seismicity rate change before the irpinia m 6 9 1980 earthquake the stability of seismicity rate in central and southern italy was examined in two data sets from 1975 0 to 1995 0 with m 3 4 and from 1987 5 to 1996 0 with m 2 5 these are the approximate minimum magnitudes of complete reporting for the respective periods the first set was used to evaluate the possibility that the 23 november 1980 irpinia m 6 9 earthquake was preceded by precursory seismic quiescence the second was used to evaluate the conditions under which a current seismic quiescence could be detected in central or southern italy during the years before the irpinia earthquake the seismicity rate in the northern half of the rupture area and north of it was low whether this was a case of precursory quiescence or not is subject to interpretation because the background rate cannot be established for the years before 1975 if we accept the relatively constant seismicity rate in the irpinia volume during the decade after the mainshock as representative for the background rate we have a clear case of precursory quiescence lasting at least 1 3 yr up to the mainshock alternatively it can be postulated that the seismicity rate during the decade following this shock was elevated regionally because of the stress redistribution and that the low rates seen before it represent the normal background rate even if this reasoning is accepted the fact remains that a volume including the northern part of the rupture produced no m 3 4 earthquakes during 1 3 yr before the irpinia earthquake but produced 10 earthquakes during the 4 7 previous yr given these facts we favor the interpretation that the irpinia 1980 earthquake was preceded by precursory seismic quiescence in the entire data set there are three other cases of quiescence of higher significance without a mainshock following since no other mainshock with m 6 exists in the data set no missed event exists we propose that in italy precursory seismic quiescence may precede mainshocks and that it may be detected in the future by the improved catalog of the modern data set beginning in 1987 5 major magnitude scale changes give the mistaken appearance that fewer large magnitude earthquakes occur in italy now than in years before 1987 we postulate that the rate of earthquakes has not changed and that the magnitude scale should be adjusted

comparison of berkeley and calnet magnitude estimates as a means of evaluating temporal consistency of magnitudes in california abstract magnitude estimates have been calculated independently by berkeley and the u s geological survey for a large number of events in central california the berkeley magnitudes have been determined using a stable set of wood anderson seismometers for many decades this relative stability allowed us to compare calnet magnitudes with the berkeley magnitudes in an attempt to evaluate the temporal stability of the calnet magnitudes the comparisons were carried out in six different regions of central california for events with 2 5 m berkeley

a test of two techniques for recognizing systematic errors in magnitude estimates using data from parkfield california abstract selections of events from seismicity catalogs on the basis of size are universally made on the basis of magnitude such a selection implicitly assumes that these magnitudes provide a temporally consistent measure of earthquake size or that systematic errors in magnitudes are constant several techniques can be used to test this assumption results of application of these techniques to local and teleseismic catalogs indicate that in many cases this assumption cannot be justified two different techniques for identifying changes in systematic errors in magnitude are described here and applied to recent seismicity data from parkfield california one technique relies on comparisons of seismicity rates before and after a possible change in magnitudes the other uses station magnitude corrections to redetermine magnitudes both of these techniques indicate that a systematic decrease in magnitudes by 0 18 to 0 19 units occurred at parkfield during november 1984 this decrease was associated with the installation of six low gain stations in the parkfield region it is clear that changes in stations distributions can have significant effects on magnitudes and that these changes must be accounted for in all seismicity studies which use magnitude as a selection criteria the results of past studies which have not accounted for these changes must be reevaluated

precursory seismic quiescence a preliminary assessment of the hypothesis numerous cases of precursory seismic quiescence have been reported in recent years some investigators have interpreted these observations as evidence that seismic quiescence is a somewhat reliable precursor to moderate or large earthquakes however because failures of the pattern to predict earthquakes may not in general be reported and because numerous earthquakes are not preceded by quiescence the validity and reliability of the quiescence precursor have not been established

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

is the quiescence of major earthquakes m 7 5 since 1952 in the himalaya and northeast india real the earthquake catalog for the himalaya and the northeast india regions latitude 20 n to 38 n and longitude 75 e to 100 e comprising of portions of the himalaya and arakan yoma fold belt for the period 1897 to may 1995 shows that there have been 14 major earthquakes m 7 5 during the period 1897 to 1952 and no major earthquakes after 1952 to investigate the possibility that this quiescence is an artifact of nonuniform magnitude scales over the period of study we examined three global catalogs and found that there is indeed an absence of major earthquakes after 1952

testing for the predictability of dynamically triggered earthquakes in the geysers geothermal field abstract the geysers geothermal field is well known for being susceptible to dynamic triggering of earthquakes by large distant earthquakes owing to the introduction of fluids for energy production yet it is unknown if dynamic triggering of earthquakes is predictable or whether dynamic triggering could lead to a potential hazard for energy production in this paper our goal is to investigate the characteristics of triggering and the physical conditions that promote triggering to determine whether or not triggering is in anyway foreseeable we find that at present triggering in the geysers is not easily predictable in terms of when and where based on observable physical conditions however triggered earthquake magnitude positively correlates with peak imparted dynamic stress and larger dynamic stresses tend to trigger sequences similar to mainshock aftershock sequences thus we may be able to predict what size earthquakes to expect at the geysers following a large distant earthquake

seismicity of the unalaska region alaska the wadati benioff zone beneath unalaska island in the eastern aleutian arc is shown to dip at approximately 48 between the depths of 50 and 150 km above this depth the seismic zone appears to dip at a more shallow angle 12 the depth of the wadati benioff zone beneath makushin volcano on unalaska island is about 100 km events located within the upper plate near the wadati benioff zone indicate that the maximum depth of seismic coupling between the subducting and overriding plates is about 30 km this suggests that the maximum width of seismic coupling between the downgoing and overriding plates is about 75 km earthquake locations based on the local network data and 20 yr of teleseismic data pde define similar seismically active and quiescent regions a major seismicity gap exists for events of magnitudes greater than at least 4 6 in the forearc region near unalaska island this seismicity gap correlates well with the eastern edge of the tsunami source area of the great mw 8 6 1957 earthquake and a large forearc basin 75 km south of unalaska island suggesting a similar process may be controlling the location of all three phenomena only one intermediate sized mb 6 1 earthquake has occurred within the seismicity gap during the past 20 yr this event is shown to be a high stress drop 690 bars intraplate event within the subducting slab at a depth of 35 km that may be related to lateral compressive stress induced by a change in slab curvature with depth a review of the historic record from about 1770 reveals that the unalaska region may have ruptured in a great earthquake in 1878 and a large earthquake in 1902 if this region is currently locked an earthquake of magnitude 8 2 could rupture this section of the alaska aleutian arc estimates of the recurrence interval for events of this size vary from between 40 and 70 yr

consistency of teleseismic reporting since 1963 abstract changes in the rate of occurrence of smaller events have been recognized in the rupture zones of upcoming large earthquakes in several postearthquake and one preearthquake study a data set in which a constant portion of the events in any magnitude band are consistently reported through time is crucial for the recognition of seismicity rate changes which are real related to some process change in the earth such a data set is termed a homogeneous data set the consistency of reporting of earthquakes in the noaa hypocenter data file hdf since 1963 is evaluated by examining the cumulative number of events reported as a function of time for the entire world in eight magnitude bands it is assumed that the rate of occurrence of events in the entire world is roughly constant on the time scale examined here because of the great size of the worldwide earthquake production system the rate of reporting of events with magnitudes above m b 4 5 has been constant or increasing since 1963 significant decreases in the number of events reported per month in the magnitude bands below m b 4 4 occurred during 1968 and 1976 these decreases are interpreted as indications of decreases in detection of events for two reasons first they occur at times of constant rates of occurrence and reporting of larger events second the decrease during the late 19609s has also been recognized in the teleseismic data reported by the international seismological centre isc this suggests that the decrease in the number of small events reported was related to facets of the earthquake reporting system which the isc and noaa share the most obvious candidate is the detection system during 1968 detection decreased in the united states central and south america and portions of the south pacific this decrease is probably due to the closure of the vela arrays bmo tfo cpo ubo and wmo during 1976 detection decreased in most of the seismically active regions of the western hemisphere as well as in the region between kamchatka and guam the cause of this detection decrease is unclear these detection decreases seriously affect the amount of homogeneous background period available for the study of teleseismic seismicity rate changes if events below the minimum magnitude of homogeneity are eliminated from the teleseismic data sets the resulting small numbers of events render many regions unsuitable for study many authors have reported seismicity rate decreases as possible precursors to great earthquakes few of these authors have considered detection decreases as possible explanations for their results this analysis indicates that such considerations cannot be avoided in studies of teleseismic data

locked and creeping patches along the hayward fault california the results of mapping locked and unlocked patches on the hayward fault using the local recurrence time method are compared with models derived from surface creep and geodetic measurements the data used were the m 1 0 earthquakes in the usgs catalog since 1981 0 located within 5 km of the fault trace along the central and southern segments agreement with the other methods is satisfactory the 1868 rupture except for its two ends is classified as a locked segment by our method in the northern part of the hayward fault the data are poor and the results of the three methods differ short local recurrence times in the northern part suggest that an asperity exists there which is capable of an m6 5 class event

precursory quiescence before the august 1982 stone canyon san andreas fault earthquakes the stone canyon earthquake sequence started during august 1982 and lasted for about four months it contained four mainshocks withm l 4 each with an aftershock zone about 4 km long these mainshocks progressing from southeast to northwest ruptured a segment of the fault approximately 20 km long leaving two gaps which were later filled by them l 4 6 mainshocks of january 14 and may 31 1986 the equivalent magnitude of the sequence ism l 5 0 precursory seismic quiescence could be identified in 1 the northernmost 10 km of the aftershock zone which contained three of the mainshocks and 2 the southern gap in the aftershock zone the fault segment containing the first mainshock and its aftershocks did not show quiescence this pattern of precursory quiescence is very similar to two cases in hawaii where the rupture initiation points of the mainshocks m s 7 2 and 6 6 respectively were located in volumes of constant seismicity rate surrounded by volumes with pronounced precursory quiescence the precursory quiescence before the august 1982 stone canyon earthquakes lasted for 76 weeks amounted to a reduction in rate of about 60 and could be recognized without any false alarms that is the anomaly was unique within the 60 km study segment of the fault and in the years 1975 through august 1982 eighteen foreshocks occurred between july 27 and august 7 1982 we conclude that the august 1982 mainshocks could have been predicted based on seismic quiescence and foreshocks

