middle pleistocene deposits at frog hall pit stretton on dunsmore warwickshire english midlands and their implications for the age of the type wolstonian organic sediment from frog hall pit near coventry has produced pollen plant macrofossil insect ostracod and molluscan data indicative of the early part of a temperate episode in the middle pleistocene the regional stratigraphy and clast lithological characteristics of the gravels underlying the temperate deposits show that the whole sequence at the site post dates the major glaciation the wolstonian sensu mitchell et al 1973 of the midlands amino acid d l ratios from molluscan shells give mean values of 0 24 which is consistent with an age in oxygen isotope stage 9 and comparable with those from the hoxnian interglacial of east anglia this age estimate for the frog hall organic deposit places a minimum age on the wolstonian glaciation of the midlands in oxygen isotope stage 10 and therefore close in time to the anglian oxygen isotope stage 12 cold stage 1997 john wiley sons ltd

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 before the 1994 kurile earthquake mw 8 3 revealed by three independent seismic catalogs we have found that the m w 8 3 kurile earthquake on october 4 1994 followed an outstanding seismic quiescence starting 5 6 years before the mainshock near the ruptured area we have analyzed three independent seismic catalogs institute of seismology and volcanology hokkaido university isv japan meteorological agency jma and international seismology center isc in spite of selecting different magnitude bands and time windows all three catalogs presented the common feature of the seismic quiescence this fact strongly suggests that the seismic quiescence should not be a man made change but actually occurred moreover we have confirmed that the seismic quiescence was the most significant and the earthquake was the largest in the past twenty five years in this region therefore we confidently interpret this seismic quiescence as an indication of a preparation process for the m w 8 3 kurile earthquake

significance of the record provided by pleistocene fluvial deposits and their included molluscan faunas for palaeoenvironmental reconstruction and stratigraphy case studies from the english midlands abstract the vast majority of pleistocene fluvial deposits in northwest europe are of cold climate origin with the most important sediment type being coarse sands and gravels formed under nival regimes less commonly sands and silts of interglacial deposition are preserved in the lower levels of major aggradations or in channels preserved beneath them molluscan faunas are common in both types of deposit although the fine grained temperate sediments show the best preservation and the most diverse assemblages this paper will discuss the types of molluscan faunas found in fluvial deposits and assess their suitability for both climatic reconstruction and stratigraphic studies while it has been clear for many years that reliable local environmental reconstructions can be made using mollusca they have been less used for regional climatic assessment work in england over the past thirty years shows that faunas obtained from fluvial sediments particularly if they contain both freshwater and terrestrial species can provide a basis for regional climatic reconstruction mollusca may also allow the separation from each other of interglacials and interstadials and permit these episodes to be more precisely defined than is allowed by other means such as palynology molluscan faunas may offer potential for the identification of temperature episodes which may have the same climatic status as interglacials but which are not recognised as such by other palaeontological evidence such as pollen the use of molluscan faunas for biostratigraphy has been firmly rejected by previous authors however recent work concentrating on sites of similar facies within single catchments has shown that both presence and absence of individual species particularly those now exotic to the british isles e g belgrandia marginata michaud and corbicula fluminalis muller can be a useful guide to relative age examples illustrating the significance of these faunas in the stratigraphic record are largely taken from the fluvial deposits of the major rivers of the english midlands warwickshire avon great ouse nene but reference is also made to other studies on the deposits of the thames the ages of the faunas described range from the cromerian interglacial to the devensian glacial stage and includes data from sites in integlacials identified in the stratigraphic record but so far not formally named

detailed observations of california foreshock sequences implications for the earthquake initiation process we find that foreshocks provide clear evidence for an extended nucleation process before some earthquakes in this study we examine in detail the evolution of six california foreshock sequences the 1986 mount lewis ml 5 5 the 1986 chalfant ml 6 4 the 1986 stone canyon ml 4 7 the 1990 upland ml 5 2 the 1992 joshua tree mw 6 1 and the 1992 landers mw 7 3 sequence typically uncertainties in hypocentral parameters are too large to establish the geometry of foreshock sequences and hence to understand their evolution however the similarity of location and focal mechanisms for the events in these sequences leads to similar foreshock waveforms that we cross correlate to obtain extremely accurate relative locations we use these results to identify small scale fault zone structures that could influence nucleation and to determine the stress evolution leading up to the mainshock in general these foreshock sequences are not compatible with a cascading failure nucleation model in which the foreshocks all occur on a single fault plane and trigger the mainshock by static stress transfer instead the foreshocks seem to concentrate near structural discontinuities in the fault and may themselves be a product of an aseismic nucleation process fault zone heterogeneity may also be important in controlling the number of foreshocks i e the stronger the heterogeneity the greater the number of foreshocks the size of the nucleation region as measured by the extent of the foreshock sequence appears to scale with mainshock moment in the same manner as determined independently by measurements of the seismic nucleation phase we also find evidence for slip localization as predicted by some models of earthquake nucleation

