the state of stress on some faults of the san andreas system as inferred from near field strong motion data we present a simple method to calculate the stress produced on an earthquake fault during rupture this method allows the complete evaluation of the stress spatio temporal history over the fault we apply this approach to study the changes in shear stress produced during four of the largest earthquakes which occurred along the san andreas fault system over the last 20 years the imperial valley earthquake of 1979 the morgan hill earthquake of 1984 the loma prieta earthquake of 1989 and the northridge earthquake of 1994 we use for this study the tomographic models of the fault rupture obtained from the inversion of the near field seismic data recorded during these earthquakes the results obtained show that the static and the dynamic stress drops vary greatly over the fault the peak values obtained for the four earthquakes studied range from about 20 to 100 mpa these high values imply that the initial shear stress level on the fault at the onset of the earthquake was high on at least a significant portion of the fault the regions of the fault which break with a high stress drop are also the regions where slip is large this suggests that most of the slip produced in a large earthquake takes place over the strong areas of the fault low slip regions tend to break with low stress drops after the earthquake the shear stress is increased over a significant portion of the fault which corresponds to low slip regions aftershock activity tends to be concentrated in these areas of stress increase the apparent strength of the fault before the earthquake that is the local shear stress increase which is required for rupture is also extremely heterogeneous the rupture velocity seems to be inversely correlated with this apparent fault strength the rupture accelerating over the weak areas of the fault and slowing down over the high strength areas

short term and intermediate term geochemical precursors detection of precursory phenomena in observation data is essential to earthquake prediction studies continuous monitoring of radon concentration in groundwater in japan in one case showed a short term anomaly related to a nearby earthquake with the exception of the 1978 izu oshimakinkai earthquake m7 0 however no abnormal change has been noted this may be due partially to difficulty in detecting insignificant precursory signals from observation data which ordinarily contains a noise induced fluctuations and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena in order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater hydrologic precursors with significant features are examined in this paper complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed

the effect of bandwidth limitations on the inference of earthquake slip weakening distance from seismograms numerous researchers have obtained estimates of slip weakening distance dc and fracture energy for recent earthquakes dc is often observed to be a significant fraction of the total slip and tends to correlate with total slip although these observations may well be true of real earthquakes we show that low pass filtering of strong motion seismograms can also produce some of these effects in inverted rupture models we test the accuracy of dc estimates by calculating them in low pass filtered versions of models a and b of guatteri and spudich 2000 models a and b are two different rupture models for a hypothetical m 6 5 earthquake and they have nearly identical rupture time slip and stress drop distributions and nearly identical predicted seismograms but dc for model b is about twice that for model a by low pass filtering slip models a and b at 1 0 hz we simulate the blurring effects of band limited waveform inversions on these slip models at each point on a fault graphic 1 is defined to be the slip at the time of the peak slip speed at that point low pass filtering the slip models causes an upward bias in dc inferred from stress slip curves and it causes an artificial correlation between graphic 2 and the total slip low pass filtering might also bias fracture energy high and radiated energy low these biases should be considered when interpreting dc derived from band limited slip models of real earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

idealized simulations of the intertropical convergence zone and its multilevel flows abstract a mesoscale numerical model with an idealized tropical channel environment is used to study the dynamics of intertropical convergence zones itczs and the recently identified shallow return flow srf and midlevel inflow mli four idealized sea surface temperature sst distributions are used a meridionally symmetric sst profile with a sharply peaked sst maximum at the equator a similar profile with the maximum sst shifted off the equator a cosine shaped sst profile with zero gradient at the equator and an idealized sst profile modeled after the observed sst of the eastern pacific the simulations show that both the srf and the mli are robust features of the itcz the prior result that the srf is a sea breeze like response to surface temperature gradients is further supported whereas the mli is caused by the upper level maxima in diabatic heating and vertical motion simulations with the sst maximum at the equator generate long lasting convectively coupled kelvin waves when the sst maxi

geographic variability in the export of moist static energy and vertical motion profiles in the tropical pacific 1 column integrated moist static energy mse budgets were calculated using daily data from three reanalyses 1998 2001 and isccp radiative cooling the mse export by the circulation was separated into vertical and horizontal mse advection components in order to examine how observationally derived vertical motion profiles affect gross moist stability calculations in a 2000 km wide region in the central eastern pacific itcz vertical motions import mse implying a negative gross moist stability horizontal mse advection is negative and of similar magnitude to vertical mse advection in rainy regions geographic differences in export of mse by the vertical circulation are primarily due to differences in the shape of the vertical motion profile in the west pacific warm pool rainy regions mean horizontal convergence extends up to 300 mb while in parts of the pacific itcz where meridional sst gradients are strong the vertical motion profile is bottom heavy with convergence below 800 mb and divergence above on daily timescales the mode of vertical motion variability has little dependence on precipitation rate and is consistent with observed regional differences in the vertical structure of trmm pr reflectivities

the dependence of traction evolution on the earthquake source time function adopted in kinematic rupture models 1 we compute the temporal evolution of traction by solving the elasto dynamic equation and by using the slip velocity history as a boundary condition on the fault plane we use different source time functions to derive a suite of kinematic source models to image the spatial distribution of dynamic and breakdown stress drop strength excess and critical slip weakening distance d c our results show that the source time functions adopted in kinematic source models affect the inferred dynamic parameters the critical slip weakening distance characterizing the constitutive relation ranges between 30 and 80 of the total slip the ratio between d c and total slip depends on the adopted source time functions and in these applications is nearly constant over the fault we propose that source time functions compatible with earthquake dynamics should be used to inter the traction time history

large scale characteristics of the atmospheric boundary layer in the eastern pacific cold tongue itcz region abstract observations from the eastern pacific investigation of climate 2001 epic2001 field campaign and a simple mixed layer model are used to study the large scale structure and dynamics of the atmospheric boundary layer abl in the eastern pacific vertical and latitudinal distributions of the meridional pressure gradient winds and other variables are examined and the momentum balance of the mixed layer is explored for a latitudinal range from 0 to 10 n along 95 w including the equatorial cold tongue sea surface temperature sst front and convective region at the latitude of the intertropical convergence zone itcz the surface meridional pressure gradient is partitioned into contributions from the abl largely controlled by the gradient in sst and from the troposphere above the boundary layer mainly controlled by elevated heating and atmospheric wave activity the mean meridional gradient in surface pressure is dominated 90 by the abl contribution however its temporal variability prim

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

dynamics of the shallow meridional circulation around intertropical convergence zones the generally accepted view of the meridional circulation in the tropical east pacific is that of a single deep overturning cell driven by deep convective heating in the intertropical convergence zone itcz similar to the zonal mean hadley circulation however recent observations of the atmosphere from the tropical eastern pacific have called this view into question in several independent datasets significant meridional return flows out of the itcz region were observed not only at high altitudes but also at low altitudes just above the atmospheric boundary layer this paper presents a theory and idealized simulations to understand the causes and dynamics of this shallow meridional circulation smc fundamentally the smc can be seen as a large scale sea breeze circulation driven by sea surface temperature gradients when deep convection is absent in the itcz region a simple model of this circulation is presented using observed values the sea breeze model shows that the pressure gradient above the boundary can indeed reverse leading to the pressure force that drives the shallow return flow out of the itcz the weather research and forecast model wrf is used to simulate an idealized hadley circulation driven by moist convection in a tropical channel the smc is reproduced with reasonable similarity to the circulation observed in the east pacific the simulations confirm that the smc is driven by a reversal of the pressure gradient above the boundary layer and that the return flow is strongest when deep convection is absent in the itcz and weakest when deep convection is active the model also shows that moisture transport out of the itcz region is far greater in the low level shallow return flow than in the high altitude return flow associated with the deep overturning and that a budget for water transport in and out of the itcz region is grossly incomplete without it much of the moisture carried in the shallow return flow is recycled into the boundary layer but does not appear to contribute to enhanced cloudiness in the subtropical stratocumulus poleward of the itcz

water s two height scales the moist adiabat and the radiative troposphere summary the temperature structure of the tropical troposphere resembles a moist adiabat with a lapse rate transition toward dry adiabatic where water becomes scarce at an altitude hma n 8 km 350 hpa infrared emission by water vapour cools a deeper layer extending up to hd 14 km 160 ma five consequences of these unequal heights are reviewed 1 upper tropospheric relative humidity is often low highly variable and bimodal due to the rapidity of drying by radiative subsidence 2 large scale divergent circulations e g equatorial u wind exhibit a two celled vertical structure with an elevated convergence layer near 8 10 km in the rising branch 3 the dominant deep convective heating process changes from latent heating at low levels to eddy heat flux convergence in the upper troposphere this requires a substantial updraught environment temperature difference which leads to large entrainment near hma yielding stratiform anvil clouds which also contribute radiative heating 4 the rising branches of deep hd vertical circulations export more heat than they import as moisture so that large scale tropical dynamics can be characterized by a gross moist stability 5 divergent motions with a vertical wavelength 8 km corresponding to kelvin or gravity wave speeds of 15 m s are excited by simple e g uniform heating profiles extending through the lapse rate change near hma

coseismic changes in groundwater temperature of the usu volcanic region observations of groundwater temperature to an accuracy of 0 001 c or better have been made at about 30 wells in various areas of impending earthquakes in japan the main aim of the observations was to monitor the crustal strain and or the movement of groundwater which relate to earthquake occurrence one thermometer was installed at a depth of 200 m in an active volcanic area usu where an upward movement of the magma is occurring we report here that there was a generally increasing temperature trend at this location 0 3 c in the half year of observation decreases in the rate of increase preceded intense local earthquake activity temperature jumps were accompanied by large local earthquakes with magnitudes up to 4 2 and the polarity of the steps corresponded to the location of hypocentres this is probably the first microtemperature measurement made in the proximity of seismic activity

complexity of the rupture process during the 2009 l aquila italy earthquake summary in this study we investigate the rupture history of the 2009 april 6 mw 6 1 l aquila normal faulting earthquake by using a non linear inversion of strong motion gps and dinsar data both the separate and joint inversion solutions reveal a complex rupture process and a heterogeneous slip distribution slip is concentrated in two main asperities a smaller shallow patch of slip located updip from the hypocentre and a second deeper and larger asperity located southeastwards along strike direction the key feature of the source process emerging from our inverted models concerns the rupture history which is characterized by two distinct stages the first stage begins with rupture nucleation and with updip propagation at relatively high 4 0 km s 1 but still subshear rupture velocity the second stage starts nearly 2 0 2 5 s after nucleation and it is characterized by the along strike rupture propagation the largest and deeper asperity fails during this stage of the rupture process the rupture velocity is larger in the updip than in the along strike direction the updip and along strike rupture propagation are separated in time and associated with a mode ii and a mode iii crack respectively the comparison between the source models inferred in this study with the poisson ratio anomalies in the crustal volume containing the fault plane allows the interpretation of the delay in along strike rupture propagation in terms of a structural control of the rupture history our results show that the l aquila earthquake featured a very complex rupture with strong spatial and temporal heterogeneities suggesting a strong frictional and or structural control of the rupture process

slip weakening distance estimated at near fault stations we estimated the slip weakening distance from the seismograms recorded at near fault stations considering the effect of spatio temporal filtering for a continuous propagation of rupture this effect is usually observed at some distance away from the fault we used a green s function for 2 d anti plane rupture propagating with constant rupture velocity and instantaneous slip at the crack tip as a source time function we used a regularized yoffe function which is a kinematically good approximation of dynamic slip weakening behavior by convolving these functions near fault waveforms are computed as a proxy of slip weakening distance d c we used d c which is defined as a slip at the time of peak slip velocity then d c values can be computed as a function of the distance from the fault this procedure is applied to the observation of the 2000 western tottori japan earthquake m w 6 6 as well as the 2002 denali alaska earthquake m w 7 9 we estimated d at about 0 3 m at gsh station 100 m away from the fault for the tottori earthquake and that at about 2 5 m at ps10 station 3 km away from the fault for the denali earthquake we confirmed that both estimates are not affected by the spatio temporal smoothing

comparison of postseismic groundwater temperature changes with earthquake induced volumetric strain release yudani hot spring japan we observed temporal variations of the groundwater temperature during two observation periods may 1983 july 1984 september 1991 august 1995 at yudani hot spring in tottori prefecture japan the groundwater temperature is affected by tides atmospheric pressure changes and earthquakes assuming that volumetric strain change is the cause of these temperature changes we calculated the respective strain sensitivities of the groundwater temperature as a result the sensitivities estimated from theoretical volumetric strain changes by earthquake fault models are more than 1 000 times larger than those from tides and atmospheric pressure we infer that the actual volumetric strain changes near yudani hot spring due to the earthquakes are larger than theoretical strain changes calculated by earthquake fault models

using robust satellite technique rst to determine thermal anomalies before a strong earthquake a case study of the saravan earthquake april 16th 2013 mw 7 8 iran abstract employing an efficient and robust prediction system along with early warnings is useful to reduce the effects of devastating earthquakes thermal anomaly as an earthquake precursory is widely confirmed in this study to characterize the thermal anomalies within a 10 year specific observation interval of land surface temperature lst satellite data products obtained from modis aqua march 16th to may 16th every year from 2004 to 2013 were analyzed using robust satellite technique rst method the saravan earthquake april 16th 2013 mw 7 8 iran were used for validation phase and the year 2012 as a relatively seismically unperturbed year no earthquakes with mw 3 5 regarding target time and region was taken for confutation phase for the first time to reduce the effects of the topography with respect to vegetation cover using unsupervised classification the study area was divided into the low and high elevation regions the results of the present study showed the significant sequences of lst anomalies sslas from several days before and immediately after the saravan earthquake appeared in the north south and center of the study area however no anomalies were observed in a seismically unperturbed year 2012 therefore the results confirmed the existence of space time thermal anomalies related to destructive earthquakes and revealed that the rst method is a reliable approach to detect disturbances of the earth s thermal emission

the vertical structure of the eastern pacific itczs and associated circulation using the trmm precipitation radar and in situ data the atmospheric circulation associated with the eastern pacific single and double itczs particularly its vertical structure is little known due to the sparce observations using precipitation profiles from the tropical rainfall measure mission trmm precipitation radar with approximations to the liquid water and energy budget equations we estimated vertical profiles of latent heating and vertical velocity in the far eastern pacific 95 w 85 w itczs in the 800 730 hpa layer we combined this with eastern pacific investigation of climate campaign epic2001 and other in situ data to produce a preliminary characterization of the meridional vertical circulation we found evidence of a double cell structure in boreal fall between the itcz and the equator with both shallow and upper level peaks in vertical velocity in spring the flow poleward of the two itczs has a single cell structure although around the equator it shows some hints of the double cells reanalysis and satellite based data are shown to be unreliable for describing the vertical structure of the circulation

assessing the potential of thermal infrared satellite surveys for monitoring seismically active areas the case of kocaeli izmit earthquake august 17 1999 abstract space time anomalies of earth s emitted radiation in the thermal infrared spectral range tir measured from satellite months to weeks before the occurrence of earthquakes have been interpreted by several authors as pre seismic signals the claimed connection of tir emission with seismic activity has been considered up to now with some caution by the scientific community mainly for the insufficiency of the validation data sets and the scarce importance attached by those authors to other causes e g meteorological that rather than seismic activity could be responsible for the observed tir signal fluctuations in this paper a robust satellite data analysis technique is described which permits us to identify anomalous space time tir signal transients even in very variable observational satellite view angle land topography and coverage etc and natural e g meteorological conditions a statistically well founded definition of tir anomaly is given and proposed as a suitable tool for satellite tir surveys in seismically active regions eight years of meteosat tir observations have been analyzed in order to characterize the tir signal behavior at each specific observation time and location space time tir signal transients have then been analyzed both in the presence validation and in the absence of confutation seismic events looking for possible space time relationships the devastating earthquake which occurred in turkey izmit august 17 m s 7 8 in 1999 has been considered as a test case for validation relatively unperturbed periods no earthquakes with m 5 were taken for confutation purposes quite intense s n 3 5 and rare spatially extensive and time persistent tir signal transients were identified appearing eight days before the izmit main shock in greece moving to turkey on august 13 and disappearing moving back to greece some days after possible implications of such results together with present limitations of the proposed technique will also be discussed in the light of the improved performances expected by its extension to other existing or future satellite packages

the interaction of clouds and dry air in the eastern tropical pacific cloud radar observations of eastern pacific intertropical convergence zone cloud vertical structure are interpreted in light of soundings 100 km scale divergence profiles calculated from precipitation radar doppler velocities and surface rain gauge data from a ship at 10 n 95 w during the 2001 east pacific investigation of climate epic experiment the transition from convective to stratiform rain is clear in all four datasets indicating a coherence from local to 100 km scale a novel finding is dry air intrusions at altitudes of 6 8 km often undercutting upper level ice clouds two distinct dry air source regions are identified one is a relatively dry area overlying the cooler waters of the costa rica oceanic thermocline dome centered approximately 400 km east northeast of the ship site the other is the even drier nearequatorial subsidence zone south of 6 7 n the former source is somewhat peculiar to this specific ship location so that the ship sample is not entirely representative of the region the 20 25 september period is studied in detail as it depicts two influences of the dry air on cloud vertical structure one is the modulation of small scale surface based convection evident as a weakening and narrowing of cloud radar reflectivity features the other springs from intense sublimation cooling as differential advection brought snowing anvil clouds over the dry layers during one half day period of strong sublimation the cooling rate is inferred to be several tens of degrees per day over a 100 hpa layer based on a heat budget estimate at 100 km scale involving the horizontal wind divergence data this is consistent with fluxing ice water contents of 0 05 0 10 g m 3 derived from the cloud radar reflectivities the temperature profile shows the dynamically expected response to this cooling a positive negative positive temperature anomaly pattern centered on the sublimating layer a buoyancy sorting diagnostic model of convection indicates that these upper troposphere temperature anomalies can cause premature detrainment of updrafts into the lower part of the cloudy layer a feedback that may actively maintain these long lasting dense anvils middle troposphere southerly dry air inflow is also evident in large scale analysis given the proximity of the dry equatorial subsidence zone to the eastern tropical pacific the differential advection of dry and cloudy air the ensuing sublimation and its dynamical aftereffects may play a role in establishing the region s climate although the extent of their significance needs to be further established

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

shallow meridional circulations in the tropical atmosphere abstract a shallow meridional circulation smc in the tropical atmosphere features a low level e g 700 hpa flow that is in the opposite direction to the boundary layer monsoon or trade wind flow and is distinct from the meridional flow above representations of the smc in three global reanalyses show both similarities and astonishing discrepancies while the smc over west africa appears to be the strongest it also exists over the eastern atlantic and eastern pacific oceans and over the indian subcontinent with different strength and structure all smcs undergo marked seasonal cycles the smcs are summarized into two types one associated with the marine itcz and the other with the summer monsoon the large scale conditions for these two types of smcs are similar a strong meridional gradient in surface pressure linked to surface temperature distributions and an absence of deep moist convection the processes responsible for these conditions are different for the two types of smcs as are their str

trmm observed shallow versus deep convection in the eastern pacific related to large scale circulations in reanalysis datasets abstractover the eastern pacific recent studies have shown that a shallow large scale meridional circulation with its return flow just above the boundary layer coexists with a deep hadley circulation this study examines how the vertical structure of large scale circulations is related to satellite observed individual precipitation properties over the eastern pacific in boreal autumn three reanalysis datasets are used to describe differences in their behavior the results are compared among reanalyses and three distinctly different convection periods which are defined according to their radar echo depths shallow and deep circulations are shown to often coexist for each of the three periods resulting in the multicell circulation structure deep shallow circulations preferentially appear in the mostly deep shallow convection period of radar echo depths thus depth of convection basically corresponds to which circulation branch is dominant this anticipated relationship between the circulation stru

magnitude of velocity anomalies prior to earthquakes a model is presented which allows us to reexamine the interpretation of velocity anomalies observed before some earthquakes occur this model extends the well known dilatancy models by accounting for two scales of heterogeneities the variations in pore crack compressibility at a microscopic scale and the variations in the spatial fluid distribution for partially saturated rocks at a much larger scale this model is relevant for cracked rocks which are partially saturated such a situation is likely to develop in impending earthquake source areas although previous models have considered cracked rocks and partially saturated rocks none of the above heterogeneity induced effects has been considered previously so that the previous predictions are in fact shown to be inappropriate at earthquake or exploration seismic frequencies 1 100 hz saturation inhomogeneity can play a prominent role and this results in velocity dispersion so that high frequency predictions may not be valid and low frequency velocities should be calculated in order to do that we assume that crustal rocks are described by a saturated matrix in which spherical undersaturated pockets are embedded the matrix is itself made of a rock containing an isotropic distribution of cracks then low and high frequency velocities are calculated coupling the biot gassmann domenico theory with the effective medium approach differential self consistent method if the diffusion dilatancy model of scholz et al 1973 is superimposed on our theoretical velocity curves it appears that the low frequency predicted velocity anomaly is quite high when saturation heterogeneities are ignored it is however quite small if this effect is taken into account this result can explain the lack of observations of precursory changes of seismic velocities before many events

processes leading to double intertropical convergence zone bias in cesm1 cam5 abstractthe double intertropical convergence zone itcz bias in the eastern pacific in the community earth system model version 1 with community atmosphere model version 5 cesm1 cam5 is diagnosed in cam5 standalone the northern itcz is associated with inertial instability and the southern itcz is thermally forced after air sea coupling the processes on both hemispheres are switched because the spatial pattern of sea surface temperature sst is changed biases occur during boreal spring in both cam5 and the ocean model in cam5 alone weaker than observed equatorial easterly in the tropical eastern south pacific leads to weaker evaporation and an increase in local sst the shallow meridional circulation overly converges in the same region in the cam5 standalone simulation the planetary boundary layer and middle troposphere are too humid and the large scale subsidence is too weak at the middle levels these biases may result from excessive shallow convection behavior in cam5 the extra moisture wou

trampoline effect in extreme ground motion in earthquake hazard assessment studies the focus is usually on horizontal ground motion however records from the 14 june 2008 iwate miyagi earthquake in japan a crustal event with a moment magnitude of 6 9 revealed an unprecedented vertical surface acceleration of nearly four times gravity more than twice its horizontal counterpart the vertical acceleration was distinctly asymmetric the waveform envelope was about 1 6 times as large in the upward direction as in the downward direction which is not explained by existing models of the soil response we present a simple model of a mass bouncing on a trampoline to account for this asymmetry and the large vertical amplitude the finding of a hitherto unknown mode of strong ground motion may prompt major progress in near source shaking assessments

a statistical procedure for the analysis of seismotectonically induced hydrochemical signals a case study from the eastern carpathians romania changes in the stress field of an aquifer system induced by seismotectonic activity may change the mixing ratio of groundwaters with different compositions in a well leading to hydrochemical signals which in principle could be related to discrete earthquake events due to the complexity of the interactions and the multitude of involved factors the identification of such relationships is a difficult task in this study we present an empiric statistical approach suitable to analyse if there is an interdependency between changes in the chemical composition of monitoring wells and the regional seismotectonic activity of a considered area to allow a rigorous comparison with hydrochemistry the regional earthquake time series was aggregated into an univariate time series this was realized by expressing each earthquake in form of a parameter beq taking into consideration both energetic magnitude of a seismic event and spatial parameters position of epi hypocentrum relative to the monitoring site the earthquake and the hydrochemical time series were synchronised aggregating the e parameters into bearthquake activityq functions e which takes into account the time of sampling relative to the earthquakes which occurred in the considered area for the definition of the aggregation functions a variety of different beq parameters were considered the set of earthquake functions e was grouped by means of factor analysis to select a limited number of significant and representative earthquake functions e to be used further on in the relation analysis with the multivariate hydrochemical data set from the hydrochemical data a restricted number of hydrochemical factors were extracted factor scores allow to represent and analyse the variation of the hydrochemical factors as a function of time finally regression analysis was used to detect those hydrochemical factors which significantly correlate with the aggregated earthquake functions this methodological approach was tested with a hydrochemical data set collected from a deep well monitored for two years in the seismically active vrancea region romania three of the hydrochemical factors were found to correlate significantly with

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

synoptic scale dual structure of precipitable water along the eastern pacific itcz abstractusing 10 yr high resolution satellite and reanalysis data the synoptic scale dual structure of precipitable water pw in which the southern and northern bands straddled at the itcz produce zonally propagating meridional dipoles is observed over the eastern pacific ep during boreal summer and fall composites indicate that the pw dipole concurrent with the dipole like filtered divergence has a shift to the west of the anomalously cyclonic circulation the vertical structure of filtered meridional wind is characterized by a wavenumber 1 baroclinic mode and the vertical motion has two peaks situated at 850 and 300 hpa respectively to the east of the pw dipole the shallow convection is embedded within the deep convection forming a multilevel structure of meridional wind on the itcz equatorward side to the west of the pw dipole the deep convection tends to be suppressed because of the invasion of midlevel dry air advected by northerly flows the generation and propagation of the dual pw

groundwater microtemperature in earthquake regions microtemperature measurements of groundwater with a relative precision better than 1 1000 c have been made in several seismically active areas in japan the measured temperatures show clear coseismic signals as well as a correlation with atmospheric pressure simultaneous observations at various depths have shown that these temperature changes were not induced by simple groundwater level changes also distinctive signals occurred before several earthquakes and seem to be caused by a different mechanism than the coseismic signals the microtemperature at some observation sites shows excellent correlation with records of nearby sensitive borehole strainmeters simultaneous recording of microtemperature and strain has been initiated in some boreholes

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

shallow meridional circulation in the tropical eastern pacific abstract based on four independent datasets this study presents observational evidence of a shallow meridional circulation cell in the eastern tropical pacific in this shallow meridional circulation cell the northerly cross equatorial return flow from the itcz into the southern hemisphere is found immediately above the atmospheric boundary layer in contrast to the classic concept of the hadley type deep meridional circulation whose northerly return flow resides in the upper troposphere the strength and depth of this shallow meridional circulation undergo a distinct annual cycle possible causes and climatic implications of this shallow meridional circulation are discussed

a robust satellite technique for monitoring seismically active areas the case of bhuj gujarat earthquake abstract a robust satellite data analysis technique rat has been recently proposed as a suitable tool for satellite tir surveys in seismically active regions and already successfully tested in different cases of earthquakes both high and medium low magnitudes in this paper the efficiency and the potentialities of the rat technique have been tested even when it is applied to a wide area with extremely variable topography land coverage and climatic characteristics the whole indian subcontinent bhuj gujarat s earthquake occurred on 26th january 2001 m s 7 9 has been considered as a test case in the validation phase while a relatively unperturbed period no earthquakes with m s 5 in the same region and in the same period has been analyzed for confutation purposes to this aim 6 years of meteosat 5 tir observations have been processed for the characterization of the tir signal behaviour at each specific observation time and location the anomalous tir values detected by rat have been evaluated in terms of time space persistence in order to establish the existence of actually significant anomalous transients the results indicate that the studied area was affected by significant positive thermal anomalies which were identified at different intensity levels not far from the gujarat coast since 15th january but with a clearer evidence on 22nd january and near the epicentral area mainly on 21st january on 25th january 1 day before gujarat s earthquake significant tir anomalies appear on the northern indian subcontinent showing a remarkable coincidence with the principal tectonic lineaments of the region thrust himalayan boundary on the other hand the results of the confutation analysis indicate that no meaningful tir anomalies appear in the absence of seismic events with m s 5

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

estimation of the breakdown slip from strong motion seismograms insights from numerical experiments fukuyama and mikumo 2007 presented a method to extract informa tion about the friction controlling earthquake rupture directly from near field seismo grams recorded out to several kilometers from a fault this method computes a parameter d 00 approximating the breakdown slip dc from the rake parallel dis placement at the time of the peak particle velocity the validation of the method was based on simple 2d steady state green s functions an approach lacking sufficient physics of the rupture process to support their conclusions here we use 3d simula tions of subshear strike slip spontaneous rupture propagation to demonstrate that d 00 is almost always controlled by rupture and wave propagation effects rather than the fault friction process only if rupture reaches the earth s surface and within a short distance from the fault rc is it possible to extract information about dc from strong motion data due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process beyond rc d 00 is controlled by the dynamic stress drop from the earthquake rupture without information about dc rc is comparable to the length of the fault cohesive zone where the breakdown process takes place during rupture and approximately equal to 80 of the wavelength associated with the break down frequency defined as the reciprocal of the time span required by the stress to drop to the dynamic level our findings suggest that the dc estimate by fukuyama and mikumo 2007 for the 2000 mw 6 6 tottori earthquake is unrelated to the breakdown slip moreover the very narrow widths for rc obtained from our simulations are in agreement with previous studies challenging the resolution of bandlimited strong motion data to estimate dc from kinematic rupture models guatteri and spudich 2000 spudich and guatteri 2004

rupture process of the 2008 iwate miyagi nairiku japan earthquake derived from near source strong motion records abstract we derive the rupture process of the 2008 iwate miyagi nairiku japan earthquake m jma 7 2 during which the largest ground acceleration to date namely 4022 cm sec 2 was recorded at a hanging wall station iwth25 station of kik net just above the hypocenter velocity waveform data 0 1 1 hz at 14 strong motion stations of k net and kik net including the borehole records of iwth25 are inverted using the multi time window linear waveform inversion method we assume a horizontally layered velocity structure model having low velocity subsurface layers for each station in order to calculate the green s functions the waveform inversion indicates that there are two major slip patches one patch extends from the hypocenter to the southern shallower part of the fault a particularly large slip area in this patch is centered approximately 8 km to the south of the hypocenter with a maximum slip of 6 2 m the area ruptured between 4 and 9 sec after the initial break the other patch with smaller slip is located in the northern part which broke after the rupture of the southern slip patch the initial 0 4 sec rupture occurred beneath iwth25 contributing to the synthesis of a distinctive upward velocity pulse at this station examination of the slip contribution to the synthetic velocity waveforms and comparison of the isochrones with the slip distribution suggest that a peak acceleration greater than 4000 cm sec 2 observed at iwth25 was generated from the area that is closest to the hypocenter in the southern particularly large slip area

the effect of thermal pressurization on dynamic fault branching s u m m a r y we numerically investigate the effect of thermal pressurization tp on fault branch behaviour during dynamic rupture propagation a situation likely to occur during large earthquakes at subduction interfaces we consider a 2 d mode ii in plane rupture in an infinite medium that propagates spontaneously along a planar main fault and encounters an intersection with a pre existing branching fault the fault system is subjected to uniform external stresses we adopt the values used by kame et al we use the 2 d boundary integral equation method and the slip weakening friction law with a coulomb failure criterion allowing the effective normal stress to vary as pore pressure changes due to tp we reveal that tp can alter rupture propagation paths when the dip angle of the main fault is small the rupture propagation paths depend on the branching angle when tp is not in effect on either of the faults as described by kame et al however the dynamic rupture processes are controlled more by tp than by the branching angle when tp is in effect on the main fault only the rupture propagates along the main fault it propagates along the branch when tp is in effect on both faults finally we considered the case where there is a free surface above the branch fault system in this case the rupture can propagate along both faults because of interaction between the free surface and the branch fault in addition to tp on the main fault

a low level circulation in the tropics abstract deep convective tropical systems are strongly convergent in the midtroposphere horizontal wind measurements from a variety of rawinsonde arrays in the equatorial pacific and caribbean are used to calculate the mean dynamical divergence profiles of large scale arrays 1000 km in diameter in actively convecting regions somewhat surprisingly the magnitude of the midtropospheric divergence calculated from these arrays is usually small in principle the midlevel convergence of deep convective systems could be balanced on larger scales either by a vertical variation in the radiative mass flux of the background clear sky atmosphere or by a divergence from shallow cumuli the vertical variation of the clear sky mass flux in the midtroposphere is small however so that the offsetting divergence must be supplied by shallow cumuli on spatial scales of 1000 km the midlevel convergent inflow toward deep convection appears to be internally compensated or screened by a divergent outflow from surr

itcz breakdown in three dimensional flows the intertropical convergence zone itcz is observed to undulate and at times break down into a series of tropical disturbances in several days some of these disturbances may develop into tropical cyclones and move to higher latitudes while others dissipate and the itcz may reform in the original region it has been proposed that the itcz may break down because of its heating induced potential vorticity pv anomalies here this process is examined in three dimensional simulations using a primitive equation model a simulation of the itcz in a background state of rest is compared to simulations in different background flows the effect of different vertical structures of the prescribed heating is also examined deep heating induces a positive pv anomaly in the lower troposphere leading to a reversal of the pv gradient on the poleward side of the heating while the induced pv anomaly at upper levels is negative leading to a reversal of the pv gradient on the equatorward side of the heating the response at upper levels leads to a weaker pv gradient change but the response is greater in areal extent than the lowertropospheric response for shallow heating the lower tropospheric pv response is greater than that for deep heating and there is no upper tropospheric pv response the itcz lasts longer before breaking in this case than in the deep heating case effects of the background flow are mainly felt in the deep heating cases when the background flow enforces the pv induced wind field itcz breakdown occurs more rapidly whereas when the background flow is opposite to the pv induced flow itcz breakdown takes longer and the itcz may dissipate before breakdown

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

on large scale circulations in convecting atmospheres the dominant thinking about the interaction between large scale atmospheric circulations and moist convection holds that convection acts as a heat source for the large scale circulations while the latter supply water vapour to the convection we show that this idea has led to fundamental misconceptions about this interaction and offer an alternative paradigm based on the idea that convection is nearly in statistical equilibrium with its environment according to the alternative paradigm the vertical temperature profile itself rather than the heating is controlled by the convection which ties the temperature directly to the subcloud layer entropy the understanding of large scale circulations in convecting atmospheres can therefore be regarded as a problem of understanding the distribution in space and time of the subcloud layer entropy we show that the subcloud layer entropy is controlled by the sea surface temperature the surface wind speed and the large scale vertical velocity in the convecting layer and demonstrate how the recognition of this control leads to a simple physically consistent view of large scale flows ranging from the hadley and walker circulations to the 30 50 day oscillation in particular we argue that the direct effect of convection on large scale circulations is to reduce by roughly an order of magnitude the effective static stability felt by such circulations and to damp all of them

the itcz in the central and eastern pacific on synoptic time scales the itcz in the central and eastern pacific on synoptic time scales is highly dynamic the active season extends roughly from may through october during the active season the itcz continuously breaks down and re forms and produces a series of tropical disturbances the life span of the itcz varies from several days to 3 weeks sixty five cases of itcz breakdown have been visually identified over five active seasons 1999 2003 in three independent datasets itcz breakdown can be triggered by two mechanisms 1 interaction with westward propagating disturbances wpds and 2 the vortex rollup vr mechanism results show that the frequency of occurrence of itcz breakdown from these two mechanisms is the same the vr mechanism may have been neglected because the produced disturbances are rather weak and they may dissipate quickly the itcz shows a strong tendency to re form within 1 2 days in the same location the itcz may break down via the vr mechanism without any other support and thus it may continuously generate numerous tropical disturbances throughout the season there are two main differences between the two mechanisms 1 the wpds induced itcz breakdown tends to create one or two vortices that may be of tropical depression strength the vr induced itcz breakdown generates several nearly equal sized weak disturbances 2 the wpds tend to disturb the itcz in the eastern pacific only disturbances generally move along the mexican coast after shedding off from the itcz and do not further disturb the itcz in the central pacific therefore the vr mechanism is observed more clearly and is the dominating mechanism for itcz breakdown in the central pacific

time variable response characteristics of groundwater radon to earthquakes a clear coseismic anomaly of groundwater radon was observed for a magnitude 5 6 earthquake that occurred on may 11 1992 the coseismic radon anomaly was observed at a station which is located right on a major active fault in northeast japan and about 140 km away from the hypocenter this was the first time that an earthquake with m 6 had ever been accompanied by a clear radon anomaly at the station although we had observed 12 similar coseismic radon anomalies at the station during the observation period from 1984 to 1987 all of the earthquakes that were accompanied by radon anomalies in that period had been with magnitude 6 0 and over surprisingly the radon concentration has become more sensitive to show coseismic anomalies even for m 5 earthquakes since october 1992 this enhancement of sensitivity of the coseismic radon response may be attributed to the progress of micro crack formation in the fracture zone of the active fault which could be related to unusual stress accumulation in the region

estimation of the high frequency radiation of the 2000 tottori japan earthquake based on a dynamic model of fault rupture application to the strong ground motion simulation abstract in the present study we investigate the high frequency hf radiation mechanism of the 2000 tottori earthquake in japan based on a 3d spontaneous fault rupture dynamic model we generalize the model of hf radiation of a suddenly stopping circular crack madariaga 1977 boatwright 1982 to the radiation from a general 3d rupture in a planar fault where hf is radiated during gradual changes of rupture velocity at the rupture front local rupture velocity changes are expressed as the divergence of local rupture velocity vectors that are derived from gradients of rupture times from the dynamic model our numerical model of the tottori earthquake indicates that rupture velocity changes are largely induced by barriers locally stronger fault sections across the fault plane and that hf radiation mainly originates within asperities large stress drop regions in areas where the product of dynamic stress drop and rupture velocity changes is maximum we develop a strong ground motion simulation methodology that incorporates hf radiation inferred from a dynamic fault rupture model using this methodology we investigate the hf radiation of the tottori earthquake by inverting observed near source acceleration envelopes of the earthquake our inversion results corroborate that hf radiation originates within asperities and show that significant hf radiation represents no more than a 20 of the total asperity area our results show that the incorporation of a directivity factor on the basis of a well defined physical rupture model to the radiation pattern leads to a significant improvement in fitting of observed ground motions our simulated near source strong ground motions of the tottori earthquake are also able to reproduce the 2 radiation theoretically predicted in 2d dynamic fault rupture models

a new biem for rupture dynamics in half space and its application to the 2008 iwate miyagi nairiku earthquake summary we developed a code for dynamic rupture propagation on arbitrarily shaped faults embedded in half space using boundary integral equation method biem it is based on an existing code for the full space case in which virtual free surface elements were introduced computations in half space are definitely necessary for the modelling of shallow dipping fault ruptures first we describe the implementation and conduct some validation tests that demonstrate the accuracy of the code the validation tests are carried out by comparing the biem results both with the analytical static solution and with the seismic wavefield obtained by a discrete wavenumber method then we apply the code to the study of the 2008 iwate miyagi japan earthquake mw 6 9 rupture dynamics the average stress drop was estimated to be rather large 16 mpa in the asperity area while the average strength excess was 5 mpa the average fracture energy inside the asperity was found to be 36 mjm 2 finally the free surface effect examination showed that the stress drop and the fracture energy were overestimated at shallow depth in the full space computation

on the inference of absolute stress levels from seismic radiation abstract spudich p k p 1992 on the inference of absolute stress levels from seismic radiation in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 99 106 this paper determines the conditions under which it is possible to learn the absolute stress level at a subset of points on a fault from observation of the fault kinematics specifically the points on a rupturing fault can be divided into two groups those points at which the rake rotates during the rupture process and those points at which the rake does not rotate if it is true that sliding frictional traction is collinear with the instantaneous velocity of one side of a fault then at the former group of points having rotating rakes there is a unique absolute stress consistent with the motion while at the latter group of points having rakes that do not rotate the absolute stress is unspecified by the motion published dislocation solutions for the 1979 imperial valley 1986 north palm springs 1987 whittier narrows and 1989 loma prieta california earthquakes are examined for evidence of temporal rotations of rake at the hypocenters and largest asperities the 1986 north palm springs earthquake shows evidence of a possible rake rotation at the hypocenter this may imply a low absolute stress level

breakdown and reformation of the intertropical convergence zone in a moist atmosphere abstract the effects of moisture on the intertropical convergence zone itcz over the eastern pacific on the synoptic time scale are investigated using an intermediate complexity atmospheric circulation model the quasi equilibrium tropical circulation model qtcm1 on an aquaplanet the dry simulation shows results consistent with those of simple dynamic models except that a slightly stronger heating rate is needed owing to different model designs in the moist simulations the most important result is the formation of a tail southwest of a vortex during and after the itcz breakdown this tail may extend zonally more than 60 longitude and last for more than two weeks in an idealized simulation in the eastern north pacific this phenomenon is often observed in cases that involve easterly waves in a sense the formation of the tail suggests a possible mechanism that forms an itcz efficiently this study shows that the surface convergent flow induced by a disturbance initializes a positive wind evapor

maintenance of the intertropical convergence zones and the large scale tropical circulation on a water covered earth abstract how the surface boundary heating sea surface temperature and cumulus adjustment process affect the location structure energetics and dynamics of the intertropical convergence zones itczs is investigated a series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature sst an aqua planet all experiments are run using equinoctal insolation with no longitudinal variation in sst two different convective parameterization schemes kuo and moist convective adjustment and several different zonally symmetric sst distributions are used in these experiments the location of the itcz is found to be sensitive to the convective parameterization scheme and the sst distribution the model with the moist convective adjustment scheme produces an itcz over the tropical sst maximum even under conditions where the sst gradient is weak by contrast the model with the kuo convective parameterization is not as sensit

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

moisture related weakening and strengthening of a fault activated at seismic slip rates 1 from high velocity friction experiments on gabbro rock at a rate of 85 mm s we found that a fault with a thin gouge layer experienced slip weakening with a drop of about 80 in the friction coefficient at room humidity conditions the fault subsequently recovered its complete strength over an interval of several minutes after the slip terminated the strength recovery did not occur under dry n2 gas saturated condition this result can be interpreted as the interaction of moisture with gouge particles moisture drained weakening due to frictional heating and moisture absorbed strengthening due to cooling this new mechanism can cause dynamic weakening of faults which controls earthquake rupture propagation

on the tropical atmospheric signature of el nino abstractthe linear atmospheric signature of enso obtained by regressing fields of geopotential height z wind vertical velocity and rainfall upon the nino 3 4 sea surface temperature sst index is partitioned into zonally symmetric and eddy components the zonally symmetric component is thermally forced by the narrowing and intensification of the zonally averaged equatorial rain belt during el nino and mechanically forced by the weakening of the upper tropospheric equatorial stationary waves and their associated flux of wave activity the eddy component of the enso signature is decomposed into barotropic bt and baroclinic bc contributions the latter into first and second modal structures bc1 and bc2 separable functions of space x y and pressure p using eigenvector analysis bc1 exhibits a nearly equatorially symmetric planetary wave structure comprising three dumbbell shaped features suggestive of equatorial rossby waves with out of phase wind and geopotential height perturbations in the

stress transfer and nonlinear stress accumulation at subduction type plate boundaries application to the aleutians a study of stress accumulation in seismic gaps and of stress transfer along linear plate boundaries is presented time dependent reloading of plate boundaries following seismic ruptures is modeled by a modified elsasser model of a coupled lithosphere asthenosphere plate system this model is applied to study a series of large earthquakes in the aleutian islands and the alaska peninsula in 1938 1965 it is found that the rat island earthquake and the 1948 earthquake in the central aleutians are likely to have been triggered by adjacent ruptures in the sense that their occurrence would have come at a later time had their neighboring segments not been ruptured stresses in the unalaska gap and the shumagin gap are at a relatively high level and these segments of the plate boundary may be expected to rupture in the near future in general in the ten years about 16 of the earthquake cycle for the aleutians following an earthquake the stress recovery in the rupture zone is highly nonlinear resulting in a much more rapid stress accumulation than the linear case even at a later stage of an earthquake cycle adjacent ruptures can cause an acceleration of loading rate in addition to the coseismic stress jump a good example is the influence of the 1964 alaska earthquake on the 1938 rupture zone a general conclusion of this work is that long term earthquake prediction models must take into account the nonlinear stress accumulation behavior in seismic gaps also we have shown the interaction of adjacent plate boundary segments which suggests that some large earthquakes may have been triggered by nearby ruptures

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

pre seismic responses of underground water level and temperature concerning a 4 8 magnitude earthquake in greece on october 20 1988 abstract it is widely known that level and temperature changes of the underground waters are associated with earthquake activity in this paper we present results obtained from a simple and indeed inexpensive underground water level and temperature monitoring network established for the first time in a seismic zone of greece sharp changes in the underground water level and temperature have been recorded mainly as pre seismic events of the earthquake of magnitude 4 8 which occurred in the area of the network on october 20 1988

dynamic stress drop and rupture dynamics of the october 15 1979 imperial valley california earthquake abstract a dynamic faulting model is constructed to determine the dynamic stress drop and relative strength distribution for the october 15 1989 imperial valley earthquake and to study the dynamics of rupture propagation for this event reproduction of the kinematic quantities of the strike slip rate strike slip final offset rupture time and rupture duration bu varying the dynamic parameters of dynamic stress drop and yield strength is attempted the fault plane is discretized in 1 5 km square grids the model incorporates first order corrections for the effect of the free surface and material property heterogeneity on the calculation of rupture at depth the strike slip particle velocities final offsets and rupture durations of the kinematic model are matched within about 40 everywhere below about 5 km except in the hypocentral region and in a high displacement region 20 km north of the epicenter the strike slip rate of the dynamic model is half and rupture duration double those of the kinematic model in the epicentral region the rupture durations and strike slip final offsets are two thirds those of the kinematic model in a high stress drop region beneath the el centro crossing array two slip concentrations correspond to stress drop concentrations one of about 80 bar at 20 km from the epicenter and at 8 km depth and the other of about 70 bar at 30 km from the epicenter and 10 km depth most of the dynamic stress drop occurs between the depths of 9 and 11 km averaging about 60 bar stress drops in the 7 9 km range vary between 25 and 35 bar while stress drops in the 5 7 km depth range vary between 10 and 15 bar this depth dependence of stress drop was a consistent feature across nearly 20 km of the fault stress drop appeared to be well correlated with rock type negative stress drop was found in the sediment regions and the regions at depth while positive stress drop was found in the metasediment regions between the depths of 5 and 11 km yield strength and rupture velocity are inversely related high yield strength is found in regions of low rupture velocity and vice versa rupture was found to terminate at the northern end of the fault by collision with a high strength barrier a region of supersonic rupture velocity was found to occur in a region of high stress drop and low fracture strength the kinematic rupture velocity at the northern end of the fault was found to be unreasonably low results show that this region reaches its peak stress before the kinematic break time yield strength increased with depth in the seismogenetic zone until the base of the zone was reached below which it tapered off slightly

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

regional study of the anomalous change in apparent resistivity before the tangshan earthquake m 7 8 1976 in china electrical resistivity measurements have been conducted as a possible means for obtaining precursory earthquake information before five great earthquakes m 7 h 25 km in china the apparent resistivity a showed systematic variations within a region 200 km from the epicenters in particular 9 stations in the tangshan tianjin beijing region prior to the tangshan earthquake m 7 8 h 11 km 27 july 1976 showed a consistent decrease of apparent resistivity around the epicenter with a maximum resistivity change of 6 and a period of variation of 2 3 years simultaneous water table observations in this region showed a declining water table and ground surface observations indicated a slight 5 mm uplift in the epicenter region relative to its surroundings

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

physics based 3 d simulation for earthquake generation cycles at plate interfaces in subduction zones the generation of interplate earthquakes can be regarded as a process of tectonic stress accumulation and release driven by relative plate motion we completed a physics based simulation system for earthquake generation cycles at plate interfaces in the japan region where the pacific plate is descending beneath the north american and philippine sea plates and the philippine sea plate is descending beneath the north american and eurasian plates the system is composed of a quasi static tectonic loading model and a dynamic rupture propagation model developed on a realistic 3 d plate interface model the driving force of the system is relative plate motion in the quasi static tectonic loading model mechanical interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across them on the basis of dislocation theory for an elastic surface layer overlying maxwell type viscoelastic half space in the dynamic rupture propagation model stress changes due to fault slip motion on non planar plate interfaces are evaluated with the boundary integral equation method the progress of seismic dynamic or aseismic quasi static fault slip on plate interfaces is governed by a slip and time dependent fault constitutive law as an example we numerically simulated earthquake generation cycles at the source region of the 1968 tokachi oki earthquake on the north american pacific plate interface from the numerical simulation we can see that postseismic stress relaxation in the asthenosphere accelerates stress accumulation in the source region when the stress state of the source region is close to a critical level dynamic rupture is rapidly accelerated and develops over the whole source region when the stress state is much lower than the critical level the rupture is not accelerated this means that the stress state realized by interseismic tectonic loading essentially controls the subsequent dynamic rupture process

direct seismic energy modeling and application to the 1979 imperial valley earthquake 1 the seismic energy associated with an earthquake has two representations the work of the seismic waves done against a distant surface or a fault representation for a fault subject to slip weakening friction the energy density is the difference between an elastostatic work and a work density spent in fracture and relaxation we apply this to a dynamic simulation of the 1979 imperial valley earthquake whose initial conditions are inspired by previous kinematic studies a large area of the fault has a negative energy density and the emission of energy is roughly confined to small parts of the fault with large positive energy density we compute the work of the seismic waves against the surface of a sphere enclosing the source and we find the same amount of energy we produce a map of energy directivity that shows that 40 of the energy passes through only 6 5 of the sphere

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

numerical simulation of earthquake faults with gouge toward a comprehensive explanation for the heat flow paradox the particle based lattice solid model is used to simulate transform faults with and without fault gouge stick slip frictional behavior is observed in two dimensional numerical experiments of model faults both with and without gouge when no gouge is present the fault is strong and the heat generation and stress drops are correspondingly high in disaccord with observations surrounding the heat flow paradox in contrast when a gouge is specified the fault is weak and the heat generation as well as stress drops are low in quantitative agreement with observational constraints the heat flow is low on average and during short periods of aseismic creep seismic efficiencies are compatible with observationally based bounds counter intuitively the fault strength decreases as the intrinsic friction between particles is increased beyond a given threshold the mechanism for low fault strength and heat is rolling and jostling of fault gouge grains during slip this allows macroscopic movement of the fault with only minimal slip between surfaces of the gouge grains as this dynamical mechanism operates during seismic and aseismic slip it provides an explanation for the lack of a heat flow anomaly in both the seismic and creeping parts of the san andreas fault the simulation results provide the first comprehensive and quantitative possible explanation of the heat flow paradox and suggest that fault gouge plays a fundamental role on the dynamics of earthquake faults whether rolling and jostling of fault gouge particles provides the explanation for the heat flow paradox in nature remains to be validated by observation evidence

fault dynamic rupture simulation of the hypocenter area of the thrust fault of the 1999 chi chi taiwan earthquake a 2d discrete element model was employed to simulate the rupture propagation and near source ground motion in the epicentral area of the 1999 chi chi taiwan earthquake the observations show that the hanging wall side is characterized by larger particle motions than the footwall side the simulation results reproduce the main features of the recorded ground motion and show that the particle velocity on the hanging wall side and on the footwall side are symmetric in the deeper fault region however as the crack approaches the free surface the hanging wall side is characterized by larger particle motions than the footwall side these results suggest that the difference in the particle motion on the hanging wall and on the footwall is due mainly to the asymmetric geometry of hanging wall and footwall thus the model used leads to good approximations in the vicinity of the epicenter

evolution of marine atmospheric boundary layer structure across the cold tongue itcz complex the structure of the marine atmospheric boundary layer mabl over the tropical eastern pacific ocean is influenced by spatial variations of sea surface temperature sst in the region as the mabl air is advected across a strong sst gradient associated with the cold tongue itcz complex ctic substantial changes occur in the thermodynamic structure surface fluxes and cloud properties this study attempts to define and explain the variability in the mabl structure and clouds over the ctic using data collected on research cruises from the fall seasons of 1999 2001 composite soundings were created for both the cold and warm sides of the sst front to describe the mean atmospheric boundary layer abl structure and its evolution across this front the average difference in sst across this front was 6 c much of this difference was concentrated in a band only 50 km wide during the fall seasons on the cold side of the gradient a well defined inversion exists in all years below this inversion both fair weather cumulus and stratiform clouds are observed as the mabl air moves over the sst front to warmer waters the inversion weakens and increases in height the mabl also moistens and eventually supports deeper convection over the itcz both the latent and sensible heat fluxes increase dramatically across the sst front because of both an increase in sst and surface wind speed cloudiness is variable on the cold side of the sst front ranging from 0 2 to 0 9 coverage on the warm side cloud fraction was quite constant in time with values generally greater than 0 8 the highest cloud top heights 3 km are found well north of the sst front indicating areas of deeper convection an analysis using energy and moisture budgets identifies the roles of various physical processes in the mabl evolution

tectonic leakage of fault bounded aquifers subject to non isothermal recharge a mechanism generating thermal precursors to seismic events abstract the thermal consequences of flow transients generated by deformation induced leakage at fault zones intersecting confined aquifers have been examined using a simple analytical model the recharge of the aquifer is assumed to take place by vertical infiltration through the confining layers the energy equation relevant in this case has been derived by evaluating enthalpy fluxes associated with lateral and vertical components of fluid flows as well as that due to volume changes in the permeable layer generated by deformation induced alterations in the hydraulic head results of numerical simulations indicate that thermal transients arise during the stress build up period when the infiltrating fluids mix with those in the aquifer but relatively rapid return to equilibrium conditions occur as soon as the leakage is cut off the model is thus capable of reproducing the characteristic features of thermal precursors found in observational records according to model results the growth of thermal perturbation as well as the time for attaining steady state conditions is proportional to the recharge rate the magnitude of the perturbation is related to the thermal gradients in the confining layers but permeability contrast between the confining layer and the aquifer also plays a significant role the model results also indicate that precursory signals are likely to be significant only in areas close to the fault plane where tectonic leakage has a direct influence on the hydraulic head of the aquifer if the fault plane is sensitive to deformation the tectonic leakage rate may undergo substantial changes in response to changing stress patterns and this in turn may easily lead to abrupt and substantial changes in the local thermal regime some of the transient thermal anomalies observed in records of temperatures in boreholes in tectonically active areas have characteristics similar to those predicted by the deformation induced leakage model examples are presented illustrating model fits to thermal transients identified as precursors to seismic events in firjusa turkmenistan didiweli georgia and izu peninsula japan the possibility of obtaining complementary information on processes responsible for fluid flow during pre seismic periods is pointed out it appears that the occurrence of thermal anomalies associated with small scale tectonic deformation may not be uncommon its detection depends on availability of suitable boreholes and of the facilities for monitoring of temperatures using high precision sensors over periods comparable to local recurrence periods of earthquakes

correction to earthquake fracture energy inferred from kinematic rupture models on extended faults 1 in the paper earthquake fracture energy inferred from kinematic rupture models on extended faults by e tinti p spudich and m cocco journal of geophysical research 110 b12303 doi 10 1029 2005jb003644 2005 all values of work density wb and we and total work eb should be corrected by multiplication by a factor 2 because of a systematic error in the calculational subroutine this correction applies to all the average and point estimates to make them consistent with equation 1 we include here a corrected table 2 we regret to point out that the breakdown work shown in figures 7 8 9 10 and 11 must be multiplied by a factor of 2 because this change is systematic it does not modify the inferred scaling relationships with seismic moment and slip journal of geophysical research vol 113 b07301 doi 10 1029 2008jb005829 2008

tropical cyclogenesis due to itcz breakdown idealized numerical experiments and a case study of the event in july 1988 abstractthe mechanism of tropical cyclogenesis due to the breakdown of the intertropical convergence zone itcz breakdown and the structure of associated vortices are studied by numerical experiments using a nonhydrostatic mesoscale model first an idealized numerical experiment in which a simple initial state without external disturbances is assumed is performed without cumulus parameterization a zonally uniform forcing of high sea surface temperature sst is imposed to generate an itcz like structure this itcz starts to undulate and eventually breaks down to form several tropical cyclones tcs these tcs merge and end up with a single tc the energy budget analysis shows that barotropic instability of the low level flow associated with the itcz is responsible for the genesis of vortices and tc scale buoyancy production soon takes over to contribute to the intensification of tcs conversion from the cumulus scale kinetic energy into the tc scale kinetic energy is found to be insignificant duri

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a