three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

reviewing megathrust slip behavior for recent mw 8 0 earthquakes along the peru chilean margin from satellite goce gravity field derivatives abstract the characterization of a seismogenic zone associated with the rupture process that occurs during great megathrust earthquakes has been approached from different perspectives different studies lightened the structural complexity and compositional heterogeneity of the interplate region in this work we address this relationship from the analysis of density contrasts provided by satellite gravity data and comparing these results with slip behavior along the rupture zone we performed the calculation of gravity anomalies and gradients both corrected by the effect of topography and sediments then we analyzed this relation with the rupture zones of four megathrust earthquakes mw 8 along the peru chilean coast associated with the largest earthquakes that occurred in the last years along this setting finding that the maximum vertical displacements were located close to gravity minimums in the forearc zone we finally obtained density models by inverting four trench parallel profiles from the gravity disturbance finding low density contrasts related to the maximum slips and high density contrasts at its edges related to a decrease of the displacement or to the lateral ending of the rupture the along strike seismic segmentation observed previously in the gravity derivatives is also observed along dip being slip increased at gravity lows and arrested at gravity highs probably indicating that the forearc structure plays a key role in across strike rupture behavior in depth our results agree with the hypothesis that persistent tectonic features modeled at a high degree by the oceanic plate morphology may control strain accumulation and release along the megathrust

measuring slow slip offshore tsunami earthquakes are rare events and are distinguished by an anomalously shallow source depth and slow rupture propagation speed 1 2 they can be particularly dangerous because they generate less high frequency seismic energy than a normal earthquake consequently they are not preceded by the strong shaking that would warn coastal residents that a locally generated tsunami is on the way a better understanding of the range of slip behaviors in the offshore portion of subduction zones is needed to constrain models and improve earthquake hazard forecasts on page 701 of this issue wallace et al 3 present the first offshore geodetic data from a slow slip event on the hikurangi subduction zone offshore from new zealand see the figure this segment of the hikurangi subduction zone is unusual in that it experienced two tsunami earthquakes in 1947 continuous global positioning system gps instrumentation onshore indicates that the southern part of the subduction zone is locked above a plate depth of 40 km with slow slip events occurring at greater depth similar to what is observed in many other subduction zones 4 5 in contrast the northern part of the hikurangi subduction zone appears to accommodate plate motion primarily through geodetically detected slow slip events at shallow depths the up dip extent of slow slip however cannot be determined from onshore data only and offshore locking models depend strongly on model assumptions

a tem investigation of shock metamorphism in quartz from the vredefort dome south africa the origin of the vredefort structure in south africa is still debated several causes have been discussed namely asteroid impact internal gas explosion or tectonic processes evidence of dynamic rock deformation is pervasive in the form of planar features in quartz grains shatter cones veins of pseudotachylite and occurrence of coesite and stishovite high pressure quartz polymorphs a number of these characteristics is widely believed to support an impact origin however the planar features in quartz which are generally considered as one of the strongest indicators of impact are in the vredefort case considered as anomalous when compared with those from accepted impact structures we have investigated by optical and transmission electron microscopy tem the defect microstructures in quartz grains from different lithologies sampled at various places at the vredefort structure whatever the locality only thin mechanical brazil twin lamellae in the basal plane are observed by tem so far such defects have only been found in quartz from impact sites but always associated with sets of thin glass lamellae in rhombohedral planes 10 1n with n 1 2 3 and 4 at the scale of the optical microscope brazil twins in 0001 are easily detected in vredefort quartz grains because of the numerous tiny fluid inclusions which decorate them similar alignments of tiny fluid inclusions parallel to other planes are also detected optically but at the tem scale no specific shock defects are detected along their traces if these inclusion alignments initially were shock features they are now so severely weathered that they can no longer be recognized as unambiguous shock lamellae fine grained coesite was detected in the vicinity of narrow pseudotachylite veinlets in a quartzite specimen but stishovite was not found even in areas where its occurrence was previously reported finally definite evidence of high temperature annealing was observed in all the samples these observations lead us to the conclusion that our findings regarding microdeformation in quartz are consistent with an impact origin for the vredefort structure most of the original shock defects are now overprinted by an intense post shock annealing episode only the thin mechanical twin lamellae in the basal plane have survived

long term effects of water diversions on the longitudinal flow and bed profiles abstractwater diversions along alluvial rivers cause water and sediment loss and thereby affect morphological development assuming spatially continuous diversions along a constant width channel previous studies suggest a longitudinally convex bed at the equilibrium state however the validity of a convex bed profile for practically discrete diversions in natural channels of longitudinally varying width remains to be justified moreover such equilibrium analysis does not reveal the morphological time scale mts associated with water diversions to solve these issues a general theoretical framework is proposed for predicting the equilibrium state of the fluvial system which is applicable to both continuous and discrete water diversions in a longitudinally width varying channel numerical experiments complement the mts studies for water diversions the effects of diversion intensity diversion placement discrete and continuous and diversion scheme pure water and water sediment mixture are also s

geophysical and structural criteria for the identification of buried impact structures with reference to australia the discovery of large asteroid impact structures likely and possible impact structures onshore and offshore the australian continent woodleigh 120 km 360 ma gnargoo 75 km lower permian upper cretaceous tookoonooka 55 65 km 125 ma talundilly 84 km 125 ma mount ashmore 100 km end eocene and warburton twin structures 400 km pre end carboniferous requires re examination of the diagnostic criteria used for their identification bouguer anomalies of established impact structures chicxulub 170 km 64 98 0 05 ma woodleigh impact structure and gnargoo probable impact structure display a unique structural architecture where pre impact structural ridges are intersected and truncated by the outer ring of the circular structure seismic reflection data outline circular central uplift domes basement plugs and rim synclines sharp circular seismic tomography anomalies indicate low velocity columns under both the woodleigh impact structure and warburton probable impact hinting at deep crustal fracturing deformed curved and clouded intra crystalline planar deformation features in quartz qz pdfs displaying miller indices 10 11 10 12 10 13 diagnostic of shock metamorphism abound around exposed established impact structures vredefort 298 km 2023 4 ma sudbury 250 km 1850 3 ma charlevoix 54 km 342 15 ma manicouagan 100 km 214 1 ma tookoonooka and talundilly deformed qz pdfs allow recognition of shock metamorphism in buried impact structures where original qz pdfs were bent recrystallized and or clouded during formation of the central uplift and hydrothermal activity triggered by the impact planar deformation in quartz can also occur in explosive pyroclastic units but are limited to boehm lamella brazil twins with single lamella sets 0001 it has been suggested that a class of microstructures in quartz referred to as metamorphic deformation lamella qz mdl occur in endogenic tectonic metamorphic terrains however no type locality has been established for qz mdl of non impact origin

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

using centroid time delays to characterize source durations and identify earthquakes with unique characteristics the relationship between m 0 and the rupture duration is often difficult to establish this is particularly true for large earthquakes for which the moment rate functions mrf generally have complicated shapes and the estimated durations can vary considerably depending on the methodology used to evaluate the mrf in this work we show that the centroid time delay c provides an alternative estimate of the source duration inverted mrfs often end gradually making the end of coseismic rupture difficult to detect in such cases when the rupture duration is not well defined the time delay c is a useful quantity to represent the first order temporal characteristics of the rupture process variations in stress parameter can be investigated by assuming a standard scaling relationship between the seismic moment m0m0 and c this simple scaling relationship can also be used to identify unusual earthquakes with unique source properties such as events involving complicated rupture processes or earthquakes characterized by unusual rupture velocities stress drops or aspect ratios

rupture characteristics of major and great mw 7 0 megathrust earthquakes from 1990 to 2015 2 depth dependence depth varying characteristics of high frequency seismic radiation for megathrust earthquakes have been inferred from several recent giant earthquakes and large tsunami earthquakes to quantify any depth dependence more extensively we analyzed 114 m w 7 0 thrust faulting earthquakes with centroid depths from 5 to 55 km on circum pacific megathrusts using teleseismic body wave finite fault inversions and source spectrum determinations large tsunami earthquakes and some other shallow events at depths less than about 18 km have unusually long source durations and low values of static stress drop e v r 3 e and apparent stress with relatively depleted high frequency radiation deeper events have no clear global trend with source depth for moment normalized centroid time or total duration static stress drop moment scaled radiated energy apparent stress or radiation efficiency regional behavior among the 17 sampled subduction zones generally conforms to the global composite the source spectra have high frequency logarithmic spectral decay slopes averaging 1 6 there is relative enrichment in high frequency spectral levels with increasing source depth manifested in reduced high frequency spectral decay slope the ratio of high frequency 0 3 1 hz radiated energy to total energy increases correspondingly these observations suggest that overall dynamic rupture processes are relatively insensitive to source depth but varying scale lengths of megathrust heterogeneity may contribute to modest enrichment of high frequency seismic radiation for events deeper on the megathrust a weak correlation of higher estimated average megathrust temperature at 30 km depth with higher spectral decay rate indicates that the depth varying pattern may in part result from frictional properties being influenced by temperature variations or by systematic reduction of average attenuation with increasing depth along the megathrust

the age and thermal evolution of the vredefort impact structure a single grain upb zircon study abstract single grain u pb shrimp analyses of a heterogeneous zircon population from a small granite body in the archean basement core of the vredefort dome indicate an age of 2017 5 ma for the granite which is identical within errors to the previously reported age determinations for the vredefort impact event petrographic evidence from the granite indicates that it crystallized after the impact shock event but some doubt remains whether it is a true impact melt a decompression melt generated during rapid uplift of the crater basement following the impact event or a melt generated during an earlier 2 05 2 06 ga granulite facies anatectic event that was still at least partially molten at the time of the vredefort impact event rare zircon xenocrysts displaying planar microdeformation features and giving discordant archean ages are overgrown by polycrystalline zircon rims with u th compositions similar to that of the main 2 02 ga zircon population but with discordant 207pb 206pb ages indicating more recent pb loss

effects of kinematic constraints on teleseismic finite source rupture inversions great peruvian earthquakes of 23 june 2001 and 15 august 2007 two great underthrusting earthquakes that occurred along the coast of peru in 2001 and 2007 involve spatiotemporal slip distributions that differ from the predominantly unilateral or bilateral rupture expansion of many great events commonly used finite source rupture model parameterizations with specified rupture velocity and or short duration of slip at each grid point applied to the seismic data for these two events lead to incorrect slip distributions or inaccurate estimation of rupture velocities as a result of intrinsic kinematic constraints imposed on the model slip distributions guided by large aperture array back projections of teleseismic broadband p wave signals that image slip locations without imposing a priori kinematic constraints on the rupture process we exploit the availability of large global broadband body and surface wave data sets to consider the effects of varying the kinematic constraints in teleseismic finite source waveform inversions by allowing longer than usual rupture durations at each point on the fault using a flexible subfault source time function parameterization we find that the anomalous attributes of the 2001 and 2007 peru earthquake ruptures are readily recognized and accounted for by compound rupture models the great 23 june 2001 m w 8 4 8 4 earthquake involved an initial modest size event that appears to have triggered a much larger secondary event about 120 km away that developed an overall slip distribution with significant slip located back along the megathrust in the vicinity of the initial rupture the great 15 august 2007 m w 8 0 8 0 earthquake was also a composite event with a modest size initial rupture followed by a 60 sec delayed larger rupture that initiated 50 60 km away and spread up dip and bilaterally when back projections indicate greater rupture complexity than captured in a simple slip pulse type rupture model one should allow for possible long subfault slip duration or composite triggered sequences and not overly constrain the earthquake slip distribution

slip weakening distance and energy budget inferred from near fault ground deformation during the 2016 mw7 8 kaikōura earthquake the 2016 m7 8 kaik ura new zealand earthquake struck the east coast of the northern south island resulting in strong ground shaking and large surface fault slip since the earthquake was well recorded by a local strong motion seismic network near fault data may provide direct measurements of dynamic parameters associated with the fault weakening process here we estimate a proxy for slip weakening distance dc defined as double the fault parallel displacement at the time of peak ground velocity from accelerograms recorded at a near fault station three component ground displacements were recovered from the double numerical integration of accelerograms and the corresponding final displacements are validated against coseismic displacement from geodetic data the estimated dc is 4 9 m at seismic station keks located 2 7 km from a segment of the kekerengu fault where large surface fault slip 12 m has been observed the inferred dc is the largest value ever estimated from near fault strong motion data yet it appears to follow the scaling of dc with final slip for several large strike slip earthquakes the energy budget of the m7 8 kaik ura earthquake inferred from the scaling of dc with final slip indicates that a large amount of energy was dissipated by on and off fault inelastic deformation during the propagation of the earthquake rupture resulting in a slower average rupture speed 2 0 km s

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

intraplate and interplate faulting interactions during the august 31 2012 philippine trench earthquake mw 7 6 sequence on august 31 2012 a large m w 7 6 thrust earthquake occurred within the subducting philippine sea plate seaward of a low seismicity region of the plate boundary 9 5 n 11 5 n possibly as a result of horizontal compressional stress accumulation offshore of a locked megathrust the mainshock ruptured from 30 50 km depth with high radiated energy seismic moment ratio and enriched short period p wave radiation the nine largest aftershocks with global centroid moment tensor solutions m w 5 2 5 6 were shallow 10 13 km normal faulting outer rise events and a waveform template analysis using regional broadband data indicates many 48 110 similar normal faulting events m b 4 0 5 5 and a few 8 110 likely shallow thrust faulting events on the megathrust with additional very small unidentified events coulomb stress perturbations may contribute to the mix of intraplate and interplate faulting geodetic assessment of any slip deficit on the megathrust is essential for quantifying the potential for a future large interplate rupture in this region

origin of pseudotachylite in the lower witwatersrand supergroup vredefort dome south africa constraints from metamorphic studies small sub millimetre to centimetre thick pseudotachylite veins in metapelitic rocks of the lower witwatersrand supergroup in the collar of the vredefort dome are recrystallized to a biotite cordierite paragenesis indicating the attainment of lower amphibolite facies metamorphic conditions t 500 c following their formation the veins occur along ubiquitous anastomosing fracture networks displaying millimetre to centimetre scale displacements and truncate and incorporate fragments of an older ca 2 05 ga mid amphibolite facies peak metamorphic assemblage the post pseudotachylite metamorphism is attributed to the same event that caused highly variable annealing of ca 2 02 ga shock microdeformation features in rocks across the dome together with the disproportionately large volume of pseudotachylite in the rocks relative to that found in tectonic provinces and the absence of evidence of genetically related large scale shear or fault zones this metamorphic evidence suggests an origin for the pseudotachylite related to the 2 02 ga vredefort bolide impact event that produced the dome possible origins for the pseudotachylite include shock brecciation and melting post shock decompression melting and friction melting associated with the post impact high velocity excavation and modification phases of crater formation the post pseudotachylite metamorphism is attributed to the combined effects of an elevated pre impact crustal geotherm 25 c km related to the waning stages of the 2 05 ga peak metamorphism release of elastic strain energy from the impact shock event and contact effects beneath the impact melt body

the application of a multichannel laser raman microprobe microdil 28 to the analysis of fluid inclusions abstract the application to the analysis of fluid inclusions of laser excited raman microspectrometry with a multichannel detection system has two important features connected with the very short time needed to acquire one single spectrum 1 5 s the accumulation of a great number of the same spectral range results in an averaged spectrum with a very high signal to noise ratio with corresponding low detection limits and good counting statistics on the other hand the rapid acquisition of spectra enables the analysis of many individual inclusions in a relatively short time

a review of the structure petrology and dynamic deformation characteristics of some enigmatic terrestrial structures abstract we review three categories of enigmatic terrestrial structures that have a variety of macroscopic and microscopic dynamic deformation features the first category includes the midcontinent united states cryptoexplosion structures they are of shallow origin and illustrate the effects that might be expected from a meteorite impact on a sedimentary rock terrane the second category includes the well known vredefort and sudbury plutons or basement uplifts the lesser known precambrian basement uplifts at steen river manson and carswell and the diatreme breccia dikes at the slate islands they are of relatively deep seated origin and illustrate the effects that might be expected from deep crustal or mantle processes of an explosive nature the third category includes the large landslides in areas of crystalline rocks at koefels and langtang the dynamic deformation features at these latter locations appear to be related to high strain rate tectonic processes associated with the landslide itself we conclude that microscopic dynamic deformation features which occur in natural materials may have originated from meteorite impacts from internal explosions or from high strain rate tectonic process

triggering of tsunamigenic aftershocks from large strike slip earthquakes analysis of the november 2000 new ireland earthquake sequence 1 the november 2000 new ireland earthquake sequence started with a mw 8 0 left lateral main shock on 16 november and was followed by a series of aftershocks with primarily thrust mechanisms the earthquake sequence was associated with a locally damaging tsunami on the islands of new ireland and nearby new britain bougainville and buka results from numerical tsunami propagation models of the main shock and two of the largest thrust aftershocks mw 7 0 indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock off the southern tip of new ireland aftershock 1 numerical modeling and tide gauge records at regional and far field distances indicate that the main shock also generated tsunami waves large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event most of the damage on bougainville and buka islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands modeling of changes in the coulomb failure stress field caused by the main shock indicate that aftershock 1 was likely triggered by static stress changes provided the fault was on or synthetic to the new britain interplate thrust as specified by the harvard cmt mechanism for other possible focal mechanisms of aftershock 1 and the regional occurrence of thrust aftershocks in general evidence for static stress change triggering is not as clear other triggering mechanisms such as changes in dynamic stress may also have been important the 2000 new ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike slip earthquakes similar tectonic regimes that include offshore accommodation structures near large strike slip faults are found in southern california the sea of marmara turkey along the queen charlotte fault in british columbia and near the alpine fault of new zealand results from this study and previous stress modeling studies suggest that the likelihood of local tsunamis in these regions may significantly increase after a great strike slip earthquake

dynamic wedge failure reveals anomalous energy radiation of shallow subduction earthquakes abstract dynamically induced coulomb failure in the overriding wedge significantly affects energy radiation of shallow subduction earthquakes for a wedge on the verge of failure extensive fluid assisted coseismic failure due to updip rupture causes significant seafloor uplift above a shallow dipping basal fault the large inelastic uplift greatly enhanced by the presence of free surface significantly dilates the fault behind the rupture front during the rupture propagation which reduces the effective normal stress and sliding friction on the fault and increases the dynamic stress drop and slip velocity as a result slip velocity time histories in the shallow section of the fault tend to have a snail like shape leading to depletion of high frequencies in the slip velocity field and the resultant source time function we also show that the failure in the wedge acts as a large energy sink while contributing to seismic moment giving rise to distributed heat generation i e small heat flow anomaly across the fault low moment scaled radiated energy slow rupture velocity and small directivity which provides a unifying interpretation for nearly all anomalous observations documented for shallow subduction earthquakes

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

pseudotachylite in impact structures generation by friction melting and shock brecciation a review and discussion abstract fault related pseudotachylites are generated as the result of brittle or brittle ductile deformation related to seismic faulting it is generally accepted among tectonic workers that while cataclasis plays a role in pseudotachylite formation friction melting is involved in addition pseudotachylite and pseudotachylite like breccias have been repeatedly described from the basement exposures of impact and cryptoexplosion structures and as veinlets in shocked meteorites and lunar samples the relevant literature is reviewed with regard to controversial usage of the term pseudotachylite and attention is drawn to several problematic aspects 1 the term pseudotachylite is currently used both as a purely descriptive term and with genetic implications 2 no unambiguous criteria for comparison and distinction of tectonically and impact generated pseudotachylites have been identified 3 it needs to be considered that in impact structures pseudotachylite could be generated by two distinct processes namely by shock brecciation melting and by friction melting pseudotachylite in impact structures could be the result of either of these two processes or of both 4 it is recommended to adhere more stringently when describing breccias from impact or cryptoexplosion structures to nomenclature accepted for the description of fault rocks in tectonic environments this would help to avoid confusion when discriminating between melt rocks pseudotachylite impact melt rock fragmental breccias cataclasite fragmental impact breccia and mylonitic rocks 5 no criteria for the distinction of melt bearing impact breccias impact melt rock and pseudotachylite have been established either in order to solve these problems close interaction between structural geologists and impact workers is warranted it is suggested that the understanding of breccias in impact structures would be improved by paying particular attention to the temporal relationships between different breccia types this would facilitate recognition of possibly different formational processes for impact produced melt and fragmental breccias and their distinction from pre and post shock deformation products

the diversity of large earthquakes and its implications for hazard mitigation with the advent of broadband seismology and gps significant diversity in the source radiation spectra of large earthquakes has been clearly demonstrated this diversity requires different approaches to mitigate hazards in certain tectonic environments seismologists can forecast the future occurrence of large earthquakes within a solid scientific framework using the results from seismology and gps such forecasts are critically important for long term hazard mitigation practices but because stochastic fracture processes are complex the forecasts are inevitably subject to large uncertainty and unexpected events will continue to surprise seismologists recent developments in real time seismology will help seismologists to cope with and prepare for tsunamis and earthquakes combining a better understanding of earthquake diversity with modern technology is the key to effective and comprehensive hazard mitigation practices

the azuara impact structure spain new insights from geophysical and geological investigations a progress report on geophysical and geological investigations in the 35 40 km diameter azuara probable impact structure northeast spain is given the target is a 10 km thick sequence of palaeozoic mesozoic and cenozoic sediments gravity measurements establish a negative residual anomaly of about 100 m s2 and a mass deficiency of 1 24 1014 kg they suggest the existence of a buried inner ring with half the size of the outer ring the result of preliminary model calculations is compatible with the assumption of a flat structure only a few kilometers deep measurements of the total intensity of the earth s magnetic field do not indicate causative bodies related to the structure geological mapping reveals a tectonic style which is characterized by folds and faults with radial and tangential elements and a strong horizontal component ejecta abundant monomict and polymict breccias dislocated megablocks inverted stratigraphy and a megabreccia up to 80 m thick in the outer ring are evidence for intense and violent deformation networks of typical breccia dikes well known from many impact structure cut through nearly all stratigraphical units various types and generations of breccia dikes occur in addition to previously described shock deformation in quartz and mica we present further evidence of high pressure and high temperature signatures in rocks the age of the impact is estimated to be upper eocene or oligocene we conclude that the formation of the azuara structure is difficult to explain by mechanisms other than impact and we discuss our observations within the scope of the contact compression excavation and modification stages of impact cratering with special attention directed to the peculiarities of the azuara sedimentary target

the october 28 2012 mw 7 8 haida gwaii underthrusting earthquake and tsunami slip partitioning along the queen charlotte fault transpressional plate boundary the pacific north american plate boundary is undergoing predominantly right lateral strike slip motion along the queen charlotte and fairweather transform faults the queen charlotte fault qcf hosted the largest historical earthquake in canada the 1949 m s 8 1 strike slip earthquake which ruptured from offshore northern haida gwaii several hundred kilometers northwestward on january 5 2013 an m w 7 5 strike slip faulting event occurred near the northern end of the 1949 rupture zone along central and southern haida gwaii the relative plate motion has 20 oblique convergence across the left stepping plate boundary there had been uncertainty in how the compressional component of plate motion is accommodated the october 28 2012 m w 7 8 haida gwaii earthquake involved slightly 20 oblique thrust faulting on a shallow 18 5 northeast dipping fault plane with strike 320 parallel to the qcf consistent with prior inferences of pacific plate underthrusting beneath haida gwaii the rupture extended to shallow depth offshore of moresby island beneath a 25 30 km wide terrace of sediments that has accumulated in a wedge seaward of the qcf the shallow thrusting caused seafloor uplift that generated substantial localized tsunami run up and a modest far field tsunami that spread across the northern pacific prompting a tsunami warning beach closure and coastal evacuation in hawaii although ultimately tide gauges showed less than 0 8 m of water level increase the mainshock rupture appears to have spread with a 2 3 km s rupture velocity over a length of 150 km with slip averaging 3 3 m concentrated beneath the sedimentary wedge the event was followed by a substantial aftershock sequence in which almost all of the larger events involve distributed intraplate normal faulting extending 50 km oceanward from the qcf the highly oblique slip partitioning in southern haida gwaii is distinctive in that the local plate boundary parallel motion on the qcf may be accommodated either by infrequent large strike slip ruptures or by aseismic creep as seems to be the case for deeper oblique relative plate motion beneath haida gwaii while the sedimentary terrace accumulates plate boundary perpendicular compressional strain that releases in almost pure thrust faulting earthquakes seaward of the qcf

structural analysis of the collar of the vredefort dome south africa significance for impact related deformation and central uplift formation landsat tm aerial photograph image analysis and field mapping of witwatersrand supergroup meta sedimentary strata in the collar of the vredefort dome reveals a highly heterogeneous internal structure involving folds faults fractures and melt breccias that are interpreted as the product of shock deformation and central uplift formation during the 2 02 ga vredefort impact event broadly radially oriented symmetric and asymmetric folds with wavelengths ranging from tens of meters to kilometers and conjugate radial to oblique faults with strike slip displacements of typically tens to hundreds of meters accommodated tangential shortening of the collar of the dome that decreased from 17 at a radius from the dome center of 21 km to 5 at a radius of 29 km ubiquitous shear fractures containing pseudotachylitic breccia particularly in the metapelitic units display local slip senses consistent with either tangential shortening or tangential extension however it is uncertain whether they formed at the same time as the larger faults or earlier during the shock pulse in addition to shatter cones quartzite units show two fracture types a cm spaced rhomboidal to orthogonal type that may be the product of shock induced deformation and later joints accomplishing tangential and radial extension the occurrence of pseudotachylitic breccia within some of these later joints and the presence of radial and tangential dikes of impact melt rock confirm the impact timing of these features and are suggestive of late stage collapse of the central uplift

planar deformation features in shocked quartz a transmission electron microscopy investigation abstract we present a detailed investigation by transmission electron microscopy tem of the fine structure of planar deformation features pdf in quartz grains within which shock metamorphism has been detected optically and which originate from various sites slate islands la malbaie and manicouagan lake canada ries crater germany the toba caldera sumatra the vredefort complex in south africa and the k t boundary at raton basin colorado pdfs appear on tem micrographs as straight and very narrow tem reveals many more pdfs than are optically detected probably because only concentrations of such defects in narrow areas can induce an optically detectable contrast caution should therefore be exercised when applying criteria based on the optical observation of single or multiple sets of pdfs pdfs in samples from slate islands and raton basin exhibit a peculiar morphology a high density of very tiny bubbles precipitated on the dislocation lines comparison with the behavior of wet quartz strongly suggests that these materials experienced lengthy annealing at moderate pressure and temperature

dissipative intraplate faulting during the 2016 mw 6 2 tottori japan earthquake the 2016 m w 6 2 tottori earthquake occurred on 21 october 2016 and produced thousands of aftershocks here we analyze high resolution relocated seismicity together with source properties of the mainshock to better understand the rupture process and energy budget we use a matched filter algorithm to detect and precisely locate 10 000 previously unidentified aftershocks which delineate a network of sharp subparallel lineations exhibiting significant branching and segmentation seismicity below 8 km depth forms highly localized fault structures subparallel to the mainshock strike shallow seismicity near the main rupture plane forms more diffuse clusters and lineations that often are at a high angle in map view to the mainshock strike an empirical green s function technique is used to derive apparent source time functions for the mainshock which show a large amplitude pulse 2 4 s long we invert the apparent source time functions for a slip distribution and observe a 16 km 2 patch with average slip 3 2 m 93 of the seismic moment is below 8 km depth which is approximately the depth below which the seismicity becomes very localized these observations suggest that the mainshock rupture area was entirely within the lower half of the seismogenic zone the radiated seismic energy is estimated to be 5 7 10 13 j while the static stress drop is estimated to be 18 27 mpa these values yield a radiation efficiency of 5 7 which indicates that the tottori mainshock was extremely dissipative we conclude that this inefficiency in energy radiation is likely a product of the immature intraplate environment and the underlying geometric complexity

seismological constraints on source properties of the mb 4 0 1985 ardsley new york earthquake a characteristic rupture on october 19 1985 a magnitude 4 0 earthquake occurred in southern westchester county new york approximately 30 km north of central manhattan barstow et al 1988 concluded that this earthquake consisted of two sub events with the larger sub event occurring 0 6 s after the first one we present analysis of data for the main shock as well as aftershocks and foreshocks which were recorded on the new york state seismic network because this data set includes a range of source magnitudes from less than 2 to 4 recorded for virtually identical source receiver pairs an empirical green s function technique can be used to study the source characteristics of the larger events the corner frequency of the main shock and an attenuation parameter t are resolved from the initial portion of the seismogram at station pal in palisades new york 8 km northwest of the epicenter spectra of small foreshocks and aftershocks can then be corrected for attenuation using t following an iterative procedure it is then possible to make reliable determinations of seismic corner frequency for these events several conclusions are obtained 1 the spectrum of the first subevent in the main shock can be well modelled by a brune spectrum from 1 to 10 hz with a corner frequency of 7 1 hz at higher frequencies the source spectrum contains sharp peaks which do not fit an omega square model and may reflect complexities in the rupture process 2 the average stress drop of the sequence is 205 bars the stress drop of the main event is 540 bars but no stress drop dependency on moment is resolved over the magnitude range 1 8 4 0 3 attenuation parameters t are obtained for the 8 km northwestward path from ardsley to palisades and for a 52 km westward path to a station in the hudson highlands and their similarity suggests an increase of q with depth 4 assuming that the two main shock sub events did not rerupture the same area but were contiguous a maximum rupture dimension is 440 680 m the rupture diameter of the largest aftershock mb 3 is determined to be approximately 320 meters the combined rupture for the sequence inferred from spectral methods is consistent with the size of the rupture inferred from the area surrounded by the early aftershocks 700 m diameter the rupture dimension of the ardsley sequence may be characteristic of the dobbs ferry fault and other seismogenic faults in the manhattan prong which are segmented with characteristic dimensions of 0 5 2 km seeber and dawers 1989 assuming that the range of stress drops in the ardsley sequence is also characteristic of the manhattan prong this range of dimensions corresponds to a range of characteristic magnitudes between mb of 3 3 and 5 5 we note that this magnitude range encompasses the five largest known earthquakes in the new york city seismic zone the 1985 ardsley main shock and events in 1737 1783 1884 and 1895

evolution of the amphibolite granulite facies transition exposed by the vredefort impact structure kaapvaal craton south africa abstract geological mapping is integrated with high precision u pb zircon and monazite geochronology to document in detail the nature and temporal evolution of the amphibolite granulite facies boundary exposed in the vredefort impact structure of the central kaapvaal craton our study has revealed that the preimpact configuration of the amphibolite granulite facies boundary is best preserved in panels between impact related brittle faults and that past concepts of the boundary must be revised a regional lithologic transition exists between amphibolite facies outer granite gneiss 3 084 3 09 ga and a heterogeneous assemblage of granulite facies gneisses ca 3 1 3 3 ga tabular deformed quartz syenite bodies dated at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cy

dynamic deformation of volcanic ejecta from the toba caldera possible relevance to cretaceous tertiary boundary phenomena plagioclase and biotite phenocrysts in ignimbrites erupted from the toba caldera sumatra show microstructures and textures indicative of shock stress levels higher than 10 gpa strong dynamic deformation has resulted in intense kinking in biotite and with increasing shock intensity the development of plagioclase of planar features shock mosaicism incipient recrystallization and possible partial melting microstructures in quartz indicative of strong shock deformation are rare however and many shock lamellae if formed may have healed during post shock residence in the hot ignimbrite they might be preserved in ash falls peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures possibly including shock features observed near the cretaceous tertiary boundary 38 references 3 figures

teleseismic estimates of radiated seismic energy the e m 0 discriminant for tsunami earthquakes we adapt the formalism of boatwright and choy for the computation of radiated seismic energy from broadband records at teleseismic distances to the real time situation when neither the depth nor the focal geometry of the source is known accurately the analysis of a large data set of more than 500 records from 52 large recent earthquakes shows that this procedure yields values of the estimated energy ee in good agreement with values computed from available source parameters for example as published by the national earthquake information center neic the average logarithmic residual being only 0 26 units we analyze the energy to moment ratio by defining log10 ee m0 for regular earthquakes this parameter agrees well with values expected from theoretical models and from the worldwide neic catalogue there is a one to one correspondence between values of that are deficient by one full unit or more and the so called tsunami earthquakes previously identified in the literature as having exceedingly slow sources and believed due to the presence of sedimentary structures in the fault zone our formalism can be applied to single station measurements and its coupling to automated real time measurements of the seismic moment using the mantle magnitude mm should significantly improve real time tsunami warning

co 2 rich fluid inclusions along planar elements of quartz in basement rocks of the vredefort dome south africa along a nw se profile through the basement core starting below the sedimentary unconformity and ending in the center of the nearly circular structure the constituent quartz grains and their fluid inclusions exhibit the following characteristics

egyptian mummies record increasing aridity in the nile valley from 5500 to 1500 yr before present abstract oxygen isotope compositions were measured in teeth n 29 and bones n 41 from egyptian mummies of humans n 48 in order to track the 18o evolution of the nile from 5500 to 1500 b p the combination of 18o values of apatite carbonate and phosphate was used to filter the database for post mortem alteration of bioapatites while 87sr 86sr ratios were used to detect potential allochthonous people buried in the various archeological sites located along the nile this approach led to only five apatite samples out of seventy to be discarded from the database the remaining oxygen isotope compositions of both tooth and bone phosphates from ancient egyptians were converted into the composition of ingested water ultimately originating from the nile it was found that 18o of nile waters increases progressively from 1 6 to 1 5 vsmow from the predynastic 5500 b p through the late period 2550 b p this trend towards higher nile 18o values acquired in more recent times is coherent with a general drying trend in northeast africa which was not limited to a drying spell at the end of the nabtian pluvial ca 12 000 b p ca 6000 b p but extended far into the following millennia nearly to the beginning of the common era 1950 b p

large earthquake rupture process variations on the middle america megathrust the megathrust fault between the underthrusting cocos plate and overriding caribbean plate recently experienced three large ruptures the august 27 2012 m w 7 3 el salvador september 5 2012 m w 7 6 costa rica and november 7 2012 m w 7 4 guatemala earthquakes all three events involve shallow dipping thrust faulting on the plate boundary but they had variable rupture processes the el salvador earthquake ruptured from about 4 to 20 km depth with a relatively large centroid time of 19 s low seismic moment scaled energy release and a depleted teleseismic short period source spectrum similar to that of the september 2 1992 m w 7 6 nicaragua tsunami earthquake that ruptured the adjacent shallow portion of the plate boundary the costa rica and guatemala earthquakes had large slip in the depth range 15 to 30 km and more typical teleseismic source spectra regional seismic recordings have higher short period energy levels for the costa rica event relative to the el salvador event consistent with the teleseismic observations a broadband regional waveform template correlation analysis is applied to categorize the focal mechanisms for larger aftershocks of the three events modeling of regional wave spectral ratios for clustered events with similar mechanisms indicates that interplate thrust events have corner frequencies normalized by a reference model that increase down dip from anomalously low values near the middle america trench relatively high corner frequencies are found for thrust events near costa rica thus variations along strike of the trench may also be important geodetic observations indicate trench parallel motion of a forearc sliver extending from costa rica to guatemala and low seismic coupling on the megathrust has been inferred from a lack of boundary perpendicular strain accumulation the slip distributions and seismic radiation from the large regional thrust events indicate relatively strong seismic coupling near nicoya costa rica patchy zones of strong seismic coupling in the shallowest megathrust region along nicaragua and el salvador and small deeper patchy zones of strong seismic coupling near guatemala which can be reconciled with the geodetic observations as long as the strong coupling is limited to a small fraction of the megathrust area

shock metamorphism of quartz in nature and experiment ii significance in geoscience the occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies its utility is due to its almost ubiquitous occurrence in terrestrial rocks its overall stability and the fact that a variety of shock metamorphic effects occurring over a range of shock pressures have been well documented these shock effects have been generally duplicated in shock recovery experiments and thus serve as shock pressure barometers after reviewing the general character of shock effects in quartz the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored the short pulse lengths in experiments may account for the difficulty in synthesizing the high pressure polymorphs coesite and stishovite compared to natural occurrences in addition post shock thermal effects are possible in natural events which can affect shock altered physical properties such as refractive index and cause annealing of shock damage and recrystallization the orientations of planar microstructures however are unaffected by post impact thermal events except if quartz is recrystallized and provide the best natural shock barometer in terms of utility and occurrence the nature of planar microstructures particularly planar deformation features pdfs is discussed in some detail and a scheme of variations in orientations with shock pressure is provided the effect of post impact events on pdfs is generally limited to annealing of the original glass lamellae to produce decorated pdfs resulting from the exsolution of dissolved water during recrystallization basal 0001 pdfs differ from other pdf orientations in that they are multiple mechanical brazil twins which are difficult to detect if not partially annealed and decorated the occurrence and significance of shock metamorphosed quartz and its other phases namely coesite stishovite diaplectic glass and lechatelierite are discussed for terrestrial impact structures in both crystalline non porous and sedimentary porous targets the bulk of past studies have dealt with crystalline targets where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures in sedimentary targets the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets this is discussed along with examples of variations in the relative abundances of planar microstructures and their orientations which are attributed to textural variations in sedimentary target rocks examples of the shock metamorphism of quartz in distal ejecta such as at the k t boundary and from nuclear explosions are illustrated and are equivalent to that of known impact structures except with respect to characteristics that are due to long term post shock thermal effects finally the differences between the deformation and phase transformation of quartz by shock and by endogenic tectonic and volcanic processes are discussed we confirm previous conclusions that they are completely dissimilar in character due to the vastly different physical conditions and time scales typical for shock events compared to tectonic and volcanic events well characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

rupture evolution of the 2006 java tsunami earthquake and the possible role of splay faults abstract the 2006 mw 7 8 java earthquake was a tsunami earthquake exhibiting frequency dependent seismic radiation along strike high frequency global back projection results suggest two distinct rupture stages the first stage lasted 65 s with a rupture speed of 1 2 km s while the second stage lasted from 65 to 150 s with a rupture speed of 2 7 km s high frequency radiators resolved with back projection during the second stage spatially correlate with splay fault traces mapped from residual free air gravity anomalies these splay faults also colocate with a major tsunami source associated with the earthquake inferred from tsunami first crest back propagation simulation these correlations suggest that the splay faults may have been reactivated during the java earthquake as has been proposed for other tsunamigenic earthquakes such as the 1944 mw 8 1 tonankai earthquake in the nankai trough

global evaluation of large earthquake energy from 1997 through mid 2010 1 we develop an updated radiated seismic energy e catalog of global earthquakes with seismic moment m0 1019 nm mw 6 7 from 1997 through mid 2010 recording 342 events using 17849 seismograms station specific corrections and event duration dependent total p wave group calculations allow for improved e determinations for large and long duration earthquakes we find the global mean energy to moment ratio log10 e m0 4 59 0 36 robust deviations are found for thrust t 4 74 strike slip ss 4 44 and normal n 4 51 faulting events for two regions with recent energy deficient tsunami earthquakes tse we examine all large thrust earthquakes with m0 5 1017 nm mw 5 7 to identify a regional characterization in their relative radiated energy to moment ratio while thrust events along java indonesia the site of two tse events in 1994 and 2006 are comparable t jv 4 91 to the global thrust average events along the middle america trench mat the site of the 1992 nicaragua tse are consistently deficient t mat 5 15 along the mat a trend of increased deficiency in radiated energy to the southeast occurs in the direction of more rapid plate convergence global thrust mechanisms become increasingly deficient in radiated seismic energy at shallow depths with tse events representing the shallowest and most energetically deficient end member of the events in the study results suggest thrust events are highly variable but tend to increase in apparent stress from about 15 kpa near the surface to 2 mpa near 70 km depth

vredefort shatter cones revisited shatter cones have been described from a number of circular and polygonal structures worldwide the origin of which has been alternatively ascribed to the impacts of large extraterrestrial projectiles or to catastrophic endogenic processes despite their association with enigmatic catastrophic processes the nature of shatter cones and the physics involved in their formation have not been comprehensively researched results of detailed field and laboratory studies of shatter cones from three areas in the collar of the vredefort dome in south africa are presented vredefort shatter cones are directly related to a widely displayed fracture phenomenon termed multiply striated joint sets msjs msjs are planar to curviplanar fractures occuring at spacings of 1 to several millimeters the joint sets have a fractal character when a new measurement protocol is used in the field involving study of all joint surfaces and all steps and striae exposed on these surfaces new information is gained on the genesis and significance of the msjs and on their relationship to striated conical fractures the internal constitution of a rock specimen with msjs was examined in detail by documenting the precise geometry of many fractures in a suite of parallel thin sections transecting the specimen the steps and striae on shatter cone surfaces have the characteristics of displacement fractures microfaults along which evidence of melting is observed shatter cone and msjs surfaces are often covered with glassy films we evaluate whether these fracture phenomena are linked to the formation of pseudotachylitic friction melt our field and petrographic observations can be interpreted as consistent with the generation of shatter cones msjs relatively late in the formation of the vredefort structure this scenario contrasts sharply with the widely held view that shatter cones are formed during the early compression phase of a shock event that affected horizontal strata

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

the metamorphic history of the vredefort dome at approximately 2 ga as revealed by coesite stishovite bearing pseudotachylites the vredefort dome 2 0 ga represents the central uplift of a very large impact structure this uplift exposed a nearly complete cross section through the continental crust in the region which is 25 30 km thick two metamorphic events took place at about the same time as the impact the first event so called static metamorphism is pre impact and produced lithologies varying from low grade shale to high grade hornfels it resembles contact metamorphism by its lack of schistosity but is more regional as it extends over a large area and is not associated with large intrusions the second event the post shock metamorphism is responsible for the recrystallization of the shock features the investigation of this event has been focused on the degree of alteration of the coesite stishovite bearing pseudotachylite veins that formed during the transit of the shock wave these high pressure silica polymorphs are only present in the upper part of the stratigraphic sequence downward they have been converted to fibrous quartz at the highest grade the fibrous quartz is in turn replaced by triple junctioned mosaic quartz the post shock metamorphism was generated by the heat of the rock before shock plus the heat released by the shock wave the isograds plotted on a map can be translated into depth of burial and therefore provide valuable information regarding the geological setting immediately before impact at the time of impact the rocks were relatively cool and the static metamorphism had ceased with several tens of millions of years separating the two metamorphic events the static metamorphism was probably caused by continental crustal extension in a stress free environment and the lack of deformation is probably due to rapid uplift during the later stages of the impact event

the finite kinematic rupture properties of great sized earthquakes since 1990 abstract here i present a database of 160 finite fault models for all earthquakes of m 7 5 and above since 1990 created using a consistent modeling approach the use of a common approach facilitates easier comparisons between models and reduces uncertainties that arise when comparing models generated by different authors data sets and modeling techniques i use this database to verify published scaling relationships and for the first time show a clear and intriguing relationship between maximum potency the product of slip and area and average potency for a given earthquake this relationship implies that earthquakes do not reach the potential size given by the tectonic load of a fault sometimes called moment deficit calculated via a plate rate over time since the last earthquake multiplied by geodetic fault coupling instead average potency or slip scales with but is less than maximum potency dictated by tectonic loading importantly this relationship facilitates a more accurate assessment of maximum earthquake size for a given fault segment and thus has implications for long term hazard assessments the relationship also suggests earthquake cycles may not completely reset after a large earthquake and thus repeat rates of such events may appear shorter than is expected from tectonic loading this in turn may help explain the phenomenon of earthquake super cycles observed in some global subduction zones

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

geophysical anomalies and quartz microstructures eastern warburton basin north east south australia tectonic or impact shock metamorphic origin abstract the eastern warburton basin northeast south australia features major geophysical anomalies including a magnetic high of near 200 nt centred on a 25 km wide magnetic low 30 000 km large eastern warburton basin the qz pe include multiple intersecting planar to curved sub planar elements with relic lamellae less than 2 m wide with spacing of 4 5 m qz pe are commonly re deformed displaying bent and wavy patterns accompanied with fluid inclusions u stage measurements of a total of 243 planar sets in 157 quartz grains indicate dominance of 10 12 10 13 and subsidiary 11 22 22 41 m 10 11 and x 51 61 planes transmission electron microscopy tem analysis displays relic narrow 1 m wide lamellae and relic non sub grain boundaries where crystal segments maintain optical continuity extensive sericite alteration of feldspar suggests hydrothermal alteration to a depth of 500 m below the unconformity which overlies the qz pe bearing warburton basin terrain the data are discussed in terms of a tectonic metamorphic deformation and b impact shock metamorphism producing planar deformation features qz pdf deformed qz pe are compared to re deformed qz pdfs in the sudbury vredefort manicouagan and charlevoix impact structures a 4 5 km uplift of the big lake granite suite during 298 295 ma is consistent with missing of upper ordovician to devonian strata and possible impact rebound the occurrence of circular seismic tomography anomalies below the east warburton basin the poolowana basin and the woodleigh impact structure signifies a potential diagnostic nature of circular tomographic anomalies

megathrust and accretionary wedge properties and behaviour in the makran subduction zone this work forms part of the nerc and esrc funded project earthquakes without frontiers and was partially supported by the nerc large grant looking inside the continents from space cp is funded by an nerc studentship the facilities of iris data services and specifically the iris data management center were used for access to waveforms related metadata and or derived products used in this study iris data services are funded through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation under cooperative agreement ear 1261681

the 12 june 2017 mw 6 3 lesvos island aegean sea earthquake slip model and directivity estimated with finite fault inversion abstract on 12 june 2017 utc 12 28 38 26 a magnitude mw 6 3 earthquake occurred offshore lesvos island in se aegean sea which was widely felt caused 1 fatality and partially ruined the village of vrisa on the south eastern coast of the island i invert broad band and strong motion waveforms from regional stations to obtain the source model and the distribution of slip onto the fault plane the hypocentre is located at a depth of 7 km in the upper crust the mainshock ruptured a wnw ese striking sw dipping normal fault projecting offshore and bounding the lesvos basin the strongest and most aftershocks clustered away from the hypocentre at the eastern edge of the activated area this cluster indicates the activation of a different fault segment exhibiting sinistral strike slip motions along a plane striking wnw ese the slip of the mainshock is confined in a single large asperity wnw from the hypocentre with dimensions 20 km 10 km along fault strike and dip respectively the average slip of the asperity is 50 cm and the peak slip is 1 m the rupture propagated unilaterally towards wnw to the coastline of lesvos island at a relatively high speed 3 1 km s the imaged slip model and forward modelling was used to calculate peak ground velocities pgvs in the near field the damage pattern produced by this earthquake especially in the village of vrisa is compatible with the combined effect of rupture directivity proximity to the slip patch and the fault edge spectral content of motions and local site conditions

along strike variability of rupture duration in subduction zone earthquakes 1 subduction zone earthquakes exhibit a wide spectrum of rupture times that reflect conditions on the megathrust fault tsunami earthquakes are examples of slower than expected ruptures that produce anomalously large tsunamis relative to the surface wave magnitude one model explaining tsunami earthquakes suggests slip within patches of low rigidity material at shallow depths heterogeneous fault conditions such as having patches of low rigidity material surrounded by higher strength material should produce heterogeneous earthquake rupture parameters here we investigate along strike variation in rupture duration for 427 shallow thrust earthquakes mw 5 0 7 0 in the peru chile alaska tonga kuril izu and java sumatra subduction zones to explore how heterogeneous seismic and tectonic characteristics such as differences in sediment type thickness and roughness of subducting bathymetry affect earthquake properties earthquake source parameters including rupture durations are estimated using multi station deconvolution of teleseismic p and sh waves to solve for earthquake source time functions and all events are relocated using additional depth phase information we classify events into shallow 26 km and deep 26 km and 61 km groups based on the overall mean depth and focus on the longest duration events with moment normalized rupture durations of 1 standard deviation above the mean duration for each group we find long duration events at all depths within the study regions except peru and chile we find no correlation with incoming sediment thickness or type and limited spatial correlation with regions of past tsunami earthquakes regions of observed afterslip and subducting bathymetric features

an investigation by transmission electron microscopy of planar deformation features in naturally shocked quartz we have investigated by transmission electron microscopy tem the planar deformation features pdf in quartz from various sites where shock metamorphism has been detected optically impact sites the vredefort complex south africa and the k t boundary at raton basin colorado pdfs are straight narrow bands of glass or microtwins or huge densities of dislocations such contrasting microstructures must reflect different shock scenarios in the vredefort complex the post shock thermal history has strongly overprinted the shock induced defects in the raton basin samples very tiny bubbles have precipitated on the dislocations strongly suggesting a lengthy annealing at moderate pressure and temperature this new information should be taken into account in any model of the origin of the k t transition in any case observation of pdfs by optical microscopy alone is not sufficient to unambiguously conclude on their origin

reconciling teleseismic and regional estimates of seismic energy estimates of the radiated seismic energy based on teleseismic and regional data often differ by up to an order of magnitude with a tendency for regional estimates to be larger than teleseismic estimates for the same event in this study we compare the velocity spectrum determined from teleseismic data after correction for radiation pattern and propagation effects with the velocity spectrum determined from regional data after the corresponding corrections for nine earthquakes in the middle america subduction zone of mexico this comparison of the corrected spectra is used to identify and reduce the sources of the regional versus teleseismic energy discrepancy which is about an order of magnitude for these events we find that the teleseismic attenuation operator needs to be calibrated in our case for the tectonic environment of the mexican subduction zone we need a teleseismic attenuation operator that is stronger at high frequencies than the global average a larger factor however is the correction needed to account for site amplification this correction has an impact on both regional and teleseismic data but it has a larger influence on the regional estimates because the angle of incidence for teleseismic waves is steep and the stations are located on more competent rock by modifying the teleseismic attenuation operator and applying site corrections based on a generic site model we essentially eliminate the order of magnitude discrepancy between teleseismic and regional estimates of the radiated seismic energy for these events

fluid inclusions planar elements and pseudotachylites in the basement rocks of the vredefort structure south africa abstract the basement rocks of the vredefort structure are characterized by high temperature static metamorphism in the course of which a violent shock event occurred quartz in these rocks contains numerous fluid inclusions that consist of almost pure co 2 commonly such fluid inclusions are aligned along planar elements in quartz that were formed during the shock event crystallographic orientations of the planar elements were used to estimate minimum shock pressures of 75 100 30 kbar the fact that fluid inclusions are situated on planar elements indicates that the co 2 gas must have been available immediately after the shock event measurements of the homogenization temperatures of the fluid inclusions in samples from the vredefort basement allow subdivision of the co 2 inclusions into three groups the main group type 1 representing nearly 99 of the co 2 inclusions homogenizes to liquid in the range 26 30 c and therefore has densities of between 0 6 and 0 7 g cm 3 inclusions of this most important group are generally situated on planar elements high density type 2 and low density type 3 inclusions occur isolated in coarse unshocked quartz grains without planar elements in post shock recrystallized quartz grains and in mafic minerals apparently unaffected by the shock event type 2 inclusions with densities of about 0 9 g cm 3 are believed to belong to an early generation which was formed during the granulite facies metamorphism predating the static high temperature vredefort metamorphism low density inclusions of type 3 homogenizing to the gaseous state could be explained as a very late generation of inclusions formed under near surface conditions on the basis of the observation that type 1 inclusions are located on shock induced planar elements the time of entrapment must have been immediately after the shock event and a minimum pressure for co 2 between 2 and 5 kbar can be determined for this time within the entire basement based on independent temperature estimations the observations that a multitude of type 1 inclusions has been found in a minute millimetre sized pseudotachylite vein produced by the shock event is explained by recrystallization of diaplectic glass with this knowledge of microstructures in the vredefort basement rocks it is suggested that the ubiquity of co 2 and the shock event are related to each other

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

formation mechanisms of planar deformation features in naturally shocked quartz abstract shock waves induce peculiar defects in quartz shock mosaics high pressure polymorphs coesite and stishovite diaplectic glass and planar deformation features pdfs together these features are the indices of shock metamorphism pdfs appear under the optical microscope as straight and narrow defects parallel to the 10 1n rhombohedral planes with n 3 and 2 as most frequent values although n 1 4 and i e basal plane are also found we report in the first part of this paper a detailed investigation by transmission electron microscopy of the fine structure of pdfs in shocked quartz grains from a variety of sites slate islands la malbaie and manson in north america the vredefort complex in south africa the ries crater in germany and the cretaceous tertiary boundary layer at raton basin colorado we distinguish four pdf fine structures 1 bands of dislocations 2 lamellae of mixtures in various proportions of amorphous silica and small crystallites 3 thin brazil twin lamellae 4 short parallel lamellae forming serrated ladder structures the possible formation mechanisms of these pdfs are discussed in the second part of the paper it is suggested that the dislocation bands are probably not original pdf structures but stem from a later recrystallization stage the brazil twins have been produced by relatively large deviatoric stresses which accompanied the shock wave the other pdf structures which consist of partial amorphization in the 10 1 n planes must result from elastic instabilities of the shear modulus of the quartz structure at high pressure in these planes theoretical estimates of the elastic stiffness coefficients indicate that amorphization should start at approximately 10 gpa the growth of the straight and narrow amorphous lamellae would be driven by the front of the shock wave

the february 6 2013 mw 8 0 santa cruz islands earthquake and tsunami the santa cruz islands region has high seismicity near a 90 bend in the boundary between the pacific and australian plates southward along the vanuatu island arc the australian plate under thrusts the pacific plate in a well defined subduction zone westward a transpressional predominantly transform boundary extends to the southern solomon islands subduction zone the santa cruz islands region has upper plate strike slip and normal faulting plate boundary under thrusting outer rise extensional faulting and intraplate compressional faulting on february 6 2013 the largest under thrusting earthquake mw 8 0 that has been instrumentally recorded in the region ruptured the megathrust the epicenter 10 738 s 165 138 e is about 1 north of epicenters of prior large shallow under thrusting events in vanuatu in 1934 m 7 8 and 1966 ms 7 9 and there is overlap of all three events aftershock zones but not their large slip regions at least 10 lives were lost with 6 more missing due to tsunami 1 5 m high striking the town of lata and several villages on the main santa cruz island of nendo ndeni and a nearby small island nibanga inundation of 500 m flooded the lata airport the tsunami was well recorded by dart buoys spanning an unusually wide three quadrant azimuthal aperture iterative modeling of teleseismic broadband p waves and the deep water tsunami recordings resolves the slip distribution there are two large slip patches with a southeastward rupture expansion at about 1 5 km s with the second patch appearing to have ruptured with large slip at the trench the event has relatively low short period seismic wave energy release but a typical overall moment scaled total energy the shallow rupture depth may be associated with the low level of short period energy and a near total stress drop may account for a lack of underthrusting aftershocks among a highly productive aftershock sequence that included three events with m w 7 0

thermal annealing of experimentally shocked feldspar crystals single crystals of sanidine orthoclase microcline oligoclase and labradorite as well as polycrystalline bytownite were shocked experimentally to peak pressures as high as 45 gpa and subsequently annealed under dry conditions for various times at 800 c 900 c and 1000 c these experiments reveal that alkali feldspars do not change their al si distribution due to shock alone but when subjected to shock pressures 22 gpa and then annealed microcline and orthoclase rapidly transform to sanidine displaying a highly disordered al si distribution high diffusivity of k na and ca was observed in a labradorite sample shocked to 26 gpa subsequent annealing may thus disturb chemical structural and isotopic characteristics of shocked minerals and rocks more easily than of unshocked specimens this is of considerable importance for the interpretation of isotopic age data of impact breccias recrystallization textures of annealed diaplectic plagioclase glasses are very distinctive and may be used as a relative measure of the shock pressure experienced by the samples

characterization of magnetite particles in shocked quartz by means of electron and magnetic force microscopy vredefort south africa submicroscopic opaque particles from highly shocked granite gneisses close to the core of the vrede fort impact structure have been investigated by means of micro analytical techniques with high spatial resolution such as electron diaraction orientation contrast imagery and magnetic force microscopy the opaque particles have been identified as nano to micro sized magnetite that occur in several distinct modes in one sample magnetite occurs along relict planar deformation features pdfs in quartz generally accepted as typical shock lamellae the magnetite particles along shock lamellae in quartz grains virtually all show uniform crystallographic orientations in most instances the groups of magnetite within diaerent quartz grains are systematically misori entated such that they share a subparallelh101i direction the magnetite groups of all measured quartz grains thus appear to have a crystallographic preferred orientation in space in a second sample orientations of magnetite particles have been measured in microfractures non di agnostic of shock of quartz albite and in the alteration halos e g biotite grains breaking down to chlorite the crystallographic orientations of magnetite particles are diverse with only a minor portion having a preferred orientation scanning electron microscopy shows that magnetite along the relict pdfs is invariably asso ciated with other microcrystalline phases such as quartz k feldspar and biotite petrographic observations sug gest that these microcrystalline phases crystallized from locally formed micro melts that intruded zones of weakness such as microfractures and pdfs shortly after the shock event the extremely narrow widths of the pdfs suggest that heat may have dissipated rapidly re sulting in melts crystallizing relatively close to where they were generated magnetic force microscopy confirms the presence of magnetic particles along pdfs the smallest particles 5 lm with high aspect ratios 15 1 usually exhibit intense uniform magnetic signals characteristic of single domain magnetite consistent oasets between attractive and repulsive magnetic signals of individual single domain particles suggest consistent directions of magnetization for a large proportion of particles

the 2017 mw 8 2 chiapas mexico earthquake energetic slab detachment on 8 september 2017 a great m w 8 2 normal faulting earthquake ruptured within the subducting cocos plate 70 km landward from the middle american trench beneath the tehuantepec gap iterative inversion and modeling of teleseismic and tsunami data and prediction of gps displacements indicate that the steeply dipping rupture extended 180 km to the northwest along strike toward the oaxaca coast and from 30 to 70 km in depth with peak slip of 13 m the rupture likely broke through the entire lithosphere of the young subducted slab in response to downdip slab pull the plate boundary region between the trench and the fault intersection with the megathrust appears to be frictionally coupled influencing location of the detachment comparisons of the broadband body wave magnitude m b and moment scaled radiated energy e r m 0 establish that intraslab earthquakes tend to be more energetic than interplate events accounting for strong ground shaking observed for the 2017 event