic moment with period results from interference between parts of the fault the earthquake resulted from subduction of the indian plate beneath the burma microplate a sliver plate between the indian and sunda plates hence the rate and direction of convergence depends on the motion of the burma plate which is not well known convergence would be highly oblique if the rate of motion between burma and sunda is that inferred from spreading in the andaman sea and less if a slower rate is inferred from the sagaing fault the december earthquake was much larger than expected from a previously proposed relation based on the idea of seismic coupling in which such earthquakes occur only when young lithosphere subducts rapidly moreover a global reanalysis finds little support for this correlation hence we suspect that much of the apparent differences between subduction zones such as some trench segments but not others being prone to m w 8 5 events and hence oceanwide tsunamis may reflect the short earthquake history sampled this possi bility is supported by the variability in rupture mode at individual trench segments

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

fault kinematics in northern central america and coupling along the subduction interface of the cocos plate from gps data in chiapas mexico guatemala and el salvador new gps measurements in chiapas mexico guatemala and el salvador are used to constrain the fault kinematics in the north america na caribbean ca and cocos co plates triple junction area the regional gps velocity field is first analysed in terms of strain partitioning across the major volcano tectonic structures using elastic half space modelling then inverted through a block model we show the dominant role of the motagua fault with respect to the polochic fault in the accommodation of the present day deformation associated with the na and ca relative motion the na ca motion decreases from 18 22 mm yr 1 in eastern guatemala to 14 20 mm yr 1 in central guatemala assuming a uniform locking depth of 14 28 km down to a few millimetres per year in western guatemala as a consequence the western tip of the ca plate deforms internally with 9 mm yr 1 of east west extension 5 mm yr 1 across the guatemala city graben alone up to 15 mm yr 1 of dextral motion can be accommodated across the volcanic arc in el salvador and southeastern guatemala the arc seems to mark the northern boundary of an independent forearc sliver ar pinned to the na plate the inversion of the velocity field shows that a four block na ca co and ar model that combines relative block rotations with elastic deformation at the block boundaries can account for most of the gps observations and constrain the overall kinematics of the active structures this regional modelling also evidences lateral variations of coupling at the co subduction interface with a fairly high coupling 0 6 offshore chiapas and low coupling 0 25 offshore guatemala and el salvador

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

interseismic plate coupling and strain partitioning in the northeastern caribbean summary the northeastern caribbean provides a natural laboratory to investigate strain partitioning its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary here we use gps and earthquake slip vector data to produce a present day kinematic model that accounts for secular block rotation and elastic strain accumulation with variable interplate coupling on active faults we confirm that the oblique convergence between caribbean and north america in hispaniola is partitioned between plate boundary parallel motion on the septentrional and enriquillo faults in the overriding plate and plateboundary normal motion at the plate interface on the northern hispaniola fault to the east the caribbean north america plate motion is accommodated by oblique slip on the faults bounding the puerto rico block to the north puerto rico subduction and to the south muertos thrust with no evidence for partitioning the spatial correlation between interplate coupling strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate facilitating strike slip faulting in the overriding plate the model slip rate deficit together with the dates of large historical earthquakes indicates the potential for a large m w7 5 or greater earthquake on the septentrional fault in the dominican republic similarly the enriquillo fault in haiti is currently capable of a m w7 2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today the model results show that the puerto rico lesser antilles subduction thrust is only partially coupled meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion this does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes but whose location and geometry are not resolvable with the present data distribution slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and together with stress changes due to historical earthquakes derive the recent stress evolution in the ne caribbean

a simple discrete element model for large multiplet earthquakes adjacent segments of the plate boundary may fail separately as earthquakes that occur very close in time when the time between events is a small fraction of the recurrence interval then the sequence is referred to as doublets or multiplets in the first part of this paper we determine the frequency of occurrence of large multiplet earthquakes we count the number of multiplet earthquakes present in the abe catalogue with aftershocks removed ms 7 1 using a series of space time and magnitude filters we compare this number to the number of multiplet earthquakes present in the abe catalogue where origin times of earthquakes are randomized and epicentral locations and magnitudes are kept constant the difference between the observed and random number of multiplets gives us the percentage of multiplets that do not occur randomly we find that this percentage ranges from 2 to 7 of all large earthquakes based on the best choice of space time and magnitude filters in the second part of this paper we model multiplet earthquakes using three simple frictional slider models the models consist of slider blocks resting on a frictional conveyer belt and interconnected by springs the seismogenic portion of the plate interface is represented by blocks that exhibit stick slip behavior asperities aseismic creep within the seismogenic zone is represented by creepers the creepers are blocks that obey a simple linear creep law the three models differ in that the positions of the creeping blocks within the system of asperities and creepers are different we find that model 3 produces a complex sequence of events consisting of single double and multiplet earthquakes these synthetic sequences of events are comparable to the earthquake cycle observed along nankai trough model 3 produces a high percentage of multiplet earthquakes when the creeper is allowed to relax within a small fraction of the maximum recurrence time of the event sequence this implies that the details of the frictional law invoked for the creeper blocks does not influence the model results significantly the time evolution of model 3 is compared to the postseismic phase of the loading cycle at muroto point japan we suggest that the rapid postseismic deformation that occurs immediately after the nankaido earthquake is due to a rapid creeping zone that is in this region

sedimentary fill of the chile trench 32 46 s volumetric distribution and causal factors the chile trench of the convergent continental margin of central chile is a sediment filled basin that stretches over 1500 km in a north south direction the sediment fill reflects latitudinal variations in climate as well as in the morphology and geology of chile but also of sediment transport processes to the trench and within the trench we try to untangle these signals by calculating the total volume and the latitudinal volume distribution of trench sediments and by relating this distribution to a number of factors that affect this pattern the volume calculation is based on a model geometry of the top of the subducting oceanic plate that is buried beneath trench sediments and the sea floor as measured by swath bathymetry we obtain the model geometry of the subducting plate by interpolating between depth converted seismic reflection profiles that cross the trench the total volume of the trench fill between 32 and 46 s is calculated to be 46000 500 km 3 the resulting latitudinal volume distribution is best explained by a sedimentation model that alternates between 1 glacial phases of high sediment flux from southern chile combined with active latitudinal sediment transport within the trench and 2 interglacial phases over which sediment input is dominated by local factors supplementary material top of the oceanic basement tob grid is available as ascii raw data files xyz at www geolsoc org uk sup18664

seismotectonic constraints on the convergence rate between the rivera and north american plates there are two significantly different types of models for the convergence rate between the rivera and north american plates the first type the high rate model bandy 1992 predicts convergence rates of approximately 5 0 cm yr near the southern end of the rivera north america subduction zone and between 2 0 and 3 0 cm yr at its northern end in contrast the second type the low rate model e g demets and stein 1990 predicts convergence rates of between 2 0 and 3 3 cm yr near the southern end of the rivera north america subduction zone and between 0 6 and 1 7 cm yr at its northern end seismotectonic relationships which relate seismic characteristics of subduction zones maximum magnitudes maximum seismic depths etc to plate tectonic parameters convergence rates age of the oceanic lithosphere etc provide a means of distinguishing between the two different models three such relationships suggest that the rivera north american and cocos north american convergence rates should be roughly equal across the rivera cocos plate boundary favoring the high rate model employing the high rate model one can evaluate the magnitude and distribution of the strike slip component of forearc motion vss produced by oblique convergence between the rivera and north american plates the analysis indicates both a progressive increase and clockwise reorientation of vss northwestward along the plate contact zone of the rivera north america subduction zone such a distribution in vss should produce a northwestward movement of and nw se oriented extension within the interior of the jalisco block consistent with previous proposals of jalisco block motions also such a distribution in vss should produce a slight clockwise rotation of the jalisco block in the vicinity of bahia de banderas consistent with paleomagnetic data

