analysis of the reliability and resolution of the earthquake source history inferred from waveforms taking the chi chi earthquake as an example summary in the inversion of observed waveforms to obtain the earthquake source faulting process some uncertain factors may influence the reliability of the results several numerical tests have been analysed in this paper in order to understand the effect of some of these uncertain parameters such as the number and width of multiple time windows that define the source time function the assumed strike and dip of the fault the velocity structure and noise also the influence of the sampling rate the time window of the data and the distribution of observational stations is studied our research indicates the near source waveform data can adequately recover the source rupture process of the shallow part of the fault however they poorly constrain the slip distribution on the deep part of the fault using near source and teleseismic waveform data jointly can provide a more complete view of the rupture process of the whole fault the result using near fault data is very sensitive to the assumed strike and dip parameters of the fault model a 2 deviation of the presumed strike and a 5 deviation of the presumed dip from that of the true fault will lead to a distorted inversion result the influence of the uncertainty of the seismic velocity structure for the chi chi earthquake might be ignored if we can take the difference between ma et al s model and wu et al s model as the measure of the media uncertainty

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

distribution of dynamic and static stress changes during 2000 tottori japan earthquake brief interpretation of the earthquake sequences foreshocks mainshock and aftershocks 1 the dynamic and static stress changes during the 2000 tottori earthquake have been recovered from the results of waveform inversion we use the dem to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model the resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions we conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity this suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks the foreshock distribution was confined to a finite localized zone in the central part of the fault suggesting that this zone was bordered by barriers

rupture reactivation during the 2011 mw 9 0 tohoku earthquake dynamic rupture and ground motion simulations near source ground motion observations and kinematic source inversions suggest that the rupture process of the 2011 m w 9 0 tohoku earthquake involved rupture reactivation that is repeated rupture nucleation in the same hypocentral area this unusual phenomenon may have provided a second breath to the rupture that enhanced its final size here we propose that rupture reactivation may have been governed by a slip weakening friction model with two sequential strength drops the second one being activated at large slip such frictional behavior has been previously observed in laboratory experiments and attributed to pressurization of fault zone fluids by mineral decomposition reactions activated by shear heating such as dehydration and decarbonation further evidence of this double slip weakening friction model is obtained here from the dynamic stress changes in the hypocentral region derived from a finite source inversion model we incorporate this friction model in a dynamic rupture simulation comprising two main asperities constrained by source inversion models and several deep small asperities constrained by backprojection source imaging studies our simulation produces ground motion patterns along the japanese coast consistent with observations and rupture patterns consistent with a kinematic source model featuring rupture reactivation the deep small asperities serve as a bridge to connect the two main asperities and the rupture reactivation mechanism is needed to reproduce the observed ground motion pattern therefore we argue that rupture reactivation during the 2011 tohoku earthquake is consistent with a second strength drop possibly caused by activation of thermochemical weakening processes at large slip online material movie of simulated rupture and wave propagation and ground velocities recorded at the kik net and k net seismic networks

controls on precambrian sea level change and sedimentary cyclicity abstract although uniformitarianism applies in a general sense to the controls on relative and global sea level change some influences thereon were more prominent in the precambrian short term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide low gradient precambrian shelves the lack of evidence for global glacial events in the precambrian record implies that intraplate stresses and cyclic changes to earth s geoid were more likely explanations for third order sea level change than glacio eustasy higher heat flow in the earlier precambrian may have led to more rapid tectonic plate formation transport and destruction along with an increased role for hot spots aseismic ridges and mantle plumes superplumes all of which may have influenced cyclic sedimentation within the ocean basins a weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first order supercontinental cycle sea level change second order cyclicity in the precambrian largely reflects the influences of thermal epeirogeny changes to mid ocean ridge volume as well as to ridge growth and decay rates and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism third order cycles of sea level change in the precambrian also reflected cyclic loading unloading within flexural foreland basin settings and filling deflation of magma chambers associated with island arc evolution the relatively limited number of studies of precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity archaean greenstone basins appear to have had first and second order cycle durations analogous to phanerozoic equivalents supporting steady state tectonics throughout earth history in direct contrast however preserved basin fills from neoarchaean palaeoproterozoic cratonic terranes have first and second order cycles of considerably longer duration than phanerozoic examples supporting less evolved tectonism affecting cratonic plates it is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates the wide range of controls on precambrian sea level change allied to their apparent variability in rates and periodicity through precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study this underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of precambrian basins based on the relative importance of sequences rather than their temporal duration

evaluating the compatibility of dynamic rupture based synthetic ground motion with empirical ground motion prediction equation we performed an assessment of a database of synthetic ground motion generated by a suite of dynamic rupture simulations to verify compatibility of the peak ground amplitudes with respect to empirical ground motion prediction equations gmpes the dynamic rupture model database developed by dalguer and mai 2011 is composed of 360 earthquake scenarios with moment magnitudes in the range of 5 5 7 for three mechanisms of faulting reverse normal and strike slip and for both buried faults and surface rupturing faults having depth and non depth dependent normal stresses initial shear stress distribution follows a von karman stochastic distribution overall we show quantitatively that the upper frequency limit of the suite of simulations is 1 0 hz up to this frequency the synthetic data are compatible with the empirical model which means that the residuals defined as the differences between observed and predicted ground motions fall in the range of of the empirical gmpe characteristics of the mean values along distance 10 45 km and period t 1 0 s including standard deviation of the synthetic response spectra and peak ground velocity are comparable to their counterpart empirical gmpe at very near source 1 2 km synthetics show supersaturation of the mean peak values which is different from the saturation features predicted by the gmpes the effect of source parameters such as stress drop peak slip velocity and rupture speed and of surface and buried rupture as well as hanging wall and footwall are highly sensitive to ground motion suggesting that these effects contribute to the variability of ground motion near the source and that inclusion of them in the source terms may contribute to reducing uncertainties in gmpes