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

sedimentology palaeoecology and geochronology of last interglacial deposits from deeping st james lincolnshire england pollen plant macrofossil molluscan and coleopteran data from organic muds below the low terrace of the river welland at deeping st james lincolnshire indicate deposition in the mixed oak forest phase of a late pleistocene interglacial coleopteran and molluscan data suggest summer temperatures up to 4 c warmer than at present in eastern england and plant macrofossil material suggests a climate more continental than that of britain in the holocene no direct analogue of this biota however exists currently in europe biostratigraphical indications from the pollen coleoptera and mollusca suggest an age in the ipswichian interglacial thermoluminescence dates between 120 ka and 75 ka and amino acid ratios with a mean of 0 11 show that deposition of the sediments took place during oxygen isotope stage 5 this accurate dating of a partial ipswichian succession allows discussion of the ages of a number of other interglacial sites in eastern england of assumed ipswichian age copyright 1999 john wiley sons ltd

precursors to the kalapana m 7 2 earthquake the kalapana hawaii earthquake of november 1975 had a rupture length of 40 to 50 km and was located on the south flank of the active volcano kilauea the source mechanism was dip slip normal faulting on a plane dipping 20 degrees to the se with the greatest principal stress oriented in that direction and accumulated by volcanic intrusions into kilauea s rifts the source area of the 1975 earthquake was subject to intensive geological and geophysical research for many years before this earthquake because of its proximity to the volcano we studied the distribution of epicenters for small earthquakes from 1962 to 1975 seven seismographs located within 3 km of the aftershock area had been in operation for 3 to 10 years before the mainshock and geodetic triangulations and trilaterations in the source area had been carried out repeatedly since 1914 we found that precursory changes occurred throughout most of the rupture area but in two distinctly different patterns in the larger outer anomalous area the seismicity rate was decreased by 50 during the 3 8 years before the mainshock in addition several geodetic lines indicated anomalous strain release during this time within two inner areas the seismicity remained high then increased shortly before the mainshock in one of the inner areas a p wave travel time delay of 0 2 s could be detected which began about 3 5 years before the mainshock within the other inner anomalous area geodetic strain was accumulating until the first half of 1975 when 3 5 10 4 strain 35 bars was released aseismically by contrast the outer anomalous volume was experiencing strain softening from 1970 1971 on we interpret these observations as indicating that strain softening by fault creep in the outer anomalous area transferred stress into two major asperities locked portions of the fault a velocity decrease and foreshocks were observed in one asperity and high stress accumulation in the other implying that dilatancy of the crust probably occurred our model is qualitatively supported by the independent evidence of strong motion records which show that the kalapana earthquake was a complex multiple rupture we conclude that the kalapana earthquake was preceded by a preparatory process which lasted 3 8 0 3 years and which had dimensions of 45 10 km covering approximately the aftershock area

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

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

multiple asperity model for earthquake prediction large earthquakes often occur as multiple ruptures reflecting strong variations of stress level along faults dense instrument networks with which the volcano kilauea is monitored provided detailed data on changes of seismic velocity strain accumulation and earthquake occurrence rate before the 1975 hawaii 7 2 mag earthquake during the 4 yr of preparation time the mainshock source volume had separated into crustal volumes of high stress levels embedded in a larger low stress volume showing respectively high and low stress precursory anomalies