the lunar rayed crater population characteristics of the spatial distribution and ray retention abstract the global statistics for young impact craters on the moon is used to unravel potential spatial asymmetries that may have been introduced by the particular orbital configuration of a synchronously rotating satellite only craters that exhibit bright ejecta rays extending for several crater radii were considered in this study this crater population is younger than about 750 ma the shape of the crater size frequency distribution does not show strong dependence on the target properties mare vs highlands however slightly lower frequencies indicate a shorter retention of the visibility of rays in mare units when their visibility is purely due to immaturity and not due to composition rays of small craters fade away much faster large old rayed craters sustain their visibility longer than the average crater population because of the compositional contrast between rays and mare material and thus obscure the cratering record when investigated for spatial variations using the existence of rays purely based on optical maturity instead of visibility as marker horizon for the copernican eratosthenian boundary suggests a shift from 1 1 ga to 750 ma the spatial distribution of lunar rayed craters namely the latitudinal and longitudinal frequency variations does not agree with previous analytical and numerical studies although there is an apparent hemispherical asymmetry centred close to the apex the density distribution is patchy and no predicted spatial pattern could be confirmed spatial distribution corrections accounting for the lower frequencies in the mare areas did not result in a better agreement with the analytical estimates density variations are less than 15 over vast parts of the lunar surface and the uncertainties for absolute surface ages are similar however variations of up to 50 are found even for the more numerous small craters these extreme values are located at high latitudes a combination of crater forming projectile flux distribution and micrometeorite bombardment which acts on maturation of the ray systems could prove as an explanation for the contradicting observed rayed crater distribution an analysis of the older craters is more challenging on the moon because earlier geological processes complicate the setting and the orbital configuration of the moon earth sun projectile system altered with time

global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones abstract the maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on earth with some subduction zone segments producing giant subduction zone thrust earthquakes e g chile alaska sumatra andaman japan and others producing relatively small earthquakes e g mariana scotia here we show how such variability might depend on various subduction zone parameters we present 24 physical parameters that characterize these subduction zones in terms of their geometry kinematics geology and dynamics we have investigated correlations between these parameters and the maximum recorded moment magnitude m w for subduction zone segments in the period 1900 june 2012 the investigations were done for one dataset using a geological subduction zone segmentation 44 segments and for two datasets rupture zone dataset and epicenter dataset using a 200 km segmentation 241 segments all linear correlations for the rupture zone dataset and the epicenter dataset r 0 00 0 30 and for the geological dataset r 0 02 0 51 are negligible low indicating that even for the highest correlation the best fit regression line can only explain 26 of the variance a comparative investigation of the observed ranges of the physical parameters for subduction segments with m w 8 5 and the observed ranges for all subduction segments gives more useful insight into the spatial distribution of giant subduction thrust earthquakes for segments with m w 8 5 distinct narrow ranges are observed for several parameters most notably the trench normal overriding plate deformation rate v opd i e the relative velocity between forearc and stable far field backarc trench normal absolute trench rollback velocity v t subduction partitioning ratio v sp v s the fraction of the subduction velocity that is accommodated by subducting plate motion subduction thrust dip angle st subduction thrust curvature c st and trench curvature angle t the results indicate that m w 8 5 subduction earthquakes occur for rapidly shortening to slowly extending overriding plates 3 0 v opd 2 3 cm yr slow trench velocities 2 9 v t 2 8 cm yr moderate to high subduction partitioning ratios v sp v s 0 3 1 4 low subduction thrust dip angles st 30 low subduction thrust curvature c st 2 0 10 13 m 2 and low trench curvature angles 6 3 t 9 8 epicenters of giant earthquakes with m w 8 5 only occur at trench segments bordering overriding plates that experience shortening or are neutral v opd 0 suggesting that such earthquakes initiate at mechanically highly coupled segments of the subduction zone interface that have a relatively high normal stress deviatoric compression on the interface i e a normal stress asperity notably for the three largest recorded earthquakes chile 1960 alaska 1964 sumatra andaman 2004 the earthquake rupture propagated from a zone of compressive deviatoric normal stress on the subduction zone interface to a region of lower normal stress neutral or deviatoric tension stress asperities should be seen separately from frictional asperities that result from a variation in friction coefficient along the subduction zone interface we have developed a global map in which individual subduction zone segments have been ranked in terms of their predicted capability of generating a giant subduction zone earthquake m w 8 5 using the six most indicative subduction zone parameters v opd v t v sp v s st c st and t we identify a number of subduction zones and segments that rank highly which implies a capability to generate m w 8 5 earthquakes these include sunda north sulawesi hikurangi nankai northern ryukyu kamchatka kuril japan aleutians alaska cascadia mexico central america south america lesser antilles western hellenic and makran several subduction segments have a low score most notably scotia new hebrides and mariana

roughness characteristics of oceanic seafloor prior to subduction in relation to the seismogenic potential of subduction zones we have developed a new approach to characterize the seafloor roughness seaward of the trenches as a proxy for estimating the roughness of the subduction interface we consider that abrupt elevation changes over given wavelengths play a larger role in the seismogenic behavior of the subduction interface than the amplitude of bathymetric variations alone the new database subrough provides roughness parameters at selected spatial wavelengths here we mainly discuss the spatial distribution of short 12 20 km and long wavelength 80 100 km roughness rsw and rlw respectively along 250 km wide strips of seafloor seaward of the trenches compared with global trend seamounts show distinct roughness signature of much larger amplitudes at both wavelengths whereas aseismic ridges only differ from the global trend at long wavelengths fracture zones cannot be distinguished from the global trend which suggests that their potential effect on rupture dynamics is not the consequence of their roughness at least not at these wavelengths based on rlw amplitude segments along subduction zones can be defined from rough to smooth subduction zones like the solomons or the ryukyus appear dominantly rough whereas others like the andes or cascadia are dominantly smooth the relative contribution of smooth versus rough areas in terms of respective lateral extents probably plays a role in multipatch rupture and thus in the final earthquake magnitude we observe a clear correlation between high seismic coupling and relatively low roughness and conversely between low seismic coupling and relatively high seafloor roughness

asymmetrical distribution of rayed craters on the moon the synchronous rotation of the satellite ought to cause a spatial variation in the cratering rate over its surface the crater density is expected to be maximum at the apex of the orbital motion and decrease with the increase of the angular distance from the apex the ratio of the density at the apex maximum to that of the antapex minimum depends on the average encounter velocity of impactors to the satellite although the moon is also in a state of the synchronous rotation it has been supposed that the asymmetry in the crater density on the moon can be hardly observed we report here a spatial variation in the density of rayed craters on the moon which may be associated with the synchronous rotation since the lifetime of a ray is relatively short 0 8 billion years the results provide information on recent impacts rayed craters are identified on clementine 750 nm mosaic images we investigate craters in a lower latitude zone from 42 n to 42 s to avoid an effect of material difference on the ray preservation we analyze craters on the highland from 70 e to 290 e in east longitude a total of 222 rayed craters larger than 5 km in diameter are identified in the study area of about 1 4 107 km2 the average density of rayed craters on the leading side is substantially higher than that on the trailing side the crater density decreases as a sinusoidal function of the angular distance from the apex the observed ratio of the density at the apex to that at the antapex is about 1 5 the ratio suggests that recent craters on the moon are formed mainly by near earth asteroids rather than comets with higher encounter velocities

