outer rise earthquakes and seismic coupling outer rise earthquakes can be separated into two basic categories based on focal mechanism compressional and tensional events reflecting compressional and tensional outer rise stress regimes we propose a model that connects the stress regime in the outer rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer rise earthquakes we find that compressional outer rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones or equivalently just prior to large subduction zone earthquakes the compressional stress regime is probably caused by slip in adjacent subduction zone segments there are two modes of occurrence for tensional outer rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones in coupled subduction zones tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer rise in subduction zones that are inherently uncoupled tensional events can occur at any time therefore in uncoupled subduction zones the outer rise is always in tension and only tensional outer rise events occur there while in coupled subduction zones the outer rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

long term interactions between intermediate depth and shallow seismicity in north chile subduction zone we document interactions between intermediate depth and interplate seismicity in the north chile subduction zone over a 25 year period 1990 2015 we show that the 2005 mw 7 8 tarapaca slab pull earthquake was followed by 9 years of enhanced deep and shallow seismicity together with the decrease of eastward average gps velocities and associated interplate coupling eventually leading to the 2014 mw 8 1 iquique megathrust earthquake in contrast megathrust ruptures e g mw 8 0 antofagasta in 1995 or mw 8 1 iquique in 2014 initiate several years of silent background seismicity in the studied area both at shallow and intermediate depths the plunge of a rigid slab into a viscous asthenospheric mantle could explain the observed synchronization between deep and shallow seismicity and their long term interactions

thrust and extensional faulting under the chilean coast 1965 1971 aconcagua earthquakes summary earthquakes under coastal northern chile from 18 s to 33 s occur at two very different depths the shallower interplate events have the typical thrust mechanisms associated with subduction of the nazca plate under south america the deeper close to 70 km events have normal fault mechanisms with a tension axis approximately parallel to the dip of the downgoing slab we study in detail a couple of ms 7 5 events that took place about 60 km north of valparaiso chile the 1971 july 9 event was a shallow thrust interplate event at 40 km depth while the 1965 march 28 earthquake had a normal fault mechanism and a depth of 72 km we carry out a detailed analysis of long period p and surface waves observed in the wwssn network of stations in order to improve fault plane solutions and depth determinations for the 1971 event we find a seismic moment of 5 6 1027 dyne cm from both p and surface waves the source area for this event is relatively small compared to that of other underthrust events with similar moments assuming a circular fault shape and a rigidity of 7 1011 dyne cm 2 we find a stress drop of 38 bar the 1965 event is more complex seismic moments of 1 8 and 1 0 1027 dyne cm are found from surface and body waves respectively the stress drop estimated from p waves and a circular fault model is close to 91 bar the existence of earthquakes at two different depths near the chilean coast may be interpreted in terms of a double layered benioff zone as has been found in honshu kuriles or central peru unfortunately the hypo central determinations of events in this region are not precise enough to separate the two layers an alternative method to demonstrate the existence of a double benioff zone is to look for compressional events associated with the upper layer of the down going slab a search among available fault plane solutions is ambiguous three shallow coastal events are found in stauder s catalogue with horizontal pressure axes normal to the trench but they might be intra continental plate events

dynamic modelling of the subduction zone of central mexico summary in central mexico some significant normal faulting events have occurred within the subducted oceanic cocos plate just below or near the down dip edge of the strongly coupled interface these normal faulting shocks followed large shallow thrust earthquakes in other subduction zones such events generally precede the up dip thrust events a vertical 2 d finite element modelling has been used to simulate the subduction of the cocos plate beneath the north american plate when the slab is driven by an active convergence velocity or slab pull we find that the latter mechanism plays only a minor role due to shallow subduction the modelling results show that the stress pattern is very sensitive to the geometry of the plates in particular normal faulting earthquakes that follow large thrust events can be explained on the basis of the flexural response of the overriding and subducting plates to the peculiar geometry of this subduction zone where the subducting slab becomes horizontal at about 100 km from the trench this horizontal part of the subducting plate down dip with respect to the main thrust zone is under an extensional stress field this provides an alternative explanation to the slab pull for the occurrence of normal faulting intraplate earthquakes in order for normal faulting earthquakes to occur in the early part of the seismic cycle it is necessary that the large up dip thrust events have a partial stress drop we find that for small fractional stress drop a wide region of extension remains below the down dip edge of the main fault plane following a large thrust earthquake thus the main thrust earthquakes do not invert the polarity of the active stress field which is compressional and extensional up dip and down dip respectively with respect to the main thrust fault larger fractional stress drops result in larger delays in the occurrence of normal faulting events after the main thrust events