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

increased long range intermediate magnitude earthquake activity prior to strong earthquakes in california we study the space time relationships between strong earthquakes in california and the intermediate magnitude earthquakes that both precede and follow them all 11 earthquakes in california with nominal magnitudes greater than or equal to 6 8 from 1941 to 1993 were preceded by an increase in the rate of occurrence of earthquakes having magnitudes greater than 5 1 ten of the 11 earthquakes occurred when or shortly after the intermediate magnitude activity was greater than its 75th percentile three of these strong earthquakes are in a conventional space time foreshock aftershock relationship with others of the 11 strong events the precursory activity is concentrated in regions having linear dimensions of the order of a few hundred kilometers these dimensions are significantly larger than the estimated fracture lengths of the ensuing strong earthquakes the correlations are ill defined for smaller earthquakes and are almost unidentifiable for earthquakes with magnitudes less than about 4 6 the precursors to the strong earthquakes appear over a time interval of the order of 5 to 10 years before the strong earthquake although the onset was about 25 years before the san francisco earthquake in the case of the loma prieta and san francisco earthquakes the onset of increased activity appears to be relatively abrupt the increased activity is either switched off abruptly to distances of the order of hundreds of kilometers shortly after the occurrence of a strong earthquake or the strong events are themselves part of a precursory pattern of continuing high activity before a second strong earthquake that takes place soon thereafter with subsequent extinction of activity after it thus the intermediate magnitude precursors do not directly influence the time and location of the subsequent strong event but the strong event has a strong influence on the stress field in the vicinity of intermediate magnitude earthquakes to distances of the order of many times the scale size of the strong earthquake

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

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

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

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

background and precursory seismicities along and surrounding the kunlun fault before the ms8 1 2001 kokoxili earthquake china abstract the ms8 1 kokoxili china earthquake on 14 november 2001 occurred on the western portion of the kunlun fault by analyzing data from geological surveys and records of historical and modern earthquakes we know that at least 8 ms6 9 8 1 earthquakes occurred along the kunlun fault from 1879 ad to 2000 ad the spatial arrangement of these ruptures indicates the existence of two rupture gaps the kokoxili and the maqu on the fault before 2001 the kokoxili gap and surrounding area experienced a long term seismicity quiescence of ms 5 earthquakes and developed the corresponding background seismic gap at least from 1966 to 2001 the 2001 kokoxili earthquake occurred on the kokoxili gap the maqu gap on the eastern portion of the kunlun fault was found to be a site where the seismicity rate of smaller earthquakes increased anomalously about 3 4 years before the kokoxili earthquake we analyze this anomalous increase in seismicity rate and conclude that it was a significant precursor of the kokoxili earthquake the cases in this study suggest that rupture gaps on a great inland strike slip fault zone could be sites of potentially major or great earthquakes or sites of precursory seismicities emerging prior to major or great earthquakes on the same fault zone

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

pattern dynamics and forecast methods in seismically active regions large extended fault systems such as those in california demonstrate complex space time seismicity patterns which include repetitive events precursory activity and quiescence and aftershock sequences although the characteristics of these patterns can be qualitatively described a systematic quantitative analysis remains elusive our research suggests that a new pattern dynamics methodology can be used to define a unique finite set of seismicity patterns for a given fault system in addition while a long sought goal of earthquake research has been the reliable forecasting of these events very little progress has been made in developing a successful consistent methodology in this report we document the discovery of systematic space time variations in seismicity from southern california using a new technique here we present examples of this analysis technique on data obtained prior to events in seismically active areas that show coherent regions associated with the future occurrence of major earthquakes in the same areas these results strongly support the hypothesis that seismic activity is highly correlated across many space and time scales within large volumes of the earth s crust

application of a modified pattern informatics method to forecasting the locations of future large earthquakes in the central japan we propose a modification of the pattern informatics pi method that has been developed for forecasting the locations of future large earthquakes this forecast is based on analyzing the space time patterns of past earthquakes to find possible locations where future large earthquakes are expected to occur a characteristic of our modification is that the effect of errors in the locations of past earthquakes on the output forecast is reduced we apply the modified and original methods to seismicity in the central part of japan and compared the forecast performances we also invoke the relative intensity ri of seismic activity and randomized catalogs to constitute null hypotheses we do statistical tests using the molchan and relative operating characteristic roc diagrams and the log likelihoods and show that the forecast for using the modified pi method is generally better than the competing original pi forecast and the forecasts from the null hypotheses using the bootstrap technique with monte carlo simulations we further confirm that earthquake sequences simulated based on the modified pi forecast can be statistically the same as the real earthquake sequence so that the forecast is acceptable the main and innovative science in this paper is the modification of the pi method and the demonstration of its applicability showing a considerable promise as an intermediate term earthquake forecasting tool

anomalous seismicity of the knin area yugoslavia prior to the m 5 5 earthquake of 1986 abstract a case of seismicity changes prior to the m 5 5 knin yugoslavia earthquake has been analysed in addition to the well expressed seismic quiescence significant b value strain release and seismicity rate temporal changes have been observed the estimated precursor time of t 6 8 yrs is longer than expected on the basis of published log t m relationships a much better agreement is obtained if log t is compared to the longest dimension of the aftershock

