seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

comparative vertical distributions of iron in the japan sea the bering sea and the western north pacific ocean 1 the vertical distributions of dissolvable unfiltered fe concentrations in semi closed oceanic regions such as the japan sea and the bering sea are characterized by a gradual increase with depth in the intermediate and deep waters however there is a rapid decrease in the dissolvable fe concentration over the narrow depth range between deep and bottom waters with constantly lower concentrations observed in the bottom waters of the japan sea japan basin probably from the injection of newly formed bottom water in addition the rapid increase in dissolvable fe concentrations in bottom waters in the western north pacific ocean may be due to the resuspension of sediments from the seafloor or the slope however there are no differences of labile dissolved filtered fe concentrations and fe iii hydroxide solubility between deep and bottom waters revealing that dissolved fe concentrations in deep waters may be controlled primarily by fe iii complexation with natural organic ligands dissolved fe concentrations humic type fluorescence intensity and fe iii solubility correlate well with po4 with different slopes between intermediate and deep waters in the north pacific ocean however there is no different depth regime between them in semi closed oceanic regions the most statistically significant correlation between the fe iii solubility and fluorescence intensity was found with a nearly linear relation in intermediate and deep waters at all stations of the semi closed and open oceanic regions this result suggests that the distributions of humic type fluorescent organic matter may be responsible for fe iii solubility and dissolved fe concentrations in deep oceanic waters

small and large earthquakes can have similar starts a long standing question in seismology is whether small and large earthquakes have similar or different onsets an analysis of earthquakes around japan shows that in some cases these onsets are almost identical an analysis of earthquakes along the japan trench

seasonal climatic forcing of alpine glaciers revealed with orbital synthetic aperture radar the evolution of four dynamic radar glacier zones at the surface of an alpine icefield in british columbia is monitored using a time series of 35 first european remote sensing satellite ers 1 synthetic aperture radar sar images acquired from 1992 to 1994 these zones result from changing wetness and textural properties and appear to represent 1 cold snow with no liquid water present 2 an initial melt front with an upper boundary near the elevation of the 0 isotherm 3 metamorphosed rapidly melting first year snow with a rough or pitted surface and 4 bare ice this interpretation is aided by temperature and runoff data air photographs and field measurements of snowpack properties acquired simultaneously with two ers i sar scenes ice surface elevations derived from 1 50 000 topographic maps and simulations of radar backscatter from a geometric optics model of surface scattering meltwater production is affected by the development of zones 2 3 and 4 which form migrate up elevation and disappear each year between april and september

local observations of the onset of a large earthquake 28 june 1992 landers california the landers earthquake mw 7 3 of 28 june 1992 had a very emergent onset the first large amplitude arrivals are delayed by about 3 sec with respect to the origin time and are preceded by smaller scale slip other large earthquakes have been observed to have similar emergent onsets but the landers event is one of the first to be well recorded on nearby stations we used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release and to determine the slip function of the 3 sec nucleation process relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2 5 sec three station array analysis of the p wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals indicating that the large amplitude source was several kilometers deeper than the initial onset an ml 2 8 foreshock located close to the hypocenter was used as an empirical green s function to correct for path and site effects from the first 3 sec of the mainshock seismogram the resultant deconvolution produced a slip function that showed two subevents preceding the main energy release an mw 4 4 followed by an mw 5 6 these subevents do not appear anomalous in comparison to simple moderate sized earthquakes suggesting that they were normal events which just triggered or grew into a much larger earthquake if small and moderate sized earthquakes commonly detonate much larger events this implies that the dynamic stresses during earthquake rupture are at least as important as long term static stresses in causing earthquakes and the prospects of reliable earthquake prediction from premonitory phenomena are not improved

comparison of field and laboratory weathering rates in carbonate rocks from an eastern mediterranean drainage basin the rates of carbonate rock weathering affect the global carbon cycle over timescales of hundreds to thousands of years while field measurements show that the rate of carbonate denudation increases with rainfall significant variability exists to determine whether the mineralogical composition of the rocks causes this variability we compare published long term field denudation rates determined from cosmogenic isotopes 36 cl with the weathering rates measured in laboratory experiments conducted on the same rock samples the samples were collected from natural rock outcrops across the soreq drainage basin israel that experience similar mean annual precipitation but exhibit long term denudation rates that vary from 6 mm ky 1 to 20 mm ky 1 in laboratory experiments we found that the laboratory rates also varied decreasing as the ratio of dolomite to calcite increased however no correlation was evident between the long term denudation rates and mineral composition suggesting that the variability in field rates was not controlled by the kinetics of dissolution other factors such as rain intensity biological activity and mechanical erosion are likely to control the variability in the rates by inhibiting or accelerating the weathering of carbonate surfaces in natural settings

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

estimation of glacier ice extinction using long wavelength airborne pol insar in the recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research this paper describes the estimation of ice extinctions through the modeling of polarimetric interferometric sar pol insar coherences as a combination of a surface contribution from the snow firn interface and wind induced sastrugi features and a volume response ground to volume scattering ratios derived from a novel polarimetric decomposition are used in conjunction with pol insar coherence magnitudes to invert the extinction of the ice layer the inversion is performed for experimental airborne pol insar data at l band and p band acquired by the german aerospace center s dlr e sar system over the austfonna ice cap in svalbard norway as part of the 2007 icesar campaign extinction dependences on frequency and glacier facie are investigated and validation is performed comparing ground penetrating radar data to sar backscatter and extinction values best extinction results are obtained at shallow incidence angles with small wavenumbers and for low ground to volume scattering ratios for swath areas in mid range to far range accuracies of 25 in extinction are anticipated when averaging over 100 effective looks for a four baseline inversion constraining solutions to vertical wavenumbers of 0 01 kz 0 1 to allow inversion using single baseline pol insar the proposed model is of limited complexity suggested extensions for a more realistic scattering scenario include incorporating multiple englacial ice scattering layers and improving the way multiple baselines are combined

characteristic repeating earthquakes in an arc continent collision boundary zone the chihshang fault of eastern taiwan abstract creeping crustal faults often generate a large number of microearthquakes and less commonly they may also produce major earthquakes that rupture the brittle crust the chihshang fault in eastern taiwan is characterized by such behavior and has been known to undergo 2 3 cm yr surface creep making it one of the most active creeping thrust faults known in the world it gives an excellent opportunity to study how a creeping fault can generate large earthquakes however the understanding of fault behavior at depth in this area has been limited due to sparse sampling from seismic and geodetic stations in this study we determine and evaluate a population of repeating earthquakes to improve the understanding of deep fault deformation we propose a repeating sequence identification scheme in the region where the station coverage is sparse and one sided using this identification method we found 30 m 2 3 characteristic repeating sequences under the northern half of the chihshang fault at 7 23 km depth slip estimates from these sequences indicate an average slip rate of 3 cm yr which is consistent with the rate inferred from surface geodetic measurements we infer that the 30 km long chihshang fault is creeping along its northern half and locked in the south consistent with the occurrence of the 2003 ml 6 4 earthquake on the southern fault section

the lithobiontic ecological niche with special reference to microorganisms abstract revised terminology is proposed that describes the ecological niches of microorganisms within hard mineral substrates organisms attached to the external surfaces of the rock are termed epiliths while those in the interior of the rock are all termed endoliths the latter are called chasmoendoliths if they inhabit fissures in rocks cryptoendoliths if they dwell within structural cavities and euendoliths if they actively penetrate calcareous substrates

initial rupture of earthquakes in the 1995 ridgecrest california sequence close examination of the p waves from earthquakes ranging in size across several orders of magnitude shows that the shape of the initiation of the velocity waveforms is independent of the magnitude of the earthquake a model in which earthquakes of all sizes have similar rupture initiation can explain the data this suggests that it is difficult to estimate the eventual size of an earthquake from the initial portion of the waveform previously reported curvature seen in the beginning of some velocity waveforms can be largely explained as the effect of anelastic attenuation thus there is little evidence for a departure from models of simple rupture initiation that grow dynamically from a small region the results of this study indicate that any precursory radiation at seismic frequencies must emanate from a source region no larger than the equivalent of a m0 5 event i e a characteristic length of 10 m the size of the nucleation region for magnitude 0 to 5 earthquakes thus is not resolvable with the standard seismic instrumentation deployed in california

snow mapping in alpine regions with synthetic aperture radar active microwave sensors can discriminate snow from other surfaces in all weather conditions and their spatial resolution is compatible with the topographic variation in alpine regions using data acquired with the nasa airsar in the otztal alps in 1989 and 1991 the authors examine the usage of synthetic aperture radar sar to map snow and glacier covered areas by comparing polarimetric sar data to images from the landsat thematic mapper obtained under clear conditions one week after the sar flight the authors found that sar data at 5 3 ghz c band can discriminate between areas covered by snow from those that are ice free however they are less suited to discrimination of glacier ice from snow and rock the overall pixel by pixel accuracies 74 from vv polarization alone with topographic information 76 from polarimetric sar without any topographic information and 79 from polarimetric sar with topographic information are high enough to justify the use of sar as the data source in areas that are too cloud covered to obtain data from the thematic mapper this is especially true for snow discrimination where accuracies exceed 80 because mapping of a transient snow cover during a cloudy melt season is often difficult with an optical sensor the airsar survey was carried out in summer during a heavy rainstorm when the snow surfaces were unusually rough even better results for snow discrimination can be expected for mapping in the spring when snow is usually smoother

earthquakes as multiscale dynamic ruptures with heterogeneous fracture surface energy 1 we propose a model of the wide scale growth of dynamic rupture during an earthquake based on our multiscale simulation of a planar crack in a three dimensional homogeneous elastic space a simple slip weakening law governs the fracture friction processes and its characteristic parameters slip weakening distance and fracture surface energy have multiscale heterogeneous distributions we consider a set of randomly distributed circular patches whose diameter is proportional to the fracture surface energy each patch represents an asperity between irregular fault surfaces and the size number relation of the patches obeys power law statistics we assess rupture propagation from a small instability using a boundary integral equation method with a renormalization technique although most events stop shortly after their initiation some grow triggering neighboring patches of similar size small and large events show statistically self similar properties of rupture growth and stop spontaneously without requiring a special stopping mechanism the rupture velocity locally exceeds the shear wave speed but globally remains subshear speed due to the increase of the average fracture energy as the rupture grows the relation between size and frequency of events is a power law which is explained by the triggering probability between patches as a consequence of statistically self similar random triggering growth we observe a distinct main phase in seismic waves similar to those of natural earthquakes but we cannot estimate the final size of the event from the initial part of the seismic waves if this is true for the real earthquakes predicting the size of a future earthquake would be quite difficult

characterization of arctic sea ice thickness using high resolution spaceborne polarimetric sar data in this paper we have investigated the relationship between the depolarization effects and the wintertime sea ice thickness in the landfast ice region where smooth thick first year ice fyi and deformed old ice coexisted by using c and x band spaceborne polarimetric synthetic aperture radar sar data radarsat 2 and terrasar x we have found a strong correlation between the in situ sea ice thickness and the sar derived depolarization factors copolarized correlation and cross polarized ratio the observed relationships have demonstrated not only a categorical difference between fyi and multiyear ice myi but also a one to one continuity in the scatter plots rather than being clustered it clearly shows that the observed correlations are not merely from the categorical difference in scattering mechanism between fyi and myi and that there might exist a one to one relationship between thickness and depolarization factors at least in our deformed ice case this suggests that depolarization factors could be effective sar parameters in the estimation of wintertime sea ice thickness numerical model simulations explained some portions of the correlation by employing multiple scattering on the sea ice surface and volume scattering within the low density subsurface layer

radar polarimetry analysis tools and applications the authors have developed several techniques to analyze polarimetric radar data from the nasa jpl airborne sar for earth science applications the techniques determine the heterogeneity of scatterers with subregions optimize the return power from these areas and identify probable scattering mechanisms for each pixel in a radar image these techniques are applied to the discrimination and characterization of geologic surfaces and vegetation cover and it is found that their utility varies depending on the terrain type it is concluded that there are several classes of problems amenable to single frequency polarimetric data analysis including characterization of surface roughness and vegetation structure and estimation of vegetation density polarimetric radar remote sensing can thus be a useful tool for monitoring a set of earth science parameters

biomechanical and biochemical weathering of lichen encrusted granite textural controls on organic mineral interactions and deposition of silica rich layers the crustose lichen rhizocarpon geographicum weathers the lower devonian shap granite by both biomechanical and biochemical means biomechanical weathering is mediated by fungal hyphae that penetrate into the rock via intergranular boundaries at 0 002 0 003 mm year 1 once inside the granite hyphae exploit intragranular pores along cleavage and fracture planes in biotite alkali and plagioclase feldspar grains of biotite exposed at the lichen granite interface have been fragmented by biomechanical action in 122 years after an extended period of biomechanical weathering of 10 kyr outcrop surfaces sub mm sized fragments of biotite and plagioclase feldspar abound in lower parts of the lichen s thallus grains of biomechanically weathered biotite show the clearest evidence for biochemical weathering typically k and fe are leached from the biotite but other cations may also be removed leaving a silica dominated relic the silica rich remains of biotite and possibly also feldspar have been redistributed along the lichen granite interface forming a silica rich layer this silica rich material also cements fractures and pores beneath the interface alkali feldspars from outcrop surfaces have been weathered chemically as indicated by etch pits on cleavage surfaces and fractures but it is not obvious that lichen was involved in the dissolution the etch pits were probably formed during earlier phases of non biochemical weathering that widened intergranular and intragranular pores facilitating subsequent access of fungal hyphae into the granite despite evidence for biomechanical and biochemical weathering it is unlikely that colonisation of granite surfaces by r geographicum at shap significantly enhances their weathering rate relative to bare rock surfaces the lichen may actually retard weathering by protecting the surface from frost action binding fragmented mineral grains and depositing protective silica rich layers

measuring snow and glacier ice properties from satellite satellite remote sensing is a convenient tool for studying snow and glacier ice allowing us to conduct research over large and otherwise inaccessible areas this paper reviews various methods for measuring snow and glacier ice properties with satellite remote sensing these methods have been improving with the use of new satellite sensors like the synthetic aperture radar sar during the last decade leading to the development of new and powerful methods such as sar interferometry for glacier velocity digital elevation model generation of ice sheets or snow cover mapping some methods still try to overcome the limitations of present sensors but future satellites will have much increased capability for example the ability to measure the whole optical spectrum or sar sensors with multiple polarization or frequencies among the methods presented are the satellite derived determination of surface albedo snow extent snow volume snow grain size surface temperature glacier facies glacier velocities glacier extent and ice sheet topography in this review emphasis is put on the principles and theory of each satellite remote sensing method an extensive list of references with an emphasis on studies from the 1990s allows the reader to delve into specific topics

firn line detection on austre okstindbreen norway with airborne multipolarization sar we examine the ability of synthetic aperture radar sar to detect the equilibrium line on the glacier austre okstindbreen norway using multipolarization sar images in c and l band acquired with the electromagnetic institute of the technical university of denmark s airborne emisar sensor during the european multisensor airborne campaign emac 95 the late summer snowline approximating the equilibrium line cannot be seen on the sar images instead photographs from austre okstindbreen show that a distinct boundary visible on the c band sar images corresponds to the firn line created by old snow from many previous years this is better seen on the cross polarized sar images hv and vh which in general reveal more detail than the hh and vv polarized images we model the stratigraphy from net balance and glacier velocity data to calculate the firn line altitude fla modelled fla and the observed boundary are separated by 50 m in elevation but considering errors during co registration and modelling we conclude that the observed boundary on austre okstindbreen is the firn line monitoring fla rather than equilibrium line altitude ela for mass balance studies with remote sensing is therefore suggested

mapping seasonal snow with sir c x sar in mountainous areas abstract the objective of this study is to examine the capability of sir c x sar to map seasonal snow covers in alpine regions we develop two classification trees the first classifier can map snow and discriminate dry from wet snow but it requires a digital elevation model dem for radiometric terrain correction and reduction of the effect of local incidence angle the second classifer can map wet snow without using a dem we demonstrate some processing techniques that are necessary to discriminate wet snow from smooth bare surfaces and to discriminate dry snow from short vegetation for validation we compare our results with snow maps of both binary and snow fraction classifications obtained from the landsat thematic mapper tm at about the same time the sar is about 77 as accurate as the tm binary classification but it underestimates snow cover when compared with snow fraction classification with the major differences occurring for mixed pixels of snow and trees

scaling of earthquake rupture growth in the parkfield area self similar growth and suppression by the finite seismogenic layer 1 we propose a new framework on the scaling of earthquake rupture growth time history and we scale the moment rate and the cumulative moment functions of earthquakes over a wide magnitude range mw 1 7 6 0 in parkfield california the moment rate and the cumulative moment functions of the small and medium earthquakes mw 1 7 4 6 are derived by slip inversion analyses with the empirical green s function technique the moment rate functions of the investigated earthquakes except the mw 6 0 event are similar to each other increasing rapidly in the first half growth stage and decelerating in the latter half decline stage in the growth stage the cumulative moment functions are approximated by mo t nm 2 1017 t s 3 independent of the final size of the earthquakes the proportionality of the cumulative moment to the cube of time implies self similarity during earthquake rupture growth in the decline stage the cumulative moment function veers off the common rupture curve the mw 6 0 event also grows along the same rupture curve until 1 s after which the cumulative moment function is proportional to time from the onset itself this is because the finite seismogenic layer limits the vertical extent of dynamic rupture our method and results contribute to our understanding of earthquake source physics especially on earthquake rupture growth processes which may help to improve earthquake early warning techniques

classification of surface types using sir c x sar mount everest area tibet imaging radar is a promising tool for mapping snow and ice cover in alpine regions it combines a high resolution day or night all weather imaging capability with sensitivity to hydrologic and climatic snow and ice parameters we use the spaceborne imaging radar c x band synthetic aperture radar sir c x sar to map snow and glacial ice on the rugged north slope of mount everest from interferometrically derived digital elevation data we compute the terrain calibration factor and cosine of the local illumination angle we then process and terrain correct radar data sets acquired on april 16 1994 in addition to the spectral data we include surface slope to improve discrimination among several surface types these data sets are then used in a decision tree to generate an image classification this method is successful in identifying and mapping scree talus dry snow dry snow covered glacier wet snow covered glacier and rock covered glacier as corroborated by comparison with existing surface cover maps and other ancillary information application of the classification scheme to data acquired on october 7 of the same year yields accurate results for most surface types but underreports the extent of dry snow cover

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

polarimetric decomposition of l band polsar backscattering over the austfonna ice cap over the last 30 years the use of airborne and satellite remote sensing techniques has revolutionized glaciology through unequaled improvements in the scale and in the temporal and spatial resolutions of cryospheric observations in this sense the use of synthetic aperture radar sar configurations likely was the greatest advance of the past two decades in the monitoring of the earth s cryosphere this paper describes a novel polarimetric scattering model to interpret polarimetric sar polsar measurements of glaciers and ice sheets different scattering components are considered according to the specific glacier facies in order to infer physical parameters of the ice volume total backscattering is modeled as the incoherent sum of possible surface and volume contributions surface scattering is described using the x bragg model in order to account for roughness whereas clouds of spheroidal scatterers either prolates or oblates are considered to model volume scattering the model includes differential propagation effects related to firn anisotropy and is therefore able to interpret polarimetric phase differences often present in polsar data acquired over glaciers the developed model is used to interpret different scenarios imaged at l band in fully polarimetric mode by the e sar sensor of the german aerospace center dlr over test sites located on the austfonna ice cap svalbard norway as part of the icesar2007 campaign the obtained results are consistent with the reference information provided by the available ground measurements about the subsurface structure of the study area and encourage the use of dedicated scattering models for the different glacier zones

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

foreshocks and pre events associated with the nucleation of large earthquakes we propose a theoretical model which can explain the occurrence of foreshocks and pre events associated with the nucleation of large earthquakes we consider a broad weak zone with a locally strong part asperity on a fault plane in a two dimensional framework and examine the transition process from quasistatic nucleation to high speed rupture propagation through numerical simulations the dynamic rupture of the asperity occurs in three different manners as aseismic slip foreshock or pre event depending on the peak stress of the asperity in all cases the rupture of the asperity accelerates the nucleation of main rupture

rupture nucleations in the 1995 hyogo ken nanbu earthquake and its large aftershocks summary local seismograms of the hyogo ken nanbu earthquake m 7 2 and its largest aftershocks show that a slow rising initial phase precedes the main p phase high dynamic range short period seismograms of the foreshocks mainshock and aftershocks were recorded by the japan meteorological agency jma network and the net hyogo using these seismograms we investigate the initial rupture process of the mainshock and large aftershocks using an empirical green s function method the deconvolved moment rate function of the mainshock shows that it begins with a small pre event mw 4 0 then the moment releases gradually and after about 0 6 s it increases rapidly the first 0 7 s of the deconvolved moment rate functions are inverted to obtain the spatio temporal images of the initial rupture process the results show that at the hypocentral area less than 1 km from the hypocentre slip velocity rises slowly with a low peak in the surrounding area 1 km east and downward from the hypocentre slip velocity rises rapidly with a high peak it is also found that during the initial rupture process the slip velocity pulse grows continuously these observations are in accord with a theoretical model of the transition process from nucleation to high speed dynamic rupture in which slip velocity rises slowly at the nucleation zone we also analyse the initiation and the main dynamic rupture of large aftershocks spatio temporal images of the largest aftershocks m 5 1 and m 4 8 show that there is a clear initial rupture process with a low moment release and after about 0 2 s slip velocity increases rapidly we compare the initial rupture process of the mainshock with those of the large aftershocks m 4 0 5 1 the duration 0 6 s of the initial phase of the mainshock is longer than those 0 02 0 3 s of the large aftershocks furthermore the slip velocity of the initial rupture process of the mainshock is several times larger than those of the two largest aftershocks these results suggest that the mainshock starts in the region where the stress drop and fracture energy is higher

patterns of limestone and dolomite weathering by lichens and blue green algae and their palaeoclimatic significance abstract surface weathering of massive turonian limestones was studied along a transect from the judean mountains to the dead sea with mean annual rainfall ranging from 550 mm mediterranean zone to 100 mm desert in the mediterranean zone micro grooves 0 1 mm deep occur between colonies of endolithic lichens producing a pattern which looks like a jigsaw puzzle in the vicinity of the 300 mm isohyet there are no endolithic lichens instead the rock faces are entirely covered with blue green algae living in 0 1 to 0 3 mm deep pits similar algae carve pits and channels 10 to 30 mm deep in the area with 100 mm of rainfall remnants of the jigsaw puzzle like weathering characteristic for mediterranean conditions have repeatedly been observed on hard limestone in semi arid and arid zones these are interpreted as indicating more humid climatic conditions prevailing there in the past similarly fossil deep pitting and channelling observed in the mediterranean zone on rock surfaces protected from weathering are evidence of a former arid climate

shuttle imaging radar sir c x sar reveals near surface properties of the south patagonian icefield shuttle imaging radar c x band synthetic aperture radar sir c x sar views of the south patagonian icefield in southern chile and argentina demonstrate the ability of spaceborne multiparameter radar to detect climatically driven intra annual changes in the snow and ice conditions on glaciers the sir c x sar system aboard space shuttle endeavor acquired images during two 11 day missions in april and october 1994 the radar signatures of differing snow and ice conditions are distinctive and homogeneous over large areas of the ice fields the signatures are characterized mainly by 1 backscatter amplitude levels 2 relative amplitudes of the c and l bands wavelengths of 5 7 and 24 cm respectively and 3 polarization properties indicative of volumetric or surface scattering the radar signatures are interpreted by correlating the radar characteristics with elevation of the snow and ice surfaces and with changes in the meteorological conditions we are able to define four radar glacier zones zone a a relatively dry snow zone with dominant c band returns zone b a moderately wet snow zone with dominant l band returns zone c a wet snow zone with weak returns in all bands and zone d bare ice and or heavily crevassed surfaces with strong returns in all bands the spatial changes in the radar glacier zones between april and october are consistent with colder temperatures recorded in october producing drier snow conditions at lower elevations than in april

source parameters of a m4 8 and its accompanying repeating earthquakes off kamaishi ne japan implications for the hierarchical structure of asperities and earthquake cycle 1 we determine the source parameters of a m4 9 0 1 characteristic earthquake sequence and its accompanying microearthquakes at 50 km depth on the subduction plate boundary offshore of kamaishi ne japan the microearthquakes tend to occur more frequently in the latter half of the recurrence intervals of the m4 9 0 1 events our results show that the microearthquakes are repeating events and they are located not only around but also within the slip area for the 2001 m4 8 event from the hierarchical structure of slip areas and smaller stress drops for the microearthquakes compared to the m4 8 event we infer the small repeating earthquakes rupture relatively weak patches in and around the slip area for the m4 8 event and their activity reflects a stress concentration process and or change in frictional property healing at the area we also infer the patches for the m4 9 0 1 and other repeating earthquakes undergo aseismic slip during their interseismic period

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

pre and postseismic slow slip surrounding the 2011 tohoku oki earthquake rupture abstract slow aseismic slip that accommodates part of the long term plate motion on subduction megathrusts is thought to be strongly related to the occurrence of large earthquakes on the same fault zone however the temporal evolution and spatial distribution of the aseismic slip before major earthquakes and of accelerated postseismic afterslip are largely unconstrained we estimate cumulative offsets of small repeating earthquakes that are interpreted to reflect the in situ aseismic slip history on the subduction zone offshore northeastern japan these data reveal contrasting aseismic slip patterns between the coseismic rupture area of the mw 9 0 tohoku oki earthquake and surrounding portions of the subduction thrust the rupture area is characterised by low and variable slip rates before 2008 and the slip stopped almost completely after the earthquake the region surrounding the rupture area exhibited higher aseismic fault slip rates before the earthquake and clear postseismic slip of up to 1 6 m within 9 months following the main shock the frictional fault properties and complete relief of ambient stress in the central rupture zone of the main shock probably control the observed distribution the postseismic slip shows a more abrupt increase in the region closer to the source suggesting outwards propagation of afterslip small but distinct increases in the slip rate in the 3 yr before the earthquake near the area of large coseismic slip suggests preseismic unfastening of the locked area in the last stage of the earthquake cycle

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

seasonal and short term variability of multifrequency polarimetric radar backscatter of alpine terrain from sir c x sar and airsar data signatures of glaciated and ice free areas were analyzed from polarimetric sar data at c l and p band and single polarization x band data the data base includes an airsar scene from june 25 1991 and sir c x sar images from april and october 1994 srl 1 and srl 2 acquired over the high alpine test site o spl uml tztal in austria the environmental conditions were different at the time of the three experiments ground measurements meteorological observations and backscattering modeling are the basis for interpreting the backscattering signatures seasonal differences are due mainly to the presence or absence of snow and due to changes of its properties short term variations of snow conditions can be monitored at c and x band for unglaciated areas the surface roughness has a dominant influence on backscattering in all seasons the dependence of the mean backscattering and correlation coefficients on the incidence angle was analyzed spectral and depolarization ratios and the magnitude of the hhvv correlation coefficient were selected as components of the multidimensional feature vector for studying the target separability good separability was found between the accumulation and ablation areas on the glaciers whereas on ice free areas the dominance of surface roughness limits the discrimination of different surface types short term variations of backscattering have significant impact for the classification of accumulation and ablation areas on glaciers as verified by comparisons with field data

limestone weathering rates accelerated by micron scale grain detachment the weathering of carbonate rocks plays a critical role in the evolution of landscapes the erosion of buildings and monuments and the global scale shifting of carbon from the atmosphere to the ocean chemical dissolution is often assumed to govern the rates of weathering of carbonate rocks although some studies have suggested that mechanical erosion could also play an important role quantifying the rates of the different processes has proved challenging in part due to the high degree of variability encountered across different scales in both field and laboratory conditions to constrain the rates and mechanisms controlling long term limestone weathering we analyze a lidar scan of the western wall a roman period edifice located in jerusalem we find that extreme erosion rates in fine grained micritic limestone blocks are as much as two orders of magnitude higher than the average rates estimated for coarse grained limestone blocks at the same site atomic force microscope imaging of dissolving micritic limestone suggests that these elevated reaction rates are likely to be the result of rapid dissolution along micron scale grain boundaries followed by mechanical detachment of tiny particles from the surface our analysis indicates that such grain detachment could be the dominant erosional mode for fine grained carbonate rocks in many regions on earth

seismic cycles and earthquake predictability on east pacific rise transform faults the concept of a seismic cycle where the stress on a fault repeatedly builds up over a long period of time and then is rapidly released in a large earthquake influences studies of both the basic physics of faulting and applied research aimed at estimating earthquake hazards this hypothesis suggests that large earthquakes might be quasi periodic and that the probability of a particular portion of a fault rupturing twice in quick succession should be low however this basic hypothesis has been difficult to verify owing to the long repeat times of the largest earthquakes on most faults east pacific rise epr transform faults are an advantageous location to evaluate the seismic cycle hypothesis owing to their fast slip rates and the moderate size m w 6 of their largest earthquakes using surface wave based determinations of the relative separations between earthquake centroids i document 16 pairs of m w 5 5 events that had overlapping ruptures the distribution of interevent times for these pairs is tightly clustered around 5 yr with a coefficient of variation 0 2 indicating that quasi periodicity may be prevalent for the largest events on these faults moreover i find no pairs of overlapping m w 5 5 6 2 earthquakes separated by less than 50 cm of elapsed plate motion indicating that the two basic features of the seismic cycle hypothesis are evident in the timing of large epr transform mainshocks i have also confirmed earlier results demonstrating a high degree of short term predictability of epr mainshocks by combining teleseismic and hydroacoustic earthquake catalogs thus there appears to be a high degree of both short and long term predictability on epr transforms

implications of a composite source model and seismic wave attenuation for the observed simplicity of small earthquakes and reported duration of earthquake initiation phase an examination of p waves recorded on near source velocity seismograms generally shows that most small earthquakes mw 2 to 3 are simple on the other hand larger earthquakes mw 4 are most often complex the simplicity of the seismograms of mw 2 to 3 events may reflect the simplicity of the source and hence may imply that smaller and larger earthquakes are not self similar or may be a consequence of attenuation of seismic waves to test whether the attenuation is the cause we generated synthetic p wave seismograms from a composite circular source model in which subevent rupture areas are assumed to follow a power law distribution the rupture of an event is assumed to initiate at a random point on the fault and to propagate with a uniform speed as the rupture front reaches the center of a subevent patch all of which are circular a p pulse is radiated that is calculated from the kinematic source model of sato and hirasawa 1973 synthetic p wave seismograms which are all complex are then convolved with an attenuation operator for different values of t the results show that the observed simplicity of small events mw 2 to 3 may be entirely explained by attenuation if t 0 02 sec the composite source model predicts that the average time delay between the initiation of the rupture and the rupture of the largest patch scales as m 1 3 such that log 1 3 log m 8 462 this relation is very similar to that reported by umeda et al 1996 between m and the observed time difference between the initiation of the rupture and the rupture of the bright spot it roughly agrees with the relation between m and the duration of the initiation phase reported by ellsworth and beroza 1995 and beroza and ellsworth 1996 the relation also fits surprisingly well the data on duration of slow initial phase t sip and m reported by iio 1995 one possible explanation of this agreement may be that the composite source model which is essentially the cascade model successfully captures the evolution of the earthquake source process and that the rupture initiation and the abrupt increase in the velocity amplitude observed on seismograms by previous researchers roughly corresponds to the rupture of the first subevent and the breaking of the largest subevent in the composite source model

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

applications of bacterial carbonatogenesis to the protection and regeneration of limestones in buildings and historic patrimony abstract the ability of the so called carbonatogenic bacteria may be used for producing surficial protecting coatings biocalcin on limestones buildings monuments and statuary this is the concept of biomineralisation laboratory experiments were undertaken in order to choose the most active bacterial strains and to improve the composition of the nutritional media suitable for stimulating the nitrogen cycle metabolic pathways which are the only ones to be used in aerobic and or microaerophilic conditions life size experiments subsequent measurements and observations show that this natural process of biomineralisation is feasible within the frame of industrial constraints this concept of further developments includes the creation of patinas and the manufacturing of biological mortars and cements which were also improved in the laboratory the biomineralisation recreates a material that is remarkably similar to the limestone substrate because it uses natural microbial mediation which follows the same natural processes that formed many limestones

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

limestone biopitting in coastal settings a spatial morphometric sem and molecular microbiology sequencing study in the mallorca rocky coast balearic islands western mediterranean abstract biological agency on rock coasts has been widely recognised over recent decades this study deals with the distribution and morphometric characteristics of microforms features developed by cyanobacteria rivularia sp on coastal limestone outcrops these coastal microforms known as biopits have a small rounded basin shape a few millimetres in size environmental and geological data were collected from 100 random rock surface spots from punta des farallo cape mallorca western mediterranean from which major controls on the spatial distribution of biopits were established additionally morphological data on 382 biopits determined the diagnostic morphometry of these features and their enlargement mechanisms the results indicated that biopits exhibit a preferential location in shaded exposures and sheltered areas from prevailing winds and waves avoiding direct insolation and desiccation other major controls on these microforms location and development were variables such as the rock surface slope and the distance to the coast i e influence of splash and spray shadow spots displayed higher biopits density than other locations according to the patterns determined by environmental and geomorphological factors at the study site morphometric analyses showed that biopits have a width twice their depth the average width of the microforms was 6 49 2 40 mm and the average depth 2 46 1 09 mm most frequently the width depth ratio was 2 or larger this characteristic shape ratio was an additional factor that plays a role in maintaining the necessary humidity for microorganisms associated with biopits

spectral signature of alpine snow cover from the landsat thematic mapper mapping of snow and estimation of snow characteristics from satellite remote sensing data require that we distinguish snow from other surface cover and from clouds and compensate for the effects of the atmosphere and rugged terrain the spectral signature of the snowpack is calculated from a radiative transfer model accounting for scattering and absorption by the ice grains water inclusions and particulates in interpreting the spectral reflectance measured from the thematic mapper or from any other satellite we need to account for topographic effects without requiring that satellite data be precisely registered to digital elevation data because the poor quality of most digital elevation data introduces considerable noise into calculations of slope and azimuth for a range of snow types atmospheric profiles and topographic illumination conditions i estimate typical spectral signatures for the landsat thematic mapper tm images of the southern sierra nevada are analyzed to distinguish several classes of snow from other surface covers snow can be reliably distinguished from other surfaces and from clouds at all sun angles encountered in the mid latitudes in tm band 1 or 2 snow is brighter than other natural surfaces and in band 5 clouds are usually much more reflective than snow therefore the intersection of the following criteria maps the snow cover planetary reflectance rp in tm band 1 is greater than about 0 16 rp tm5 is less than about 0 2 the normalized band 2 5 difference rp tm2 rp tm5 rp tm2 rp tm5 is greater than about 0 4 large surface grain sizes can be distinguished from areas where the grain size is finer at the snow surface using tm bands 2 4 and 5 because of saturation in tm band 1 estimation of the degree of contamination by absorbing aerosols is not feasible rp tm2 rp tm5 rp tm2 rp tm5 is

effects of shear heating slip induced dilatancy and fluid flow on diversity of 1 d dynamic earthquake slip we theoretically study effects of thermal pressurization slip induced dilatancy and fluid flow on slip evolution assuming 1 d fault model we generalize the analysis made in our former papers by introducing an upper limit for the inelastic porosity evolution the expression for nondimensional parameter ta which is related to the upper limit is derived in the present paper we find that the parameter ta together with two nondimensional parameters su and su derived in our former papers completely determine the qualitative nature of system behavior once the initial condition is given for example changes in su and ta generate two qualitatively different slip behaviors both of which can be models for ordinary earthquake the slip is accelerated with time after experiencing an initial deceleration in one of them while the slip ceases after monotonic deceleration in the other the initial slip deceleration observed in the former case may be interpreted as a dynamic event preceding the main shock in seismological observations we mathematically derive the expression for the ranges of the nondimensional parameters in which the above two slip behaviors appear slow earthquakes are also modeled in the same framework and nonzero values of the nondimensional parameter su together with relatively large values of su and ta are found to contribute to the generation of such slow earthquakes the mathematical framework constructed here can be applied to understanding of some other natural phenomena such as a kind of reaction diffusion system

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

frequent observations of identical onsets of large and small earthquakes every gigantic earthquake begins as a tiny rock failure at almost a point followed by successive slip of the complex fault system before radiating strong shaking from a vast rupture area extending over hundreds of kilometres whether the growth process of the rupture of a large earthquake is predictable and whether it produces observable signatures different from that of smaller events1 5 are fundamental questions related to the potential for earthquake early warning and probabilistic forecasting inspired by a recent discovery that large earthquakes might have seismic waves and probably rupture processes that are almost identical to those of smaller events6 8 we show that such similarity characterized by large cross correlation is a common feature of earthquakes in the tohoku hokkaido subduction zone japan a systematic comparison of 15 years of high sensitivity seismograph records for approximately 100 000 events reveals 80 extremely similar and 390 very similar pairs of large moment magnitude m 4 5 and small m 4 0 earthquakes co located within about 100 metres an extremely high similarity is observed for pairs of subduction type earthquakes 170 of 899 large events separated by a long period of up to 15 years whereas for pairs of other types of large earthquakes only the foreshocks and aftershocks are similar this frequently occurring similarity between different sized subduction type earthquakes suggests repeated cascading rupture processes in a widespread hierarchical structure9 12 along the plate interface and indicates a specific but probabilistically limited predictability of the final size of the earthquake that is the location and a set of possible sizes of an earthquake are well predicted but its final size is not at all well constrained analysis of a dataset of high sensitivity tohoku hokkaido seismograph records shows that pairs of subduction type earthquakes of different sizes have very similar initial characteristics implying that the final size of an earthquake cannot be reliably predicted from these

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

foreshock sequence of the 1992 landers california earthquake and its implications for earthquake nucleation the june 28 1992 landers california earthquake mw 7 3 was preceded for about 7 hours by a foreshock sequence consisting of at least 28 events in this study we examine the geometry and temporal development of the foreshocks using high precision locations based on cross correlation of waveforms recorded at nearby stations by aligning waveforms rather than trying to obtain travel time picks for each event independently we are able to improve the timing accuracy greatly and to make very accurate travel time picks even for emergent arrivals we perform a joint relocation using the improved travel times and reduce the relative location errors to less than 100 m horizontally and less than 200 m vertically with the improved locations the geometry of the foreshock sequence becomes clear the landers foreshocks occurred at a right step of about 500 m in the mainshock fault plane the nucleation zone as defined by the foreshock sequence is southeast trending to the south and nearly north trending to the north of the right step this geometry is confirmed by the focal mechanisms of the foreshock sequence which are right lateral and follow the trend as determined by the foreshock locations on the two straight segments of the fault and are rotated clockwise for foreshocks that occur within the step the extent of the foreshock sequence is approximately 1 km both vertically and horizontally modeling of the coulomb stress changes due to all previous foreshocks indicates that the foreshocks probably did not trigger each other this result is particularly clear for the mw 4 4 immediate foreshock since stress transfer in the sequence appears not to have played a significant role in its development we infer an underlying aseismic nucleation process probably aseismic creep other studies have shown that earthquake nucleation may be controlled by fault zone irregularities this appears to be true in the case of the landers earthquake although the size of the irregularity is so small that it is not detectable by standard location techniques

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

circular polarization radar properties of high altitude ice western kunlun shan and central andes full polarization synthetic aperture radar images of high altitude glaciers and ice fields in the western kunlun shan of tibet and the central andes near santiago chile made with the shuttle imaging radar display regions with circular polarization ratios c in excess of unity the mountainous topography at both locales allows reconstruction of the angular scattering behavior the behavior is very similar to that displayed by greenland s percolation zone glaciologic evidence from the tibetan site confirms ice pipes and lenses embedded in the firn which have been identified as the scatterers producing c 1 in greenland this demonstrates that the cold snow percolation facies radar signature exists outside of greenland the greenland radar behavior had been suggested as an analogue for that of the icy galilean satellites we like previous workers find that the near nadir backscatter is too specular to be considered analogous to that of the jovian moons we also present a crevasse region in tibet that exhibits c 1 and a possible detection of the ice substrate of a rock covered glacier in the andes

complexity in earthquake sequences controlled by multiscale heterogeneity in fault fracture energy 1 a series of dynamic rupture events under constant tectonic loading is simulated on a fault with multiscale heterogeneity and a stochastic rupture initiation process the fracture energy of the fault plane is assumed to have multiscale heterogeneous distribution using fractal circular patches the stochastic rupture initiation process as a function of the accumulated stress is introduced in order to take account of unknown smaller scale heterogeneity and variability five realizations of a statistical spatial distribution of fracture energy fault heterogeneity maps are tested for the simulations of earthquake sequences during a few seismic cycles the diversity of earthquake sequences is principally controlled by the spatial distribution of the patches the effect of dynamic rupture appears in the residual stress after the characteristic events because of their directivity and this localizes the subsequent sequences although the characteristic earthquakes occur rather regularly in time and similarly in different seismic cycles some irregular behavior is found based on the heterogeneity maps and the randomness of the preceding earthquake sequence leading to a visible anomaly in the seismicity such anomalies are not predicable but understandable through the analysis of the considered earthquakes during the cycle the similarity and the diversity simulated in this study governed by the structure of an inherent distribution of multiscale heterogeneity suggest the importance of the pre existing heterogeneity field along the fault for the appearance of earthquake sequences including those that are characteristic

the effect of topography on sar calibration during normal synthetic aperture radar sar processing a flat earth is assumed when performing radiometric corrections such as antenna pattern and scattering area removal the authors examine the effects of topographic variations on these corrections local slopes will cause the actual scattering area to be different from that calculated using the flat earth assumption it is shown that this effect may easily cause calibration errors larger than a decibel ignoring the topography during antenna pattern removal may also introduce errors of several decibels in the case of airborne systems the effect of topography on antenna pattern removal is expected to be negligible for spaceborne sars the authors show how these effects can be taken into account if a digital elevation model is available for the imaged area the errors are quantified for two different types of terrain a moderate relief area near tombstone az and a high relief area near oetztal in the austrian alps the authors show errors for two well known radar systems the c band ers 1 spaceborne radar system and the three frequency nasa jpl airborne sar system airsar

partitioned fault movement and aftershock triggering evidence for fault interactions during the 2017 mw 5 4 pohang earthquake south korea

polarimetric decomposition over glacier ice using long wavelength airborne polsar in recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research however due to the medium s complexity sar backscattering from ice remains poorly understood including the relative importance of scattering from surface and volume layers and also dependences on frequency and glacier zone extreme weather conditions can result in quickly changing surface conditions influencing backscatter signatures while leaving the underlying volume of interest unchanged surface and volume components must thus be separated in order to infer information regarding the properties of the ice volume this paper describes a three component scattering model to decompose polarimetric sar polsar images of glacier ice total backscatter is modeled as the incoherent summation of surface volume and sastrugi wind induced feature components the proposed model adapts and extends the freeman and durden decomposition for an ice volume scenario in which the volume is a dielectric medium forms of the model for both random and oriented volumes are considered and a new oriented sastrugi component is introduced which is able to explain backscatter behavior between different winter scenes validation is performed with airborne polsar data at l and p band collected using the e sar system of the german aerospace center over the austfonna ice cap in svalbard norway as part of the icesar campaign

glacier velocity estimation by means of a polarimetric similarity measure the contribution of polarimetric synthetic aperture radar polsar images compared with that of single channel sar images in terms of temporal scene characterization has been found and described to add valuable information in the literature however despite a number of recent studies focusing on single polarized glacier monitoring the potential of polarimetry to estimate the surface velocity of glaciers has not been explored due to the complex mechanism of polarization through glacier snow in this paper a new approach to the problem of monitoring glacier surface velocity is proposed by means of temporal polsar images using a basic concept from information theory i e mutual information mi the proposed polarimetric tracking method applies the mi to measure the statistical dependence between temporal polarimetric images which is assumed to be maximum if the images are geometrically aligned since the proposed polarimetric tracking method is very powerful and general it can be implemented into any kind of multivariate remote sensing data such as multichannel optical and single channel sar images the proposed polarimetric tracking is then used to retrieve the surface velocity of the aletsch glacier in switzerland and the inylchek glacier in kyrgyzstan with two different sar sensors the experimental sar airborne l band fully polarimetric and envisat c band single polarized systems respectively the effect of the number of channels polarimetry into tracking investigations demonstrated that the presence of snow as expected affects the location of the phase center in different polarization and frequency channels as for the glacier tracking with temporal hh compared to temporal vv channels in this paper it is shown how it is possible to optimize these two different contributions considering the multichannel sar statistics

high amplitude seismic waves radiated from the bright spot of an earthquake abstract in the source region of a large shallow earthquake there is likely to be a small spot characterized by the production of high accelerations and a gap in the aftershocks on the seismograms of most large shallow earthquakes and on some seismograms of moderate main shocks two types of p waves may be detected the relatively low amplitude waves following phase p 1 and the predominant high frequency waves following phase p 2 the duration of the seismic waves following phase p 1 the p 1 p 2 time increases proportionately with the earthquake magnitude this fact strongly suggests that the preliminary rupture period is closely related to the radiation of the predominant high frequency seismic waves to explain the above observation the shear strain waves radiated from a moving rupture are calculated because the seismic wave velocity is generally higher than the rupture propagation velocity maximum shear strains by seismic waves usually precede the rupture front if the total shear strain which is equal to the static pre earthquake shear strain plus dynamic shear strain excited by seismic waves exceeds the critical shear strain 10 4 the secondary ruptures break out in the forward direction from the initial rupture the rupture processes of large or moderate earthquakes occur in two stages one is the initiation of rupture corresponding to phase p 1 and the other is the development of secondary ruptures triggered by seismic shear strain waves the latter process generates an earthquake bright spot which radiates high amplitude seismic waves

large nucleation before large earthquakes is sometimes skipped due to cascade up implications from a rate and state simulation of faults with hierarchical asperities 1 does a large earthquake have a large quasi static preparation a hierarchical asperity model in which a large tough patch patch l contains smaller fragile patches patch s enables a large earthquake to start with only small preparation because of cascade up rupture growth we realized such a model in a rate and state framework by heterogeneous distributions of the state evolution distance and its consequences are investigated by earthquake sequence simulations focus is put on elementary processes the interaction between two scales one patch l containing one patch s is simulated with their size ratio as a parameter if patch s is larger than the nucleation size of patch l the system falls into a limit cycle consisting of only one earthquake that starts with patch s nucleation and grows dynamically to rupture entire patch l if patch s is considerably smaller than the nucleation size of patch l small earthquakes never dynamically cascade up and the large earthquakes are initiated by large quasi static nucleation in between large earthquakes start in various ways by large nucleation dynamic cascade up or delayed cascade up in the final stage of quasi static nucleation the preseismic moment release rate increases roughly inversely proportional to the time to failure tf with its amplitude depending on the nucleation size for a patch s rupture to cascade up strength in the adjacent region must have been reduced manifested by a higher creep velocity before the patch s nucleation starts following 1 tf acceleration large nucleation sometimes has a precursory small earthquake characterized by larger afterslip than nonprecursory ones