strong seismic coupling underneath garhwal kumaun region nw himalaya india abstract no great earthquake has occurred in the garhwal kumaun region of nw himalaya in the past 500 years or more we report results of continuous gps measurements from 28 sites from the region to suggest that the convergence rate in this part of the himalaya is about 18 mm yr which is leading to strain accumulation in the region the main himalayan thrust mht in the frontal part of the himalaya under the outer and southern lesser himalaya is strongly coupled for a width of about 85 km the midcrustal ramp where earthquakes of himalayan seismic belt occur exhibits low coupling strong coupling on the mht beneath the outer and lesser himalaya is homogeneous except in the very shallow updip part of the mht subduction of sediments of the indo gangetic plains or the delhi hardwar ridge does not seem to influence coupling a high rate of strain accumulation which has continued for more than 500 years on a strongly coupled mht makes this one of the most earthquake vulnerable segments of the himalayan arc

discovery of active hydrothermal venting in lake taupo new zealand the horomatangi geothermal system of lake taupo new zealand is a sub lacustrine equivalent of subaerial geothermal activity nearby in the taupo volcanic zone tvz the setting of this system is rare within the tvz as it is directly associated with an individual volcanic feature that of the 1 8 ka taupo eruption vent two distinct hydrothermal vent areas named te hoata and te pupu have been discovered during dives with the submersible jago venting of gases was seen at both sites and hot water up to 45degreesc discharges at the te pupu site dilute water samples have concentrations of so4 cl na and sio2 above ambient lake water values gas samples have compositions similar to other tvz geothermal systems gas geothermometers indicate the existence of a high temperature hydrothermal environment beneath the lake with reservoir temperatures in excess of 300degreesc chimney structures were found at the te pupu site they are up to 30 cm tall and mineralized by an epithermal suite of elements including s hg as sb and tl the walls of the chimneys are largely composed of diatoms and strands of silicified filamentous bacteria embedded in an amorphous silica groundmass bacterial mats are commonly associated with the gas vents and also occur at two hot springs close to the vents commonly perched on top of dead chimneys and or exposed outcrops are dense assemblages of what are probably a new species of sponge of the genus heterorotula the sponges host a notably diversified associated invertebrate fauna and represent a previously unseen biomass on the lake floor the sponges appear to have bored into the mineralized chimneys c 2002 elsevier science b v all rights reserved

tsunamigenic earthquakes past and present milestones we review a number of events which taken individually have significantly affected our understanding of the generation of tsunamis by earthquake sources and our efforts at mitigating their hazards notably through the development of warning algorithms starting with the 1700 cascadia earthquake we examine how significant tsunamis have changed our views in fields as diverse as seismotectonics the diversity of earthquake cycles the development of warning algorithms the response of communities at risk to warnings and their education the latter being either formal or rooted in ancestral heritage we discuss in detail lessons from the 2004 sumatra disasters and review the performance of warning centers and the response of affected populations during the nine significant tsunamis which have taken place since 2004

a probabilistic tsunami hazard assessment for western australia the occurrence of the indian ocean tsunami on 26 december 2004 has raised concern about the difficulty in determining appropriate tsunami mitigation measures in australia due to the lack of information on the tsunami threat a first step in the development of such measures is a tsunami hazard assessment which gives an indication of which areas of coastline are most likely to experience tsunamis and how likely such events are here we present the results of a probabilistic tsunami hazard assessment for western australia wa compared to other parts of australia the wa coastline experiences a relatively high frequency of tsunami occurrence this hazard is due to earthquakes along the sunda arc south of indonesia our work shows that large earthquakes offshore of java and sumba are likely to be a greater threat to wa than those offshore of sumatra or elsewhere in indonesia a magnitude 9 earthquake offshore of the indonesian islands of java or sumba has the potential to significantly impact a large part of the west australian coastline the level of hazard varies along the coast but is highest along the coast from carnarvon to dampier tsunamis generated by other sources e g large intra plate events volcanoes landslides and asteroids were not considered in this study

seismic potential associated with subduction in the northwestern united states despite good evidence of present day convergence of the juan de fuca and north american plates there has been remarkably little historical seismic activity along the shallow part of the juan de fuca subduction zone although we cannot completely rule out the possibility that the plate motion is being accommodated by aseismic creep we find that the juan de fuca subduction zone shares many features with other subduction zones that have experienced great earthquakes

a search for clustering among the meteoroid impacts detected by the apollo lunar seismic network abstract we examined temporal clustering of meteoroid impacts detected by the apollo lunar seismic network and found a distinct difference between small meteoroids masses smaller than about 1 kg and large meteoroids masses larger than about 1 kg small meteoroids show strong clustering many of which are identified with showers known from terrestrial meteor studies in contrast little clustering is found for large meteoroids suggesting that they represent meteoroids of type and origin different from those of the small meteoroids overall 28 of the small events and 15 of the large events occur as clusters the small meteoroids appear to be mostly cometary while the large meteoroids may be derived from near earth asteroids and short period comets two swarms of large meteoroids detected in june 1975 and january 1977 possibly contain high density meteoritic objects and thus may represent meteorite streams

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

plate coupling along the manila subduction zone between taiwan and northern luzon abstract we use gps data trench parallel gravity anomaly tpga and bathymetry to infer plate coupling patterns along the manila subduction zone using a block model and a fault geometry constrained by seismicity we simultaneously solve for the location of euler pole and angular velocity between the sunda and luzon blocks as well as the slip deficit rate on plate interface our estimates show that the euler pole between the sunda and luzon blocks is situated at southern palawan near 8 3 n and 119 4 e with the angular velocity of 4 6 myr 1 the estimated convergence rate along the manila trench continuously decreases southward from 91 mm yr at the northern tip of luzon to 55 mm yr north of mindoro the inversion of gps data reveals partially locked fault patches extending from the west luzon trough to the east of scarborough seamount chain the slip deficit rate in this region is in the range of 20 30 mm yr corresponding to a coupling ratio of 0 4 however the fault slip behavior is not well resolved near the north luzon trough based on a good correlation between locations of large subduction zone earthquakes and areas possessing gravity low we investigate a variety of tpga based plate coupling models assuming different scaling between tpga values and plate coupling ratios the tpga based plate coupling models offer plausible rupture scenarios which are not constrained by current gps data the partially locked fault zone near 15 16 5 n may be associated with the subducted scarborough seamount wherein oceanic floor is highly fractured the great subduction zone earthquake propagates beneath the scarborough seamount seems to be unlikely the densification of gps network in central luzon and seafloor geodetic observations close to trench axis are crucial to distinguish the detailed fault coupling patterns and the role of subducted seamounts

weathering of pumice in the sediments as a possible source of major ions for the waters of lake taupo new zealand abstract the mass flows of major ions na k ca mg so 4 cl and hco 3 into lake taupo with the surface waters draining the lake catchment are less than the mass flows of major ions leaving the lake some of these differences are the result of geothermal fluid entering the lake and the mass contributions from this fluid are estimated from the li budget for the lake an accurate hydrological balance for the lake suggests a groundwater inflow of 8 m 3 s 1 by assuming that this groundwater has the same composition as spring waters entering the lake from pumice aquifers the mass contributions from groundwater are included in the majorion budgets combination of all these mass flows in the budgets still leaves unexplained differences between the quantities of major ions entering the lake and the quantities leaving the lake despite the water budget being complete it is shown that the remaining mass flows in the budgets could be due to the dissolution of pumice within the lake na concentrations in the interstitial waters of lake sediments are higher than in the overlying lake water and the calculated flux of na ions from the sediment into the lake water would satisfy the mass budget for na it is concluded that the dissolution of pumice in lake sediments could contribute major ions to the waters of some lakes in volcanic regions