comparison of a complex rupture model with the precursor asperities of the 1975 hawaii m s 7 2 earthquake a simplified multiple source model was constructed for the 1975 hawaiims 7 2 earthquake by matching synthetic signals with three component accelerograms at two stations located approximately 45 km from the epicenter six major subevents were identified and located approximately the signals of these are larger by factors of 1 4 to 3 2 than that of theml 5 9 foreshock which occurred 70 minutes before the main rupture and also triggered the sam 1 recorders at the two stations dividing the rupture length 40 km by the duration of strong ground shaking 50 sec an average rupture velocity of 0 8 km sec about 25 of s velocity is obtained thus it is likely that the rupture stopped between subevents the approximate epicenters of the 6 major subevents and of the foreshock support the hypothesis that they were located in high stress asperities which rupture during the main shock except for the last events which is interpreted as a stopping phase generated at a barrier these asperities have been previously defined on the basis of differences in the precursor pattern before the mainshock thus it appears that both the details of the precursors and of the main rupture depended critically on the heterogeneous tress distribution in the source volume this suggests that main rupture initiation points and locations of high rupture accelerations may be identified before the mainshock occurs based on precursor anomaly patterns a satisfactory match of synthetic signals with the observations could be obtained only if the aximuth of the fault plane of subevents was rotated from n60 e to n90 e and back to n30 e these orientations are approximately parallel to the nearest kilauea rift segments hence the slip directions and greatest principal stresses were oriented perpendicular to the rifts everywhere from this analysis and other work it is concluded that this fault surface consisted of three types of segments with different strength hard asperities radius 5 km soft but brittle segments between the asperities radius 5 km and a viscous half 10 40 km which slipped during the mainshock but where microearthquakes and aftershocks are not common

local magnitudes and apparent variations in seismicity rates in southern california redetermination of local magnitudes for moderate earthquakes recorded by the southern california seismographic network scsn from 1932 to 1990 has shown that the magnitudes have not been consistently determined over that time period the amplitudes of ground velocities recorded on wood anderson instruments were systematically overestimated prior to 1944 compared to present reading procedures leading to a significant overestimation of local magnitudes in addition the change from human to computerized estimation of event magnitude from a suite of amplitudes in 1975 led to slightly lower event magnitudes for the time after 1975 compared to the time before these changes contribute to an apparently higher rate of seismicity in the 1930s and 1940s than later in the catalog which had been interpreted as a decrease in seismicity rate after the 1952 kern county m w 7 5 earthquake wood anderson amplitudes have been reread and consistent magnitudes recalculated using uniform procedures for all earthquakes with a catalog magnitude of 4 5 and greater within the scsn from 1932 to 1943 and those with a catalog magnitude of 4 8 and greater from 1944 to 1990 so as to create a complete list of all earthquakes with a modern local magnitude of 5 0 or greater using these new magnitudes we find that the rate of m l 5 0 and greater earthquakes in southern california over this 59 year period to be poissonian with no changes in rate significant above the 90 level from this rate in any 30 year period the poissonian probability of a m 6 earthquake is 99 7 the probability of an m 7 earthquake is 65 and the probability of an m 8 event is 18

seismic activity changes progressing simultaneously with slow slip in the tokai area abstract anomalous movements were detected simultaneously in both the seismic and the gps observations in the tokai area the central part of the japanese islands from the late 1990s to 2000 the anomalies are of great concern since the pending risk of a large megathrust earthquake in this area has been predicted for more than 20 years the gps data revealed that a slow slip on the plate interface had commenced beneath lake hamana the center of which is positioned around the edge of the assumed focal zone on the other hand the seismic data indicated that a delicate but clear quiescence appeared over a wide area that spreads into the main focal zone analyses of the seismicity changes in space and time confirmed that the contrast in the seismicity rate is distinct inside the focal zone while the integrated seismicity indicated quiescence some locations were distinguished as activated zones possibly indicating the appearance of asperities the rise of the seismicity rate in a quasi stationary manner suggests an increase in the stress rate at that location the following hypothesis is proposed based on the simultaneously detected evidences the slow slip progressing beneath lake hamana will induce a stress shift that invades the interior of the main locked zone which will increase the contrast of the seismicity rate possibly reflecting inhomogeneity in the locking strength even in this stage the activated zones still maintain a locked state to prevent overall breakage investigations of the b value changes and of tidal dependence in seismicity that reveal the stress concentrated state also support the hypothesis if this is the case the observed change in seismicity would indicate the process of stress redistribution in the locking state which represents the preparatory process toward final breakage tracking such seismicity changes would yield valid information for predictions of the next tokai earthquake

