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

inversion of complex body waves ii abstract after our previous paper we developed a method to deconvolve body waves into a multiple shock sequence we first consider a general case where a rupture process consists of subevents with arbitrary source parameters and next a special case where a source process consists of subevents with two different fault mechanisms a simple criterion to check the significance of solution is given by a statistical consideration on the estimated values the method is applied to two large earthquakes the 1976 tangshan earthquake and the 1976 east turkey earthquake in both cases the earthquake sources consist of major strike slip events and minor thrust events the total seismic moments of the major events are comparable to the values obtained by surface wave analyses the 1968 borrego mountain earthquake is also analysed by the same method for comparison a single mechanism solution results in a good waveform match and no significant secondary mechanism is required for this event

source spectral characteristics of two large intra slab earthquakes along the southern kurile hokkaido arc abstract in 1993 and 1994 two large earthquakes occurred along the southern kurile hokkaido arc the 1993 kushiro oki earthquake 15 january mw 7 6 and the 1994 shikotan earthquake 4 october mw 8 2 these were intra slab earthquakes that ruptured through a substantial part of the subducting oceanic lithosphere we study source spectral characteristics of these large intra slab earthquakes based on strong motion records for the kushiro oki earthquake the s wave spectra on three rock site stations are directly compared with the theoretical spectra based on the omega squared source model and the source parameters estimated from long period seismic waves the observed spectra are roughly consistent with the theoretical ones at low frequencies

teleseismic time functions for large shallow subduction zone earthquakes broadband vertical p wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum pacific in the last 45 yr most of the records studied come from a common instrument the pasadena california benioff 1 90 seismometer propagation and instrument effects are deconvolved from the p wave records using a damped least squares inversion to obtain the teleseismic source time function the inversion has the additional constraint that the time function be positive everywhere the period band over which the time functions are considered reliable is from 2 5 to 50 sec fourier displacement amplitude spectra computed for each of the 1 90 p wave trains indicate spectral slopes measured between 2 and 50 sec of 1 0 to 2 25 with an average value of 1 5 these values assume an average attenuation of t 1 0 the seismic moments derived from the p wave time functions compare well with other published values for earthquakes having moments smaller than 2 5 10 28 dyne cm m w 8 2 because the 1 90 seismometer has little response at very long periods this technique underestimates the moments of the very largest events the time functions are characterized using five parameters 1 spectral slope between 2 and 50 sec 2 roughness of the time function 3 multiplicity of sources 4 pulse widths of individual sources and 5 overall signal duration the 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere convergence rates and maximum size of earthquakes comparing the time function parameters with age rate and m w of the subduction zone does not yield obvious global trends however most of the subduction zones do behave characteristically and can be grouped accordingly

decouverte de microstructures de nodules polymetalliques dans les mineralisations manganesiferes metamorphiques de falotta et de parsettens grisons suisse les mineralisations manganesiferes de falotta et de parsettens grisons suisse se manifestent dans les radiolarites du jurassique superieur et elles sont deposees sur les ophiolites du domaine pennique ce minerai presente des microstructures botryoidales caracteristiques des nodules polymetalliques les phases mineralogiques des nodules sous l effet du metamorphisme alpin se transforment de facon progressive en braunite faiblement cristallisee avec un important exces en sio2 a la peripherie des structures botryoidales par contre vers la partie centrale de ces structures la braunite est souvent largement cristallisee sa teneur en sio2 est normale de fines veinules constituees de termes intermediaires de la serie isostructurale de la cryptomelanehollandite recoupent la mineralisation de braunite et indiquent la deuxieme etape dans l evolution du minerai oxyde de falotta et parsettens la troisieme etape est representee par la presence de la todorokite et de la birnessite due a l oxydation des veinules posterieures de rhodonite ces deux oxydes n ont aucun rapport direct avec la mineralisation primaire l existence de structures sedimentaires et volcaniques non deformees dans les ecailles superieures de la nappe de platta permet d expliquer la conservation de microstructures primaires de nodules polymetalliques dans le minerai de braunite la variation de la teneur en sr2 observee lorsque l on va de falotta vers parsettens dans les termes intermediaires de la serie isostructurale de la cryptomelane hollandite ainsi que la destabilisation de la braunite au voisinage des veinules seraient liees a la difference du degre de deformation entre ces deux zones il est important de remarquer que les parametres geochimiques fe mn ou mn co cu ni couramment utilises dans les travaux sur les nodules polymetalliques sont inadequats meme dans les structures les mieux preservees

sources of tsunami and tsunamigenic earthquakes in subduction zones we classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface typical interplate events earthquakes at the outer rise within the subducting slab or overlying crust intraplate events and tsunami earthquakes that generate considerably larger tsunamis than expected from seismic waves the depth range of a typical interplate earthquake source is 10 40km controlled by temperature and other geological parameters the slip distribution varies both with depth and along strike recent examples show very different temporal change of slip distribution in the aleutians and the japan trench the tsunamigenic coseismic slip of the 1957 aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long this asperity ruptured again in the 1986 andreanof islands and 1996 delarof islands earthquakes by contrast the source of the 1994 sanriku oki earthquake corresponds to the low slip region of the previous interplate event the 1968 tokachi oki earthquake tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes tsunami hazard assessments must include such events similarity in macroseismic data from two southern kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights most moment release of tsunami earthquakes occurs in a narrow region near the trench and the concentrated slip is responsible for the large tsunami numerical modeling of the 1996 peru earthquake confirms this model which has been proposed for other tsunami earthquakes including 1896 sanriku 1946 aleutian and 1992 nicaragua

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

regional difference in scaling laws for large earthquakes and its tectonic implication we compiled 67 large earthquakes which occurred at and around plate boundaries for the last 140 yrs and classified them into four groups interplate strike slip events intraplate strike slip events underthrust events at island arc subduction zones and underthrust events at continental margin subduction zones for each group of earthquakes we examined relations between seismic moment m 0 fault length l fault width w and average fault slip d and found the following scaling laws in the case of interplate strike slip events the well known l cubed dependence of seismic moment breaks down when l exceeds 30 km because the extent of the seismogenic zone is limited in depth 12 km for large events l 30 km d and m 0 increase with l as d overline delta tau l mu left alpha l beta right and m 0 overline delta tau w l 2 left alpha l beta right respectively where the mean fault width bar w is 12 km and the mean stress drop overline delta tau is 1 8 mpa here and are structural parameters for intraplate strike slip events we obtained nearly the same relations except for significantly higher stress drop 3 1 mpa the difference in stress drop between interplate and intraplate events may be ascribed to the difference in stress accumulation rates and thus the recurrence time of earthquakes in the case of underthrust events at island arc subduction zones we also found the saturation of fault width bar w 120km and the breakaway from the l cubed dependence of m 0 for events larger than l 200 km if we consider the average dip angle of plate boundaries at island arc subduction zones to be 20 30 this indicates that the extent of the seismogenic zone in depth is limited to 40 60 km in the case of continental margin subduction zones on the other hand we could not find the saturation of fault width nor the breakaway from the l cubed dependence of m 0 from the analysis of the present data set w 200 km l 1000 km for sufficiently large earthquakes in general the downward rupture growth is limited to a certain depth due to the existence of a ductile unstressed region which extends under the brittle seismogenic zone since the brittle ductile transition occurs at 300 400 c the difference in the lower limit of the seismogenic zones between tectonically different regions may be attributed to the difference in thermal state there

