testing probabilistic seismic hazard estimates by comparison with observations an example in italy summary an evaluation of the actual reliability of probabilistic seismic hazard psh assessments provided by existing numerical techniques is mandatory to orientate new researches and improvements two procedures devoted to this task are proposed which are based on the comparison of the hazard estimates with empirical observations e g strong motion data these procedures have been applied to the estimates provided by the methodology adopted for most recent seismic hazard evaluations in italy the analysis shows that a significant mismatch exists between peak ground acceleration values characterized by an exceedence probability of 10 per cent in 30 yr and what has actually been observed at 68 accelerometric stations located on stiff soil where continuous seismicity monitoring has been performed in the last 30 yr although this finding should be considered with caution it suggests that a future re examination of the adopted psh computational model could be useful to avoid possible underestimates of seismic hazard in italy

mantle phase changes and deep earthquake faulting in subducting lithosphere inclined zones of earthquakes are the primary expression of lithosphere subduction a distinct deep population of subduction zone earthquakes occurs at depths of 350 to 690 kilometers at those depths ordinary brittle fracture and frictional sliding the faulting processes of shallow earthquakes are not expected a fresh understanding of these deep earthquakes comes from developments in several areas of experimental and theoretical geophysics including the discovery and characterization of transformational faulting a shear instability connected with localized phase transformations under nonhydrostatic stress these developments support the hypothesis that deep earthquakes represent transformational faulting in a wedge of olivine rich peridotite that is likely to persist metastably in coldest plate interiors to depths as great as 690 km predictions based on this deep structure of mantle phase changes are consistent with the global depth distribution of deep earthquakes the maximum depths of earthquakes in individual subductions zones and key source characteristics of deep events

seismicity of the aegean and surrounding area abstract seismicity parameters based on instrumental and historical data are given for 36 seismic sources of shallow earthquakes and for 6 seismic sources of intermediate depth earthquakes in the aegean and surrounding area 34 n 43 n 18 e 30 e these parameters are of two categories parameters of the first category are useful for seismic hazard evaluation a and b values of the frequency magnitude relation maximum earthquake magnitude number of shocks larger than certain magnitude per year while parameters of the second category are proper for describing the spatial distribution of seismicity mean return period most probable magnitude in a certain time period moment rate shallow seismicity is highest along the convex side of the hellenic arc but close to the coast ionian islands south peloponnesus south of crete south of karpathos and rhodos in central greece patraikos corinthiakos evoikos gulfs thessalia and along a seismic belt which includes the northwestern anatolia fault zone the northernmost part of the aegean sea and the serbomacedonia zone the intermediate depth seismic activity is distributed in two parts of the benioff zone which dips from the convex side eastern mediterranean to the concave side aegean sea of the hellenic arc the one part shows a low dip angle and includes earthquakes with focal depths between 70 km and 100 km this part has a high seismicity earthquake magnitudes up to 8 0 and is situated below the inner slope of the sedimentary part of the hellenic arc eastern peloponnesus north of crete rhodos based on the fact that this part of the benioff zone is a continuation of the seismic zone of shallow earthquakes along the hellenic arc and that both zones have the same seismicity it is concluded that they constitute a continuous seismic belt on which coupling occurs between the subducted eastern mediterranean lithosphere and the overthrusted aegean lithosphere the other inner part of the benioff zone shows low seismicity maximum earthquake magnitude up to 7 1 with earthquakes of focal depths between 100 km and 180 km it dips at a mean angle of 38 below the volcanic arc of the southern aegean sea and is the result of the subduction of the front part of the eastern mediterranean lithosphere without coupling with the aegean lithosphere

a new self organizing mechanism for deep focus earthquakes the mechanism of deep focus earthquakes has been a puzzle since their discovery almost 70 years ago1 2 because brittle fracture and frictional sliding at depths in excess of 100 200 km would require unrealistic rock strengths3 4 rock strength does increase with pressure but a few hundred mpa equivalent to 10 20 km depth suffices to inhibit most fracture and elevated temperature activates ductile mechanisms that operate at stresses less than the fracture stength a range of mechanisms has been proposed for deep earthquakes including plastic instabilities5 7 shear induced melting8 11 and instabilities accompanying recrystallization12 13 or polymorphic phase transformation14 23 each of these proposed mechanisms has exhibited certain inherent weaknesses see kirby22 for review and discussion here we report experimental observations of high pressure faulting of metastable mg2geo4 olivine as it undergoes incipient transformation to a spinel 24 25 structure we present a model in which this faulting arises from the generation propagation and linking up of spinel filled anticracks26 when applied to the olivine spinel transformation in the earth s mantle the anticrack model27 satisfactorily accounts for the similarities and differences between shallow and deep earthquakes and removes the problems associated with frictional sliding

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

tectonic implications of serpentinite weakening summary the observation that serpentinite becomes weak and brittle at its dehydration temperature provides an experimental basis for the hypothesis that mantle earthquakes are caused by shear fracturing where interstitial fluid pressure effectively reduces the frictional resistance to a low or negligible value if convection currents in the mantle turn down at the foredeeps of the pacific island arcs dehydration of an oceanic crust of serpentinite and downward convection of the dehydration products beneath the island arc would give rise to the anomalously low shallow mantle velocities and heat flows in the region between the trenches and island arcs seismic activity would be confined to the zone along which the weak and brittle dehydration products move downward against the immobile continental mantle and would be concentrated at the leading edge of the focal zone due to release of stored elastic strain upon the initiation of weakening pore fluid pressures giving rise to faulting in the deepest earthquakes are considered to be due to interstitial magma

an investigation of motions of the equatorial anomaly crest using more than 350 ionospheric images reconstructed tomographically studies on the motion of the anomaly crest and its geophysical implications are carried out on an average day the crest forms at 09 00 lt and in the next two hours moves poleward with a speed of about 1 per hour as it intensifies this poleward motion is slowed as the crest reaches its highest latitude where it stays for several hours until early afternoon thereafter the crest starts to weaken as it recedes with a speed of about 0 5 per hour equatorward during 12 00 14 00 lt the crest latitude is found to correlate with the fountain strength and the total number of electrons in a cross sectional plane at the observational longitude of the whole equatorial ionosphere

electrodynamics of the equatorial evening ionosphere 1 importance of winds in different regions the importance of winds at different altitudes and latitudes for the electrodynamics of the low latitude evening ionosphere is examined with a model of the global coupled ionosphere thermosphere system the model reproduces the main observed features of the evening equatorial plasma vortex and the prereversal enhancement pre of the vertical drift the electrodynamics is driven primarily by the zonal wind forced by the diurnally varying zonal pressure gradient force the zonal wind lags the zonal pressure gradient force owing to inertia when ion drag is important the time lag of the wind behind the pressure gradient force is shortened and the high altitude evening wind turns eastward earlier than the wind at lower altitudes where ion drag is less important therefore a vertical shear of the zonal wind tends to develop at altitudes around the transition between small and large ion drag at the bottom of the f region this wind shear is closely associated with the vertical shear in the zonal convection velocity that is part of the evening plasma vortex unlike previous studies we find that the winds driving the pre lie mainly on field lines with apexes above the peak of the equatorial f layer field lines that extend in magnetic latitude out to nearly 30 and encompass the entire evening equatorial ionization anomaly region contrary to previous suggestions the westward convection in the bottomside of the evening plasma vortex is found to weaken rather than strengthen the pre daytime winds have relatively little influence on the low latitude evening electrodynamics

