direct evidence of active deformation in the eastern indian oceanic plate conventional plate tectonics theory postulates that plates only deform on their boundaries to the contrary there is ample evidence of intraplate deformation in the equatorial indian ocean west of the ninetyeast aseismic ridge prior to this study no direct evidence of deforma tion east of the ninetyeast ridge was available we present the results of a multipurpose geo physical cruise showing that intraplate deformation also occurs in this area long at least 1000 km left lateral north south strike slip faults are active and reactivate fossil fracture zones this style of deformation is strikingly different from the east west folds and reverse faults that affect the region west of the ninetyeast ridge contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation west of the ninetyeast ridge there is a continent continent collision and east of the ridge oceanic lithosphere subducts along the sumatra trench the ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas

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

the 2012 sumatra great earthquake sequence the equatorial indian ocean is a well known place of active intraplate deformation defying the conventional view of rigid plates separated by narrow boundaries where deformation is confined on 11 april 2012 this region was hit in a couple of hours by two of the largest strike slip earthquakes ever recorded moment magnitudes mw 8 6 and 8 2 broadband seismological observations of the mw 8 6 mainshock indicate a large centroid depth 30 km and remarkable rupture complexity detailed study of the surface wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents to account for these observations we developed a procedure to invert for multiple point source parameters the optimum source model at long period consists of two point sources separated by about 209 km with magnitudes mw 8 5 and 8 3 to explain the remaining discrepancies between predicted and observed surface waves we can refine this model by adding directivity along the wnw ese axis however we do not exclude more complicated models to analyze the mw 8 2 aftershock we removed the perturbation due to large surface wave arrivals of the mw 8 6 mainshock by subtracting the corresponding synthetics computed for the two subevent model analysis of the surface wave amplitudes suggests that the mw 8 2 aftershock had a large centroid depth between 30 km and 40 km this major earthquake sequence brings a new perspective to the seismotectonics of the equatorial indian ocean and reveals active deep lithospheric deformation

excitation of basin wide modes of the pacific ocean following the march 2011 tohoku tsunami this study is an attempt towards understanding the sources of long oscillations observed within the pacific ocean following the 11 march 2011 tohoku earthquake we present evidence that extremely long modes of the pacific ocean in the range of 2 48 h were excited by this giant tsunami a numerical approach was employed to calculate the basin wide modes of the pacific ocean resulting in 49 modes in the range of 2 48 h we studied 15 tide gauge records around the pacific ocean in order to extract basin wide modes of the pacific ocean excited by this transoceanic tsunami spectral analysis of these tide gauge records showed that some of the calculated basin wide modes were indeed excited by the tohoku tsunami the observed modes ranged from 2 to 49 8 h we attributed the long oscillations of the pacific ocean during the 2011 tohoku tsunami to the excitation of these basin wide modes which can be grouped into global modes 15 48 h and regional modes 2 15 h we classified the signals on the tide gauges into three groups 1 basin wide modes 1 5 h 2 the tsunami source periods 20 90 min and 3 local bathymetric effects 20 min the average contributions to the total tsunami energy were 6 4 for the basin wide mode 64 1 for the tsunami source and 29 5 for the local bathymetry although the ratios varied from station to station simulations suggest that the amount of contribution of basin effects to the total tsunami energy depends on the location of the tsunami source

tsunamis from the 29 march and 5 may 2015 papua new guinea earthquake doublet m w 7 5 and tsunamigenic potential of the new britain trench we characterized tsunamis from the 29 march and 5 may 2015 kokopo papua new guinea mw 7 5 earthquake doublet teleseismic body wave inversions using various rupture velocities vr showed similar source time functions and waveform agreements but the spatial distributions of the slips were different the rupture durations were 45 and 55 s for the march and may events with their peaks at 25 and at 17 s respectively tsunami simulations favored source models with vr 1 75 and 1 50 km s for the march and may earthquakes the largest slip on the fault was similar 2 1 and 1 7 m but the different depths and locations yielded maximum seafloor uplift of 0 4 and 0 2 m tsunami simulation from hypothetical great earthquakes m 8 4 and 8 5 on the new britain trench showed that tsunami amplitudes may reach up to 10 m in rabaul but most tsunami energy was confined within the solomon sea