simulation of long period ground motion near a large earthquake we estimated the possible range of long period ground motion for sites located on a soft sedimentary basin in the immediate vicinity of a large earthquake since many large cities in the world e g los angeles san francisco and tokyo where many large structures have been recently constructed are located in this type of environment a better understanding of long period ground motion is becoming increasingly important our objective is to estimate the possible range of long period ground motion rather than ground motion for a specific fault model we computed ground motion time series and pseudo velocity response spectra pvs for more than 5 000 models for the 1923 kanto japan earthquake m w 7 9 using 180 slip distributions eight rupture geometry and rupture velocities ranging from 1 5 to 3 0 km sec two seismograms recorded in tokyo during the 1923 kanto earthquake are used for comparison the response spectra computed using seismologically reasonable sets of source parameters for the 1923 kanto earthquake vary by more than an order of magnitude at periods of 10 to 13 sec they range from 25 to 170 cm sec in tokyo for some combinations of model parameters the response spectra exhibit peaks in the range of 10 to 13 sec many of the computed response spectra have peaks at periods longer than 10 sec which is considerably longer than the dominant period 6 to 8 sec estimated from studies of small earthquakes and microtremor measurements thus the dominant period of the subsurface structure determined locally may not be representative of the dominant period of ground motion from a nearby large earthquake which is controlled by rupture directivity and source depth we performed a similar simulation for a hypothetical m w 7 5 earthquake located beneath the los angeles basin for a site just above the center of the fault the ground motion spectral amplitude at a period of 10 sec can vary from 50 to 350 cm sec this range though very large is what is expected for a seismologically plausible range of source parameters

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

long term dynamics of a fault with two asperities of different strengths summary a fault made of two segments or asperities having different strengths and subject to a constant strain rate is considered the fault is modelled by a discrete dynamical system made of two blockscoupledbyaspringandpulledatconstantvelocityonaroughplane wegiveacomplete analytical solution for the evolution of the system the long term behaviour of the fault is studied by calculating the orbits of the system in the phase space the dynamics of the system has four different modes and produces a variety of behaviours the asperities may slip one at a time originating a medium size earthquake or simultaneously originating a large earthquake in the latter case the focus may be at one asperity or at the other in some cases the weaker asperity may slip twice both before and after the failure of the stronger asperity the time pattern of the seismic events generated by the fault is controlled by the stress distribution on the asperities and may include many different behaviours we devise suitable correspondence rules allowing application of the discrete model to real fault systems as an example the model is applied to the 1964 great alaska earthquake which was originated by the failure of two asperities and a possible evolution of this fault system is discussed

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

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

geochemical processes controlling the relationship between co mn and fe in early diagenetic deep sea nodules abstract early diagenetic manganese nodules from the northeast pacific nodule belt and from the southeast pacific peru basin show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10 amanganate a1 substance and amorphous material which is composed of an intimate mixture of ferric hydroxide silicate and mno 2 a2 substance the formation of rhythmic sequences of a1 and a2 microlayers is explained by physico chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface a upward diffusion of mn 2 in the interstitial water as a result of decay of organic matter and mn mobilization b oxidation of mn 2 and formation of 10 amanganate in the upper part of the peneliquid sediment layer leading to ph depression in the microenvironment of the nodule surface which decreases the mobility of silicate resulting in formation of a2 layers c restoration of ph and renewed precipitation of 10 amanganate based on data of 171 bulk analyses and on electron microprobe investigations interelement relationships between co mn and fe are pointed out fe and co show a significant positive correlation r 0 84 while mn and co are poorly negatively correlated r 0 21 assuming linear regression the enrichment of co within the amorphous a2 phase is attributed to specific surface adsorption and subsequent oxidation of co 2 to co 3 in the strong electric field of si 4 robust complexes of co iii and feh 2 sio 4 prevent most of the co from being available for the 10 amanganate precipitation concerning the relation between mn and fe and co respectively the highest correlation coefficients are obtained using an inverse logarithmic regression under early diagenetic conditions the concentration and precipitation of mn 2 in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter the nernst equation describes the relationship as a reciprocal logarithmic function however the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential these different characteristics in the precipitation of mn and the fe and si rich colloidal phase may cause the significantly negative logarithmic correlation of mn versus fe and co respectively

characteristics of sediments and their dispersal systems along the shelf and slope of an active forearc margin eastern hokkaido northern japan abstract this study revealed sediment distributions and their dispersal systems in a shelf slope setting along an active forearc margin off eastern hokkaido northern japan where the pacific plate is being subducted beneath the okhotsk north american plate at the 7 km deep kuril trench the findings were based on analyses of the textures and structures of surface sediments components of the sampled sand fractions high resolution acoustic reflection records and sediment budgets the studied margin has a 20 30 km wide shelf and steep 5 10 slope marked by faults and folds associated with transpressional tectonics the shelf sediments are classified into gravelly coarse to fine sand from the shelf edge to the uppermost slope 110 1000 m water depth gravel and coarse sand on the shelf off hanasaki fine sand on the middle outer shelf off kiritappu and very fine sand on the shelf off akkeshi the coarse sediments on the eastern shelf off hanasaki and the shelf margin are interpreted to represent lag deposits from coastal erosion associated with a post glacial transgression across topographic highs the two depocenters of shelf sediments subsequent to the last glacial maximum are situated in the middle outer shelf off kiritappu and in the inner middle shelf off akkeshi these are interpreted as transgressive highstand sequences whose locations were controlled by ridges on the shelf margin and topographic highs on the shelf the shelf sediment thickness reaches 20 m and the total volume is estimated at ca 6 km3 the slope sediments are grouped into medium fine sand on the uppermost and upper slopes 150 2000 m water depth and mud dominated sediments on the upper to middle slope 1000 3000 m water depth the sandy sediments on the slope at water depths greater than 1000 m are regarded as being derived from the shelf break by gravitational redistribution the occurrence of diamictite like sediments around gullies that incise into the slope indicates that mass movement and sediment gravity flows play an important role in the redistribution of sediments upon the slope on the upper middle slope hemipelagic fallout and advection of turbid water from the shelf edge provide a supply of suspended material the main contributor of sediment supply to the area is coastal erosion 1 81 mt y 1 along with a lesser contribution from fluvial input 0 10 mt y 1 during the latest quaternary the rates of sediment accumulation upon the shelf are estimated to have been 0 47 mt y 1 the remainder of the material transported into the sea is probably redistributed to deeper parts of the slope via gravitational sediment flows or transported outside of the study area by alongshore and tidal currents the studied shelf that kept less than a quarter of the mass from land is comparable with other active margin shelves of new zealand and california although they are fed by high sediment laden rivers