late middle pleistocene pollen biostratigraphy in britain pitfalls and possibilities in the separation of interglacial sequences abstract recent work on late middle pleistocene interglacials in britain has shown that sites formerly attributed to the hoxnian include representatives of two different interglacials which have been correlated with oxygen isotope stages 11 and 9 palynology has long been used to characterize and correlate temperate sequences in britain however the quality of the palynological record is considerably better in lacustrine sequences than in fluvial and estuarine sediments the former have longer sequences and higher resolution whereas more rapid deposition in fluvial and estuarine environments leads to sequences representing only fragments of interglacials the latter type of site however is more likely to have multi proxy evidence and to be readily fitted into a stratigraphical framework the problems are reviewed in the light of new work in the west midlands where some of the most complete british late middle pleistocene lacustrine sequences are preserved lacustrine sites here have a strong affinity with hoxnian sites of the type area in east anglia a critical question remains as to whether the two interglacials conflated under the term hoxnian can be separately characterized in terms of their pollen assemblages details of lacustrine sequences in the north birmingham area and east anglia show remarkable similarities perhaps suggesting that the same interglacial is recorded in all of them as many of these sites are thought to be kettle holes or glacially overdeepened basins the first interglacial following the anglian glaciation is the most likely to be represented suggesting that all the lacustrine hoxnian sites might date from ois 11 in areas not glaciated since the anglian interglacials after ois 11 are likely to be represented only by fragmentary non lacustrine sequences difficult if not impossible to separate using palynology alone

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

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

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

the late middle pleistocene biostratigraphy of the thames valley england new data from eastern essex abstract coring investigations at east hyde near tillingham essex have revealed a sequence of fluvial and estuarine deposits infilling a channel incised into london clay these deposits are of thames origin and were deposited after the river s diversion into eastern essex late in the anglian stage the detailed litho and biostratigraphy of the deposits are described ostracod and molluscan data confirm that the lower parts of the sequence accumulated in a quiet fluvial environment rich in aquatic vegetation the upper sediments accumulated in an inner estuarine environment under conditions of rising sea level pollen assemblages from both units show strong biostratigraphical affinities with the hoxnian stage particularly with the hoxnian late temperate substage ho iii the sequence has also yielded a rare assemblage of freshwater fluvial molluscs the rhenish fauna which migrated into the thames following a link with the rivers of continental europe the occurrence of theodoxus serratiliniformis is exceptionally rare representing only the second record of the species in the entire british pleistocene the molluscan assemblages show striking similarities with those at clacton in northeast essex and swanscombe kent and provide strong evidence that the three sites are contemporaneous and were connected in the same fluvial system the timing of the migration of the rhenish fauna into britain and the implications for sea level reconstruction in the southern north sea region are discussed the episode of major climatic warmth and high eustatic sea level represented at east hyde is correlated with stage 11 of the deep sea record

increased mean depth of earthquakes at parkfield the mean focal depth of earthquakes in the northern and southern parts of the parkfield segment of the san andreas fault was greater than long term average by 1km during the last 4 years approximately it is proposed that this is a precursor to the next characteristic parkfield earthquake because the same phenomenon occurred before at least three other mainshocks along the san andreas fault in the northern segment the increase in mean depth is mostly due to reduction of shallow activity in the southern segment deeper than usual activity seems to have increased within about 8 km from the 1966 epicenter no significant increase of mean depth is observed but seismic quiescence wyss et al 1990a and a decrease in deformation rate wyss et al 1990b was documented these observations are interpreted to suggest that the precursory process at parkfield varies along strike and that the next rupture may extend further north than the last one

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

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

differentiation of the british late middle pleistocene interglacials the evidence from mammalian biostratigraphy abstract acknowledgement of the climatic complexities of the marine oxygen isotope 18o record has inspired fresh investigations into methods of identifying and separating interglacial deposits on land biostratigraphical analysis of fossil mammalian assemblages particularly those from long fluvial sequences has proved to be a uniquely valuable technique in the differentiation of the various temperate episodes of the late middle pleistocene in britain thereby enabling a sequence of diagnostic mammalian assemblage zones to be established the scheme has provided an important means of correlation between geographically distant localities and between different types of depositional environment using mammalian biostratigraphical information this paper explores the evidence for three post anglian interglacials prior to the last ipswichian interglacial correlated with stages 11 9 and 7 of the oxygen isotope record and presents the case for the recognition of much smaller scale environmental and climatic oscillations within these interglacials possibly corresponding to marine isotopic substages