fault slip distribution of the 2014 iquique chile earthquake estimated from ocean wide tsunami waveforms and gps data we applied a new method to compute tsunami green s functions for slip inversion of the 1 april 2014 iquique earthquake using both near field and far field tsunami waveforms inclusion of the effects of the elastic loading of seafloor compressibility of seawater and the geopotential variation in the computed green s functions reproduced the tsunami traveltime delay relative to long wave simulation and allowed us to use far field records in tsunami waveform inversion multiple time window inversion was applied to tsunami waveforms iteratively until the result resembles the stable moment rate function from teleseismic inversion we also used gps data for a joint inversion of tsunami waveforms and coseismic crustal deformation the major slip region with a size of 100 km 40 km is located downdip the epicenter at depth 28 km regardless of assumed rupture velocities the total seismic moment estimated from the slip distribution is 1 24 1021 n m mw 8 0

fluid mobile element budgets in serpentinized oceanic lithospheric mantle insights from b as li pb pges and os isotopes in the feather river ophiolite california abstract serpentinized oceanic lithosphere may be an important source for boron and other fluid mobile elements that are anomalously enriched in arc volcanic rocks however the integrated water rock ratios associated with different styles of serpentinization may be variable for example large water rock ratios are involved in the serpentinization of abyssal peridotites exhumed to the seafloor whereas much lower water rock ratios are likely to dictate serpentinization along deep faults and fractures to address how fluid mobile element enrichments vary with serpentinization at different settings we investigated serpentinized harzburgites from the feather river ophiolite fro in northern california major and trace element systematics indicate that serpentinization of the fro ultramafics involved seawater however fro serpentinites have unradiogenic os isotopic compositions and near chondritic platinum group element relative abundances contrasting with serpentinized abyssal peridotites which have radiogenic os isotopic compositions and disturbed platinum group element systematics these observations indicate that the integrated water rock ratio involved in fro serpentinization was smaller than that involved in abyssal peridotite serpentinization b concentrations in the fro 5 15 ppm while substantially higher than primitive mantle

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

tsunamis from strike slip earthquakes in the wharton basin northeast indian ocean march 2016 mw7 8 event and its relationship with the april 2012 mw 8 6 event

spectral analysis of tsunami waves separation of source and topography effects a new approach is proposed to separate the influence of source and topography in observed tsunami spectra and to reconstruct the initial source spectrum the method assumes a linear tide gauge response to external forcing and is based on comparative analysis of tsunami and background spectra evaluation of the ratio of tsunami to background spectra gives functional characteristics that are invariant of station location and dependent only on the source parameters three events the urup tsunami of december 22 1991 northwest pacific the hokkaido southwest okushiri tsunami of july 12 1993 sea of japan and the shikotan tsunami of october 4 1994 northwest pacific are used as examples of the proposed approach the source spectra reconstructed from the analysis of different tide gauges were found to be in good agreement with each other and with the seismological geodetic and field survey data

the june 2000 mw 7 9 earthquakes south of sumatra deformation in the india australia plate 1 two large mw 7 9 earthquakes occurred on 4 and 18 june 2000 south of sumatra beneath the indian ocean both earthquakes were predominantly left lateral strike slip on vertical n s trending faults that we interpret to be reactivated fracture zones the 4 june enggano earthquake occurred at the edge of the rupture area of the 1833 subduction earthquake the first strike slip subevent within the subducting plate triggered a thrust subevent on the plate interface which comprised at least 35 of the total moment and ruptured se away from the 1833 earthquake the 18 june earthquake in the wharton basin is one of the largest shallow strike slip faulting earthquakes ever recorded a small second subevent with reverse slip is required to fit the body waves the orientation of both subevents in our preferred model is consistent with the current stress field in the region both the june 2000 earthquakes are consistent with recent models of distributed deformation in the india australia composite plate the occurrence of the enggano earthquake implies that the stress field within the indian plate continues to a depth of 50 km in the subducting slab the purely strike slip source model of the wharton basin earthquake obtained by robinson et al 2001 matches the p waves very poorly and fits the s waves no better than our preferred model the strike slip subevents of both earthquakes had few aftershocks and higher stress drops than the subduction thrust subevent of the enggano earthquake this difference is consistent with previous observations of oceanic and subduction earthquakes

bbe systematics in subduction related metamorphic rocks characterization of the subducted component the mobility of b and be in h2o rich fluids and felsic silicate liquids produced during metamorphism of subducted oceanic slab and sediments has been investigated through analysis of subduction zone metamorphic rocks of the catalina schist california in metasedimentary rocks b be and the range in b be decrease with increasing metamorphic grade mean 72 std dev 41 for lowest grade lawsonite albite fades rocks mean 21 std dev 11 for higher grade greenschist and epidote amphibolite facies equivalents this decrease to more uniformly low b be may be attributed to the preferential removal of b in h2o rich fluids produced by devolatilization reactions over the approximate temperature interval of 350 600 c metamafic rocks do not show pronounced decrease in b be with increasing metamorphic grade however all metamafic samples have b be 30 lower than values for many altered seafloor basalts in amphibolite grade exposures felsic leucosomes and pegmatites reflecting partial melting have low b be similar to their metasedimentary and metamafic hosts which presumably experienced prior reduction in b be during lower temperature devolatilization this evidence for b and be mobility during high p t metamorphism complements studies of b be systematics in arc volcanic rocks in further characterizing mechanisms by which slab derived elements can be added to the source regions of arc lavas before subducted mafic and sedimentary rocks reach wadati benioff zone depths beneath arcs 80 150 km the b be of these rocks is likely to have decreased to 30 thus highly fractionated slab derived hydrous fluids may be necessary to generate the high b be signatures observed in many arcs b be of up to 200 the b be data together with previously presented stable isotope data for the catalina schist demonstrate that subduction zone metamorphic processes are capable of homogenizing presubduction variability in the concentrations of particularly fluid mobile elements in rocks and may through mixing produce fluids which trend toward uniform trace element and isotopic compositions these homogeneous fluids could infiltrate parts of the mantle wedge and contribute to the characteristic trace element and isotopic signatures of arc magma source regions in hotter subduction zones e g involving subduction of young hot oceanic lithosphere silicate melts derived from previously devolatilized sedimentary and mafic rocks may contribute relatively low b be signatures to arc source regions thus significant variations among arcs in the ranges of b be observed in front rank volcanoes e g for the bismarck arc b be 20 190 for the cascades arc b be 5 may be related in part to varying thermal structure which could govern both the b be of hydrous fluids and the relative proportions of hydrous fluid and silicate melt derived from the subducted slab and sediments

stress triggering of the great indian ocean strike slip earthquakes in a diffuse plate boundary zone 1 on april 11 2012 two great magnitude 8 earthquakes occurred within a two hour period off the west coast of northern sumatra indonesia in the broadly distributed india australia plate boundary zone the magnitude 8 6 mainshock holds the distinction of being both the largest instrumentally recorded strike slip earthquake and the largest earthquake away from a recognized plate boundary fault the mainshock involved sequential ruptures of multiple fault planes oriented nearly perpendicular to each other the adjacent 2004 megathrust earthquake statically loaded the northern wharton basin oceanic lithosphere on both of the 2012 mainshock fault plane orientations and greatly enhanced the rate of earthquake activity in the region for a year viscoelastic relaxation of the asthenosphere following the 2004 and 2005 megathrust earthquakes continued to positively stress the offshore region correlating with the locations of later strike slip earthquakes including two magnitude 7 and the 2012 magnitude 8 earthquakes

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

serpentinization of cumulate ultramafic rocks from the north arm mountain massif of the bay of islands ophiolite abstract partially serpentinized dunites and wehrlites comprise the bulk of the cumulate ultramafic unit at the north arm mountain massif of the bay of islands ophiolite complex newfoundland in a suite of 59 dunites and werhlites from the base of the unit the serpentinized portions consist of lizardite chrysotile brucite accessory magnetite the ratio of lizardite chrysotile to brucite 8 2 weight percent petrographic observations show that most serpentinization occurred at the expense of olivine only limited amounts of clinopyroxene were serpentized an estimated volume increase of 32 accompanied serpentinization of the peridotites reconstructions of the primary modal proportions of wehrlites made taking this volume increase into account contain an average of 6 more clinopyroxene and 6 less olivine than do modal reconstructions that ignore the volume increase mass balance calculations provide no clear evidence for appreciable metasomatism of al2o3 cao feo mgo or sio2 during serpentinization the presence of brucite the evidence that most serpentinization occurred at the expense of olivine and the lack of appreciable metasomatism suggest that the primary reaction that controlled serpentinization of the peridotites is 2mg 2 sio 2 3h 2 o mg 3 si 2 o 5 oh 4 mg oh 2 olivine added serpentine brucite

supershear rupture on multiple faults for the mw 8 6 off northern sumatra indonesia earthquake of april 11 2012 1 we perform a back projection method to image the rupture propagation and short period energy release of the 2012 off northern sumatra earthquake mw8 6 using hi net data recorded in japan the results show a complex pattern of four conjugate faults over about 180 sec there is a striking correspondence between the lengths and orientations of our rupture pattern with the distribution of aftershocks each of the first three stages of the rupture corresponds to a clear lineation in the aftershocks with lengths of 200 to 400 km rupture speeds for several of the fault segments were very high about 5 km s and exceed the local s wave velocity this is the first example of an oceanic earthquake with supershear rupture speed

constraining the source of the m w 8 1 chiapas mexico earthquake of 8 september 2017 using teleseismic and tsunami observations the september 2017 chiapas mexico normal faulting intraplate earthquake mw 8 1 occurred within the tehuantepec seismic gap offshore mexico we constrained the finite fault slip model of this great earthquake using teleseismic and tsunami observations first teleseismic body wave inversions were conducted for both steep np 1 and low angle np 2 nodal planes for rupture velocities vr of 1 5 4 0 km s teleseismic inversion guided us to np 1 as the actual fault plane but was not conclusive about the best vr tsunami simulations also confirmed that np 1 is favored over np 2 and guided the vr 2 5 km s as the best source model our model has a maximum and average slips of 13 1 and 3 7 m respectively over a 130 km 80 km fault plane coulomb stress transfer analysis revealed that the probability for the occurrence of a future large thrust interplate earthquake at offshore of the tehuantepec seismic gap had been increased following the 2017 chiapas normal faulting intraplate earthquake

the marine osmium isotope record over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research several analytical developments particularly in the past few years have significantly increased our ability to study the behaviour of osmium in the surficial environment the 187os 188os and osmium concentration of seawater river water rain and hydrothermal vent fluids have been measured directly recently the behaviour of osmium in estuaries critical for estimating the marine residence time of osmium has been studied our knowledge of the surficial osmium cycle has thus significantly improved in addition reconstructions of past variations in the marine 187os 188os recently have been extended back into the mesozoic this review attempts to summarize our current understanding of the marine osmium system present and past the 187os 188os of seawater during the cenozoic to first order mimics the marine 87sr 86sr record it is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic tectonic processes however the marine osmium isotope system differs fundamentally from the marine strontium isotope system this review emphasizes three important differences first large impacts are capable of resetting the 187os 188os to unradiogenic values without significantly affecting the marine strontium system second organic rich sediments are characterized by high 187re 188os resulting 187os 188os ingrowth trajectories are similar to the average slope of the cenozoic 187os 188os seawater record trends towards more radiogenic 187os 188os seawater therefore can be caused by weathering of organic rich sediments at a constant rate third the marine residence time of osmium is sufficiently short to capture short periodic glacial interglacial fluctuations that are inaccessible to the buffered marine strontium isotope system this offers the opportunity to discriminate between high frequency climatic and low frequency tectonic forcing

comparative study of two tsunamigenic earthquakes in the solomon islands 2015 mw 7 0 normal fault and 2013 santa cruz mw 8 0 megathrust earthquakes the july 2015 mw 7 0 solomon islands tsunamigenic earthquake occurred 40 km north of the february 2013 mw 8 0 santa cruz earthquake the proximity of the two epicenters provided unique opportunities for a comparative study of their source mechanisms and tsunami generation the 2013 earthquake was an interplate event having a thrust focal mechanism at a depth of 30 km while the 2015 event was a normal fault earthquake occurring at a shallow depth of 10 km in the overriding pacific plate a combined use of tsunami and teleseismic data from the 2015 event revealed the north dipping fault plane and a rupture velocity of 3 6 km s stress transfer analysis revealed that the 2015 earthquake occurred in a region with increased coulomb stress following the 2013 earthquake spectral deconvolution assuming the 2015 tsunami as empirical green s function indicated the source periods of the 2013 santa cruz tsunami as 10 and 22 min

a nd and sr isotopic study of the trinity peridotite implications for mantle evolution field evidence indicates that the trinity peridotite was partially melted during its rise as a part of the upwelling convecting mantle at a spreading center a sm nd mineral isochron for a plagioclase lherzolite yields an age t 427 32 ma and initial e nd 10 4 0 4 which is distinctly higher than that expected for typical depleted mantle at this time this age is interpreted as the time of crystallization of trapped melt in the plagioclase lherzolite p t field this time of crystallization probably represents the time when the massif was incorporated as a part of the oceanic lithosphere the sm nd model age of the plagioclase lherzolite total rock is t chur nd 3 4 ae this suggests that the trinity peridotite was derived from a mantle that was depleted rather early in earth history the peridotite contains many generations of pyroxenite dikes and some microgabbro dikes we report data for two dikes that clearly crosscut the main metamorphic fabric of the peridotite a microgabbro dike yields a sm nd mineral isochron age of t 435 21 ma and e nd 6 7 0 3 a pyroxenite dike yields an initial e nd 7 3 0 4 the initial e nd values for the pyroxenite and gabbro dikes are fairly similar to those for the depleted mantle at this time and are distinct from the lherzolite demonstrating that they are not genetically related rb sr data do not give any coherent pattern however some bounds can be put on initial sr values of e sr 21 for the plagioclase lherzolite and e sr 8 7 for the microgabbro dike it is plausible that the dikes represent cumulates left behind from island arc magmas that rose through the the oceanic lithosphere within the vicinity of a subduction zone major and trace elements and sm nd isotopic data indicate a multiple stage history for the trinity peridotite a small melt fraction was extracted from an undepleted source 3 4 ae or more ago to produce the proto lherzolite a large fraction of melt 12 to 23 was extracted from the proto lherzolite to produce the present rock the lherzolite was then crosscut by dikes from average depleted mantle 0 44 ae ago the data are compatible with the depleted mantle source being formed very early in earth history although most available data indicate that the depleted upper mantle has been relatively well stirred through time the trinity data suggest that very ancient nd isotopic values are preserved and thus chemical and physical heteorgeneities are sometimes preserved in the depleted source of mid ocean ridge basalts as well as the oceanic lithosphere which they intrude

tsunami simulations of the sulawesi m w 7 5 event comparison of seismic sources issued from a tsunami warning context versus post event finite source the 28 september 2018 sulawesi earthquake generated a much larger tsunami than expected from its mw 7 5 magnitude and from its dominant strike slip mechanism within a few minutes after the earthquake the tsunami devastated the seafront of palu bay destroying houses and infrastructures over a few hundred meters coastal subsidence and slumping at various locations around the bay were also observed there is debate in the scientific community as to whether submarine landslides and shore collapses contributed to the generation of strong and destructive waves locally the objective of this study is threefold first to determine whether standard seismic inversions could predict the source in the context of tsunami early warning second to define a new seismic source built from optical image correlation and based on the geological and tectonic context third to assess whether the earthquake alone is able to generate up to 9 m wave heights at the coast numerical simulations of the tsunami propagation are performed for different seismic dislocation sources nonlinear shallow water equations are solved by a finite difference method in grids with 200 m and 10 m resolutions the early cmt focal solutions calculated by seismological institutes show dominant strike slip mechanisms with a homogenous slip distribution these sources produce maximum tsunami heights of 40 cm on the coast of palu city two heterogeneous sources are tested and compared the usgs finite fault model calculated from seismic inversion and a new hybrid source inferred from different techniques the latter is based on a segmented fault in agreement with the geological context and built from both from seismic parameters of a cmt solution and the observed horizontal ground displacements this source produces water wave heights of 4 to 5 m in the palu bay the observed inundation heights and distances are reproduced satisfactorily by the model at pantoloan and at the southwestern tip of palu bay however the hybrid source is unable to reproduce the largest 8 to 12 m water heights as reported from field surveys thus even though this hybrid source produces most of the reported tsunami energy we cannot exclude that the numerous coastal collapses observed in palu bay contributed to increase the local tsunami run up

estimation of seismic centroid moment tensor using ocean bottom pressure gauges as seismometers we examined the dynamic pressure change at the seafloor to estimate the centroid moment tensor solutions of the largest and second largest foreshocks mw 7 2 and 6 5 of the 2011 tohoku oki earthquake combination of onshore broadband seismograms and high frequency 20 200 s seafloor pressure records provided the resolution of the horizontal locations of the centroids consistent with the results of tsunami inversion using the long period 10 min seafloor pressure records although the depth was not constrained well whereas the source locations were poorly constrained by the onshore seismic data alone also the waveforms synthesized from the estimated cmt solution demonstrated the validity of the theoretical relationship between pressure change and vertical acceleration at the seafloor the results of this study suggest that offshore pressure records can be utilized as offshore seismograms which would be greatly useful for revealing the source process of offshore earthquakes

beryllium systematics in young volcanic rocks implications for 10 be beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior be analyses conducted on well characterized oceanic and arc volcanic rock suites as well as on marine sediments suggest a bulk solid liquid distribution coefficient of 0 03 0 06 for melting of the mantle and crystallization of basalts the be nd ratio for many volcanic rocks from diverse tectonic environments is approximately 05 similar to the ratio in chondrites be data for samples from volcanic arcs show that there are significant variations in 10be 9be among different arcs and that variations in 10be are not due to variations in be concentration alone for at least one volcano bogoslof the 10be 9be ratio is constant for samples that vary by a factor of three in both their be and 10be concentrations suggesting that 10be is an inherited magmatic signature and not simply a result of contamination near the surface in addition the be nd and pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the bogoslof source region provided the mantle wedge has the isotopic characteristics of depleted morb since 10be exists only in the uppermost tens of meters of oceanic sediments the data suggest an efficient return flux of sediment to the mantle at subduction zones

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

the 2 march 2016 wharton basin mw 7 8 earthquake high stress drop north south strike slip rupture in the diffuse oceanic deformation zone between the indian and australian plates the diffuse deformation zone between the indian and australian plates has hosted numerous major and great earthquakes during the seismological record including the 11 april 2012 m w 8 6 event the largest recorded intraplate earthquake on 2 march 2016 an m w 7 8 strike slip faulting earthquake occurred in the northwestern wharton basin in a region bracketed by north south trending fracture zones with no previously recorded large event nearby despite the large magnitude only minor source finiteness is evident in aftershock locations or resolvable from seismic wave processing including high frequency p wave backprojections and love wave directivity analysis our analyses indicate that the event ruptured bilaterally on a north south trending fault over a length of up to 70 km with rupture speed of 2 km s and a total duration of 35 s the estimated stress drop 20 mpa is high comparable to estimates for other large events in this broad intraplate oceanic deformation zone

modeling the 2012 wharton basin earthquakes off sumatra complete lithospheric failure a sequence of large strike slip earthquakes occurred west of sunda trench beneath the wharton basin first reports indicate that the main shock was extremely complex involving three to four subevents m w 8 with a maze of aftershocks we investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data using the m w 7 2 foreshock we developed hybrid green s functions for the regional stations to approximate the mixture of oceanic and continental paths the main shock fault geometry is defined based on the back projection results point source mechanisms aftershock distribution and fine tune of grid searches the fault system contains three faults labeled f1 89 289 for dip strike f2 74 20 and f3 60 310 the inversion indicates that the main rupture consisted of a cascade of high stress drop asperities up to 30 mpa extending as deep as 50 km the rupture propagated smoothly from one fault to the next f1 f2 and f3 in sequence with rupture velocities of 2 0 2 5 km s the whole process lasted about 200 s and the major moment release 70 took place on the n s oriented f2 the m w 8 2 aftershock happened about 2 h later on a n s oriented fault with a relatively short duration 60 s and also ruptured as deep as 50 km the slip distributions suggest that the earthquake sequence was part of a broad left lateral shear zone between the australian and indian plates and ruptured the whole lithosphere these earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great sumatran earthquake of 2004

historical seismicity and implications for diffuse plate convergence in the northeast indian ocean large historical earthquakes provide constraints on the geographical extent and kinematics of the slow diffuse plate boundary extending from the central indian ridge to the sumatra trench the fault parameters of pre 1963 earthquakes are derived using a grid search for the best fit between observed and synthetic body waveforms surface wave spectral amplitudes and polarity and polarization constraints and location uncertainties are determined using a bootstrap resampling method the march 9 1928 ninetyeast ridge m 7 7 event shows left lateral strike slip faulting along a plane approximately coincident with the orientation of the ninetyeast ridge two small events which occurred at the location of the 1928 event in 1980 show focal mechanisms nearly identical to that determined for the 1928 earthquake and apparently reactivated the same fault the 1928 waveforms can also be fit by a thrust faulting solution with ene striking fault planes but a variety of evidence including the recent strike slip earthquakes at the same location suggest the strike slip solution these earthquakes are located along the western scarp of the ridge and do not represent reactivation of the ninetyeast fracture zone to the east of the edifice which was a major plate boundary in the early cenozoic the january 23 1949 m 6 75 and march 22 1955 m 7 0 wharton basin earthquakes although only 350 km apart show different strike slip and thrust faulting mechanisms all earthquakes show a regionally consistent pattern of horizontal compressional stress which changes from nw se in the wharton basin to n s in the central indian basin the compressional axes are oriented perpendicular to linear gravity anomalies associated with lithospheric flexure indicating little change in stress orientation since the onset of folding seismic deformation along the diffuse boundary consists of sinistral strike slip faulting associated with n s features such as the ninetyeast ridge and the 86 e fracture zone and thrust or reverse faulting in regions between fracture zones assuming transform motion the approximate slip rate along the northern ninetyeast ridge calculated from the summed moments of earthquakes is 2 8 mm yr this value is an order of magnitude less than previous estimates and suggests that at most only a small fraction of the current relative plate motion 7 mm yr occurs along the ridge the geographic distribution of seismicity suggests that the wharton basin east of the ninetyeast ridge is nearly as seismically active as the central indian basin to the west this result along with observed long wavelength gravity anomalies in the wharton basin indicates that the india australia plate boundary intersects the sumatra trench along a diffusely deforming region several thousand kilometers long rather than along a discrete transform zone

insights on the source of the 28 september 2018 sulawesi tsunami indonesia based on spectral analyses and numerical simulations the 28 september 2018 sulawesi tsunami has been a puzzle because extreme deadly tsunami waves were generated following an mw 7 5 strike slip earthquake while such earthquakes are not usually considered to produce large tsunamis here we obtained processed and analyzed two sea level records of the tsunami in the near field pantoloan located inside the palu bay and far field mamuju located outside the palu bay and conducted numerical simulations to shed light on the tsunami source the two tide gauges recorded maximum tsunami trough to crest heights of 380 and 24 cm respectively with respective dominating wave periods of 3 6 4 4 and 10 min and respective high energy wave duration of 5 5 and 14 h the two observed waveforms were significantly different with wave amplitude and period ratios of 16 and 3 respectively we infer tsunamigenic source dimensions of 3 4 4 1 km and 32 5 km for inside and outside of the palu bay respectively our numerical simulations fairly well reproduced both tsunami observations in pantoloan and mamuju except for the arrival time in mamuju however it was incapable of reproducing the maximum reported coastal amplitudes of 6 11 m it is possible that these two sources are different parts of the same tectonic source a bay oscillation mode of 85 min was revealed for the palu bay through numerical modeling actual sea surface disturbances and landslide generated waves were captured by two video recordings from inside the palu bay shortly after the earthquake it is possible that a large submarine landslide contributed to and intensified the sulawesi tsunami we identify the southern part of the palu bay around the latitude of 0 82os as the most likely location of a potential landslide based on our backward tsunami ray tracing analysis however marine geological data from the palu bay are required to confirm such hypothesis

laboratory and field investigations of rockburst phenomena using concurrent geotomographic imaging and acoustic emission microseismic techniques the progress made on three phases of a research project started in 1986 to investigate mining induced seismicity rockburst phenomena using concurrent geotomographic imaging and microseismic monitoring techniques is described phase i is the geotomographic software development and laboratory calibration trials phase ii is the enhancement of traditional microseismic monitoring instrumentation with a waveform acquisition system so that source mechanism studies can be carried out on mining induced seismic events phase iii is the field trials of the hybrid technique which will be used to monitor changing rock mass physical properties in response to mining preliminary results from all three phases are given together with an outline of current and future research planned

the 21 may 2003 tsunami in the western mediterranean sea statistical and wavelet analyses we report the statistical and wavelet analyses of the 21 may 2003 tsunami produced by an mw 6 8 6 9 thrust earthquake in the western mediterranean sea using 19 tide gauge records the largest trough to crest wave height was 196 cm recorded at the sant antoni station in the lee of the incoming tsunami wave except at one station the first wave was not the largest wave at all the analyzed stations and the largest wave arrived several hours after the first arrival in addition the tsunami waves persisted for more than 1 day at most stations as the spectra of coastal tide gauge stations are strongly influenced by topographic features special care was taken here while interpreting the results of spectral and wavelet analysis our wavelet analysis shows that only a peak at around 23 min is persistent for long duration and other peaks at 14 30 45 and 60 min appeared at short durations the 23 min signal is possibly associated with the width of the source fault whereas the fault length contributed to the 45 min signal based on these dominant periods the tsunami source dimensions are estimated as 95 km 45 km the statistical and wavelet analyses performed here provide some new insights into the characteristics of the tsunami that was generated and propagated in the western mediterranean basin

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

rupture process of the 2016 wharton basin strike slip faulting earthquake estimated from joint inversion of teleseismic and tsunami waveforms the 2016 wharton basin strike slip faulting earthquake generated a small tsunami that was clearly recorded at deep ocean stations teleseismic inversions were made on four different nodal planes suggested by gcmt and w phase solutions tsunami waveforms computed for the north south striking westward dipping plane were most similar to the observations with this fault plane joint inversions of teleseismic and tsunami waveforms were used to estimate the kinematic rupture process the weights of teleseismic and tsunami waveforms were found to make both datasets equally contribute to the solution misfit analysis of both datasets favored a rupture model with rupture front speed of 2 0 km s the seismic moment was estimated to be 7 69 1020 nm mw 7 9 most of it was released within 30 s and it peaked at 15 s subfaults with slip larger than 5 m were located from near surface to 30 km depth

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

geologic implications of seawater circulation through peridotite exposed at slow spreading mid ocean ridges peridotite denuded by tectonic extension and exposed at the seafloor adjacent to slow spreading centers hosts hydrothermal circulation of seawater the reaction of seawater with peridotite causes serpentinization which generates a high ph strongly reducing fluid rich in methane and hydrogen and is accompanied by as much as 40 volume expansion complete serpentinization of peridotite requires tectonic activity to open fluid paths sealed by volume expansion diffuse venting of serpentinization fluids causes lithification of calcareous ooze on the seafloor to chalk like limestone this may be the main mechanism of deposition of ophicarbonates common in ophiolites the degree of induration is a function of the fluid flux through the sediment column calcareous ooze infiltrates faults and fractures and can be deformed following lithification focused venting of serpentinization fluids may lead to deposition of large chimneys composed of calcite aragonite and brucite such as those in the recently documented lost city vent field 30 n mid atlantic ridge geophysical implications of serpentinization include 1 creation of magnetic anomalies due to growth of magnetite in serpentinite and 2 lowered seismic velocity integrated studies of geologic and geophysical effects of serpentinization may aid in a more complete understanding of the structure of oceanic lithosphere and the mechanisms that expose mantle peridotite at the seafloor

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

source model of the 16 september 2015 illapel chile m w 8 4 earthquake based on teleseismic and tsunami data teleseismic data were provided by the incorporated research institutions for seismology http www iris edu wilber3 find event tide gauge data can be found at the intergovernmental oceanographic commission website http www ioc sealevelmonitoring org dart records were provided by noaa http nctr pmel noaa gov dart earthquake catalogs by the usgs national earthquake information center http earthquake usgs gov earthquakes search and global instrumental earthquake catalogue 1900 2009 of international seismological centre global earthquake model http www globalquakemodel org what seismic hazard instrumental catalogue were used in this study we used the gmt software for drawing the figures wessel and smith 1998 this article benefited from constructive review comments by costas e synolakis university of southern california usa and yuichiro tanioka hokkaido university japan for which we are grateful we acknowledge financial supports from the japan society for the promotion of science

new insights into the source of the makran tsunami of 27 november 1945 from tsunami waveforms and coastal deformation data we constrain the source of the 27 november 1945 tsunami in the makran subduction zone msz using available tsunami waveforms recorded on tide gauges at mumbai india and karachi pakistan and that inferred at port victoria seychelles and coseismic deformation data along the makran coast spectral analysis of the tsunami waveforms shows that the tsunami governing period was 40 50 min at karachi whereas it was around 22 min at mumbai the inferred tsunami waveform at port victoria also indicated a period of around 21 min for the tsunami tsunami numerical simulations from the previously proposed source models failed in reproducing the observed tsunami waveforms and coseismic deformation data sensitivity analysis showed that the source fault needs to be extended offshore into deep water in order to reproduce the first 22 min signal at mumbai based on the inversion of the observed tsunami waveforms we propose a four segment fault with varying slip amounts as the final source this source includes a slip of 4 3 m onshore near ormara pakistan and a slip of 10 m offshore at water depth of around 3 000 m the total fault length is 220 km and the average slip is 6 1 m this source first reproduces fairly well the observed tide gauge records at mumbai and karachi second produces 1 m of uplift at ormara and 1 m of subsidence at pasni and third gives a moment magnitude of 8 3 for the earthquake which is in the acceptable range of seismic data the computed 1 m uplift at ormara is in the uplift range of 1 3 m reported in the literature as the tide gauge stations were located in the far field our proposed source explains mainly the tectonic source of the tsunami

the 2012 mw 8 6 indian ocean earthquake deep nucleation on a listric like fault abstract the 2012 mw 8 6 indian ocean earthquake the largest instrumentally recorded strike slip event has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region reported estimates of its depth vary from 10 to 45 km while the maximum depth of its inferred rupture extends to 50 60 km the complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation with debates on the geometry of the causative faults results from recent seismic surveys enable a fresh look at the earthquake fault geometry nucleation depths and lithospheric rheology in the present study these new findings are incorporated into 22 forward models using a revised velocity structure and n s geometries that flatten with depth the rupture initiation is modeled in the uppermost mantle 25 30 km as well as in the upper mantle at 45 km the latter of which is 15 20 km below the commonly accepted values of maximum depth for frictional failure our study shows that the westward directionality of wave propagation is achieved for strike slip failure on a listric like fault in contrast to subvertical geometries as previously suggested this propagation is persistent for a strike slip failure only for events nucleating at upper mantle depths 45 km rather than for those set to originate at depths between 25 and 30 km however for a dip slip failure the westward propagation is found to be consistent at both nucleation depths on a listric like fault this study highlights a deep nucleation within the lithospheric mantle for the 2012 mw 8 6 earthquake that could be due to strain localization induced by fluid rock interaction and or mineral transformation crystallization near the 680 c isotherm at 45 km depth 1 4 gpa which correlates with deep serpentinization on faults

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting