inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

damage to coastal villages due to the 1992 flores island earthquake tsunami a field survey of the 1992 flores island earthquake tsunami was conducted during december 29 1992 to january 5 1993 along the north coast of the eastern part of flores island we visited over 40 villages measured tsunami heights and interviewed the inhabitants it was clarified that the first wave attacked the coast within five minutes at most of the surveyed villages the crust was uplifted west of the cape of batumanuk and subsided east of it in the residential area of wuring which is located on a sand spit with ground height of 2 meters most wooden houses built on stilts collapsed and 87 people were killed even though the tsunami height reached only 3 2 meters in the two villages on babi island the tsunami swept away all wooden houses and killed 263 of 1 093 inhabitants tsunami height at riang kroko village on the northeastern end of flores island reached 26 2 meters and 137 of the 406 inhabitants were killed by the tsumani evidence of landslides was detected at a few points on the coast of hading bay and the huge tsunami was probably formed by earthquake induced landslides the relationship between tsunami height and mortality was checked for seven villages the efficiencies of trees arranged in front of coastal villages and coral reefs in dissipating the tsunami energy are discussed

tsunami generation of the 1993 hokkaido nansei oki earthquake heterogeneous fault motion of the 1993 hokkaido nansei oki earthquake is studied by using seismic geodetic and tsunami data and the tsunami generation from the fault model is examined seismological analyses indicate that the focal mechanism of the first 10 s when about a third of the total moment was released is different from the overall focal mechanism a joint inversion of geodetic data on okushiri island and the tide gauge records in japan and korea indicates that the largest slip about 6 m occurred in a small area just south of the epicenter this corresponds to the initial rupture on a fault plane dipping shallowly to the west the slip on the northernmost subfault which is dipping to the east is about 2 m while the slips on the southern subfaults which are steeply dipping to the west are more than 3 m tsunami heights around okushiri island are calculated from the heterogeneous fault model using different grid sizes computation on the smaller grids produces larger tsunami heights that are closer to the observed tsunami runup heights tsunami propagation in the nearly closed japan sea is examined as the free oscillation of the japan sea the excitation of the free oscillation by this earthquake is smaller than that by the 1964 niigata or 1983 japan sea earthquake

some aspects of energy balance and tsunami generation by earthquakes and landslides tsunamis are generated by displacement or motion of large volumes of water while there are several documented cases of tsunami generation by volcanic eruptions and landslides most observed tsunamis are attributed to earthquakes kinematic models of tsunami generation by earthquakes where specified fault size and slip determine seafloor and sea surface vertical motion quantitatively explain far field tsunami wave records on the other hand submarine landslides in subduction zones and other tectonic settings can generate large tsunamis that are hazardous along near source coasts furthermore the ongoing exploration of the oceans has found evidence for large paleo landslides in many places not just subduction zones thus we want to know the relative contribution of faulting and landslides to tsunami generation for earthquakes only a small fraction of the minimum earthquake energy less than 1 for typical parameter choices for shallow underthrusting earthquakes can be converted into tsunami wave energy yet this is enough energy to generate terrible tsunamis for submarine landslides tsunami wave generation and landslide motion interact in a dynamic coupling the dynamic problem of a 2 d translational slider block on a constant angle slope can be solved using a green s function approach for the wave transients the key result is that the largest waves are generated when the ratio of initial water depth above the block to downslope vertical drop of the block h 0 w sin is less than 1 the conversion factor of gravitational energy into tsunami wave energy varies from 0 for a slow velocity slide in deep water to about 50 for a fast velocity slide in shallow water and a motion abruptly truncated to compare maximum tsunami wave amplitudes in the source region great earthquakes produce amplitudes of a few meters at a wavelength fixed by the fault width of 100 km or so for submarine landslides tsunami wave heights as measured by b block height are small for most of the parameter regime however for low initial dynamic friction and values of h 0 w sin less than 1 tsunami wave heights in the downslope and upslope directions reach b and b 4 respectively wavelengths of these large waves scale with block width for significant submarine slides the value of b can range from meters up to the kilometer scale thus the extreme case of efficient tsunami generation by landslides produces dramatic hazards scenarios

