thermal and dynamical changes of the zonal mean state of the thermosphere during the 2009 ssw gaia simulations changes of the zonal mean state of the thermosphere during the 2009 stratospheric sudden warming ssw have been investigated using the ground to topside model of atmosphere and ionosphere for aeronomy gaia model both the zonal mean thermal and dynamical structure of the thermosphere exhibit pronounced changes during the ssw in terms of zonal mean temperature and winds first the zonal mean temperature above 100 km altitude drops at all latitudes except for in a narrow band around 60 n such temperature perturbations are found to be dominantly caused by changes in direct heating cooling processes related to solar radiation and thermal heat conduction at high latitudes but by dynamical processes in tropical regions second the zonal mean zonal wind experiences a strong westward perturbation in the tropical thermosphere along with distinct change in the meridional circulation this change consists of two parts one is a global scale north to south flow accompanied with upwelling downwelling in the northern southern polar region the other is a fountain like flow in tropical lower thermosphere the large enhancement of semidiurnal tides is suggested to be the primary cause for the fountain like flow

simultaneous rupture along two conjugate planes of the wharton basin earthquake analysis of broadband teleseismic data shows that the 18 june 2000 wharton basin earthquake a moment magnitude 7 8 intraplate event in the region of diffuse deformation separating the indian and australian plates consisted of two subevents that simultaneously ruptured two near conjugate planes this mode of rupture accommodates shortening by a mechanism different from that previously known elsewhere in the region the larger subevent occurred on a fossil fracture zone with a relatively high stress drop of about 20 megapascals showing that large stresses can accumulate in regions of distributed deformation

thermospheric zonal mean winds and tides revealed by champ we present direct global observations of longitudinally averaged champ zonal winds gathered between 2003 and 2007 a diurnal variation dominates the global zonal wind westward flows are observed from the early morning through afternoon hours while eastward flows peak in the evening a semidiurnal harmonic is also present with magnitudes that are approximately one third of the diurnal harmonic the time mean wind indicates westward winds over much of the globe with weak superrotation e or eastward winds that is symmetric about the equator during equinox and confined to the winter hemisphere at solstice diurnal and time mean champ winds agree fairly well with the whole atmosphere model some differences are observed in the semidiurnal and higher order tidal winds that underscore the challenges of modeling the sources sinks and mean wind effects upon tides between the surface and 400 km

a study of a self generated stratospheric sudden warming and its mesospheric lower thermospheric impacts using the coupled time gcm ccm3 1 a stratospheric sudden warming episode was self consistently generated in the coupled national center for atmospheric research thermosphere ionosphere mesosphere and electrodynamics general circulation model climate community model version 3 time gcm ccm3 taking advantage of the unique vertical range of the coupled model ground to 500 km we were able to study the coupling of the lower and upper atmosphere in this warming episode planetary wave 1 is the dominant wave component in this warming event analysis of the wave phase structure and the wave amplitude indicates that the wave may experience resonant amplification prior to the peak warming the mean wind in the high latitude winter stratopause and mesosphere decelerates and reverses to westward due to planetary wave forcing and forms a critical layer near the zero wind lines the wind deceleration and reversal also change the filtering of gravity waves by allowing more eastward gravity waves to propagate into the mesosphere and lower thermosphere mlt which causes eastward forcing and reverses the westward jet in the mlt this also changes the meridional circulation in the upper mesosphere from poleward downward to equatorward upward causing a depletion of the peak atomic oxygen layer at 97 km and significant reduction of green line airglow emission at high latitudes and midlatitudes planetary waves forced in situ by filtered gravity waves in the mlt grow in the warming episode their growth and interaction with tides create diurnal and semidiurnal variabilities in the zonal mean zonal wind

equatorial vertical drift modulation by the lunar and solar semidiurnal tides during the 2013 sudden stratospheric warming during the 2013 stratospheric sudden warming ssw period the jicamarca unattended long term investigations of the ionosphere and atmosphere julia radar at jicarmarca peru observed low latitude vertical drift modulation with lows of 0 12 m s daytime maximum drifts between 6 13 and 22 25 january and enhanced drifts up to 43 m s between 15 snd 19 january the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model reproduces the prevailing vertical drift feature and is used to examine possible causes the simulations indicate that the modulation of the vertical drift is generated by the beating of the semidiurnal solar sw2 and lunar m2 tides during the ssw period the beating is observable since the magnitudes of lunar and solar semidiurnal tidal amplitudes are comparable the theoretical beating frequency between sw2 and m2 is 1 15 13 day which may be modified due to phase changes this study highlights the importance of the lunar tide during ssw periods and indicates that the equatorial vertical drift modulation should be observable at other longitudes as well

time domain observations of a slow precursor to the 1994 romanche transform earthquake low frequency spectral anomalies have indicated that some large earthquakes are preceded by extended episodes of smooth moment release but the reality of these slow precursors has been debated because they have not been directly observed in the time domain high gain seismograms from the 14 march 1994 romanche transform event moment magnitude m w 7 0 show a precursory ramp with a moment of 7 1018 newton meters beginning about 100 seconds before the arrival of the high frequency p waves this precursor was the initial phase of a slow component of slip that released nearly half of the total moment of the earthquake such behavior may be typical for large earthquakes on the oceanic ridge transform system

mesosphere and lower thermosphere zonal wind variations over low latitudes relation to local stratospheric zonal winds and global circulation anomalies long term observations from medium frequency and meteor radars 1993 2012 and rocket soundings 1979 1990 and 2002 2007 are used to study mesosphere and lower thermosphere mlt zonal wind variations in relation to the stratospheric winds over northern low latitudes the combined data set provides a complete height profile of amplitude of semiannual oscillation sao up to 100 km with an exception around 75 80 km the sao signal has maxima around 50 km and 82 km and a minimum around 65 km the mlt zonal winds show remarkable interannual variability during northern hemispheric spring equinox and much less during fall equinox zonal wind mesospheric spring equinox enhancements msee appear with a periodicity of 2 3 years suggesting a modulation by the quasi biennial oscillation which we identified with the strength of stratospheric westward winds out of 20 years of observations the stratospheric westward winds are strong during 11 years non msee and weak during 9 years six of these 9 years show large mlt winds msee and 3 years 1999 2004 and 2006 show small mlt winds missing msee these unexpected small winds occur in years with global circulation anomalies associated with strong sudden stratospheric warmings and an early spring transition of zonal winds with the proposed three msee classes we take into account local and global forcing factors