systematics of deep focus earthquakes along the kuril kamchatka arc and their implications on mantle dynamics subduction along the kuril kamchatka arc has been proposed as a primary example in which subducted lithosphere plunges steeply into the lower mantle with little deformation the occurrence of several unusual earthquakes along this arc during the last few years places new constraints on the configuration and the state of strain of the down going slab we systematically determined the source parameters of 27 large to moderate sized earthquakes mb 5 5 that occurred between 1963 and 1990 at depths greater than 200 km along this subduction zone to our surprise our results show that the configuration and strain due to earthquakes in subducted lithosphere are highly variable along both the strike and dip of the arc approximately 75 km farther west of the deepest earthquakes in the northern portion of the arc the earthquake of august 14 1988 occurred at a comparable depth of 636 17 km thus at least part of the slab has been displaced in a direction perpendicular to the overall strike of the wadati benioff zone earthquakes in the central part of the arc delineate shoaling of the subducted slab at a depth of approximately 570 km reminiscent of the configuration of subducted lithosphere along the tonga arc both observations indicate that the subducted slab is deforming probably in response to resistance encountered near the 670 km discontinuity for all earthquakes north of 48 n focal mechanisms of all events deeper than 200 km show a remarkably consistent pattern of downdip compression strain in the southern kuril the sakhalin island earthquake m0 8 1019n m of may 12 1990 is one of three large deep focus earthquakes that have occurred over 150 km farther west of the well defined wadati benioff zone the relationship between the source region of these events and the rest of the subducted slab is equivocal due to the lack of background seismicity nonetheless for earthquakes south of 48 n net downdip extension dominates between depths of 200 450 km before switching to downdip compression below 540 km thus the strain field within the slab is segmented both along strike and dip if the slab in southern kuril kamchatka can serve as a stress guide down to depths of 615 km the changeover from extension to compression occurs at an unusually large depth within the transition zone of the upper mantle alternatively the deep focus events west of the island of sakhalin could have occurred in a detached piece of lithosphere as a whole the configuration and state of strain of the subducted slab along the kuril kamchatka arc are highly variable close to a microcosm of variations among different deep subduction systems observed on a global scale in particular the subducted lithosphere is apparently undergoing considerable deformation as it approaches the base of the upper mantle our results do not preclude the possibility of subducted lithosphere ever reaching the lower mantle nevertheless it seems unlikely that the down going slab along the kuril kamchatka arc penetrates into the lower mantle unhindered

depth distribution of coseismic slip along the nankai trough japan from joint inversion of geodetic and tsunami data coseismic slip distribution on the fault plane particularly in the downdip direction associated with large subduction earthquakes can be estimated by joint inversion of geodetic and tsunami data two large earthquakes the 1944 tonankai earthquake mw 8 1 and the 1946 nankaido earthquake mw 8 3 occurred on the nankai trough southwestern japan where the philippine sea plate is subducting beneath the eurasian plate the source areas of these events extended over both land and ocean coseismic crustal movements on land were measured by leveling while those in ocean were recorded as tsunami waveforms on tide gauges the coseismic slip distribution inverted from these data shows that the slip on the shallower part of the fault plane is comparable to that on the deeper parts this indicates that large coseismic slip can occur beneath an accretionary wedge where current seismicity is low the result has implications for other subduction zones having a similar tectonic environment such as for the pacific northwest region of the united states although the possibility of a large earthquake there is still debated should a large subduction earthquake occur in this region coseismic slip on the shallow part could be large and the potential for large tsunamis is high

comparison of strong motion spectra with teleseismic spectra for three magnitude 8 subduction zone earthquakes we studied strong motion spectra observed for three m w 7 8 to 8 0 earthquakes the 1985 michoacan mexico 1985 valparaiso chile and 1983 akita oki japan earthquakes we determined the decay of spectral amplitude with distance from the station considering different measures of distance from a finite fault we compared strong motion spectra fourier acceleration spectra observed for these three earthquakes with those estimated from the source spectrum determined from teleseismic p waves we scaled the teleseismic source spectra to produce reference strong motion spectra at periods from 1 to 10 sec using a simple physical model of far field s body waves from a point source recorded at the surface of a homogeneous half space for all three earthquakes the reference spectral amplitudes at periods of 1 to 5 sec are about half the observed ones at distances of about 50 km the difference increases as the distance increases at distances of 200 to 300 km the reference spectrum is about 1 10 of the observed one the difference between the reference and the observed spectrum is attributed to the contribution of phases other than direct s waves and to site response we applied corrections for the finiteness spatial extent of the source using a simple model of rupture propagation on a dipping two dimensional fault including the source finiteness did not improve the estimate substantially at periods from 1 to 20 sec but it modeled significant changes in the signal duration as a function of azimuth for the 1985 michoacan earthquake our results can be used to establish empirical relations between the observed spectra and the half space responses depending on the distance and the site condition if such empirical relations can be established source spectra determined from teleseismic records may be used to estimate strong motions

effect of depth dependent shear modulus on tsunami generation along subduction zones estimates of the initial size of tsunamis generated by subduction zone earthquakes are significantly affected by the choice of shear modulus at shallow depths analysis of over 360 circum pacific subduction zone earthquakes indicates that for a given seismic moment source duration increases significantly with decreasing depth bilek and lay 1998 1999 under the assumption that stress drop is constant the increase of source duration is explained by a 5 fold reduction of shear modulus from depths of 20 km to 5 km this much lower value of shear modulus at shallow depths in comparison to standard earth models has the effect of increasing the amount of slip estimated from seismic moment determinations thereby increasing tsunami amplitude the effect of using depth dependent shear modulus values is tested by modeling the tsunami from the 1992 nicaraguan tsunami earthquake using a previously determined moment distribution ihmle 1996a we find that the tide gauge record of this tsunami is well matched by synthetics created using the depth dependent shear modulus and moment distribution because excitation of seismic waves also depends on elastic heterogeneity it is important particularly for the inversion of short period waves that a consistent seismic tsunami shear modulus model be used for calculating slip distributions

inversion of long period p waves from great earthquakes along subduction zones abstract long period p waves from subduction zone earthquakes in the moment range from 7 1027to 8 1029dyn cm are analyzed using an iterative deconvolution method in addition to discrete subevents which effectively contribute to the observed seismograms the long period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long period surface waves it is shown that great earthquakes can be described by several subevents with a duration of about 10 s which changes little from earthquake to earthquake in the above moment range the long period component of the moment rate function becomes larger for a greater earthquake the greatest earthquakes of mw 9 additionally involve subevents with another duration scale much longer than 10 s it is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane the constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes these observations suggest an essential similarity in the mode of dislocation distribution

