random variability explains apparent global clustering of large earthquakes 1 the occurrence of 5 mw 8 5 earthquakes since 2004 has created a debate over whether or not we are in a global cluster of large earthquakes temporarily raising risks above long term levels i use three classes of statistical tests to determine if the record of m 7 earthquakes since 1900 can reject a null hypothesis of independent random events with a constant rate plus localized aftershock sequences the data cannot reject this null hypothesis thus the temporal distribution of large global earthquakes is well described by a random process plus localized aftershocks and apparent clustering is due to random variability therefore the risk of future events has not increased except within ongoing aftershock sequences and should be estimated from the longest possible record of events

nonlinear dynamical triggering of slow slip on simulated earthquake faults with implications to earth 1 among the most fascinating recent discoveries in seismology are the phenomena of dynamically triggered fault slip including earthquakes tremor slow and silent slip during which little seismic energy is radiated and low frequency earthquakes dynamic triggering refers to the initiation of fault slip by a transient deformation perturbation most often in the form of passing seismic waves determining the frictional constitutive laws and the physical mechanism s governing triggered faulting is extremely challenging because slip nucleation depths for tectonic faults cannot be probed directly of the spectrum of slip behaviors triggered slow slip is particularly difficult to characterize due to the absence of significant seismic radiation implying mechanical conditions different from triggered earthquakes slow slip is often accompanied by nonvolcanic tremor in close spatial and temporal proximity the causal relationship between them has implications for the properties and physics governing the fault slip behavior we are characterizing the physical controls of triggered slow slip via laboratory experiments using sheared granular media to simulate fault gouge granular rock and glass beads are sheared under constant normal stress while subjected to transient stress perturbation by acoustic waves here we describe experiments with glass beads showing that slow and silent slip can be dynamically triggered on laboratory faults by ultrasonic waves the laboratory triggering may take place during stable sliding constant friction and slip velocity and or early in the slip cycle during unstable sliding stick slip experimental evidence indicates that the nonlinear dynamical response of the gouge material is responsible for the triggered slow slip

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

spatio temporal network modelling and analysis of global strong earthquakes mw 6 0 we employ a spatio temporal network modelling approach to identify possible relations between strong earthquakes and spatial regions worldwide a global strong earthquake dataset containing 7736 events mw 6 0 from 1964 to 2018 is used statistical results identify power law relationships and heavy tail phenomena in the spatial patterns of strong earthquakes the interactions between regions follow the same law with a few regions that may be hit by successive strong earthquakes with high probability also we find that the interconnections between regions are mainly related to the succession of events in time whereas the distribution of events is extremely inhomogeneous in space this study provides a research prototype for the spatio temporal analysis of global strong earthquakes laying a foundation for obtaining insights into the network modelling approach for global strong earthquakes

identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics 1 seismicity clusters within fault zones can be connected to the structure geometric complexity and size of asperities which perturb and intensify the stress field in their periphery to gain further insight into fault mechanical processes we study stick slip sequences in an analog laboratory setting analysis of small scale fracture processes expressed by acoustic emissions aes provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events the present work connects x ray computer tomography ct scans of faulted rock samples with spatial maps of b values slope of the frequency magnitude distribution seismic moments and event densities our current experimental setup facilitates the creation of a series of stick slips on one fault plane thus allowing us to document how individual stick slips can change the characteristics of ae event populations in connection to the evolution of the fault structure we found that geometric asperities identified in ct scan images were connected to regions of low b values increased event densities and moment release over multiple stick slip cycles our experiments underline several parallels between laboratory findings and studies of crustal seismicity for example that asperity regions in lab and field are connected to spatial b value anomalies these regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes

large earthquake triggering clustering and the synchronization of faults large earthquakes are sometimes observed to trigger other large earthquakes on nearby faults the magnitudes of the calculated coulomb stress transfers presumed to cause the triggering are 10 2 10 3 of the earthquake stress drops the earthquake stress drops and the triggering delay times are similarly small with respect to the natural recurrence time of the earthquakes this requires that both faults be simultaneously very close to the ends of their seismic cycles paleoseismological data show that for the same regions prior earthquakes have occurred in clusters of ruptures of several faults separated by long quiescent periods both observations suggest that synchronization is occurring between faults theory and observations indicate that synchronization can occur between nearby faults with positive stress coupling and intrinsic slip velocities within an entrainment threshold in the south iceland seismic zone the central nevada seismic belt and the eastern california shear zone several synchronous clusters that apparently act independently can be recognized this behavior is the 3d equivalent of the phase locking that results in the seismic cycle of individual faults being dominated by large characteristic earthquakes and for synchronization of fault segments along a given fault rupture patterns of repeated individual earthquakes or earthquake clusters are not identical in either the 2d or 3d cases the state of this system which exhibits strong indications of synchrony without exact repetition may be called fuzzy synchrony