evolution of the eastern indian ocean since the late cretaceous constraints from geosat altimetry we propose a new model for the tectonic evolution of the eastern indian ocean from the late cretaceous to the present two types of data are used to improve previously published reconstructions first recent reinterpretations of seafloor magnetic anomalies between australia and antarctica and in the wharton basin provide new constraints on spreading rates and the timing of major reorganizations second vertical deflection profiles i e horizontal gravity anomaly derived from 22 repeat cycles of geosat altimeter data reveal the tectonic fabric associated with fracture zones these new geosat data provide tight constraints on paleospreading directions for example three prominent fracture zones can be traced from south of tasmania to the george v basin antarctica providing an important constraint on the relative motions of australia and antarctica through the late eocene in addition the geosat profiles are used to locate the conjugate continental margins and continent ocean boundaries of australia and antarctica as well as the conjugate rifted margins of kerguelen plateau and broken ridge based on a compilation of magnetic anomaly data from the crozet basin the central indian basin the wharton basin and the australian antarctic basin ten plate tectonic reconstructions are proposed reconstructions at chrons 5 11 ma 6 21 ma 13 36 ma and 18 43 ma confirm that the southeast indian ridge behaved as a single plate boundary since chron 18 the constraints from the geosat data provide an improvement in the fit of the kerguelen plateau and broken ridge at chron 20 46 ma to avoid overlaps between broken ridge and the kerguelen plateau prior to their breakup our model includes relative motions between the northern and southern provinces of the kerguelen plateau finally we examine the implications of our model for the relative motions of india australia and antarctica on the tectonic evolution of the kerguelen plateau and broken ridge and the adjacent labuan basin and diamantina zone as well as the emplacement of the ninetyeast ridge and the kerguelen plateau over a fixed hot spot

the importance of the dynamic source effects on strong ground motion during the 1999 chi chi taiwan earthquake brief interpretation of the damage distribution on buildings the 1999 chi chi taiwan earthquake that originated on a low angle reverse fault showed complexity and uncommon characteristics the records show that the hanging wall side is characterized by larger particle motions than the foot wall and the ground motion is stronger in the northern part than in the southern part of the causative fault although the strongest ground motion occurred near the north ern part of the trace structural damage was heavier in the southern part in order to get a better understanding of the complex damage distribution caused by this earth quake the dynamic rupture process was numerically simulated because of the dif ferences between the observed features of the rupture process in the northern and southern parts of the fault each part was modeled independently by using a 2d discrete element model dem the principal results of the simulation show that the velocity ground motions in the northern part in the frequency range of 0 5 2 hz natural frequency range of standard structures are small near the surface break thus light structural damage might be predicted near the surface rupture moreover in the northern part the fault rupture propagation reaches the surface with a very slow velocity about 1 2 km sec however in the southern part the rupture propa gation reaches the surface with higher velocity about 3 0 km sec these differences between the models could explain why the ground motion near the surface rupture in the northern part caused less damage in structures than the ground motion in the southern part

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

dynamic rupture processes on a dipping fault and estimates of stress drop and strength excess from the results of waveform inversion summary the dynamic rupture processes on a dipping fault in a horizontally layered medium are investigated on 3 d spontaneous shear crack models the wave equations for the 3 d space are solved numerically by a finite difference method under appropriate boundary conditions the displacement components right above and right below the dipping fault plane have been obtained by solving the boundary conditions across the fault it was found that the final fault slip on the hanging wall side is appreciably larger than that on the foot wall side and that their amount is quite sensitive to the fault depth and the elastic heterogeneities of the medium particularly of the existence of low velocity surface layers on the basis of the above model the dynamic rupture process of the 1961 kita mino earthquake in central japan has been investigated with constraints of the fault parameters derived from the results of waveform inversion analysis for this purpose a locking fracture criterion was introduced for rupture propagation from which a lower bound of the maximum shear stress before the rupture and hence of the strength excess has been estimated the dynamic stress drop has also been evaluated by repeated iterations to minimize the difference between the dynamic and kinematic fault slips the results revealed quite heterogeneous distribution of strength excess indicating large values near the sw section of the fault at shallow depths and in the central bottom section in contrast to small values at mid depths in the ne section around the rupture nucleus zone the distribution of stress drop was also found to be heterogeneous with the existence of high stress drop zones in the ne shallow and bottom sections and a low stress drop zone at most of mid depths except in the sw section these results suggest that the dynamic rupture of this earthquake initiates at a small nucleus zone with low strength excess and small stress drop then broke the shallower and deeper fault sections with moderate strength excess and high stress drop and finally ruptured barrier zones with high strength excess these zones may be interpreted as weak and strong asperities and barriers respectively

