determination of mmax from background seismicity and moment conservation we describe a simple method to determine the probability distribution function of the magnitude m max and return period t r of the maximum plausible earthquake on crustal faults the method requires the background seismicity rate estimated from instrumental data and the rate of interseismic moment buildup the method assumes that the moment released by the seismic slip is in balance with the moment deficit accumulated in between earthquakes it also assumes that the seismicity obeys the gutenberg richter gr law up to m max we took into account the aftershocks of large infrequent events that were not represented in the instrumental record so that we could estimate the average seismicity rate over the entire fault history we extrapolated the instrumental record using the gr law to model the frequency of larger events and their aftershocks this increased the frequencies of smaller events on average when these smaller events were newly extrapolated they predicted a higher frequency of larger events we iterated this process until stability was reached and then we assumed moment balance when we found the maximum magnitude we have found this method to be appropriate in applications involving examples of fault with good historical catalogs we then showed examples of applications to faults with no historical catalogs we present results from nine cases for the san andreas fault system we find m max 8 1 0 3 with t r380 950 120 yrs for the north anatolian fault m max 8 0 0 3 with t r275 650 135 yrs for the main himalayan thrust m max 9 0 0 2 with t r1200 2700 550 yrs for the japan trench m max 9 3 0 3 with t r520 1200 220 yrs for the sumatra andaman trench m max 9 0 0 3 with t r200 450 80 yrs for the bocono fault m max 7 3 0 3 with t r160 360 70 yrs for the altyn tagh fault m max 8 0 0 3 with t r900 2000 400 yrs for the dead sea transform m max 7 8 0 3 with t r1000 2400 450 yrs and for the kunlun fault m max 8 0 0 3 with t r1000 2000 450 yrs

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

southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

comment on changes of reporting rates in the southern california earthquake catalog introduced by a new definition of ml by thessa tormann stefan wiemer and egill hauksson abstract earthquake catalogs can be inhomogeneous because of changes in the definition of earthquake magnitude provided that a sufficient number of events have magnitudes defined in more than one system it is possible to apply a monte carlo method to the observed joint distribution to convert sets of magnitudes from one system to another improving any statistical analysis of the catalog i demonstrate the method for the southern california catalog in which the definition of local magnitude has recently been changed monte carlo magnitude mapping appears to eliminate temporal changes that are otherwise present

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

changes of reporting rates in the southern california earthquake catalog introduced by a new definition of ml starting january 2008 local magnitudes m l for southern california are determined by a new calibration that provides various improvements for determining m l for small earthquakes magnitudes for the previous years are being recalculated and the catalog continuously updated with the first year of overlapping data now being available recalibrating a magnitude scale can cause a break in homogeneity of reporting and often produces artifacts in the catalog statistics that can influence a wide range of seismicity studies to search for such a break we compare the old m l and the new m l catalogs for 2007 we find 1 the two magnitude values differ for 96 of the m l events and hand determined magnitudes are also revised 2 the magnitude differences are irregular from magnitude increases of up to 1 5 units to reductions by as much as 2 3 units with an average change of 0 13 units 3 the number of events above m 1 8 decreases by 32 for the new magnitude scale 4 the completeness magnitude apparently drops by 0 3 units from 1 6 to 1 3 5 the b value reduces by approximately 0 2 units dropping from 1 16 to 0 95 6 the new magnitude calibration produces a more stable b value estimate and can therefore be regarded as the better scaling we document selected examples of how the change in magnitude calibration may affect seismicity and hazard related analyses that are based on the southern california seismic network scsn catalog especially the change of the b value from 1 1 to 0 9 has potentially major implications for hazard related applications

a revised earthquake catalogue for south iceland in 1991 a new seismic monitoring network named sil was started in iceland with a digital seismic system and automatic operation the system is equipped with software that reports the automatic location and magnitude of earthquakes usually within 1 2 min of their occurrence normally automatic locations are manually checked and re estimated with corrected phase picks but locations are subject to random errors and systematic biases in this article we consider the quality of the catalogue and produce a revised catalogue for south iceland the area with the highest seismic risk in iceland we explore the effects of filtering events using some common recommendations based on network geometry and station spacing and as an alternative filtering based on a multivariate analysis that identifies outliers in the hypocentre error distribution we identify and remove quarry blasts and we re estimate the magnitude of many events this revised catalogue which we consider to be filtered cleaned and corrected should be valuable for building future seismicity models and for assessing seismic hazard and risk we present a comparative seismicity analysis using the original and revised catalogues we report characteristics of south iceland seismicity in terms of b value and magnitude of completeness our work demonstrates the importance of carefully checking an earthquake catalogue before proceeding with seismicity analysis

systematic survey of high resolution b value imaging along californian faults inference on asperities understanding and forecasting earthquake occurrences is presumably linked to understanding the stress distribution in the earth s crust this cannot be measured instrumentally with useful coverage however the size distribution of earthquakes quantified by the gutenberg richter b value is possibly a proxy to differential stress conditions and could therewith act as a crude stress meter wherever seismicity is observed in this study we improve the methodology of b value imaging for application to a high resolution 3 d analysis of a complex fault network in particular we develop a distance dependent sampling algorithm and introduce a linearity measure to restrict our output to those regions where the magnitude distribution strictly follows a power law we assess the catalog completeness along the fault traces using the bayesian magnitude of completeness method and systematically image b values for 243 major fault segments in california we identify and report b value structures revisiting previously published features e g the parkfield asperity and documenting additional anomalies e g along the san andreas and northridge faults combining local b values with local earthquake productivity rates we derive probability maps for the annual potential of one or more m6 events as indicated by the microseismicity of the last three decades we present a physical concept of how different stressing conditions along a fault surface may lead to b value variation and explain nonlinear frequency magnitude distributions detailed spatial b value information and its physical interpretation can advance our understanding of earthquake occurrence and ideally lead to improved forecasting ability

simultaneous dependence of the earthquake size distribution on faulting style and depth author s petruccelli a gasperini p tormann t schorlemmer d rinaldi ap vannucci g wiemer s abstract 2019 american geophysical union all rights reserved we analyze two high quality southern californian earthquake catalogues one with focal mechanisms to statistically model and test for dependencies of the earthquake size distribution the b values on both faulting style and depth in our null hypothesis b is assumed constant we then develop and calibrate one model based only on faulting style another based only on depth dependence and two models that assume a simultaneous dependence on both parameters we develop a new maximum likelihood estimator corrected for the degrees of freedom to assess models performances our results show that all models significantly reject the null hypothesis the best performing is the one that simultaneously takes account of depth and faulting style our results suggest that differential stress variations in the earth s crust systematically influence b values and that this variability should be considered for contemporary seismic hazard studies

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

size distribution of parkfield s microearthquakes reflects changes in surface creep rate s u m m a r y the nucleation area of the series of m6 events in parkfield has been shown to be characterized by low b values throughout the seismic cycle since low b values represent high differential stresses the asperity structure seems to be always stably stressed and even unaffected by the latest main shock in 2004 however because fault loading rates and applied shear stress vary with time some degree of temporal variability of the b value within stable blocks is to be expected we discuss in this study adequate techniques and uncertainty treatment for a detailed analysis of the temporal evolution of b values we show that the derived signal for the parkfield asperity correlates with changes in surface creep suggesting a sensitive time resolution of the b value stress meter and confirming near critical loading conditions within the parkfield asperity

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

tonian ediacaran tectonomagmatic evolution of west avalonia and its ediacaran early cambrian interactions with ganderia an example of complex terrane transfer due to arc arc collision

intermediate and deep seismicity and lateral structure of subducted lithosphere in the circum pacific region in this paper we present a region by region review of the wadati benioff zone structure of most of the world s seismically active subduction zones focusing primarily on the intermediate and deep seismicity lateral changes in wadati benioff zone structure are common in every major subduction zone in this study we use these changes to define possible boundaries between portions or segments of lithosphere with differing subduction geometries although earthquake data seldom have the resolution to show conclusively whether these boundaries separate independent blocks of lithosphere the available data indicate that the active process at most of these segment boundaries is ductile deformation of the subducting plate rather than tearing we found the strongest evidence for the existence of tears where tears are geometrically necessary such as where a transform boundary terminates a trench as at the new hebrides tonga and south sandwich trenches weak evidence suggesting other tears does exist in some regions such as taiwan the japan izu bonin corner and the philippines the causes of these changes in structure are in most cases unclear only about 34 of the possible segment boundaries coincide with subducting bathymetric features some boundaries occur where there is apparent lateral strain caused by anomalous trench geometry we have designed a simple modeling procedure which incorporates published plate motion and the observed geometry of trenches and wadati benioff zones to estimate the lateral strain in subduction zones throughout the circum pacific region although no observed subduction zone has a perfectly strain free geometry there is a broad range of geometries for which the lateral strain is small indeed the observed geometry of most subduction zones involve relatively little lateral strain comparison with centroid moment tensor focal mechanisms indicates that in zones where the modeling predicted little lateral strain the mechanisms of intermediate and deep earthquakes show no effects of lateral stress and downdip stresses are clearly dominant in regions such as the mariana arc where the model predicts very large lateral extension lateral tension is very evident in the focal mechanisms in regions such as the hokkaido corner where the modeling predicts large compressional strains the plate appears to buckle and bending stresses parallel to the trench are evident in general this study finds that subducted lithosphere is remarkably cohesive and rigid and only rarely deforms by breaking or stretching

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

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

the age of blueschist metamorphism in anglesey north wales evidence from 40ar 39ar mineral dates of the penmynydd schists the 9penmynydd9 schists of se anglesey include several high p low t lithologies including 1 metasedimentary quartz phengite schist and 2 mafic blueschist with barroisite crossite assemblages that appear to have developed from an earlier actinolitic greenschist facies protolith one phengite and three amphibole concentrates have been analysed by incremental release 40 ar 39 ar dating methods and display discordant age spectra with anomalously young apparent ages recorded in low t increments ages increase systematically throughout intermediate t portions of the analyses to define high t plateaux of c 550 560 ma barroisite crossite rich concentrates and c 580 590 ma actinolite rich concentrate the phengite concentrate also displays an internally discordant spectrum with intermediate t increments defining ages similar to those recorded by barroisite crossite and high t increments giving ages similar to those of actinolite the amphibole and phengite ages are interpreted as dating post metamorphic cooling following a regional low p ml greenschist metamorphism c 580 590 ma and a high p m2 metamorphism c 550 560 ma 40 ar 39 ar ages suggest multiple metamorphism of oceanic crust before the arrival of the blueschist terrane and its accretion to the late precambrian basement of southern britain immediately prior to development of the welsh basin an age of c 550 560 ma for blueschist metamorphism on anglesey provides a likely maximum age for ignimbrites within the pre late lower cambrian arfon group exposed in nw wales

an unusual pattern of recurring seismic quiescence at kalapana hawaii an unusual pattern of recurring seismic quiescence is observed in the kalapana hawaii region of kilauea volcano statistically significant intervals of quiescence preceded the kalapana earthquakes of 1975 m7 2 and 1989 m6 1 and a third quiescence is presently underway the sensitivity of the volcano flank to continuing magmatic activity in the nearby east rift zone complicates interpretation of these observations the current quiescence episode may be caused by magmatic processes in the east rift zone or by changes within the flank of kilauea the latter possibility if correct may represent a precursor to another earthquake

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

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

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

reconstruction of ocean plate stratigraphy in the gwna group nw wales implications for the subduction accretion process of a latest proterozoic trench forearc abstract the gwna group in anglesey island and lleyn peninsula wales consists of a latest proterozoic volcano sedimentary trench melange which has a complicated accretionary structure and is poorly constrained by isotopic ages the melange contains oceanic trench rocks including pillow basalts cherts mudstones and sandstones which have not previously been interpreted as ocean plate stratigraphy ops we reconstructed imbricated ops at 5 localities in the coastal lleyn peninsula in order to constrain the depositional u pb age of the upper clastic sediments detrital zircons separated from 9 clastic sediments were analyzed with a nu attom single collector inductively coupled plasma mass spectrometer the ages indicate that there are two gwna groups maximum depositional ages of 1 at 608 601 ma and 2 at 564 539 ma that were deposited between the late neoproterozoic and the middle cambrian contemporaneously with dated calc alkaline arc magmatism and regional metamorphism in the anglesey lleyn complex the age spectra of the detrital zircons show a prominent peak at ca 650 600 ma and several proterozoic and archean ages to account for the older ages we integrated our new isotopic data with published radiometric and fossil ages and conclude that the clastic sediments at the top of the ops were deposited in a trench on the western active margin of avalonia when it was close to the amazonian craton and that the gwna group ops began to be incorporated into an accretionary wedge in an active subduction zone in the latest proterozoic

reply to comments by yavor kamer and stefan hiemer on analysis of the b values before and after the 23 october 2011 mw 7 2 van ercis turkey earthquake

fluid mediated influence of adjacent thrusting on the seismic cycle at parkfield the san andreas fault near parkfield california has experienced moderate to large earthquakes about every 20 years since 1881 the most recent of which occurred in 19661 3 statistical recurrence and precursory quiescence models1 4 5 led to a prediction of the next event for 1992 or before but this event has not yet occurred here i present a model6 that attributes the non occurrence of the expected earthquake to the influence of adjacent thrusting on the rate of fault weakening from increasing pore pressures within the fault zone reductions in fault normal strain rates7 9 and the onset of seismic quiescence along the san andreas fault both coincide with adjacent blind thrust faulting in the 1982 85 earthquake sequence of new idria coalinga and kettleman hills these events turned off a compaction induced weakening mechanism and extended the proposed seismic cycle at parkfield a model simulation of this effect shows a strong correlation in space and time of calculated and observed earthquake hypocentres and shows that observed seismicity patterns from 1969 95 can be explained by reduced compaction rates brought on by adjacent thrusting the model may have applications to other linked thrust strike slip fault systems such as are found in southern california and other transpressional regions

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

crustal growth and late precambrian early palaeozoic plate tectonic evolution of england and wales comparison of the basement rocks of britain reveals major contrasts to the n and s of the iapetus suture solway shannon line north of the suture polymetamorphic high grade basement schists and gneisses and igneous rocks date from about 2900 ma to c 400 ma the latter age corresponding to closure of the iapetus ocean by contrast s of the suture in england and wales the basement is dominantly low grade metamorphic rock together with intrusive and extrusive igneous and sedimentary rocks there is little geological or geochemical evidence for the presence of basement older than c 900 ma below this area and the predominant expression of crustal growth in england and wales is indicated by radiometric ages between c 700 ma and 450 ma reflecting late precambrian palaeozoic magmatism and metamorphism palaeomagnetic data from scotland demonstrate that the crust in northern britain developed as an integral part of the laurentian shield during mid proterozoic times 1600 1000 ma the palaeomagnetic record from the pre ordovician rocks of england and wales shows that this area was unrelated to the laurentian shield prior to closure of the iapetus ocean the apparent polar wander a p w path is that of a distinct microplate involved in rapid growth of iapetus during early cambrian times and emplaced in its present configuration adjacent to northern britain as a result of subduction of the ocean basin between cambrian and silurian times we conclude that whereas the basement to the north of the iapetus suture formed an essentially continental unit from 2900 to 400 ma the basement of england and wales is a result of crustal growth from about 900 ma to 400 ma and formed by accretion of island arcs associated accretionary prisms and fore arc basin sediments within the iapetus ocean

mapping seismic quiescence in california the decrease of microearthquake activity is a controversial possible precursor for mainshock prediction the calculation of seismic quiescence is a convenient tool to quantify this decrease however the actual size of an anomaly significantly depends on the calculation parameters the necessary averaging over space and time acts as 3d lowpass filter the sliding statistics windows introduce highpass behavior and the magnitude threshold shall ensure catalog completeness but also biases the data selection to argue on any claimed anomaly the only conclusive solution would be an exhaustive search over all parameters over an area significantly larger than just the epicenter region and against a test of the null hypothesis qmap is a new mapping approach to process full catalogs that is some twenty years of data for areas of one million km 2 with one fixed set of parameters it utilizes fractil statistics to avoid errors otherwise induced by clusters of aftershock series qmap features two different scaling modes one to display absolute decrease and a second for weighted anomalies by erosion filtering applied to california one can recognize quiescence anomalies of regional scale prior to the coalinga and loma prieta earthquakes but there are more and greater anomalies distributed all along the san andreas fault system without further criteria to understand these patterns the additional anomalies degrade seismic quiescence to an observation with high false alarm rate for earthquake prediction

seismotectonics of the central denali fault alaska and the 2002 denali fault earthquake sequence in this article we analyze the spatial and temporal variations in the seismicity and stress state within the central denali fault system alaska before and during the 2002 denali fault earthquake sequence seismicity for 30 years prior to the 2002 earthquake sequence along the denali fault was very light with an average of four events with magnitude m l 3 per year we observe a significant increase in the seismicity rate prior to the m w 7 9 event of 3 november 2002 within its epicentral region starting about 8 months before its occurrence the majority of the aftershocks of the m w 7 9 event are located within the upper 11 km of the crust and form several persistent clusters with a few aseismic patches along the ruptured fault the most active aftershock source is associated with the epicentral region of the earthquake the overall b value of the aftershock sequence is 0 96 with the highest b values within the epicentral region we estimate that it will take 14 years for the seismicity rate to drop back to the background level the stress regime across the region varies in space and time the inferred stress regime prior to the 2002 sequence is predominately strike slip along the central part of the rupture zone the orientations of the least and intermediate stress axes are reversed after the 2002 earthquake sequence the maximum compressive stresses along the denali fault rotate clockwise by up to 35 the greatest rotations occur in the area of the rupture step over from the denali to the totschunda fault the inferred stress regime after the 2002 sequence reflects an interchanging thrusting and strike slip faulting along the ruptured fault the thrust faulting is concentrated in the epicentral region of the m w 7 9 event and along the rupture segments showing the largest surface offsets

the magnitude distribution of dynamically triggered earthquakes large dynamic strains carried by seismic waves are known to trigger seismicity far from their source region it is unknown however whether surface waves trigger only small earthquakes or whether they can also trigger large earthquakes to partially address this question we evaluate whether current data can distinguish between the magnitude distribution of triggered and untriggered small earthquakes we use a mixing model approach in which total seismicity is decomposed into two classes triggered events initiated or advanced by far field dynamic strains and untriggered spontaneous events consisting of everything else the b value of a mixed data set bmix is decomposed into a weighted sum of b values of its constituent components bt and bu we utilize the previously observed relationship between triggering rate and dynamic strain amplitude to identify the fraction of triggered events in populations of earthquakes and then invert for bt for californian seismicity data are consistent with a single parameter gutenberg richter hypothesis governing the magnitudes of both triggered and untriggered earthquakes

pre mesozoic iawsonite in anglesey northern wales preservation of ancient blueschists the existence of lawsonite blueschists in the mona complex of anglesey northern wales has been confirmed using optical and microprobe data the blueschists occur locally along the eastern margin of one of three belts of fine grained mylonitic schists known as the penmynydd zone of metamorphism the penmynydd zone is interpreted as representing remnants of deep seated ductile shear zones produced by the movement of sialic basement up into low grade melange the lawsonite schists display complex textures resulting from the overprint of blueschist conditions on greenschist facies rocks followed by a subgreenschist dynamic metamorphism the blueschist minerals are interpreted as a late product of shear zone metamorphism under conditions of decreasing temperature and high fluid pressure the schists are no younger than cambrian probably middle cambrian lawsonite of this age is exceptionally rare older examples are reported only from russia rather than invoking a change in crustal isotherms through time the paucity of pre mesozoic blueschists may simply be a result of the rapid exhumation needed to expose such rocks the appearance of a blueschist at earth s surface will be transient unless the uplift responsible for its exposure either slows or ceases

remotely triggered seismicity in the yellowstone national park region by the 2002 mw 7 9 denali fault earthquake alaska coincident with the arrival of low frequency large amplitude surface waves of the mw 7 9 denali fault earthquake dfe an abrupt increase in seismicity was observed in the yellowstone national park region despite the large epicentral distance of 3100 km within the first 24 hr following the dfe mainshock we located more than 250 earthquakes which occurred throughout the entire yellowstone na tional park region the elevated seismicity rate continued for about 30 days and followed a modified omori law decay with a p value of 1 02 0 07 for a declus tered earthquake catalog the seismicity following the 2002 dfe uniquely stands out with a significance of 30r the increase in seismicity occurred over all magnitude bands in general we observed that seismicity following the dfe outlined the spatial pattern of past seismicity routinely observed in the yellowstone national parkregion however we found significant differences in triggered seismicity inside and outside the caldera earthquakes inside the yellowstone caldera occurred preferentially as clusters close to major hydrothermal systems were of larger magnitude and seis micity decayed more rapidly this suggests that either different trigger mechanisms were operating inside and outside the caldera or that the crust responded differently to the same trigger mechanism depending on its different mechanicalstate compared with other sites that experienced remote earthquake triggering following the 2002 dfe yellowstone showed the most vigorous earthquake activity we attribute this to strong directivity effects of the dfe which caused relatively large peak dynamic stresses 0 16 0 22 mpa in yellowstone and to the volcanic nature of yellowstone

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

neoproterozoic high pressure low temperature metamorphic rocks in the avalon terrane southern new brunswick canada high p low t metamorphic rocks of the hammondvale metamorphic suite hms are exposed in an area of 10 km2 on the nw margin of the caledonian avalon terrane in southern new brunswick canada the hms is in faulted contact on the se with c 560 550 ma volcanic and sedimentary rocks and co magmatic plutonic units of the caledonian terrane the hms consists of albite and garnet porphyroblastic mica schist with minor marble calc silicate rocks and quartzite pressure and temperature estimates from metamorphic assemblages in the mica schist and calc silicate rocks using twq indicate that peak pressure conditions were 12 4 kbar at 430 c peak temperature conditions were 580 c at 9 0 kbar 40ar 39ar muscovite ages from three samples range up to 618 615 ma a minimum age for high p low t metamorphism in this unit these ages indicate that the hms is related to the c 625 600 ma subduction generated volcanic and plutonic units exposed to the se in the caledonian terrane the ages are also similar to those obtained from detrital muscovite in a neoproterozoic cambrian sedimentary sequence in the caledonian terrane suggesting that the hms was exposed by latest neoproterozoic time and supplied detritus to the sedimentary units the hms is interpreted to represent a fragment of an accretionary complex similar to the sanbagawa belt in japan it confirms the presence of a major cryptic suture between the avalon terrane sensu stricto and the now adjacent brookville terrane

the effect of uncertainties on estimates of background seismicity rate abstract identifying changes in the rate of background earthquakes is a common method to detect transients in seismic activity rates and these transients can often be linked to changes in physical properties of the crust or to the recording homogeneity of seismic networks in this article we consider the effect that various sources of uncertainty have on seismicity rate estimation and we describe a monte carlo method to compute the statistical significance of seismicity rate changes we consider real earthquake catalogs and synthetic catalogs that represent poissonian background seismicity we find that the choice of declustering algorithm and the variation in the related parameter values have the greatest impact on seismicity rate change calculations this sensitivity is a direct consequence of the fact that there is no unique or universally applied approach to separate aftershocks and foreshocks from background events hypocenter location uncertainty also influences the statistical significance of seismicity rate changes its relevance depends on the ratio of the location uncertainty to the extension of the seismicity rate anomaly we find that magnitude uncertainty and edge effects associated with seismicity declustering have less impact than the other factors but their influence is not negligible in an example application we suggest that when uncertainties are considered the reported seismicity rate changes prior to the 1992 landers and big bear mainshocks decrease significantly

geochronology of the swift current granite and host volcanic rocks of the love cove group southwestern avalon zone newfoundland evidence of a late proterozoic volcanic subvolcanic association zircon fractions from the variably deformed and metamorphosed swift current granite and host volcanic rocks of the love cove group record individually discordant u pb ages with well defined upper c