precise location of san andreas fault tremors near cholame california using seismometer clusters slip on the deep extension of the fault 1 we examine a 24 hour period of active san andreas fault saf tremor and show that this tremor is largely composed of repeated similar events utilizing this similarity we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake lfe master template located using p and s wave arrivals to be 26 km deep to compensate for low signal to noise we estimate event pair differential times at clusters of nearby stations rather than at single stations we find that the locations form a near linear structure in map view striking parallel to the saf and near the surface trace therefore we suggest that at least a portion of the tremor occurs on the deep extension of the fault likely reflecting shear slip similar to subduction zone tremor if so the saf may extend to the base of the crust 10 km below the deepest regular earthquakes on the fault

earthquake synchrony and clustering on fucino faults central italy as revealed from in situ cl 36 exposure dating we recover the holocene earthquake history of seven seismogenic normal faults in the fucino system central italy we collected 800 samples from the well preserved limestone scarps of the faults and modeled their 36cl concentrations to derive their seismic exhumation history we found that 30 large earthquakes broke the faults in synchrony over the last 12 ka the seven faults released strain at the same periods of time 12 9 ka 5 3 ka and 1 5 1 ka on all faults the strain accumulation and release occurred in 3 6 ka supercycles each included a 3 5 ka phase of slow 0 5 2 mm yr strain accumulation in relative quiescence followed by a cluster of three to four large earthquakes or earthquake sequences that released most of the strain in 1 2 ka the large earthquakes repeated every 0 5 0 3 ka during the paroxysmal phases and every 4 3 0 9 ka between those phases earthquakes on the northern faults produced twice larger surface slips 2 m and had larger magnitudes mw 6 2 6 7 than those on the southern faults on most faults the relative strain level was found to control the amount of slip and the time of occurrence of the next large earthquake faults entered a phase of clustered activity once they had reached a specific relative strain threshold the tre monti fault is identified as the most prone to break over the next century our data document earthquake synchrony and clustering at a broader space and time scale than has been reported to date

triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes the passage of radiating seismic waves generates transient stresses in the earth s crust that can trigger slip on faults far away from the original earthquake source the triggered fault slip is detectable in the form of earthquakes 1 3 and seismic tremor 4 7 however the significance of these triggered events remains controversial 8 9 in part because they often occur with some delay long after the triggering stress has passed here we scrutinize the location and timing of tremor on the san andreas fault between 2001 and 2010 in relation to distant earthquakes we observe tremor on the san andreas fault that is initiated by passing seismic waves yet migrates along the fault at a much slower velocity than the radiating seismic waves we suggest that the migrating tremor records triggered slow slip of the san andreas fault as a propagating creep event we find that the triggered tremor and fault creep can be initiated by distant earthquakes as small as magnitude 5 4 and can persist for several days after the seismic waves have passed our observations of prolonged tremor activity provide a clear example of the delayed dynamic triggering of seismic events fault creep has been shown to trigger earthquakes 10 12 and we therefore suggest that the dynamic

episodic tremor and slip on a frictional interface with critical zero weakening in elastic solid summary non volcanic tremor nvt and related relatively weak and slow slip events termed episodic tremor and slip ets are observed below the seismogenic sections of numerous subduction zones and several major strike slip faults these events have various characteristics that distinguish them from regular tectonic earthquakes here we show that a frictional fault in elastic solid with a region below the seismogenic zone having on average a critical near zero weakening during slip provides a simple unified explanation for the diverse observed phenomenology of nvt ets the results imply that nvt ets have little predictive power on the occurrence of large events in the overriding seismogenic zone additional model predictions that may be tested with future high resolution observations are fractal slip distributions and failure areas discrete power law frequency moment statistics with exponent 3 2 and exponential tapering overall scale invariant potency moment magnitude time histories triggered periodic nvt with evolving size and rate correlated with the stressing rate of the periodic triggering mechanisms and parabolic or exponential source time functions for event sizes measured by duration or moment potency

possible deep fault slip preceding the 2004 parkfield earthquake inferred from detailed observations of tectonic tremor 1 earthquake predictability depends in part on the degree to which sudden slip is preceded by slow aseismic slip recently observations of deep tremor have enabled inferences of deep slow slip even when detection by other means is not possible but these data are limited to certain areas and mostly the last decade the region near parkfield california provides a unique convergence of several years of high quality tremor data bracketing a moderate earthquake the 2004 magnitude 6 0 event here i present detailed observations of tectonic tremor from mid 2001 through 2008 that indicate deep fault slip both before and after the parkfield earthquake that cannot be detected with surface geodetic instruments while there is no obvious short term precursor i find unidirectional tremor migration accompanied by elevated tremor rates in the 3 months prior to the earthquake which suggests accelerated creep on the fault 16 km beneath the eventual earthquake hypocenter