the rupture process and tectonic implications of the great 1964 prince william sound earthquake we have determined the rupture history of the march 28 1964 prince william sound earthquake m w 9 2 from long period wwssn p wave seismograms source time functions determined from the long period p waves indicate two major pulses of moment release the first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture the second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds because of the large size of this event and thus a deficiency of on scale digitizable p wave seismograms it is impossible to uniquely invert for the location of moment release however if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault the first moment pulse most likely initiated near the epicenter at the northeastern down dip edge of the aftershock area and then spread over the fault surface in a semi circular fashion until the full width of the fault was activated the rupture then extended toward the southwest approximately 300 km ruff and kanamori 1983 the second moment pulse was located in the vicinity of kodiak island starting at 500 km southwest of the epicenter and extending to about 600 km although the aftershock area extends southwest past the second moment pulse by at least 100 km the moment release remained low we interpret the 1964 prince william sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major but smaller asperity in the kodiak island region

source scaling of earthquakes in the shumagin region alaska time domain inversions of regional waveforms the scaling of pulse duration to seismic moment is estimated for earthquakes along an interplate thrust zone from digital waveforms recorded by short period and broad band instruments of the east aleutian shumagin seismic network we measure pulse duration using an empirical green s function technique based on damped time domain deconvolution from several thousand events 22 earthquakes with magnitudes 3 0 7 0 and depths 23 56 km are found to give reliable estimates of pulse duration durations are also determined directly from one parameter nonlinear inversions for a variety of simple functional forms of source time functions symmetric source pulses boxcar or triangle shapes fit waveforms better than an asymmetric model t exp 2t d for most 62 per cent of the waveform pairs while the asymmetric model fits best for only 8 per cent of the data pulse duration increases with the size of events from 0 1 to 10s over the seismic moment m0 range of 1014 to 3 1019 nm when normalized by the cube root of seismic moment pulse durations show 8 x variation comparable static stress drop estimates range from 0 2 to 135 mpa contrary to predictions of some laboratory and theoretical studies earthquakes at the deepest part of the thrust zone do not show significantly higher stress drops than do shallower events rupture properties however show a strong dependence on earthquake size the three largest events m0 5 1018nm have the three longest normalized durations on average 3 8 times longer than those for smaller events the durations require smaller events to have 10 100 x larger static stress drops or 4 x faster rupture velocities or some combination of the two possibly the largest events rupture both strong and weak patches while smaller events just rupture strong patches on the fault surface the characteristic dimension that separates large from small events 3 15 km is comparable to characteristic wavelengths of pacific basin bathymetry and may reflect the influence of the subducted sea floor upon fault zone heterogeneity

short and long period subevents of the 4 february 1965 rat islands earthquake short and long period records of the p wave of the 1985 rat islands earthquake were analyzed to locate subevents within the main rupture four subevents were identified on the short period records in the first 100 sec and on the two long period records in the first 30 sec the short period subevents cluster in an area 100 km south of the initial epicenter which appears to be off of the main fault plane an area in which two larger aftershocks have relatively high stress drops the long period subevents are located 90 km west of the initial epicenter the times and locations of the first short and long period subevents indicate they were triggered by a front moving near the p wave velocity 16 references 13 figures 3 tables

la presence du strontium dans les oxydes manganesiferes du gisement de st marcel praborna v aoste italie des oxydes de manganese riches en strontium ont ete decouverts dans l un des niveaux a piemontite du gisement de st marcel praborna val d aoste italie ces oxydes sont toujours associes a la braunite les examens microscopiques et a l aide des rayons x permettent d affirmer que ces oxydes se rettachent a la serie isostructurale de la cryptomelane hollandite coronadite ils representent des termes intermediaires entre un pole strontifere et les poles potassique et barytique

possible focal mechanism change during reactivation of a previously ruptured subduction zone and stress tensor implications summary body waveform inversion methods usually assume a constant double couple source or a combination of such subevents previous studies suggest that the source rupture of mature sources in terms of coupling along smooth subduction zones are usually resolved on this assumption however for events where the source area overlaps previously ruptured zones the conventional inversion methods fail to resolve the source process for such events the subduction coupling may vary between the mature source area and the previously ruptured zone causing a variation in the focal mechanism too we study the implications on the stress tensor of the coexistence of two such focal mechanisms using a major aftershock of the 1985 chilean earthquake m 6 0 the 1978 kurile m 7 6 and 1980 santa cruz islands m 7 7 earthquakes for the first event we use the two different sets of focal parameters obtained by a study which describes a focal mechanism change during the process the epicentres of the latter two large events are located in the spots which had remained unbroken in the preceding large events e g the 1963 and 1969 kurile earthquakes and the 1966 santa cruz is earthquake respectively for each event one of the focal mechanism solutions shows a substantial strike slip component the stress tensors are examined under the constraints that the shear stress is parallel to the slip vector and a friction law is satisfied two particular families of stress tensors examined are 1 the tensors that are optimally orientated with respect to the mature source area and 2 the tensors that have a vertical principal stress direction the first type of tensors can fully account for the observed slip orientation only for the chile aftershock but it comes close to the observed one in the case of the kurile island event and would indeed reactivate the decoupled area at a reasonably low stress level the second type of tensors can be compatible with the two observed slip orientations in all cases however for the santa cruz is and kurile is earthquakes the friction law which should be satisfied on each plane requires too high a stress deviation

slip distribution of the 1963 great kurile earthquake estimated from tsunami waveforms the 1963 great kurile earthquake was an underthrust earthquake occurred in the kurile kamchatka subduction zone the slip distribution of the 1963 earthquake was estimated using 21 tsunami waveforms recorded at tide gauges along the pacific and okhotsk sea coasts the extended rupture area was divided into 24 subfaults and the slip on each subfault was determined by the tsunami waveform inversion the result shows that the largest slip amount of 2 8 m was found at the shallow part and intermediate depth of the rupture area large slip amounts were found at the shallow part of the rupture area the total seismic moment was estimated to be 3 9 1021 nm mw 8 3 the 2006 kurile earthquake occurred right next to the location of the 1963 earthquake and no seismic gap exists between the source areas of the 1963 and 2006 earthquakes

seismic moment tensors and source depths determined by the simultaneous inversion of body and surface waves we present a linear moment tensor inversion method that incorporates both body and surface wave data the source coordinates are fixed during the inversion and the source depth is determined by applying the inversion at several depths and taking the depth that produces the minimum residual the inversion is carried out in the time domain for body wave data and in the frequency domain for surface wave data the fundamental rayleigh waves at the period of 256 s from ida stations and the long period p waves from wwssn and gdsn stations whose angular distances are from 30 to 90 are used as the data the simultaneous inversion of both body and surface wave data sets has several merits because of the body wave constraints the present method gives reasonable solutions at shallow depths 30 km where long period surface wave inversions become unstable although the inversion using only body wave data is unstable in the sense that it allows for a variety of solutions with a slight change in the assumed depth probably because of the noise present and poor coverage of body wave data to determine the source mechanisms the inclusion of surface wave data makes the solution stable this is because the surface wave data constrain nodal plane strikes we may also expect better resolution in source depth by including the body wave data because the local crustal structure above the source can be taken into account to generate the green s function we applied our method to two large earthquakes one occurring at the triple junction off boso peninsula central honshu on 18 september 1984 and another at the outer rise area off the chile trench on 16 october 1981 the scalar moments of the boso oki and chile earthquakes are estimated to be 3 2 1026 dyn cm and 6 3 1026 dyn cm respectively the ratio of the minimum absolute eigenvalue of the moment tensor to the maximum which may measure the non double couple component is less than 10 for both earthquakes this suggests that their sources are essentially a double couple the source depths of both events are determined as 30 km the boso oki event is indicative of hinge faulting within the pacific slab at the triple junction the chile event is consistent with compressional bending stress in the deeper part of the lithosphere at the trench outer rise area off chile

coseismic slip in the 1964 prince william sound earthquake a new geodetic inversion the 1964 prince william sound earthquake march 28 1964 m w 9 2 caused crustal deformation over an area of approximately 140 000 km 2 in south central alaska in this study geodetic and geologic measurements of this surface deformation were inverted for the slip distribution on the 1964 rupture surface previous seismologic geologic and geodetic studies of this region were used to constrain the geometry of the fault surface in the kodiak island region 28 rectangular planes 50 by 50 km each oriented 218 with a dip varying from 8 nearest the aleutian trench to 9 below kodiak island define the rupture surface in the prince william sound region 39 planes with variable dimensions 40 by 50 km near the trench 64 by 50 km inland and orientation 218 in the west and 270 in the east were used to approximate the complex faulting prior information was introduced to constrain offshore dip slip values the strike slip component and slip variation between adjacent planes our results suggest a variable dip slip component with local slip maximums occurring near montague island up to 30 m further to the east near kayak island up to 14 m and trenchward of the northeast segment of kodiak island up to 17 m a single fault plane dipping 30 corresponding to the patton bay fault with a slip value of 8 m modeled the localized but large uplift on montague island the moment calculated on the basis of our geodetically derived slip model of 5 0 1029 dyne cm is 30 less than the seismic moment of 7 5 x 1029 dyne cm calculated from long pe riod surface waves kanamori 1970 but is close to the seismic moment of 5 9 1029 dyne cm obtained by kikuchi and fukao 1987

are asperity patterns persistent implication from large earthquakes in papua new guinea 1 we studied the distribution of asperities for large recent earthquakes along the new britain trench papua new guinea to investigate if they are the same for repeated ruptures of the subduction boundary we determined the slip distributions of two earthquakes mw 8 in 1971 using pdiff waveforms and an earthquake mw 7 9 in 1995 using direct teleseismic p waves combining these findings with previous results for two earthquakes mw 7 5 in 2000 we compared the source areas and asperity distributions for this region of the new britain trench our results show that the locations of the asperities for the individual earthquakes did not significantly overlap although the same portion of the subduction zone seems to have reruptured this fact supports the idea that asperities are not persistent features when portions of the new britain subduction zone slip in large earthquakes

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

stress fields associated with metastable phase transitions in descending slabs and deep focus earthquakes inside subducting slabs the interaction of different metastable phase transformations olivine spinel spinel spinel spinel perovskite magnesiowustite associated with the latent heat release and absorption for these transitions can result in a complex thermal slab structure thermokinetic coupling processes cause thermal anomalies and buoyancy contrasts between slab and mantle that strongly influence the stress field within subducting plates we have described the thermal field within the downgoing slab in a lagrangian framework by a self consistent high resolution two dimensional thermokinetic coupling model which also incorporates the effects of nucleation site saturation using an adaptive method the threshold for the nucleation site saturation is found to be less than 0 1 transformation degree in the cold slab interior this can significantly shift the metastable wedge of olivine deeper as suggested from previous thermokinetic slab models however this effect is compensated by the latent heat release during the olivine spinel and spinel spinel phase transitions latent heat release produce very sharp phase boundaries in the slab for fast slabs the phase boundaries reveal significant metastable perturbations from the equilibrium state in the cold interior however the strong thermal interaction between both ongoing phase transitions results in sharp overlapping phase boundaries with dramatic consequences for the slab stress field we have investigated the detailed physical properties and the state of stress in the deeper portion of a subducting plate by using up to date temperature field and physical properties determined from recent high p t experiments we find that the slab is denser up to 100 kg m 3 than the surrounding mantle remarkable denser portions up to 260 kg m 3 are located just below the uplifted and equilibrium phase transitions while lighter portions up to 210 kg m 3 can be found just above the depressed spinel to perovskite magnesiowustite transition and for the metastable wedge of olivine these density differences effectively act as a body force and produce a significant stress field which we calculated with a two dimensional finite element code the results show that the buoyancy induced forces produce maximum shear stress up to 23 mpa along the metastable wedge and deeper portion just above the depressed last phase transition involving spinel for the latter the dominant state of stress is down dip compression the calculated p t dependent state of stress is very similar to the depth distribution of deep focus

source times and scaling relations of large earthquakes source time is a kinematic fault parameter corresponding to the duration of seismic source time functions and is accurately determined from phase spectra of long period surface waves source times are determined for 36 large earthquakes during the last three decades scaling relations among source times seismic moments and fault dimensions are derived seismic moment is proportional to the cube of source time and fault dimension is proportional to source time source times for low angle thrust earthquakes along deep sea trenches are found to be longer than those of other types such as intraplate shocks and deep shocks they are also significantly longer than the rupture times expected from a haskell model suggesting that generally there exists an introductory stage of faulting that precedes the main stage of the rupture propagation

hierarchy in earthquake size distribution abstract we propose a fault model in which there are a finite number of characteristic lengths between the smallest and the largest scales e g between a grain size and a size of great earthquakes a fault plane in one scale is segmented into blocks of statistically similar sizes by the barriers of statistically similar heights rupture expands by successively climbing the barriers the average barrier height is proportional to the average block size which defines the characteristic length of the relevant scale stresses before and after rupturing are assumed to be independent of earthquake size with these assumptions the probability for rupture to grow further is shown to be independent of the scale of barrier structure the rupture in one scale however tends to grow more easily as it grows so that once the rupture exceeds some critical size it no longer stops until it encounters the barriers in the next larger scale rupture grows by repeating this cycle which starts with rupturing of a unit block in one scale and ends with one in the next larger scale our model involves two parameters which must be determined empirically one is the length ratio r between two successive scales the other is the critical number of blocks n c which defines the critical size for unstable rupture growth in one scale we suggest values of 5 for both r and n c with these values our model explains a diversity of earthquake phenomena such as the magnitude frequency relation the seismic gap and the magnitude gap the magnitude difference between a main shock and its largest aftershock the occurrence of multiplet earthquakes the generation of high frequency seismic waves the incoherency of the near field acceleration and the recent observation by furumoto and nakanishi that the main rupture is often preceded by a precursory rupture whose time duration in general scales with seismic moment

