earthquake rupture complexity due to dynamic nucleation and interaction of subsidiary faults we numerically study the dynamic interaction of propagating cracks it is assumed that propagating cracks can nucleate and drive subsidiary cracks because of shear strain enhancement near the propagating crack tips the critical strain fracture criterion is assumed in the analysis intense interaction is expected to occur among the cracks all the cracks are assumed to be parallel and antiplane strain deformation is assumed in the computation

complex source processes and the interaction of moderate earthquakes during the earthquake swarm in the hida mountains japan 1998 abstract this paper presents a set of detailed source models of 18 moderate m4 5 earthquakes that were part of the swarm activity beneath the hida mountains in central japan in 1998 to reveal the detailed rupture process this study uses a waveform inversion procedure with the empirical green function egf most of our models show a complicated rupture process that includes several separate rupture areas and that involves ruptures that in some events seem to repeat at almost the same location in our models we measured as characteristic values the maximums of slip slip rate stress drop and average rupture propagation velocity in comparison with the models for larger events determined by similar methods the maximum slip scales with the cubic squares of the seismic moment for large stress drop events only the slip rate has an upper limit of about 1 2 m s and the stress drop is distributed widely from 1 to 50 mpa the average stress drops estimated using the corner frequency are almost uniform at about 1 mpa the first event in each swarm cluster tends to have a large maximum stress drop which reflects the change in the stress field during swarm activity the average rupture velocity determined by the least squares method is relatively slow and shows a negative relationship with the maximum stress drop this finding cannot be explained by simple crack models and instead suggests a very complicated mechanism like the interactive fault system the interaction between the slip areas of neighbor events resulted in a non overlapping slip distribution this finding indicates that previous rupture areas restrict the size and location of later events even in such complex swarm activities

dynamic nucleation process of shallow earthquake faulting in a fault zone two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes low frequency and low amplitude waves following the onset of a p wave p1 are interrupted by the arrival of the second impulsive phase p2 enriched with high frequency components this observation suggests that a large shallow earthquake involves two qualitatively different stages of rupture at its nucleation we propose a theoretical model that can naturally explain the above nucleation behaviour the model is 2 d and the deformation is assumed to be anti plane a key clement in our model is the assumption of a zone in which numbers of pre existing cracks are densely distributed this cracked zone is a model for the fault zone dynamic crack growth nucleated in such a zone is intensely affected by the crack interactions which exert two conflicting effects one tends to accelerate the crack growth and the other tends to decelerate it the accelerating and decelerating effects are generally ascribable to coplanar and non coplanar crack interactions respectively we rigorously treat the multiple interactions among the cracks using the boundary integral equation method biem and assume the critical stress fracture criterion for the analysis of spontaneous crack propagation our analysis shows that a dynamic rupture nucleated in the cracked zone begins to grow slowly due to the relative predominance of non coplanar interactions this process radiates the p1 phase if the crack continues to grow coalescence with adjacent coplanar cracks occurs after a short time then coplanar interactions suddenly begin to prevail and crack growth is accelerated the p2 phase is emitted in this process it is interpreted that the two distinct phases appear in the process of the transition from non coplanar to coplanar interaction predominance

scaling relationships between sizes of nucleation regions and eventual sizes of microearthquakes abstract we investigate the initial rupture process of microearthquakes to reveal relationships between nucleation region sizes and eventual earthquake sizes in order to obtain high quality waveform data we installed a trigger recording system with a sampling frequency of 10 khz at the base of a deep borehole at the nojima fault japan we analyze waveform data of 31 events around the borehole with seismic moment ranging from 4 2 10 9 nm to 7 1 10 11 nm we use both a circular crack model with an accelerating rupture velocity sk model sato t kanamori h 1999 beginning of earthquakes modeled with the griffith s fracture criterion bull seism soc am 89 80 93 which generates a slow initial phase of velocity pulse and a circular crack model with a constant rupture velocity sh model sato t hirasawa t 1973 body wave spectra from propagating shear cracks j phys earth 21 415 431 which generates a ramp like velocity pulse source parameters of these two models are estimated by waveform inversion of the first half cycle of the observed velocity pulse applying both a grid search and a non linear least squares method 14 of 31 events are never reproduced by the sh model with a constant q operator but sk model with a constant q operator provides a size of the pre existing crack corresponding to the size of the nucleation regions and a size of the eventual crack we recognize that i the eventual seismic moment is approximately scaled as the cube of the size of pre existing cracks ii the eventual seismic moment is scaled as the cube of the size of eventual cracks and iii the size of eventual cracks is roughly proportional to the size of pre existing cracks we thus conclude that the size of eventual earthquakes is controlled by the size of the nucleation regions