remotely triggered microearthquakes and tremor in central california following the 2010 mw 8 8 chile earthquake 1 we examine remotely triggered microearthquakes and tectonic tremor in central california following the 2010 mw 8 8 chile earthquake several microearthquakes near the coso geothermal field were apparently triggered with the largest earthquake ml 3 5 occurring during the large amplitude love surface waves the chile mainshock also triggered numerous tremor bursts near the parkfield cholame section of the san andreas fault saf the locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from coso but can be identified by applying high pass or matched filters both triggered tremor along the saf and the ml 3 5 earthquake in coso are consistent with frictional failure at different depths on critically stressed faults under the coulomb failure criteria the triggered tremor however appears to be more phase correlated with the surface waves than the triggered earthquakes likely reflecting differences in constitutive properties between the brittle seismogenic crust and the underlying lower crust

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

do weak global stresses synchronize earthquakes insofar as slip in an earthquake is related to the strain accumulated near a fault since a previous earthquake and this process repeats many times the earthquake cycle approximates an autonomous oscillator its asymmetric slow accumulation of strain and rapid release is quite unlike the harmonic motion of a pendulum and need not be time predictable but still resembles a class of repeating systems known as integrate and fire oscillators whose behavior has been shown to demonstrate a remarkable ability to synchronize to either external or self organized forcing given sufficient time and even very weak physical coupling the phases of sets of such oscillators with similar though not necessarily identical period approach each other topological and time series analyses presented here demonstrate that earthquakes worldwide show evidence of such synchronization though numerous studies demonstrate that the composite temporal distribution of major earthquakes in the instrumental record is indistinguishable from random the additional consideration of event renewal interval serves to identify earthquake groupings suggestive of synchronization that are absent in synthetic catalogs we envisage the weak forces responsible for clustering originate from lithospheric strain induced by seismicity itself by finite strains over teleseismic distances or by other sources of lithospheric loading such as earth s variable rotation for example quasi periodic maxima in rotational deceleration are accompanied by increased global seismicity at multidecadal intervals

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

triggered tremor phase locking and the global clustering of great earthquakes abstract a system of non linear coupled relaxation oscillators is used to show how the communication between large earthquakes on a global scale can align their seismic cycles to produce a worldwide clustering of large events our model builds on recent observations that the seismic waves from a large earthquake can trigger an episode of non volcanic tremor at the base of a distant fault we assume that tremor is indicative of creep on the ductile extension of the fault zone that loads its overlying seismogenic layer thus advancing the fault toward failure if this advance is larger toward the end of the seismic cycle we show that two or more interacting faults will align their cycles even if their recurrence intervals are not identical

trace elements and cathodoluminescence of quartz in stockwork veins of mongolian porphyry style deposits the combination of scanning electron microscope cathodoluminescence cl fluid inclusion analysis and high resolution electron probe microanalysis of al ti k and fe in vein quartz has yielded results permitting a greater understanding of the complex mineralisation of the central oyu tolgoi and zesen uul porphyry style deposits southern mongolia these data demonstrate the relationship between quartz precipitation dissolution and ore deposition as the mineralising fluid chemistry changed through time four major quartz generations are identified in the a type veins from the stockworks of both the central oyu tolgoi oti to otiv and zesen uul deposits zui to zuiv despite differences in the associated alteration and mineralisation style the observed cl textures and trace element signatures of the quartz generations are comparable between deposits the oti and zui stage formed both the primary network of a type veins and pervasive silicification of the host rock using the ti in quartz geothermometer crystallisation temperatures for oti and zui of between 598 c and 880 c are indicated the main stage of sulphide mineralisation was accompanied by the dissolution of pre existing quartz oti and zui and precipitation of a weakly luminescent generation of quartz otii and zuii with a low ti content reflected in a calculated temperature drop from approximately 700 c to 340 c in central oyu tolgoi and 445 c in zesen uul otii and zuii stage quartzes show high and variable al concentrations the next stage of quartz in both deposits otiii and zuiii forms a fine network of veins in cracks formed in pre existing quartz otiii and zuiii quartz contain measurable fluid inclusions of moderate salinity 3 17 1 wt nacl eq entrapped in the temperature range 256 c to 385 c otiii and zuiii are not related to any sulphide mineralisation the final otiv and zuiv stages are characterised by quartz calcite micro breccias that penetrate the a type veins based on the calculated entrapment temperatures the otiv zuiv stage crystallised between 212 c and 335 c and the quartz is characterised by elevated but variable al and fe contents the cl and trace element signatures of the oti to otiii and zui to zuiii stages of the two mongolian porphyries show similar features to those observed in porphyry style deposits from other regions this suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper systems

the lillooet terraces of fraser river a palaeoenvironmental enquiry the history of holocene fluvial terraces was investigated by stratigraphic morphological and palaeohydrologic methods the terraces were formed in glaciofluvial and glaciolacustrine sediments by the fraser river degradation alternated with episodes of stability and aggradation the uppermost terraces four nonpaired surfaces were occupied by a braided river vertical stability was controlled either by the water and sediment discharge of the river or by backwater effects from downstream landslides the lower terraces two paired surfaces and associated fluvial sediments provide evidence for at least two cycles of aggradation and downcutting these can be attributed to the effects of landslides that occurred a short distance downstream climatic variations may also have influenced terrace formation but direct evidence is lacking palaeohydraulic investigations based on gravel texture terrace gradients and geometry of palaeochannels provide results that although approximate conform with conclusions

long range and long term fault interactions in southern california paleoseismological data suggest the occurrence of four bursts of seismic moment release in the los angeles region during the past 12 000 yr the historic period appears to be part of an ongoing lull that has persisted for about the past 1000 yr these periods of rapid seismic displacement in the los angeles region have occurred during the lulls between similar bursts of activity observed on the eastern california shear zone in the mojave desert which is now seismically active a kinematic model in which the faults of the greater san andreas system suppress activity on faults in the eastern california shear zone and vice versa can explain the apparent switching of activity between the two fault networks combined with the observation that short term geodetic and longer term geologic rates co vary on major southern california fault systems this suggests that either 1 a temporal cluster of seismic displacements on upper crustal faults increases ductile deformation on their downward extensions or 2 rapid ductile slip in the lower crust beneath faults loads the upper crust driving a seismic cluster we suggest that alternating periods of rapid seismic displacement may be the expected mode of seismicity when two fault systems accommodate the same plate boundary motion and slip on one system suppresses slip on the other

evidence for a global seismic moment release sequence temporal clustering of the larger earthquakes foreshock mainshock aftershock followed by relative quiescence stress shadow are characteristic of seismic cycles along plate boundaries a global seismic moment release history based on a little more than 100 years of instrumental earthquake data in an extended version of the catalog of pacheco and sykes 1992 illustrates similar behavior for earth as a whole although the largest earthquakes have occurred in the circum pacific region an analysis of moment release in the hemisphere antipodal to the pacific plate shows a very similar pattern monte carlo simulations confirm that the global temporal clustering of great shallow earthquakes during 1952 1964 at m 9 0 is highly significant 4 random probability as is the clustering of the events of m 8 6 0 2 random probability during 1950 1965 we have extended the pacheco and sykes 1992 catalog from 1989 through 2001 using harvard moment centroid data immediately after the 1950 1965 cluster significant quiescence at and above m 8 4 begins and continues until 2001 0 5 random probability in alternative catalogs derived by correcting for possible random errors in magnitude estimates in the extended pacheco sykes catalog the clustering of m 9 persists at a significant level these observations indicate that for great earthquakes earth behaves as a coherent seismotectonic system a very large scale mechanism for global earthquake triggering and or stress transfer is implied there are several candidates but so far only viscoelastic relaxation has been modeled on a global scale

s wave triggering of tremor beneath the parkfield california section of the san andreas fault by the 2011 tohoku japan earthquake observations and theory the dynamic stresses that are associated with the energetic seismic waves generated by the m w 9 0 tohoku earthquake off the northeast coast of japan triggered bursts of tectonic tremor beneath the parkfield section of the san andreas fault saf at an epicentral distance of 8200 km the onset of tremor begins midway through the 100 s period s wave arrival with a minor burst coinciding with the shsh arrival as recorded on the nearby broadband seismic station pkd a more pronounced burst coincides with the love arrival followed by a series of impulsive tremor bursts apparently modulated by the 20 to 30 s period rayleigh wave the triggered tremor was located at depths between 20 and 30 km beneath the surface trace of the fault with the burst coincident with the s wave centered beneath the fault 30 km northwest of parkfield most of the subsequent activity including the tremor coincident with the shsh arrival was concentrated beneath a stretch of the fault extending from 10 to 40 km southeast of parkfield the seismic waves from the tohoku epicenter form a horizontal incidence angle of 14 with respect to the local strike of the saf computed peak dynamic coulomb stresses on the fault at tremor depths are in the 0 7 10 kpa range the apparent modulation of tremor bursts by the small strike parallel rayleigh wave stresses 0 7 kpa is likely enabled by pore pressure variations driven by the rayleigh wave dilatational stress these results are consistent with the strike parallel dynamic stresses s associated with the s shsh and surface wave phases triggering small increments of dextral slip on the fault with a low friction 0 2 the vertical dynamic stresses d do not trigger tremor with vertical or oblique slip under this simple coulomb failure model