a summary of cenozoic tectonic history along the ipod japan trench transect along the international program of ocean drilling ipod japan trench transect a mid cenozoic period of tectonism without arc volcanism separated an earlier cretaceous to paleogene and a later neogene period of plate convergence and subduction the cretaceous to early paleogene period of convergence is evidenced by andesitic volcanism associated with a large syncline probably a forearc basin the seaward flank of the basin is a tectonically thickened sediment sequence inferred to be an accretionary complex the arc the syncline and the thickened sediment sequence resemble an arc trench system of the size and structure of the great valley forearc basin and franciscan accretionary complex of california and they were probably continuations of the yezo geosyncline and associated sequences exposed to the north on hokkaido the arc trench system is contemporaneous with the adjacent shimanto arc trench system southwest of tokyo bay in the early paleogene volcanism ceased and part of the thickened sediment sequence of the cretaceous paleogene margin was emergent as a 160 km wide landmass which is recognized in seismic records as a later paleogene sediment source at the end of the paleogene this landmass began to subside and volcanism began again but it was located first briefly on the east and then on the west of the cretaceous arc along the present arc of northern honshu the land mass erosion surface is clearly visible as an angular unconformity in multichannel seismic reflection records the sequence of neogene sediment explosive volcanism and benthic foraminiferal assemblages recording subsidence from subareal conditions to the present bathyal depths have been studied in deep sea drilling project dsdp cores cretaceous subduction appears to have resulted in a very extensive accretionary complex whereas the neogene subduction period appears to have been marked by little net accretion in the forearc area but massive subsidence and some erosion of the front of the convergent margin

an early soda ocean in analogy to modern soda lakes commonly associated with volcanic regions it is postulated that the ancient sea had a high alkalinity a high ph and low ca and mg concentrations the change towards nacl dominance as observed in the present day ocean can best be explained by a series of mineral equilibria crustal differentiation and life processes in principle hydrothermal leaching of chlorine from the oceanic crust caused this ion to accumulate in the sea while at the same time dissolved carbonates became gradually removed by organisms and carbonates the switch from a soda to a halite ocean was accomplished 1 ga ago critical biochemical events marking the chemical evolution of the precambrian sea and their implications for the pco2 in air will be discussed

frequency size distribution of competent lenses in a block in matrix melange imposed length scales of brittle deformation 1 this study explores the frequency size distribution of competent lenses phacoids in the chrystalls beach complex a melange shear zone within the otago schist accretion collision assemblage new zealand the distribution of phacoids within a cleaved pelitic matrix follows a power law distribution with exponent 1 18 d 2 37 2 d at outcrop scale whereas distributions at thin section scale have higher d than the outcrop they were sampled from d relates to volume fraction and distribution of competent material where high d correlates with small aspect ratio phacoids and high matrix volume fraction in outcrops which experienced mixed continuous discontinuous deformation d 1 4 0 2 it is suggested that d 1 4 indicates dominant continuous deformation whereas d 1 4 is indicative of localized deformation on shear discontinuities in this melange d therefore appears a function of dominant deformation style actively deforming melange shear zones likely exhibit a range of seismic styles and earthquake magnitudes at length scales limited by lithological layering and shear zone thickness a hypothesis is suggested where strongly coupled shear zone segments may be distinguished by a high volume fraction of competent material low d while aseismically creeping regions are characterized by a high proportion of incompetent rock high d as the b value in the gutenberg richter frequency magnitude relationship also tends to be high in coupled and low in creeping fault segments it may be that d is analogous to b and the b value is also related to the ratio of incompetent competent material and dominant fault zone deformation style

a new source of water in seismogenic subduction zones 1 seismogenic plate boundary faults at accretionary margins e g the nankai margin southwest japan may occur where the uppermost part of subducting oceanic crust composed of basaltic rocks is in contact with the overriding plate of a lithified accretionary prism the plate boundary faults in ancient accretionary complexes typically record high velocity slip under fluid rich conditions although previous studies have emphasized the mechanical significance of fluids in terms of dynamic slip weakening the source of fluid in seismogenic subduction zones remains poorly constrained in this work we focus on the hydrous smectite in the uppermost oceanic crust an alteration product of intact basalt before arrival at the trench axis a comparison between 1 new mineralogical data on basalt drillcore recovered by integrated ocean drilling program iodp expedition 322 at site c0012 a reference site for subduction input to the nankai trough and 2 mineralogical data on basalt within ancient oceanic crust embedded in a fossil accretionary complex of the shimanto belt southwest japan suggests that progressive smectite chlorite conversion would liberate bound fluids at a rate of 0 34 to 0 65 10 14 s 1 along the plate interface this rate of fluid production appears to be more than an order of magnitude greater than that from other possible sources including from overlying sediments via smectite illite conversion and the expulsion of pore fluids and may facilitate seismic slip along plate boundary faults

cyclic ridge subduction at an inter plate locked zone off central japan 1 there are significant variations in the size especially lateral extent of the co seismic rupture zones and inter plate locked zones for an inter plate mega thrust earthquake obvious factors controlling those variations have been still unsolved questions we designed integrated seismic profiles including a wide angle seismic profile and a multichannel reflection seismic profile at the eastern nankai trough in central japan refraction tomography and pre stack depth migration of wide angle seismic data successfully image a trough parallel cyclic ridge subduction with thickness of 13 20 km and wavelength of 35 50 km at a geodetically determined inter plate locked zone in a non rupture zone during the 1944 tonankai mega thrust earthquake this result suggests a first direct evidence for the subducted seamount strongly locked hypothesis

material transfer and its influence on the formation of slope basins along the south central chilean convergent margin insights from scaled sandbox experiments abstract material transfer along and across a subduction zone determines not only the morphology of an accretionary prism but also the architecture and tectono sedimentary development of their forearc basins however the nature of these processes is not fully resolved yet we investigated through analog simulations the relationship among parameters influencing material transfer along the south central chilean margin and the marine basin evolution seismic lines revealed half graben basins controlled by subvertical faults governing differential uplift and subsidence through the slope the identified sedimentary pattern evidenced three main seismic sequences which have been linked to major climatic fluctuations and episodes of accretion non accretion or tectonic erosion which operate since the pliocene our experimental set up was motivated by the coupled tectonic climatic history of the chile peru trench fill i e climatic episodes represent variations in sediment supply and also in frictional properties of the materials entering in a convergent margin by using three key sandbox experiments we tested two main parameters i variable trench sediment thickness and ii basal frictional properties we highlight that by changing frictional conditions of sediments along the plate interface and the length of adjacent weak and strong segments we modified the evolution of the wedge from frontal to basal accretion in addition we obtained sub vertical faults with potential reactivation such as the observed geometry in seismic lines the change from a long segment of low basal friction to one of high basal friction offered an efficient mechanism to transport a long sand layer similar to a subduction channel this controlled the activation of thrust faults towards the backstop driving shortening and differential uplift with small individual extensional basins forming along the top of the wedge during further underplating the total volume of accommodation space in slope basins decreased whereas the volume of shelf basins tended to increase