examination of scaling between proposed early signals in p waveforms and earthquake magnitudes summary we examine seismic waveforms generated by clusters of similar earthquakes and additional events located on the karadere duzce branch of the north anatolian fault to investigate possible scaling between proposed early signals in the p waveforms and magnitudes the employed signals can be divided into two classes the first is associated with ellsworth beroza and iio type signals that are assumed to reflect signatures of seismic nucleation phases the second are associated with nakamura type period and wu zhao type maximum displacement in the early waveforms that are related to measures of the corner frequency and local magnitude respectively the impact on each signal of artefacts generated by the finite impulse response fir filter is also examined the use of repeating event clusters reduces considerably the variability of path and site effects compared to previous regional and global studies this allows us to focus more accurately on variations of the potential scaling parameters with the source magnitude however the magnitude range of the employed events is limited to about 4 units the fir filter artefacts can generate spurious signals prior to the p wave arrival potentially affecting the ellsworth beroza type signals but are not a significant influence on any of the other measurements the results indicate that candidates for the ellsworth beroza signals associated with identification of a weak arrival before the main p phase exist in less than 20 per cent of the cases the iio type signals can be determined by definition on all waveforms both of these potential signatures of nucleation phases show little or no scaling with the final event size in the examined data in contrast the nakamura and wu zhao type signals in the first few seconds which can also be determined by definition on all waveforms appear to scale with the final event magnitude albeit with large scatter the relatively large time windows used in the analysis compared to the rupture time of the employed events implies that the results provide little if any information on the physical process of the rupture initiation the scaling of the nakamura and wu zhao type early signals with the final event size may be explained by statistical tendency of stronger initial rupture phases to propagate larger distances

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

forecast model for moderate earthquakes near parkfield california earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation in the forecast procedure proposed here repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters the early part of the model simulation corresponds to the available field data and the subsequent part constitutes an estimate of future faulting and ground deformation in particular the time location and size of unstable faulting are estimates of the pending earthquake parameters the forecast accuracy depends on the model realism and parameter resolution the forecast procedure is applied to fault creep and trilateration data measured near parkfield california where at least five magnitude 5 5 to 6 earthquakes have occurred regularly since 1881 the last in 1966 the quasi static model consists of a flat vertical plane embedded in an elastic half space spacially variable fault slip of strike slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle strain softening fault the field data are consistent with these approximate values of patch parameters radius of 3 km patch center 5 km deep and 8 km southeast of the 1966 epicenter and maximum brittle strength of 26 bars fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21 8 year recurrence interval however the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake as predicted by the model

earthquake core inferred from near field observations abstract the source processes of large shallow earthquakes are investigated based on the various field phenomena and on the seismograms recorded at short focal distances the results from coseismic and postseismic field surveys in some source regions strongly show that there must be a particular region characterized by a large dislocation large acceleration and extremely low aftershock activity this specific region seems to have a relatively small dimension compared with the length of the main fault the predominant short period waves on the strong motion seismograms are concentrated within the short intervals at the initial parts of p and s waves this fact also suggests that the rupture elements generating the predominant short period waves are not distributed over the entire surface of a single main fault but are concentrated in a small region we call this confined small region in the source area earthquake core the earthquake core is formed a little later than the start of smoothing dislocation and it may be located at some distance from the starting point of rupture

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

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

evolution of hierarchical self similar geometry of experimental fault zones implications for seismic nucleation and earthquake size 1 the geometry of fault zones and its evolutionary trend were experimentally investigated for samples of calcareous siltstone nodule through a repetitive procedure of axial loading to grow faults a little close up photographing of faults that appeared on the side surface of the samples and axial loading again irrespective of their size fault zones are composed of three or four fault segments and compression type fault jogs smaller segment jog structures are nested in larger segments forming a hierarchical fault zone structure as a whole and they show self similarities fault zones grow keeping this self similar hierarchical structure on the basis of this fault zone geometry we successfully derived the gutenberg richter s law as well as the previously known relationship of seismic nucleation sizes to seismic moments these results suggest that fundamentally any seismic rupture nucleates at a smaller jog asperity of a lower hierarchical rank and terminates eventually at a larger jog barrier of a higher rank mimicking the hierarchical fault zone geometry

possible mechanisms of dynamic nucleation and arresting of shallow earthquake faulting abstract the nucleation and arresting mechanisms of large shallow earthquakes are investigated from both observational and theoretical viewpoints we show that two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes the first phase denotes the onset of the p wave which shows a very gradual increase in amplitude with time this gradual change is interrupted by the arrival of the second phase which causes an abrupt change in the amplitude our seismological observation shows that the time interval between the onset of the two phases is strongly correlated with the magnitude of the earthquake it is probable that the above two phases are related to some aspect of inhomogeneities in the earth s crust one of the important sources of such inhomogeneities is known to be preexisting cracks and their interactions we theoretically show in this paper that a rupture occurring in a zone of densely distributed cracks radiates elastic waves that can simulate the features of the above two phases note that such a rupture is considerably affected by crack interactions theoretical calculation is also carried out to investigate the effect of crack interactions on the arresting of rupture propagation a propagating crack can excite subsidiary cracks ahead of its crack tip which gives rise to crack interactions we show that these interactions sometimes facilitate the arresting of rupture propagation

dynamic high speed rupture from the onset of the 2004 parkfield california earthquake 1 we investigated the 2004 parkfield earthquake using a multiscale slip inversion the multiscale approach allows us to both focus on the details of the early stages of the rupture process and to model the entire earthquake at a larger scale our model indicates that the parkfield earthquake began with bilateral high speed rupture with fast slip rate up to 4 m s and fast propagation velocity of about 3 0 km s rupture propagation to the southeast was arrested 3 s after onset while propagation to the northwest continued generated a large slip patch at 5 s and ceased within 10 s a similar rapid initiation was observed for the 2004 mid niigata prefecture japan earthquake in a previous study high speed initial rupture suggests that large earthquakes may initiate and grow in the same way as small earthquakes and that the final size is difficult to predict from the early stages of an earthquake

properties of the seismic nucleation phase abstract near source observations show that earthquakes begin abruptly at the p wave arrival but that this beginning is weak with a low moment rate relative to the rest of the main shock we term this initial phase of low moment rate the seismic nucleation phase we have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1 1 8 1 the size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake the seismic nucleation phase is characteristically followed by quadratic growth in the moment rate consistent with self similar rupture at constant stress drop in this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it

high accelerations produced by the western nagano prefecture japan earthquake of 1984 many boulders were thrown out of their former sockets by the western nagano prefecture japan earthquake of 1984 mjma 6 8 the anomalous high accelerations of 4 16 g were estimated from the displacement of thrown out boulders assuming that the seismic waves had a frequency range of 5 10 hz almost all of the thrown out boulders were found on the mountain tops ridges and saddles the topographic amplifications of seismic waves were estimated using five aftershocks recorded on the mountain top and at the foot average amplitude ratios mountain top foot of seismic waves are 2 7 in the frequency range concerned the high acceleration area defined by the distribution of thrown out boulders is very small 1 3 km compared with the length 12 km of the assumed main fault many cracks were also found in this limited small area which is characterized by extremely low activity of aftershocks and relatively large dislocation

examination of scaling between earthquake magnitude and proposed early signals in p waveforms from very near source stations in a south african gold mine 1 we analyze near source seismograms recorded in a deep south african mine for scaling between signals early in p waveforms and the magnitude m of the events the data consist of recordings at 26 stations of 122 events with 1 5 0 implying that the final earthquake size is affected statistically by the initial rupture process if these correlations hold for larger earthquakes as suggested by other studies the early predominant period and peak displacement are useful for early warning systems

sulfides oxides and sphene in high pressure schists from new caledonia in the new caledonia high pressure schists pyrite pyrrhotite chalcopyrite rutile and sphene are common phases while hematite and ilmenite are rare and magnetite is absent the parageneses of these minerals were clarified from their occurrence as inclusions in garnet from phase relations in the cu fe s and fe ti o s systems and from phase rule considerations for the multi component system the sulfur fugacity estimated for pelites and basites containing pyrrhotite pyrite and rutile increased with increasing metamorphic grade the oxygen fugacity in these schists was less than 10 27 6 bars at 400 c 10 kb and 10 22 3 bars at 500 c 11 kb among the other components of the metamorphic fluid in pelites h2o was major ch4 co2 and h2s minor and h2 co cos and so2 rare the fluid composition altered with advancing metamorphic grade such that h2o decreased while co2 ch4 and h2s increased and this change was linked to concurrent massive decarbonization in the rock matrices

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

scaling relationship of initiations for moderate to large earthquakes 1 we investigate the initiation sizes of earthquakes over a wide range of moderate to large events using the model of sato and kanamori which is based on griffith crack theory for a circular fault we estimate the initial crack sizes of earthquakes using high quality data recorded at close hypocentral distances taking into account the local attenuation and the dynamic stress drop of the earthquakes we estimate trigger factors and initial crack radii for 35 events in japan and taiwan with magnitudes of 3 5 to 7 9 our results show that all of the earthquakes can be explained with a small trigger factor and initial crack sizes of 12 96 m for the large range of earthquake sizes this is a small range of initial crack sizes there does not appear to be a clear scaling relationship between initial crack size and final earthquake size instead our results show that all the moderate to large earthquakes initiate with initial crack radii on the order of tens of meters

comparison of the aftershock distribution and the fault plane size of the m 4 9 kameoka earthquake on may 28 1987 japan abstract it has been pointed out in several investigations that an aftershock gap exists in the neighborhood of the main shock where the main shock slip is large for large earthquakes since the source process of small earthquakes is thought to be less complex than that of large earthquakes it is expected that by comparing the size of the fault plane and the pattern of aftershock distribution for small earthquakes the physical meaning for large earthquakes may be clarified the 28 may 1987 kameoka earthquake with m 4 9 occurred in the midst of a telemetered seismic network and the data therefore were recorded with high accuracy the aftershocks were relocated by means of the master event technique with the aftershock gap found in the neighborhood of the hypocenter of the main shock p wave forms radiated by the kameoka earthquake were observed with low gain velocity seismographs having a natural period of 10 s without saturation the fault plane size was estimated by comparing observed seismograms having small hypocentral distances with synthetic seismograms obtained by forward modeling it was shown that the gap of aftershocks was comparable to the fault plane size of the small earthquake such as the m 4 9 kameoka earthquake

the use of holocene bovid fossils to infer palaeoenvironment in africa in this paper we develop an original statistical method to infer palaeoenvironmental conditions from fossil taxonomical assemblages based on the present day observed environmental characteristics of these taxa we illustrate this method by analysing present day and holocene african bovid artiodactyla mammalia species assemblages firstly the modern bovid species occurrences in african environments ranging from tropical rainforest to desert are compiled in order to define the environmental characteristics of each species analysed secondly these modern characteristics are considered in order to construct a statistical model of prediction of actual environmental conditions from the sets of most likely environments associated with each present day location station the model then allows us to infer palaeoenvironmental conditions associated with archaeozoological evidence of 53 holocene localities from western africa our results show that a tree cover was well established near rivers and uplands and constituted refuge areas for human occupation during times of climatic desiccation this conclusion is discussed in the climatic environmental and archaeological contexts of the holocene evolution and prehistory of western africa

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