a comparative study of the sumatran subduction zone earthquakes of 1935 and 1984 a m s 7 7 earthquake struck the western equatorial coast of sumatra in december 1935 it was the largest event in the region since the two devastating giant earthquakes of 1833 and 1861 historical seismograms of this event from several observatories around the world provide precious information that constrains the source parameters of the earthquake to more precisely quantify the location geometry and mechanism of the 1935 event and to estimate the coseismic deformation we analyze the best of the available teleseismic historical seismograms by comparing systematically the records of the 1935 earthquake with those of a smaller event that occurred in the same region in 1984 first we constrain the source parameters of the 1984 event using teleseismic records then we compare the records of the 1935 event with those of 1984 from the same sites and instruments to do this we choose several time windows in the corresponding seismograms that contain clearly identifiable phases and deconvolve the modern event from the older one the deconvolutions result in very narrow pulses with similar sizes thus confirming similar locations and mechanisms for the events the initiation of the 1984 event was on the subduction interface at a depth of 27 2 km its m 0 is 6 5 x 10 19 n m m w is 7 2 the sense of slip was nearly pure thrust on a plane dipping 12 the 1935 event also involved rupture of the shallow subduction interface but was about five times larger m 0 3 3 x 10 20 n m m w 7 7 and initiated a few kilometers to the southeast along strike the 1935 rupture propagated unilaterally toward the southeast the along strike rupture length was about 65 km from these source parameters we calculate the surface deformations assuming an elastic multilayered medium these deformations compare favorably with those actually recovered from paleoseismic data in the form of coral microatolls

broadband source spectrum seismic energy and stress drop of the 1989 macquarie ridge earthquake i compute the broadband source spectrum at periods from 1 to 50 seconds using teleseismic p body waves of the may 23 1989 macquarie ridge earthquake mw 8 1 recorded by the gdsn geoscope and ida networks the average source spectrum is obtained by windowing tapering and fourier transforming p waves removing from the spectra the effects of attenuation geometrical spreading and radiation pattern and averaging logarithmically over the stations the source spectrum for the strike slip macquarie ridge earthquake is higher than an average source spectrum of seven recent large earthquakes scaled to be comparable to a mw 8 1 earthquake by a factor of 2 to 3 at periods of 1 to 20 seconds these other earthquakes were underthrusting events in subduction zones using haskell s formulation assuming a point source with no directivity i estimate the seismically radiated energy from the source spectrum by integrating the square of the source spectrum in velocity and scaling the result the seismic energy thus estimated for the macquarie ridge earthquake is 3 to 8 1023 ergs an orowan stress drop can be obtained from the seismic energy and moment the orowan stress drop for the macquarie ridge earthquake is about 20 to 50 bars much higher than similarly determined stress drops of other recent large earthquakes there is a correlation between the orowan stress drops and time since the last earthquake of comparable or larger magnitude for seven recent large earthquakes this correlation suggests that a healing process operates that may control the mechanical strength of the fault and is important on time scales of tens to hundreds of years

bathymetric effects on body waveforms from shallow subduction zone earthquakes and application to seismic processes in the kurile trench resolution of earthquake source characteristics is limited by structural complexities in the source region this study explores the effects of dipping near source bathymetry and structure on long period teleseismic body waveforms from shallow subduction zone earthquakes ray theory synthetics calculated for shallow double couple sources and velocity structures incorporating planar dipping interfaces suggest that p waveforms are most sensitive to water depth and sea bottom orientation for sources beneath a substantial water layer the seafloor dip of the inner trench slope can give rise to prominent later arrivals and waveform complexity not found on synthetics calculated for horizontal bathymetry sediment thickness and the dip of the sediment crust and crust mantle interfaces generally have lesser effects the high amplitude arrivals result largely from changes in the source takeoff angles of the reverberations these arrivals present difficulties for source depth and time function determination from p waveforms and may cause spurious complexity in the derived pattern of earthquake moment release sh waveforms show little effect of sea bottom orientation or local structure for shallowly dipping thrust faulting events suggesting that sh waveform analysis can stabilize source parameter studies with respect to unknown or incompletely parameterized bathymetry and structure effects of nonhorizontal structure are observed in the p waveforms from shallow kurile trench events ms 5 8 7 2 which show prominent later arrivals not observed on sh waveforms synthetics calculated for a dipping water crust interface provide a better fit to these arrivals than those calculated for a horizontal interface suggesting that the p waveforms show systematic effects of seafloor dip the synthetics are highly sensitive to the assumed orientation of the seafloor the data are fit best for seafloor orientations consistent with the dip of the inner trench slope the distorting effect of the water layer gives rise to systematic differences in p wave complexity between shallow events near the seismic front which occur beneath a thick water layer and show numerous later arrivals and deeper arcward events which occur beneath a thin water layer and show simple waveforms large reverberations in the p waveforms of the october 20 1963 and june 10 1975 kurile tsunami earthquakes have previously been used as evidence for a long source duration and a change in focal mechanism during rupture however sh waveforms suggest simple source time functions with durations of 25 and 43 s inversion of p and sh waveforms and amplitudes yields shallowly dipping thrust mechanisms with no conclusive evidence for a previously proposed steepening of the fault dip during rupture the large p wave reverberations cannot be fit using a point source and a horizontal seafloor detailed modeling of the 1963 event as an upward propagating rupture extending through low velocity sediments to the ocean bottom combined with the effects of the dipping seafloor allow the reverberation amplitudes to be matched the anomalous tsunami excitation appears to be related to the location of the sources at shallow depths within low velocity sediments

effects of fault heterogeneity on seismic energy and spectrum abstract we study the effects of friction heterogeneity on the dynamics of a seismogenic fault to this aim we consider a fault model containing two asperities with different static frictions and a rate dependent dynamic friction we consider the seismic events produced by the consecutive failure of the two asperities and study their properties as functions of the ratio between static frictions in particular we calculate the moment rate the stress evolution during fault slip the average stress drop the partitioning of energy release the seismic energy the far field waveforms and the spectrum of seismic waves these quantities depend to various extent on the friction distribution on the fault in particular the stress distribution on the fault is always strongly heterogeneous at the beginning of the seismic event seismic energy and frictional heat decrease with increasing friction heterogeneity while seismic efficiency is constant we obtain an equation relating seismic efficiency to the parameters of the friction law showing that the efficiency is maximum for smaller values of dynamic friction the seismic spectrum depends on the friction distribution as to the positions and the values of the minima however under the model assumption that the slip durations are the same for both asperities the corner frequency is independent of the friction distribution but it depends on the friction law and on the coupling between asperities the model provides a relation between the total radiated energy and the seismic moment that is consistent with the empirical relation between the two quantities the fault model with one asperity is also considered as a particular case the model is applied to the 1965 rat islands alaska earthquake and shows the role of fault heterogeneity in controlling the spatial distribution of stress drop as well as the time dependence and the final amount of radiated energy

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

rupture process of the february 4 1965 rat islands earthquake the great rat islands underthrusting earthquake mw 8 7 of february 4 1965 represents subduction of the pacific plate beneath the north american plate along a 600 km segment of the western end of the aleutian islands body wave inversion techniques are used to determine the spatial and temporal heterogeneities associated with the rat islands earthquake we have deconvolved world wide standard seismograph network long period teleseismic p wave seismograms to obtain source time functions directivity associated with the three major pulses of moment release in the source time functions indicates a total source duration of 160 s unilateral rupture in the direction 300 fault length of 420 km and average rupture velocity of 2 5 km s the three pulses of moment release are located along the fault and these regions of high moment release are interpreted as asperities the first asperity extends from the epicenter to 100 km to the wnw this is the largest asperity and corresponds to a smooth pulse of moment release in the source time function with a duration of 50 s the second pulse of moment release is very jagged is less coherent between stations and is centered 200 km wnw of the epicenter the third pulse of moment release extends from 360 to 420 km wnw of the epicenter although the aftershock area is 600 km in length we can not resolve any moment release from the p waves beyond 420 km wnw of the epicenter the rat islands event was closely followed by a large tensional outer rise event on march 30 1965 ms 7 5 which is located oceanward of the largest moment release associated with the rat islands mainshock rupture detailed analysis of the p waves for this large outer rise event confine the depth extent to the upper 30 5 km of the crust the spatial and temporal association between the february 4 mainshock and the march 30 tensional outer rise event suggests the tensional event may have been triggered by the large displacement near the mainshock epicenter the overriding plate along the western aleutian subduction zone is laterally segmented into a series of rigid tectonic blocks separated by fault controlled canyons and extensional basins geist et al 1988 we suggest that the central undeformed parts of the blocks have the strongest coupling with the down going plate and hence are the sites of the largest moment release during an underthrusting earthquake the three asperities determined from the p waves correspond to the rat buldir and near tectonic blocks respectively hence the p wave seismic moment release of the rat islands earthquake is controlled by the lateral segmentation of the overriding plate

source process of the great 1971 solomon islands doublet abstract large underthrusting earthquakes in the solomon islands tend to occur as multiplets separated by a few hours to several days in time and 30 100 km in space the largest sequence a doublet on july 14 1971 m w 8 0 and july 26 1971 m w 8 1 is particularly unusual in that it occured at the junction of two trenches with the july 14 event in the solomon islands trench preceding the july 26 rupture in the new britain trench the location and large moment release of this doublet as well as an incompatibility of published body wave and surface wave focal mechanisms for the july 14 event motivated a detailed study of the source process of the 1971 sequence to satisfy both the surface wave and body wave data we explored the possibility of a change in the faulting geometry during rupture for the july 14 event a fault model that changes orientation from a northwest southeast striking shallow dipping plane similar to the mechanisms of neighboring underthrusting events in the solomon islands trench to a more north south striking plane 70 s after rupture initiation is consistent with the observed rayleigh and love wave amplitude patterns this change in mechanism is suggested by systematic variations in the mechanisms of smaller earthquakes near the cusp in the solomon islands plate a simultaneous inversion of wwssn p wave seismograms for the time location seismic moment and focal mechanism of individual subevents gives results in agreement with the surface wave model although the precise change in mechanism is not well resolved the spatiotemporal distribution of subevents reveals two major pulses of moment release the first occurred on the initial fault near the epicenter at the origin time of the earthquake the second occurred on the north south striking fault 50 70 km northwest of the epicenter 70 s after the origin time the change in mechanism appears to reflect contortion of the slab near the trench junction inversion of wwssn p wave seismograms for the rupture history of the july 26 event reveals a westerly propagating rupture extending 60 km along the new britain trench for both of the 1971 earthquakes regions of high moment release are located in the vicinity of the solomon islands new britain trench junction contortion of the subducting lithosphere as it bends around the arc arc junction may have enhanced the degree of mechanical coupling between the subducting and overriding plates concentrating stress in this region and in turn promoting efficient triggering across the trench junction

seismic structure and seismogenesis off sanriku region northeastern japan summary in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeastern japan nej arc the objectives of this experiment were to clarify seismic structures of the forearc region off sanriku japan using airgun obs data and to understand the nature of the japan trench seismogenic zone fundamental features of the structure are as follows i the subduction angle becomes steeper from east to west from 3 to 8 to 11 with the top of the plate located at depths of 11 km 40 km west from the trench 21 km 120 km west from the trench and 28 km 140 km west from the trench respectively ii the nej moho beneath the forearc is defined at a depth of approximately 20 km iii p wave velocity of the island arc upper mantle is approximately 8 km s 1 iv the p wave velocity of the cretaceous sedimentary layer exhibits significant lateral variability 4 0 5 5 km s 1 i nthe e w direction v the upper crust of nej forearc also has the significant lateral heterogeneity 5 0 6 3 km s 1 i nthe e w direction but not in the n s direction vi the middle crust defined on land extends in some locations 40 km east of the coastline vii lateral variability in the p wave velocity of the lower crust 6 7 7 0 km s 1 i ssmall compared with that of the upper crust according to these results it is suggested that the rupture areas of large earthquakes m7 in this region are limited within the contact zone between the nej arc crust and the subducting oceanic crust although a thin layer with low velocity is probably present within this contact zone the serpentinization of uppermost mantle wedge of the nej arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited this might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km

mode of stress release within a subducting slab of lithosphere implication of source mechanism of deep and intermediate depth earthquakes we inverted the long period p wave seismograms of 28 deep and intermediate depth earthquakes including 16 tonga events to their sources the results are incorporated with our previous results for 18 deep and intermediate depth earthquakes to obtain a general picture of slab earthquakes a large event with seismic moment mo 5 1027 dyn cm tends to be a multiplet that consists of several subevents a small event with mo 5 1026 dyn cm remains a singlet stress drop of the largest subevent is 800 bar on average and significantly higher than 200 bar of the largest subevent for interplate thrust earthquakes stress drop tends to scatter for smaller earthquakes beyond the resolution limit of our analysis deep and intermediate depth shocks in the tonga region possess higher indicating a significant regionality in the mode of stress release within a subducting slab fault planes have in general preferred orientation according to the focal depth indicating alignment of weak planes within the slab the slab is therefore not simply elongated or shortened under down dip extension or compression but rather rotates by bulk simple shear we suggest that this bulk shear is a dominant mechanism for the deformation of a subducting plate including its bending and unbending near deep sea trenches