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

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

the middle pleistocene deposits of waverley wood pit warwickshire england a complex of channels underlying the baginton lillington gravel baginton formation at waverley wood quarry warwickshire is described fossil pollen and plant macrofossils coleoptera ostracoda mollusca and mammalia are described from the channel fill deposits consideration of all the evidence allows the identification of four separate stages of channel fill which largely occurred under a cool temperate climate at the top of channel 2 evidence for a cold continental climatic episode can be recognised suggesting that the whole complex was deposited under a fluctuating climate at the end of a temperate stage at two levels in the channels human artefacts were recovered confirming the presence of palaeolithic people in warwickshire during the deposition of the sediments amino acid geochronology suggests an age within the cromerian complex stage for the channels the small vertebrate and molluscan faunas indicate that the deposits are no older than the latter part of the cromerian complex stage of east anglia the regional stratigraphic significance of the waverley wood succession is outlined

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

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

towards a late middle pleistocene non marine molluscan biostratigraphy for the british isles abstract the fossils of non marine mollusca are among the most prominent in pleistocene deposits they were one of the first fossil groups to be noted in the literature as early as the beginning of the 18th century with the stabilisation of taxonomies in the 19th century numerous publications appeared with faunal lists of interglacial taxa but few attempts were made to use the data for interpretation work from 1950 onwards especially by sparks and kerney in britain puissegur in france and by lo ek in central europe used a quantitative approach to sorting counting and interpreting assemblages despite the adoption of this rigorous methodology to molluscan studies interglacial faunas were used primarily to reconstruct past environments and although faunal changes through the pleistocene were recognised it was thought that non marine mollusca were inherently badly fitted for use as tools for dating in the classic geological sense recent work coupled with the re evaluation of sites described in the literature has allowed non marine molluscan faunas to be used as biostratigraphic indicators biostratigraphic schemes evolved from this work are comparable with parallel investigations using mammalia coleoptera and lithostratigraphy calibrated by a number of geochronometric methods but may be at variance with pollen biostratigraphies

heterogeneities of the instrumental seismicity catalog 1904 1980 for strong shallow earthquakes we analyze the world wide consistency of teleseismic reporting completeness of the seismicity record and homogeneity of magnitude determination for strong shallow earthquakes magnitude m 6 depth h 70 km in the period 1904 to 1980 for earthquakes with magnitude m 7 we used the catalog given by abe 1981 which lists the surface wave magnitude ms of every reported large event that occurred between 1904 and 1980 according to the original formulation of gutenberg 1945 under the postulate that the rate of earthquake occurrence for the entire world as a whole is consistent on a time scale of decades and that since the installation of the world wide standardized seismograph network in the early 1960s the earthquake catalog for strong m 6 shocks is complete and the seismicity rates are typical of all periods in the century we find that for instrumental related reasons the ms of large events prior to 1908 have been systemically overestimated by at least 0 5 magnitude unit and the ms of events in the period 1908 to 1948 have been consistently overestimated by 0 2 unit relative to the ms assigned to shocks occurring after 1948 when these corrections are taken into account the catalog of events with ms 7 0 is shown to be largely complete i e nearly all the large shallow shocks which occurred in the earth are listed for most of the world since early in the century for earthquakes as the magnitude 6 level we used the international seismological center isc tape and regional catalogues of earthquakes this file compiles the earthquake data given by gutenberg and richter 1954 for the first half of the century and data from various international agencies after 1945 we find a highly incomplete seismicity catalog at this magnitude level for the first half of the century mainly due to numerous increases and decreased in the earthquake detection and reporting capabilities a more complete but extremely inhomogeneous catalog for the period 1950 to 1963 due to the use of different formulations and criteria to calculate and report the parameter magnitude by the various seismological agencies and a largely complete and homogeneous in ms record since 1964

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

a long pollen record from lac du bouchet massif central france for the period ca 325 to 100 ka bp ois 9c to ois 5e abstract pollen analysis was carried out on sediments older than the wurm pleniglacial ois 4 in two new sequences h and i derived from the centre of lac du bouchet massif central the inferred vegetation history enables for the first time in france five temperate episodes to be defined which pre date the last interglacial these temperate episodes alternate with episodes during which the changes in vegetation are indicative of glacial climates comparison of these climatic episodes with the oceanic isotope record shows that the pollen record of sequences h and i from lac du bouchet spans the time interval from ois 9c ussel interstadial to ois 5e ribains eemian interglacial in the organic sediments from the amargiers interstadial ois 9a a trachytic layer ar ar dated to ca 275 ka enables a correlation to be established with the upper part of a sequence derived from the nearby praclaux crater the lower part of this sequence being of holsteinian age ois 11c the cross dating of the pollen sequences from lac du bouchet cores h i and d and from praclaux provides a complete record from the massif central southern france of successive glacial and interglacial episodes that span the last ca 400 ka that is the interval from the holsteinian to the holocene

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

seismic quiescence precursor to the 1983 kaoiki ms 6 6 hawaii earthquake a remarkable seismicity rate decrease of 65 per cent occurred in most of the aftershock volume 2 4 yr before the 1983 kaoiki ms 6 6 main shock if the background seismicity rate 1978 to mid 1981 is extrapolated to the time of the main shock more than 300 earthquakes of ml 1 8 are missing because of the quiescence subvolumes measuring 5 5 km on a side and located within the aftershock zone showed seismicity rate decreases ranging from 0 to 90 per cent the volume of no change had dimensions of approximately 10 3 km it contained the main shock hypocenter and was located near the center of the 10 km radius aftershock area the seismic quiescence in different subvolumes of the aftershock volume surrounding this central nonquiet zone varied somewhat in starting time amount of rate decrease and statistical significance according to the standard deviate z test the reported rate decrease is the most pronounced example of precursory quiescence defined to date the seismicity pattern before the 1983 kaoiki shock conformed to the quiescence hypothesis proposed on the basis of the precursors to the 1975 hawaii main shock no quiescence was observed within the immediate surrounding of the hypocenter while strong rate decreases occurred in most of the rest of the main shock source volume it is thus hypothesized that major asperities which contain high stress levels and from which main ruptures can emanate may be recognizable as volumes of constant seismicity rate within surrounding volumes of quiescence provided that decreases of seismicity rate as a function of time can be defined quantitatively

an experiment in earthquake prediction and the 7 may 1986 andreanof islands earthquake abstract the occurrence of the 7 may 1986 andreanof islands earthquake provides the opportunity to evaluate the earthquake forecast and specific prediction that had been formulated and promulgated starting more than 2 yr before the prediction experiment was based on the observation of seismic quiescence in the part of the aleutian subduction zone monitored by the central aleutians adak seismic network the magnitude estimate m s 7 to 7 5 was based on the size of the quiescent zone and the seismic history of the adak region since 1900 the time of occurrence was predicted as a test of the discovery by habermann of a quiescence lasting about 3 yr prior to the 2 may 1971 adak canyon event and the hypothesis that a characteristic precursor time is a valid concept the place was originally forecast as near adak island then specified with epicenter at the eastern margin of adak canyon rupturing to the west under the canyon the 7 may 1986 earthquake had magnitude m s 7 7 m w 8 0 with epicenter 140 km east of the predicted place rupturing east of adak canyon and stopping in the area predicted as the nucleation point the time of this event was 6 months later than predicted thus the specifically predicted event has not happened the largest part of the rupture did go through the segment that had been most active before the onset of quiescence and which experienced the sharpest and most persistent quiescence a cause and effect relation between preparation for this earthquake and the quiescence is still to be firmly established but the distribution of the pattern of quiescence relative to the epicentral location and the site of the greatest moment release suggest a physical connection between earthquake and seismicity patterns the predictions of location and time were acknowledged throughout as highly speculative no firm basis exists for quantitative estimation of the uncertainties to be assigned to the elements of an intermediate term prediction this experiment lends support to the validity of quiescence as a precursor at least for some earthquakes and demonstrates the need for local network data to provide the high resolution of seismicity required for prediction efforts based on seismicity patterns

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

occurrence of a predicted earthquake on the san andreas fault in may 1985 we predicted1 that an earthquake would occur on the san andreas fault near stone canyon california within a year the prediction was based on the observation of seismic quiescence defined as a significant decrease in the average occurrence rate of earthquakes within the source volume of the future mainshock a mainshock of magnitude ml 4 6 occurred on 31 may 1986 rupturing exactly the specified segment of the fault this is the first successful prediction of an earthquake along the san andreas fault and the probability to have come true by chance is 5 although the prediction addressed only a small main shock its success was significant because the location size and occurrence time were correctly specified for an earthquake in a populated area larger earthquakes will undoubtedly be successfully predicted by the same method in the future but the major segments of the san andreas fault near san francisco and los angeles have such a low background seismicity rate that the method will probably not be applicable there