double seismic zones and stresses of intermediate depth earthquakes data from japanese local seismograph networks suggest that the stresses in double seismic zones are in plate compression for the upper zone and in plate tension for the lower zone the stresses do not necessarily appear to be down dip it may therefore be possible to identify other double seismic zones on the basis of data which indicate that events with differing orientations of in plate stresses occur in a given segment of slab a global survey of published focal mechanisms for intermediate depth earthquakes suggests that the stress in the slab is controlled at least in part by the age of the slab and the rate of convergence old and slow slabs are under in plate tensile stresses and the amount of in plate compression in the slab increases with increasing convergence rate or decreasing slab age young and fast slabs are an exception to this trend all such slabs are down dip tensile since these slabs all subduct under continents they may be bent by continental loading double seismic zones are not a feature common to all subduction zones and are only observed in slabs which are not dominated by tensile or compressive stresses unbending of the lithosphere and upper mantle phase changes are unlikely to be the causes of the major features of double zones although they may contribute to producing some of their characteristics sagging or thermal effects possibly aided by asthenospheric relative motion may produce the local deviatoric stresses that cause double zones

the depth of the october 1981 off chile outer rise earthquake ms 7 2 estimated by a comparison of several waveform inversion methods the determination of source depth of the october 1981 ms 7 2 outer rise earthquake off the chilean coast has important implications for the stress state of the subducting plate we analyze the chile earthquake using three different waveform inversion methods in order to check the consistency of these methods and to estimate the source depth the methods we used are 1 1 honda and seno s 1989 inversion method in which we incorporate both long period p waves and surface waves 2 2 nab lek s 1984 body wave inversion methods for long period p and sh waves 3 3 seno and honda s 1988 deconvolution method in which we assume vertically distributed point sources and use long period p waves these methods give consistent results which suggest that the centroid depth and depth extent of the chile earthquake lies between 20 to 45 km measured from the sea surface this conclusion is contradictory to those obtained by the previous workers who prefer a shallow 25 km source depth we found that the gdsn long period data alone cannot constrain the source depth well the shape of deconvolved source time function is found to be strongly dependent on the assumption of point and distributed sources and the crustal structure used in the deconvolution the source depth obtained in this study shows that the 1981 chile outer rise earthquake possibly occurred because of the compression associated with the bending of the subducting plate

a triple planed structure of seismicity and earthquake mechanisms at the subduction zone off miyagi prefecture northern honshu japan abstract a detailed cross section of seismicity combined with types of earthquake mechanisms was constructed for the subduction zone off miyagi prefecture northern honshu japan where a large m s 7 5 earthquake occurred on june 12 1978 nodal plane solutions were determined for fourteen earthquakes with body wave magnitudes 5 4 using data recorded at wwssn and japanese stations for smaller magnitude events the types of focal mechanism were analysed using p wave first motion data recorded at regional stations the results obtained are 1 for the area 150 200 km landward from the trench axis the cross section suggests a triple planed seismic zone that is the zone of thrusting overlaps the so called double planed seismic zone the upper and lower planes of the double planed seismic zone are characterized by down dip compression and down dip tension respectively 2 thrusting terminates at a depth of 60 km where the aseismic front in the area is located and it merges into the zone of down dip compression in the deeper part in a down dip direction in contrast the depth of the zone of down dip compression appears to shift by 10 km at the aseismic front 3 the extension of the zone of down dip compression seaward beyond the aseismic front and the shift of the depth of the zone may be caused by loading within the descending slab through a mechanical coupling between the plates at the focal area of the 1978 earthquake prior to its occurrence

the 13 january 2001 el salvador earthquake a multidata analysis 1 on 13 january 2001 a large normal faulting intermediate depth event mw 7 7 occurred 40 km off the el salvadorian coast central america we analyze this earthquake using teleseismic regional and local data we first build a kinematic source model by simultaneously inverting p and sh displacement waveforms and source time functions derived from surface waves using an empirical green s function analysis in an attempt to discriminate between the two nodal planes 30 trenchward dipping and 60 landward dipping we perform identical inversions using both possible fault planes after relocating the hypocentral depth at 54 km we retrieve the kinematic features of the rupture using a combination of the neighborhood algorithm of sambridge 1999 and the simplex method allowing for variable rupture velocity and slip we find updip rupture propagation yielding a centroid depth around 47 km for both assumed fault planes with a larger variance reduction obtained using the 60 landward dipping nodal plane we test the two possible fault models using regional broadband data and near field accelerograms provided by universidad centro americana 2001 near field data confirm that the steeper landward dipping nodal plane is preferred rupture propagated mostly updip and to the northwest resulting in a main moment release zone of approximately 25 km 50 km with an average slip of 3 5 m the large slip occurs near the interplate interface at a location where the slab steepens dip significantly the occurrence of this event is well explained by bending of the subducting plate

slab pull and slab push earthquakes in the mexican chilean and peruvian subduction zones we studied intermediate depth earthquakes in the chile peru and mexican subduction zones paying special attention to slab push down dip compression and slab pull down dip extension mechanisms although slab push events are relatively rare in comparison with slab pull earthquakes quite a few have occurred recently in peru a couple slab push events occurred in 1991 and one slab pull together with several slab push events occurred in 1970 near chimbote in mexico several slab push and slab pull events occurred near zihuatanejo below the fault zone of the 1985 michoacan event in central chile a large m 7 1 slab push event occurred in october 1997 that followed a series of four shallow mw 6 thrust earthquakes on the plate interface we used teleseismic body waveform inversion of a number of mw 5 9 slab push and slab pull earthquakes in order to obtain accurate mechanisms depths and source time functions we used a master event method in order to get relative locations we discussed the occurrence of the relatively rare slab push events in the three subduction zones were they due to the geometry of the subduction that produces flexure inside the downgoing slab or were they produced by stress transfer during the earthquake cycle stress transfer can not explain the occurence of several compressional and extensional intraplate intermediate depth earthquakes in central chile central mexico and central peru it seemed that the heterogeneity of the stress field produced by complex slab geometry has an important influence on intraplate intermediate depth earthquakes 2002 elsevier science b v all rights reserved

statistical relationships between piezocone measurements and stress history of clays a database containing piezocone soundings from 205 clay sites around the world has been compiled for the calibration of an analytical cone penetration model and the development of statistical correlations yield stresses from laboratory oedometer tests were used as reference values for determining the stress history of natural clay deposits both simple and multiple regression analyses were performed on these data to evaluate correlative trends several simplified empirical relationships were identified for use in practice with the most reliable in relating preconsolidation stress to net cone tip resistance key words cone tip resistance overconsolidation ratio ocr preconsolidation pressure piezocone statistical relationships stress history

double seismic zones kinematics the kinematics of a double seismic zone of subducting lithosphere at an intermediate depth is studied a simple geometrical argument shows that the strain rate due to unbending of subducting lithosphere can be as large as 10 15 s 1 and large enough to account for the seismic strain rate in this depth range the geometrical unbending of subducting lithosphere in the mantle and the presence of a double seismic zone there can be therefore considered essentially equivalent phenomenon we model a double seismic zone required from this unbending in order to investigate what constraint the presence of a double seismic zone can place on the properties of the descending lithosphere the thickness of a double seismic zone is controlled by the thermal structure and the rheological properties of the subducting slab a preliminary result for the double seismic zone beneath tohoku japan indicates a possibility that the currently available flow law of dry olivine does not properly describe the double seismic zone or at least presents some inconsistency in our knowledge of the mechanical properties e g thermal structure rheology of oceanic lithospheres

partial breaking of a mature seismic gap the 1987 earthquakes in new britain to better understand the mechanics of subduction and the process of breaking a mature seismic gap we study seismic activity along the western new britain subduction segment 147 e 151 e 4 s 8 s through earthquakes with m b 5 0 in the outer rise the upper area of subducting slab and at intermediate depths to 250 km from january 1964 to december 1990 the segment last broke fully in large earthquakes of december 28 1945 m s 7 9 and may 6 1947 m s 7 7 and its higher seismic potential has been recognized by mccann et al 1979 recently the segment broke partially in two smaller events of february 8 1987 m s 7 4 and october 16 1987 m s 7 4 leaving still unbroken areas

seismicity in the outer rise forearc region and configuration of the subducting lithosphere with special reference to the japan trench along nine subduction zones where the largest mw or ms 7 6 normal faulting earthquakes have occurred beneath the outer rise there is an apparent correlation between a large curvature of the subducting slab and regions of low background seismicity in the forearc in six cases a gentle inner trench is also observed taking advantage of the excellent coverage of teleseismic stations and extensive previous studies using local data we investigate the nature of this spatial correlation between seismicity and bathymetry along the honshu forearc in some detail an aseismic region in the forearc lies directly west of the rupture zone of the 1933 sanriku earthquake mw 8 4 a great normal faulting earthquake that most likely has ruptured the entire brittle portion of the lithosphere in the outer rise along this particular cross section of the japan trench large to moderate sized interplate earthquakes span a short interval of depths between approximately 14 and 31 km about half the interval observed along an adjacent profile to the south 12 45 km the aseismic portion of the plate interface between depths of approximately 30 and 45 km has persisted for over 100 years the occurrence of lithospheric normal faulting earthquakes in the outer rise region indicates that bending moment within the subducting slab limited by yield strength of the lithosphere has nearly reached an asymptotic value moment saturation at this state the curvature of the plate can increase with little increase in bending moment as such any stresses transmitted across the plate interface will be relaxed by a permanent increase in the plate s curvature and little elastic strain can accumulate across the interplate thrust zone to produce large earthquakes thus the saturation of bending moment in the subducting lithosphere offers a straightforward interpretation for the observed correlation between seismicity in the outer rise forearc region and configuration of the subducting lithosphere

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

cyclic stressing and seismicity at strongly coupled subduction zones we use the finite element method to analyze stress variations in and near a strongly coupled subduction zone during an earthquake cycle deformation is assumed to be uniform along strike plane strain on a cross section normal to the trench axis and periodic earthquake slip is imposed consistent with the long term rate of plate convergence and degree of coupling simulations of stress and displacement rate fields represent periodic fluctuations in time superimposed on an average field the oceanic plate descending slab and continental lithosphere are assumed here to respond elastically to these fluctuations and the remaining mantle under and between plates is assumed to respond as maxwell viscoelastic in the first part of the analysis we find that computed stress fluctuations in space and time are generally consistent with observed earthquake mechanism variations with time since a great thrust event in particular trench normal extensional earthquakes tend to occur early in the earthquake cycle toward the outer rise but occur more abundantly late in the cycle in the subducting slab downdip of the main thrust zone compressional earthquakes when they occur at all have the opposite pattern our results suggest also that the actual timing of extensional outer rise events is controlled by the rheology of the shallow aseismic portion of the thrust interface the second part of the analysis shows the effects of mantle relaxation on the rate of ground surface deformation during the earthquake cycle models without relaxation predict a strong overall compressional strain rate in the continental plate above the main thrust zone with the strain rate constant between mainshocks however with significant relaxation present a localized region of unusually low compressional or even slightly extensional strain rate develops along the surface of the continental plate above and somewhat inland from the downdip edge of the locked main thrust zone the low strain rate starts in the middle or late part of the cycle depending on position this result suggests that the negligible or small contraction measured on the shumagin islands alaska during 1980 to 1991 may not invalidate an interpretation of that region as being a moderately coupled subduction zone in contrast mantle relaxation causes only modest temporal nonuniformity of uplift rates in the overriding plate and of extensional stress rates in the subducting plate even when the maxwell time is an order of magnitude less than the recurrence interval

triple seismic zone and the regional variation of seismicity along the northern honshu arc the regional variation of seismicity along the northern honshu arc japan is studied using accurate focal depths and focal mechanism types we use focal depths determined from pp p time intervals reported in the isc bulletins for submarine earthquakes depths are corrected by considering the pp phase reported in the bulletins as the pwp phase the reflection from the ocean surface out of more than 600 well located earthquakes selected from the isc bulletins we determine the types of the focal mechanisms of 184 events using p wave first motion data based on historical seismicity of great and large earthquakes we divide the zone of thrust type earthquakes at the plate interface into two regions the shallow thrust zone 0 40kin where great earthquakes ms 8 0 occur and the deep thrust zone 40 60km where large earthquakes ms 7 4 occur the activity of great or large earthquakes shows a variation along the are in some regions both the shallow and deep thrust zones are active and in other regions only one of the thrust zones is active the seismicity of recent moderate size earthquakes mb 4 combined with the focal mechanism type shows a variation along the are which reflects the variation of the activity of great or large earthquakes where large earthquakes do not occur in the deep thrust zone neither thrust type nor down dip compression tension type events occur in and beneath the deep thrust zone where large earthquakes do occur in the deep thrust zone we find a number of thrust type earthquakes further in the latter case in some regions the down dip compression and tension type events of the double seismic zones extend seaward just beneath the deep thrust zone and form a triple planed structure of seismicity the triple seismic zone this study confirms the hypothesis of previous workers seno and pongsawat 1981 on the causal relation between the strong seismic coupling of two converging plates at the deep thrust zone and extension of the double seismic zone i e the presence or absence of activity within the slab beneath the deep seismic zone occurs when the deep thrust zone has a strong or weak coupling respectively here the weak coupling could be interpreted as either aseismic slip or as low stress buildup since the last large event occurred at the deep thrust zone triple seismic zones are found offshore of miyagi prefecture where the deep thrust zone has been broken recently in 1978 and offshore of fukushima prefecture we expect a future large earthquake at the deep thrust zone offshore of fukushima prefecture because the presence of the triple seismic zone suggests stress has been accumulating and 40 years have passed since the deep thrust zone was ruptured in 1938

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

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

intermediate term seismic precursors for some coupled subduction zones the paper discusses model results and then reviews observational data concerning some aspects of the mechanics of mature seismic gaps in coupled subduction zones the concern is with space and time varying stresses as signalled by the presence and mechanisms of earthquakes in the outer rise zones adjacent to main thrust areas of large subduction events and down dip from such areas in the downgoing slab observations are shown to be consistent with the expectation that in mature seismic gaps as a result of interplate boundary locking in presence of sustained gravitational driving forces at least the deeper portions of the ocean plate in the outer rise zones are under increased compression and the downgoing slab is under increased tension the observational data cover two cases of closed seismic gaps namely the region of the chilean valparaiso earthquake of march 3 1985 and the earthquake of october 4 1983 four other cases concern still to be closed gaps in northern chile and along the coast of guatemala and also the kurile islands trench gap and the northern new hebrides gap it is concluded that the intermediate term precursor consisting of a combination of compressional outer rise earthquake s and tensional intermediate depth intra plate events in the downgoing slab which mechanically signals the latter part of the earthquake cycle could be useful in evaluating the maturity and hence great earthquake potential of a seismic gap

a critical review of methods used in the appraisal of onshore sand and gravel resources in britain abstract the systematic assessment of british onshore sand and gravel resources has been based traditionally on walk over geological surveys supported by specially commissioned programmes of drilling pitting sampling and more recently by geophysical surveying various other more cost effective methods of resource appraisal are now being encouraged these procedures involve minimal sampling and are based on a combination of geomorphological mapping based on the interpretation of air photographs analysis of glaciofluvial sediment landform assemblages and general models of quaternary landscape evolution it is argued strongly that no specific resource appraisal procedure will succeed universally because of the diverse nature of sand and gravel deposits in order to judge the utility of such procedures in britain it is possible to subdivide the country into three provinces of contrasting geomorphology and quaternary geology on the basis of glacierization during the devensian pre devensian glacierization only and no glacierization the principal sand and gravel resources of each terrain are summarised and compared from the point of view of resource appraisal the model proposed for britain may be applicable in other regions of the world that have been affected by quaternary glaciations

interplate coupling and temporal variation of mechanisms of intermediate depth earthquakes in chile we investigated the temporal variation of the mechanism of large intraplate earthquakes at intermediate depths in relation to the occurrence of large under thrusting earthquakes in chile focal mechanisms were determined for three large events 1 march 1934 m 7 1 d 120 km 20 april 1949 m 7 3 d 70 km and 8 may 1971 m w 7 2 d 150 km which occurred down dip of the great 1960 chilean earthquake m w 9 5 rupture zone the 1971 event is down dip compressional strike 12 dip 80 and rake 100 the 1949 earthquake focal mechanisms is 350 70 and 130 the data available for the 1934 event are consistent with a down dip tensional mechanism thus the two events which occurred prior to the great 1960 chilean earthquake are down dip tensional published fault plane solutions of large intermediate depth earthquakes 28 march 1965 and 7 november 1981 which occurred down dip of the valparaiso earthquakes of 1971 m w 7 8 and 1985 m w 8 0 are also down dip tensional these results suggest that before a major thrust earthquake the interplate boundary is strongly coupled and the subducted slab is under tension at intermediate depths after the occurrence of an interplate thrust event the displacement on the thrust boundary induces transient compressional stress at intermediate depth in the down going slab this interpretation is consistent with the hypothesis that temporal variations of focal mechanisms of outer rise events are due to changes of interplate coupling

kinematic rupture process of the 2007 tocopilla earthquake and its main aftershocks from teleseismic and strong motion data summary we study a large m w 7 6 earthquake that occurred on 2007 november 14 in the northern chile seismic gap near the city of tocopilla using a variety of seismic data we show that this earthquake ruptured only the lower part of the interplate seismic zone and generated a series of plate interface aftershocks two large aftershocks on 2007 november 15 ruptured the interplate zone oceanwards of the mejillones peninsula a major geographical feature in the antofagasta region on 2007 december 16 a large m w 6 8 aftershock that occurred near the southern bottom of the fault plane of the main event is shown to be a slab push earthquake located inside the subducted nazca plate and triggered by along slab compression aftershocks of this event demonstrate that it occurred on an almost vertical fault the tocopilla earthquake took place just after the installation of a new seismological network by chilean german and french researchers the accelerometric data combined with far field seismic data provide a quite complete and consistent view of the rupture process the earthquake broke a long 130 km and narrow about 30 50 km zone of the plate interface just above the transition zone using a non linear kinematic inversion method we determined that rupture occurred on two well defined patches of roughly elliptical shape we discuss the consequences of this event for models of gap filling earthquakes in chile proposed in the 1970s