medium scale traveling ionospheric disturbances observed with the superdarn hokkaido radar all sky imager and gps network and their relation to concurrent sporadic e irregularities 1 we present midlatitude medium scale traveling ionospheric disturbances mstids observed with a super dual auroral radar network superdarn hf radar at around 10 mhz in hokkaido japan in combination with a 630 nm all sky imager and a gps network geonet that provides total electron content tec data mstids propagating southward from high latitudes are detected at first with the hf radar and then with the imager and geonet we analyze two mstid events one in winter event 1 and the other in summer event 2 to find that mstids appear simultaneously at least at 55 25 n it is shown that nighttime mstids propagate toward the southwest over a horizontal distance of about 4000 km and daytime mstids do so toward the southeast daytime radar echoes are due to ground sea surface gs scatter while nighttime echoes in event 1 return from 15 m scale f region field aligned irregularities fais and those in event 2 are due to gs scatter doppler velocities of the nighttime f region fai echoes in event 1 are negative motion away from the radar within strong echo regions and are positive motion toward the radar within weak echo regions this fact suggests that the strong weak echoes return from suppressed enhanced airglow tec areas in line with previous observations over central japan the nighttime mstids in events 1 and 2 are often accompanied by concurrent coherent echoes from fais in sporadic e es layers the es echo areas in event 2 rather coincide with suppressed airglow tec areas in the f region that are connected with the echo areas along the geomagnetic field indicating the existence of e and f region coupling at night

evidence for a metastable olivine wedge inside the subducted mariana slab abstract an anomalous seismic velocity structure is revealed inside the subducted pacific plate at northern mariana near the deepest earthquake foci we observe anomalous later phases in the p wave coda for a small cluster of deep earthquakes and an anomalous differential p wave slowness between a few pairs of the earthquakes belonging to the cluster we interpret these observations with a 5 low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km the wedge is bounded by two steeply dipping 60 70 transition layers with the thickness of about 4 km the highly localized seismic anomaly inside the slab represents a wedge of metastable olivine embedded in dry ringwoodite deep earthquakes occur across only one of the boundaries of the metastable wedge with some of them outside the wedge the mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

interaction between a southwestward propagating mstid and a poleward moving wsa like plasma patch on a magnetically quiet night at midlatitude china region

implications of oceanic intraplate seismicity for plate stresses driving forces and rheology abstract recent studies of earthquakes occurring within the oceanic lithosphere provide valuable information about stresses in the lithosphere plate tectonic driving forces and the rheology of the lithosphere asthenosphere and mantle focal mechanisms indicate that oceanic lithosphere older than 35 million years is almost entirely in deviatoric compression both compressional and extensional events occur in younger lithosphere in young lithosphere mechanisms generally indicate compressive stress in the spreading direction or extension oblique to the spreading direction extension in the spreading direction is not observed using the constraint of compression in the spreading direction in old lithosphere models of the stresses produced by a combination of ridge push and basal drag forces require the magnitude of the drag be less than a few bars for rapidly moving plates and a few tens of bars for slow moving plates assuming that basal drag results from mantle return flow the upper limits on drag can be converted to constraints on the viscosity structure of the asthenosphere and mantle using simple two dimensional models if return flow occurs in a mantle of viscosity 10 22 poise comparable to the results from glacial rebound studies the predicted basal drag is too high unless a thin asthenosphere with viscosity less than 10 19 to 10 20 poise depending on flow depth is present the intraplate stress data thus are consistent with the idea of oceanic plates largely decoupled from the underlying mantle the strength of the lithosphere is constrained by the maximum depth of oceanic intraplate seismicity which increases with lithospheric age and appears to be bounded by a 700 800 c isotherm this limiting depth is approximately equal to the flexural elastic thickness of the lithosphere and is consistent with experimental olivine rheologies which predict rapid weakening at high temperatures similar phenomena are important for estimating the fraction of seismic and aseismic slip on transform faults and in determining the extent of rupture for large trench normal faulting events

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

transformation shear instability and the seismogenic zone for deep earthquakes we use a numerical model for olivine spinel transformation to study deep earthquake nucleation and to delineate the seismogenic region within a subducting slab the model includes laboratory derived flow laws latent heat release and phase transformation kinetics we calculate deformation transformation state grain growth and rheology for several paths within a subducting slab strain rate perturbations are imposed to define the necessary conditions for instability strain rate perturbations decay for a critical value c and thus the coldest interior portion of the metastable wedge deforms stably for c strain rate perturbations grow shear strength decreases with strain and the system is potentially unstable the instability condition is mapped to delineate the seismogenic zone within a subducting slab the model seismogenic zone is bounded by c and at larger percent transformations by coarsening of spinel grains and saturation of the transformation weakening effect the model predicts a narrow seismogenic region along the outer edges of the metastable wedge and thus a double seismic zone consistent with some seismic observations several simplifying assumptions are required due to lack of thermo kinetic data and incomplete knowledge of constituent mineralogy and rheology however the model provides a quantitative definition of the instability condition and a framework for testing the hypothesis of transformation induced instability

case studies of coupling between the e and f regions during unstable sporadic e conditions 1 simultaneous f region airglow e region coherent scatter radar and ionosonde observations were made in greece during the summer sporadic e season in 2002 in this paper we report on two case studies during which patchy sporadic e layers were accompanied by midlatitude spread f coherent vhf radar echoes including two stream echoes and traveling ionospheric disturbances registered by the airglow instrument we argue that these events give strong evidence that polarization electric fields are built up in the e region and are mapped upward to the f region creating rising and falling regions in the bottomside plasma the resulting structure creates conditions for midlatitude spread f as detected by the ionosonde this correlation between patchy sporadic e and midlatitude spread f is further supported in a companion paper upward coupling of this sort is particularly efficient in regions of f region plasma uplift and airglow depletion since the f region pedersen conductivity is low which reduces the electrical load on the e region generator

vs30 κ regional attenuation and mw from accelerograms application to magnitude 3 5 french earthquakes summary we investigate recordings from weak to moderate earthquakes with magnitudes ranging between about 3 and 5 recorded by the french accelerometric network s wave spectra are modelled as a product of source propagation and site terms inverting large data sets of multiple earthquakes recorded at multiple stations allows us to separate the three contributions source parameters such as moment magnitude corner frequency and stress drop are estimated for each earthquake we provide the first complete and homogeneous catalogue of moment magnitudes for france for the events with magnitude greater than 3 that occurred between 1996 and 2006 stress drops are found to be regionally dependent as well as magnitude dependent and range from about 0 1 mpa 1 bar to about 30 mpa 300 bars the attenuation parameters show that in france on a nationwide scale variations of attenuation properties do exist site transfer functions are also computed giving the level of amplification at different frequencies with respect to the response of a generic rock site characterized by an average 30 m s wave velocity vs30 of 2000 m s 1 from these site terms we compute the high frequency fall off parameter modelled as exp f with f the frequency for 76 stations we also determine rock stations vs30 and we show the vs30 relationship for 21 rock stations

the horizontally lying slab an unusual earthquake mb 6 2 occurred in the izu bonin island region in july 1982 the event occurring at a depth of 545 km was clearly separated from the main inclined seismic zone by a distance of about 200 km to diagnose the situation we have considered two possibilities 1 the event might be an unusual event in the sense that its location is unrelated to the position of the subducted slab and that there is probably no slab around it or 2 the slab at this depth might be lying horizontally on top of the 650 km discontinuity and the unusual event occurred in this horizontal part both possibilities have been modeled structurally we have computed the p wave travel times for the present event as well as for two other events located unambiguously in the inclined part of the seismic zone by employing a 3 d ray tracing program the computed travel time residuals have been compared with the observations at stations in western japan the observations are found to be consistent with the model of the horizontally lying slab our result thus suggests that the slab might be horizontal at this depth in this part of the izu bonin islands