intraplate seismicity and stresses in young oceanic lithosphere we have conducted a systematic study of oceanic intraplate seismicity in the period 1964 1983 occurring in lithosphere younger than 35 million years focal mechanisms determined for 26 events using first motions p wave modeling and surface wave amplitude radiation patterns along with 13 previously determined mechanisms indicate a diversity of faulting styles and stress orientations in young oceanic lithosphere there is no evidence for a worldwide transition from extension to compression at a specific lithospheric age tensional axes of normal faulting events are oriented oblique to the spreading direction and do not show extension in the spreading direction congressional axes of thrust events show a weak preferred orientation in the spreading direction presumably due to ridge push stresses however stress axes of thrust events in very young lithosphere age 9 ma do not show a correlation with the spreading direction suggesting that the ridge push force is small near the ridge these observations indicate that tensional stress in the spreading direction is concentrated in a very narrow zone at the ridge axis in agreement with models which assume that the axial region has very little tensile strength normal faulting events occur at greater depths and temperatures than thrust events possibly because rocks under tensional stress have strength maxima at higher temperatures alternatively the depths of the normal faulting events may be a result of the higher thermal gradients at depth in young lithosphere if thermoelastic stresses are important in generating this seismicity differential thermal contraction along fracture zones does not seem to be a significant source of near ridge intraplate seismicity high seismicity rates in young lithosphere noted previously on a global scale seem characteristic of all three major ocean basins additionally most of the total oceanic intraplate moment release takes place in young lithosphere however most of the events and more than 96 of the total moment release of the near ridge intraplate seismicity are contained in five areas two zones in the indian ocean one near chagos bank and the other in the amsterdam st paul region indicate tension parallel to the trend of the plate boundary a region of high seismicity near the east pacific rise between 3 and 7 n shows both normal and thrust faulting while another region on the cocos plate west of the panama fracture zone is characterized by strike slip faulting thrust strike slip and normal faulting events are found in a small seismically active zone of the south central pacific the extremely uneven distribution of seismicity if not a result of the relatively short time period studied 20 years indicates local perturbations strongly affect near ridge seismicity

impacts of sudden stratospheric warming on general circulation of the thermosphere impacts of sudden stratospheric warming ssw on the thermosphere were studied using a gravity wave gw resolving whole atmosphere model during an ssw event the mesosphere at high latitudes cools and the lower thermosphere becomes warm at the peak of the ssw event a temperature drop occurs above an altitude of 150 km at high latitudes our results indicate that the ssw event strongly affects meridional circulation and gw drag in the thermosphere in the lower thermosphere upward wind in the arctic region southward wind in the region between the north pole and the south pole and downward wind in the antarctic region are dominant before ssw occurs the ssw event reverses meridional circulation at altitudes between 90 and 125 km in the northern hemisphere during the ssw event downward wind in the arctic region and northward wind in the northern hemisphere prevail in the lower thermosphere a detailed analysis revealed that during the ssw event the change in meridional circulation is caused by the attenuation of the gw drag and we identified the mechanism responsible for this attenuation moreover we assessed the impacts of ssw on temperatures in the equatorial region and southern hemisphere

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

strike slip earthquakes in the oceanic lithosphere observations of exceptionally high apparent stress summary the radiated energies e s and seismic moments m0 for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses a e s m0 where is the modulus of rigidity the globally averaged a for shallow earthquakes in all tectonic environments and seismic regions is 0 3 mpa however the subset of 49 earthquakes with the highest apparent stresses a greater than about 5 0 mpa is dominated almost exclusively by strike slip earthquakes that occur in oceanic environments these earthquakes are all located in the depth range 7 29 km in the upper mantle of the young oceanic lithosphere many of these events occur near plate boundary triple junctions where there appear to be high rates of intraplate deformation indeed the small rapidly deforming gorda plate accounts for 10 of the 49 high a events the depth distribution of a which shows peak values somewhat greater than 25 mpa in the depth range 20 25 km suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere a recently proposed envelope for apparent stress derived by taking 6 per cent of the strength inferred from laboratory experiments for young less than 30 ma deforming oceanic lithosphere agrees well with the upper bound envelope of apparent stresses over the depth range 5 30 km the corresponding depth dependent shear strength for young oceanic lithosphere attains a peak value of about 575 mpa at a depth of 21 km and then diminishes rapidly as the depth increases in addition to their high apparent stresses which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10 30 km our set of high a earthquakes show other features that constrain the nature of the forces that cause interplate motion first our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of a for the two types secondly many of the intraplate events have focal mechanisms with the t axes that are normal to the nearest ridge crest or subduction zone and p axes that are normal to the proximate transform fault these observations suggest that forces associated with the reorganization of plate boundaries play an important role in causing high a earthquakes inside oceanic plates extant transform boundaries may be misaligned with current plate motion to accommodate current plate motion the pre existing plate boundaries would have to be subjected to large horizontal transform push forces a notable example of this is the triple junction near which the second large aftershock of the 1992 april cape mendocino california sequence occurred alternatively subduction zone resistance may be enhanced by the collision of a buoyant lithosphere a process that also markedly increases the horizontal stress a notable example of this is the aleutian trench near which large events occurred in the gulf of alaska in late 1987 and the 1998 march balleny sea m 8 2 earthquake within the antarctic plate

aftershocks of the 2012 off coast of sumatra earthquake sequence abstract aftershocks of the 2012 off coast of sumatra earthquake sequence exhibit a complex and diffuse spatial distribution the first order complexity in aftershock distribution is clear and well beyond the influence of typical earthquake location uncertainty the sequence included rupture of multiple fault segments spatially separated we use surface wave based relative centroid locations to examine whether at the small scale the distribution of the aftershocks was influenced by location errors surface wave based relative location has delineated precise oceanic transform fault earthquake locations in multiple regions however the relocated aftershocks off the coast of sumatra seldom align along simple linear trends that are compatible with the corresponding fault strikes as estimated for the gcmt catalog the relocation of roughly 60 moderate earthquake epicentroids suggests that the faulting involved in the 2012 earthquake aftershock sequence included strain release along many short fault segments statistical analysis and temporal variations of aftershocks show a typical decay of the aftershocks but a relatively low number of aftershocks as is common for intraplate oceanic earthquakes coulomb stress calculations indicate that most of the moderate magnitude aftershocks are compatible with stress changes predicted by the large event slip models the patterns in the aftershocks suggest that the formation of the boundary and eventual localization of deformation between the indian and australian plate is a complicated process

