forecasting cyclic coastal erosion on a multi annual to multi decadal scale southeast african coast abstract coastal erosion on the southeast african coastline shows an apparent 18 year cycle which last peaked in 2006 it is in phase with the longshore sediment transport cycle both these cycles appear to be in phase with the lunar nodal cycle lnc however the dominant tidal erosion driver on this coast appears to be the 4 4 year lunar perigean subharmonic lps we suggest that the apparent 18 year coastal erosion and longshore sediment budget cycle is a response to the 18 year mean annual precipitation cycle this cycle is 180 out of phase with the apparent coastal erosion and longshore sediment transport cycles the summer rainfall areas of southeastern africa show an 18 year map cyclicity which drives river runoff and hence controls sediment input to the coast and nearshore environment the map cycle dominates the coastal sediment budget during the lnc trough and suppresses the lps coastal erosion cycle during this time this explains why lps coastal erosion occurs close to the lnc peak thus although the lps cycle dominates the coastline it is masked during the wet portion of the 18 year map cycle it seems very likely that the lnc drives the map cycle in some way but this process is not known nevertheless these relationships can be used to predict in a general way both cyclic coastal erosion and the longshore sediment volume fluctuation this can be translated into a vital coastal planning tool which has the potential to forecast cyclic coastal erosion and hence significantly reduce the sea defense expenditure bill based on this severe cyclic coastal erosion is anticipated in 2023 and 2024

the philippine sea new survey results reveal the structure and the history of the marginal basins the hydrographic department of japan initiated a long term geological and geophysical survey of the philippine sea in 1983 we here summarize the bathymetry and magnetic anomalies of this area focusing on the structure and the evolutionary process of the marginal basins the shikoku and parece vela basins developed as one backarc system in the later phase of their formation the significant difference between the two basins however is clearest near the extinct spreading centers the steep oki daito escarpment located in the northern west philippine basin was mapped for the first time during this survey the n s trending spreading fabric north of the escarpment is in striking contrast to the nw se to e w lineament in the south our data reveal a more complicated history of the western philippine sea than has been proposed in previous studies

seismicity in the incoming subducting philippine sea plate off the kii peninsula central nankai trough 1 along the nankai trough southwestern japan the philippine sea plate phs is subducting beneath the eurasian plate and large interplate earthquakes have occurred repeatedly the latest large thrust earthquake at the central nankai trough off the kii peninsula was the 1944 tonankai earthquake mw 8 2 although a previous ocean bottom seismograph obs experiment from november 2001 to february 2002 showed seismicity around the rupture area of the 1944 tonankai earthquake there were large uncertainties regarding hypocenter locations especially with respect to depth we conducted another obs experiment to obtain accurate locations of earthquakes and their focal mechanisms the new results show earthquake clusters at the trough axis within the oceanic crust the clusters were located near faults cutting the oceanic crust and thus the earthquakes may have occurred along preexisting faults in the incoming phs seismicity in the subducting phs is characterized by seismic quiescence in the oceanic crust of the coseismic rupture area of the 1944 tonankai earthquake the change in seismicity in the oceanic crust can be explained by a change in the stress in the incoming subducting phs the stress in the oceanic crust of the phs changes from trough normal tension at the trough axis caused by the bending of the phs to downdip compression beneath the kii peninsula the seismicity in the subduction zone likely relates to the balance of stress in the incoming and the subducting plate as well as to coupling between the subducting and overriding plates

coral islands defy sea level rise over the past century records from a central pacific atoll the geological stability and existence of low lying atoll nations is threatened by sea level rise and climate change funafuti atoll in the tropical pacific ocean has experienced some of the highest rates of sea level rise 5 1 0 7 mm yr totaling 0 30 0 04 m over the past 60 yr we analyzed six time slices of shoreline position over the past 118 yr at 29 islands of funafuti atoll to determine their physical response to recent sea level rise despite the magnitude of this rise no islands have been lost the majority have enlarged and there has been a 7 3 increase in net island area over the past century a d 1897 2013 there is no evidence of heightened erosion over the past half century as sea level rise accelerated reef islands in funafuti continually adjust their size shape and position in response to variations in boundary conditions including storms sediment supply as well as sea level results suggest a more optimistic prognosis for the habitability of atoll nations and demonstrate the importance of resolving recent rates and styles of island change to inform adaptation strategies

automatic characterization of rock mass discontinuities using 3d point clouds abstract direct contact measurements for rock mass discontinuities are generally difficult to perform time consuming biased and often dangerous this paper presents an automatic characterization method for rock mass discontinuities that uses 3d point clouds which can be obtained through non contact measuring techniques such as photogrammetry and light detection and ranging lidar in this method five discontinuity parameters namely the orientation trace spacing roughness and aperture are extracted automatically the overall methodology is as follows 1 orientation is determined by using an improved k means clustering method 2 trace segments are detected by using the normal tensor voting theory and four post processing techniques are employed to compute the trace length 3 spacing is calculated by plotting virtual normal scan lines on the projected traces 4 roughness is evaluated by the correlation between the joint roughness coefficient jrc and the root mean square of the discontinuity surface profile and 5 aperture is obtained by computing the average minimum width based on sub pixel edge detection the proposed method was applied to a drill and blast rock tunnel where the extracted discontinuity parameters were used to calculate the rock mass rating rmr value and geological strength index gsi of the rock mass the application results showed that photogrammetry was more objective and efficient for acquiring rock mass discontinuity information and that it could be used as a potential alternative to the traditional discontinuity mapping method

bending of the subducting oceanic plate and its implication for rupture propagation of large interplate earthquakes off miyagi japan in the japan trench subduction zone 1 we present the results of an onshore offshore wide angle refraction and reflection experiment off miyagi in the central japan trench forearc region there are two rupture zones of large interplate earthquakes here the landward rupture zone and the trenchward rupture zone to examine the influence of plate boundary geometry on the distributions of the rupture zones we determined reflector geometries from reflections the subducting oceanic plate increases its dip from about 5 to 13 around 143 2 e this bending point in the oceanic plate corresponds to the eastern edge of the trenchward rupture zone moreover another bending point may be present at approximately 142 3 e which corresponds to the eastern edge of the landward rupture zone the coincidence between bending points in the oceanic plate and the edges of rupture zones suggests that changes in the plate boundary geometry may affect rupture propagation of interplate earthquakes in the direction of plate convergence

a composite rate and state dependent law for rock friction existing constitutive laws of rock friction cannot describe both observed strengthening in the absence of slip and frictional behavior around steady state sliding combining existing rate and state dependent friction laws we propose a new friction law which expresses logarithmically time dependent healing at sliding velocities smaller than a cut off velocity v c and approaches the so called slip law at velocities larger than v c numerical simulations show that the new friction law adequately explains experimental results of velocity stepping tests and slide hold slide tests which have widely been used to examine velocity time and displacement dependent property of rock friction because the new friction law has a simple form and appears appropriate for a wide range of conditions it is useful for application to numerical modeling of seismic cycles

discontinuity spacing analysis in rock masses using 3d point clouds abstract the complete characterization of rock masses implies the acquisition of information of both the materials which compose the rock mass and the discontinuities which divide the outcrop recent advances in the use of remote sensing techniques such as light detection and ranging lidar allow the accurate and dense acquisition of 3d information that can be used for the characterization of discontinuities this work presents a novel methodology which allows the calculation of the normal spacing of persistent and non persistent discontinuity sets using 3d point cloud datasets considering the three dimensional relationships between clusters this approach requires that the 3d dataset has been previously classified this implies that discontinuity sets are previously extracted every single point is labeled with its corresponding discontinuity set and every exposed planar surface is analytically calculated then for each discontinuity set the method calculates the normal spacing between an exposed plane and its nearest one considering 3d space relationship this link between planes is obtained calculating for every point its nearest point member of the same discontinuity set which provides its nearest plane this allows calculating the normal spacing for every plane finally the normal spacing is calculated as the mean value of all the normal spacings for each discontinuity set the methodology is validated through three cases of study using synthetic data and 3d laser scanning datasets the first case illustrates the fundamentals and the performance of the proposed methodology the second and the third cases of study correspond to two rock slopes for which datasets were acquired using a 3d laser scanner the second case study has shown that results obtained from the traditional and the proposed approaches are reasonably similar nevertheless a discrepancy between both approaches has been found when the exposed planes members of a discontinuity set were hard to identify and when the planes pairing was difficult to establish during the fieldwork campaign the third case study also has evidenced that when the number of identified exposed planes is high the calculated normal spacing using the proposed approach is minor than those using the traditional approach

the modified bruun rule extended for landward transport article i nfo the bruun rule bruun 1954 1962 provides a relationship between sea level rise and shoreline retreat and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates the bruun rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises although overwash during storms and landward aeolian transport clearly indicate otherwise herein we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the bruun rule that considers the full range of parsing cross shore transport from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile a methodology is proposed that more appropriately represents the long term processes and beach response however an improved quantitative understanding of landward transport is required for optimal application of the proposed method published by elsevier b v

the 18 6 yr nodal cycle and its impact on tidal sedimentation abstract the 18 6 yr nodal cycle modulates tidal amplitudes and currents and consequently sedimentation in tide influenced sedimentary environments data are presented which show that such effects are obvious along the coast of the dutch barrier islands and in the sedimentary fill of abandoned channels

long term tidal cycle influences on a late holocene clay mineralogy record from the cariaco basin abstract recent analyses of coastal mudbank dynamics along northeastern south america indicate significant sediment remobilization associated with the 18 6 y lunar nodal tide over the last 20 y we present a near annually resolved record of quartz and illite illite smectite abundances spanning the last 800 y from the cariaco basin venezuela that suggests effects of the lunar nodal tide have played an important role in coastal processes over the last 8 centuries spectral analysis results of the clay and fine silt data include a statistically significant peak at 18 3 y in both the quartz and illite illite smectite records that is identified with the 18 6 y lunar nodal tide remobilization of shelf sediments by mean high water line variations driven by the lunar nodal tide is presented as the probable explanation of this signal in the cariaco basin mineral content since the period of this astronomically determined signal is constant with time it can be used to calibrate high resolution age models we modify our existing age model by tuning the 18 3 y component of the illite data to the 18 6 y period and explore its impact on the age depth relationship we suggest that the 18 6 y signal can be used to refine existing chronologies where detected

automated method for extracting and analysing the rock discontinuities from point clouds based on digital surface model of rock mass abstract often when rock discontinuities with complex distributions occur in steep terrain it is difficult to rapidly survey and accurately measure their spatial distribution by traditional surveying and mapping methods this paper presents a methodology for automated extraction of rock discontinuities from a point cloud and the resulting 3d digital surface model of the rock mass first feature planes of rock discontinuities are identified and classified using both their orientation and position in a double nested mean shift clustering algorithm second the points corresponding to feature planes are extracted using a region growth algorithm and seed points finally geological information is acquired by analysing the geometric features of the extracted sub set of points from the point cloud this approach can directly extract planar features associated with joints and it eliminates spurious points in a point cloud associated with objected such as vegetation a case study of a rock slope along a highway is presented using the proposed method a sensitivity analysis of relevant clustering parameters in the mean shift clustering algorithm is conducted to acquire their optimal values and to assess their robustness the proposed method produces results that agree with the traditional survey methods and greatly improves the survey efficiency

extreme erosion on high energy embayed beaches influence of megarips and storm grouping abstract megarips have long been recognised as an important yet poorly documented mechanism of beach erosion on high energy embayed beaches the persistence and cumulative effect of megarips during storm groups are described from three embayed beaches arrifana mt clerigo and amoreira exposed to high energy wave conditions in the mesotidal bedrock dominated southwestern coast of portugal morphological changes determined by topographic monitoring and supplemented by interpretation of digital imagery over two years revealed the development of storm induced megarips which exerted a major influence on beach erosion differences in megarip influence within and between beaches are related to embayment geometry and orientation which significantly influence the nearshore wave field rip location is topographically controlled being determined by alongshore variations in breaking wave height and obliquity along with interaction of wave driven circulation patterns and embayment nearshore topography moderate beach sand loss during individual storms was linked to the development of megarips with associated rip neck and feeder channels extreme erosion however occurred when megarips and feeder channels persisted during successive storms promoting continued erosion and seaward sediment export observations show that once initiated megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non storm conditions the maintenance of such rip circulation systems driven by morphodynamic feedback reduces beach recovery ability until the rip neck and feeder channels are infilled

a fault model of the 1946 nankaido earthquake derived from tsunami data abstract a fault model of the 1946 nankaido earthquake m 8 2 is determined by the use of tsunami records of uwajima shimotsu and hososhima which were located within or near the area of major coseismic crustal deformation synthetic tsunamis computed for various fault models are matched with the observed tsunamis to determine the fault parameters a low angle thrust model slightly revised from a previous model by ando is consistent with the observed tsunamis the duration of faulting is constrained as less than 10 min based upon the tsunami the fault is divided into an eastern and a western segment corresponding to areas associated with and without aftershocks respectively the fault area and dislocation for the western segment are 150 70 km2 and 6 m and those for the eastern segment are 150 70 km2 and 3 m respectively the total seismic moment is 4 7 1028 dyn cm significantly smaller than that obtained from a geodetic model by fitch and scholz but still larger than that of the seismic model by kanamori the discrepancy in seismic moment between the seismic and the present models ran2 could be interpreted in terms of a slow dislocation on the fault but this interpretation does not match the seismic intensity distribution and damage pattern and the slow slip model for the nankaido earthquake is rejected the discrepancy between the two seismic moments is considered insignificant within error involved in data and modeling assumptions if the revised geodetic model ran2 is modified the seismic moment required to explain the observed tsunamis would be reduced further by 30 if we consider the uncertainties involved in the fault model of kanamori and the fault finiteness effect affecting the amplitude of seismic waves the seismic moment required to interpret the seismic wave data could be increased possibly being more than twice that of kanamori thus the two seismic moments from the different data sets could be close to each other within allowable tolerance this implies that the rise time of the nankaido earthquake was short enough to generate short period seismic waves from both the western and the eastern fault segments

the 1946 nankai earthquake and segmentation of the nankai trough abstract we perform a simple subevent analysis of seismic p waveforms from historical records of the 1946 nankai earthquake the results of this analysis establish that the earthquake rupture consisted of two main subevents one lying within the 1 day aftershock area off the kii peninsula while the other lies much farther to the west in the area of pronounced crustal deformation of western shikoku these conform to two segments of the nankai trough which have long been referred to in studies of historical earthquakes and geology of the nankai trough but to our knowledge have not previously been established as having distinct megathrust rupture behavior we show that these two subevents are bounded by pronounced features in the geometry of the subducting philippine sea plate psp a tear in the plate to the east beneath the kii peninsula and a subducting seamount farther to the west we speculate that these features may be associated with low strength parts of the upper and or lower plates that may be susceptible to permanent anelastic deformation which prevents the accumulation of the elastic strain energy necessary to sustain seismic rupture

late quaternary sea level change in south africa abstract a late quaternary sea level curve for south africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations available evidence suggests that sea level in south africa broadly follows that described from the caribbean but that deviations occur during sea level highstands during the last interglaciation oxygen isotope stage 5 and the late holocene coastal emergence produced higher sea levels in south africa than those identified in the caribbean during the same time intervals this is tentatively ascribed to predicted lithospheric deformation in continental margin settings

sedimentation on the narrow 8km wide oceanic current influenced continental shelf off durban kwazulu natal south africa abstract the narrow transform margin of southeast africa and its associated sedimentological and hydrodynamic setting differs to other documented continental margins the durban bluff continental shelf is extremely narrow and steep 8 km wide with a gradient ranging from 2 to 8 characterised by a wave and oceanic current dominated regime seismic sequence boundary 2 developed during the last interglacial regression spans the entire shelf separating the holocene sediment wedge seismic unit h from underlying pleistocene deposits a wave ravinement surface marks the holocene transgression comprising a pavement lag of well sorted gravels and bioclastics overlain by inshore reef derived carbonate rich sediments and offshore by quartzose mid shelf sands the shelf sands represent the transgressive holocene to modern sediment wedge forming a seaward thinning unit stacked against the pleistocene blood reef aeolianite beachrock substrate the sediment wedge is dynamic and constantly redistributed by currents associated with the durban eddy inshore of the agulhas current and bottom surge associated with high swells and marine storm events these have been instrumental in shaping large scale shoreface attached and detached sand ridges the presence of mud lenses in the vicinity of blood reef represents deposition from turbid flood waters with preservation facilitated by the morphology of the durban bluff and blood reef palynological results reflecting the local subtropical vegetation and recently introduced neophytes together with radiocarbon dates provide a very recent age for this sediment supporting a terrestrial origin and deposition from a single large flood event

apparent dynamic stability of the southeast african coast despite sea level rise the coast of southeast africa is dominated by sandy beaches that tend to be confined within log spiral or headland bound embayments investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast we show that conclusions drawn from this data with respect to the high water mark hwm position are fraught with errors which include tidal state pressure regime beach slope high swell erosion seasonal and multi annual changes we highlight and discuss these sources of error together with their magnitudes the most significant of these are the high swell seasonal and multi annual variations from case studies we show that the seasonal beach rotation and long term beach width variation are responsible for tens of metres of unaccounted hwm variation 30 to 50 m is common with maximums reaching 60 to 100 m overall the southeast african coastline appears to be in a state of long term dynamic equilibrium there is no evidence of any sea level rise forced transgression in the coastal sediment budget despite sea level rise slr if such a signal is in fact present it is lost within the beach width variation some southeast african coastal reaches are suffering chronic erosion but these are related to anthropogenic impacts the extreme difficulty of placing a hwm with any temporal validity on this coast precludes the routine use of the bruun rule although no transgressive signature is found there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change or both this decrease in the coastal sand volume is likely to result in increased future erosion copyright 2016 john wiley sons ltd

a cause of rupture segmentation and synchronization in the nankai trough revealed by seismic imaging and numerical simulation 1 a giant earthquake occasionally occurs in a subduction zone owing to a simultaneous rupture in adjacent segments which have been previously ruptured by large earthquakes however it is still unknown if a giant earthquake coincidentally occurs or if there is a causal factor to control its generation in this study we show a cause and a growth process of a giant earthquake which may occur along southwestern japan on the basis of seismic images obtained from wide angle seismic data and a numerical simulation incorporating the structural images the wide angle seismic data were acquired along three trough parallel profiles crossing the rupture segmentation boundary between the 1944 tonankai moment magnitude mw 8 1 and the 1946 nankai mw 8 4 earthquakes the seismic imaging detected a high seismic velocity body forming a strongly coupled patch at the segmentation boundary the numerical simulation explained the historic rupture patterns and shows the occurrence of a giant earthquake along the entire nankai trough a distance of over 600 km long mw 8 7 the growth process revealed from the simulated slip history in and around the strongly coupled patch is 1 prior to the giant earthquake a small slow event or earthquake occurs near the segmentation boundary 2 this accelerates a very slow slip slower than the plate convergent rate at the strong patch which reduces a degree of coupling and 3 then a rupture easily propagates through the strong patch when the next earthquake is nucleated near the segmentation boundary consequently growing into a giant earthquake

low frequency sea level fluctuations along the coasts of namibia and south africa summary sea level records at nine ports along the coasts of namibia and south africa are used to establish the existence of coastal trapped disturbances in sea level as a response to the passage of synoptic weather systems using spectral analysis the characteristics and spatial variability of the sea level fluctuations are identified the results of cross correlation analyses performed on sea level data at adjacent ports for two periods during 1982 are discussed in detail to examine the propagation of coastal trapped waves round the coast sea level records from coastal areas in southern africa exhibit extra tidal fluctuations on several different time scales associated with local or remotely forced atmospheric phenomena these scales include the synoptic or event scale of period 2 20 day the seasonal scale of period 3 6 month and the interannual or long term scale with a period of a few years the seasonal and long term components of sea level variability along the west coast of southern africa have been discussed by brundrit 1984 he concluded that there is a clear difference between the seasonal response at the northern and southern ports associated with the difference in winds affecting these two regions the long term component was found to be similar at all ports suggesting large scale non local forcing the theoretical response of sea level to pressure changes at the low frequencies associated with the passage of weather systems is that of an inverted baromei er robinson 1964 records should show a decrease in sea level of 1 01 cm for an increase in atmospheric pressure of 1 mb this assumes an ocean such that the total pressure at any fxed point on the bottom is constant in coastal areas over continental shelves this is rarely valid changes in atmospheric pressure are accompanied by changes in the velocity and direction of the wind and hence wind stress and these also contribute to fluctuations in sea level robinson

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

hypocenters in the nankai trough determined by using data from both ocean bottom and land seismic networks and a 3d velocity structure model implications for seismotectonic activity abstract we investigated the hypocenter distribution along the nankai trough off the kii peninsula japan by using data from both ocean bottom and land based seismic networks because seismic velocity structures differ greatly below land and ocean we used a 3d velocity model based on a structural model of the philippine sea plate phs which provides much more accurate estimations of source locations than 1d velocity models derived from either onshore or ocean bottom seismic data alone especially for sources between the coast and the trough axis we identified intensive seismic activity below the axis of the nankai trough which we interpreted to be aftershocks of the 2004 off the kii peninsula earthquakes m jma 7 1 7 4 and 6 5 but found much less seismic activity along the subducting phs the earthquake sources below the trough axis lie on dipping planes within the phs from which we inferred that a fracture zone is developing within the phs our estimated focal mechanisms for these earthquakes showed that their p axes were oriented north south to northeast southwest similar to those of the 2004 events which were rotated clockwise by 45 90 from the northwest southeast direction of convergence between the phs and the eurasian plates we consider that the fracture zone represents a boundary between the phs and the izu microplate which are converging in a north south direction and that the 2004 earthquakes and subsequent seismic activity were caused by the collision of these plates

crustal structure across the coseismic rupture zone of the 1944 tonankai earthquake the central nankai trough seismogenic zone 1 differences in the coseismic rupture process between the 1944 tonankai and the 1946 nankaido earthquakes have been studied by many fault models to understand what factors control coseismic rupture zones it is important to investigate differences in deep crustal structures of the rupture zones between the 1944 and 1946 earthquakes the previously published crustal structure of the rupture zone of the 1946 earthquake shows that the coseismic rupture extends to the neogene quaternary accretionary prism however little is known about the structure of the rupture zone of the 1944 earthquake to obtain a complete image of the seismogenic zone of the 1944 earthquake a wide angle seismic survey was performed across the presumed coseismic rupture zone of the 1944 earthquake from ocean to land our model for the crustal structure is based on ocean bottom seismographic data the crustal structure appears characteristic for subducting oceanic crust and a neogene quaternary accretionary prism bounded by an island arc crust the neogene quaternary accretionary prism reaches a maximum thickness of 7 km at 50 km distance landward from the deformation front the subducting oceanic crust can be traced down to 35 km the subduction angle becomes steeper landward reaching up to 11 beneath the island arc crust the depth of the top of subducting oceanic crust at the downdip limit of the rupture zone is 23 km while the updip limit is located beneath the island arc upper crust similar structures of the updip and downdip limits are also published for several other subduction zones

subducted seamount imaged in the rupture zone of the 1946 nankaido earthquake the nankai trough is a vigorous subduction zone where large earthquakes have been recorded since the seventh century with a recurrence time of 100 to 200 years the 1946 nankaido earthquake was unusual with a rupture zone estimated from long period geodetic data that was more than twice as large as that derived from shorter period seismic data in the center of this earthquake rupture zone we used densely deployed ocean bottom seismographs to detect a subducted seamount 13 kilometers thick by 50 kilometers wide at a depth of 10 kilometers we propose that this seamount might work as a barrier inhibiting brittle seismogenic rupture

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

segmentation of the vp vs ratio and low frequency earthquake distribution around the fault boundary of the tonankai and nankai earthquakes 1 beneath the kii peninsula the distribution of low frequency earthquakes lfes forms three clusters a previous study shows that one of the clusters has anomalously less amount of cumulative slip than the others to understand the cause of this variation we applied a tomographic analysis using arrival times of earthquakes recorded by both ocean bottom seismometers and onshore stations as a result we identified segmentation about the vp vs ratio around the subducting plate interface corresponding to the distribution of lfes one of the segments has low a vp vs ratio that coincides with the small slip lfe cluster another segment has a high vp vs ratio in which almost no lfes occur we conclude that the relatively low pore fluid pressure within the low vp vs segment contributes to the small slip lfe cluster and that the gap of lfes within the high vp vs segment corresponds to stable slip area due to high pore fluid pressure

the effect of seamount subduction on seismic coupling it has long been speculated that the subduction of seamounts may have profound mechanical consequences particularly on the generation of large subduction zone earthquakes we consider this problem as a special case of the seismic coupling model of scholz and campos the model predicts that the subduction of a large seamount will increase the normal stress across the subduction interface and hence will enhance seismic coupling in the case of coupled arcs this increased coupling will result in a large increase in the recurrence intervals of earthquakes such events will therefore appear rare in the instrumental record as is observed for decoupled arcs the subduction of a large seamount should cause them to become locally coupled three of the latter localities have been found with satellite altimetry data two on the tonga kermadec trench and one on the izu bonin trench the diagnostic feature is a shallowing or obstruction of the trench axis adjacent to a chain or group of large seamounts on the subducting plate in each case the small to moderate plate interface seismicity typical of decoupled seismic zones is almost completely absent in a 100 200 km arc segment indicating that the subduction zone is locally locked as predicted by the model the occurrence of large interplate earthquakes at both tonga sites confirms that they are seismically coupled

control of forearc density structure on megathrust shear strength along the chilean subduction zone abstract unveiling how the interaction of friction pore pressure p and normal stress n controls the shear strength distribution along megathrust faults at convergent plate boundaries is crucial to our understanding of processes leading to the occurrence of devastating earthquake and the construction of mountains an existing density model of the chilean margin 18 45 s allows the computation of the so called vertical stress anomaly vsa that accounts for the component of normal stress due to the weight of the overlying crustal column a spatial correlation between vsa surface geology and several earthquake parameters suggests a significant control exerted by the geologically dominated density structure of the crust on megathrust shear strength the very seismogenic forearc in front of the high central andes 18 34 s has positive vsa values up to 60 mpa and a mafic dominated crust which suggest high values of shear strength at the megathrust that are partially controlled by the weight of a dense forearc crustal column in addition to a likely dry subduction channel characterized by high and low p in contrast the southern andean forearc 34 45 s shows neutral to negative vsa down to 30 mpa correlated with a felsic dominated crust which added to a presumably wet subduction channel low and high p configures a rather weak megathrust below a light forearc earthquakes here are concentrated around the arauco peninsula a first order morpho structural anomaly characterized by comparatively higher values of vsa than the rest of this segment which is the nest of the giant mw 9 5 valdivia 1960 earthquake and the southern rupture termination of the recent mw 8 8 maule earthquake the ultimately giant size of the 1960 earthquake resulted from rupture propagation along a 1000 km long region characterized by negative vsa values the correlation between vsa and the along strike segmentation of the andean orogen indicates that the geologically inherited density structure of the forearc also rules long term mechanical coupling between converging plates and prescribes the possible structure of the orogen because central and southern andes represent two extremes in terms of orogenic structure and seismogenic behavior results presented here have significant implications for the general comprehension of processes occurring at short and long time scale at convergent margins

slab segmentation revealed by anisotropic p wave tomography 1 seismic anisotropy is a useful indicator for identifying the physical and chemical condition of the earth s interior such as stress and flow fields and in situ constituent minerals using traveltime tomography we examined three dimensional anisotropic p wave velocity structure of the kii peninsula southwest japan where source regions of megathrust earthquakes along the nankai trough are presumed to exist the tomography revealed that the philippine sea slab beneath the peninsula is segmented i e a high velocity slab with e w anisotropy obtained during seafloor spreading is broken by an anomalous low velocity region with n s anisotropy the anomaly lies along the segmentation boundary of two previous rupture zones the 1944 tonankai and 1946 nankai earthquakes and can be explained by the occurrence of a fracture zone with n s oriented fractures and fault planes revealed by wide angle seismic data it is likely that this anomalous region will form a clear segmentation boundary during future earthquakes

backbeach deflation aprons morphology and sedimentology backbeach deflation aprons are heterogeneous coarse clastic deposits associated with active transverse dune fields the apron comprises variously angular rounded fractured cracked polished and ventifacted clasts of bedrock local and exotic beachrock and bioherm fragments coral and worm reef terrestrial and anthropogenic clasts from archeological sites deflated dunes flotsam and shipwrecks are also present the unit forms as a lag deposit on top of a gently sloping ca 0 008 planar sandy deflation surface and is typically only one clast thick it is up to 100 m wide and extends for tens of kilometers along the coast it is replaced landward by a steep ca 0 1 deflated soil surface armored with a layer of iron concretions backbeach deflation aprons are compound deposits that result from marine storm eolian and human activity since the mid holocene the depositional model proposed involves periodic storm deposition of coarse clasts of beachrock bedrock and biogenic origin and flotsam shipwreck and other floating debris on the backbeach or dunes some clasts are deposited directly into interdune depressions and enter the deflation plain immediately others are deposited initially on dune surfaces dune migration results in winnowing of the storm deposited coarse clasts together with rhizoliths and any other coarse material in the dune until they come to rest on the deflation surface the lag deposit is subsequently buried and uncovered multiple times by dune migration during which time it is exposed to polishing and subaerial weathering consequently the lag comprises a variety of materials that reflect both storm and eolian processes the clasts exhibit variable degrees of rounding polishing and ventification according to how long they have been in the deposit backbeach deflation aprons are characteristic of sandy beaches along approximately 475 km 10 of the total length of the south african east coast they develop in association with large scale transverse dunefields on the backbeach which in turn depend on reversing shore parallel winds and high sediment abundance the variable degree of polishing and weathering planar surface low elevation and back beach location along extensive shoreline distances distinguish backbeach deflation aprons from tsunami or marine storm deposits

sand bypass and updrift beach evolution after jetty construction at an ebb tidal delta abstract the evolution of an ebb tidal delta guadiana south portugal and its updrift beach after jetty construction in 1972 1974 is analysed based on 24 ortho rectified aerial photographs 1940 2012 and 13 bathymetric maps 1969 2014 the objectives are to evaluate the re establishment of the sand bypassing process and if the disruption of the historical delta may affect the updrift beach evolution post jetty progradation of the updrift beach resulted from two large accretion events the second largest event 110 m progradation in 1985 1994 was due to beach attachment of a shoal produced by the erosion of a broad shallow area relict of the historical delta the reworking of sand from this relict area also enables the individualisation of a lateral updrift bar simultaneously with the new ebb shoal proper formation both morphological features were close to volume equilibrium in 1995 indicating that most of the sand was transported towards the downdrift side of the inlet at that time this study shows that erosion of the historical delta may enhance significantly the updrift shoreline progradation and may promote the re establishment of sand bypassing after jetty construction

geostatistical method for inferring rmr ahead of tunnel face excavation using dynamically exposed geological information abstract rock mass rating rmr is a rock mass classification system that is often used to select appropriate excavation methods and rock support systems in tunnel projects this paper presents a geostatistical method for inferring rmr values quantitatively ahead of excavation of the tunnel face the study makes full use of geological information exposed on excavated tunnel faces to capture the spatial correlation of rock mass quality and later predicts the rmr value using the kriging method predictions are constantly updated during the tunnel construction process the advantages of the proposed method are as follows 1 the rmr prediction uncertainty is quantified by accounting for spatial variability and model uncertainty therefore the resulting prediction can consider the geological conditions of the worst scenario 2 the spatial variability of the geological condition is represented as a variogram model that is updated by observation data on the new excavated faces and as the tunnel advances the rmr prediction accuracy improves and 3 the periodicity of geological conditions can be considered in rmr prediction the proposed method is applied to a rock tunneling project the mingtang tunnel in anhui province china the method achieves approximately 80 prediction accuracy therefore it has high potential as a tool for predicting rmr information ahead of tunnel face excavation

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

optimization of lidar scanning and processing for automated structural evaluation of discontinuities in rockmasses terrestrial light detection and ranging lidar can be used for the delineation and evaluation of geomechanically controlled hazards the united states geological survey 1 has adopted the use of lidar through numerous projects as discussed in 2 other examples of the use of lidar surveys for geological data collection include discussion of the process of acquiring digital outcrop models for stratigraphic modelling 3 mapping basalt flow units 4 structural mapping of a large landslide 5 and evaluation of rockfall source and accumulation zones 6 7 in non geologicalbased applications lidar has been used for projects ranging from volumetric analysis in open pit mines 8 to recording and cataloguing archaeological digs in ancient ruins 9 the equipment mobility accuracy and rate of data collection in comparison to conventional surveying and stereophotogrammetric methods have allowed existing surface analysis projects to proceed at unprecedented levels of detail and have promoted new applications the use of terrestrial ground based lidar as a structural analysis and measurement tool has been investigated in detail by kemeny and post 10 feng and roshoff 11 pringle et al 12 slob et al 13 and others once the data is acquired and the primary 3d model is generated as x y z data points with intensity scalars or mapped colourization via photo coupling the analytical process can proceed in a similar fashion to modern photogrammetric techniques such as those applied by haneberg et al 14 both applications can replace traditional field mapping processes including the use of a compass or inclinometer to measure orientation photos and notebooks to keep records and manual data entry further the conventional measurement of

petrological model of the northern izu bonin mariana arc crust constraints from high pressure measurements of elastic wave velocities of the tanzawa plutonic rocks central japan abstract ultrasonic compressional wave velocities vp and shear wave velocities vs were measured with varying pressure up to 1 0 gpa in a temperature range from 25 to 400 c for a suite of tonalitic gabbroic rocks of the miocene tanzawa plutonic complex central japan which has been interpreted as uplifted and exposed deep crust of the northern izu bonin mariana ibm arc the vp values of the tonalitic gabbroic rocks increase rapidly at low pressures from 0 1 to 0 4 gpa and then become nearly constant at higher pressures above 0 4 gpa the vp values at 1 0 gpa and 25 c are 6 3 6 6 km s for tonalites 56 4 71 1 wt sio2 6 8 km s for a quartz gabbro 53 8 wt sio2 and 7 1 7 3 km s for a hornblende gabbro 43 2 47 7 wt sio2 combining the present data with the p wave velocity profile of the northern ibm arc we infer that 6 km thick tonalitic crust exists at mid crustal depth 6 1 6 3 km s vp overlying 2 km thick hornblende gabbroic crust 6 8 km s vp our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers being consistent with the strong reflector observed at 12 km depth in the ibm arc the measured vp of tanzawa hornblende bearing gabbroic rocks 7 1 7 3 km s is significantly lower than that vp modeled for the lowermost crustal layer of the northern ibm arc 7 3 7 7 km s at 15 22 km depth we propose that the ibm arc consists of a thick tonalitic middle crust and a mafic lower crust

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

depth variation of the crustal structure of the subducting plate along the nankai trough off kii channel japan a seismic refraction reflection experiment using ocean bottom seismometers with artificial sources comprising airguns and explosions was conducted at off kii channel the nankai trough where interplate earthquakes occurred periodically using p wave travel time analyses including non linear travel time inversion the depth variation of the crustal structure along the nankai trough was revealed the results show that the subducting depth of the philippine sea plate changes at off kii channel the plate is subducting at a shallow location at the west side and at a deep location at the east side the depth of the plate boundary is about 8 km at the west side and about 9 km at the east side this result and former studies indicate that the variation of subducting depth exists beneath kii channel and off kii channel regions this depth change of the plate boundary might affect the process of interplate earthquake occurrence

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

deformable backstop as seaward end of coseismic slip in the nankai trough seismogenic zone abstract wide angle seismic surveys performed in the last decade have clarified the 3 d crustal structure along the nankai trough the geometry and velocity structure of the southwestern japan subduction zone are now well constrained comparing these observations with the rupture distribution of historic great thrust earthquakes it appears that the coseismic rupture occurred along plate boundaries deeper than the wedge backstop boundary the boundary between the neogene quaternary accretionary wedge and the crust forming the backstop from the view of spatial relationship both rupture distributions of the last two large events and the crust forming the backstop are considerably retreated from the trough axis in the west and east off the kii peninsula in both areas seamount or ridge subduction is apparent in seismic results geomorphological data and geomagnetic data the landward indentation of the deformable backstop which corresponds to the crustal block of old accreted sediments may be formed by seamount subduction according to published results of sandbox modeling in particular the subducted seamount may be a structural factor affecting the recession of the crustal block forming the backstop

microseismicity at the seaward updip limit of the western nankai trough seismogenic zone 1 the seismogenic zone at subduction zones does not normally extend to the trench axis the shallowest part of the plate interface is considered to be seismically decoupled the location of the seaward updip limit of the seismogenic zone and its relation to the crustal structure are important for understanding the transition process from aseismic slip to the seismic rupture at the plate interface the nankai trough seismogenic zone southwestern japan is one of the most well studied subduction seismogenic zones in the world however the offshore seismicity around the nankai trough is very low and hypocenters are not determined accurately by the on land seismic network we performed microseismicity observations using ocean bottom seismographs off cape muroto hypocenters were determined by using a three dimensional vp and vs structure based on seismic survey results the observed microseismicity seems to be classifiable into two types the first is earthquakes that occur around the plate interface the second is a group of earthquakes that occur in the uppermost mantle of the subducting oceanic plate the seismicity around the plate interface forms several clusters the seaward limit of the clusters is characterized by earthquakes with a similar waveform these similar waveform earthquakes are considered to occur at small asperities in the aseismic seismogenic transition zone of the plate interface the seismicity in the uppermost mantle may be related to dehydration embrittlement of subducting serpentinized mantle

heterogeneous crustal structure across a seismic block boundary along the nankai trough the nankai trough which runs along the western japanese islands is widely known for its systematic activity of large earthquakes with the magnitudes greater than 7 according to the fault plane studies of these earthquakes a major seismic block boundary is supposed to run off the kii peninsula almost perpendicular to the trough axis a seismic experiment was conducted across this boundary region in order to determine seismic crustal structure p wave travel time analyses were applied to the data from the obss deployed along the trough axis including travel time nonlinear inversion the result shows an abrupt change in thickness of the subducting philippine sea plate s crust at the expected location of the seismic block boundary the crust is thicker in the east by about two kilometers and the interface between the overriding and subducting plates runs shallower in the east these structural features may affect the mode of earthquake occurrence

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

nonlinear refraction traveltime tomography a few important issues for performing nonlinear refraction traveltime tomography have been identified they include the accuracy of the traveltime and raypath calculations for refraction the physical information in the refraction traveltime curves and the characteristics of the refraction traveltime errors consequently we develop a shortest path ray tracing method with an optimized node distribution that can calculate refraction traveltimes and raypaths accurately in any velocity model we find that structure ambiguity caused by short and long rays in the seismic refraction method may influence the inversion solution significantly therefore we pose a nonlinear inverse problem that explicitly minimizes the misfits of the average slownesses ratios of traveltimes to the corresponding ray lengths and the apparent slownesses derivatives of traveltimes with respect to distance as a result we enhance the resolution as well as the convergence speed to regularize our inverse problem we use the tikhon

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

extraction and statistics of discontinuity orientation and trace length from typical fractured rock mass a case study of the xinchang underground research laboratory site china abstract the geological parameters of rock discontinuities are of great significance for the evaluation of high level radioactive waste repository and underground research laboratory url site characteristics to provide sufficient basis for the construction of the xinchang url site this paper presents a comprehensive set of methods for acquisition of discontinuity parameters in this set of methods a high precision three dimensional point cloud model of an outcrop with real geographic information is established based on close range photogrammetry technology from which not only planar discontinuities but also linear discontinuities can be identified and extracted by a semi automatic method a new fast fuzzy clustering method is proposed to cluster discontinuity sets the statistics method based on topographic window projection is improved to increase the rationality of estimating the geometric characteristics of fracture traces as a preliminary validation the results of this case study reveal that these methods have good applicability in acquiring discontinuity parameters which is also conducive to the establishment of a deterministic stochastic discrete fracture network dsdfn model to further analyze the properties of fractured rock mass in addition it is preliminarily found that some outcrops different locations have structures with similar geological features to a certain extent moreover the fractures exposed on the outcrop surface have distribution characteristics similar to those in the granite body obtained by drilling above all the presented multidisciplinary methods could provide an alternative and practical approach for low cost and accurate acquisition of discontinuity parameters and thus to study the properties of fractured rock mass effectively

detailed coseismic slip distribution of the 1944 tonankai earthquake estimated from tsunami waveforms coseismic slip distribution on the fault plane of the 1944 tonankai earthquake is estimated from inversion of tsunami waveforms three improvements from a previous study satake 1993 are made these are 1 smaller subfaults are used to resolve detailed slip distribution 2 the sub faults fit better to the plate interface geometry and 3 finer and more accurate bathymetry data is used the inversion result shows that a maximum slip of about 3 m occurred on the plate interface off shima peninsula the total seismic moment is estimated to be 2 0 1021 nm mw 8 2 the result confirms that the 1944 tonankai earthquake did not rupture the plate interface beneath the tokai region and supports the existence of the seismic gap in the tokai region suggested by ishibashi 1981 the slip of about 1 5 m on the plate interface beneath atsumi peninsula northeast of the large slip area is necessary to explain the observed tsunami waveforms although no seismic moment release was estimated from strong motion data by kikuchi et al 1999 this may suggest that the rupture beneath atsumi peninsula was slow

a model for complex slip behavior on a large asperity at subduction zones 1 3 d numerical simulations for rupture process of a large asperity on a subduction fault are carried out in order to examine whether the whole area of an asperity always breaks at once or not during an earthquake our quasi static simulation in an elastic half space includes a rate and state dependent friction we examine the effect of lateral dimension of an asperity which extends the whole seismogenic width in dip direction on the slip behavior in cases of the asperity with comparable dimension to the seismogenic width the whole area of the asperity can break at once and its seismic cycle shows a regular periodic behavior however in cases with much larger lateral dimension the asperity does not break its whole area at once in addition its slip behavior becomes complex within a certain range this suggests that the slip complexity in earthquake fault may be an intrinsic property in the system

structural factors controlling the rupture process of a megathrust earthquake at the nankai trough seismogenic zone summary the nankai trough is a vigorous subduction zone where large earthquakes have been recorded with a recurrence time of 100 200 yr the 1946 nankaido earthquake is well known as an unusual event among these earthquakes because the rupture zone estimated from long period geodetic data is more than twice as large as that derived from seismic wave data in the summer of 1999 an onshore offshore deep seismic survey was performed along a 355 km long profile in the western nankai trough seismogenic zone seismic signals both from an airgun array 207 l and land explosions maximum of 500 kg were recorded simultaneously by 98 oceanbottom seismographs and 93 land seismic stations conventional 2 d seismic reflection data were also acquired along part of the offshore profile from the wide angle seismic data we found a subducting seamount at the centre of the proposed rupture zone with dimensions of 13 km thick by 50 km wide at 10 km depth the seismic velocity image also shows that the seamount is now colliding with the japanese island arc crust from this significant structure this paper proposes that the subducted seamount functioned as a barrier at least during the 1946 earthquake i e the rupture of the 1946 earthquake extended over the entire locked zone to the east of the subducted seamount and then the rupture was deflected around the subducted seamount at the down dip end of the locked zone between cape muroto and cape ashizuri another significant structure a highly reflective layer is obtained beneath shikoku island a very slow p wave velocity 3 km s 1 is necessary in a thin layer at the base of the island arc crust in order to explain the observed high amplitude reflection phases an area of low resistivity obtained by a previous magnetotelluric study corresponds to the highly reflective layer this suggests a possible water layer at the base of the island arc crust the water may be generated by dehydration of the downgoing probably partially serpentinized mantle which is implied by a low p wave velocity 7 5 km s 1 beneath the subducted seamount a locally observed non slip region during the 1946 earthquake at the eastern part of shikoku island is interpreted as a result of weak coupling at the possible water layer

ray equation migration of wide angle reflections from southern alaska a kirchhoff style prestack depth migration algorithm is implemented for wide angle reflections in two dimensional variable velocity acoustic media extrapolation of both source and recorder wavefields is performed by ray tracing the imaging condition at each point in the image space is the total source to recorder travel time since the migration algorithm is based on ray tracing migration can be performed for any medium through which rays can be traced there is no inherent limitation on the size of the region to be imaged regions up to 3 6 103 km2 are utilized in this study the algorithm is illustrated by migration of two synthetic and three real data sets from the u s geological survey s trans alaska crustal transect program images are produced of inferred subduction assemblages in southern alaska emphasis in this paper is on obtaining reflector positions and shapes rather than detailed structural interpretations

contiguous rupture areas of two nankai trough earthquakes revealed by high resolution tsunami waveform inversion 1 we have developed a new method for inverting tsunami waveforms that reveals considerable detail in megathrust slip during subduction zone earthquakes previous methods have ensured compliance with the shallow water theory used to compute tsunami waveforms by using large subfaults that generate only long wavelength seafloor deformation we show that a better approach is to use small subfaults coupled with a smoothing criterion that ensures compliance with the shallow water approximation in an application of the method to historical earthquakes in the nankai trough southwestern japan we find that the areas with slip 1 m for the earthquakes of 1944 and 1946 which ruptured adjacent segments of the subduction zone are separated by a sharp non overlapping boundary this establishes that interseismic accumulation of strain energy extends very close to the boundary between rupture zones and strongly suggests that this boundary is associated with a physical barrier to rupture

contrasting styles of swell driven coastal erosion examples from kwazulu natal south africa during 2006 2007 the kwazulu natal coast of south africa was exposed to several large swell events ho 3 m near the peak of the lunar nodal cycle causing shoreline recession the largest swell hs 8 5 m struck the coast on the march equinox 18th 20th and generated a strong storm return flow observations made before during and after record dramatic coastal erosion shoreline recession of up to 40 m and substantial property damage this swell event removed the semi continuous nearshore bar system and conditioned the coast such that lesser subsequent swell events accomplished much greater amounts of coastal erosion than expected up to 100 m at certain erosion hotspots because waves reached the coast without significant energy dissipation subsequent bar generation rebuilt the inshore bars within six months the styles of erosion during the march 07 event and other 2007 swells were markedly different lesser swells are focused by headlands and result in megarip development and activation of erosion hotspots the march 07 event still water level was raised equinoctial spring high tide and a storm surge of 0 33 0 45 m to a level that rendered most headlands and erosion hotspots ineffective and resulted in laterally extensive erosion of soft shorelines results record cumulative effects of successive swell events on coastal behaviour that proved to be critical in enabling erosion to proceed at rapid rates after the coast had been initially destabilized unlike hurricanes and tsunamis surges associated with swell events are relatively minor and therefore extensive erosion is linked with high lunar tides there is circumstantial evidence that swell induced erosion follows the broad 18 6 yr lunar nodal tidal cycle when the chances of large swells coinciding with high water levels are increased

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

semi automatic extraction of rock mass structural data from high resolution lidar point clouds abstract in this paper a matlab tool called diana discontinuity analysis for the 2d and 3d geo structural analysis of rock mass discontinuities on high resolution laser scanning data is presented the proposed approach is able to semi automatically retrieve some relevant rock mass parameters namely orientation number of sets spacing frequency and derived rqd persistence block size and scale dependent roughness by analyzing high resolution point clouds acquired from terrestrial or aerial laser scanners in addition with a specific diana option called filterveg we are able to remove vegetation or other disturbing objects from the point cloud which is one of the main problems in lidar data processing some examples of the proposed method have demonstrated its ability to investigate rock masses characterized by irregular block shapes and suggest applications in the field of engineering geology and emergency management when it is often advisable to minimize survey time in dangerous environments and in the same time it is necessary to gather all the required information as fast as possible

estimation of rock mass deformation modulus and strength of jointed hard rock masses using the gsi system abstract rock mass characterization is required for many applications in rock engineering practice including excavation design support design stope design amongst others for these purposes it is necessary to obtain design input parameters such as deformation moduli and strength parameters for numerical modeling although such parameters can ultimately be determined from in situ tests at the preliminary design stage where access to underground is limited the practical way to obtain these parameters is to apply a rock mass classification system to characterize the rock mass and estimate the rock mass properties over the years many classification systems such as rqd rock mass rating q and geological strength index gsi systems have been developed amongst them the q system is widely used for rock support system design and the gsi system is used for estimating design parameters the gsi system is the only rock mass classification system that is directly linked to engineering parameters such as mohr coulomb hoek brown strength parameters or rock mass modulus however the application of the existing gsi system is hindered by the facts that the use of the system is to some extent subjective and requires long term experience in the present study a quantitative approach to assist in the use of the gsi system is presented it employs the block volume and a joint condition factor as quantitative characterization factors the approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness the newly developed approach adds quantitative means to facilitate use of the system especially by inexperienced engineers the gsi system is applied to characterize the jointed rock masses at two underground powerhouse cavern sites in japan gsi values are obtained from block volume and joint condition factor which in turn are determined from site construction documents and field mapping data based on gsi values and intact rock strength properties equivalent mohr coulomb strength parameters and elastic modulus of the jointed rock mass are calculated and compared to in situ test results the point estimate method is implemented to approximate the mean and variance of the mechanical properties of the jointed rock masses it is seen that both the means and variances of strength and deformation parameters predicted from the gsi system are in good agreement with field test data

forecast model for great earthquakes at the nankai trough subduction zone an earthquake instability model is formulated for recurring great earthquakes at the nankai trough subduction zone in southwest japan the model is quasistatic two dimensional and has a displacement and velocity dependent constitutive law applied at the fault plane a constant rate of fault slip at depth represents forcing due to relative motion of the philippine sea and eurasian plates the model simulates fault slip and stress for all parts of repeated earthquake cycles including post inter pre and coseismic stages calculated ground uplift is in agreement with most of the main features of elevation changes observed before and after the m 8 1 1946 nankaido earthquake in model simulations accelerating fault slip has two time scales the first time scale is several years long and is interpreted as an intermediate term precursor the second time scale is a few days long and is interpreted as a short term precursor accelerating fault slip on both time scales causes anomalous elevation changes of the ground surface over the fault plane of 100 mm or less within 50 km of the fault trace

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

contrasting subduction structures within the philippine sea plate hydrous oceanic crust and anhydrous volcanic arc crust we show contrasting subduction structures within the philippine sea plate inferred from active source wide angle reflection data previous studies showed that large amplitude reflections from the slab are observed in southwest japan and indicated that a thin low velocity layer with a high fluid content is formed along the top of the subducting oceanic crust on the contrary we found that the slab reflections have smaller amplitudes in the izu collision zone central japan where the izu bonin volcanic arc has been colliding subducting suggesting that such a low velocity layer does not exist beneath the collision zone this structural difference is also supported by p wave and s wave velocity anomalies by passive source tomography and electrical conductivity and correlates with the regional distribution of deep tremors and intraslab earthquakes both of which are induced by dehydration processes within the downgoing slab based on these comparisons we suggest that the original structure of the incoming plate controls the contrasting subducting systems typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and or seawater infiltration at outer rises whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable anhydrous forms before subduction

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

permeability structure around an ancient exhumed subduction zone fault 1 we conducted permeability measurements on rocks sampled from an exhumed ancient subduction zone fault in the cretaceous shimanto accretionary complex of japan the permeability under seismogenic environment conditions shows a heterogeneous structure across the fault zone permeability of the sandstone in turbidite sequence is the lowest whereas the highly sheared zone has the largest permeability a combination of permeability contrast between these two zones and fluid pressure source including tectonically driven burial and dehydration could result in a concentration of pore fluids along the fault which causes deep seismic reflections during underplating stage as delineated in seismic reflection studies following a rise of temperature up to 250 c the permeability of all the sampled rock types became smaller than at room temperature and also gradually decreased with increasing hold time

wave influences in contemporary and mesoarchaean stromatolites abstract contemporary shore platform stromatolites sps are becoming well known we describe the physical environment and macrostructures from contemporary shore platform stromatolites sps on the wave dominated southeast african coast this was then compared with mesoarchaean 2 97 ga stromatolites from white umfolozi 100 km inland we use the tinley manor sps occurrence as the basis for physical environmental comparison but where necessary draw on evidence from other sps environments sps and mesoarchean umfolozi stromatolites contain similar stromatolitic structures and wave deposits the sps environment is wave dominated and the occurrence of similar sedimentary structures associated with the mesoarchean umfolozi stromatolites indicates a paleoenvironment associated with waves the contemporary tinley manor sps wave climate is robust and from this locality we have identified broad limits in which sps can develop and be preserved applying this knowledge to the mesoarchaean white umfolozi stromatolites suggests that they formed in a protected wave climate where wave incursions were less frequent both these wave influenced settings are were subject to very low siliciclastic input the frequency of marine sediment input appears to be a limiting factor on microbialite growth in both the contemporary sps and archaean examples