mechanisms and depths of atlantic transform earthquakes we have studied 40 earthquakes on seven major transforms along the mid atlantic ridge the majority show the expected transform parallel strike slip motion on steeply dipping fault planes some anomalous mechanisms suggesting either unusually shallow dip or a component of dip slip motion occur near ridge transform intersections the vertical tectonism suggested by transform morphology may thus be restricted to intersections where thermal contrast across the transform is greatest and stress orientations can be oblique to both ridge and transform centroid depths determined by waveform inversion are limited to a shallow zone corresponding approximately to the area above the 400 c isotherm of the thermal structure expected from lithospheric cooling the depth extent of faulting predicted by estimating fault area from seismic moments extends approximately to the predicted 600 c isotherm assuming that the areas above the 400 c or 600 c isotherms fail seismically moment release for six of the transforms accounts for varying fractions of the slip predicted by plate motion suggesting that some aseismic slip occurs if the time period sampled is representative in contrast on the vema transform the inferred seismic slip is greater than predicted unless faulting extends to the 650 c isotherm alternatively the vema may have an unusually long recurrence time or be mechanically anomalous due to its complex history in contrast to transform events centroids for oceanic intraplate earthquakes extend to approximately the 750 c isotherm this result is intriguing if depths reflect lithospheric strength as a function of depth transforms have much higher strain rates than intraplate areas so if both had the same rheology the limiting isotherm for transforms should be higher alternatively if a weaker rheology were appropriate the higher strain rate should cancel the weakening and yield a limiting isotherm similar to that for intra plate regions transforms may thus be either weaker and or have higher temperatures than expected in the latter model the required high temperatures perhaps due to intrusion at depth predict measurable heat flow anomalies the second possibility unusual rheological weakness is reminiscent of the unexplained weakness of the san andreas fault where heat flow data exclude anomalously high temperatures

the enigma of the arthur s pass new zealand earthquake 1 reconciling a variety of data for an unusual earthquake sequence the 1994 arthur s pass earthquake mw6 7 is the largest in a recent sequence of earthquakes in the central south island new zealand no surface rupture was observed the aftershock distribution was complex and routine methods of obtaining the faulting orientation of this earthquake proved contradictory we use a range of data and techniques to obtain our preferred solution which has a centroid depth of 5 km m0 1 3 1019 n m and a strike dip and rake of 221 47 112 respectively discrepancies between this solution and the harvard centroid moment tensor together with the global positioning system gps observations and unusual aftershock distribution suggest that the rupture may not have occurred on a planar fault a second strike slip subevent on a more northerly striking plane is suggested by these data but neither the body wave modeling nor regional broadband recordings show any complexity or late subevents we relocate the aftershocks using both one dimensional and three dimensional velocity inversions the depth range of the aftershocks 1 10 km agrees well with the preferred mainshock centroid depth the aftershocks near the hypocenter suggest a structure dipping toward the nw which we interpret to be the mainshock fault plane this structure and the harper fault 15 km to the south appear to have acted as boundaries to the extensive aftershock zone trending nnw sse most of the ml 5 aftershocks including the two largest ml6 1 and ml5 7 clustered near the harper fault and have strike slip mechanisms consistent with motion on this fault and its conjugates forward modeling of the gps data suggests that a reverse slip mainshock combined with strike slip aftershock faulting in the south is able to match the observed displacements the occurrence of this earthquake sequence implies that the level of seismic hazard in the central south island is greater than previous estimates