comparison of probabilistic seismic hazard estimates in italy abstract macroseismic intensity has recently attracted attention as a tool for validating probabilistic seismic hazard assessment psha studies or as an alternative method for psha in countries where the historical catalog is much longer than the instrumental one in italy the new seismic hazard map was recently produced using the cornell mcguire approach in terms of the peak ground acceleration characterized by a 10 exceedance probability for an exposure time of 50 yr a max we compare this map with an alternative one produced using a different approach based on a nonparametric and zonation free statistical analysis of local seismic histories in this case results are expressed in terms of the maximum intensity corresponding to an exceedance probability of not less than 10 for an exposure time of 50 yr i ref in order to compare the two maps we selected 1401 control sites where local seismic history includes at least 10 intensity values relative to felt effects documented during past earthquakes the values of a max and i ref at these sites have been ranked in the respective domains the spatial distribution of rank differences of a max and i ref values shows a strong correlation with the seismogenic zoning used in the calculation of psha following the cornell mcguire approach this suggests that the adopted zoning could be incomplete some further hidden sources may exist and too rough to capture actual seismogenic sources because more detailed zoning is prevented by the amount of data available the results obtained suggest the preference of zonation free approaches for seismic hazard assessment in italy furthermore among the possible zonation free approaches those that offer better exploitation of local information about the effects of past earthquakes would be preferred

localized polymorphic phase transformations in high pressure faults and applications to the physical mechanism of deep earthquakes earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes such mechanisms in unmodified form are highly unlikely for deep earthquakes because of the expected high frictional shear stresses at depths of 300 700 km several alternative mechanisms have been proposed here i discuss a new type of shear instability observed in experiments on ordinary polycrystalline ice and polycrystalline tremolite by my colleagues and me these shear instabilities lead to rapid stress drops and sound emissions and have the following characteristics 1 a single sharp shear zone forms in the maximum shear stress orientation 2 confining pressure does not suppress the instability and under some conditions raising confining pressure pc lowers the differential stress at which it occurs 3 stress drops can occur repeatedly after reloading at about the same differential stress 4 the mean stress vs temperature conditions at which the instabilities occur in ice and tremolite place them in the fields of thermodynamic stability of ice ii and diopside talc respectively although i have not as yet confirmed the existence of these high pressure phases in the shear zones transformation in the shear zone is implicated because such shear instabilities do not occur in similar materials in which polymorphic phase changes do not occur reconstructive polymorphic phase changes localized along shear zones may be a general phenomenon in crystalline materials stressed non hydrostatically near transition boundaries moreover by analogy the reconstructive phase transformations that are thought to occur in deeply subducted lithosphere may lead to localized shear instabilities manifested by deep earthquakes and produce the observed double couple first motion distribution finally if this is the earthquake source mechanism in deeply subducted lithosphere then earthquakes should shut off when all of the polymorphic phase changes have occurred this may explain the maximum depth of earthquakes at about 680 km

kinetics of the olivine spinel transformation in subducting lithosphere experimental constraints and implications for deep slab processes abstract the persistence of metastable olivine to depths greater than 400 km in subducting slabs has implications for the generation of deep focus earthquakes the magnitude of buoyancy forces driving plate motion and the state of stress in the slab the depth to which metastable olivine can survive in a subduction zone and the depth interval over which transformation to or mg fe 2sio4 occurs have been evaluated from experimental kinetic data for the mg2geo4 and ni2sio4 transformations and the mg2sio4 transformation the data were extrapolated using a kinetic model for grain boundary nucleation and interface controlled growth under non isothermal and non isobaric conditions the results predict that metastable mg1 8fe0 2sio4 olivine survives to depths greater than 500 km in the cold interior of rapidly subducting slabs of old lithosphere the onset of transformation to mg fe 2sio4 spinel depends only on growth kinetics and coincides with the 550 50 c isotherm including the effects of latent heat production causes the transformation to occur by a runaway process over a very narrow depth interval at the onset of transformation high nucleation rates and low growth rates are consistent with the formation of very fine grained reaction products which are required for the transformational faulting mechanism of deep focus earthquakes when olivine crosses the equilibrium boundaries at higher temperatures e g higher than 700 c at 400 km depth transformation to or occurs much closer to equilibrium at a depth controlled by nucleation kinetics in this case the effect of latent heat production on the transformation kinetics is small and microstructural evolution is unlikely to result in transformational faulting below the depth of olivine breakdown cold slabs are likely to have a complex rheological structure owing to temperature dependent microstructural evolution during the phase transformation

statistical study of nighttime medium scale traveling ionospheric disturbances using midlatitude airglow images 1 we have investigated statistical characteristics of the nighttime medium scale traveling ionospheric disturbances mstids observed in 630 nm airglow images at two stations rikubetsu 43 5 n 34 8 mlat and shigaraki 34 9 n 25 4 mlat in japan for 1998 2000 near the solar maximum period most of the observed mstids propagate southwestward in the images the typical wavelength velocity period and amplitude are 100 300 km 50 100 m s 0 5 1 5 h and 5 15 respectively seasonal variations in these parameters are not clear the occurrence rate has a major peak 50 60 in summer that appears 2 months earlier at lower latitudes and a minor peak in winter similar occurrence characteristics are obtained from midlatitude spread f signatures using multipoint ionosonde data in japan though the coincidence of the spread f and the mstids in airglow images is only 10 15

time functions of deep earthquakes from broadband and short period stacks to constrain dynamic source properties of deep earthquakes we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic p waves from u s national seismic network terrascope and berkeley digital seismic network broadband stations we examined 42 earthquakes with depths from 100 to 660 km that occurred between july 1 1992 and july 31 1995 to directly compare time functions or to group them by size depth or region it is essential to scale them to remove the effect of moment which varies by more than 3 orders of magnitude for these events for each event we also computed short period stacks of p waves recorded by west coast regional arrays the comparison of broadband with short period stacks yields a considerable advantage enabling more reliable measurement of event duration a more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment producing scaled time functions with both correct timing and amplitude we find only subtle differences in the broadband time function shape with moment indicating successful scaling and minimal effects of attenuation at the periods considered here the average shape of the envelopes of the short period stacks is very similar to the average broadband time function the main variations seen with depth are 1 a mild decrease in duration with increasing depth 2 greater asymmetry in the time functions of intermediate events compared to deep ones and 3 unexpected complexity and late moment release for events between 350 and 550 km with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below the first two results are broadly consistent with our previous studies while the third is reported here for the first time the greater complexity between 350 and 550 km suggests greater heterogeneity in the failure process in that depth range

subduction zone seismicity and the thermo mechanical evolution of downgoing lithosphere in this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km with emphasis on the role of temperature and rheology in controlling the deformation of and the seismic energy release in downgoing lithosphere this is done in two steps after a brief review of earlier developments we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth dependent critical valuetcr

mantle transition zone structure beneath southeastern china and its implications for stagnant slab and water transportation in the mantle we determined depth variation of the 410 and 660 km discontinuities beneath southeastern china by common converted point stacking of rm p wave receiver functions of 121 permanent chinese seismic stations we then combined the results with seismic velocity variation to estimate temperature and water content variations in the mantle transition zone of the region previous tomographic studies have shown a stagnant slab in the mantle transition zone in eastern asia that is connected to subduction of the western pacific temperature variations obtained clearly outline the shape of the stagnant slab with its western edge at 113 5 circ e and the southern edge at 28 5 circ n the correlation between the location of the stagnant slab and surface tectonics suggests that the cenozoic extension in eastern china is closely associated with the subduction of the western pacific and its eastward migration the water content of the stagnant slab is lower than in surrounding slabs suggesting that the water has already been released from the subducting slab into the upper mantle