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

sedimentology palaeontology and archaeology of late middle pleistocene river thames terrace deposits at purfleet essex uk middle pleistocene fluvial deposits of the corbets tey formation at purfleet essex provide evidence of an un named and previously poorly recognized interglacial thought to corrrelate with oxygen isotope stage ois 9 previous attributions of the sediments to the ipswichian last interglacial stage are refuted new investigations have yielded rich molluscan mammalian and ostracod assemblages that indicate fully temperate conditions and the distal influence of marine transgression pollen analyses suggest a previously unrecorded phase of interglacial vegetational development clast composition geomorphological evidence and the occurrence of molluscs that favour large rivers all point to deposition by the thames rather than in a minor tributary as suggested previously three separate palaeolithic industries in stratigraphical superposition are recognized at purfleet these being clactonian acheulean and levallois purfleet is therefore a key locality in the understanding of the early human occupation and exploitation of southern britain as well as for the interpretation and correlation of the terrace sequence in the thames valley

late and middle pleistocene deposits at somersham cambridgeshire u k a model for reconstructing fluvial estuarine depositional environments gravel quarries at somersham cambridgeshire have yielded evidence for a pleistocene channel of the r great ouse containing temperate stage sediments between cold stage sediments in the earlier cold stage fluviatile gravels and floodplain loessic sediment accumulated in the later cold stage a further series of gravel units and floodplain sediments were deposited together with lake sediments the lake sediments are associated with lake sparks dammed by late devensian ice in the wash at ca 18 5 ka bp the lake sediments overlie gravels with a radiocarbon date from an organic horizon indicating a middle devensian age clast lithological analyses from the earlier and later gravels suggest that reworking of gravels has occurred within a relatively stable catchment the petrography of the earlier cold stage loessic sediment and temperate stage fine sediment indicates an anglian affinity which conflicts with the biostratigraphic interpretation pollen and macroscopic plant remains from sediments of both cold stages and from the temperate stage indicate respectively assemblages with a typical full glacial aspect with a rich flora of shrubs and open ground herbs including an assemblage at ca 18 ka and temperate freshwater and marine influenced organic sediments on the basis of pollen analysis these are ascribed to substages ip ii and iii of the ipswichian stage o i s 5e with a pinus quercus corylus biozone in the former and a biozone with carpinus in the latter marine influenced sediments at 3 7 to 0 3 m od indicate transgression in ip ii and regression in ip iii molluscan assemblages from the temperate stage and the later cold stage are described two are from the late devensian at a time near the maximum extension of ice into the wash foraminifer and ostracod faunas are described from post ipswichian sediments and may be reworked radiocarbon dates confirm the age of the later gravel suite as devensian and a calibration of the measurements is given amino acid ratios from corbicula fluminalis valves from temperate stage sediments are reported with measurements from different parts of the valve the results tend to support an ipswichian age tl measurements of the earlier cold stage loessic sediment and associated sand indicate a pre ipswichian age for the sediments the earlier cold stage is correlated with the pre ipswichian cold stage the wolstonian of mitchell et al 1973 problems with this correlation are discussed various periglacial phenomena including thermal contraction networks and cracks diapirs involutions and coversand are associated with the devensian sequence the complex environmental history based on stratigraphy and palaeontology is described and related to other nearby sites in southern fenland

land sea correlations in the pleistocene based on isoleucine epimerization in non marine molluscs the correlation between the oxygen isotope stratigraphy of the oceans and continental stratigraphic records is one of the main challenges for quaternary research most continental classifications however are based on techniques and hypotheses that predate recent advances nevertheless the deep sea oxygen isotope global stratigraphic framework has been extended to the continents by means of some long sequences1 but these are exceptional and regional geology is unsatisfactorily classified for correlation with the oxygen isotope signal because successive geological events produced similar evidence homotaxis geochronometric dating is essential for correlation but available methods are highly site regional or sample specific fortunately non marine molluscs are ubiquitous in time and space and here we use the time dependent epimerization of l isoleucine in these fossils to subdivide the pleistocene of the british isles and to identify more events than recognized by the existing classification2 by calibrating the relative aminostratigraphic scale with independent dating methods we have set up a geochronology which is the basis for land sea correlations back to oxygen isotope stage 15

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases