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

simultaneous seismic and magnetic measurements in the low noise underground laboratory lsbb of rustrel france during the 2001 january 26 indian earthquake since the decommission of the underground launching control room of the ground based component of the french nuclear missile system the whole installation has been turned into a cross disciplinary underground laboratory the lsbb is a unique low noise underground laboratory because of its initial military conception and its location in the regional park of luberon far from large cities industry and heavy traffic the deepest point is 500 m below the surface at this depth a huge and non conventional shielded cylindrical capsule is installed with no metal 1268 m 3 in volume with a residual electromagnetic noise lower than 2 ft hz 1 2 above 10 hz as a result fluctuations of the earth s magnetic field under 10 hz can be recorded at a very low noise level with a low t c squid 3 d magnetometer taking advantage of the main gallery topology a broad band underground seismic array has been deployed since 2001 an analysis of data recorded simultaneously by the seismic underground array and by the magnetometer sensors during the indian earthquake of 2001 january 26 is presented evidence of a magnetic field perturbation induced by the seismic waves at teleseismic distance 6250 km is supported by a polarization analysis of seismic and magnetic signals spectral analysis shows specific frequency bands of perturbation related to physical processes such as ground water flow acceleration within the mountain structure

identifying space time clustering properties of the 1983 1997 irpinia basilicata southern italy seismicity abstract the fractality of the earthquake sequence 1983 1997 of irpinia basilicata southern italy one of the most seismically active regions of the mediterranean area has been analysed by temporal and spatial fractal tools the fractal exponent estimated by the allan factor method characterises the time clustering behaviour of the set of earthquakes while the correlation dimension d c calculated by means of the correlation integral method gives information on the space clustering behaviour of the sequence of seismic events analysing the variations of both the parameters we recognised the presence of a strong space time clusterisation associated with the major events that occurred in the investigated area

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

rupture dimensions of the 1998 antarctic earthquake from low frequency waves we inverted frequency dependent phase and amplitude measurements from 1st orbit rayleigh waves at global stations for the 1st and 2nd degree polynomial moments of the stress glut rate tensor the higher moments of the slip rate distribution determine the fault plane and approximate rupture dimensions the results show strong rupture propagation to the west with an average velocity of the instantaneous centroid of 3 6 1 km s the rupture had a characteristic length of 178 46 km in the east west direction and a characteristic duration of 48 2 s the results are consistent with unilateral rupture on the east west fault plane of the focal mechanism and rule out significant rupture on the north south nodal plane

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

analysis of the temporal occurrence of seismicity at deception island antarctica a nonlinear approach deception island is characterized by small magnitude local events with constant energy flux and very low stress drop to obtain information about its origin an interevent time series of 546 events corresponding to an observational period of two month has been analyzed from a statistical point of view data satisfies a weibull distribution and presents clustering a rescaled range analysis reveals that data are not independent i e have memory and the correlation dimension saturates at 2 2 as a consequence the system can be modeled as a nonlinear iterative equation with three degrees of freedom that presents chaotic behavior taking into account that the average interevent time is of the order of 130 minutes too short to be only due to tectonic activity the above results indicate that some other mechanism may coexist with the regional tectonic one according to several geological and geophysical observations we suggest that most of the local events may be originated by pressure waves generated by a sudden change of phase of sea and fresh water infiltrated into the main fractures and faults and also from shallow and confined water saturated layers

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

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

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

fractal analysis of ulf geomagnetic data associated with the guam earthquake on august 8 1993 this paper presents a fractal analysis of the ulf electromagnetic data obtained at guam observatory during a strong ms 8 0 earthquake occurred on august 8 1993 near the guam island we have already reported the presence of seismogenic ulf emissions for this quake hayakawa et al grl 1996 the chosen period covered four months before and two months after the earthquake it was found that the spectrum of emissions at noon exhibited a power law behavior f which is typical for self organized critical dynamics the slope of the spectrum in the noon sector fluctuates in a range from 2 5 to 0 7 with a tendency to gradually decrease during the process of the earthquake preparation we consider this to be a candidate for a precursory signature the similar effect was found for the night sector we suggest that the focal zone was at the critical stage of self organized criticality process before the quake related to active microfracturing processes followed by the generation of ulf emissions as we detected

monitoring resistivity change in parkfield california 1988 1995 continuous electric field measurements from 1988 1995 with a telluric array straddling the san andreas fault in parkfield california have been analyzed for changes in electrical resistivity associated with the four largest mb 4 0 local earthquakes and three larger but more distant california earthquakes 1989 loma prieta 1992 landers 1994 northridge treatment of the propagation of errors through the analysis process yields formal estimates of the uncertainties in the results and thus a definition of anomalous variations based on statistical confidence statistically significant variations of the telluric coefficients were associated with none of the four local earthquakes and none of the california earthquakes an obvious but mistaken conclusion from this disappointing result is that resistivity changes do not occur prior to earthquakes previous observations in both the field and laboratory have shown that they do occur a more likely explanation of the current result is that the telluric array is not sufficiently sensitive to resistivity changes associated with such small earthquakes the next parkfield earthquake while overdue should be of sufficient magnitude to test this explanation results from this experiment have shown the need for continuous redundant measurements in precursory monitoring studies

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

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

geoelectric signals in china and the earthquake generation process we present original apparent resistivity records for stations located in the chinese provinces of hebei and sichuan along with seismicity patterns fault maps and limited hydrologic data these records are part of a 30 year database of geoelectric signals that have been recorded in china by a nationwide network of more than 100 stations set up by the state seismological bureau of the people s republic of china the database includes the time period during which the m 7 8 1976 tangshan and m 7 2 1976 songpan earthquakes occurred resistivity data recorded in and around the epicentral region of the tangshan event show coherent changes both temporal and in areal distribution years and months before and after the earthquakes a regional change in water table occurred more than 3 years prior to the tangshan earthquake the resistivity and water table signals appear to correlate in the 2 to 3 year period prior to the earthquake rainfall records from the region around tangshan extending to the cities of beijing and tianjin do not appear to account for the resistivity changes regional seismicity and active fault patterns in north china indicate that deformation occurs mainly along the borders of large tectonic blocks the source region for the geoelectric signals appears to lie within a large shear zone at the edge of a tectonic block undergoing rotation the tangshan epicentral area is thus only part of a larger zone of deformation we suggest that dilational strain associated with the opening of fractures may lower resistivity and water table for shallow crustal depths such as those monitored by the chinese geoelectric network dilation and resistivity changes are expected to begin at stress levels well below the peak values of the seismic cycle our study suggests that in some cases the areal extent of geoelectric signals may be significantly larger than that of the eventual earthquake source dimension the chinese geoelectric database offers an opportunity to improve our understanding of possible geoelectric precursors to earthquakes

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

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

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

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

1 fα fluctuations in geoelectrical signals observed in a seismic area of southern italy abstract recent studies have shown that many natural systems display temporal fluctuations with long range power law correlations suggesting a fractal geometry of the underlying dynamical system four geoelectrical time series measured in a seismic area of southern italy are investigated by means of spectral tools in order to evidence the existence of power law correlations results show the scaling behaviour for all the signals recorded pointing to the presence of fractal features expressing a long term correlation with scaling exponents which indicate stabilizing mechanisms furthermore our findings suggest an observational evidence of correlations between the variation of parameters describing the temporal fluctuations of geoelectrical signals and earthquakes that occurred in the area investigated

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

a new approach to investigate the correlation between geoelectrical time fluctuations and earthquakes in a seismic area of southern italy we propose a new approach to investigate the possible correlation between electrical signals and earthquakes good correlation has been found between the spectral power law exponent of geoelectrical signals and the hurst exponent of the seismicity of the area investigated a tendency of both parameters to converge toward unity typical of self organized critical dynamics is evident before the occurrence of the major event recorded in the area during the observation period

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

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

a physical model for the precursory magnetic anomalies of the m5 4 alum rock and m6 0 parkfield earthquakes here we propose an alternative physical model based on the concept of criticality for the explanation of the observed magnetic signals prior to the m6 0 parkfield and the m5 4 alum rock earthquakes motivated by an analogous experience from major earthquakes in greece where both magnetic field variations and seismic electric signals were also recorded few weeks before the main shock we suggest that in all these cases similar dynamic processes characterized by critical behaviour should govern the corresponding pre focal areas when the relevant precursory signals emerged

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

an alternative approach to reveal critical behaviour in the case of the mw 6 3 aquila earthquake an independent approach based on a power law relation interconnecting the lead time of precursory signals and the stress drop of forthcoming earthquake confirms the reported evidence that the observed magnetic field anomaly and consequently according to maxwell s laws electric field anomaly prior to mw 6 3 aquila earthquake in 2009 exhibit features of criticality precisely by inserting the data from aquila earthquake in this power law we get an exponent 0 329 which is in excellent agreement with previously found ones and falls within the range values 0 3 0 4 for critical exponents for fracture this fact implies that upon the initiation of the observed magnetic field anomaly and the associated electric signal prior to aquila earthquake the prefocal area enters into a critical stage where nonlinear dynamic processes typical behaviour of a system close to criticality prevail

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

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

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

characteristics of electromagnetic noise in the ioannina region greece a possible origin for so called seismic electric signal ses the study of electromagnetic noise in the ioannina region nw greece shows the existence of long transient electric signals duration 10 s without measurable correlated magnetic signals as is the case for seismic electric signal ses observed in the van network of short term earthquake prediction our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the ioannina region this origin can be clearly ascertained from simultaneous observation at stations in direct sight of the transmitters of four electromagnetic components two electric and two magnetic in a broad band of frequencies 10 3 10 hz relying on these observations it is proposed that the april 18 and 19 1995 electric signals interpreted by the van group as ses precursors to the may 13 kozani earthquake are due to some transmitter located far to the north of the ioa station of the van network the transmitters of this area would be of digital type as is increasingly common in radio telecommunication networks we believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals

ulf electromagnetic precursors for an earthquake at biak indonesia on february 17 1996 ulf electromagnetic emissions associated with a large earthquake occurred at biak island indonesia at 5h 59m ut on february 17 1996 magnitude mw 8 2 and depth 20 km from usgs catalog have been investigated on the basis of ulf magnetic observations at two stations biak and darwin in australia about 1 200 km apart though a simple analysis of magnetic field intensity horizontal and vertical magnetic field components at both stations was found to be closely correlated with geomagnetic kp activity a detailed analysis of the difference of h and z components at the two stations the polarization analysis z h and fractal analysis frequency spectrum slope at these two stations has yielded that the ulf emissions in the frequency range from 5 mhz to 30 mhz about 1 5 1 0 months before the quake are likely to be a precursory signature of the quake with its intensity on the order of 0 2 0 3 nt

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

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

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

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

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

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