the o i 135 6 nm airglow observations of the midlatitude summer nighttime anomaly by timed guvi 1 this study presents the o i 135 6 nm airglow observation of the middle latitude electron density enhancement during local summer nighttime by global ultraviolet imager guvi on board the thermosphere ionosphere mesosphere energetics and dynamics timed spacecraft the nighttime density enhancement at magnetic middle latitudes in the southern hemisphere known as the weddell sea anomaly wsa had been studied by using multipoint observations and a similar anomalous nighttime enhancement was also found in the northern hemisphere recently the resemblance of both anomalies at magnetic middle latitudes in the northern and southern hemispheres suggests that they should be categorized as the midlatitude summer nighttime anomaly msna to further explore the three dimensional structure of the msna and its day to day variation the two dimensional global radiance maps and the vertical electron density profiles derived from disk and limb scans of the timed guvi 135 6 nm airglow observations are utilized in this study these global observations show that the northern msna mainly occurs in asia europe and the north atlantic ocean regions while the southern msna occurs in the south america antarctica region near the wsa region the guvi day to day observations in 2006 further illustrate that the southern msna appears nightly in january february and november december while the northern msna appears in 36 out of 41 total observation nights in may june

ground motion based testing of seismic hazard models in new zealand abstract we develop a testing methodology for the new zealand national probabilistic seismic hazard psh model that builds on the groundwork of previous studies our fundamental approach is to test the full model or in other words the final output of the model ground motion exceedance for a given return period our results show that the psh model is rejected as underpredicting the historical number of exceedances for specific peak ground acceleration pga levels obtained directly from instrumental strong motion data over the last 1 4 decades however when aftershock ground motions are removed from the strong motion data the model is not inconsistent with the observations the implications for the psh model are that the lack of aftershocks in the model led to initial model rejection and that the model may perform better for short decadal time periods if aftershocks are included in the psh model the results are different from those of earlier modified mercalli intensity mmi based studies that suggested the psh model was predicting hazard slightly higher than that of the historical record our new test dataset has the advantage of using observed pga rather than pga inferred from mmi establishment of a protocol for formally testing future versions of the new zealand psh model within a testing center such as those using the collaboratory for the study of earthquake predictability protocol will require consideration of the fact that the tests are limited by the available datasets of strong earthquake shaking

resolution experiments for nw pacific subduction zone tomography we investigate the resolving power of isc neic p travel time data in tomographic inversions for the geometry of the subduction zones in the nw pacific from thermal models for the kurile japan izu bonin mariana and ryukyu slabs we generate three dimensional synthetic velocity anomalies for subducting slabs which are then projected onto a cell model for the uppermost 1400 km of the mantle using these synthetic models we compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data add gaussian noise invert the synthetic data and compare the resulting velocity structure to the initial synthetic models this comparison is illustrated for sections through the kuriles and the mariana arcs a variety of resolution artifacts are observed which in many cases resemble features visible in the tomographic results obtained from inverting the actual isc neic data

behavior of the f2 peak ionosphere over the south pacific at dusk during quiet summer conditions from cosmic data 1 the six satellite constellation observing system for meteorology ionosphere and climate cosmic mission makes routine ionospheric measurements over the entire globe using occultation techniques these observations have been used in this study to develop global scale climate maps of nmf2 and hmf2 during the southern northern summer winter enhanced electron densities that appear to be associated with the southern equatorial appleton anomaly are displaced far southward at dusk and within about an hour form the weddell sea anomaly coincidentally the height of the f2 peak increases on the northern boundary of this anomaly this height increase is also displaced southward as the enhanced electron densities are displaced southward suggesting that the electron density increases are associated with the f2 peak rising as well as being an interesting phenomenon in its own right this behavior may shed new light on the formation of the weddell sea anomaly no unambiguous explanation for this behavior can be determined from the data presently available but an examination of some possibilities suggests that an evening downward flux of plasma from the plasmasphere may be at least partly responsible for the phenomenon

isolated deep earthquakes and the fate of subduction in the mantle the locations of earthquakes with depth in the mantle provide direct evidence of the trajectory and state of stress of subducting lithosphere the occurrence over the last decade of isolated large deep earthquakes outside the main wadati benioff zones in the kurile izu bonin and chile deep seismic areas in addition to the observed flat distributions of deep seismicity beneath the banda sea and fiji plateau areas and the large number of deep earthquakes located away from the main slab in the tonga arc supports recent tomographic and other seismological studies leading to a reconsideration of slabs as simple planar structures sinking undeformed into the lower mantle the focal geometries of these isolated earthquakes which often exhibit near vertical compressional stresses are distinct from adjacent events in the main wadati benioff zone they are also different in orientation from events in the deflecting toe of the slab and from the stress orientation expected if the deflected slab acts as a stress guide these isolated mantle earthquakes are interpreted to take place in subducted lithosphere that has deflected to a horizontal posture at the base of the upper mantle conversely the deep seismicity in the adjacent wadati benioff zone is associated with the deflection of the subducting lithosphere

modifications to existing ground motion prediction equations in light of new data we compare our recent ground motion prediction equations gmpes for western north america wna boore and atkinson 2008 ba08 and eastern north america ena atkinson and boore 2006 ab06 atkinson 2008 a08 to newly available ground motion data based on these comparisons we suggest revisions to our gmpes for both wna and ena the revisions for wna affect only those events with m 5 75 while those for ena affect all magnitudes these are simple modi fications to the existing gmpes that bring them into significantly better agreement with data the wealth of new data clearly demonstrates that these modifications are warranted we therefore recommend the use of the updated equations for seismic hazard analyses and other applications more detailed studies are under way by many investigators including ourselves to develop a new generation of ground motion models in both wna and ena from scratch through a comprehensive reevaluation of source path site and modeling issues in time those more complete models will replace those proposed in this study however as the new models will be several years in development we recommend using the modified models proposed herein labeled ba08 for wna ab06 for ena and a08 for ena to replace a08 as interim updates to our existing models the proposed models are in demonstrable agreement with a rich database of ground motions for moderate magnitude earthquakes in both wna and ena and are constrained at larger magnitudes by the ba08 magnitude and distance scaling

airglow observations of nighttime medium scale traveling ionospheric disturbances from yonaguni statistical characteristics and low latitude limit the characteristics of nighttime medium scale traveling ionospheric disturbance mstid features observed over yonaguni 24 5 n 123 0 e 19 3 n dip latitude japan are studied using all sky imaging of oi 630 0 nm airglow emission the uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere typical low latitude limit of midlatitude type nighttime mstids possessing phase front alignments along the northwest to the southeast occurs in this region these mstid features are rarely sighted at dip latitudes below 15 we selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions the mstids were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods their observed range of wavelengths phase velocities phase front alignment and propagation directions are similar to those observed at typical midlatitude sites however on many occasions the phase fronts of the observed mstids did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes detailed investigation suggests that the poleward propagating enhancement of airglow intensity probably associated with the midnight pressure bulge causes the mstid features to disappear when they reach lower latitudes later in the night when the mstids reach lower latitudes well before midnight they are found to be inhibited by the equatorial ionization anomaly crest region

role of unstable sporadic e layers in the generation of midlatitude spread f 1 there is growing experimental evidence to suggest that mesoscale spread f is linked to the occurrence of midlatitude coherent backscatter from patchy sporadic e layers which are unstable to the gradient drift and farley buneman plasma instabilities to validate this suggestion we have compared e region backscatter and spread f ionosonde recordings from about 100 days of joint operation during summer and found a one to one relation in the occurrence of both phenomena also midlatitude backscatter studies over the last few years have shown the existence of enhanced electric fields inside patchy sporadic e these are believed to be polarization fields set up locally by neutral winds that transport the plasma patches horizontally and by the relatively large hall to pedersen conductivity ratios at e region altitudes moreover midlatitude echoes were found to be associated with mostly westward drifting sporadic e patches with typical scale lengths from 10 to more than 100 km and perturbed eastward electric fields from a few to maybe more than 10 to 15 mv m we propose that the enhanced polarization fields set up inside unstable sporadic e patches can easily map up the magnetic field lines to the f region and thus contribute to the formation of midlatitude spread f this new mechanism for spread f generation is basically an image process that can account for key observational properties of the phenomenon these include the rapid plasma upwelling and the abrupt changes in height uplifts of the f layer as well as the scale sizes involved and morphological characteristics

turbulent upwelling of the mid latitude ionosphere 2 theoretical framework in a companion paper data from the mu radar have been presented which show that during sunspot minimum conditions in japan the mid latitude ionosphere is sometimes characterized by regions of rapid and turbulent upwelling in this paper we explore possible mechanisms for these events the most likely process seems to be the instability of the equilibrium which occurs when the mid latitude plasma is supported against gravity either by an eastward electric field component or by a southward neutral wind as was proposed by perkins 1973 we show for example that the growth rate determined by perkins is considerably higher in sunspot minimum conditions than at sunspot maximum for comparable altitudes of the ionospheric f layer the growth rate is not very large however and we argue here that the observed structures must evolve from preexisting undulations of the bottomside of the f region which are generated by gravity waves that is the gravity waves create finite amplitude structures which are amplified by the plasma instability an intriguing feature of the gravity wave role in this process is that the echoing patches detected by the mu radar and the height bands detected by the arecibo radar which we believe to be related phenomena all seem to propagate to the west this is the same direction reported for the angle of arrival measurements of classic mid latitude spread f by a number of researchers using ionosonde techniques since the mu radar detects the upwelling regions from nonthermal 3 m irregularities there must be mechanism to create such tracers we propose that secondary structures are created at intermediate scales via the e b instability operating on the dome of the upwelling structure and by the neutral wind driven process on either the west or the east wall of the structure depending on the direction of the zonal wind the 3 m waves are then created in a cascade process which brings energy into a range of k space in which the structures are linearly damped finally we discuss the fine structure of the echoing patches and suggest several plausible mechanisms two of which involve e region coupling and one which deals with the vertical structure of the gravity wave seeding process

mesoscale field aligned irregularity structures fais of airglow associated with medium scale traveling ionospheric disturbances mstids in this paper we report the evolution generation amplification and dissipation of optically observed mesoscale field aligned irregularity structures fais similar to 150 km associated with a medium scale traveling ionospheric disturbance mstid event there have not been observations of mesoscale fais of airglow before the mesoscale fais were generated in an airglow depleted front of southwestward propagating mstids that were simultaneously observed by an all sky imager a gps monitor and a digisonde around xinglong 40 4 degrees n 30 5 degrees magnetic latitude china on 17 18 february 2012 a normalized cross correlation method has been used to obtain the velocities of mesoscale fais and mstids the mesoscale fais had an obvious northwestward relative velocity to main body mstids about 87 0 m s on average the direction of this relative velocity was roughly parallel to the depleted fronts furthermore the evolution of the mesoscale fais was mostly controlled by the intensity of the depleted fronts occurred in a highly elevated ionosphere that had a total electron content depletion associated with large negative airglow perturbations 25 the mesoscale fais grew rapidly when they experienced southeastward wind which had a speed of about 100 m s and were measured by a fabry perot interferometer a northeastward polarization electric field within a depleted airglow front can play a controlling role in the development of the mesoscale fais the electric field can significantly elevate the ionosphere and move the mesoscale fais northwestward by the e x b drift the processes for the generation and development of the polarization electric field and the mesoscale fais however need further study

rheological control of wadati benioff zone seismicity intermediate and deep focus earthquakes in wadati benioff zones are thought to occur in the cold interiors of downgoing slabs which are significantly stronger than the warmer mantle given that earthquakes in oceanic lithosphere appear restricted by an isotherm and hence a given value of lithospheric strength we investigate whether a similar formulation is useful for subducting plates strength in downgoing slabs should be affected by both pressure and temperature an effect previously treated using a depth dependent limiting temperature for seismicity wortel 1982 we find this limiting temperature implies that a possible limiting strength increases strongly with depth unless either the temperatures were too low or the activation volume too large comparison of the analytic model used by wortel with numerical thermal models appears to exclude the first possibility we explore the second possibility by using the numerical thermal model to compute strength contours for flow law constants reported from laboratory experiments and find that the expected pressure strengthening is large enough that the slab should have considerable strength well below the deepest seismicity we conclude that if laboratory results are applicable to these conditions either a strongly depth dependent limiting strength exists or factors in addition to strength control the distribution of subduction zone earthquakes

midlatitudinal special airglow structures generated by the interaction between propagating medium scale traveling ionospheric disturbance and nighttime plasma density enhancement at magnetically quiet time

subduction zone earthquakes and stress in slabs the pattern of seismicity as a function of depth in the world and the orientation of stress axes of deep and intermediate earthquakes are explained using viscous fluid models of subducting slabs with a barrier in the mantle at 670 km 670 km is the depth of a seismic discontinuity and also the depth below which earthquakes do not occur the barrier in the models can be a viscosity increase of an order of magnitude or more or a chemical discontinuity where vertical velocity is zero longn versus depth wheren is the number of earthquakes shows 1 a linear decrease to about 250 300 km depth 2 a minimum near that depth and 3 an increase thereafter stress magnitude in a subducting slab versus depth for a wide variety of models shows the same pattern since there is some experimental evidence thatn is proportional toe where is a constant and is the stress magnitude the agreement is encouraging in addition the models predict down dip compression in the slab at depths below 400 km this has been observed in earlier studies of earthquake stress axes and we have confirmed it via a survey of events occurring since 1977 which have been analysed by moment tensor inversion at intermediate depths the models predict an approximate but not precise state of down dip tension when the slab is dipping the observations do not show an unambiguous state of down dip tension at intermediate depths but in the majority of regions the state of stress is decidedly closer to down dip tension than it is to down dip compression chemical discontinuities above 670 km or phase transitions with an elevation of the boundary in the slab predict when incorporated into the models stress peaks which are not mirrored in the profile of seismicity versus depth models with an asthenosphere and mesosphere of appropriate viscosity can not only explain the state of stress observed in double benioff zones but also yield stress magnitude profiles consistent with observed seismicity models where a nonlinear rheology is used are qualitatively consistent with the linear models

midlatitude summer nighttime anomaly of the ionospheric electron density observed by formosat 3 cosmic 1 this paper presents monthly variations of the midlatitude summer nighttime anomaly msna of the ionosphere for the first time by global observations of the formosat 3 cosmic f3 c mission the anomaly is characterized by the greater nighttime 1800 lt 0200 lt ionospheric electron density than during daytime 0800 1800 lt at middle latitudes during months around june and december solstices the anomaly shown during december solstice was known as the weddell sea anomaly wsa occurring around the antarctica and nearby the pacific ocean this paper demonstrates that the wsa like feature also exists in the northern hemisphere and is most prominent near the northeast asia europe africa and central pacific longitudes around june solstice in both hemispheres the anomalies with similar electron density characteristics and variations caused by the similar mechanism prompts us to name this phenomenon the msna the monthly f3 c observations indicate that the anomaly appears as the most prominent structure of the global ionosphere around midnight hours

spatial relationship of nighttime medium scale traveling ionospheric disturbances and f region field aligned irregularities observed with two spaced all sky airglow imagers and the middle and upper atmosphere radar 1 we report simultaneous observations of medium scale traveling ionospheric disturbances mstids and field aligned irregularities fais in the f region using two all sky airglow imagers and the middle and upper atmosphere mu radar mstids propagating southwestward were observed simultaneously in 630 nm airglow images over sakata 39 0 n 139 9 e and shigaraki 34 9 n 136 1 e japan on the night of 16 june 2004 by using all sky images over both sites we estimated the altitude of the airglow layer to be 260 km by the triangulation method during the mstid event fais in the f region were observed by making multibeam measurements with the mu radar at shigaraki in order to investigate the spatial relationship between the mstids and fais the fais were mapped onto the 630 nm airglow layer altitude 260 km along the geomagnetic field lines we found that fais with an intense weak signal to noise ratio coincided with the airglow depletion enhancement caused by the mstids fai velocity obtained from a combination of the doppler velocities on the three radar beams oscillated in the northwest southeast direction with an amplitude of approximately 82 m s the fai velocity was northwestward southeastward at the airglow depletion enhancement the directions of the fai velocity were consistent with those of the e b drifts caused by the polarized electric fields associated with the mstids the northeastward polarized electric field at the airglow depletion region strengthened the background eastward effective electric field and drove the gradient drift instability generating fais this might be the reason why the fais preferred to occur at the airglow depletion region

deep earthquakes in real slabs deep earthquakes shouldn9t happen yet they do at depths greater than about 50 kilometers rock begins to flow rather than fracture and fracture is the phenomenon associated with seismic activity in their perspective stein and rubie discusses the highlights of a recent conference on subduction the geological process whereby one lithospheric plate is pushed under another deep earthquakes can take place in subducting slabs owing to the complex phase transformations that occur as minerals are heated and put under pressure as they are pushed deeper conference participants debated current models of deep seismic activity and their limitations

rupture processes of large deep focus earthquakes from inversion of moment rate functions we determine the source time histories of five recent 1994 1996 large deep focus earthquakes using a method that inverts for fault slip from far field moment rate functions the moment rate functions are obtained through the deconvolution of multiple body wave phases using broadband records from global seismic network gsn and geoscope stations tests of this method on synthetic data indicate that it is successful in determining the low frequency rupture characteristics of deep earthquakes under a variety of complicating conditions we find that source parameters such as average rupture velocity and stress drop are highly variable among the events studied and that some unusual characteristics exhibited by the june 9 1994 great bolivian earthquake are also found for other events comparison of the slip distributions with background seismicity and aftershock locations indicates that most of the moment release for large deep focus earthquakes is probably occurring within the active slab interior this provides further evidence that temperature controlled mechanisms such as transformational faulting play a large role in deep earthquake faulting most of the events studied also show a tendency for horizontal rupture propagation suggesting that isobaric processes may be an important factor in controlling progression of the rupture large gaps in the slip distributions point to possible occurrence on multiple fault planes

a large scale traveling ionospheric disturbance during the magnetic storm of 15 september 1999 enhancement of gps total electron content 1 0 10 16 m 2 multipoint and imaging observations of these parameters show that the lstid moved equatorward over japan with a velocity of 400 450 m s from a comparison with the sheffield university plasmasphere ionosphere model supim we conclude that an enhancement 250 300 m s of poleward neutral wind that is propagating equatorward caused these observational features of the lstid at midlatitudes to investigate generation of the lstid by auroral energy input we have used auroral images obtained by the polar uvi instrument magnetic field variations obtained at multipoint ground stations and the empirical joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics amie technique intense auroral energy input was observed at 0800 1100 ut 4 6 hours before the lstid probably causing equatorward neutral wind at lower latitudes it is likely that the poleward wind pulse that caused the observed lstid was generated associated with the cessation of this equatorward wind the effect of lorentz force is also discussed index terms 0310 atmospheric composition and structure airglow and aurora 2427 ionosphere ionosphere atmosphere interactions 0335 2435 ionosphere ionospheric disturbances 2437 ionosphere ionospheric dynamics 2788 magnetospheric physics storms and substorms keywords large scale traveling ionospheric disturbance thermosphere ionosphere coupling magnetic storm airglow imaging gps network ionosonde

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

deep focus earthquakes and recycling of water into the earth s mantle for more than 50 years observations of earthquakes to depths of 100 to 650 kilometers inside earth have been enigmatic at these depths rocks are expected to deform by ductile flow rather than brittle fracturing or frictional sliding on fault surfaces laboratory experiments and detailed calculations of the pressures and temperatures in seismically active subduction zones indicate that this deep focus seismicity could originate from dehydration and high pressure structural instabilities occurring in the hydrated part of the lithosphere that sinks into the upper mantle thus seismologists may be mapping the recirculation of water from the oceans back into the deep interior of our planet

statistical analysis of nighttime medium scale traveling ionospheric disturbances using airglow images and gps observations over central china statistical analyses were conducted to investigate the nighttime medium scale traveling ionospheric disturbances mstids for the first time by using airglow images and global positioning system gps data over central china during 2013 2015 our results show that the phase fronts of perturbations are aligned from northwest to southeast direction and propagate toward the southwest direction the characteristics of the nighttime mstids observed by oi 630 0 nm images are consistent with those of the nighttime mstids obtained from the gps data the phase velocity period wavelength and amplitude of nighttime mstids are 50 150 m s 0 5 1 5 h 150 400 km and 2 15 respectively as measured from 630 0 nm images and gps data in addition we utilized the simultaneous observations from oi 630 0 nm and oi 557 7 nm images to explore the relationship between nighttime mstids and gravity waves 100 km in the mesopause it is found that the nighttime mstids frequently occurred in the summer solstice which was not consistent with the occurrence of gravity wave observed in the mesopause our results indicate that the nighttime mstids may be generated by the coupling of electrodynamic processes rather than be trigged by gravity waves from the lower atmosphere

the mechanism of the deep bolivia earthquake of june 9 1994 we analyzed the iris broad band seismograms for the june 9 1994 bolivia earthquake the largest deep focus earthquake ever recorded we inverted the record sections with a duration of 330 sec which include p pp and sp phases and obtained a dip slip mechanism dip rake strike 13 4 1 or 89 103 95 with a scalar moment of mo 2 9 10 21 nm mw 8 2 this mechanism is similar to that obtained from long period 175 to 250 sec rayleigh and love waves 83 100 90 mo 3 0 10 21 nm mw 8 3 the main rupture was preceded by about 10 sec by a cluster of smaller events with a total moment of 1 2 10 20 nm mw 7 3 the main rupture starts at about 20 km east or northeast of the initial break and propagates horizontally in the east to northeast direction the source duration is 40 sec and the rupture dimension is about 40km if a fault area of 40 40km is assumed the stress drop is 110 mpa an inversion of body waves p pp and sp with 6 basis moment tensors yielded a best fit solution with a 10 implosive component this result is of marginal significance and its confirmation would require more detailed information on the structures near the source region pp bounce points and stations the observed amplitude of the radial mode 0s 0 1226 sec is consistent with a double couple model with less than 2 isotropic component