a new method for determining the long period component of the source time function of large earthquakes inversions of seismic body waves indicate that most large earthquakes involve spatial and temporal heterogeneity of the moment release but seismic body waves usually lack sufficient bandwidth to constrain the long period component of the radiation analysis of long period surface waves and free oscillations can constrain the overall source duration and moment however most procedures assume simple trapezoidal or boxcar source time histories inconsistent with the body wave complexity the authors find that source time function complexity can affect long period surface waves sufficiently to impact estimates of the source moment tensor rupture duration and centroid depth they present a procedure to objectively determine the long period component of complex source time functions in which they directly utilize results from body wave analysis the method is applied to two great normal fault events of june 22 1977 tonga m sub w 8 2 and august 19 1977 indonesia m sub w 8 5 standard long period analysis procedures underestimate the total slip duration in both cases the overall source process times of both earthquakes are longer than 120 s

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

source mechanism of two 1994 intermediate depth focus earthquakes in guerrero mexico abstract in may and december 1994 two medium size intermediate depth focus earthquakes occurred in guerrero mexico eastward of the rupture area of the great michoacan earthquake of september 19 1985 even though these are not major earthquakes 6 4 m w they were widely felt through central and southern mexico with minor damage at zihuatanejo and acapulco located along the pacific coast and mexico city both earthquakes separated by 100 km have similar focal depths and magnitudes however their focal mechanisms based upon the polarities of first arrivals show some differences the may earthquake shows a clear normal faulting mechanism 307 55 108 whereas the december earthquake mechanism solution suggests an initial thrust faulting 313 62 98 process although previous analysis including local and teleseismic stations reported a normal faulting for the december earthquake we find that modeling using the cmt focal mechanism solution fails to reproduce the first 5 sec of the observed p wave signal at the nearest broadband station 168 km and the s wave polarity at two strong ground motion local stations 32 53 km in fact the best fit for these stations is obtained using the thrust focal mechanism calculated from the first motion method seismic moment value and rupture duration time deduced from the teleseismic spectral analysis are 2 0 10 18 n m and 6 9 sec for the may event 2 8 10 18 n m and 7 1 sec for the december earthquake from the inferred seismic moment an average of 15 bars for both earthquakes is obtained inversion of teleseismic p wave data indicates a better fit using the cmt focal mechanism solution normal faulting than the first motion mechanism for both earthquakes although the adjustment9s differences are small for the may event for this earthquake the rupture consisted of two sources separated by 7 sec starting at a depth of 40 km and then propagating downdip reaching a depth of 60 km the december earthquake however released all its energy at a depth of 50 km in two main sources separated by 10 sec the non double couple components values are 0 004 and 0 01 for the may and december events respectively indicating that the december shock has a small contribution of non double couple radiation that could be the result of a changing mechanism this result agrees with the hypothesis that a slab subducting at a shallower angle our case is associated with the existence of random subfaults with different fault orientations from a tectonic point of view the complexity of the december earthquake could be the result of the observed complexity of the stress distribution around 101 w and the existence of compressional events beneath the normal faulting earthquakes near the coastline this feature permits the flexural stresses associated to the slab bending upward to become subhorizontal at the guerrero region we conclude that the may earthquake corresponds to a pure normal faulting whereas the december shock is a complex event with a variable fault geometry

the 1965 rat islands earthquake a critical comparison of seismic and tsunami wave inversions we use the 1965 rat islands earthquake to compare seismic wave inversion results for moment release distributions to tsunami wave inversion results for slip distribution inversion using the two different datasets shows a high correlation between the areas of high moment release and areas of high slip these areas of high slip correspond to the tectonic features of the western aleutians namely the rat buldir and near blocks less slip is observed between the blocks the correlation indicates that far field tsunami data is as useful as seismic data for studying moment distributions

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

ground rotational motions recorded in near source region of earthquakes large rotational motions excited by earthquakes are recorded during an earthquake swarm of march 1997 offshore ito in izu peninsula japan the largest rotational velocity recorded at kaw is 2 6 10 2 rad s around the north south axis during an earthquake of magnitude 5 2 at 14 09 gmt on march 3 the rotational motions around the vertical axis excited by the largest event is 3 3 10 3 rad s considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis

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

combined la icp ms and cryo sem eds an improved technique for quantitative analysis of major minor and trace elements in fluid inclusions in halite abstract quantitative multi element analyses of single fluid inclusions in halite and other sedimentary minerals can provide information on the origin and chemical evolution of ancient surface waters on earth integrated laser ablation inductively coupled plasma mass spectrometry la icp ms and cryogenic scanning electron microscopy energy dispersive spectroscopy cryo sem eds were used here for the quantitative analysis of fluid inclusions in halite single phase fluid inclusions in modern and ancient halite were analyzed using a 193 nm arf excimer laser ablation system coupled with a quadrupole mass spectrometer to test a new calibration technique using magnesium mg as an internal standard mg concentrations obtained by cryo sem eds analyses of fluid inclusions were used to convert la icp ms concentration ratios into absolute elemental concentrations mg concentrations of ancient fluid inclusions from cryo sem eds analyses were reproducible to better than 5 relative standard deviation rsd comparison between the chemical composition of modern dead sea brine measured using icp oes optical emission spectroscopy and the composition of fluid inclusions in dead sea halite formed from those brines shows that fluid inclusions in halite faithfully record the chemistry of the brines from which they precipitated overall la icp ms analytical precision for major ions k ca s in so4 above 50 mmol kg h2o is better than 10 rsd and accuracies range from 2 to 21 mean concentrations of li b sr rb and ba agree within 7 of their expected values and are reproducible within 15 whereas cs concentrations above detection limit are typically reproducible to within 15 to 25 rsd for trace elements in seawater such as u and mo quantitative analyses in fluid inclusions are achieved at concentrations above 20 nmol kg h2o the results from this study confirm that the precision and accuracy of major and minor elemental analysis is improved with mg as an internal standard instead of na and cl used in previous studies controlled optimized ablation of 30 m fluid inclusions in halite improved the accuracy and precision and reduced the overall limit of detection lod by one order of magnitude compared to previous studies wide ranges of lods between 0 7 nmol kg h2o and 10 mmol kg h2o reflect variations in inclusion volume and elemental concentrations analytical accuracies obtained for major elements demonstrate that cryo sem eds and la icp ms are complementary microbeam techniques for chemical analysis of individual fluid inclusions in halite