revised sequence stratigraphic interpretation of the eocene oligocene boundary interval mississippi and alabama gulf coast basin u s a abstract examination of regional stratigraphic relationships and graphic correlation of biostratigraphic data from two important localities has resulted in a new interpretation of the sequence stratigraphy of the eocene oligocene boundary interval in mississippi and alabama the much studied section at st stephens quarry in southwestern alabama does not contain all of the components of the depositional sequence at st stephens the highstand systems tract is missing and is represented by a marine hiatus condensed section at the top of the upper eocene shubuta clay as a consequence the surface of maximum starvation and the overlying sequence boundary are merged lowermost oligocene sediments which were deposited in the lowstand systems tract rest on this maximum flooding surface seque ce boundary these findings agree with those from other parts of the gulf coast where the eocene oligocene boundary has been recognized as a sequence boundary associated with a subaerial unconformity and a downward shift in coastal onlap revision of the sequence stratigraphic interpretation at st stephens quarry alleviates much of the confusion concerning the relationship between the eocene oligocene boundary and the sequence boundary this new interpretation shows that not all sections contain all components of a particular depositional sequence and that caution is warranted when sequence stratigraphic interpretations are used to evaluate observations the sequence stratigraphic interpretation of the section at st stephens has undergone revision as new observations have become available

re visiting the tectonics of the oceanic intraplate earthquake of march 25 1998 m 8 1 in the balleny sea offshore antarctica abstract the antarctic plate earthquake of march 25 1998 m 8 1 and its aftershocks are re visited to evaluate the role of the associated tectonics in stress concentration due to ambient horizontal crustal motion caused by deglaciation in antarctica using a numerical technique called the distinct element method a two dimensional structural model of the epicentral region is developed and tectonically loaded for a year along the inferred direction of the motion a spatial correlation is observed between the resulting locations of relatively high shear stresses and those of the main shock and associated aftershocks in particular seismicity is concentrated at and near the intersections of the main fault carey and gambier fracture zones where the shear stresses are significantly elevated and whose sign duplicate the inferred sense of movement along them the modeling results suggest that stress concentrations near pre existing intersecting fault and fracture zones due to a possible deglaciation induced horizontal crustal force may have been a cause of this enigmatic earthquake

neogene quaternary fault reactivation influences coastal basin sedimentation and landform in the continental margin of ne brazil we investigate the role of reactivation of precambrian basement fabric in the tectono sedimentary and geomorphological evolution of the paraiba basin continental margin of northeastern brazil during the cretaceous neogene and quaternary this basin represents part of the last bridge between south america and africa before the last breakup stage of the south atlantic rifting in the early cretaceous the paraiba basin infill is composed of siliciclastic and carbonate cretaceous units as well as aeolian fluvial and marine quaternary units we used shuttle radar imagery aeromagnetic wellbore and field data the reduced to the pole magnetic map rtp indicates the continuity of the steeply dipping precambrian basement shear zones beneath the paraiba basin the combined analysis of surface and subsurface data shows that ne sw and e w striking shear zones were subjected to brittle reactivation in the aptian middle albian during the basin opening and again in the neogene quaternary forming a system of horsts and grabens along the basin some of these structures such as the e w oriented pernambuco shear zone present modern day seismicity n s and mainly nw se striking transfer faults cut across aptian middle albian to neogene quaternary strata these four main fault directions control main river channels and alluvial valleys up to 2 km wide topographic breaks up to 50 m were created by late reactivation of rift faults which mark the boundary between horsts and grabens along the basin in addition structural data evidence syn tectonic faulting with vertical offsets up to 80 m in the cretaceous and up to 70 m in the neogene quaternary we conclude that shear zones across the study area are long lived structures that have behaved as weakness zones their neotectonic brittle reactivation has controlled sediment deposition and landform development which continued through the neogene quaternary