can strong motion observations be used to constrain probabilistic seismic hazard estimates abstract because of the new regulatory requirements that hazards have to be estimated in probabilistic terms the number of probabilistic hazard studies conducted has recently been increasing the present study aims at defining the possibilities and limits for comparing predictions from these studies and observations comparison tests based directly on the rate of ground motion occurrences are favored over the rate of earthquake occurrences based on the properties of poisson processes the minimum time window ensuring reliable occurrence rate estimates at a site is computed and evaluated for example for ground motions with a 475 yr return period at a site a minimal 12 000 yr observation time window is required for estimating the rate with a 20 uncertainty coefficient of variation standard deviation divided by the mean these values are not dependent on the seismicity level of the regions under study an analysis of recorded ground motions at the stations of the permanent french accelerometer network shows that at best the occurrence rates can be estimated with an accuracy of 30 for very low acceleration levels 0 0001 0 001 g for the station stet the same analysis carried out at two stations with longer recording histories and located in higher seismicity regions greece and california provides ground motion levels up to 0 1 g therefore the question posed is can the results of a comparison test at low acceleration levels be generalized to higher acceleration levels even if using a ground motion prediction equation uniformly valid for a wide range of accelerations

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

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

a comparison between the forecast by the united states national seismic hazard maps with recent ground motion records confidence in scientific models accumulates by continuously validating the model s predictions by observations we compared the seismic hazard forecasts of the four published versions of the u s geological survey national seismic hazard maps with observed ground motions a large dataset is necessary for a statistically meaningful comparison and so our comparison was based on an aggregated approach such that the observations and the forecast in a region california and the central and eastern united states ceus were combined and compared as a whole we used instrumental records in california and macroseismic intensity in the ceus since 2000 as the observation which was largely prospective to the hazard maps we verified that the observed seismic hazard based on macroseismic intensity was consistent with that based on instrumental records making model evaluation in the ceus for which instrumental records were almost nonexistent viable the observed hazard was found to be generally consistent with the forecasted one for peak ground acceleration pga in california and for both pga and spectral acceleration at 1 s sa1 in the ceus forecasted hazard for sa1 for california appeared to be conservative recent versions of the hazard map were in better agreement with observations in california small earthquakes as expected were found to have insignificant impact on sa1 induced earthquakes in the ceus have increased the observed seismic hazard but did not invalidate the hazard model as a whole we examined the resolving power of the test by computing its statistical power

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

the persistence of the nwa effect during the low solar activity period 2007 2009 the ionospheric nighttime winter anomaly nwa was first reported more than three decades ago based on total electron content tec and vertical sounding data the aim of this paper is to provide further evidence that the nwa effect is a persistent feature in the northern hemisphere at the american and in the southern hemisphere at the asian longitude sector under low solar activity conditions the analysis of ground based gps derived tec and peak electron density nmf2 data from radio occultation measurements on formosat 3 cosmic satellites fully confirms and further supports the findings published in earlier nwa papers so it has been confirmed and further specified that the nwa appears at longitude sectors where the displacement between the geomagnetic and the geographic equator maximizes to be more precise the nwa appears in that hemisphere where the geomagnetic latitude exceeds the geographic latitude here nwa peaks around 40 50 geomagnetic mid latitudes supporting the idea that wind induced plasma uplifting in the conjugated summer hemisphere is the main driving force for the accumulation of ionospheric plasma in the topside ionosphere and plasmasphere in parallel the midsummer nighttime anomaly msna is caused after sunset at the local ionosphere simultaneously inter hemispheric coupling causes severe downward plasma fluxes in the conjugated winter hemisphere during night strong enough to form the nwa at low solar activity lsa with increasing solar activity the downward plasma fluxes although still present lose their impact due to the much stronger increasing background ionization that masks the nwa completely and therefore making nwa invisible it has been shown that msna and related special anomalies such as the weddell sea anomaly and the okhotsk sea anomaly introduced in this paper are formed by the same major ionospheric thermospheric processes that cause also the nwa

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

the effects of phase transition kinetics on subducting slabs the effects of kinetics on the non equilibrium aspects of the olivine to spinel transition in a descending slab have been studied numerically a one dimensional model consisting of the kinetic equations and the heat diffusion equation with latent heat release has been constructed numerical results show that the position and sharpness of the kinetic phase boundary is determined by the surface tension and the activation volume for slow slab velocities less than 6 cm yr near equilibrium conditions are found finger like structures emanating from the phase boundaries are obtained in this regime these phase boundary prolusions may cause earthquakes for slab velocities of around 10 cm yr the metastable olivine region may be pushed down to a depth of about 600 km with a sharp phase boundary a direct transition from olivine to perovskite may be feasible

climatology of medium scale traveling ionospheric disturbances observed by a gps network in central china 1 the 15 month climatology of medium scale traveling ionospheric disturbances mstids during a solar minimum period has been constructed from observations of a dense gps receiver array in central china in total 793 mstid events are identified with peaks in occurrence at 1500 lt and 0100 lt the occurrence of mstids decreases following an increase in geomagnetic activity with 46 of the mstids occurring in the daytime daytime mstids are characterized by a major occurrence maximum around the winter solstice and by an equatorward propagation direction the period phase velocity azimuth and amplitude of daytime mstids are 20 60 min 100 400 m s 130 270 and 0 8 1 5 respectively the remaining 54 of the mstids occurred at night and were characterized by a peak in occurrence at the summer solstice and by a southwestward propagation direction the period phase velocity azimuth and amplitude of nighttime mstids are 20 70 min 50 230 m s 170 300 and 2 7 respectively the propagation directions and the seasonal behaviors support the view that daytime mstids are an ionospheric manifestation of atmospheric gravity waves from the lower atmosphere while a possible excitation mechanism of nighttime mstids is the electrodynamics process caused by plasma instability in the f layer

the summer evening anomaly and conjugate effects 1 the constellation observing system for meteorology ionosphere and climate cosmic gps occultation data have been analyzed in this study to provide a better understanding of the weddell sea anomaly wsa and to place it in the wider context of a general phenomenon that occurs near dusk in summer which we are calling the summer evening anomaly to better capture its global nature the terminator and the magnetically conjugate points for the terminator in the other hemisphere have been plotted on top of global maps of cosmic nmf2 and hmf2 for 2 months either side of the december and june solstices for 2006 2008 these plots show that there are distinct enhancements of nmf2 and increases in hmf2 as soon as the conjugate footprint of the field line on the winter terminator is seen at middle latitudes in the summer hemisphere this effect is most pronounced where the wsa is formed but it also occurs across the south pacific ocean in the southern summer and across much of the north atlantic ocean siberia and kamchatka during the northern summer an hmf2 increase occurs between the two terminators even at locations where there is no increase in nmf2 a similar but reversed effect occurs in hmf2 near dawn this behavior appears to be most consistent with upward and poleward ion drifts in the evening but neutral wind and downward precipitation may make important contributions to this effect

the metastable olivine wedge in fast subducting slabs constraints from thermo kinetic coupling abstract the effects of a strong non linear thermo kinetic coupling in the olivine spinel transition are investigated with a 2d model for fast subducting slabs the thermo kinetic coupling problem is solved in the lagrangian framework by the differential algebraic method and by using experimental input parameters narrow regions with metastable olivine are found in fast and cold slabs down to the 660 km discontinuity while the thermo kinetic coupling reduces the depth and width of the zone where olivine and spinel coexist in contrast to recent kinetic models both latent heat release and heat diffusion place important constraints on the structure of the metastable wedge both processes trigger the ongoing phase transformation in the cold slab interior a thermal instability over a short timescale 10 4 10 5 yr can occur due to a positive thermo kinetic feedback this effect is enhanced at greater depths the depth of the metastable wedge is found to be extremely sensitive to certain geophysical and thermodynamic parameters such as the lithospheric basal temperature slab width and the activation energy for diffusion variations in these parameters within the experimental uncertainties can cause significant changes in the depth of the metastable wedge hence predictions about the exact position of the metastable olivine wedge are rather difficult we propose that deep focus earthquakes may occur due to a thermal runaway caused by shear heating while the thermal instability is enhanced by the latent heat release associated with the olivine spinel phase transition

first tomographic observations of the midlatitude summer nighttime anomaly over japan 1 recently a chain of digital beacon receivers has been established over japan mainly for the tomographic imaging of the ionosphere these receivers are installed at shionomisaki 33 45 n 135 8 e shigaraki 34 85 n 136 1 e and fukui 36 06 n 136 e which continuously track the low earth orbiting satellites leos and the simultaneous line of sight total electron content tec data are used for tomographic reconstruction in the images obtained during july 2008 it is seen that the nighttime electron densities exceed the daytime values on almost all days over latitudes 33 34 n on several days these northern latitudes show enhanced electron densities compared to the low latitude region during nighttime these are the prominent features of the midlatitude summer nighttime anomaly msna that is recently observed in the northern hemisphere and is considered similar to the nighttime weddell sea anomaly wsa this is the first study of the msna using tomographic technique and found its significant day to day variability the ionosonde data from wakkanai 45 4 n 141 7 e ground based gps tec observations using the geonet champ in situ electron density measurements and formosat3 cosmic f3 c occultation measurements are also used to confirm the presence of msna over this region and to examine its variability it is seen that in general during the local summer period electron density over the northern latitudes is highest at 2000 2100 lt and the latitudinal enhancement in electron density also begins to appear around the same time which continues to exist even at later hours

longitudinal structure of the equatorial ionosphere time evolution of the four peaked eia structure 1 longitudinal structure of the equatorial ionosphere during the 24 h local time period is observed by the formosat 3 cosmic f3 c satellite constellation by binning the f3 c radio occultation observations during september and october 2006 global ionospheric total electron content tec maps at a constant local time map local time tec map referred as lt map can be obtained to monitor the development and subsidence of the four peaked longitudinal structure of the equatorial ionosphere from lt maps the four peaked structure starts to develop at 0800 1000 lt and becomes most prominent at 1200 1600 lt the longitudinal structure starts to subside after 2200 2400 lt and becomes indiscernible after 0400 0600 lt in addition to tec ionospheric peak altitude also shows a four peaked longitudinal structure with variation very similar to tec during daytime the four peaked structure of the ionospheric peak altitude is indiscernible at night with global local time maps of ionospheric tec and peak altitude we compare temporal variations of the longitudinal structure with variations of e b drift from the empirical model our results indicate that the observations are consistent with the hypothesis that the four peaked longitudinal structure is caused by the equatorial plasma fountain modulated by the e3 nonmigrating tide additionally the four maximum regions show a tendency of moving eastward with propagation velocity of several 10 s m s

comparison of the historical record of earthquake hazard with seismic hazard models for new zealand and the continental united states we compare the historical record of earthquake hazard experienced at 78 towns and cities sites distributed across new zealand and the continental united states with the hazard estimated from the national probabilistic seismic hazard psh models for the two countries the two psh models are constructed with similar methodologies and data our comparisons show a tendency for the psh models to slightly exceed the historical hazard in new zealand and westernmost continental united states interplate regions but show lower hazard than that of the historical record in the continental united states intraplate region factors such as non poissonian behavior parameterization of active fault data in the psh calculations and uncertainties in estimation of ground motion levels from historical felt intensity data for the interplate regions may have led to the higher than historical levels of hazard at the interplate sites in contrast the less than historical hazard for the remaining continental united states intraplate sites may be largely due to site conditions not having been considered at the intraplate sites and uncertainties in correlating ground motion levels to historical felt intensities the study also highlights the importance of evaluating psh models at more than one region because the conclusions reached on the basis of a solely interplate or intraplate study would be very different

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

space time distribution of deep seismic deformation in tonga abstract at a time when physical models for the occurrence of deep earthquakes are being proposed capable of explaining their fault like source process it is important that seismology characterizes all elements relevant to the physical occurrence of shear at depth to identify the characteristic modes of deformation of the deep subducted lithosphere in the tonga region families of events with similar faulting orientation were classified and mapped on the benioff zone using 133 centroid moment tensor solutions for all events with m 0 3 10 24 dyn cm since 1977 the existence of two principal modes of deformation acting on the subducted lithosphere is confirmed and detailed in this present study 1 the down dip compression associated with the subducting flow is a ubiquitous factor in the deformation of the whole lithosphere with families of focal mechanisms whose orientation follows strictly the local geometry of the benioff zone 2 a lateral shear involves the whole deep lithosphere associated with the relative motion between surface plates and deep mantle in addition observations are made of the presence of families of events with down dip extensional or strike slip mechanisms mostly located along the western margin of the seismicity where the lithosphere has already undergone the major compressional deformation and has rotated to a more horizontal posture the transition from the down dip compression to the new stress state takes place over a length of no more than 100 km which corresponds to the local geometry of the benioff zone the overlapping occurrence of different modes of deformation in space and time indicates that the physical mechanisms proposed for the generation of deep earthquakes should incorporate the concept that deep faults or their physical equivalent at the 600 km depth conditions are stable features of a deep subducted lithosphere whose failure behaviour sometimes obeys to a highly heterogeneous local state of stress

deep earthquakes and the thermal assimilation of subducting lithosphere two problematic aspects of deep seismic zones are investigated the maximum depth about 700 km of seismic activity and the relative maximum in seismic energy release in the 500 700 km depth range it is shown that both features can be accounted for by a model based on thermal assimilation this implies that no barrier is required at a depth of 650 700 km to explain the observations

intermittent layered convection in a model mantle with an endothermic phase change at 670 km it is not yet known whether convection in the earth s mantle occurs in cells that extend throughout the entire depth of the mantle or if the upper and lower mantle convect in independent layers both possibilities seem to be consistent with geochemical and seismologi cal observations1 4 it is generally accepted however that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change spinel perovskite mgo here we investigate the results of including this phase change in a model of mantle convection for realism and to eliminate scaling problems our calculations use commonly accepted values of geophysical parameters for a clapeyron slope y 2 106 a value close to experimental results and theoretical expectations we observe local intermittent mixing between the upper and lower mantle such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole mantle and layered convection

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

a local ground motion predictive model for turkey and its comparison with other regional and global ground motion models we examined the differences between the ground motion estimations of local and global prediction equations and explored some seismological parameters that may explain these differences to achieve this objective we first derived a set of ground motion prediction equations gmpes for estimating peak horizontal accel eration velocity and pseudospectral acceleration using the recently compiled turkish ground motion database the new gmpes are comparable with the recent global gmpes in terms of model sophistication and they are based on a well studied national dataset using global gmpes from the next generation attenuation of ground motions project power et al 2008 and the pan european akkar and bommer 2010 model we observed that the discrepancy between local and global gmpes is more prominent at small magnitudes provided that the gmpes possess similar mag nitude limits our more detailed comparisons with the pan european akkar and bom mer 2010 predictive model as well as with the estimations from a combined italian and turkish accelerometric dataset indicate that depth can be of importance for delineating the differences between local and global gmpes