breakage and shear behaviour of intermittent rock joints abstract the breakage and shear behaviour of intermittent rock joints have been investigated in a series of direct shear tests with a new shear device specifically designed for this purpose the tests have been performed on specimens of rock like material or hard rock respectively incorporating idealized non persistent joints made up of a number of short cracks in an en echelon arrangement along the central shear axis the shear behaviour of such a joint constellation has been found to be composed of different phases the first phase of shearing is that of the actual rupture initiated by the formation of wing cracks starting from the existing cracks and growing into the material bridges and concluded by the generation of additional new fractures connecting the initial cracks in the zone between the wing cracks the second phase of shearing is characterized by friction processes and volume increase in the then continuous shear zone finally the third phase of shearing reached after large shear displacements is determined by sliding processes inside the strongly fractured shear zone in a large number of shear tests the geometrical parameters of the discontinuous joints as well as the loading conditions have been found to influence the activated shear resistance in each phase of shearing to a noticeably different extent the orientation of the initial cracks and the normal stress however have been identified as the most influential parameters depending on the test conditions an initially discontinuous rock joint can activate the largest shear resistance not just before rupture but in one of the two subsequent phases of shearing as well the mechanisms which govern the different shear phases could be identified as 1 tensile rupturing 2 rolling and sliding friction of dilatant joint zones and 3 sliding within the joint filling composed of brecciated material

role of weak flaws in nucleation of shear zones an experimental and theoretical study this paper investigates the role of inherent weak flaws in the formation of plastic zones in deforming solids to understand the development of geological shear zones physical experiments were carried out on polymethylmethaacrylate pmma models containing single and multiple circular cylindrical flaws under compression maintaining plane strain condition models with single flaws show development of shear zones against a flaw in the form of conjugate sets with an average dihedral angle of 84 and oriented at an angle of 42 to the bulk compression direction the shear zones are generally tapered with increasing width away from the flaw in models with multiple flaws shear zones nucleated against individual flaws which propagated and coalesced with one another forming through going band like shear zones with inclination varying from 35 to 53 with the bulk compression direction with an increase in flaw concentration the through going shear zones defined persistent conjugate sets we applied the plane theory of elasticity for numerical simulations of ductile shear zones under the influence of a single circular weak flaw the pattern of shear zones yielded from numerical runs grossly matches with those observed in physical model experiments theoretical analysis demonstrates that the presence of a flaw promotes nucleation of shear zones at a bulk stress below the yield strength of matrix this critical stress is a non linear function of the flaw matrix competence contrast and decreases asymptotically with increasing competence contrast

a new type of numerical experiment on the spatial and temporal patterns of localization of deformation in a material with a coupling of grain size and rheology abstract the patterns of localization of deformation in recrystallising materials are investigated via a series of two dimensional grain scale numerical simulations these simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes the simulations are able to predict the mechanical microstructural and strain evolution of the polycrystals to moderate strain and allow us to examine the nature of the time dependent feedback between mechanical and microstructural behavior it was found that significant strain localization occurred only when the grain size dependence of the viscosity was non linear and was greatly enhanced by the activity of the grain size modifying processes the intensity and location of the zone of strain localization varied spatially and temporally and displayed two length and time scales with the result that the finite strain state showed a much broader and hence less intense zone of localized deformation than the instantaneous state