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

the 14 november 2001 kokoxili kunlunshan tibet earthquake rupture transfer through a large extensional step over the 14 november 2001 kokoxili tibet earthquake m w 7 8 ruptured 400 km of the western kunlun fault in northern tibet we apply two inversion methods to p and sh waves recorded by the global seismographic network to recover the spatial and temporal history of the rupture process the observed surface rupture consists of two strike slip segments offset by an extensional step over little surface rupture was observed in the graben system in this step over which is approximately 45 km long and over 10 km wide our results imply that the rupture did not jump this large gap but that the rupture was continuous through the graben the earthquake began with a small strike slip subevent presumably along the westernmost of the two segments this was followed 5 sec later by a subevent of about the same magnitude but having an oblique mechanism with a large normal faulting component the likely location for this subevent is within the graben this oblique slip event probably enabled transfer of the rupture onto the main kunlun fault the main moment release began 18 sec after rupture initiation and propagated over 350 km eastward along the kunlun fault slip on this segment was very heterogeneous averaging 2 m for the first 200 km followed by a sharp increase to a maximum of 7 5 m within the next 50 km and then a rapid decline the average rupture velocity along the main segment was high 3 6 km sec 1 and probably exceeded the local shear wave velocity the m w 7 8 kokoxili earthquake had a longer surface rupture and faster average rupture velocity radiated more energy and probably had a lower average fracture energy than the november 2002 m w 7 9 denali fault alaska earthquake evidence suggests that the velocity of the rupture front dropped significantly after passing the point of maximum slip implying a large difference in frictional strength between the two ends of the fault online material waveform fits to teleseismic body waves

global event location with full and sparse data sets using three dimensional models of mantle p wave velocity in order to improve on the accuracy of event locations at teleseismic distances it is necessary to adequately correct for lateral variations in structure along the ray paths either through deterministic model based corrections empirical path station corrections or a combination of both approaches in this paper we investigate the ability of current three dimensional models of mantle p wave velocity to accurately locate teleseismic events we test four recently published models two are parameterized in terms of relatively long wavelength spherical harmonic functions up to degree 12 and two are parameterized in terms of blocks of constant velocity which have a dimension of a few hundreds of km these models together with detailed crustal corrections are used to locate a set of 112 global test events consisting of both earthquakes and explosions with p wave travel time data compiled by the international seismological centre isc the results indicate that the supposedly higher resolution block models do not improve the accuracy of teleseismic event locations over the longer wavelength spherical harmonic models for some source locations the block models do not predict the range of observed travel time residuals as well as the longer wavelength models the accuracy of the locations largely varies randomly with geographic position although events in central asia are particularly well located we also tested the effect of reduced data sets on the locations multiple location iterations using 30 p wave travel times indicate that teleseismic events may be located within an area of 1000 km of the true location 66 of the time with only the model based corrections and increasing to 75 if calibration information is available if as few as 8 phases are available then this is possible only 50 of the time further refinement in models and or procedure such as the addition ofp phases azimuth data and consideration of p wave anisotropy may provide further improvement in the teleseismic location of small events

a rare great earthquake on an oceanic fossil fracture zone first motion solution found in this study and has a strike consistent with the fracture zone north of the bend the southern fault plane with strike 178 d ip 54 and rake 65 has a strike consistent with the portion of the fracture zone to the south of the bend and has a dip which can be explained by the style of deformation that the region is undergoing the centroid moment tensor solution of the broad band model is calculated and found to be consistent with the region of low misfit in mantle wave solution space the broad band solution has a moment of 1 53 10 21 nm mw 8 1 again consistent with the mantle wave data slip propagated bilaterally with an approximate rupture velocity of 3k ms 1 80 per cent of local shear wave speed the rupture front is less well resolved to the south of the epicentre than to the north the majority 75 per cent of moment originated from slip on the northern fault the broad band data requires significant slip below the oceanic moho with as much as 70 per cent of moment due to slip in the brittle uppermost mantle in the preferred model

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

paleoecological patterns in molluscan extinctions and recoveries comparison of the cretaceous paleogene and eocene oligocene extinctions in north america abstract exposures across the cretaceous tertiary k t and eocene oligocene e o boundaries in texas and mississippi respectively probably represent the most complete and best preserved fossil molluscan sequences across these boundary intervals in the world outcrops from both boundaries contain pristine aragonitic and calcitic molluscan shells which were deposited in fine grained sediments from open marine environments the k t and the e o extinctions exhibit very different recovery patterns probably reflecting very different causes as well as magnitudes of extinction the k t sequence contains a molluscan fossil record that is consistent with an abrupt extinction event at the k t boundary and a prolonged initial recovery in hostile oceanographic conditions the uppermost 10 m of upper cretaceous sediments contain a diverse approximately 40 species molluscan fauna dominated by suspension feeders the earliest paleocene sediments immediately above the tsunami bed contain an impoverished fauna dominated by deposit feeders the paleocene fauna slowly climbs in diversity but remains relatively impoverished and dominated by deposit feeders for several hundred thousand years after the extinction in conjunction with anomalous 13c values that suggest prolonged suppression of marine primary productivity diverse suspension feeder dominated molluscan assemblages reappear with the resumption of normal conditions of primary production in the long term early to middle paleocene gamma diversity includes evolutionary bloom taxa families that exhibit unusual speciation bursts that subside in the eocene total diversity for the gulf coast does not approach cretaceous levels until the late eocene representing a total recovery interval of nearly 25 million years while the e o event also reflects a molluscan extinction rate of over 90 in the gulf of mexico there are no signs of hostile environmental conditions in the recovery fauna early oligocene molluscan assemblages are diverse and dominated by suspension feeders characteristic of normal marine conditions the hiatus at the e o boundary however could have obscured a short term recovery fauna there is also no sign of long term perturbation by the e o extinction there are no bloom taxa and gamma diversity approaches pre extinction levels within a few million years the overall pattern of the e o extinction is consistent with extinction and or migration associated with long term cooling

the 2015 mw 7 1 earthquake on the charlie gibbs transform fault repeating earthquakes and multimodal slip on a slow oceanic transform the 2015 mw 7 1 earthquake on the charlie gibbs transform fault along the mid atlantic ridge is the latest in a series of seven large earthquakes since 1923 we propose that these earthquakes form a pair of quasi repeating sequences with the largest magnitudes and longest repeat times for such sequences observed to date we model teleseismic body waves and find that the 2015 earthquake ruptured a distinct segment of the transform from the previous 1998 earthquake the two events display similarities to earthquakes in 1974 and 1967 respectively we observe large oceanic transform earthquakes to exhibit characteristic slip behavior initiating with small slip near the ridge and propagating unilaterally to significant slip asperities nearer the center of the transform these slip distributions combined with apparent segmentation support multimode slip behavior with fault slip accommodated both seismically during large earthquakes and aseismically in between

the march 25 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake mw 8 1 occurred 250 km from the nearest plate boundary in oceanic lithosphere with an age of 35 55 my analysis of aftershock patterns shows that the earthquake ruptured a fault or series of strike slip fault segments nearly 300 km long the strike of the fault s is nearly perpendicular to the north south trending fossil fracture zones which are the most marked bathymetric features of this region moment release during the mainshock was concentrated in two large subevents clearly visible in the teleseismic body wave waveforms modeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation on the eastern end of the fault with the second large subevent occurring 220 280 km to the west the two pulses of moment release are found to be separated in time by 65 s comparison of the relative s wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by 10 occurred between the two subevents

sequence stratigraphic interpretations from palynofacies dinocyst and lithological data of upper eocene lower oligocene strata in southern mississippi and alabama u s gulf coast abstract this paper presents new information on the sequence stratigraphy of the upper eocene lower oligocene strata in southern mississippi and alabama based on palynological and lithological data from five sections by integrating lithological characteristics with palynofacies assemblages several dinocyst paleoecological groups the deflandrea group and the abundance of reworked dinocysts in samples paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area we identified a maximum flooding surface in the middle of the shubuta clay formation in southern mississippi and dated it as latest eocene in southern alabama the eocene oligocene boundary was placed within a condensed section representing about 0 19 ma and it coincided with the shubuta clay vicksburg group contact this condensed section is equivalent to the accumulation of the upper shubuta and red bluff formations in southern mississippi the forest hill mint spring contact which has been interpreted as a sequence boundary that merged with a transgressive surface does not correlate with the tejas a ta 4 3 4 4 sequence boundary of haq et al 1988 the pachuta marl and lower shubuta clay formations are constituents of a late eocene transgressive systems tract in southern mississippi but this systems tract extended to the shubuta clay vicksburg group contact in southern alabama the overlying early oligocene highstand systems tract consisted of the upper shubuta in mississippi and the red bluff bumpnose forest hill formations a thin sandstone in the mint spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern mississippi section in general the mint spring marl and marianna limestone constituted a transgressive systems tract

shallow marine ostracode turnover during the eocene oligocene transition in mississippi the gulf coast plain usa abstract the eocene oligocene transition eot is associated with a major eustatic sea level fall sea surface cooling change in ocean stratification and enhanced seasonality while these changes are well known to have significantly restructured open ocean ecosystems comparatively little is known about how these multiple environmental changes affected coastal biotas here we describe ostracode faunas in shelf deposits in the gulf coast of mexico through the late eocene to early oligocene analyzing the biostratigraphy and paleoecology of ostracodes from the mossy grove core mississippi mossy grove ostracode faunas suffered gradual extinction and diversity loss in the 150 kyr between 33 96 and 33 81 ma during the turnover 10 of 21 species disappeared seven of the 12 disappearing species became extinct while others are lazarus taxa that later re appeared in the vicksburgian 33 7 ma during the sea level fall associated with the eocene oligocene e o boundary 33 90 ma six of seven outer shelf taxa disappeared while three of four inner shelf taxa increased in abundance the major changes in ostracode assemblages occur during the eot 1 and eot 2 events prior to the oi1 isotope excursion and appear to reflect a combination of impacts from eustatic sea level fall and local enhanced surface ocean seasonality shown in stable isotope records from the st stephen s quarry core alabama

the gilbert islands republic of kiribati earthquake swarm of 1981 1983 abstract a major swarm of intraplate earthquakes at the southeastern end of the gilbert islands chain 3 5 s 177 5 e commenced in december 1981 and lasted through march 1983 no seismicity had been reported in the historical record in this region prior to 1981 but during the swarm 217 events with mb 4 0 were located by the neis with 86 events having mb 5 0 the source region is quite remote and the uniform detection level for the neis is for mb 4 8 a b value of 1 35 is found for the swarm using the maximum likelihood method four events in the sequence were large enough mb 5 6 5 9 to determine focal mechanisms teleseismically using body and surface wave analysis these events are found to have a range of mechanisms from predominantly thrust with a significant oblique component to purely strike slip the compression axes are consistent for all four events with horizontal orientation trending nne ssw this orientation is perpendicular to the direction of plate motion the events are located at depths between 15 and 20 km placing them deep in the oceanic crust or in the upper mantle no obvious bathymetric feature can be related to the fault plane orientations though there is an offset in the island chain near the epicenters while some characteristics of the swarm suggest a magmatic origin the nature of the focal mechanisms the location of the swarm and the large accumulated moment release of the sequence favor a tectonic origin

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

the 1994 java tsunami earthquake slip over a subducting seamount on june 2 1994 a large subduction thrust earthquake ms 7 2 produced a devastating tsunami on the island of java this earthquake had a number of unusual characteristics it was the first recorded large thrust earthquake on the java subduction zone all of the aftershock mechanisms exhibit normal faulting no mechanisms are similar to the main shock also the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow shallow rupture near the trench similar to the 1992 nicaragua earthquake we first relocate the main shock and the aftershocks we then invert long period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip a dip of 12 hypocenter depth of 16 km and moment of 3 5 l020 n m mw 7 6 give the best fit to the combined seismic data and are consistent with the plate interface geometry the source spectrum obtained from both body and surface waves has a single corner frequency between 10 and 20 mhz implying a stress drop of 0 3 mpa the main energy release was preceded by a small subevent lasting 12 s the main slip occurred at 20 km depth downdip and to the nw of the hypocenter this area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount we interpret the java earthquake as slip over this subducting seamount which is a locked patch in an otherwise decoupled subduction zone we find no evidence for slow shallow rupture no thrust aftershocks are expected if the entire locked zone slipped during the main shock but extension of the subducting plate behind the seamount would promote normal faulting as observed it seems probable that such a source model could also explain the size and timing of the observed tsunami

dynamic stress triggering during the great 25 march 1998 antarctic plate earthquake we investigate the coseismic stress redistribution during the 25 march 1998 great antarctic plate mw 8 1 earthquake in which the mainshock consisted of two distinct subevents separated in time by several tens of seconds we compute the dynamic stress time histories for the fault geometry and the rupture and slip history determined by henry et al 2000 using the discrete wavenumber and re flectivity method of cotton and coutant 1997 both for a homogeneous and a strat ified half space we first image the coseismic stress evolution caused by the first subevent on the fault plane of the second one for both the velocity models we compute both shear and normal stress changes and a time dependent coulomb failure function cff our results show that the shear stress changes have larger amplitudes than the other stress components and hence are the primary control on the evolution of the cff the dynamic stress amplitudes are larger than the static stress pertur bations with the largest positive dynamic stress peak on the second subevent fault plane reaching slightly less than 0 2 mpa at 60 sec and 65 sec after the nucleation for the layered and the homogeneous crustal models respectively we suggest that the dynamic stress changes caused by the first subevent promoted a nearly instan taneous failure on the second subevent fault

compound rupture of the great 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake ruptured a portion of the antarctic plate more than 200 km west of its boundary with the australian plate the harvard centroid moment tensor solution indicates that the earthquake was primarily a strike slip event but the large non double couple component of the moment tensor suggests considerable complexity in the rupture process we use a finite fault inversion method to determine details of the rupture process from teleseismic body waves recorded by the global seismic network the p waves are poorly fit by one or more subevents having only a strike slip mechanism we find that the presence of a large oblique normal faulting subevent located to the east of the hypocenter is necessary to improve the fit this subevent combines with a larger strike slip subevent to the west to comprise the main moment release in the earthquake and is the cause of the large non double couple component in the long period focal mechanism the earthquake exhibited very high slip and high stress drop compared with most interplate strike slip events and the rupture was largely confined to the upper 15 20 km of the lithosphere both constituent focal mechanisms indicate that this part of the antarctic plate is under nw se oriented tension although the origin of these stresses is unknown

glaucony and carbonate grains as indicators of the condensed section omma formation japan the fifth order depositional sequences of the early pleistocene omma formation exposed along the japan sea coast of central japan were formed by glacial eustasy during oxygen isotope stages 50 to 28 in each depositional sequence two ecostratigraphic datums are always present the appearance and disappearance datums of warm water molluscan species these datums are independent of sequence stratigraphic concepts because the establishment of them is based on immigration events of molluscan species associated with glacio eustatic sea level changes determination of time planes shows that the appearance datum seems to occur near the midpoint of sea level rise on the glacial to interglacial shift in deep sea d 18 o records in order to evaluate the significance of the condensed section in sequence stratigraphy and also to facilitate its recognition this study examines the stratigraphic relationship of the condensed section indicators glaucony and carbonate grains with respect to the position of the ecostratigraphic datums in depositional sequences of the omma formation the results show that the maximum concentration of carbonate grains is a more reliable maximum flooding surface indicator than the concentration of glaucony the combination of indicators of condensed section and ecostratigraphic datums represented by incursion epiboles enables the boundary between transgressive and highstand systems tracts to be recognized in the inner shelf parts of depositional sequences moreover truncation of ecostratigraphic datums during sea level falls demonstrates significant erosion at the sequence boundaries integration of climatic palaeoecology and sequence stratigraphy permits a level of correlational precision of the order of a few thousands of years 1998 elsevier science b v all rights reserved

approximate stochastic self similarity of envelopes of high frequency teleseismic p waves from large earthquakes a wavetrain of high frequency hf p waves from a large earthquake when recorded at a distant station looks like a segment of modulated noise with its duration close to the duration of rupture these wavetrains with their bursts and fadings look much more intermittent than a segment of common stationary random noise we try to describe quantitatively this bursty behavior to this end variogram and spectral analyses are applied to time histories of p wave envelopes squared amplitude or instant power signals in six hf bands of 1 hz width nine mw 7 6 9 2 earthquakes were examined using in total 232 records and 992 single band traces variograms of integrated instant power are approximately linear on a log log scale indicating that the correlation structure of the instant power signal is approximately self similar also estimates of the power spectrum of the instant power signal look approximately linear on a log log scale log log slopes of the variograms and spectra deliver estimates of the hurst exponent h that are mostly in the range 0 6 0 9 markedly above the value h 0 5 of uncorrelated white noise signals the preferred estimate over the entire data set is h 0 83 still this estimate may include some bias and must be treated as preliminary the inter event scatter of h estimates is about 0 04 reflecting individual event to event variations of h many of the average log log spectral plots show slight concavity that perturbs the approximately linear slope this is a secondary effect that seems to be mostly related to the limited bandwidth of the data evidence is given in support of the idea that the observed approximately self similar correlation structure of the p wave envelope originates in a similar structure of the body wave instant power signal radiated by the source so that the propagation related distortions can be regarded as limited the facts presented suggest that the space time organization of the earthquake rupture process is multiscaled and bears significant fractal features it deviates from the brittle crack model with its two well separated characteristic scales phenomenologically the high frequency body wave radiation from an earthquake source can be thought of as a product of stationary noise and the square root of a positive random envelope function with a power law spectrum from the viewpoint of applications the self similarity of body wave envelopes provides a useful constraint for earthquake source models used to simulate strong ground motions

seafloor structure near the epicenter of the great 25 march 1998 antarctic plate earthquake 1 the great antarctic plate earthquake m 8 1 that took place on 25 march 1998 was one of the largest oceanic intraplate strike slip events ever recorded but the cause of the earthquake is still unclear detailed marine geophysical surveys were conducted near the epicenter of the earthquake and the results of swath bathymetry and the magnetic and gravity anomalies are presented the data revealed the detailed structure of a seamount just south of the epicenter of the main shock two possible structures which may represent the faults of the antarctic plate earthquake during the first subevent were inferred from the geophysical data collected during the cruise by taking the uncertainties in the location of the epicenter and the distribution of the aftershocks into account and the foot of the north side escarpment of the seamount may indicate the main fault of the first strike slip subevent of the antarctic plate earthquake the north side escarpment of the seamount was most likely formed before the antarctic plate earthquake indicating that the earthquake occurred along preexisting structures the magnetic anomaly and structural trends near the seamount are different from those in adjacent areas and the area near the seamount is likely a block that was captured during ridge reorganization moreover the area near the seamount may be a crustal fragment that was formed during initial rifting between antarctica and australia

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

global cmt analysis of moderate earthquakes mw 4 5 using intermediate period surface waves a new method for calculating centroid moment tensor cmt solutions for moderate sized earthquakes is presented and tested in the new algorithm which is a modification to the standard harvard cmt method intermediate period surface waves are included in the inversion for source parameters the dispersion of teleseismic surface waves in the period range 40 to 150 sec is predicted by interpolation of recent global phase velocity maps the method is tested on a set of 20 moderate and large 5 2 mw 7 2 earthquakes with known mechanisms the retrieved mechanisms are similar to the previous results even when noise is added to the seismograms to simulate earthquakes of a smaller magnitude mw 4 5 the inversion algorithm is applied to the 1993 klamath falls mainshock and aftershock sequence and the results compare well with earlier results a catalog of mw 4 5 focal mechanisms for greece and surrounding areas for the first six months of 1995 is derived using the new method of analysis