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

link between plate fabric hydration and subduction zone seismicity in alaska subduction carries water into the earth where it can influence seismicity analysis of the structure of the alaskan subduction zone suggests fluid delivery is influenced by faults in the oceanic plate that formed at the mid ocean ridge

goce derived vertical gravity gradient delineates great earthquake rupture zones along the chilean margin abstract in the south central andes region the nazca oceanic plate that subducts beneath the south american plate is characterized by a rough topography derived from different oceanic features that collide against the continental margin these features determine an important segmentation of both the margin and of the interplate zone the chilean subduction margin has been characterized by megathrust earthquakes affecting the plate interface with large rupture areas reaching hundreds of kilometers parallel to the trench the occurrence of these phenomena has been linked among other causes to the subduction of sediments that fill the trench and their spatial relation to the relatively prominent oceanic features we calculated the topography corrected vertical gravity gradient from goce satellite data and from egm2008 model in order to delineate mass heterogeneities related to density variations along the south central chile subduction zone obtained results show a spatial relation between the subduction of the nazca oceanic highs and associated along strike segmentation of the vertical gravity gradients over the interplate zone we compared our results with the different rupture areas and found a good correspondence with the ellipses for the main earthquakes such as the valdivia 1960 and maule 2010 ones then we compared vertical gravity gradients with slip distribution obtained from different models finding that they are actually correlated with high slip over negative vertical gradient the goce derived gradient adjusts better with the main slip distribution contour since its signal has a characteristic high wavelength instead the egm2008 model presents a better performance in defining the high frequency anomalies however the last results need to be considered only in those regions where the statistical comparison with goce data shows a good performance this is because egm2008 model data present varying quality of the original terrestrial data while the quality of the goce data is locally homogeneous

relation between the subducting plate and seismicity associated with the great 1964 alaska earthquake tectonic studies of the great 1964 alaska earthquake have underappreciated the nature of the subducted plate in influencing seismicity we compare seismological observations in the prince william and kodiak areas that ruptured during this earthquake with the corresponding morphology and structure of the subducting plate the upper plate geology prince william terrane and velocity structure are the same in both areas in the prince william area where the yakutat terrane subducted the energy released and coupling were stronger than above the kodiak subduction zone where thick trench sediment subducts the conjecture that lower plate character or the amount of subducted sediment affects coupling helps explain variability in seismology geodetic inversions and the horizontal velocity of gps stations

great earthquakes and slab pull interaction between seismic coupling and plate slab coupling great earthquakes the few largest earthquakes that account for most of the earth s seismic energy release have occurred at only a few subduction zones around the world strong locking or seismic coupling of the interface between plates at certain subduction zones is often invoked to explain these great earthquakes although past studies have correlated strong seismic coupling with a compressional stress environment that is characterized by back arc compression and caused by trenchward motion of the overriding plate the consequences of this compressional environment for the tectonic forces that drive global plate motions are not yet clear to examine these consequences we compared subduction zone earthquake magnitudes to tectonically constrained estimates of the degree to which each slab transmits its excess weight as a direct pull force on a subducting plate at seismically uncoupled subduction zones that generate only moderate sized earthquakes we find that slabs must transmit nearly their entire upper mantle weight as a pull force on the subducting plate at seismically coupled subduction zones that produce great earthquakes however we find that slabs must be nearly completely detached from their subducting plates this suggests that slabs subducting in a compressional environment experience stress induced weakening that prevents the effective transmission of the slab pull force convergent mantle flow above a descending slab that becomes decoupled from its surface plate may induce additional surface compression that further locks the subduction zone and leads to additional slab decoupling and detachment the resulting redistribution of plate driving forces may be responsible for rapid changes in plate motion c 2003 elsevier b v all rights reserved

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the 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

asperity distribution and earthquake occurrence in the southern kurile islands arc the seismicity in the southern kurile islands arc is characterized by a complex overlapping of aftershock zones of a few great and many large earthquakes ms 7 0 the spatial relationships of these aftershock zones can be explained in terms of a simple pattern of fault plane heterogeneity the four largest earthquakes in this region are from north to south the 1963 kurile islands mw 8 5 the 1958 etorofu mw 8 3 the 1969 kurile islands mw 8 2 and the 1973 nemuro oki mw 7 8 events detailed body wave studies indicate that the moment release associated with each event is concentrated in a small portion of the aftershock area with scale lengths 100 km these regions of high moment release are the largest asperities the areas that surround the large asperities slip in two modes 1 coseismically during the great events and 2 as distinct large ms 7 0 earthquakes both before and after the great events the second mode involves either rupture of relatively weak regions which results in low stress drop events or rupture of smaller asperities the earthquakes produced by failure of small asperities tend to repeatedly rupture the same regions and they have impulsive source time functions indicating rupture of highly stressed regions of the fault surface by analysis of all ms 7 0 events since 1946 in this region we find a segmentation of the southern kurile islands thrust zone into strongly coupled regions with two scale lengths dominant and secondary asperities and weakly coupled regions the surrounding areas generating the low stress drop events the largest earthquakes and the smaller asperity earthquakes occur at the down dip portion of the lithospheric interface while the low stress drop events occur much closer to the trench axis this implies a difference in the degree of mechanical coupling between the subducting and overriding plates with the deeper portions having greater strength than the shallower parts

heat flow in the sediments of lake taupo new zealand heat flow measurements made in the sediments at the bottom of lake taupo during may to september 1992 show high heat flows 120 mw m2 in nine separate areas of the lake which together comprise 33 of the area of the lake and which have a total conductive heat output of 64 mw surrounding the areas of high heat flow are areas of low heat flow 50 mw m2 which cover 43 of the lake area the heat flows are thought to be the signature of geothermal systems consisting of a central plume of hot water with cold recharge water being drawn down in the surrounding area to recharge the base of the plume

invited review paper seismicity along the south american subduction zone review of large earthquakes tsunamis and subduction zone complexity abstract earthquakes along the shallow south american subduction zone exhibit heterogeneous rupture characteristics going back several centuries of the earthquake record in this area this heterogeneity is manifest in several ways such as changes in rupture mode from magnitude 8 events during one century followed by smaller ones in other time periods as well as unusual tsunami events there is also an apparent interaction between earthquake rupture and subducting plate complexity in this region significant complexity exists on the subducting nazca plate including fracture zones and ridges such as the large nazca ridge several large magnitude earthquakes have occurred in the region of ridge subduction but no earthquake rupture has ruptured through these features into adjacent regions suggesting that these subducting features act to segment the margin other features such as fracture zones and variable sediment thickness on the nazca plate appear to influence earthquake behavior over a wide range of magnitude scales upper plate features such as crustal faults also lead to heterogeneous earthquake behavior here i provide an overview of seismicity along the margin since 1850 in the context of the subduction zone structures this includes great earthquakes such as the 1906 ecuador and 1960 chile events i also present results showing increased rupture complexity in moderate magnitude earthquakes that can also be linked to certain nazca plate features

the java convergent margin structure seismogenesis and subduction processes the java margin is characterized by a distinct variation in lower to upper plate material transfer and recurring catastrophic tsunamogenic earthquakes both processes are closely linked to the subduction of oceanic basement relief resulting in varying degrees of fore arc deformation tomographic models of refraction seismic profiles and reflection seismic lines in combination with high resolution multibeam bathymetric data reveal the variability in the deep structure and deformation of the java fore arc shallow subduction processes are governed by the sediment supply in the trench as well as by the nature and fabric of the oceanic lithosphere the deep structure of the fore arc reveals a shallow upper plate crust mantle transition present along the entire java margin section the serpentinized fore arc mantle wedge governs the depth extent of the seismogenic zone here which is narrower compared to its sumatran analogue in addition offshore central java high relief oceanic basement features potentially act as asperities as well as barriers to seismic rupture limiting the possible magnitude of subduction thrust earthquakes however the potential for geohazards in particular tsunamis is high along the entire margin this results from tsunamogenic earthquakes ubiquitous splay faults and potentially tsunamogenic landslides which further increase the risk of future tsunamis

new identification of deep moonquakes in the apollo lunar seismic data abstract a new computer search of the apollo lunar seismic data set for identification of deep moonquakes using a combination of waveform cross correlation and single link cluster analysis has increased the number of positively identified deep moonquakes by more than a factor of five from the previous 1360 to 7245 at least 88 new deep moonquake source regions nests have been discovered while some source regions previously identified as separate entities are now determined to be identical reducing the number of previously known source regions from 108 to 77 the newly identified deep moonquakes and their relationships to each other are likely to revise our understanding of their spatial and temporal distributions

collision of the ganges brahmaputra delta with the burma arc implications for earthquake hazard abstract we take a fresh look at the topography structure and seismicity of the ganges brahmaputra delta gbd burma arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential the gbd the world s largest delta has been built from sediments eroded from the himalayan collision these sediments prograded the continental margin of the indian subcontinent by 400 km forming a huge sediment pile that is now entering the burma arc subduction zone subduction of oceanic lithosphere with 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land the prism starts at an apex south of the gbd shelf edge at 18 n and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit the front of the prism is blind buried by the gbd sediments thus the deformation front extends 100 km west of the surface fold belt beneath the comilla tract which is uplifted by 3 4 m relative to the delta this accretionary prism has the lowest surface slope of any active subduction zone the gradient of the prism is only 0 1 rising to 0 5 in the forearc region to the east this low slope is consistent with the high level of overpressure found in the subsurface and indicates a very weak detachment since its onset the collision of the gbd and burma arc has expanded westward at 2 cm yr and propagated southwards at 5 cm yr seismic hazard in the gbd is largely unknown intermediate size earthquakes are associated with surface ruptures and fold growth in the external part of the prism however the possibility of large subduction ruptures has not been accounted for and may be higher than generally believed although sediment clogged systems are thought to not be able to sustain the stresses and strain weakening behavior required for great earthquakes some of the largest known earthquakes have occurred in heavily sedimented subduction zones a large earthquake in 1762 ruptured 250 km of the southern part of the gbd suggesting large earthquakes are possible there a large but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism and is the only known candidate for a rupture of the plate boundary along the subaerial part of the gbd burma arc collision zone

source distribution of acoustic emissions during an in situ direct shear test implications for an analog model of seismogenic faulting in an inhomogeneous rock mass abstract we monitored acoustic emission ae events during an in situ direct shear test on a specimen composed of a slate dominant alternation of slate and sandstone measuring 0 5 m long 0 5 m wide and 0 2 m high the test was conducted in a survey tunnel for an underground powerhouse in central japan the ae epicenters located on a fractured plane are compared with the locations of joints and a loosening seam the height distribution of the fractured plane and the horizontal movement of the test block prior to failure we conclude that an initially intact region of rock bounded by the joints and the seam is fractured generating the ae considering these results in connection with asperity models of seismogenic faulting for a subduction zone earthquake the significant contrast of stress conditions derived from the geological inhomogeneity and the uneven fractured plane is analogous to that due to subducted seamounts and horst graben structures on a subducted oceanic plate for an inland earthquake the intact regions on an expected shear plane can be considered to be a portion of the fault asperity that causes strong ground motion while the weakened portion can be considered to correspond to a region of aseismic creep consequently large scale inhomogeneous rock fracturing experiments such as the in situ direct shear test may provide useful insights as analog models of seismogenic faulting furthermore understanding of inhomogeneous rock mass fracturing obtained from such experiments will not only contribute to a better understanding of the mechanism of earthquakes but also provide valuable knowledge for ae monitoring applications in rock engineering such as the predictions of rockbursts in mines and the monitoring of fractures around large underground chambers

along strike variability of rupture duration in subduction zone earthquakes 1 subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface wave magnitude one model explaining tsunami earthquakes suggests slip within patches of low rigidity material at shallow depths heterogeneous fault conditions such as having patches of low rigidity material surrounded by higher strength material should produce heterogeneous earthquake rupture parameters here we investigate along strike variation in rupture duration for 427 shallow thrust earthquakes mw 5 0 7 0 in the peru chile alaska tonga kuril izu and java sumatra subduction zones to explore how heterogeneous seismic and tectonic characteristics such as differences in sediment type thickness and roughness of subducting bathymetry affect earthquake properties earthquake source parameters including rupture durations are estimated using multi station deconvolution of teleseismic p and sh waves to solve for earthquake source time functions and all events are relocated using additional depth phase information we classify events into shallow 26 km and deep 26 km and 61 km groups based on the overall mean depth and focus on the longest duration events with moment normalized rupture durations of 1 standard deviation above the mean duration for each group we find long duration events at all depths within the study regions except peru and chile we find no correlation with incoming sediment thickness or type and limited spatial correlation with regions of past tsunami earthquakes regions of observed afterslip and subducting bathymetric features

possible influence of subducting ridges on the himalayan arc and on the ruptures of great and major himalayan earthquakes abstract subduction of bathymetric features such as ridges seamounts fractures etc on the subducting plate influences the arc morphology and earthquake ruptures we analyse their effect on the development of the arcuate shape of the himalayan arc and on the ruptures of great and major himalayan earthquakes besides the two most prominent ridges in the indian ocean namely the chagos laccadive deccan ridge and the 90 e ridge which are assumed to extend up to the himalayan arc at least three major subsurface ridges have been mapped on the underthrusting indian plate under the indo gangetic plains it appears that the subduction of the two most prominent ridges contributed to the development of the arcuate shape of the himalayan arc the interaction and subduction of the other subsurface ridges probably influenced the himalayan arc morphology by causing a localised cusp in the frontal topography also these ridges probably acted as barriers to the ruptures of the major and great himalayan earthquakes

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

the rupture process of the great 1979 colombia earthquake evidence for the asperity model we have determined the asperity distribution in the segment of the ecuador colombia subduction zone that was ruptured by the 1979 mw 8 2 and 1958 mw 7 7 earthquakes for the 1979 earthquake we are able to document directivity in the p wave source time functions and consequently have spatially located the moment release by combining results from both p wave and surface wave directivity we have defined three regions 1 from 0 to 56 km northeast of the epicenter with low moment release and a small seismic displacement 2 the asperity from 56 to 116 km northeast of the epicenter with most of the moment release and a displacement of 6 m and 3 a small displacement region from 116 to 180 240 km northeast of the epicenter thus the 1979 rupture zone is composed of an asperity 60 km in length bounded by two weak small displacement regions the displacement at the asperity is equal to the cumulative tectonic displacement between 1979 and 1906 the year of the previous great earthquake in this segment the 1958 earthquake is characterized by the rupture of a small asperity length scale approximately 25 km in the epicentral region the 1958 event continued to rupture past this small epicentral asperity and stopped near the epicenter of the following 1979 event this detailed study of the spatial variation in moment release offers strong support for the asperity model of large earthquake occurrence

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

seismic history and seismotectonics of the sunda arc historic records of the last 300 years reveal two great interplate earthquakes 1833 mw 8 1861 mw 8 8 which ruptured major segments of the sumatra fore arc in western indonesia a significant percentage of interplate slip along this portion of the plate boundary appears to occur seismically the ends of these rupture zones are coincident with clusters of large ms 7 and moderate 6 ms 7 shocks and with heterogeneities in the plate interface as inferred from geologic and geophysical data the northern extent of the 1833 rupture zone is coincident with a group of moderate and large earthquakes a structural arch in the fore arc and a fracture zone on the subducted plate the southern portion is coincident with a very prominent cluster and the along strike extension of a sediment filled trough on the subducted plate prior to this study sumatra was characterized as relatively aseismic as inferred from the lack of great earthquakes in the instrumental record of this century java and the lesser sunda islands had major ms 6 earthquakes in the historic record but none are of the same magnitude as the great events near sumatra there is no clear evidence that shocks in the java fore arc were interplate events yet geophysical data indicate recent uplift of the trench slope break and a change in strike of the trench axis where the northernmost flank of the roo rise a prominent bathymetrie high appears to be interacting with the fore arc this feature was formed at a ridge crest and is more buoyant and thus more difficult to subduct than the surrounding seafloor there is no increase in seismicity associated with this tectonism however that may indicate a lack of contact between the crystalline portions of the plates at this time we infer that a majority of slip on the plate interface near java occurs aseismically the variation in occurrence of great interplate earthquakes along the sunda arc may be interpreted in terms of a model that attributes variation in interplate coupling to the age of the subducted lithosphere great interplate earthquakes occur near sumatra where the age of the youngest crust is 46 ma the characteristics of the sunda arc and analogies with pacific arcs imply that the entire length of sumatra has the potential to produce great thrust earthquakes its seismic potential should be considered high as there has been no recurrence of the great events of 1833 and 1861 in contrast no such events have been reported off java and the lesser sunda islands where the oldest crust is 152 ma the plate interface near java and the lesser sunda islands should be considered to have low seismic potential

multibeam bathymetric survey and high resolution seismic investigations on the barbados ridge complex eastern caribbean a key to the knowledge and interpretation of an accretionary wedge abstract an important problem of active margin processes is the way accretionary wedges form in response to oceanic crust subduction new data have been obtained along the barbados ridge in front of the lesser antilles tertiary island arc they include high resolution multichannel seismic data and accurate sea beam bathymetric maps both have been used to propose a 3 dimensional interpretation of tectonic and sedimentary processes related to subduction such as oceanic off scraping ductile folding relative uplift and subsidence fore arc basin evolution and mud diapirism they all improved our knowledge of the evolution of accretionary prisms and more specifically of the barbados ridge development in plio quaternary time previous tectonic events are deduced from recently published geological data from barbados and the lesser antilles islands

do trench sediments affect great earthquake occurrence in subduction zones seismic energy release is dominated by the underthrusting earthquakes in subduction zones and this energy release is further concentrated in a few subduction zones while some subduction zones are characterized by the occurrence of great earthquakes others are relatively aseismic this variation in maximum earthquake size between subduction zones is one of the most important features of global seismicity previous work has shown that the variation in maximum earthquake size is correlated with the variation in two other subduction zone properties age of the subducting lithosphere and convergence rate these two properties do not explain all the variance in maximum earthquake size i propose that a third subduction zone property trench sediments explains part of the remaining variance in maximum earthquake size subduction zones are divided into two groups 1 those with excess trench sediments and 2 those with horst and graben structure at the trench thirteen of the 19 largest subduction zone events including the three largest occur in zones with excess trench sediments about half the zones with excess trench sediments are characterized by great earthquake occurrence most of the other zones with excess trench sediments but without great earthquakes are predicted to have small earthquakes by the age rate correlation two notable exceptions are the oregon washington and middle america zones overall the presence of excess trench sediments appears to enhance great earthquake occurrence one speculative physical mechanism that connects trench sediments and earthquake size is that excess trench sediments are associated with the subduction of a coherent sedimentary layer which at elevated temperature and pressure forms a homogeneous and strong contact zone between the plates

thick strong sediment subduction along south central chile and its role in great earthquakes abstract the south central chile margin experienced the largest and sixth largest earthquakes ever recorded the 1960 mw 9 5 valdivia and 2010 mw 8 8 maule megathrust earthquakes respectively in early 2017 we conducted a seismic survey along 1 000 km of south central chile to image these rupture zones using a 15 15 km long multi channel seismic streamer we processed these data using pre stack depth migration which provides the best look at the shallow part of the south central chile margin to date relative to other sediment dominated subduction zones where sediment is typically accreted at the toe an unusually large percentage of the thick trench sediments are consistently subducted beneath the slope with little thrust faulting or deformation analysis of the sediment p wave velocities and structure in the trench and outer wedge leads us to conclude that most of south central chile contains well drained strong sediments an exception in the vicinity of the subducting mocha fracture zone mfz has trench sediments that appear to experience localized delayed compaction thus lowering their strength and allowing the development of protothrusts similar to what is seen in other accretionary subduction zones the very shallow decollement along the south central chile allows more sediment to pass beneath the lower slope than almost all other subduction zone many of which have much thicker trench sections we conclude that subduction of the strong well drained thick sediment layer beneath the lower slope is typical for nearly all of the south central chile comparison to other thick sedimented subduction zones worldwide reveals that the subduction of such a large fraction of the trench sediment is particularly unusual this strong thick subducting sediment is likely a determining factor for developing a smooth plate interface located well above the subducted crust topography that ultimately becomes a broad megathrust with high homogeneous frictional properties and generates particularly large earthquakes along the south central chile margin

present day vertical deformation of the cascadia margin pacific northwest united states we estimate present day uplift rates along the cascadia subduction zone in california oregon and washington in the pacific northwest united states by utilizing repeated leveling surveys and tide gauge records these two independent data sets give similar profiles for latitudinal variation of contemporary uplift rates along the coast uplift rates are extended inland through east west leveling lines that connect the north south line along the coast to the north south line along the inland valleys just west of the cascades the results are summarized as a contour map of present day uplift rates for the western pacific northwest we find that rates of present day uplift vary latitudinally along the coast and inland valleys as well as longitudinally along transects connecting the coast to the inland valleys long term tidal records of neah bay astoria and crescent city indicate uplift of land relative to sea level of 1 6 0 2 0 0 0 2 and 0 9 0 2 mm yr respectively 1 standard error unlike previous estimates of relative sea level change at astoria we adjust for discharge effects of the columbia river including human management influences after approximating an absolute framework by using 1 8 0 1 mm yr to compensate for global sea level rise results indicate that much of the western pacific northwest is rising at rates between 0 and 5 mm yr the most rapid uplift rates are near the coast particularly near the olympic peninsula the mouth of the columbia river cape blanco and cape mendocino two axes of uplift are identified one trends northeast from the southwest oregon coast and the other trends south southeasterly from the olympic peninsula to the columbia river the puget sound vicinity and a small east west region from the north central oregon coast to the inland willamette valley are subsiding at rates up to 1 mm yr we interpret the overall pattern of rapid present day uplift to be generated by interseismic strain accumulation in the subduction zone this interseismic elastic strain accumulation implies significant seismic hazard

phosphorus in spring waters of the taupo volcanic zone north island new zealand abstract cold spring waters of the taupo volcanic zone new zealand contain phosphorus at concentrations up to 0 3 g m 3 and for some lakes of the region the phosphorus loading from these spring waters is substantial several spring waters derived from a rhyolitic pumice aquifer were examined together with the aquifer recharge water collected from below the forest root zone an accurate water balance was obtained for the aquifer catchment and the mass recharge to the aquifer shows that 95 of the phosphorus and some of the sodium calcium and magnesium in the spring waters are derived from within the aquifer presumably by reaction of the rhyolitic substrate with recharge water acidic due to dissolved carbon dioxide although the chemistry of the spring waters from both pumice and ignimbrite aquifers suggests hydroxyapatite as the solid phase which could limit the phosphorus concentrations in these waters thermodynamic considerations show that phosphorus can reach the high concentrations found without exceeding the solubility of this mineral because of the low less than 4 g m 3 concentrations of calcium present in these waters

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

impact cutoff frequency momentum scaling law inverted from apollo seismic data abstract we perform the analysis of both long and short period data for 40 large meteoroid impacts event gathered by the apollo lunar seismic network we extract the linear momentum released by the impact and the cutoff frequency of the recorded seismic spectrum related to the radiation process of the shock wave generated by the impact by using a proxy to the local porosity based on the density of surface craters and well correlated to the most recent grail observations we demonstrate that the seismic cutoff frequencies for 40 selected impacts correlate with this proxy and therefore likely with the porosity at the impacted areas our finding shows that lunar seismic records of meteoroid impacts represent unique geophysical data documenting medium to high energy 0 1 1 kt tnt yield impact processes including the interaction of shock waves with porous media this work can be applied to the analysis of the seismic data to be obtained by the insight mission in 2016 and the investigation of the lateral variations in the martian regolith

analysis of seismotectonic processes in subduction zones from the standpoint of a keyboard model of great earthquakes abstract the block like structure of the frontal part of the overriding plate in the subduction zones of the aleutian and kurile trenches is described both block interaction with a subducted plate and reciprocal interblock actions are considered these interactions are reflected 1 1 in the seismic regime 2 2 in the distribution of the sources of great earthquakes 3 3 in the focal mechanisms of shallow earthquakes the mechanical keyboard model proposed incorporates these interactions this model is the basis of a mathematical description of the subsequent slow accumulation of strain and fast seismic release in ajacent blocks in the course of their seismotectonic evolution some results of numerical simulations are given they are in good agreement with the main features of distribution of great earthquakes in space and time for the kuriles japan and central and south america keyboard analysis of seismic cycles can be considered as a mechanical basis for long term prediction of great earthquakes which allows the distinguishing of a number of new earthquake precursors

current bombardment of the earth moon system emphasis on cratering asymmetries abstract we calculate the current spatial distribution of projectile delivery to the earth and moon using numerical orbital dynamics simulations of candidate impactors drawn from a debiased near earth object neo model we examine the latitude distribution of impactor sites and find that for both the earth and moon there is a small deficiency of time averaged impact rates at the poles the ratio between deliveries within 30 of the pole to that of a 30 band centered on the equator is small for earth 0 958 0 001 and somewhat greater for the moon 10 0 903 0 005 the terrestrial arrival results are examined to determine the degree of am pm asymmetry to compare with the pm excess shown in meteorite fall times we find that the average lunar impact velocity is 20 km s which has ramifications in converting observed crater densities to impactor size distributions we determine that current crater production on the leading hemisphere of the moon is 1 28 0 01 that of the trailing when considering the ratio of craters within 30 of the apex to those within 30 of the antapex and that there is virtually no nearside farside asymmetry in agreement with observations of rayed craters as expected the degree of leading trailing asymmetry increases when the moon s orbital distance is decreased

cratering asymmetry on the moon new insight from the apollo passive seismic experiment 1 the synchronous rotation of the moon can lead to an asymmetry in the cratering rate between the leading and trailing sides of lunar orbital motion the observation of the apollo passive seismic experiment can be viewed as a continuous seismic observation of lunar impacts it provides information of the current bombardments and small impact events of meter sized craters to evaluate the current leading trailing cratering asymmetry on the moon we investigated the spatial distribution of impact sites determined by apollo seismic observation we determined that the number density of impacts on the leading side is substantially higher than that on the trailing side in addition we discovered a possible enhancement of the number density of 1 4 0 4 to 1 9 0 5 on the leading side relative to that of the trailing side this indicated that the cratering asymmetry predicted from historical cratering records also exists in the current low magnitude impacts

the potential for giant tsunamigenic earthquakes in the northern bay of bengal the sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community while it is now widely recognized that the risk of another giant earthquake is high off central sumatra just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar formerly burma phil cummins suggests however that giant earthquake activity is possible in this region and that a large and vulnerable population may be facing a significant earthquake and tsunami hazard there is a high potential for giant earthquake activity along the coast of myanmar indications that this may be the case include the tectonic environment historical earthquake activity and stress and crustal strain observations these findings suggest that giant earthquakes do occur off the coast of myanmar and that a very large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard the great sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community although it is now widely recognized that the risk of another giant earthquake is high off central sumatra1 just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar here i show that similar indicators suggest a high potential for giant earthquakes along the coast of myanmar these indicators include the tectonic environment which is similar to other subduction zones that experience giant megathrust earthquakes stress and crustal strain observations which indicate that the seismogenic zone is locked and historical earthquake activity which indicates that giant tsunamigenic earthquakes have occurred there in the past these are all consistent with active subduction in the myanmar subduction zone and i suggest that the seismogenic zone extends beneath the bengal fan i conclude therefore that giant earthquakes probably occur off the coast of myanmar and that a large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

background seismicity rate at subduction zones linked to slab bending related hydration tectonic properties strongly control variations in seismicity among subduction zones in particular fluid distribution in subduction zones influences earthquake occurrence and it varies among subduction zones due to variations in fluid sources such as hydrated oceanic plates however the relationship between variations in fluid distribution and variations in seismicity among subduction zones is unclear here we divide earth s subduction zones into 111 regions and estimate background seismicity rates using the epidemic type aftershock sequence model we demonstrate that background seismicity rate correlates to the amount of bending of the incoming oceanic plate which in turn is related to the hydration of oceanic plates via slab bending related faults regions with large bending may have high seismicity rates because a strongly hydrated oceanic plate causes high pore fluid pressure and reduces the strength of the plate interface we suggest that variations in fluid distribution can also cause variations in seismicity in subduction zones

strain partitioning and interplate friction in oblique subduction zones constraints provided by experimental modeling physical modeling of oblique subduction is performed to study the mechanism of strain partitioning the model is two layer and includes the elasto plastic lithosphere the overriding and subducting plates and the low viscosity liquid asthenosphere the subduction is driven by a push force from a piston and a pull force when the density contrast ap between the subducting plate and the asthenosphere is positive we vary both ap and the interplate friction frictional stresses slip partitioning is obtained only in the models with high interplate friction and only when the overrid ing plate contains a weak zone this zone in the models corresponds either to locally thinned litho sphere or to cut fault the horizontal trench normal component of the interplate friction force ffh can be comparable with the absolute value of the horizontal component of the nonhydrostatic interplate pressure force fph in the subduction zone ffh is always negative compression while fph can be either negative compressional subduction regime or positive extensional regime high friction which promotes partitioning can completely cancel the extensional suction force fph back arc tension and strike slip faulting appear thus as conflicting processes although they can coexist in the same subduction zone depending on the relative values of relevant forces it ap pears that high friction can exist only in compressional subduction zones where partitioning should develop more easily this conclusion is supported by the comparison of two oblique subduction zones having similar geometry the compressional southern kurile zone strong partitioning and extensional southern ryukyu zone no lithospheric scale partitioning other factors controlling the strain partitioning are the length of the oblique subductlon zone the boundary conditions at the transverse limits of the forearc sliver and of course the obliquity of subduction