on the influence of fault bends on the growth of sub rayleigh and intersonic dynamic shear ruptures earthquake ruptures are modeled as dynamically propagating shear cracks with the aim of gaining insight into the physical mechanisms governing their arrest or otherwise the often observed variations in rupture speeds fault bends have been proposed as being the main cause for these variations following this line of reasoning the existence of deviations from fault planarity is chosen as the main focus of this study asymmetric impact is used to generate shear loading and to propagate dynamic mode ii cracks along the bonded interfaces of two otherwise identical homogeneous constituents secondary paths inclined at various angles are also introduced to represent fault bends or kinks the experiments show that certain fault bend inclinations are favored as alternate paths for rupture continuation whereas others suppress further motion of the incoming rupture the asymptotic elastodynamic stress fields at the tip of the growing rupture are used to develop two criteria one energetic and one stress based for rupture propagation or arrest at the kinked interfaces these criteria correlate very well with the experimental results since most field evidence suggests that the average rupture speeds during crustal earthquakes are sub rayleigh this work first focuses on incoming rupture speeds that are just below the rayleigh wave speed reports of intersonic crustal fault rupture speeds having surfaced recently experiments and analyses are also performed within that speed regime

nucleation of ductile shear zones on dilatant fractures small shear zones in granitic rocks of the sierra nevada california and near roses rosas northeast spain display features which indicate that dilatant fracturing preceded the localization of ductile shear deformation many zones have sharp nearly planar boundaries between their highly deformed interiors and the undeformed wall rock the roses shear zones narrow continuously to hairline fractures at their ends mineralized microcracks oriented parallel to the shear zones cluster near the zone boundaries and are interpreted as relicts of the earlier fracturing episode dynamic recrystallization of minerals filling these microcracks demonstrates that fracturing predated the ductile deformation gradients in ductile strain suggest that deformation spread laterally into the wall rocks after nucleation of the shear zones we suggest that cracks enhance the wall rock ductility by increasing local fluid fluxes thereby promoting chemical alteration and or hydrolytic weakening

the geodetic signature of the earthquake cycle at subduction zones model constraints on the deep processes recent megathrust events in tohoku japan maule chile and sumatra indonesia were well recorded much has been learned about the dominant physical processes in megathrust zones partial locking of the plate interface detailed coseismic slip relocking afterslip viscoelastic mantle relaxation and interseismic loading these and older observations show complex spatial and temporal patterns in crustal deformation and displacement and significant differences among different margins a key question is whether these differences reflect variations in the underlying processes like differences in locking or the margin geometry or whether they are a consequence of the stage in the earthquake cycle of the margin quantitative models can connect these plate boundary processes to surficial and far field observations we use relatively simple cyclic geodynamic models to isolate the first order geodetic signature of the megathrust cycle coseismic and subsequent slip on the subduction interface is dynamically and consistently driven a review of global preseismic coseismic and postseismic geodetic observations and of their fit to the model predictions indicates that similar physical processes are active at different margins most of the observed variability between the individual margins appears to be controlled by their different stages in the earthquake cycle the modeling results also provide a possible explanation for observations of tensile faulting aftershocks and tensile cracking of the overriding plate which are puzzling in the context of convergence compression from the inversion of our synthetic gnss velocities we find that geodetic observations may incorrectly suggest weak locking of some margins for example the west aleutian margin

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

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

linear and nonlinear computations of the 1992 nicaragua earthquake tsunami numerical computations of tsunamis are made for the 1992 nicaragua earthquake using different governing equations bottom frictional values and bathymetry data the results are compared with each other as well as with the observations both tide gauge records and runup heights comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a small grid size is more effective than to include nonlinear terms in tsunami computation linear computation overestimates the amplitude for the later phase than the first arrival particularly when the amplitude becomes large the computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights the average ratio or the amplification factor is estimated to be 3 in the present case when the grid size of 1 minute is used the factor however may depend on the grid size for the computation

deformation localization at the tips of shear fractures an analytical approach abstract mechanical heterogeneities are important features in rocks which trigger deformation localization in brittle ductile or brittle ductile modes during deformation in a recent study misra et al 2009 have investigated these different processes of deformation localization at the tips of pre existing planar shear fractures the authors identified four mechanisms of deformation ranging from brittle to ductile operating at the crack tips mechanism a brittle deformation is the dominant process that forms a pair of long tensile fractures at the two crack tips mechanism b nature of deformation is mixed where the tensile fractures grow to a finite length with incipient plastic deformation at the tips mechanism c mixed mode deformation characterized by dominating macro scale shear bands and short opened out tensile fissures mechanism d localization of plastic bands in the form of a pair of shear bands at each tip without any discernible brittle fracturing the transition of the mechanisms is a function of orientation of the crack with respect to the bulk compression direction and the finite length l of the crack the aim of this study is to present a theoretical analysis to account for the variability of deformation localization in the vicinity of pre existing shear cracks considering an elastic plastic rheological model the analysis calculates the principal tensile stress 1 and the second stress invariant i 2 of the stress field at the fracture tip to explain the transition from mechanism a tensile fracturing to mechanism d ductile strain the results show that 1 at the fracture tip increases non linearly with increasing and a r aspect ratio of the shear crack and assumes a large value when 50 o promoting tensile fractures on the other hand i 2 is a maximum at

modeling the seismic source and tsunami generation of the december 12 1992 flores island indonesia earthquake on december 12 1992 a large earthquake m s 7 5 occurred just north of flores island indonesia which along with the tsunami it generated killed more than 2 000 people in this study teleseismicp andsh waves as well aspp waves from distances up to 123 are inverted for the orientations and time histories of multiple point sources by repeating the inversion for reasonable values of depth time separation and spatial separation a 2 fault model is developed next the vertical deformation of the seafloor is estimated from this fault model using a detailed bathymetric model linear and nonlinear tsunami propagation models are tested the data consist of a single tide gauge record at palopo 650 km to the north as well as tsunami runup height measurements from flores island and nearby islands assuming a tsunami runup amplification factor of two the two fault model explains the tide gauge record and the tsunami runup heights on most of flores island it cannot however explain the large tsunami runup heights observed near leworahang on hading bay and riangkroko on the northeast peninsula massive coastal slumping was observed at both of these locations a final model which in addition to the two faults includes point sources of large vertical displacement at these two locations explains the observations quite well

abnormal tsunamis caused by the june 13 1984 torishima japan earthquake an earthquake with an m s 5 6 m b 5 5 which occurred near torishima japan on june 13 1984 generated abnormally large tsunamis tsunami magnitude m t 7 3 for its relatively small earthquake magnitude the maximum amplitude of the tsunamis is not a simple function of distance as the magnitude formula implies in order to quantify the abnormal tsunamis we modeled the tsunami source using a finite difference computation on the actual bathymetry the source of these abnormal tsunamis is modeled as a water surface displacement with a radius of 12 km and maximum water height of 13 cm the displaced water volume is 4 10 13 cm 3 and the potential energy is calculated as 2 10 17 ergs if this water displacement is due to a fault motion at 5 km depth a moment magnitude m w is estimated to be 6 3 this value is larger than m w estimated from seismic waves by 0 7 but smaller than m t by 1 0 the former difference suggests that the earthquake source is very different from an ordinary faulting if we assume the source is a horizontally lying tensile crack at shallow depth about 2 km that explains both the water surface displacement and the seismic moment tensor the tensile crack is interpreted as an injection of material as suggested by a seismological study the discrepancy between m w and m t indicates that the propagation path is responsible for the observed large tsunamis the numerical computation shows a focusing of energy during the propagation of the tsunami along the shallow izu bonin ridge system thus the abnormally large tsunamis from the torishima earthquake are a result of both source and path effects

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

very broadband seismic analysis of the 1992 flores indonesia earthquake mw 7 9 the december 12 1992 flores island earthquake m w 7 9 which caused a destructive tsunami is located in the back arc of the transition zone between the sunda and banda arcs a region in active collision with the australian continental margin we study the earthquake using four seismological techniques spanning a period range of 1 1000 s and infer that the flores event may be characterized as a shallow back arc thrust with fault plane strike 70 30 dip 28 10 and rake 80 to 140 linear trade off with strike a rupture consisting of three discrete pulses with a total duration of 70 s centroid time 26 3 s and an estimated moment release between 7 5x10 20 and 8 0x10 20 n m from the slip vector we infer that compressional forces play an important role in the deformation mechanism of the back arc north of flores island body waves constrain the hypocentral depth to be 16 km with rupture mainly propagating updip to shallow depth and bilaterally along strike with most subevents located toward the northeast evidence for rupture directivity from surface wave deconvolutions is inconclusive but the overall source function is consistent with body wave results our body wave finite fault model is in rough agreement with two models proposed to explain tsunami run up observations normal mode modeling of w phase observations at periods longer than 70 s shows that slow slip is negligible from this and the slip distribution determined from the body wave analysis we infer that the seismic source is an unlikely candidate to explain anomalously high tsunami run ups measured on northeastern flores island

moment tensor inversion of complex earthquakes summary moment tensor inversion methods can be applied with success in the determination of source properties of simple earthquakes however these methods utilize the assumption of a point source which is inadequate for modelling many complicated shallow earthquakes for complex earthquakes an inversion using finite faulting models is desirable but the number of parameters involved requires that a good starting model be found or that independent constraints be placed on some of the parameters a method is presented for low pass filtering both the data and green s functions passing only signals with wavelengths greater than the dimension of the entire fault the filter tends to smooth complications in the waveforms and allows application of the point source moment tensor inversion this method is applied to body waves from the 1978 thessaloniki greece earthquake the 1971 san fernando earthquake and to a multiple point source synthetic model of the san fernando event for the thessaloniki event although a multiple source mechanism has been suggested inversion results before and after filtering were essentially identical indicating that a point source mechanism is sufficient in modelling the long period teleseismic body waves in the case of the san fernando earthquake the point source green s functions were incapable of simultaneously modelling the p and sh waves inversion of p waves alone resulted in extreme parameter resolution problems but allowed constraint in one axis of the moment tensor and suggested an overall source time function inversion of a synthetic san fernando data set yielded similar results but allowed an investigation of the shortcomings of the method under controlled circumstances although the results may require substantial interpretation the method presented represents a simple first step in the analysis of complex earthquakes

finite element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting the development of shear zones initiating on random weaker initial perturbations is modelled numerically for low deborah number viscoelastic materials considering the influence of effective viscosity contrast power law rheology strain softening and different imposed bulk deformation geometries ranging from pure to simple shear conjugate shear zones initiate at 90 to one another and rotate with increasing bulk deformation the basic pattern not being markedly influenced by the vorticity of imposed deformation the rate of propagation of individual conjugate shear zones is little affected by increased effective viscosity contrast between matrix and inclusion but is promoted by power law rheology however the most marked effect is observed for strain softening behaviour where rapid propagation produces straighter and narrower shear zones the localisation of strain is reflected in a correspondingly heterogeneous stress distribution in particular mean stress or pressure is higher in the extending near planar weaker zones of localised shear melting of gneissic or pelitic compositions is pressure dependent with free water present increased pressure promotes melting whereas the opposite is true for water absent melting for water present conditions a positive feedback could develop between localised shearing increased pressure and partial melting this is potentially more effective in concentrating melt in shear zones than shear heating where melt related softening has a negative feedback effect

melt bearing shear zones analogue experiments and comparison with examples from southern madagascar abstract analogue model experiments were conducted to investigate the influence of irregularly distributed weak sites in localising strain as an aid to understanding shear zone development in partially molten rocks the very weak inclusions consisted of vaseline in a homogeneous matrix of paraffin wax which has a power law viscous rheology boundary conditions were those of pure shear at constant natural strain rate and confining stress 3 the inclusions were initially perfect cylinders with axes parallel to the intermediate bulk strain axis y conjugate shear zones nucleate on the inclusions and link up to form an anastomosing pattern of high strain zones of concentrated shear surrounding much more weakly deformed pods of near coaxial strain the zones initiate at angles near 45 to the bulk shortening axis z but stretch and rotate towards the x axis with increasing bulk strain all inclusions nucleate shear zones so that with increasing development of the anastomosing pattern weak material occurs only within the high strain zones the restriction of migmatite leucosomes to shear zones in natural examples could also reflect a corresponding control of melt on the sites of shear zone nucleation rather than implying accumulation from the surrounding wall rock the model geometry is very similar to that observed in small scale shear zones in migmatites of southern madagascar elongate zones rich in weak inclusions originally either perpendicular or at 45 to the z axis were also modelled for direct comparison with the regional scale geometry of the pan african high grade shear zones on madagascar

shallow subduction zone earthquakes and their tsunamigenic potential summary we have examined the source spectra of all shallow subduction zone earthquakes from 1992 to 1996 with moment magnitude 7 0 or greater as well as some other interesting events in the period range 1 20 s by computing moment rate functions of teleseismic p waves after comparing the source spectral characteristics of tsunami earthquakes earthquakes that are followed by tsunamis greater than would be expected from their moment magnitude with regular events we identified a subclass of this group slow tsunami earthquakes this subclass consists of the 1992 nicaragua the 1994 java and the february 1996 peru earthquakes we found that these events have an anomalously low energy release in the 1 20 s frequency band with respect to their moment magnitude although their spectral drop ov is comparable to those of the other earthquakes from an investigation of the centroid and body wave locations it appears that most earthquakes in this study conformed to a simple model in which the earthquake nucleates in a zone of compacted and dehydrated sediments and ruptures up dip until the stable sliding friction regime of unconsolidated sediments stops the propagation sedimentstarved trenches e g near jalisco can produce very shallow slip because the fault material supports unstable sliding the slow tsunami earthquakes also ruptured up dip however their centroid is located unusually close to the trench axis the subduction zones in which these events occurred all have a small accretionary prism and a thin layer of subducting sediment ocean surveys show that in these regions the ocean floor close to the trench is highly faulted we suggest that the horst and graben structure of a rough subducting oceanic plate will cause contact zones with the overriding plate making shallow earthquake nucleation and up dip propagation to the ocean floor possible the rupture partly propagates in sediments making the earthquake source process slow two factors have to be considered in the high tsunami generating potential of these events first the slip propagates to shallow depths in low rigidity material causing great deformation and displacement of a large volume of water second the measured seismic moment may not represent the true earthquake displacement because the elastic constants of the source region are not taken into account in the standard cmt determination

backarc thrust faulting and tectonic uplift along the caribbean sea coast during the april 22 1991 costa rica earthquake surface deformation and a tsunami accompanied the destructive april 22 1991 costa rica panama earthquake ms 7 5 along a 135 km stretch of caribbean coast coseismic uplift was measured between the lower and upper limits of sessile intertidal organisms stranded on coral reefs the preearthquake and postearthquake high tide levels located from driftwood lines on beaches and the preearthquake and postearthquake tide levels as pointed out by local residents the nature and distribution of offshore vertical displacements were further constrained from analysis of measured run up heights and reported arrival times of the tsunami uplift detected along the coast jumped within 4 km from zero to 157 cm near limon and generally decreased over a distance of 70 km southward to the border with panama these data map an axis of uplift that intersects the coastal beach ridge just north of the port of moin and runs offshore to the east and south roughly parallel to the coast no surface faulting was found the earthquake and tsunami were generated by backarc thrusting along faults that bound the north panama deformed belt and dip from the caribbean sea beneath costa rica and northern panama combined geodetic and seismological data indicate that the main rupture dips landward at an angle of about 30 and is approximately 40 km wide and 80 km long dislocation models suggest 2 2 m of slip on a causative thrust fault striking between 105 and 120 we estimate that the repeat time for this type of earthquake is 200 to 1100 years the historical record and new isotopic data favor the middle of the range

multi data type source estimation for the 1992 flores earthquake and tsunami we revisit the source of the 1992 flores earthquake and tsunami using finite fault inversion we simultaneously invert teleseismic body and surface waves together with coseismic uplift subsidence datasets we then verify the inverted source against tsunami run up heights along the northern coast of flores island and the only tide gauge recording of the tsunami our preferred source model provides a good fit to all the datasets whereas previous models only explained a subset of the available data we show that the fault geometry implies segmentation of the back arc thrust system in the eastern sunda arc

the oroville earthquakes a study of source characteristics and site effects half space modeling in the time domain of broadband seismic records from the oroville aftershock sequence demonstrates that these events have simple sources systematic scaling between the far field source duration and seismic moment for the aftershocks studied here and other california earthquakes confirms brune s 1970 source model and shows that the stress drops for california earthquakes range between 10 and 100 bars these events also show no trend in stress drop as a function of size for 3 0 or m sub l or 6 4 analysis of the static deformation associated with the main shock shows that the slip occurred on a fault 81 km sup 2 in area corresponding to the zone defined by the first 3 days of aftershocks teleseismic studies indicate that the seismic source area was 50 km sup 2 corresponding to a zone completely free of aftershocks in the middle of the aftershock zone both results imply a stress drop of 29 39 bars and seismic moment between 5 7 and 8 7 x 10 sup 24 dyn cm the evidence suggests that faulting occurred seismically on the central portion of the fault and propagated out slowly enlarging the fault plane complicated waveforms recorded for the same events at nearby sites on alluvium indicatemore the critical role that propagation through complex structure plays in determining the character of the observed seismic signal at close in stations modeling of these records show that dipping structure may account for the observed waveform complexities less

inversion of teleseismic body waves for the moment tensor of the 1978 thessaloniki greece earthquake seismograms from wwssn and canadian network stations were modeled to determine the source parameters of the 20 june 1978 thessaloniki greece earthquake m s 6 4 the depth of the initial rupture was constrained to 11 1 km by comparison of the arrival times of surface reflections with synthetic short period seismograms a focal sphere plot of first motion polarities provided little constraint on other focal parameters except to indicate that predominantly normal faulting was involved a generalized inverse technique utilizing the moment tensor formalism was applied to teleseismic p and sh waves for six increments of depth the moment tensor obtained indicated a nearly horizontal n trending tension axis and a nearly vertical compression axis and yielded the following double couple source parameters strike 280 7 dip 55 3 rake 65 5 seismic moment 5 7 1025 dyne cm and a skewed triangular source time function with a rise time of about 1 sec and duration of 6 to 8 sec due to indications of multiple or finite source effects for this event and the assumption in the moment tensor formalism of a point source a low pass filter was applied to the data and the inversions were repeated the results were nearly identical with those of the original inversion suggesting that any individual sources had similar mechanisms or that the point source model is sufficient for this earthquake

control of planar fabrics on the development of tensile damage zones under high speed deformation an experimental study with granite and gneiss abstract we have investigated the laboratory scale high strain rate tensile failure processes responsible for mode i breccia dike formation in impact structures brazilian disc experiments with granite isotropic and gneiss foliated samples were performed on a split hopkinson pressure bar equipped with high speed photography for the gneiss samples the gneissic foliation was oriented at 0 45 and 90 to the compression direction time series images show the transient states of tensile rupture localization and propagation leading to in situ fragmentation of the rocks granite samples produced a single incipient tensile rupture accommodating pulverized clasts whereas the gneisses underwent failure by way of major fracture and a network of secondary tensile fractures forming large elongate clasts for gneisses greatly influenced the secondary crack growth forcing propagation trajectories to orient preferentially either along or across the foliation the two types of target rocks produced contrasting clast geometry in the fracture zones the granite had mostly small clasts