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

seismicity and geometry of a 110 km long blind thrust fault 1 the 1985 kettleman hills california earthquake the august 4 1985 kettleman hills earthquake was the third in a sequence of moderate shocks to occur beneath the northern half of a 110 km long fold chain bounding the eastern california coast ranges the 1982 mw 5 4 new idria 1983 mw 6 5 coalinga and 1985 mw 6 1 kettleman hills events define a southward progression of seismic activity beneath the fold we use teleseismic waveforms geodetic modeling hypocenters relocated in a three dimensional velocity model and subsurface structural data to investigate the kettleman hills earthquake the main shock results from motion on a shallowly dipping thrust fault buried at 10 km depth aftershocks and coseismic fault slip extend 20 km along the fold axis nearly the full extent of the kettleman hills north dome anticline aftershocks occur primarily several kilometers in front of the fault tip and in the core of the anticline the main shock and several foreshocks occurred at a 2 km right step in the quaternary fold axis which also corresponds to the southern end of the 1983 coalinga and northern end of the 1985 kettleman hills aftershock zones from this we infer that the step in the fold is caused by an offset or tear in the underlying fault the scalar seismic moment is 1 6 1018 n m consistent with the geodetic deformation and the duration of rupture is 16 s 3 4 times greater than for the average earthquake with this scalar moment the slow rate of moment release provides an explanation for the low level of ground shaking and low local magnitude reported for the event the peak of the geodetic uplift is located 5 km perpendicular to the quaternary fold axis we argue that the fault is propagating northeast into the undeformed san joaquin valley sediments and that the overlying fold is growing at about 0 5 mm yr

moment constrained finite fault analysis using teleseismic p waves mexico subduction zone abstract we examine the ability of teleseismic p waves to identify the rupture history of large earthquakes along the mexico subduction zone using a kinematic finite fault waveform inversion scheme that uses the earthquake seismic moment to stabilize the inversion process application of our procedure to the teleseismic displacement waveforms recorded for the m w 7 9 colima jalisco earthquake of october 1995 yields a slip pattern that is similar to the rupture model derived previously using a more traditional approach that incorporates stepwise adjustments to the constraint equations to recover the least complicated source model the areas of large slip inferred for both models are located at the same general position along the fault although peak slips obtained using the moment constrained approach are significantly greater synthetic tests conducted for a hypothetical interplate rupture along the guerrero portion of the mexico subduction zone indicate that the high peak slips result from a wide variability in slip amplitude for individual subfaults although the variability is less pronounced when velocity waveforms are used in the inversion the tests also show that errors in fault dip and earthquake nucleation depth affect the accuracy of the inferred slip source more significantly than errors in strike and rake also the data are relatively insensitive to variations in rupture velocity and dislocation duration suggesting that our single step approach could be used in a simplified manner to identify the first order rupture features of large earthquakes using routinely derived fault parameters a simplified analysis of the p wave ground velocities recorded for the m w 7 5 tecoman colima earthquake of january 2003 yields a slip distribution that is remarkably similar to a rupture model derived previously using teleseismic body waves and strong motion records

back propagating super shear rupture in the 2016 mw7 1 romanche transform fault earthquake how an earthquake rupture propagates strongly influences the potentially destructive ground shaking complex ruptures often involve slip along multiple faults which masks information on the frictional behaviour of fault zones geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics because strain is accommodated along a single wide fault zone that offsets the homogeneous geology here we present an analysis of the 2016 mw 7 1 earthquake on the romanche fracture zone in the equatorial atlantic using data from both nearby seafloor seismometers and global seismic networks we show that this rupture had two phases 1 upward and eastward propagation towards a weaker region where the transform fault intersects the mid ocean ridge and then 2 an unusual back propagation westwards at a supershear speed towards the centre of the fault we suggest that deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones this highlights that even earthquakes along a single distinct fault zone can be highly dynamic observations of back propagating ruptures are sparse and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments in one earthquake an oceanic transform fault ruptured in one direction and then backwards at a speed exceeding that of shear wave propagation according to an analysis of data recorded by nearby seafloor and global seismometers

location of the africa australia india triple junction and motion between the australian and indian plates results from an aeromagnetic investigation of the central indian and carlsberg ridges accepted 1994 june 7 received 1994 may 23 in original form 1993 may 24 summary prior studies have proposed and examined the hypothesis that india and australia are separate rigid plates separated by a wide near equatorial e w striking plate boundary attempts to place narrow limits on the location of the africa australiaindia triple junction have been hindered however by the lack of useful magnetic profiles crossing the eastern carlsberg ridge and northern central indian ridge herein we present near ridge portions of new profiles from an aeromagnetic survey of the carlsberg ridge east of 66 e and of the central indian ridge north of 19 s these new data are used to estimate 35 new spreading rates averaged from the middle of chron 2a 3 03 ma to the present all other plate motion data along the central indian and carlsberg ridges are also analysed to investigate the present kinematics of the indian ocean especially the motion and boundary between the indian and australian plates unlike prior efforts we objectively estimate uncertainties in the strikes of transform faults along the carlsberg and central indian ridges

the 1986 kermadec earthquake and its relation to plate segmentation to evaluate the tectonic significance of the october 20 1986 kermadec earthquake m w 7 7 we performed a comprehensive analysis of source parameters using surface waves body waves and relocated aftershocks amplitude and phase spectra from up to 93 rayleigh waves were inverted for centroid time depth and moment tensor in a two step algorithm in some of the inversions the time function was parameterized to include information from the body wave time function the resulting source parameters were stable with respect to variations in the velocity and attenuation models assumed the parameterization of the time function and the set of rayleigh waves included the surface wave focal mechanism derived 275 61 156 is an oblique compressional mechanism that is not easy to interpret in terms of subduction tectonics a seismic moment of 4 5 1020 n m a centroid depth of 45 5 km and a centroid time of 13 3 s were obtained directivity was not resolvable from the surface waves the short source duration is in significant contrast to many large earthquakes

magnetic and bathymetric investigations over the vema region of the central indian ridge tectonic implications abstract magnetic and bathymetric data were collected along n50 e profiles in the vema region 7 12 s 64 70 e across five ridge segments of the central indian ridge cir anomalies up to a5 10 ma identified by generating synthetics for each profile show asymmetric spreading though inter segmental variations in spreading rate have been observed the mean half spreading rate increases from 1 8 cm yr in the region north of vema transform to 2 1 cm yr south of the vema transform the average spreading rate for the last 10 ma has not always been symmetric the interpretation of magnetic and bathymetric data shows the complex nature of this part of the cir which could probably be attributed to i the short ridge segment ii interaction with fracture zone and iii interaction between the cir and the wide boundary zone wbz separating the indian and australian plates

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

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

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

the 2012 mw 8 6 wharton basin sequence a cascade of great earthquakes generated by near orthogonal young oceanic mantle faults we improve constraints on the slip distribution and geometry of faults involved in the complex multisegment mw 8 6 april 2012 wharton basin earthquake sequence by joint inversion of high rate gps data from the sumatran gps array sugar teleseismic observations source time functions from broadband surface waves and far field static gps displacements this sequence occurred under the indian ocean 400 km offshore sumatra the events are extraordinary for their unprecedented rupture of multiple cross faults deep slip large strike slip magnitude and potential role in the formation of a discrete plate boundary between the indian and australian plates the sugar recorded static displacements of up to 22 cm along with time varying arrivals from the complex faulting which indicate that the majority of moment release was on young wnw trending right lateral faults counter to initial expectations that an old lithospheric nne trending fracture zone played the primary role the new faults are optimally oriented to accommodate the present day stress field not only was the greatest moment released on the younger faults but it was these that sustained very deep slip and high stress drop 20 mpa the rupture may have extended to depths of up to 60 km suggesting that the oceanic lithosphere in the northern wharton basin may be cold and strong enough to sustain brittle failure at such depths alternatively the rupture may have occurred with an alternative weakening mechanism such as thermal runaway

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

global catalog of earthquake rupture velocities shows anticorrelation between stress drop and rupture velocity abstract application of the scardec method provides the apparent source time functions together with seismic moment depth and focal mechanism for most of the recent earthquakes with magnitude larger than 5 6 6 using this large dataset we have developed a method to systematically invert for the rupture direction and average rupture velocity v r when unilateral rupture propagation dominates the approach is applied to all the shallow z

teleseismic search for slow precursors to large earthquakes some large earthquakes display low frequency seismic anomalies that are best explained by episodes of slow smooth deformation immediately before their high frequency origin times analysis of the low frequency spectra of 107 shallow focus earthquakes revealed 20 events that had slow precursors 95 percent confidence level 19 were slow earthquakes associated with the ocean ridge transform system and 1 was a slow earthquake on an intracontinental transform fault in the east african rift system these anomalous earthquakes appear to be compound events each comprising one or more ordinary fast ruptures in the shallow seismogenic zone initiated by a precursory slow event in the adjacent or subjacent lithosphere

rupture length and velocity for earthquakes in the mid atlantic ridge from directivity effect in body and surface waves abstract the dimensions and rupture velocities of four earthquakes two in the mid atlantic ridge and two in iceland with strike slip mechanisms and magnitudes m w between 6 2 and 6 8 were studied using the directivity effects of rayleigh and body waves for rayleigh waves we used the directivity function for different pairs of stations and for body waves the waveforms of p and sh waves corresponding to a simple extended line source we have found that three have very shallow depths about 3 km and one 8 km fault lengths between 12 km and 21 km and a low rupture velocity of about 1 5 km s to 2 0 km s which supports the idea of the presence of slow earthquakes in transform faults

rupture characteristics of the 2003 mw 7 6 mid indian ocean earthquake implications for seismic properties of young oceanic lithosphere 1 analysis of broadband seismograms from the 15 july 2003 large earthquake m 7 6 in the central indian ocean reveals an unusual source process the source duration of longer than a minute is more than twice as long as expected from earthquake scaling relations yet 80 of the moment release occurred in two energetic asperities near the end of the rupture these two asperities were located in lithosphere with an age of 7 ma or greater a previous study has suggested that strike slip earthquakes in oceanic lithosphere having much longer than expected source durations also have a slow dissipative rupture process characterized by low radiated seismic energy and therefore low apparent stress we find no evidence for a slow rupture process to the 2003 earthquake instead the long duration appears to be due only to nucleation close to the actively spreading carlsberg ridge in lithosphere younger than 7 ma younger oceanic lithosphere may be able to generate small to moderate earthquakes but be unable to sustain slip in a large event due to steady release of strain in aseismic creep events large strike slip earthquakes within oceanic lithosphere may occur only in the central portions of long transform faults or in intraplate regions rupturing energetic asperities like those that failed in the mid indian ocean earthquake and leading to the observation that oceanic strike slip earthquakes have the largest apparent stresses among the global population of shallow earthquakes

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

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

the 2014 mw 6 1 bay of bengal indian ocean earthquake a possible association with the 85 e ridge oceanic intraplate earthquakes are known to occur either on active ridge transform structures or by reactivation of their inactive counterparts generally referred to as fossil ridges or transforms the indian ocean one of the most active oceanic intraplate regions has generated large earthquakes associated with both these types of structures the moderate earthquake that occurred on 21 may 2014 m w 6 1 in the northern bay of bengal followed an alternate mechanism as it showed no clear association either with active or extinct ridge transform structures its focal depth of 50 km is uncommon but not improbable given the similar to 90 ma age of the ocean floor with 12 km thick overlying sediments no tectonic features have been mapped in the near vicinity of its epicenter the closest being the 85 degrees e ridge located similar to 100 km to its west hitherto regarded as seismically inactive the few earthquakes that have occurred here in the past are clustered around its southern or northern limits and a few are located midway at around 10 degrees n the 2014 earthquake sourced close to the northern cluster seems to be associated with a northwest southeast oriented fracture located on the eastern flanks of the 85 degrees e ridge if this causal association is possible we believe that reactivation of fossil hotspot trails could be considered as another mechanism for oceanic intraplate seismicity

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

seismic rupture on an oceanic continental plate boundary strike slip earthquakes along the queen charlotte fairweather fault abstract we investigate the 2013 m w 7 5 craig alaska earthquake and nearby seismicity to understand better how temperature and composition may control the depth of seismic rupture along a strike slip fault offsetting contrasting lithosphere types the queen charlotte fairweather qcf fault lies between the oceanic lithosphere of the pacific plate and the accreted insular superterrane of the north american continent we use point source and finite fault modeling of teleseismic body waves to characterize the focal mechanism and the depth extent of seismic rupture of five m w 5 9 7 5 earthquakes four of the five earthquakes are consistent with rupture on the qcf fault we find that these four earthquakes have centroid depths between 11 and 18 km 3 km and aftershocks with an order of magnitude less than typical continental earthquakes finite fault modeling of the 2013 craig earthquake favors bilateral rupture along a 150 km fault with a depth range of slip between 5 and 25 km with faster rupture 4 5 km s to the north than the south 1 km s these results suggest that the transition of brittle to ductile deformation along this section of the pacific north american plate boundary is thermally controlled by a more mafic rheology than average continental crust exhibiting behavior consistent with that of an oceanic strike slip fault online material figures of best fitting point source focal mechanism and waveform fits dip sensitivity directivity tests aftershock distributions and finite fault results

frictional melting during the rupture of the 1994 bolivian earthquake the source parameters of the 1994 bolivian earthquake magnitude m w 8 3 suggest that the maximum seismic efficiency was 0 036 and the minimum frictional stress was 550 bars thus the source process was dissipative which is consistent with the observed slow rupture speed only 20 of the locals wave velocity the amount of nonradiated energy produced during the bolivian rupture was comparable to or larger than the thermal energy of the 1980 mount st helens eruption and was sufficient to have melted a layer as thick as 31 centimeters once rupture was initiated melting could occur which reduces friction and promotes fault slip

an apparent mechanism dependence of radiated seismic energy we develop an extension to the method of boatwright and choy 1986 for determining the radiated seismic energy es that accounts for factors that bias the estimate we apply our technique to 204 events worldwide during the period 1992 1999 and find that the apparent stress is on average largest for strike slip events 0 70 mpa while for reverse and normal events it is significantly smaller 0 15 and 0 25 mpa respectively these results support the mechanism dependence of es reported by choy and boatwright 1995 although we find that once likely sources of bias are accounted for the mechanism dependence is not as strong as found previously the source of the mechanism dependence is unclear but one possibility is that it reflects a mechanism dependent difference in the stress drop this hypothesis is suggested by the scaling of slip with width in large strike slip earthquakes and makes two predictions which could be used to test it the first is that the discrepancy should disappear for the very largest dip slip earthquakes as the length of the fault greatly exceeds the downdip extent the second is that the discrepancy ought to disappear for smaller earthquakes the first can not yet be tested due to a lack of recent very large dip slip earthquakes the second is supported by the lack of mechanism dependence to es for smaller earthquakes an alternative hypothesis is that the apparent mechanism dependence could result if faults are opaque during rupture blocking seismic radiation across them brune 1996 this could cause radiated seismic energy to be trapped preferentially in the crust near the source volume for dipping faults there remains however a large discrepancy between estimates of es obtained from teleseismic versus regional data this discrepancy indicates a problem with teleseismic and or regional estimates of the seismic energy and must be resolved before a definite conclusion can be drawn

kinematic and dynamic rupture models of the november 3 2002 mw7 9 denali alaska earthquake 1 regional seismic waveforms continuous and campaign mode gps data and surface slip measurements were used to obtain a kinematic model of the rupture process of the november 3 2002 mw 7 9 denali alaska earthquake the event initiated as a mw 7 0 reverse slip event on the north dipping susitna glacier fault with subsequent right lateral slip distributed over approximately 300 km of the denali fault system near shear rupture velocity is inferred from the kinematic modeling the average and maximum slips were found to be 2 14 m and 10 3 m static stress drop varies from 1 3 to 5 0 mpa over the 5 segment fault model dynamic modeling shows the rupture propagated along the susitna glacier and denali faults then transferred to the totschunda fault before stopping largely due to the totschunda s more favorable orientation with respect to the regional stress field

the great march 25 1998 antarctic plate earthquake moment tensor and rupture history we use broadband body and mantle wave data to study the 1998 antarctic intraplate earthquake the centroid moment tensor cmt has a large non double couple component there exist two pure double couple constrained solutions that fit the data almost equally well the frequent practice of taking the best double couple gives a far from optimal solution we use p and sh body waves to determine the rupture parameters of the first and larger of the two observed subevents the best rupture plane with strike 96 dip 69 and rake 18 is compatible with only one of the two cmt solutions strike 96 dip 64 rake 23 centroid location 63 1 s 148 4 e 10 km depth centroid time 0313 02 ut and m0 1 3 1021 n m mw 8 0 the first subevent is a simple primarily westward propagating 140 km rupture of 45 s duration with average velocity 3 km s 1 it has a seismic moment of 1 2 1021 n m mw 8 0 with 75 of its moment released between 10 and 27 s and a stress drop of 240 bars the rupture is physically bounded by two fracture zones at 147 5 e and 150 e the second subevent lasted from 70 to 90 s on a fault extending from 210 to 270 km west of the epicenter with a moment of 0 3 0 6 1021 n m mw 7 6 7 8 this is a spectacular example of dynamic stress triggering over a 100 km separation distance with a time delay of 40 s the complex pattern of aftershocks is primarily controlled by preexisting fracture zones on the ocean floor

fault reactivation and selective abandonment in the oceanic lithosphere 1 normal and transform faults originally formed at a spreading centre can be reactivated in diffuse plate boundary zones and in areas of lithospheric flexure such as at peripheral bulges to subduction zones using new seismic reflection profiles and modeling we investigate how the original oceanic fabric is reactivated in the simple case of fault perpendicular compression in the central indian basin well oriented normal paleofaults were reactivated with reverse motion at the very onset of deformation 9 ma but only a small subset remained active past 7 ma suggesting that most of the densely spaced small offset faults were abandoned while deformation localized onto fewer faults with larger spacing we find a similar evolution using a 2d finite element code of lithospheric shortening using a pseudoplastic rheology weak zones 3 km spaced and 30 40 weaker than the surrounding material are introduced to simulate the fabric formed at the ridge axis we show that reactivation and selective abandonment require strain weakening followed by strain rate weakening once a maturation threshold is reached a maturation fault slip of less than 50 m is needed to produce a fault network similar to that in the central indian ocean

resolution of the slow earthquake high apparent stress paradox for oceanic transform fault earthquakes 1 oceanic transform fault earthquakes exhibit some interesting and apparently contradictory properties a number of earthquakes on oceanic transforms have been identified as slow on the basis of their weak seismic radiation at high frequencies on the other hand transform fault events as a population have been found to have high apparent stress indicating strong high frequency radiation since the seismic energy is concentrated at and above the corner frequency in an attempt to reconcile these observations we analyze seventy 5 8 mw 8 3 strike slip earthquakes from around the world four of these earthquakes have both exceptionally low apparent stress and large centroid time shifts for their seismic moment all four of them are located on oceanic transform faults if we include these events in the population we find that continental and oceanic strike slip earthquakes are not significantly different in their mean apparent stress but that there is greater variation for oceanic events we also find that in contrast to the low correlation between centroid time shift and apparent stress for continental earthquakes the oceanic ridge transform earthquakes have a high correlation between these two parameters we also observe cases of both ordinary and slow earthquakes on adjacent sections of the same transform these characteristics suggest significant differences in the faulting process between oceanic transforms and continental faults

rupture processes of the 1987 1988 gulf of alaska earthquake sequence three large earthquakes occurred in the gulf of alaska during 1987 1988 one on november 17 1987 m w 7 2 the second one on november 30 1987 m w 7 8 and the third one on march 6 1988 mw 7 7 these major intraplate strike slip oceanic events occurred along conjugate trends in a region of no previous seismicity body wave modeling places their centroid depths in the upper mantle the depth of the first two events is approximately 20 km and of the third is 15 km as compared to other large events the body wave models for the two largest earthquakes have short rupture lengths 110 km and 40 km respectively and short duration times 36 and 20 s respectively for their magnitude the latter of the two events has a rupture length much shorter than that inferred from aftershock seismicity the short rupture lengths and source durations may reflect differences between the strength of oceanic and continental lithosphere and suggest that events in oceanic lithosphere have a higher moment release per unit area than similar continental events most of the moment release occurred near the epicenter and or regions of apparent structural complexities where seismicity trends intersect

global patterns of radiated seismic energy and apparent stress radiated energies from shallow earthquakes with magnitudes 5 8 that occurred between 1986 and 1991 are used to examine global patterns of energy release and apparent stress in contrast to traditional methods which have relied upon empirical formulas these energies are computed through direct spectral analysis of broadband seismic waveforms velocity squared spectra of body waves are integrated after they have been corrected for effects arising from depth phases frequency dependent attenuation and focal mechanism the least squares regression fit of energy es to surface wave magnitude ms for a global set of 397 earthquakes yields log es 4 4 1 5ms which implies that the gutenberg richter relationship overestimates the energies of earthquakes the least squares fit between es and seismic moment m0 is given by the relationship es 1 6 10 5 m0 which yields 0 47 mpa as the average global value of apparent stress however the regression lines of both es ms and es m0 yield poor empirical predictors for the actual energy radiated by any given earthquake the scatter of data is more than an order of magnitude about each of the regression lines on the other hand global variations between es and mo while large are not random when subsets of es m0 are plotted as a function of seismic region and faulting type the scatter in data is substantially reduced the es m0 fits for many seismic regions and tectonic environments are very distinctive and a characteristic apparent stress c can be derived the lowest apparent stresses 3 0 mpa are associated with strike slip earthquakes that occur at oceanic ridge ridge transforms and in intraplate environments seaward of island arcs intermediate values of apparent stress 1 5 a 3 0 mpa are associated with strike slip earthquakes at incipient or transitional plate boundaries in general the dominant mode of failure for a tectonic environment is associated with the faulting type that has the lowest apparent stress an energy magnitude me can complement moment magnitude mw in describing the size of an earthquake me being derived from velocity power spectra is a measure of seismic potential for damage mw being derived from the low frequency asymptote of displacement spectra is more physically related to the final static displacement of an earthquake when earthquake size is ranked by moment a list of the largest events is dominated by earthquakes with thrust mechanisms when earthquake size is ranked by energy the list of the largest events is dominated by strike slip earthquakes

a reassessment of the rupture characteristics of oceanic transform earthquakes 1 we investigate the long period source spectra of oceanic transform earthquakes and find that previously proposed slow rupture components can be explained as artifacts generated by the modeling procedure we use low frequency 20 mhz rayleigh and love waves to calculate the amplitude spectra of five earthquakes on the romanche and chain transform faults in the equatorial mid atlantic ocean we find that errors and approximations in the centroid depth focal mechanism and earth structure at the source have significant effects on the shape of the source spectra if global catalog values and an average crustal model are assumed the spectra exhibit apparent anomalous energy at long periods which has previously been interpreted as a result of slow rupture we recalculate the source spectra using precise independently determined depths and moment tensors and a more realistic oceanic crustal structure in the source region the resulting source spectra are flat at long periods with no indication of anomalous long period energy our results imply that oceanic transform earthquakes do not commonly have detectable slow rupture components

broadband source modeling of the november 8 1997 tibet mw 7 5 earthquake and its tectonic implications we studied the source process of a large ms 7 9 intraplate earthquake that occurred on november 8 1997 at 1002 ut in a remote region of northern tibet we used four distinct methods to investigate the broadband source process and thereby better understand the tectonic implications of this event we relocated aftershocks using a master event technique and found that the distribution of aftershocks covers a region of 200 km in lateral extent we also employed a surface wave spectral inversion technique to estimate the mainshock moment depth centroid location and centroid time and utilized an empirical green s function technique to extract rupture directivity information and a detailed source time function from observed seismograms we also inverted body waves to estimate the moment release along the fault and the source time function the 1997 earthquake ruptured a strike slip fault that appears to be an extension or splay of the kun lun fault system this fault is one of the most seismically active strike slip faults within the tibetan plateau and has had events with surface wave magnitudes of 6 1 7 4 and 7 9 in this region since 1973 the rupture released most of the energy within the first 20 s and propagated bilaterally initially with the later rupture propagating westward for 20 30 s the absence of large aftershocks suggests that the earthquake efficiently released the stored strain comparing mainshock to the largest aftershock energy ratios for this event and other large strike slip events shows that faulting within the plateau has the characteristics of weak faults e g fracture zone faulting

earthquake scaling relations for mid ocean ridge transform faults 1 a mid ocean ridge transform fault rtf of length l slip rate v and moment release rate can be characterized by a seismic coupling coefficient ae at where ae v is an effective seismic area and at l3 2v 1 2 is the area above an isotherm tref a global set of 65 rtfs with a combined length of 16 410 km is well described by a linear scaling relation 1 ae at which yields 0 15 0 05 for tref 600 c therefore about 85 of the slip above the 600 c isotherm must be accommodated by subseismic mechanisms and this slip partitioning does not depend systematically on either v or l rtf seismicity can be fit by a truncated gutenberg richter distribution with a slope 2 3 in which the cumulative number of events n0 and the upper cutoff moment mc dcac depend on at data for the largest events are consistent with a self similar slip scaling dc ac1 2 and a square root areal scaling 2 ac at1 2 if relations 1 and 2 apply then moment balance requires that the dimensionless seismic productivity 0 0 atv should scale as 0 at 1 4 which we confirm using small events hence the frequencies of both small and large earthquakes adjust with at to maintain constant coupling rtf scaling relations appear to violate the single mode hypothesis which states that a fault patch is either fully seismic or fully aseismic and thus implies ac ae the heterogeneities in the stress distribution and fault structure responsible for relation 2 may arise from a thermally regulated dynamic balance between the growth and coalescence of fault segments within a rapidly evolving fault zone

locations of mid oceanic earthquakes constrained by seafloor bathymetry 1 earthquakes associated with the creation of new oceanic crust are difficult to locate precisely because they normally occur far away from seismic stations we assume that epicenters of these events can be constrained by seafloor topography and use the harvard centroid moment tensor cmt focal mechanism of an interplate earthquake to relate the event to either a transform fault a parallel in a coordinate system defined by the pole of rotation between two plates or a mid oceanic ridge a meridian using arrival times from the international seismological center isc bulletin we have relocated about 1500 globally distributed events for the time period 1976 1998 the isc locations can be as much as 70 km away from appropriate topographic features our new locations support that large interplate earthquakes occur on or very close to the primary bathymetric features for earthquakes with unknown mechanism or magnitude below the cmt threshold or predate the cmt catalog we use a simultaneous joint hypocenter determination procedure with respect to the already relocated master events jhdme we invert for earthquakes first for the romanche fracture zone rfz and then for a region extending from 30 n to 30 s seismicity agrees well with the main active ridge or transform however a small number of events might be related to the secondary bathymetry features the improved locations for mid oceanic earthquakes based on bathymetry could help improve our understanding of the oceanic crustal and deep earth structure seismic slip and budget constraint along plate boundaries and dynamics of plate tectonics

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

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

vertical connection from the tropospheric activities to the ionospheric longitudinal structure simulated by a new earth s whole atmosphere ionosphere coupled model 1 this paper introduces a new earth s atmosphere ionosphere coupled model that treats seamlessly the neutral atmospheric region from the troposphere to the thermosphere as well as the thermosphere ionosphere interaction including the electrodynamics self consistently the model is especially useful for the study of vertical connection between the meteorological phenomena and the upper atmospheric behaviors as an initial simulation using the coupled model we have carried out a 30 day consecutive run in september the result reveals that the longitudinal structure of the f region ionosphere varies on a day to day basis in a highly complex way and that a four peak structure of the daytime equatorial ionization anomaly eia similar to the recent observations appears as an averaged feature the simulation reproduces and thus confirms the vertical coupling processes proposed so far with respect to the formation of the averaged eia longitudinal structure the excitation of solar nonmigrating tides in the troposphere their propagation through the middle atmosphere and the modulation of ionospheric dynamo which in turn affects eia generation the simulation result indicates that not only the ionospheric averaged longitudinal structure but also the day to day variation can be modulated significantly by the lower atmospheric effect

sulfide and oxide inclusions in xenoliths and host rocks of tongling area anhui province this paper presents new petrographic observations and electron microprobe analyses of sulfide and oxide melt inclusions trapped within amphibole and clinopyroxene in xenoliths and host rocks hrs from the late jurassic early cretaceous laomiaojishan xiaotongguanshan and xiaotaojia intrusions in tongling area anhui province the plutons vary in composition from quartz monzonitic diorite to granodiorite and contain mafic clots mfcs hornblende cumulates hcs and microgranular mafic enclaves mmes with gabbroic to dioritic compositions compositions of sulfide inclusions correspond to pyrrhotite chalcopyrite single sulfide solution and pentlandite in mfcs and pyrrhotite and chalcopyrite in mmes and hrs ni and cu content of the sulfide phases except for chalcopyrite in single blebs is averagely 6 91 and 0 44 0 44 and 0 07 and 0 09 and 0 42 in mfcs mmes and hrs respectively compositions of oxide blebs correspond to cr magnetite averagely 4 44 cr2o3 in mfcs and magnetite with an average cr2o3 content of 0 44 in mmes and 0 07 in hrs while compositions of oxide grains are cr magnetite averagely 6 58 cr2o3 in mfcs magnetite and cr magnetite averagely 0 86 cr2o3 in mmes and magnetite averagely 0 34 cr2o3 in hrs paragenetic associations of 1 mono sulfide solution pyrrhotite 2 mono sulfide solution chalcopyrite and 3 pyrrhotite and pentlandite chalcopyrite exist within single blebs in mfcs while paragenetic associations of pyrrhotite chalcopyrite and pyrrhotite magnetite occur within single blebs in mmes and hrs respectively crystallization temperatures of hornblendes in hcs and hornblendes and plagioclases in mmes and hrs are 860 865 714 811 and 614 733 respectively based on al and ti in calcic amphibole and amphibole plagioclase geothermometers the pressures recorded by these phases indicate that they were formed at a depth of 26 27 km 7 16 km and 3 6 km respectively based on al and ti in calcic amphibole and al in hornblende geobarometers the present petrographic observations and microprobe analyses combined with the published geochemical and mineralogical data of the pyroxene cumulates hcs mmes and hrs support an origin of sulfide and oxide melt inclusions in mfcs and hcs mmes and hrs from crystallization products of sulfide and oxide melts immiscibly separated from alkaline basaltic and somewhat evolved underplated alkaline basaltic magmas from the upper mantle to the lower crust the gabbroic to dioritic magmas in the middle to upper crust and the pyroxene or quartz monzodioritic to granodioritic magmas in the upper crust respectively the variations in the oxide and sulfide assemblage and the sulfide and oxide paragenetic association within single blebs presented above correspond to the increase in the amount of the hybridized lower and middle to upper crustal material in the magmas and the decrease in crystallization temperature and depth of the magmas in the formation process of mfcs and hcs mmes and hrs

impacts of vertically propagating tides on the mean state of the ionosphere thermosphere system the national center for atmospheric research thermosphere ionosphere electrodynamics general circulation model tie gcm is utilized to understand the role that upward propagating tides play in determining the zonal mean state of the ionosphere thermosphere system a sensitivity assessment of the tie gcm shows that tie gcm solutions greatly depend on the lower boundary conditions we also establish the veracity of our tie gcm solutions within and above the dynamo region to isolate the mean effects of tidal dissipation differences between tie gcm simulations with and without lower boundary tidal forcing as specified by the climatological tidal model of the thermosphere are investigated dissipation of the dw1 diurnal westward propagating tide with zonal wave number 1 diurnal eastward propagating tide with zonal wave number 3 and sw2 semidiurnal tide with zonal wave number 2 explains most of 10 30 m s 1 seasonal and latitudinal variability in zonal winds within the dynamo region with sw2 playing a greater role than ascribed in previous studies tidal dissipation at low latitudes causes a 9 decrease 30 increase in o o2 number densities near the f2 layer peak leading to at least a 9 decrease in peak electron density nmf2 throughout the year f2 layer peak height hmf2 differences of 4 to 2 km at low latitudes are explained by variations in the field aligned plasma motion driven by meridional wind differences induced by tidal dissipation compositional effects are mainly driven by dw1 and sw2 which differs from previous interpretations of tidal driven composition changes by dw1 tidal mixing exclusively we suggest that tides may produce a net transport of constituents in the thermosphere similar to the way that e g gravity waves can drive net transport of sodium in the mesosphere

an iterative algorithm for separation of s and scs waves of great earthquakes teleseismic sh waves are essential for imaging the rupture processes of large earthquakes however for great earthquakes m8 such as the 2004 sumatra earthquake the 2008 wenchuan earthquake and the recent tohoku oki earthquake the source duration is very long 100 s thus the direct sh waves are overlapped with scs waves for epicentral distances larger than 60 leaving contaminated s waves for source processes modelling therefore artefacts in finite fault models of large earthquake could be produced with such contaminated body waves we propose an iterative algorithm based on the slowness information of s and scs waves and stacking technique to separate s and scs waves with records from a regional seismic network tests on various synthetic data sets show that the algorithm is effective in retrieving teleseismic sh waveforms from complicated wave trains containing both s and scs separation of waveforms for the 2008 wenchuan earthquake with our algorithm clearly demonstrates the influence of scs energy suggesting necessity of recovering s waves

the motion and boundary between the capricorn and australian plates the motions between the somalian antarctic and australian plates the three plates believed to meet at the rodrigues triple junction in the indian ocean are inconsistent with the assumption that all three plates are rigid the discrepancy is best explained if the australian plate contains two component plates thus the traditionally defined indo australian plate consists of three component plates and multiple diffuse plate boundaries the pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction

space and time evolution of rupture and faulting during the 1999 izmit turkey earthquake we use the records of the ground motion obtained at near fault accelerometers to study the space and time evolution of rupture and faulting during the izmit earthquake we find that the rupture propagated at the sub rayleigh speed of about 3 km sec on the western and eastern segments of the fault but that the central segment izmit sapanca lake sakarya nearly 50 km long broke at the supershear speed of about 4 8 km sec this value within the range of uncertainties is the one theoretically predicted sqrt 2 v mathrm s in fracture dynamics for stable shear crack growth at intersonic speed we infer an average fault slip of about 2 9 m over a total rupture length of about 150 km with the largest values of up to 6 m occurring in the golcuk area to the west and in the sakarya region to the east the strong motion data also indicate that the slip diminished gradually to the west beyond the hersek peninsula over about 30 km whereas it stopped abruptly at depth at the termination of the eastern karadere segment the slip duration is between 2 and 4 sec except in the hypocentral area which slipped in about 1 sec the seismic moment inferred is about 2 5 10 20 n m

longitudinal and interhemispheric ionospheric response to 2009 and 2013 ssw events in the african european and indian east asian sectors

further evidence for the compound nature of slow earthquakes the prince edward island earthquake of april 28 1997 seismograms of the april 28 1997 prince edward island transform fault earthquake mw 6 8 show clear evidence for the superposition of two types of rupture a normal earthquake and a slow component which primarily radiated energy at low frequencies we combined low frequency spectral data with p waveform data to invert for a source time function that satisfied data from 0 001 to 2 5 hz the results show that the earthquake started with a slow event which began 15 s before the fast mainshock and was part of a slow earthquake which lasted over 30 s the smoothness of the initial event is inferred from the low amplitude of high frequency energy at regional stations during the initial portion of the p wave arrival directivity analysis shows that the two components of the rupture occurred on different faults the slow event occurred on the main transform and the fast event occurred on a parallel fault 40 km to the east a similar compound sequence involving both slow and fast components and rupture on multiple faults occurred on the romanche transform in 1994 these and other results for slow earthquakes suggest that many large events on oceanic transform faults are compound events

seismic crustal structure and morphotectonic features associated with the chain fracture zone and their role in the evolution of the equatorial atlantic region oceanic transform faults and fracture zones fzs represent major bathymetric features that keep the records of past and present strike slip motion along conservative plate boundaries although they play an important role in ridge segmentation and evolution of the lithosphere their structural characteristics and their variation in space and time are poorly understood to address some of the unknowns we conducted interdisciplinary geophysical studies in the equatorial atlantic ocean the region where some of the most prominent transform discontinuities have been developing here we present the results of the data analysis in the vicinity of the chain fz on the south american plate the crustal structure across the chain fz at the contact between 10 and 24 ma oceanic lithosphere is sampled along seismic reflection and refraction profiles we observe that the crustal thickness within and across the chain fz ranges from 4 6 5 9 km which compares with the observations reported for slow slipping transform discontinuities globally we attribute this presence of close to normal oceanic crustal thickness within fzs to the mechanism of lateral dike propagation previously considered to be valid only in fast slipping environments furthermore the combination of our results with other data sets enabled us to extend the observations to morphotectonic characteristics on a regional scale our broader view suggests that the formation of the transverse ridge is closely associated with a global plate reorientation that was also responsible for the propagation and for shaping lower order mid atlantic ridge segmentation around the equator

on the depth of oceanic earthquakes brief comments on the thermal structure of oceanic and continental lithosphere by mckenzie d jackson j and priestley k earth plan sci let 233 2005 337 349

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

breaking into the plate a 7 6 mw fracture zone earthquake adjacent to the central indian ridge 1 on 15 july 2003 an extremely large 7 6 mw strike slip earthquake initiated on or near the end of an active transform along the northern central indian ridge the event propagated away from the plate boundary along the typically inactive fracture zone with a sense of slip that opposes the active transform slip direction seismically and hydroacoustically determined aftershock locations delineate a 210 25 km long mainshock rupture the seismic moment and rupture dimensions imply a stress drop of 4 5 6 5 mpa and a mean slip of 3 0 0 5 m the largest aftershock 5 6 nw occurred on the active portion of a neighboring transform at a distance of 160 km where mainshock induced static stress changes are predicted to promote failure near axis fracture zone earthquakes may promote and inhibit ridge parallel diking along different spreading segments perhaps contributing to inter segment variability in the rate and asymmetry of spreading

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

rupture process of the 1999 kocaeli turkey earthquake estimated from strong motion waveforms the multiple time window linear waveform inversion is applied to study the source process of the 1999 kocaeli turkey earthquake using strong motion data two peculiar observations characterize this event the first one is a conflicting observation of the long surface ruptures and short source duration resulting from the observed strong motion waveforms the second is an anomalously short s p time observed at a station skr considering its hypocentral distance a supershear rupture propagation ellsworth and celebi 1999 and the p wave triggering of an asperity anderson et al 2000 were both proposed to explain the record at skr our waveform inversion study is aimed to examine these possibilities in order to clarify the relation between the spatial distribution of the surface ruptures and coseismic slips we divide the assumed fault plane into three parts and look for the first time window front propagation velocity propagation velocity of triggering front of the first time window at each subfault in each part by performing numerous inversions changing the first time window front propagation velocity separately in each part and selecting the best first time window propagation velocities that give largest variance reduction at the same time appropriate smoothness of spatiotemporal slip distribution is searched for by performing inversions with different strength of smoothing constraints against the observational equations and judging the relative appropriateness of inversion results in terms of the akaike s bayesian information criterion the best source model is characterized by an asperity that is about 35 km east of the epicenter and near a segment boundary at sapanca lake triggered by the first time window front with 5 8 km sec close to p wave velocity the time progression of the rupture suggests a scenario where a p wave arriving from the hypocenter or somewhere around the hypocenter triggered the second largest asperity near the junction of the segments at sapanca lake which is a preferable interpretation the first time window propagation velocities west of the hypocenter and east of skr are expected to be 3 0 km sec manuscript received 20 august 2000

the april 2012 indian ocean earthquakes seismotectonic context and implications for their mechanisms the 11 april 2012 earthquakes m w 8 6 and m w 8 2 were sourced within the northern wharton basin in the northeastern part of the indo australian diffuse plate boundary this unusually active oceanic intraplate region has generated many large earthquakes in the past most of which are believed to have occurred by strike slip motion triggered by the nw se oriented compressional stresses acting across the indian and australian plates in the aftermath of the 2004 megathrust earthquake along the nearby sunda trench increased seismicity in the northern wharton basin is attributed to the stress transfer from the sumatra andaman plate boundary models proposed for the april 2012 earthquakes differ somewhat in details but partly attribute their complex rupture to the reactivation of pre existing structures these structures include previously mapped n s trending fracture zones within the northern wharton basin and e w lineations across the ninetyeast ridge in this paper we review the regional tectonics and past seismicity on the indo australian plate in order to understand the seismotectonic setting of the april 2012 indian ocean earthquakes c 2014 elsevier b v all rights reserved

crustal structure of north atlantic fracture zones seismic studies have established that large offset transforms along the slow spreading mid atlantic ridge exhibit anomalous crustal structures that fall well outside the range typically associated with oceanic crust seismically fracture zone crust in the north atlantic is extremely heterogeneous in both thickness and internal structure it is frequently quite thin 1 2 km thick and is characterized by low compressional wave velocities and the absence of a normal seismic layer 3 a more gradual crustal thinning can extend up to several tens of kilometers from these fracture zones anomalously thin crust has also been inferred from both seismic and gravity studies at smaller ridge axis discontinuities along the mid atlantic ridge the geological nature of the seismically anomalous crust found within atlantic fracture zones and how this crust forms are still controversial one interpretation consistent with available seismic observations is that the crust within north atlantic fracture zones consists of a thin intensely fractured and hydrothermally altered basaltic section overlying ultramafics that are extensively serpentinized in places variations in apparent seismic crustal thickness along fracture zones may reflect different degrees of serpentinization of the upper mantle section or changes in the thickness of the igneous crust the existence of a thinner crustal section in fracture zones can be explained by a reduced magma supply within a broad region near ridge offsets due to the three dimensional nature of upwelling beneath a segmented spreading center and by tectonic dismemberment of the crust by large scale detachment faults that form preferentially in the cold brittle lithosphere near the ends of segments