constraints on the evolution of the japan sea based on 40ar 39ar ages and sr isotopic ratios for volcanic rocks of the yamato seamount chain in the japan sea 40 ar 39 ar and sr isotope analyses were performed on basalts and andesites dredged from the yamato seamount chain in the japan sea the 40 ar 39 ar plateau ages range from about 11 to 17 ma though most samples show ages between 10 and 14 ma the seamounts seem to have formed within a period of a few million years although some of them might have formed earlier based on the present results together with previously reported radiometric age data it is thought that the yamato basin formed during some period prior to 17 ma and probably later than around 25 ma taking into account the radiometric age data on rocks from the japan basin it is conjectured that the opening of the japan sea might have started almost at this time or a little earlier the observed 87 sr 86 sr ratios range from 0 70357 to 0 70388 suggesting incorporation of some time integrated components enriched in incompatible elements such as continental crustal materials this may indicate that in the japan sea area at least the yamato basin had not developed enough to show the characteristics of typical n type morb source materials without being affected by pre existing continental crustal materials

arc deformation and marginal basin opening japan sea as a case study we discuss the opening mechanism of the japan sea in miocene time using 1 tectonic and published paleomagnetic data along the eastern margin from the north of hokkaido island to sado island 2 a mechanical model which is tested by small scale physical modeling and 3 crustal structure and bathymetric features in the japan sea which constrain our kinematic model and preopening reconstructions our main conclusions are the following the eastern margin of the japan sea was as a whole a dextral shear zone about 100 km wide this conclusion is supported by the existence of a ductile dextral shear zone in central hokkaido hidaka mountains and associated brittle deformation in western hokkaido and northeastern honshu the stress field during the opening which ended about 12 ma ago at the end of the middle miocene changes from right lateral transpression in the north to right lateral transtension in the south the western margin along the korean peninsula during the same period also was an active dextral shear zone paleomagnetic results indicate that clockwise rotations occurred in the south during the opening and counterclockwise rotations in the north we propose a model of right lateral pull apart deformation with clockwise rotations of rigid blocks in the southern transtensional domain and counterclockwise rotations in the transpressional one small scale physical models show that the clockwise rotation in transtension is possible provided that the eastern boundary pacific side is free of stress the opening stopped and compression subsequently began about 12 ma ago finally we show that the dextral shear which is distributed over the whole japan sea area is accommodated by n s trending right lateral faults and rotation of blocks located between these right lateral faults

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

simulation of tensile crack generation by three dimensional dynamic shear rupture propagation during an earthquake 1 as there is no evidence that cracks are created directly in modes ii and iii shear cracks probably occur only along a weakness plane as in a preexisting fault mode i fracture therefore may be an important factor in crack formation during shallow earthquakes a three dimensional shear dynamic rupture process was simulated on the assumption that shear slip occurs only in a preexisting fault and the possibility of introducing new internal cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method dem was used to solve this problem because it can introduce internal tensile cracks the simple slip weakening model was used as the friction law on the preexisting fault for shear rupture propagation for new tensile cracks fracture follows classical griffith theory when the critical value for tensile fracture surface energy is reached the proposed model was used to simulate the rupture process of a strike slip shallow fault results show that the generation of new cracks is affected by rupture directivity in terms of the hypocenter and asperity location as well as by fault geometry with respect to the free surface cracks develop a flower like structure that surrounds the preexisting fault when the asperity is located at less than a certain depth the flower like structure that originates from the top of the fault reaches the free surface we consider that this is the mechanism for forming the flower structure near surface during a strike slip shallow earthquake

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

fracture control on type morphology and distribution of parasitic volcanic cones an example from mt etna italy abstract this paper uses a coupled morphometric and stratigraphic analysis of several tens of parasitic pyroclastic cones of the se flank of mt etna volcano italy to explain the structure of a poorly understood actively deforming zone of the volcano moreover we present a new general classification of pyroclastic cones based on the parameterisation of coeval eruption points along the same magma feeding fracture each cone has been studied in detail in order to define its stratigraphic position morphometric characteristics growth evolution in relation to fracture distribution and orientation stress field and morphology of the substratum end members of this classification are at one side a simple circular or elongated edifice that grew around a single eruption point and can be related to a magma feeding fracture constrained by a relatively high confining stress in the substratum or a low magma pressure the other end member is a multiple rifted strongly elongated cone formed along multiple eruption points of a magma feeding fracture constrained by a relatively low confining stress or a high magma pressure lithostratigraphic and historical analyses demonstrate that the cones in this area developed between 15 ka bp and historical times the most recent one in 1669 ad testifying to a high rate of lateral eruption occurrence in the area these cones show n s elongated maximum crater axes n s trending axis of the depressed points of the crater rim and southward and southeastward breaching directions while coeval cones are n s aligned these morphometric characteristics reflect the geometry of n s magma feeding fractures the area can be regarded as a transitional weakness zone between the n s rift and the releasing system represented by the transtensional trecastagni and mascalucia faults indicating an e w oriented local component of extension possibly related to the interplay between the regional timpe fault system and the eastward gravitational spreading of the volcano the azimuth of breaching is controlled by magma feeding fracture orientation and substrate morphology especially in the eastern part of the area where it is influenced by the scarps related to the timpe regional fault system but it is also sensitive to cone development

paleomagnetism of cretaceous pacific seamounts revisited the paleomagnetism of cretaceous pacific seamounts is reexamined herein techniques for nonuniform magnetic modeling are applied to determine paleomagnetic pole positions and their associated confidence limits modeling techniques are presented for reconstruction of both uniform and nonuniform components of the seamount magnetization the uniform component yields an estimate of the paleomagnetic pole position and the nonuniform component accounts for irregularities in the seamount magnetization a seminorm minimization approach constructs maximally uniform magnetizations and is used to represent seamount interiors a statistical modeling approach constructs random nonuniform magnetizations and is used to determine the confidence limits associated with each pole position mean paleopoles are calculated for groups of seamounts including their associated error bounds the mean paleopole for seven reliably dated upper cretaceous seamounts is located close to the position predicted by pacific hotspot relative motion the paleopole for five seamounts with cretaceous minimum dates is located west of the hotspotpredicted apparent polar wander path and may represent a lower cretaceous or upper jurassic pole