precursory seismic quiescence before the january 1982 hilea hawaii earthquakes abstract two earthquakes of m l 5 4 occurred within half an hour of each other within the hilea area of southern hawaii on 21 january 1982 the aftershock distribution suggests that together they ruptured an area of approximately 5 km radius and their joint equivalent magnitude was 5 6 the first motions indicate faulting on a near horizontal plane at 10 km depth with the crust slipping to the southeast the seismicity rate in the source area was studied using the earthquake catalog of the hawaiian volcano observatory this catalog contains some reporting rate changes that affect the count of smaller earthquakes strongly with a period of low reporting during 1974 to 1977 although we have used 2 5 as the minimum magnitude of homogeneous reporting after 1971 some of the artificial rate changes are still present in the data the catalog was declustered using reasenberg9s algorithm and a magnitude correction of 0 1 was applied to the data between 1974 and 1984 the seismicity rate for the period of november 1971 through 1985 was examined in four adjacent regions one of these contained the aftershocks the aftershock volume and the 3 km annulus around it showed a period of 46 weeks of low seismicity rate immediately before january 1982 during which the rate was decreased by 87 per cent the seismicity rate in the other three volumes was normal during this time we conclude that this low reporting rate was not likely due to artificial changes in the catalog the fact that the quiescence anomaly coincided in space with the 1982 aftershock volume and that its termination coincided with the 1982 main shocks suggests that the quiescence was a precursor comparing the seismicity rate within all possible 46 week windows to the background rate we found that the precursory rate decrease was more significant than any other rate decrease in all volumes studied except artificial low rate periods thus this quiescence precursor could be recognized without false alarms however the statistical significance estimated by the z and tests was low 75 per cent and 49 per cent respectively more case histories are needed to determine empirically the thresholds of these tests for accepting precursory anomalies without too many false alarms the m 6 6 kaoiki earthquake that was located about 25 km north of the 1982 source area was preceded by 125 weeks of quiescence while the m 7 2 kalapana earthquake quiescence precursor lasted about 200 weeks these observations suggest that in hawaii quiescence precursor times may be a function of magnitude

a densely spaced array of sea level monitors for the detection of vertical crustal deformation in the shumagin seismic gap alaska a network of sea level gauges has been installed with about 40 km spacing in the shumagin islands in order to detect relative vertical motion in particular possible crustal motion precursory to an expected major earthquake this required the development and deployment of a pressure sensor sea level gauge suitable for installation on remote and harsh coastlines data are collected in near real time via satellite both in order to exploit fully any precursors that may be observed and to provide continuous information on the status of the instruments using wiener filtering techniques it has been determined conservatively that no relative vertical crustal motion greater than 0 1 m between stations has occurred during 1981 1985 this is consistent with independent geodetic leveling and trilateration data though evidence exists for more rapid deformation during 1978 1980 the sea level data collected so far have an rms noise level of about 0 04 m after processing this is limited in part by the pressure sensor and associated electronics improved prressure gauges with better long term stability have recently been installed a short baseline tiltmeter operating in a tunnel has demonstrated that suitably designed and located land based tiltmeters have a lower noise level and hence better precursor detection characteristics than the sea level gauges at monthly and shorter periods

seismicity patterns are they always related to natural causes by analyzing data from two catalogs of seismicity one local and one regional examples are drawn that demonstrate artificial seismicity patterns which can arise when changes in magnitude reporting or in detection ability are introduced by changes in operating procedures of a seismic network in the first case a catalog which comprises seismic data from guerrero mexico is revised and a correction is applied to magnitudes suspected of being affected by different operative practices next several time windows are analyzed which compare the seismicity rate within the window to that of the total record mapped as a function of space the same procedure is applied to the original i e uncorrected catalog a significant seismic quiescence apparent in the original data set in the center of the seismic network all but disappears in the corrected data indicating that this anomaly is not naturally induced in the second case we investigate the homogeneity of seismicity reporting for the interior of alaska we computed the standard deviate z as a function of time by comparing the overall seismicity rate with the rate in a 3 year window the maps z values were inspected for all times the most outstanding rate change is found around 1992 5 since the b value remained unchanged the most reasonable explanation for the observed rate change around mid 1992 is a decrease in the detection ability of the network in the interior of alaska both case studies demonstrate the usefulness of systematic comparisons of the cumulative and noncumulative frequency magnitude distribution and of spatial and temporal mapping of the seismicity rates as a tool to investigate the homogeneity of earthquake reporting

seismicity patterns 1963 1983 as stress indicators in the shumagin seismic gap alaska earthquakes 1963 to 1983 of magnitude 5 0 to 6 5 form a rim of high seismic activity around a central region of relative seismic quiescence that coincides with the shumagin seismic gap this pattern which can be inferred both from local network and teleseismic earthquake locations shows high activity near the eastern and western ends of the seismic gap and along the down dip end of the main thrust zone the rim of seismicity surrounding an area of seismic quiescence may reflect strong couplign along the elastic brittle part of the plate boundary where the great earthquakes occur the temporal behavior of the microseismicity recorded by the shumagin network is characterized by a burst of activity in 1978 and 1979 and a low or average level of activity from 1980 to january 1983 the increased microearthquake activity during 1978 1979 is located mainly near the down dip end of the main thrust zone and along the benioff zone down to 100 to 200 km depth composite fault plane solutions of earthquakes occurring in 1978 1979 show down dip tension between 50 to 120 km depth in the upper plane of the benioff zone composite fault plane solutions of 1981 earthquakes however indicate in plate compression in the same region hence the rate of occurrence and focal mechanisms of microearthquakes located in the benioff zone below the main thrust both show coincident temporal and spatial variations that may reflect fluctuations in local stresses

reporting history of the central aleutians seismograph network and the quiescence preceding the 1986 andreanof island earthquake the earthquake catalog of the central aleutian seismic network casn was searched systematically for significant rate changes in the period from 1976 through 1985 the magnitude signatures for the nine changes were modeled by synthetic signatures by this method six of the rate changes could be identified as artificial based on the criteria that the rate change was confined to small magnitude events and that magnitude shifts were present for each of these changes an artificial cause existed that affected the network within one to two months of the time of change as estimated from the catalog analysis one of these cases was a rate decrease by a factor of 2 associated with a storm that had put out of operation two thirds of the network another change coincided with the introduction of digital data processing the four remaining cases were artificial reporting rate increases due to installation of several new stations or to repair of several stations that had failed the three rate changes that could not be identified unambiguously as artificial or natural on the basis of magnitude signatures were all rate decreases by factors of approximately 2 two of these were clearly due to disasters that had put out of operation more than half of the network the third was the proposed precursory quiescence to the 1986 andreanof island m 7 9 earthquake from this we conclude that without knowledge of the network history many of the artificial reporting rate changes in earthquake catalogs can be identified as artificial and that their onset time can be estimated to within one to two months an earthquake count independent from the adak catalog was obtained from the helicorder records of the station adak for the years 1978 through 1985 for the vicinity of adak island of a total of 1831 events 335 were not in the adak catalog and 981 were located within the 1986 aftershock area the helicorder earthquake count showed a pronounced decrease by about 50 per cent similar in amount to that in the adak catalog however the decrease started in 1980 at a time when in the central subregion covered by the adak catalog only m 2 9 events decreased while the smaller magnitude bands show a maximum decrease in 1982 we conclude that the possibility could not be ruled out that electronics changes contributed to the reporting rate decrease starting in the years 1980 to 1982 however it seems very unlikely that a network that was at its healthiest during the precursor time would be reduced by an improvement in the electronics to a detection level approximately equal to that in two short periods when only one third of the stations were operating therefore the seismic quiescence reported and interpreted as a precursor by kisslinger et al 1985 was most likely a natural phenomenon

the implications of regional microseismic activities a lesson from 2008 ms 8 0 wenchuan earthquake abstract the ms 8 0 wenchuan earthquake has greatly perturbed the crustal stress in longmenshan fault zone lfz and its neighboring regions and hence significantly changed the regional seismicity pattern convectional coulomb stress change model based on half space dislocation source of layered elastic or viscoelastic crust can only provide brief reference to estimate the after shock sequences roughly in this study we apply the z test statistical method to examine the earthquake catalogue five years before and after this event to detect the changes of regional seismicity intensity and their statistical significance in lfz and its neighboring regions we analyze changes of the z values with respect to time and seismic magnitude in each region our results reveal that after the wenchuan earthquake seismicity intensity has significantly increased in eastern kunlun fault southern longmenshan fault longquanshan fault and huayingshan fault in sichuan basin but has significantly decreased in northern and central longmenshan fault vicinity of the songpan minjiang fault and fubianhe fault in bayankala block respectively seismicity rate change in northern and central anninghe zemuhe fault zone is not correlated with the wenchuan earthquake these results remain within 99 confidence level of the z test statistical method we compare our statistical analysis results with calculations of coseismic coulomb failure stress change due to the wenchuan earthquake from previous studies in most of the regions and fault zones the sign of the seismicity rate change agrees with the sign of the coulomb stress change

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

seismic quiescence a test of the hypothesis and a precursor to the next parkfield california earthquake summary the parkfield segment of the san andreas fault shows seismic quiescence for m 2 0 earthquakes since early to mid 1986 the rate decreases by 45 to 70 per cent depending on the magnitude band we interpret this change as real because it is concentrated in the larger magnitudes and cannot be explained by a reasonable magnitude shift the rate decrease is present in the parkfield segment of the fault between 35 6 and 36 1 n and no other rate change as significant has been observed during the time when high quality data were available since 1975 we interpret this observation as a seismic quiescence precursor to the next parkfield mainshock although information on the expected duration of precursory quiescence is weak we estimate that the parkfield earthquake should occur in the interval 1990 february to 1992 february precursory seismic quiescence which lasted approximately 1 5 yr was found in and possibly around the source volume of an earthquake withm 3 6 which occurred on 1986 august 29 in the parkfield area this observation demonstrates that the quiescence hypothesis is applicable to the parkfield segment of the san andreas fault the false alarm rate was estimated in a detailed analysis as a function of alarm level for the fault segments surrounding the m 5 0 stone canyon 1982 august and m 3 6 parkfield 1986 august mainshocks for these two events the duration and statistical significance of false alarms as a function of space time and magnitude band was determined we propose that in this tectonic environment and with the data characteristics of these earthquake catalogues attempts to predict mainshocks based on the quiescence hypothesis may be successful and generate one to two false alarms covering about 10 per cent of the time space dimensions of the catalogue

ergodicity and earthquake catalogs forecast testing and resulting implications recently the equilibrium property of ergodicity was identified in an earthquake fault system tiampoet al phys rev lett 91 238501 2003 phys rev e 75 066107 2007 ergodicity in this context not only requires that the system is stationary for these networks at the applicable spatial and temporal scales but also implies that they are in a state of metastable equilibrium one in which the ensemble averages can be substituted for temporal averages when studying their behavior in space and time in this work we show that this property can be used to identify those regions of parameter space which are stationary when applied to the seismicity of two naturally occurring earthquake fault networks we apply this measure to one particular seismicity based forecasting tool the pattern informatics index tiampoet al europhys lett 60 481 487 2002 rundleet al proc national acad sci u s a suppl 1 99 2463 2002 in order to test the hypothesis that the identification of ergodic regions can be used to improve and optimize forecasts that rely on historic seismicity catalogs we also apply the same measure to synthetic catalogs in order to better understand the physical process that affects this accuracy we show that in particular ergodic regions defined by magnitude and time period provide more reliable forecasts of future events in both natural and synthetic catalogs and that these improvements can be directly related to specific features or properties of the catalogs that impact the behavior of their spatial and temporal statistics

response of the san andreas fault to the 1983 coalinga nunez earthquakes an application of interaction based probabilities for parkfield 1 the parkfield cholame section of the san andreas fault site of an unfulfilled earthquake forecast in 1985 is the best monitored section of the world s most closely watched fault in 1983 the m 6 5 coalinga and m 6 0 nunez events struck 25 km northeast of parkfield seismicity rates climbed for 18 months along the creeping section of the san andreas north of parkfield and dropped for 6 years along the locked section to the south right lateral creep also slowed or reversed from parkfield south here we calculate that the coalinga sequence increased the shear and coulomb stress on the creeping section causing the rate of small shocks to rise until the added stress was shed by additional slip however the 1983 events decreased the shear and coulomb stress on the parkfield segment causing surface creep and seismicity rates to drop we use these observations to cast the likelihood of a parkfield earthquake into an interaction based probability which includes both the renewal of stress following the 1966 parkfield earthquake and the stress transfer from the 1983 coalinga events we calculate that the 1983 shocks dropped the 10 year probability of a m 6 parkfield earthquake by 22 from 54 22 to 42 23 and that the probability did not recover until about 1991 when seismicity and creep resumed our analysis may thus explain why the parkfield earthquake did not strike in the 1980s but not why it was absent in the 1990s we calculate a 58 17 probability of a m 6 parkfield earthquake during 2001 2011 index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 7260 seismology theory and modeling keywords coalinga earthquake parkfield stress change earthquake probability seismicity rate

analysis of temporal and spatial heterogeneity of magnitude frequency distribution inferred from earthquake catalogues summary statistical models are introduced for the simultaneous estimation of the changes of the b value and detection rate of earthquakes in a catalogue which develops in time or varies in space the three characteristic parameters including b for the magnitude frequency distribution of detected earthquakes are represented by respective three b spline functions of time or location in a space an objective bayesian method is adopted for the optimal estimate of such functions with many unknown coefficients the present procedure is applied to earthquake catalogues for japanese seismic activity

seismic quiescence before the urakawa oki earthquake abstract there were significant changes in seismicity preceding a large earthquake the urakawa oki earthquake of 21 march 1982 this event a m jma 7 1 thrust fault crustal earthquake is the largest from a data set of 35 000 earthquakes beneath the southeastern corner of hokkaido island japan during the period july 1976 through december 1986 there was a quiescence for the 2 years preceding the main shock surrounding but not including the immediate epicenter and only for magnitudes 3 during the same time span there was an increase in the number of small magnitudes 2 4 events restricted to the general focal region of the main shock the magnitude dependence of the precursory seismicity patterns is a departure from self similarity one of the currently prevalent assumptions in earthquake source models these seismicity anomalies can be seen using conventional methods such as cumulative number versus time for selected magnitudes in a bounded geographical region however such displays require a priori knowledge or assumptions about the prospective target region and magnitude range for this anomaly there was no reason to target the epicentral region in advance and the usual assumption that quiescence should be most evident at small magnitudes was not appropriate here we have developed an efficient objective procedure for alerting one to the possible existence of a developing anomaly and then analyzing its spatial bounds and its magnitude dependence this procedure has potential value as a general monitoring tool

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

seismic b value anomalies in the sumatran region seismotectonic implications abstract the spatial variations in the seismic b value seismic moment bouguer gravity change and fault plane solution are estimated in the sumatran region based on homogeneous seismicity data from june 2005 to march 2012 to investigate the seismotectonic characteristics and tectonic activity between the 2004 sumatran earthquake and the 2012 east indian ocean earthquakes based on changes in the seismicity rate this time period is divided into five intervals with different earthquake distributions and faulting styles the seismic b values faulting mechanisms and seismic moment release values are mapped throughout the sumatran region and the gravity change every two years between the 2004 event and the 2012 events are determined from satellite grace gravity data the b values vary from 0 45 to 1 59 and an inverse correlation is observed between the b values and convergence rates low b values are located at depths between 20 km and 40 km in the subduction zone and between 20 km and 35 km in the oceanic plate the lowest b values are located at a depth of approximately 28 km in both regions which indicates a homogeneous fault system between them the areas with low b values are associated with megathrust and strike slip mechanisms while the area with the lowest b values is dominated by a megathrust mechanism seismically active regions have low b values associated with a high stress accumulation and high seismic moment release low b value areas are located mainly along the andaman sunda trench and andaman nicobar sumatra forearc temporal variations in the seismicity distribution and faulting style are recognized with temporal variations in the b values in each period relationships exist between the epicenter of the 2004 event and the location of the maximum bouguer gravity change in 2012 and between the epicenters of the 2012 events and the location of the maximum bouguer gravity change in 2004 furthermore a zone of continuous 2 year positive gravity change is located near the nicobar islands the 2004 event boost the 2012 events and intraplate seismicity via stress transfer the seismicity distributions in individual periods within the studied timeframe highlight the active and locked portions of the fault systems

seismic cycles along the aleutian arc analysis of seismicity from 1957 through 1991 we catalog and relocate aleutian arc seismicity between 1957 and 1991 two great earthquakes ruptured the same 250 km long portion of the central aleutian arc the 1957 aleutian islands earthquake and the 1986 andreanof islands earthquake because accurate estimates of the moment distribution of the 1957 earthquake are not available the spatial distribution of aftershocks for each of these events is compared and tested against models describing the modes of occurrence of great subduction zone earthquakes earthquake relocations are based on p wave arrival times published in the international seismological summary the bureau central international seismologique and the international seismological centre bulletins and include corrections for the near source velocity structure associated with the down going slab magnitude estimates are extracted from bulletins and prior to 1964 are estimated by us from microfilmed records our catalog is complete above magnitude 5 5 aftershocks associated with the 1957 and 1986 earthquakes appear to occur in different areas east of the main shock epicenters aftershock locations are anticorrelated west of the main shock epicenter aftershocks of the 1986 earthquake tended to concentrate along the updip edge of aftershock clusters associated with the 1957 earthquake if we assume aftershocks rim the distribution of seismic moment release associated with each event these observations imply that the moment distribution of the 1986 earthquake was different from that of the 1957 earthquake this suggests that we should use caution in identifying mechanically strong portions of a fault asperities by simply mapping the moment distribution of a single great earthquake a fundamental tenet of the asperity model that rupture always occurs on the strongest portions of the fault with weaker portions rupturing either aseismically or dynamically as a result of rupture on a strong fault patch may in the case of the central aleutian arc not be correct thus observing the moment distribution from a single great earthquake may tell us little about what the distribution of moment release will look like during the next earthquake

anomalously high b values in the south flank of kilauea volcano hawaii evidence for the distribution of magma below kilauea s east rift zone abstract the pattern of b value of the frequency magnitude relation or mean magnitude varies little in the kaoiki hilea area of hawaii and the b values are normal with b 0 8 in the top 10 km and somewhat lower values below that depth we interpret the kaoiki hilea area as relatively stable normal hawaiian crust in contrast the b values beneath kilauea s south flank are anomalously high b 1 3 1 7 at depths between 4 and 8 km with the highest values near the east rift zone but extending 5 8 km away from the rift also the anomalously high b values vary along strike parallel to the rift zone the highest b values are observed near hiiaka and pauahi craters at the bend in the rift the next highest are near makaopuhi and also near puu kaliu the mildest anomalies occur adjacent to the central section of the rift the locations of the three major and two minor b value anomalies correspond to places where shallow magma reservoirs have been proposed based on analyses of seismicity geodetic data and differentiated lava chemistry the existence of the magma reservoirs is also supported by magnetic anomalies which may be areas of dike concentration and self potential anomalies which are areas of thermal upwelling above a hot source the simplest explanation of these anomalously high b values is that they are due to the presence of active magma bodies beneath the east rift zone at depths down to 8 km in other volcanoes anomalously high b values correlate with volumes adjacent to active magma chambers this supports a model of a magma body beneath the east rift zone which may widen and thin along strike and which may reach 8 km depth and extend from kilauea s summit to a distance of at least 40 km down rift the anomalously high b values at the center of the south flank several kilometers away from the rift may be explained by unusually high pore pressure throughout the south flank or by anomalously strong heterogeneity due to extensive cracking or by both phenomena the major b value anomalies are located sse of their parent reservoirs in the direction of motion of the flank suggesting that magma reservoirs leave an imprint in the mobile flank we hypothesize that the extensive cracking may have been acquired when the anomalous parts of the south flank now several kilometers distant from the rift zone were generated at the rift zone near persistent reservoirs since their generation these volumes may have moved seaward away from the rift but earthquakes occurring in them still use the preexisting complex crack distribution along the decollement plane at 10 km depth the b values are exceptionally low b 0 5 suggesting faulting in a more homogeneous medium

large occurrence patterns of new zealand deep earthquakes characterization by use of a switching poisson model the paper studies the statistical properties of deep earthquakes around north island new zealand we first evaluate the catalogue coverage and completeness of deep events according to cusum cumulative sum statistics and earlier literature the epicentral depth and magnitude distributions of deep earthquakes are then discussed it is worth noting that strong grouping effects are observed in the epicentral distribution of these deep earthquakes also although the spatial distribution of deep earthquakes does not change their occurrence frequencies vary from time to time active in one period relatively quiescent in another the depth distribution of deep earthquakes also hardly changes except for events with focal depth less than 100 km on the basis of spatial concentration we partition deep earthquakes into several groups the taupo bay of plenty group the taranaki group and the cook strait group second order moment analysis via the two point correlation function reveals only very small scale clustering of deep earthquakes presumably limited to some hot spots only we also suggest that some models usually used for shallow earthquakes fit deep earthquakes unsatisfactorily instead we propose a switching poisson model for the occurrence patterns of deep earthquakes the goodness of fit test suggests that the time varying activity is well characterized by a switching poisson model furthermore detailed analysis carried out on each deep group by use of switching poisson models reveals similar time varying behavior in occurrence frequencies in each group

seismicity and mean magnitude variations correlated to the strongest earthquakes of the 1997 umbria marche sequence central italy 1 nearby faults can interact affecting the timing of a future earthquake a large earthquake can alter the static stress surrounding faults possibly activating an aftershock sequence here we test the hypothesis of earthquake triggering by examining the earthquakes that affected the umbria marche region central italy during september 1997 to april 1998 the analysis was performed combining information contained in parameters a and b of the gutenberg richter relationship before and after the strongest main shocks using a catalog of 6211 earthquakes m 1 5 by analyzing the changes in space of the a parameter we found that colfiorito main shocks mw 5 7 and 6 0 on 26 september 1997 increased the seismicity rate within 40 50 km of the epicenter we interpret this behavior as the effect of stress redistribution after analyzing the b value changes in space and time we found the strongest increase in mean magnitude in the sellano area between the colfiorito shocks and the two strong events mw 5 2 and 5 6 respectively which hit this region on 12 and 14 october 1997 this area was also the location of the strongest increase in change of the local occurrence rate density on the basis of these observations we postulate that temporal variations in both a and b values indicate a probable causal connection between the largest earthquakes in the sequence

cohesive sediment transport processes abstract the general aim of the project cohesive sediment of the mast programme g6 coastal morphodynamics is to advance the knowledge and modelling of physical processes related to cohesive sediment in coastal environments better insights are given into deposition modelling consolidation theories and associated constitutive relationships laboratory experiments of liquefaction by waves only or combined waves and currents modelling of flow sediment interaction and turbulence in the water column and the conduct of laboratory erosion experiments short term recordings of deposition events wave effects consolidation and bottom turbulence in muddy environments emphasise the distance which remains to be covered in order to understand and predict the processes in the field

inadvertent changes in magnitude reported in earthquake catalogs their evaluation through b value estimates a simple procedure is presented for analyzing magnitudes and seismicity rates reported in earthquake catalogs in order to discriminate between inadvertently introduced changes in magnitude and real seismicity changes we assume that the rate and the frequency magnitude relation of the independent background seismicity do not change with time observed differences in the frequency magnitude relation a and b values between data from two periods are modeled as due to a transformation of the magnitude scale the transformation equation is found by a least squares fitting process based on the seismicity data for earthquakes large enough to be reported completely and by comparing the linear relation of one period to the other for smaller events an additional factor accounting for increased decreased detection is allowed this fitting technique is tested on a data set from parkfield for which two types of magnitudes amplitude and duration were computed for each earthquake we found that the b value fitting technique yielded virtually the same result as a linear regression assuming the same errors in the two magnitudes the technique is also applied to interpret the nature of reporting rate changes in a local guerrero mexico and a regional italy earthquake catalog in guerrero a magnitude change in 1991 37 can be modeled about equally well by m new m old 0 5 or by m new 1 02 m old 0 38 but residuals with the latter transformation are smaller in italy a magnitude change in 1980 21 cannot be modeled satisfactorily by a simple magnitude shift but is well described by a compression of the magnitude scale given by m new 0 67 m old 1 03 the proposed b slope fitting method provides a means to interpret quantitatively and in some cases correct for artificial reporting rate changes in earthquake catalogs

case 25 application of the concentration parameter of seismoactive faults to southern california in this paper we evaluate the present state of the seismic regime in southern california using the concentration parameter of seismogenic faults k sf sobolev andzavyalov 1981 the purpose of this work is to identify potential sites for large earthquakes during the next five or ten years the data for this study derived from the california institute of technology s catalog of southern california earthquakes and spanned the period between 1932 to june 1982 we examined events as small asm l 1 8 but used a magnitude cutoff atm l 3 3 for a detailed analysis the size of the target earthquakes m m was chosen as 5 3 and 5 8 the algorithm for calculatingk sf used here was improved over the algorithm described bysobolev andzavyalov 1981 in that it considered the seismic history of each elementary seismoactive volume the dimensions of the elementary seismoactive volumes were 50 km 50 km and 20 km deep we found that the mean value ofk sf within 6 months prior to the target events was 6 1 2 0 for target events withm l 5 3 and 5 4 1 8 for targets withm l 5 8 seventy three percent of the targets withm l 5 8 occurred in areas wherek sf was less than 6 1 the variance of the time between the appearance of areas with lowk sf values and the following main shocks was quite large from a few months to ten years so this parameter cannot be used here for accurate predictions of occurrence time regions where the value ofk sf was below 6 1 at the end of our data set june 1982 are proposed as the sites of target earthquakes during the next five to ten years the most dangerous area is the area east of san bernardino wherek sf values are presently between 2 9 and 3 7 and where there has been no earthquake withm l 5 3 since 1948

man made changes of seismicity rates seismicity catalogs contain important information about processes which occur in seismically active regions of the earth many authors have examined these catalogs for patterns and variations in patterns which might reflect changes in these processes we have found that these catalogs include a complex mixture of real and man made changes one must identify and account for the man made changes before the real ones can be identified and understood many man made changes in seismicity catalogs are manifested as changes in seismicity rates and can therefore be identified through careful examination of these rates obvious effects include increases or decreases in the detection and reporting of smaller events which accompany the installation or closure of seismic stations these types of changes can be recognized by examining the distribution of seismicity rate changes in the magnitude domain they are characterized by increases or decreases in the number of small events in the catalog at times when the number of larger events remains constant systematic changes in the magnitudes assigned to events can also be identified by examining seismicity rates because they cause apparent changes in rates of data sets with magnitude cutoffs the sign of the apparent rate change depends on the sign of the magnitude change and the type of cutoff used the effects of detection changes can be easily remedied by using a magnitude cutoff which eliminates the smaller events from consideration the techniques we have developed allow one to determine the optimum cutoff magnitude corrections are necessary for remedying the effects of systematic changes in magnitude estimates these corrections can be determined through modeling of observed rate changes caused by these shifts man made changes are present in all seismicity catalogs whether local regional or teleseismic they must be accounted for if these catalogs are to provide meaningful information on real process changes in the earth

some premonitory phenomena of the 1995 hyogo ken nanbu kobe earthquake seismicity b value and fractal dimension abstract this paper presents a detailed and complex analyses of the spatio temporal evolution of seismic activity between 1976 and 1998 in a broad area surrounding the epicentre of the 1995 hyogo ken nanbu kobe earthquake as well as in the source area various precursory changes in seismicity such as quiescence followed by increased seismic activity b value and fractal dimension correlation dimension d2 anomalies appear approximately two years before the occurrence of the major event an increased level of background seismicity is clearly observed after the occurrence of the kobe earthquake particularly in the northeast extension of the source area all these anomalous changes in seismic activity before and after the occurrence of the 1995 hyogo ken nanbu earthquake appear in a relatively large region surrounding the epicentre of the main shock as well as in the source area

seismic quiescence before the landers m 7 5 and big bear m 6 5 1992 earthquakes the landers earthquake of 28 june 1992 was preceded by a seismicity rate decrease of 75 in a volume approximately 11 by 23 by 15 km located adjacent to and north of the epicenter this anomaly started for all magnitude bands in january 1988 lasting 4 5 yr up to the mainshock a smaller volume 7 by 14 by 15 km to the south of the epicenter showed a seismicity rate decrease of 75 starting in november 1989 the big bear earthquake of the same day was preceded by a 100 decrease of the seismicity rate within a volume of approximately 13 by 22 by 15 km around the hypocenter this volume contained 192 earthquakes of m 1 6 during the background period of 9 yr but none during the 1 6 yr from december 1990 to 27 june 1992 the standard deviate z values characterizing these rate changes are very high 6 3 and 12 3 respectively and the anomalies are unique not surpassed in significance by any other rate decrease in portion of the southern california earthquake catalog examined 117 06 w to 115 40 w and 33 45 n to 35 10 n no seismicity rate change was found in the vicinity of the m 6 1 joshua tree earthquake of 23 april 1992 based on magnitude signatures and frequency magnitude analyses we conclude that the two quiescence anomalies could not have been due to a shift or a compression of the magnitude scale and we interpret them as precursor anomalies this analysis was carried out using the declustered earthquake catalog for the landers area with corrections of 0 2 and 0 1 august 1985 and may 1990 for two suspected magnitude shifts with a new visualization technique we can investigate the stability and changes of the seismicity rate as a function of time and space by mapping z values for rate changes at every time interval and in volumes centered on a dense grid of points latitude longitude this computer code furnishes an almost continuous sequence of smooth contour maps of the degree of rate changes any anomalies artificial or real may thus be defined accurately

precursory seismic quiescence in the mudurnu valley north anatolian fault zone turkey the seismicity rate in the mudurnu valley of turkey was studied using an earthquake catalogue that reports events homogeneously down to magnitude 2 3 for the years 1985 1989 and covers the area between latitudes 40 2 and 41 0 n and longitudes 30 0 and 31 5 e during this period the only two main shocks m 4 0 and m 4 3 occurred on 1988 september 6 and 1988 december 9 within about 30km of each other a highly significant seismic quiescence is evident in the area surrounding these main shocks while the seismicity rate in the rest of the area covered by the catalogue remains constant the quiescence becomes more pronounced the smaller the area around the main shocks that is studied the smallest areas that can be studied contain about 60 earthquakes and have dimensions of approximately 25km on each side the decreases in seismicity rates are 50 80 per cent depending on the volume and period used for defining the quiescence the quiescence started in 1988 january and lasted about seven months with approximately 4 5 months of normal activity separating it from the main shock of december the precursor time of 12 months for an m 4 3 main shock is similar to those observed in california it is concluded that it is possible to resolve precursory quiescence before moderate and large earthquakes in the mudurnu area with the existing seismograph network

seismic quiescence at parkfield an independent indication of an imminent earthquake the parkfield segment of the san andreas fault midway between san francisco and los angeles has experienced six moderate sized earthquakes since 1850 with an average recurrence time of about 22 years based on this regular behaviour and the occurrence of the most recent earthquake in 1966 a shock of local magnitude ml 5 7 is expected to occur by 19931 2 here we suggest that a current lack of small earthquakes on this segment could be a precursory anomaly to the next characteristic parkfield earthquake only four earthquakes of m 2 5 have occurred on the segment since january 1986 whereas twenty would have been expected extrapolating from the mean background rate comparison with other cases of precursory quiescence suggests that the m 5 7 earthquake should occur in the next two years rupturing the same 35 km fault segment that ruptured in 19663

robust and exploratory analysis of active mesoscale tectonic zones in japan utilizing the nationwide gps array abstract a monitoring gps array recently developed in japan can yield nationwide maps of active inland tectonic zones atzs on a mesoscale approximately 70 to several hundred kilometers in lateral extent but it has been difficult to characterize atzs in japan as they are in fact operational on multiple scales and our efforts are often hindered by various irregularities in the data the key to overcoming these problems would be to gain an insight into the available data before any precise kinematic modeling is performed with indefinite assumptions in this study horizontal velocity fields deduced from the nationwide gps array were treated with a set of techniques in robust smoothing and exploratory data analysis that brought out exceptionally powerful mesoscale atzs and made them easier to characterize the resolved atzs were then retrospectively monitored to study their regional and temporal variations using a set of approx 840 observation stations about 30 km apart for a 4 year series of fixed observation time intervals 810 days each the smoothing operation involved three steps 1 imputation of the velocity fields for the purpose of anti aliasing 2 robust smoothing of the velocity fields with the median operative and 3 visualization of deformation rate distributions in several coordinate independent parameters and post filtering the geometrical resolvability of mesoscale atzs was confirmed by calibrating the smoothing scheme against synthetic tectonic boundary models before it was applied to the case study in japan atzs in japan which are essentially visible as systematic deviations in the velocity fields on the international terrestrial reference frame itrf and as strain rate anomalies were highlighted sharply along some known tectonic zones chains of active volcanoes and areas above low seismic velocity anomalies in the crust and upper mantle all of which generally paralleled the offshore trench axes the geometrical agreements among the mapped atzs and the physical anomalies in the crust are presumably due to their common structural weakness on the mesoscale in the four main islands of japan all but 30 40 of the strain rate anomalies persisted during the entire 6 years of the case study period while the rest sporadically appeared or disappeared in a period from several months to a few years the transient shifts in the deformation rates were remarkably synchronous with some nearby major tectonic episodes large earthquakes and slow events differential plate coupling strengths along the subduction zones can also be inferred from the persistent pattern of rotational strain rate anomalies forming clockwise and counterclockwise pairs along the pacific our empirical observations suggest that the first order features of interseismic crustal deformations in japan can be characterized as collateral processes behaving in response to fluctuations of the tectonic stresses on multiple scales likely influenced by changes of plate coupling strengths on the contiguous subduction faults

spatial seismicity variations along convergent plate boundaries summary five major convergent plate boundaries south america izu bonin marianas new hebrides tonga kermadec and indonesia show strong variations in levels of background seismicity on scales ranging from tens to thousands of kilometres these variations were tested using two statistical approaches and we conclude that small earthquakes are not distributed randomly along these zones two types of large scale seismicity variations termed first order were recognized first regions with dimensions on the order of 100 km with extremely high seismicity levels first order actives one such region was recognized in each of the zones studied second large scale 500 to several thousand kilometres differences in the level of background seismicity along a given plate boundary regions with consistent levels of background seismicity are termed first order segments we examined each first order segment for smaller scale variations ten regions ranging in length from 40 to 170 km with anomalously high seismicity levels were recognized fifty three regions ranging in length from 25 to 355 km were found to have anomalously low seismicity levels thus areas with anomalously high levels of activity are rare in subduction zones these observations indicate that background seismicity in subduction zones is not randomly distributed along the strike of the zones it seems likely that the observed variations reflect tectonic differences in fact many of the seismicity variations which we observed appear to be spatially related to features on the seafloor or on the overriding plate if this is so then they may provide a powerful tool for characterizing subduction zones and understanding the mechanisms of earthquake generation

a statistical space time magnitude analysis on the aftershocks occurrence of the july 21th 2017 mw 6 5 bodrum kos turkey earthquake abstract in this study a detailed space time magnitude assessment on the aftershock sequence of july 21th 2017 mw 6 5 bodrum kos earthquake turkey is carried out by focusing on the analyses of aftershock parameters b value p value dc value and mamax b value is estimated as 0 90 0 05 with a completeness magnitude mc 1 6 and this relatively small b value may be resulted from the abundance of aftershocks with magnitude ml 4 0 however it is well represented by the gutenberg richter law with a typically b 1 0 p value is estimated as 1 04 0 02 with a c value 0 224 0 039 and is well characterized nearly close to the global p 1 0 this relatively high p value may be a result of the relative fast decay rate of the aftershock activity dc value is calculated as 1 74 0 09 and it means that aftershocks are homogeneously distributed temporal distribution of b value shows that small b values may be due to a stepwise increase in effective stress before the occurrence of larger aftershocks regional changes range from 0 5 to 1 2 in b value from 0 4 to 1 3 in p value and from 3 0 to 5 2 in mamax the smallest b values are found in and around mainshock including karaada bodrum akyarlar and turgutreis and these regions have high stress as well as coseismic deformation the largest p values are found in and around the mainshock epicenter including karaada and it is interpreted that this situation may be caused by coseismic deformation mamax values larger than 4 4 are observed in and around mainshock epicenter including bodrum and akyarlar and there is a clear correlation between spatial variations of b values and mamax these results show that stress changes and coseismic deformation seem highly effective on b and p value variations therefore a special interest needs to be given to these anomaly regions since aftershock hazard is highly associated with these parameters and may be developed considering their space time magnitude distribution

a study on the variations of recent seismicity in and around the central anatolian region of turkey abstract variations of the recent seismicity in and around the central anatolian region of turkey were evaluated based on the seismic b value standard normal deviate z value genas modelling annual probabilities and return periods of the earthquakes the catalog includes 16 702 earthquakes between 1974 and 2019 with magnitudes from 1 0 to 6 3 time distribution of b value shows that there is a tendency to decrease after the year of 2002 and b value decreased from 1 58 0 03 to 1 25 0 05 at the beginning of 2019 annual probabilities for magnitude ranges of 3 0 4 0 have the values between 3 and 30 return periods for magnitude levels of 5 0 5 5 have the values from 5 to 20 years and a value of 80 years for magnitude level of 6 0 the genas results show the significant temporal variations in the number of earthquakes smaller and larger than specific magnitude intervals by supplying the beginning periods of increases and decreases in the earthquake activity rate remarkable reductions in region time distribution of b value at the beginning of 2019 were detected in the regions covering nigde fault and its vicinity along the south west northwest and southwest directions among the mut fault zone karsanti karaisali fault zone and karatas osmaniye fault zone in and around surgu fault and along its northwest direction between surgu fault and east anatolian fault zone significant seismic quiescence areas in z value distribution include the northwest ends of the tuzgolu fault zone and study area including akpinar fault the northeast of salanda fault between salanda fault and the central anatolian fault zone the northeast parts of the central anatolian fault zone the west of malatya fault between surgu fault and the east anatolian fault zone the southeast end of the tuzgolu fault zone karsanti karaisali fault zone and its vicinity the southwest of tuzgolu thus these anomaly areas observed in the central anatolian region and its vicinity at the beginning of 2019 may be one of the most likely zones for the next strong large earthquake occurrences

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

broad region of no sediment in the southwest pacific basin a broad region nearly the size of the mediterranean sea exists in the central south pacific ocean that is devoid of sediment and has been so since the late cretaceous the requirements for remaining sediment free are very low biological productivity a shallow calcite compensation depth essentially no dust input and no deposition of hydrothermal oxides and hydroxides one or two of these conditions are common but nowhere else do all four occur the combined effect of these sediment inhibiting factors is a consequence of crustal age seawater chemistry and atmospheric oceanographic and physiographic isolation furthermore this unique combination of conditions has prevailed for more than 80 million years

seismic quiescence and asperities in the tonga kermadec arc highly significant temporal and spatial seismicity rate changes were found along the tongaskermadec plate boundary the standard deviate z test was used to compare systematically the rates in different periods and different volumes and to test for uniqueness of anomalies found the noaa hypocenter data file showed a pronounced decrease in the number of small magnitude earthquakes reported after 1969 at the same time as such a reporting decline exists in the worldwide data therefore only earthquakes with mb 4 9 were studied a search for quiescence before recent mainshocks yielded two uniquely significant precursory anomalies one missed mainshock and one false alarm quiescence started 63 months before the january 1976 m 8 0 kermadec and 25 months before the june 1977 tonga m 7 2 earthquakes the december 1975 m 7 5 shock was not preceded by a seismicity rate change the seismic gaps in the tonga kermadec arc with sufficient seismicity for analysis 17 22 and 31 34 show constant rates up to the present therefore on the basis of the quiescence hypothesis earthquakes are not forecast for these segments the stress drops of 380 interface events were estimated using the mb ms method the average was uniform along the island arc with the exception of two segments with average of less than half the normal values these segments coincided with the two largest recent interface ruptures however in the northern tonga the was low before the 1975 rupture whereas in the kermadec the 1976 aftershocks showed low asperities could not be identified on the basis of high stress drops a systematic study of the seismicity rate as a function of space defined large variations along the arc the areas of highest and lowest seismicity rate correlate with the northern end of the trench and with the louisville ridge intersection respectively however other large rate contrasts exists between arc segments without obvious tectonic differences this implies that seismicity doughnut patterns do not reliably define precursors one segment of outstandingly high seismicity rate 30 31 s is identified as a major asperity because it contains a large number of m 6 events and a large number of recent mainshock aftershock sequences and because it stopped the great 1976 rupture we propose that the only other segment of high seismicity rate near 20 5 s also represents a major asperity

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

seismic quiescence before the m 7 1988 spitak earthquake armenia a detailed analysis of the 35 yr of seismicity between 1962 and 1997 using a gridding technique shows that the m7 spitak earthquake of 1988 december 7 was preceded by a quiescence anomaly that started at approximately 1984 0 5 and lasted about 5 0 5 yr up to the main shock this quiescence anomaly had a radius of about 20 3 km estimated from circular areas with 75 per cent rate decrease centred at the point of maximum significance of the anomaly the quiescence was clearly present in the aftershock volume during the 5 yr before the 1988 main shock but its statistically strongest expression was located 30 km nw of the epicentre this anomaly fulfills the association rules between precursory quiescence anomalies and main shocks even for a tight definition and is therefore proposed as a case of precursory quiescence the largest value of the standard deviate z found by random selection of samples by gridding was z 14 for a time window of tw 3 yr using a sample size of n 300 events this makes this anomaly the strongest observed so far and it is the first documented in an environment of continental collision there are no false alarms exceeding in significance the precursor the armenian earthquake catalogue used for this study had 4600 earthquakes with m mmin 2 2 in the area bounded by 39 5 to 42 n 42 5 to 47 e from the point of view of homogeneous reporting this is the best catalogue we have analysed so far the limits of the data used and the density of the grid are dictated by the data and have no influence on the results the choice of free parameters does not influence the results significantly within the following limits 100 n 500 2 tw 7 2 2 mmin 2 8

case 23 nomination of precursory seismic quiescence as a significant precursor several cases of extremely strong quiescences have been investigated in great detail and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity several additional cases of quantitatively measured quiescence have been documented the method of measuring quiescence has progressed from using visual means to using a quantitative approach and the understanding of the noise sources has significantly advanced during the last few years therefore i feel that quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the list of significant precursors although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process

eruption characteristics and cycles at pavlof volcano alaska and their relation to regional earthquake activity abstract pavlof volcano 55 25 n 161 54 w exhibits two eruption styles magmatic eruptions of one to two days duration and phreatic phreatomagmatic activity lasting several days to two months thirty four eruptions have occurred in historic times of these the largest are volcano explosivity index 3 nine magmatic and 13 phreatomagmatic eruptions occurred between 1973 1983 all the magmatic eruptions occurred in the fall between sept 9 nov 20 four magmatic eruptions occurred during november 11 15 but in four different years a 3 year long period of eruptive activity between 1973 1976 bears striking resemblance to a period of activity between 1980 1983 no locatable shallow earthquakes 100 km are clustered beneath pavlof and several other volcanoes their t axes show downdip tension within the slab deep teleseisms 160 km mostly occurred between 1977 1979 when the volcano was not erupting catalogued volcanic activity throughout the alaska aleutian arc shows a weak tendency to increase around the time of great m 7 8 earthquakes

a nonplanar slow rupture episode during the 2000 miyakejima dike intrusion magmatic intrusions release extensional strain in the earth s crust upon availability of magma intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes the 2000 miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far with five ml 6 earthquakes we analyze the seismicity and deformation induced by the miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode in six earthquake bursts lasting few hours and migrating at 1 km h 1 we find candidates for slow earthquakes each burst nucleated at the tips of previous bursts suggesting stress interaction the variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time such as those induced by a dike based on dislocation models we find that deformation is best explained by aseismic slip in addition to the seismic burst with a moment 1 3 to 2 3 times larger than the earthquakes seismic moment and opening of 0 20 0 07 m on the dike the aseismic slip occurred over a few hours with moment duration and migration velocity consistent with that of previously observed slow slip events we argue that the seismic bursts are likely driven by slow slip sharing most properties with tectonic slow slip events and swarms but occurring on a set of nonaligned faults

precursory seismic quiescence past present and future precursory seismic quiescence has played a major role in most of the succesful earthquake predictions made to date in addition to these successes the number of detailed post mainshock documentations of precursory quiescence is steadily growing these facts suggest that precursory quiescence will play an important role in earthquake prediction programs of the future for this reason it is important to critically evaluate the present state of knowledge concerning this phenomenon the history of observations of precursory seismic quiescence includes work on seismic gaps and seismic preconditions as well as actual studies of temporal quiescence these papers demonstrated the importance of quantitative evaluation of seismicity rates and the benefits of systematic analysis during the early 1980 s the impact of man made effects on seismicity rates was demonstrated for the first time despite progress in catalog understanding the identification and correction of man made seismicity changes remains as the major barrier to earthquake prediction using these data effects of man made changes are apparent in many past studies of seismicity patterns making the results difficult to evaluate recent experience with real time anomalies has demonstrated the necessity of determining the false alarm rates associated with quiescence precursors determination of false alarm rates depends on quantitative definitions of anomalies and statistical evaluations of their significance a number of successful predictions which have been made on the basis of seismic quiescence provide important lessons for present and future work there are many presently unanswered questions regarding seismic quiescence which must be answered before we can determine the reliability of this phenomena as a precursor

seismicity anomalies of the 2003 bam iran earthquake abstract the bam earthquake occurred in an area without any historically recorded major earthquake based on active tectonics and cmt solutions the area is under the influence of shortening and right lateral strike slip faulting seismicity is of a shallow crustal type which is mainly distributed within the koohbanan golbaf lakarkooh shahdad gowk fault systems and the terminal sections of zagros in order to detect temporal seismicity anomalies before this earthquake we compiled a catalog from the isc events and then analyzed it for the magnitude of completeness after declustering this catalog changes in seismicity were assessed by the z value test the temporal variations indicate a relative decrease in z value before the bam earthquake additional to seismic quiescence and decrease in b value before the main shock there are pieces of evidence corresponding to increase in triggered background seismicity after this earthquake

two current seismic quiescences within 40 km of tokyo summary two highly significant seismic quiescence anomalies that started in 1993 0 exist currently within about 40 km of tokyo they are located in central saitama province at 35 99 n 139 56 e and in tokyo bay south of funabashi at 35 59 n l39 94 e the radii of the anomalous volumes are approximately 15 km centred at about 25 and 20 km depth respectively the seismicity rate during the quiescence was less than 10 per cent background rate in both cases the significance of these quiescences measured by the standard deviate z test comparing the rate of the last three years to the backgound rate is higher than for any other rate changes present in the catalogue zmax 7 5 and 7 2 respectively however episodes of highly significant quiescences which could have been interpreted as precursors but were not followed by main shocks also exist in the data set a third seismic quiescence was found to be in progress since 1993 3 0 5 in nw saitama province at 36 18 n 139 22 e it has a radius of 14 km and is less significant than the other two anomalies zmax 6 8 in a polygon that covers the areas of all three quiescences defined above the seismicity rate since 1994 is only 30 per cent of the previous background rate i e 100 earthquakes that would normally have occurred did not this analysis is based on the earthquake catalogue of the national institute for earth science and disaster prevention for the years 1980 1996 2 and mmin 1 0 as well as for the years 1986 2 1996 2 with mmin 0 1 the anomalies are equally clear in the clustered and in the full catalogues to avoid contamination by explosions only nighttime data 19 00 to 7 00 hours local time were used the frequency magnitude distributions in the quiescent volumes at central saitama nw saitama and funabashi have b values of 1 3 1 5 and 1 1 respectively based on the hypothesis that crustal volumes with high b values may not be capable of m6 earthquakes these three quiescent volumes may be ruled out as source volumes for main shocks of these magnitudes using lilt seismic quiescence hypothesis alone it is a reasonable interpretation to suggest that m 6 5 0 5 earthquakes are expected to terminate each of the three quiescences within 1 year 1 year from now with a 50 per cent probability each the interpretation that all three quiet volumes could rupture together in a large earthquake seems less likely however based on the information that the quiescences are located in volumes with b values above the average b 0 8 it can be argued that the three current quiescences are false alarms the fact that these two lines of evidence allow opposing interpretations in these cases shows that neither hypothesis is sufficiently tested thus the quiescence hypothesis is not advanced enough for issuing earthquake predictions nevertheless it is important that scientific tests of prediction scenarios are formulated in real time so we can learn how to modify our hypotheses to make them useful for prediction in the future

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

background seismicity rates and precursory seismic quiescence imperial valley california the problem of recognizing precursory seismicity rate changes consists of two steps first a background or normal rate must be determined and second anomalous rates must be recognized in this paper we address the first of these steps determining a background seismicity rate two problems must be dealt with if a meaningful background rate is to be determined first dependent events must be recognized and removed from consideration and second detection or reporting changes must be accounted for a number of techniques are available for recognizing dependent events we used the one developed by mcnally 1976 in this work the technique we used for recgonizing detection and reporting changes was developed by habermann 1983 we demonstrate these techniques on seismicity from the imperial valley region of california after a reasonable background rate is determined we examine seismicity rates in this region prior to the imperial valley earthquake of 15 october 1979 the source area of the earthquake shows a possible precursory quiescence which started during july 1979 the time of this rate decrease is close to the time of a change in the seismic instrumentation in the imperial valley which makes it difficult to determine whether the decrease is real or related to detection several other seismicity rate changes observed in the imperial valley appear to be related to changes in the operation of the network there these include quiescent periods which occur only if magnitude cutoffs are applied to the data and periods of low reporting of events with m 2 5 these observations suggest that magnitudes were not reported for some events during several time periods all of these observations indicate that determination of detection histories is crucial for meaningful seismicity studies

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

transition from aftershock to normal activity the 1965 rat islands earthquake aftershock sequence a transition from aftershock to normal activity is identified 2200 days after the occurrence of the 1965 rat islands earthquake of mw 8 7 after this time we observe a significant departure of the seismicity in the focal region from the extrapolated trend of the aftershock activity predicted by the modified omori formula proposed by utsu in 1961 the maximum likelihood estimate of the parameters for the formula and the selection of a statistical model based on the akaike information criterion show that the whole aftershock sequence is best modeled by the combination of an ordinary aftershock sequence and secondary aftershock activity associated with the largest aftershock fitting of the activity after the transition period to the modified omori formula results in an unusually low value of the decay constant we interpret that this activity represents normal or background seismicity and not another secondary aftershock sequence defining background activity in a focal region of a large earthquake is essential for detection of seismic quiescence prior to the next major event

quantitative mapping of a precursory seismic quiescence to the izu oshima 1990 m6 5 earthquake japan a highly significant seismic quiescence with a standard deviate z 10 1 corresponding to a 99 per cent confidence level lasted from 1987 7 up to the 1990 february 20 izu oshima m 6 5 earthquake the quiescent volume had dimensions of 30 km n s and 10 km e w and was centred below 14 km depth within the recently upgraded seismograph network of the earthquake research institute eri this main shock was the only one with a magnitude m 5 8 in the upper 30 km of the crust for which the precursory quiescence hypothesis could be tested within a radius of 50 km and during the observation period 1983 5 1995 9 there were no other 1 5 yr or longer periods of quiescence that were rated z 6 5 in the declustered earthquake catalogue except one that was associated with volcanic activity the total space time covered by alarms including the volcanic one was less than 1 per cent at the z 6 5 level the rarity of highly significant episodes of quiescence and the correlation in space and time suggest that a precursory seismic quiescence started 2 5 yr before the izu oshima 1990 earthquake in its source volume and to the north of it and that it can be recognized with an alarm level of z 6 0 generating no false alarms during the 1 5 yr quiescence window only 10 earthquakes occurred in the quiet volume whereas 50 events were expected based on the rate seen at other times in randomly selected volumes containing 50 100 and 200 events the anomaly scored z 6 1 to 10 1 on the basis of the data from may 1983 to 1995 there is no highly significant quiescence currently present in the izu oshima area

comments on preseismic quiescence before large earthquakes in the aegean and surrounding area by karakaisis et al 1987 commentaire et reponse a l article de karakaisis g f panagiotopoulos d g krimnianiotou m ch papazachos b c 1987 ann geophysicae 5b 2 155 160

mean state and wave disturbances during phases i ii and iii of gate based on era 40 abstract using ecmwf s second generation reanalysis era 40 the large scale mean state and synoptic scale features associated with african easterly wave disturbances aews are examined over west africa and the adjacent eastern atlantic ocean during the three 21 day observing periods of the global atmospheric research program garp atlantic tropical experiment gate in 1974 phase i 26 june 16 july phase ii 28 july 17 august phase iii 30 august 19 september results are partitioned into four geographical boxes in order to highlight differences among the aew vortices as they propagate westward along two tracks northern and southern over west africa land and the adjacent eastern atlantic ocean water this marks the first time that a detailed diagnosis of the northerly track aews has been conducted results are also compared to previous gate studies and a 30 yr climatology is extracted from era 40 in general the subjectively analyzed wind fields presented in earlier studies compare favorabl

artificial and natural changes in the rates of seismic activity a case study of the garm region tadjikistan cis summary seismicity rate variations observed in earthquake catalogues can be natural i e associated with temporal variations in the seismic process or they can be artificial i e related to changes in the networks of seismic stations used to create these catalogues such artificial changes must be identified and corrected before real variations can be reliably examined this paper demonstrates techniques for modelling of the observed changes in seismicity rates in order to determine their origin the main technique used here has been previously applied to a number of catalogues to identify times of rate changes it can be used to demonstrate the magnitude dependence of these changes and the existence of two major types of possible artificial rate variations detection changes and magnitude shifts in addition two new techniques are applied one of them the variable window technique makes use of windows of different sizes to sample the data thus addressing some of the shortcomings of the original approach the other new technique catalogue randomization helps analyse the cause of some of the rate changes it is most helpful in the cases of pure magnitude shifts the use of these techniques is demonstrated examining data from the garm region tadjikistan former soviet union the garm earthquake catalogue includes more than 85 000 events for the period 1955 january 1989 april and covers an 80 km x 100 km area in the collisional zone between the indian and eurasian plates known changes in the garm network recently documented in detail were compared with the rate changes identified with the above techniques of the 18 main rate variations identified at least two thirds were found to be artificial most of them were readily associated with reported changes in the network such as closure and opening of stations and or changes in instrumentation of the rate changes determined to be natural most prominent were the ones associated with a possible quiescence preceding a m6 3 event and its aftershock sequence finally other authors reports of linear trends and annual periodicity in the seismic activity at garm are critically examined

earthquakes plate subduction and stress reversals in the eastern aleutian arc plate subduction beneath the 1500 km long segment of the eastern aleutian arc between kodiak and atka islands 154 w and 176 w longitude is studied with observations from teleseismic data the primary data base consists of hypocenters of earthquakes for the period 1965 1975 carefully selected from the bulletins of the international seismological centre and of 44 new focal mechanism solutions the principal results of this study are that hypocenters of intermediate depth earthquakes in the eastern aleutians appear to define a weakly developed double seismic zone at depths between 70 and 170 km additional evidence for a double seismic zone comes from focal mechanisms which generally show downdip directed p axes for earthquakes in the upper zone and downdip directed t axes in the lower zone major features of the double zone can be explained by thermoelastic stresses in the downgoing plate the observed predominant downdip stress polarity at intermediate depths in the descending plate reverses along strike of the arc this stress reversal coincides in map view with a change from a continental to an oceanic arc the coincidence may result from spatial differences either in the coupling between the plates at shallow depths or in the rheology of the surrounding oceanic versus continental mantle alternatively the stress reversal may be related to the time since the last great earthquake if the observed stress polarity relates to the elapsed time since the last great earthquake it may be a significant observation for long to intermediate term prediction of great thrust earthquakes in subduction zones portions of the eastern aleutian arc where downdip tension predominates contain one or more seismic gaps that appear to have a high probability for great earthquakes in the next few decades a moderate sized bathymetric feature in the pacific plate the amlia fracture zone modifies subduction and produces a bend or offset in the downgoing plate as well as an offset in the line of active volcanoes in the upper plate subduction of the fracture zone appears also to cause formation of summit basins on the arc platform and some aseismic behavior of a 100 km long segment of the main thrust zone

variations of b values at the western edge of the ryukyu subduction zone north east taiwan using earthquakes relocated in north east taiwan we estimated b value distribution along a cross section located near the ryukyu slab edge and four b value anomalous areas are evidenced 1 a high b value body lying on top of a low vp low vs and high vp vs sausage like body was considered as a region of enhanced partial melt or water supply above which seismicity occurs 2 beneath the ilan plain an anomalous area characterized by b values slightly higher than 1 1 might give evidence to the magma conduits to the kueishantao island 3 above the ryukyu wadati benioff zone at depths ranging from 90 to 110 km a high b value anomaly might correspond to the depth where dehydration occurs in the subducting oceanic plate and 4 a low b value area located within the ryukyu slab at depths ranging from 70 to 90 km might be linked to the compressive mechanisms shown by focal mechanisms and the bending of the subducting plate

seismicity rate variations and systematic changes in magnitudes in teleseismic catalogs abstract seismicity rate variations are commonplace in teleseismic catalogs these changes have two possible causes they could be real or they could be related to changes in the networks used to detect the events it is clearly important to differentiate between these two possibilities we demonstrate a technique for making this differentiation using uniform data generated with known rates and magnitude shifts we then apply this technique to data from large regions of the world all of these regions show significant variations in seismicity rates for sets with magnitude cutoffs of 5 0 and 5 5 we show that most of these changes have distributions in the magnitude domain which are consistent with systematic changes in magnitudes of between 0 1 and 0 2 units these results suggest that most observed rate variations in teleseismic sets with high magnitude cutoffs are related to systematic changes in magnitudes and are therefore not real this result has important implications for earthquake prediction and tectonic studies which interpret these variations

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

seismicity rate changes along the central california coast due to stress changes from the 2003 m 6 5 san simeon and 2004 m 6 0 parkfield earthquakes abstract we investigated the relationship between seismicity rate changes and modeled coulomb static stress changes from the 2003 m 6 5 san simeon and the 2004 m 6 0 parkfield earthquakes in central california coulomb stress modeling indicates that the san simeon mainshock loaded parts of the rinconada hosgri and san andreas strike slip faults along with the reverse faults of the southern los osos domain all of these loaded faults except for the san andreas experienced a seismicity rate increase at the time of the san simeon mainshock the parkfield earthquake occurred 9 months later on the loaded portion of the san andreas fault the parkfield earthquake unloaded the hosgri fault and the reverse faults of the southern los osos domain which both experienced seismicity rate decreases at the time of the parkfield event although the decreases may be related to the decay of san simeon triggered seismicity coulomb stress unloading from the parkfield earthquake appears to have altered the aftershock decay rate of the southern cluster of san simeon aftershocks which is deficient compared to the expected number of aftershocks from the omori decay parameters based on the pre parkfield aftershocks dynamic stress changes cannot explain the deficiency of aftershocks providing evidence that static stress changes affect earthquake occurrence however a burst of seismicity following the parkfield earthquake at ragged point where the static stress was decreased provides evidence for dynamic stress triggering it therefore appears that both coulomb static stress changes and dynamic stress changes affect the seismicity rate

teleseismic detection in the aleutian island arc recently it has become apparent that teleseismic detection has decreased substantially in many regions of the world the major decrease was related to the closure of the vela arrays in the united states during the late 1960 s this detection decrease has been recognized in south and central america mexico the kuriles the caribbean tonga and the new hebrides in this paper the effect of the closure of these arrays on the reporting of events in the aleutian island arc is examined in the aleutians the detection history is complicated by the short term installation of a local network on and near amchitka island during the early 1970 s the temporal coincidence of the installation of this network and the closure of the vela arrays delayed the detection decrease in the central aleutians until the amchitka network was closed in early 1973 reporting in the eastern aleutians was unaffected by the installation of the amchitka network in that region the detection decreased between 1968 and 1970 the time of the closure of the vela arrays new techniques have been developed which make it possible to determine the effect of station installation or closure on the reporting in some regions these techniques rely on plots which show the distribution of an observed seismicity rate change in the magnitude domain these plots make it possible to recognize probable detection changes and to determine quantitatively magnitude cutoffs which avoid these changes the magnitude level at which these cutoffs are made is termed the minimum magnitude of homogeneity mmin h the reporting of events with mb 4 6 in the aleutians decreased substantially during the mid 1970 s so mmin h in this region is 4 7 this is different from the magnitude of completeness mmin c which is mb 5 0 0 1 if one is interested in examining seismicity rates for changes which may be precursors to earthquakes then awareness of detection related changes and magnitude cutoffs which avoid these changes are essential for meaningful results

time dependent earthquake occurrence rates along the hellenic arc seismicity rate changes in the hellenic subduction zone southern aegean sea were studied by applying the dieterich 1994 rate state dependent friction model combined with static coulomb stress changes cff the coseismic slip of the strongest earthquakes with moment magnitude m w 6 0 was considered to contribute to the stress field evolution along with the continuous tectonic loading stress changes were calculated just after each strong event and their influence was examined in connection with the smaller magnitude earthquake occurrence rates qualitative and quantitative comparison between the observed seismicity rates smoothed by the means of a probability density function and the expected ones as they were forecasted by the rate state model were investigated for the interseismic periods study periods between subsequent strong earthquakes the calculations aim to identify areas of expected increased seismicity rates as candidates to accommodate enhanced seismic activity results strongly depend on the determination smoothing of the unperturbed reference seismicity rates and data adequacy seismicity rate results were filtered by certain criteria and constraints in an attempt to overcome model uncertainties epicentral errors rupture models parameter values and to provide reliable results for specific areas of major interest that is in areas with increased positive coulomb stress changes values the modeling approach resulted in satisfactory correlation between observed and synthetic seismicity rates and in particular the two strong m w 6 earthquakes that occurred in 2013 are located in areas of increased expected seismicity rates

earthquake triggering during preparation for great earthquakes seismic quiescence has been proposed as a precursor to many large earthquakes in this paper we present two cases in which precursory quiescence is interrupted several years prior to great earthquakes by triggered events in the upcoming rupture areas this triggering results in complex precursory patterns which include seismic quiescence and triggered events prior to the kermadec earthquake of 1976 ms 8 0 events in the rupture zone were triggered by a quake on the outer rise and one near the future mainshock epicenter events were triggered by an earthquake on an adjacent segment of the plate interface and by one near the epicenter of the new hebrides earthquake of 1980 ms 8 0 we propose that two preconditions must be fulfilled for triggering to occur first the stress in the region must be close to the failure stress and second nearby events must occur which are large enough to affect the stress field but not large enough to cause an immediate mainshock

crustal heterogeneity highlighted by spatial b value map in the wellington region of new zealand summary we map the b value in the subduction zone of the wellington region new zealand using a high quality earthquake catalogue relocated with a 3 d seismic velocity model consisting of 50 314 events that occurred between 1990 and 2005 in order to investigate heterogeneity in the crust of the overlying plate and in the upper plane of the wadati benioff zone wbz we analyse a series of cross sections perpendicular to the strike of the subduction zone we calculate the b values selecting events with magnitude of completeness 2 4 and depth 65 km and projecting the seismicity within 20 km on each side of the cross sectional planes we observe areas of high b value 1 7 near the plate interface and regions of low b value anomalies are detected both in the wbz in the northwest region below 40 km depth and in the overlying plate in the northern south island at 10 km depth the anomalies are statistically significant based on utsu s p test and the bootstrap method and are not data processing method or parameter dependent we compare the b value distribution with previously determined 3 d distributions of vp vp vs and qp from seismic tomography this comparison suggests that material inhomogeneity caused by fluid filled cracks resulting from dehydration of the subducted slab and subducted sediments is the predominant cause of b value variation in the shallow part of this subduction zone our observations are consistent with a previously proposed conceptual model that fluid distribution in the shallow part of this subduction zone is controlled by the permeability of geological terranes in the overlying plate

detection of triggered deep low frequency events from the 2003 tokachi oki earthquake 1 we show the level of increased decreased seismicity mapped across japan immediately following the 2003 tokachi oki earthquake mw 8 1 of september 25 2003 ut by use of the statistic significant dynamic triggering of events is found near the nankai subduction zone 900 1400 km from the earthquake the events are inferred to be dynamically triggered deep low frequency earthquakes of a type that often occur in this region the triggering appears to be caused by the long period oscillations of the surface waves which may be effective in triggering fluid related events the region that showed the highest level of triggered events was an area of elevated activity in the bungo strait where a slow slip event was in progress

seismic quiescence stress drops and asperities in the new hebrides arc the rate of occurrence of earthquakes shallower than 100 km during the years 1963 to 1980 was studied as a function of time and space along the new hebrides island arc systematic examination of the seismicity rates for different magnitude bands showed that events with mb 4 8 were not reported consistently over time the seismicity rate as defined by mb 4 8 events was examined quantitatively and systematically in the source volumes of three recent main shocks and within two seismic gaps a clear case of seismic quiescence could be shown to have existed before one of the large main shocks if a major asperity was excluded from the volume studied the 1980 ms 8 rupture in the northern new hebrides was preceded by a pattern of 9 to 12 yr of quiescence followed by 5 yr of normal rate this pattern does not conform to the hypothesis that quiescence lasts up to the mainshock which it precedes the 1980 rupture also did not fully conform to the gap hypothesis half of its aftershock area covered part of a great rupture which occurred in 1966 a major asperity seemed to play a critical role in the 1966 and 1980 great ruptures it stopped the 1966 rupture and both parts of the 1980 double rupture initiated from it in addition this major asperity made itself known by a seismicity rate and stress drops higher than in the surrounding areas stress drops of 272 earthquakes were estimated by the ms mb method time dependence of stress drops could not be studied because of changes in the world data set of ms and mb values areas of high stress drops did not correlate in general with areas of high seismicity rate instead outstandingly high average stress drops were observed in two plate boundary segments with average seismicity rate where ocean floor ridges are being subducted the seismic gaps of the central and northern new hebrides each contain seismically quiet regions in the central new hebrides the 50 to 100 km of the plate boundary near 18 5 s showed an extremely low seismicity rate during the entire observation period low seismicity could be a permanent property of this location in the northern new hebrides gap seismic quiescence started in mid 1972 except in a central volume where high stress drops are observed this volume is interpreted as an asperity and the quiescence may be interpreted as part of the preparation process to a future large main shock near 13 5 s

spatial variation in the frequency magnitude distribution of earthquakes under the tectonic framework in the middle east abstract spatial variations of seismic energy released and b value over the middle east region are investigated based on a seismicity catalog from 1995 to 2007 the goal is to use these seismic parameters and based on other geodetic and geophysical observations such as gps measurements strain rate model fault distribution focal mechanism crustal model q model and gravity measurements etc to uncover spatial patterns that seem anomalous areas of high energy released cumulative seem to correspond to the areas of relatively high b values areas of high energy released and high b values seem to correspond very well with the location of continental collision where earthquake activities are high the divergent boundary between arabia and african plates and subduction zone at makran seem to correspond to low to moderate energy release northern pamir azerbaijan caucasus the lower part of zagros mountains eastern turkey owen fracture zone strait of bob el mandeb and south of the sulaiman shear zone seem to correspond to high cumulative energy released high strain rate high b values and high fault density while the central and eastern iran southern zagros northern pakistan gulf of aden alborz southwest of the caspian sea western caucasus and kopeh dagh seem to correspond with lower b values the cross section map for hindu kush shows general decreasing of the b values with depth however a region of high b value is observed underneath pamir at depths from 170 to 230 km this anomaly region can be due to dehydration of pamir crustal slab at depth

evaluation of precursory seismic quiescence in sixteen subduction zones using single link cluster analysis this paper describes a new method single link cluster analysis slc to evaluate percursory quiescence for shallow earthquakes in sixteen subduction zones using data from the isc catalog to define quiescent regions we divided the catalog into time intervals with a durationt overlapping byt 2 we considered all earthquakes having magnitudes larger than some magnitudemmin lying within a specified distance of a great circle which is approximately coincident with the trench near a subduction zone within each time interval we connected or linked all earthquakes lying within some cutoff distanced of one another we then projected all these links onto the great circle and defined a region to be quiescent if it was not covered by the projection of any links for this study t was two years mmin wasmb 4 9 and we variedd from 100 to 400 km we defined an earthquake as following quiescence if it occurred within two years following and within 75 km of a quiescent zone as defined above the primary conclusion of this study was that earthquakes with surface wave magnitudes 7 2 and greater were about 5 15 more likely to follow quiescence than were the smaller background earthquakes withmb 4 9 a chi squared analysis shows that this result is significant at the 99 level in contrast earthquakes with surface wave magnitude of 6 7 to 7 1 were no more likely to follow quiescence than were background earthquakes of sixteen individual regions central america japan and peru chile were the only regions where large earthquakes were more likely to occur following quiescence than were background earthquakes for a cutoff link length of 300 km only in central america was the difference between large earthquakes and background earthquakes significant at the 95 level of significance for a cutoff link length of 250 km the significance level exceeded 95 only in japan the slc method is an objective quantitative method for evaluating large data catalogs or for monitoring quiescence in regions where quiescence is conjectured to precede large earthquakes