paleomagnetism of tertiary rocks on the korean peninsula tectonic implications for the opening of the east sea sea of japan abstract two different distributions of declinations with dual polarities are found in the tertiary rocks of the yeonil basin and yangnam basin along the yangsan fault in the southeastern part of the korean peninsula these are northward declinations in the middle miocene yeonil group and strong eastward declinations in the early miocene yangbuk group and in the eocene volcanic rocks this is interpreted by invoking 1 the yangsan fault as a dextral wrench fault system by spreading in the uleung basin of the east sea sea of japan and 2 a clockwise vertical rotation caused by the movement of the fault at around 17 3 ma just prior to the sedimentation of the yeonil group the timing of the deflection found in korea is distinguished from that in southeastern and northwestern japan at around 15 ma two stages of spreading are thus constrained in the east sea area parallel at 23 15 ma and pivotal at around 15 ma crustal thinning also occurred a reliable pole position 84 9 n 292 6 e d p d m 3 3 4 8 for the miocene about 15 ma in korea is obtained from the yeonil group

shape analysis of pacific seamounts abstract shape statistics have been compiled from 85 profiles of well surveyed pacific seamounts in the height range 140 3800 m a flat topped cone was fit to each seamount s cross sectional profile maintaining the slopes of the sides as closely as possible on each profile a basal width d b a summit width d t and a maximum height h were measured the height to basal radius ratio is h is estimated by the ratio 2hd b and flatness f by the ratio d t d b slope angle arctan e is estimated from e 2h d b d t summit height and basal radius are found to be highly correlated r 0 93 the 85 point sample mean of the height to basal radius ratio is h 0 21 0 08 implying that a seamount s summit height is typically one fifth its basal radius despite the high correlation individual points show some scatter and there may be groupings into different morphological types for example all but one of the seamounts with summit heights above 1000 m have values of h that are larger than the sample mean the 85 point sample mean of flatness is f 0 31 0 18 data points show a large scatter with values of f varying between 0 a pointy cone and 0 69 a flat topped cone a histogram representation of flatness however indicates that certain values of f may be more common than others the histogram shows a bimodal distribution with maxima occurring at values of f in the ranges 0 10 0 20 and 0 35 0 50 moreover there is some evidence that the mean flatness decreases with summit height so that the preferred shape of a large sized seamount may be a pointy cone slope angle has an 85 point sample mean of 18 6 individual values of vary between 5 and 36 in addition to having a lower than average mean flatness seamounts with heights above 2600 m also have a lower than average mean slope angle 15 to determine which variables account for most of the observed variation in the seamount shapes a multivariate principal component analysis was performed on the data using five shape variables summit height basal radius summit radius flatness and slope the analysis indicates that most of the variation is described by two variables flatness and summit height

nonuniform magnetization of seamounts a least squares approach residual total magnetic field anomalies relative to the best fitting uniform magnetization models are large and spatially coherent over three small tertiary seamounts on the cocos plate furthermore the paleomagnetic parameters determined from the uniform magnetization models in some cases disagree significantly with those predicted from models of absolute motion for the cocos plate inversion of the sea surface magnetic anomaly using a least squares procedure which allows magnetization to vary among different sections of each seamount shows clear polarity reversals in two of the seamounts studied the reversed zones constitute about 10 of the seamount volume for the third seamount the nonuniform magnetization solution more correctly determines the paleomagnetic inclination and declination for the only section of the dipolar anomaly not obscured by a magnetic lineation traversing the area the polarities indicated in the least squares solutions were confirmed by magnetic gradiometer measurements from the submersible alvin for all three seamounts the paleomagnetic latitudes and or rotation angles in the nonuniform magnetization solutions changed appreciably by as much as 20 to agree better with plate motion models the nonuniform magnetization models reveal that growth rates for such volcanoes approach 1000 km3 ma with the final phase of volcanism consisting of summit as opposed to flank eruptions the largest of the three volcanoes formed off ridge on lithosphere at least 0 5 ma old and may have remained active for 1 ma hydrothermal activity apparently persists at least 0 7 ma after the last major phase of volcanism

geology of tok island korea eruptive and depositional processes of a shoaling to emergent island volcano detailed mapping of tok island located in the middle of the east sea sea of japan along with lithofacies analysis and k ar age determinations reveal that the island is of early to late pliocene age and comprises eight rock units trachyte i unit p i unit p ii trachyandesite 2 7 0 1 ma unit p iii trachyte ii 2 7 0 1 ma trachyte iii 2 5 0 1 ma and dikes in ascending stratigraphic order trachyte i is a mixture of coherent trachytic lavas and breccias that are interpreted to be subaqueous lavas and related hyaloclastites unit p i comprises massive and inversely graded basaltic breccias which resulted from subaerial gain flows and subaqueous debris flows a basalt clast from the unit derived from below trachyte i has an age of 4 6 0 4 ma unit p ii is composed of graded and stratified lapilli tuffs with the characteristics of proximal pyroclastic surge deposits the trachyandesite is a massive subaerial lava ponded in a volcano tectonic depression probably a summit crater a pyroclastic sequence containing flattened scoria clasts unit p iii and a small volume subaerial lava trachyte ii occur above the trachyandesite suggesting resumption of pyroclastic activity and lava effusion afterwards shallow intrusion of magma occurred producing trachyte iii and trachyte dikes

effects of the hanging wall and footwall on ground motions recorded during the northridge earthquake abstract systematic differences in ground motion on the hanging wall and footwall during the northridge earthquake are evaluated using empirical data an empirical model for the hanging wall effect is developed for the northridge earthquake this empirical model results in up to a 50 increase in peak horizontal accelerations on the hanging wall over the distance range of 10 to 20 km relative to the median attenuation for the northridge earthquake in contrast the peak accelerations on the footwall are not significantly different from the median attenuation over this distance range recordings from other reverse events show a similar trend of an increase in the peak accelerations on the hanging wall indicating that this systematic difference in hanging wall peak accelerations is likely to be observed in future reverse events

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

origin and causes of complex magnetic anomalies of dokdo and neighboring guyots abstract to identify the causes of complex magnetic anomalies on the three guyots located in the northeastern part of the ulleung basin east sea a linear least squares inversion method was implemented modeling under the assumption that the guyots are uniformly magnetized did not yield reliable results however an inhomogeneously magnetized model shows relatively high goodness of fit parameters and low residual magnetic anomalies indicating that these guyots are considerably nonuniformly magnetized our modeling results show that all three guyots show similar magnetic patterns magnetic anomalies north of guyots have different magnetic polarities at similar depths in the south indicating that these magnetic anomalies were formed at different times these results suggest that relatively short wavelengths and complicated magnetic anomalies in the study area are the compound result of different magnetic polarities paleomagnetic analysis on trachyandesite lavas and pyroclastic breccia indicates a thermo chemical remagnetization activity after reunion subchron 2 138 2 122 ma this result also suggests that remagnetization contributes to the creation of complex magnetic anomalies to some extent as well in addition the upward continuation results up to 1500 m using a fft routine show high positive magnetic anomalies with a linearly segmented shape at the base of guyots these linear and positive magnetic anomalies are interpreted as volcanic eruptions along fissures because mafic lava should have much higher magnetic anomalies compared to continental crust where guyots are located therefore we interpret that the complex magnetic anomalies distributed in the study area are due to polarity reversals occurring at least twice and were formed during the formation of the current guyots as volcanic eruptions derived from fissures

a new biem for rupture dynamics in half space and its application to the 2008 iwate miyagi nairiku earthquake summary we developed a code for dynamic rupture propagation on arbitrarily shaped faults embedded in half space using boundary integral equation method biem it is based on an existing code for the full space case in which virtual free surface elements were introduced computations in half space are definitely necessary for the modelling of shallow dipping fault ruptures first we describe the implementation and conduct some validation tests that demonstrate the accuracy of the code the validation tests are carried out by comparing the biem results both with the analytical static solution and with the seismic wavefield obtained by a discrete wavenumber method then we apply the code to the study of the 2008 iwate miyagi japan earthquake mw 6 9 rupture dynamics the average stress drop was estimated to be rather large 16 mpa in the asperity area while the average strength excess was 5 mpa the average fracture energy inside the asperity was found to be 36 mjm 2 finally the free surface effect examination showed that the stress drop and the fracture energy were overestimated at shallow depth in the full space computation

ferrihydrite and allophane in four andepts from hawaii and implications for their classification abstract the mineralogy and composition of the waimea kukaiau akaka and hilo soils on the island of hawaii were studied using methods which included moessbauer spectroscopy and chemical dissolution the hilo soil which experiences 3000 mm year rainfall and the akaka soil 3800 mm year rainfall both contain large amounts about 25 of iron oxides of short range order together with other iron oxides gibbsite and allophane the iron oxides of short range order have characteristics similar to those of the reactive mineral ferrihydrite which is known to occur in a wide range of soils these characteristics however in two respects x ray diffraction and acid oxalate solubility do not rule out the presence or admixture of the much less known feroxyhite another closely related iron oxide of short range order most samples from these two soils dry irreversibly to give hard aggregates a property probably related to the presence of the iron oxides of shortrange order both the hilo and the akaka soils are classified as hydrandepts in the current usda soil taxonomy in the new proposed order of andisols these two soils would become hydrudands it is desirable to recognise the presence of short range order iron oxides in these soils the kukaiau soil currently classified as a dystrandept which occurs in a lower rainfall zone 1500 mm year contains about 25 allophane and lesser amounts of ferrihydrite other iron oxides and gibbsite the waimea soil occurs in the lowest rainfall zone 1000 mm year and the dominant mineral is halloysite but some allophane ferrihydrite and hematite are also present this soil is currently classified as a eutrandept under the andisol proposal the kukaiau and waimea soils would be a hapludand and a haplustand respectively quartz mica and other layer silicates were present in all four of the soils suggesting that there have been additions of eolian material

magnetic surveys of iceland abstract data from a 1968 1980 aeromagnetic survey of iceland and a 1972 1973 marine magnetic survey of a part of the shelf around iceland have been digitized and upgraded additional aeromagnetic survey lines were flown in 1985 1986 after appropriate low pass filtering and regridding a new multicolor map of geomagnetic field intensity anomalies over the island and its surroundings was produced the main features of the anomaly field are of two types the first 1 a comprises broad lineations subparallel to currently active or extinct spreading zones these are believed to be mostly due to tilled basalt lava flows of alternating remanence polarity in quaternary regions other extrusives of subglacial origin also contribute to the lineations the second 2 b comprises localized anomalies of the order of 10 km or less at individual volcan c centers we describe some of these features in terms of current knowledge of the age structure and magnetic properties of the uppermost crust in iceland

quantification of hanging wall effects on ground motion some insights from the 1999 chi chi earthquake accelerometric records of the chi chi earthquake from sites on the hanging wall exhibit larger acceleration than those from the footwall based on ground accelerations recorded at 79 near field stations 10 hanging wall stations and 69 footwall stations respectively and precise mapping of fault rupture traces the hanging wall footwall effects of the chi chi earthquake have been fully studied we show that the hanging wall effects cannot be simply accounted for by a proper choice of distance metric the closest distance to the rupture plane d rup is then selected to develop an empirical ground motion model by using the data collected during the mainshock of the chi chi earthquake that struck taiwan with the exception of some sites immediately next to the rupture traces d rup 5 km the acceleration residuals between this empirical model and the recorded data at the footwall stations are close to zero for stations in the distance range from 5 to 50 km on the other hand the average acceleration amplification on the hanging wall is equal to the natural logarithmic values of 0 64 0 4 for all hanging wall sites within 20 km of d rup the hanging wall footwall effects have also been evaluated for several response spectral periods it is observed that both the horizontal and vertical components of spectral acceleration are apparently amplified for sites on the hanging wall at a distance from 5 to 20 km for spectral periods 0 02 to 0 5 sec whereas the vertical component has less amplification than the horizontal in all the spectral periods considered the horizontal component of spectral acceleration at the hanging wall sites also shows a larger value for the long period motion relative to the footwall for periods larger than 1 0 sec the hanging wall effects are relatively constant at low frequencies as the distance extends to about 20 km this observation cannot be explained by the simplified empirical model rather it suggests that waves trapped in the hanging wall wedge may have been involved

wave planation surfaces in the mid western east sea sea of japan indicators of subsidence history and paleogeographic evolution of back arc basin abstract this study focuses on revealing the origin of deep marine wave planation surfaces and its geomorphic and tectonic implications for the back arc evolution based on multi channel seismic reflection profiles acquired from the mid western east sea sea of japan on seismic reflection profiles the wave planation surfaces are recognized as continuous and high amplitude single reflectors outlining the flattened top of submarine terraces or isolated topographic highs the wave planation surfaces are classified into four types depending on the geomorphic characteristics and origins of substratal landmasses i e continental margin terrace type 1 rifted continental fragment type 2 volcanic edifices type 3 and uplifted sedimentary successions type 4 which have common origin of wave erosion near the sea level but different subsidence history the mean subsidence rate of wave planated substratum is calculated by dividing the maximum depth of a wave planation surface below modified datum sea level d e by the time elapsed since the onset of subsidence t information of local subsidence history enables reconstruction of paleogeographic evolution of mid western east sea during the neogene quaternary time 1 incipient continental rifting and onset of marine incursion ca 23 18 ma 2 progressive continental rifting and onset of wave planation ca 18 11 ma 3 final eruption of post rift volcanoes ca 11 ma 4 uplifting of shelf margin banks and onset of the pliocene holocene volcanic activities ca 11 2 5 ma 5 change in the locus of volcanic eruption and cessation of contractile uplifting in the basin margin ca 2 5 0 ma

generation of new cracks accompanied by the dynamic shear rupture propagation of the 2000 tottori japan earthquake the 2000 tottori japan earthquake caused fracture zones of surface rupture at some places away from the trace of the main causative fault in order to explain this observation the 3d dynamic rupture process of the 2000 tottori japan earthquake was simulated the attractive feature of the problem under consideration is the possibility of introducing internal new cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method was used to solve this problem because it can introduce internal tensile cracks for the shear rupture propagation the simple slip weakening model was used as a friction law on the fault the new tensile cracks occur following the classical griffith theory when the critical value of tensile fracture surface energy has been reached the first step to solve the problem was the estimation of the dynamic parameters such as stress drop strength excess and critical slip which were recov ered from the results of waveform inversion in the second step a shear dynamic rupture process was simulated assuming that shear slip occurs only on the pre existing fault and the tensile stress concentration resulting from shear slip causes the new cracks that propagate away from the pre existing fault the results which are consistent with the observations show a free surface rupture caused by the new cracks and the development of a flowerlike structure springing from the borders of the pre existing fault and main asperity

reunion hotspot magma chemistry over the past 65 m y results from leg 115 of the ocean drilling program leg 115 of the ocean drilling program recovered basalts from four locations along the hotspot track that leads from the deccan flood basalts in india to reunion island in the western indian ocean sites 706 707 713 and 715 the drilled basalts range in age from 35 ma site 706 to 64 ma site 707 and including the deccan basalts 66 to 68 ma mauritius island 0 2 to 8 ma and reunion island 0 to 2 ma seven sites are provided for sampling the volcanic record of the 5 000 km long hotspot track chemical and age comparisons indicate that site 707 lavas correlate with basalt units near the top of the deccan flood basalt sequence the lavas of site 715 55 to 60 ma are most similar to the islands of mauritius and reunion site 713 basalts 48 ma are similar to the earliest lavas of the deccan province and site 706 basalts are intermediate in chemistry between those of central indian spreading ridge basalts and reunion differences in lava compositions along the hotspot track can be related to variable mixing of plume and asthenospheric mantle depending on the changing position of spreading ridge segments and the hotspot during the opening of the indian more ocean alternatively time dependent changes in the composition of hotspot melts may be due to a decrease in partial melting of a heterogeneous plume or to intrinsic changes in the composition of material supplied by the plume less

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

density and size distribution of seamounts in the eastern pacific inferred from wide beam sounding data theoretical expressions relating the distribution of apparent seamount heights per unit length of ship track to the distribution of actual seamount heights per unit area of seafloor are derived for both narrow beam and wide beam echo sounders the shapes of seamounts are approximated as truncated right circular cones of constant slope e height to radius ratio and flatness f i e a seamount of basal radius r has a height h r a flat top of radius fr and a slope angle of arctan e the set of all seamounts in a given physiographic province is assumed to be a poissonian ensemble specified by a function v r the average number of seamounts per unit area for which r r a simple choice for the size distribution of seamounts and one shown to be consistent with data in the eastern pacific is to specify that it decays exponentially with r v r vo exp r in the case of a profile of length l taken in water of depth d with a wide beam echo sounder half beam width the shallow slope deep water approximation e 1 e d yields that the expected number of seamounts with apparent heights h h is n h l 2 1 ed 2 fh lv0e h we apply this sampling theory to apparent height data measured from 44 020 km of wide beam profiles on pacific crust of post mesozoic age although the spatial distribution of seamounts in the eastern pacific is certainly not poissonian the abundance statistics do not involve spatial correlations and we show they are robust with respect to deviations from the poisson model provided the statistics are interpreted as averages over the area actually sampled by the track lines the observed falloff of apparent heights in the eastern pacific is very nearly exponential justifying our use of an exponential model of seamount size distribution the shape parameters are estimated from multibeam surveys of pacific seamounts an analysis of 30 features in the height range 200 4000 m yields 0 21 0 011 and f 0 21 0 028 using these parameters we obtain vo 4 0 1 1 10 9 m 2 and 6 3 0 8 10 4 m 1 these values imply that per 106 km2 in the eastern pacific there are 1600 400 seamounts with summit heights greater than 300 m and 200 60 greater than 1000 m integrated over the entire size distribution seamounts occupy about 6 of the seafloor area and constitute about 0 4 of the oceanic crustal volume our estimates of seamount abundance are appreciably greater than those of most other authors a discrepancy we attribute primarily to the sampling bias of previous studies which generally used uncorrected map counts this hypothesis is corroborated by a comparison of our statistics with map count data for seamounts of heights exceeding 2000 m compiled for the eastern central pacific from the scripps charts above 3000 m the map counts are consistent with the predictions of the exponential model but below this height they are biased to low values

amount of clockwise rotation of southwest japan fan shape opening of the southwestern part of the japan sea abstract paleomagnetic measurements have been carried out on welded tuffs ranging in age between 58 ma and 112 ma from yamaguchi and go river areas in the central part of southwest japan the new data together with those of younger igneous rocks published previously define the change of paleomagnetic field direction during the late mesozoic cenozoic period for southwest japan the paleomagnetic direction from this area has pointed 56 3 clockwise from the expected field direction estimated from apwp apparent polar wandering path of the whole of eurasia during the period between 100 and 20 ma in comparison with the expected one from the eastern margin of eurasia korea china siberia the cretaceous field direction of southwest japan shows the clockwise deflection by 44 49 these results establish that while the eastern margin of eurasia including southwest japan was rotated more or less with respect to the main part of eurasia during last 100 ma southwest japan was rotated clockwise through more than 40 with respect to the eastern margin of eurasia since 20 ma the large amount of rotation for southwest japan implies that it is rotated by an opening of the southwestern part of the japan sea which widens northeastward fan shape opening the tectonic feature of southwest japan and the japan sea is analogous to that of corso sardinia and the ligurian sea in the mediterranean indicating that the fan shape opening is a specific feature of the rifting of the continental sliver at the continental rim

a time slice approach to the history of cenozoic sedimentation in the indian ocean abstract results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which represent snap shots of the changing patterns of sediment accumulation in the indian ocean through the cenozoic the maps clearly delineate the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeography tectonics paleocirculation and or climate paleogene sediment accumulation rates were generally low with significant accumulation in only limited areas suggesting weak ocean circulation and stable well stratified conditions by contrast the vigorous thermohaline circulation of the neogene resulted in substantial widespread sedimentation accumulation rates were generally high and displayed a wide range of values following rapid growth of the east antarctic ice sheet in the mid miocene carbonate sedimentation has been progressively restricted to the shallow ridges and plateaus of the western indian ocean but accumulates there with locally high rates the link between tectonics and terrigenous sedimentation is exemplified by the major deep sea fans off east africa zambezi fan and india indus and bengal fans which developed in response to uplift and erosion beginning in late oligocene time in the east african rift system and the himalayas respectively although maps from only five widely spaced times are shown the methodology is such that a continuous series of maps at intervals as close as 1 m y can readily be generated ultimately the combination of such time slice maps with the results of detailed time series studies will provide a powerful tool for understanding past oceanic environments

volcanogenic sediment distributions in the indian ocean through the cretaceous and cenozoic and their paleoenvironmental implications abstract volcanogenic sediments are significant components of the cores that have been drilled over the past two decades by the deep sea drilling project dsdp and the ocean drilling program odp the spatial distribution of these sediment components were used in connection with paleogeographical reconstructions to determine the primary dispersal processes direct air fall input surface circulation or atmospheric circulation for volcanic material across the indian ocean the identification of volcanic rich intervals in cores is based on the recognition of primary and secondary authigenic components or where sediment samples have not been obtained from analysis of downhole logging results e g spectral gamma ray and whole core magnetic susceptibility the data generated from dsdp cores by vallier and kidd 1977 have been upgraded in this study to fit a new integrated timescale that has been adopted for synthesis of odp and dsdp drilling data kidd et al 1992 it is now possible to map the distributions of volcanic rich sediments on paleogeographic reconstructions at 1 ma intervals through a review of its tectonic development the timing of accumulations of volcanic components in the indian ocean can be related to rifting of continents formation of new crust at ridge crests and at hotspots and to landmass volcanism linked to subduction along the indonesian arc the kerguelen and reunion hotspots were the dominant sources of volcanogenic sediments to the indian ocean since the early cretaceous the main accumulations of volcanogenic sediments occur within the basal sequences of drillholes immediately above basement controls on the transport of volcanic components were linked to atmospheric surface and possibly deeper water circulation patterns the opening indian ocean experienced a change from westerly surface currents generated by the high latitude westerly winds during the mesozoic to a gyral circulation pattern in the cenozoic the northwest indian ocean has also experienced seasonal reversal of winds since the development of the monsoon system during the late miocene to recent these changes in the wind and water circulation patterns are reflected in the distribution patterns of volcanogenic sediments in the indian ocean the kerguelen hotspot led to the development of kerguelen plateau which was formed above sea level during the albian 110 ma and remained above sea level for the next 30 40 ma volcaniclastic material from this source was mainly distributed to the northeast in contrast the reunion hotspot has contributed volcanic material mainly to the northwest during much of its evolution volcanism related to the reunion and kerguelen hotspots has apparently influenced volcanogenic sediment distributions in the developing indian ocean basins more than the regional rates of sea floor spreading which were previously thought to exert a major control valluer and kidd 1977

paleomagnetism of line islands seamounts evidence for late cretaceous and early tertiary volcanism seamount magnetic anomaly studies have been conducted on eight volcanoes in the line islands seamount chain the magnetic anomalies of these seamounts were inverted to obtain paleomagnetic information four of these gave paleomagnetic pole positions consistent with other pacific cretaceous pole positions of these three have reliable radiometric ages ranging from 72 to 85 ma the remaining four seamounts gave geomagnetic poles that agree with other eocene early oligocene pacific paleomagnetic data and one has a reliable radiometric age of 39 ma all of the apparently eocene volcanoes occur in the central line islands between 8 n and 3 s we suggest that the eocene volcanic event was approximately coincident with the profound change in pacific plate motion recorded by the bend in the hawaiian emperor seamount chain that occurred at approximately 43 ma this volcanism may have resulted from the large change in intraplate stress accompanying the change of plate motion the change in stress might have pulled apart a zone of weakness caused by the original formation of the line islands detailed paleomagnetic modeling of the line islands seamounts was necessary to obtain good results as seven of the eight seamounts appear to be inhomogeneously magnetized to some extent despite these inhomogeneities the high goodness of fit parameters and the excellent agreement of these results with other pacific paleomagnetic data suggest that the paleopoles derived from these seamounts are reliably determined

dynamics of thrust faulting 2d lattice model particle motions in a foam rubber model of shallow angle thrust faulting show many features different from those commonly assumed in dislocation models of subduction thrusts brune 1996 as a complement to a physical foam rubber experiment we have carried out dynamic simulation using a 2d lattice numerical model the model is constructed as a triangular block sliding over a rectangular elastic block it consists of a 2d set of particles interacting with each other by nonlinear hooke s forces and obeying newton s equations of motion rough surfaces are introduced on the contact plane of the two blocks to simulate realistic friction the numerical simulations demonstrate several key features of thrust faulting including stick slip fault opening and strong breakout and shaking at the hanging wall toe the wedge shaped tip of the outcropping hanging wall block of the thrust fault all consistent with the foam rubber experiments the stick slip motion shows an approximate time and slip repeatable behavior each slip event is characterized by a self healing pulse associated with fault opening and frictional locking the rupture pulse propagates steadily along the fault when rupture reaches the toe of the fault outcrop the hanging wall breaks away from the foot wall and creates a large opening vibration of the hanging wall the peak acceleration observed at the hanging wall toe of the fault outcrop is about 3 to 4 times the peak acceleration in the center part of the fault and about 2 to 3 times the motion of the foot wall such a large increase in peak acceleration at the toe is caused mainly by multiply reflecting stress waves trapped in the wedge shaped hanging wall of the fault the strong asymmetry of the particle velocity between the hanging wall and foot wall is an important feature of the results consistent with the foam rubber model but different from standard dislocation models this dynamic result illustrates the important effects of thrust faulting geometry on fault slip and ground motion

fault dynamic rupture simulation of the hypocenter area of the thrust fault of the 1999 chi chi taiwan earthquake a 2d discrete element model was employed to simulate the rupture propagation and near source ground motion in the epicentral area of the 1999 chi chi taiwan earthquake the observations show that the hanging wall side is characterized by larger particle motions than the footwall side the simulation results reproduce the main features of the recorded ground motion and show that the particle velocity on the hanging wall side and on the footwall side are symmetric in the deeper fault region however as the crack approaches the free surface the hanging wall side is characterized by larger particle motions than the footwall side these results suggest that the difference in the particle motion on the hanging wall and on the footwall is due mainly to the asymmetric geometry of hanging wall and footwall thus the model used leads to good approximations in the vicinity of the epicenter