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

localization of intermediate term earthquake prediction relative seismic quiescence within a region which has already been diagnosed as having entered a time of increased probability tip for the occurrence of a strong earthquake can be used to refine the locality in which the earthquake may be expected to occur a simple algorithm with parameters fitted from the data in northern california preceding the 1980 magnitude 7 0 earthquake offshore from eureka depicts relative quiescence within the region of a ttp the procedure was tested without readaptation of parameters on 17 other strong earthquake occurrences in north america japan and eurasia most of which were in regions for which a tip had been previously diagnosed the localization algorithm successfully outlined a region within which the subsequent earthquake occurred for 16 of these 17 strong earthquakes the area of prediction in each case was reduced significantly ranging between 7 and 25 of the total area covered by the tip

dense shelf water formation along the south west australian inner shelf 1 hydrological data from a repeated cross shore transect obtained using teledyne webb research slocum electric gliders offshore two rocks in south western australia over 13 months are presented the data revealed that formation of dense water inshore and its transport across the shelf as a near bed gravity current defined as dense shelf water cascade dswc was a regular occurrence particularly during autumn and winter months in autumn the dense water is mainly formed through changes in salinity resulting from evaporation whilst in winter temperature change through surface cooling was the dominant factor the mean wind speeds also decrease during the transition during autumn the speed of the dswc was estimated to be 0 01 0 02 m s 1 and similar to that measured in other selected regions globally the offshore transport from the shelf is a significant component of the alongshore wind driven transport

seasonal cross shelf flow structure upwelling relaxation and the alongshelf pressure gradient in the northern california current system abstractmoored observations are used to investigate the seasonal change in vertical structure of the cross shelf circulation at a midshelf location in the northern california current system a streamwise normal coordinate system is employed to eliminate meander and eddy induced biases in the cross shelf flow that are unaccounted for with an alternative commonly applied approach the resulting flow structure develops an organized pattern midway through the upwelling season in particular under upwelling favorable conditions an onshore return layer occurs just beneath the offshore surface flow and a third offshore directed layer exists at depth that does not appear to satisfy ekman dynamics to within 9 m of the bottom both subsurface layers strengthen in time over the upwelling season mechanisms to explain the mean structure are evaluated and it is suggested that the timing of the development and strengthening of both the interior onshore return flow and the offshore near bottom layer are consisten

satellite remote sensing reveals coastal upwelling events in the san matias gulf northern patagonia abstract coastal upwelling events are effective in fluxing nutrients upward to the euphotic layer thus promoting the growth of marine phytoplankton satellite data may provide useful information to detect and characterize upwelling events in regions of sparse in situ observations we analyze the coastal upwelling process on the western san matias gulf on the northern continental shelf of argentina based on the analysis of remote sensing and in situ data upwelling events are characterized by their frequency of occurrence and magnitude during the austral summer we found roughly 6 upwelling favorable wind events per year satellite derived sea surface temperature sst data provide evidence of upwelling in 85 of the cases between 2000 and 2008 analysis of specific events provides clues on the wind forcing characteristics required to generate upwelling and on characteristic space and time scales of the process on february 2005 sst data reveal a narrow coastal band 10 km of relative cold water extending 100 km along the west coast of smg the sst in this band was 1 5 c lower than further offshore near bottom temperature fluctuations from in situ daily observations collected at two near shore locations are significantly correlated with along shore wind stress suggesting that coastal upwelling is a dominant process controlling high frequency temperature fluctuations near shore a simple quantitative estimate reveals a volume of upwelled water reaching the sea surface of about 10 10 m 3 during one relatively intense upwelling event

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

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

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

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

the longer it has been since the last earthquake the longer the expected time till the next we adopt a iognormal distribution for earthquake interval times and we use a locally determined rather than a generic coefficient of variation to estimate the probability of occurrence of characteristic earthquakes we extend previous methods in two ways first we account for the aseismic period since the last event the seismic drought in updating the parameter estimates second in calculating the earthquake probability we allow for uncertainties in the mean recurrence time and its variance by averaging over their likelihood both extensions can strongly influence the calculated earthquake probabilities especially for long droughts in regions with few documented earthquakes as time passes the recurrence time and variance estimates increase if no additional events occur leading eventually to an affirmative answer to the question in the title the earthquake risk estimate begins to drop when the drought exceeds the estimated recurrence time for the parkfield area of california the probability of a magnitude 6 event in the next 5 years is about 34 per cent much lower than previous estimates furthermore the estimated 5 year probability will decrease with every uneventful year after 1988 for the coachella valley segment of the san andreas fault the uncertainties are large and we estimate the probability of a large event in the next 30 years to be 9 per cent again much smaller than previous estimates on the mojave pallett creek segment the catalog includes 10 events and the present drought is just approaching the recurrence interval so the estimated risk is revised very little by our methods

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

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

the 5500 km long boundary flow off western and southern australia 1 the path of the shelf edge flow off southwestern australia is documented using results from satellite altimetry and sea surface temperature sst and a climatogical in situ analysis during austral winter a continuous current is shown to extend from its origin at north west cape to the southern tip of tasmania a distance of 5500 km satellite sst observations and surface buoy tracks confirm the location and continuity of the current trajectory while the leeuwin current is forced by the strong alongshore pressure gradient associated with the meridional portion of the western australian coastal boundary our results suggest that the essentially zonal shelf edge flow along the southern australian coast arises from the setup of coastal sea level by onshore ekman flow driven by the winter westerly wind and possibly a further alongshore pressure gradient the timing of these two different forcing mechanisms means that the west coast pressure gradient delivers the leeuwin current to the south coast just as the winds reverse and are thus able to maintain the eastward passage of the current the shelf edge flow consists of two main water masses a low salinity warm water type of tropical origin associated with the leeuwin current and a high salinity warm water inflow formed on the western end of the great australian bight continental shelf a naming convention is proposed the leeuwin current representing flow from north west cape to the great australian bight gab the south australian current between the eastern gab and western bass strait and the zeehan current off western tasmania

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

on the global estimates of geostrophic and ekman surface currents surface currents in oceanic environments are of crucial importance because they transport momentum heat salt and tracers over large distances that regulate both the local and large scale climate conditions and because they contribute to the lagrangian displacement of floating material ranging from living resources to marine pollution in recent decades the understanding of surface currents has benefited from the opportunity of observing sea level and wind stress via satellite derived measurements combining these parameters into geostrophic and wind driven components provides an estimate of surface currents with a quarter degree horizontal resolution at a global scale and at a daily time scale in the present study improvements are made on the consideration of the time dependence of the main parameters implied in the determination of the ekman wind driven component and on the treatment of the equatorial singularity the resulting geostrophic and ekman current observatory gekco estimates were validated with independent observations from both lagrangian and eulerian perspectives the statistics of comparison were significant over the globe for the 2000 2008 period the only exception was the estimation of meridional current along the equator which requires further developments of the dynamic model and probably more accurate measurements applications using our gekco surface current estimates in cross disciplinary approaches from physical oceanography to marine ecology are presented and discussed

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

the combined effect of transient wind driven upwelling and eddies on vertical nutrient fluxes and phytoplankton dynamics along ningaloo reef western australia we investigate the influence of wind stresses stratification and coastal mesoscale eddies on upwelling intensity vertical nutrient fluxes and phytoplankton biomass on the continental shelf off ningaloo reef in northwestern australia during an austral spring summer period a three dimensional 3 d hydrodynamic model roms regional ocean modeling system was coupled with a four component nitrogen based biogeochemical npzd model nitrogen phytoplankton zooplankton detritus to resolve the shelf circulation as well as the coupled nutrient and phytoplankton dynamics within a broad shelf region surrounding ningaloo reef the simulated currents temperatures and chlorophyll a concentrations generally agreed well with both the remotely sensed satellite images and observational data collected during a field experiment from september to november 2010 scenario tests for an individual wind driven upwelling event under a variety of hypothetical physical forcing conditions showed that shelf currents and biogeochemical variables were largely a function of wind stress and stratification however the functional relationships derived from this single wind event could not be extrapolated to other periods of the upwelling season due to the additional influence of 3 d mesoscale processes on the shelf the presence intensification and propagation of a coastal anticyclonic eddy during the study period strongly influenced the spatial and temporal variations in nutrient profiles which in turn caused fluctuations in vertical nutrient fluxes that were largely independent of wind stress these results emphasize that it is necessary to fully capture the 3 d details of the mesoscale and submesoscale coastal dynamics to properly predict upwelling induced coastal phytoplankton dynamics in eddy intensive shelf regions such as ningaloo reef

some features of aftershock patterns in greece summary a quantitative study of 12 aftershock sequences which occurred in greece and the surrounding regions from 1971 to 1980 has been made the aim of the study was to investigate the temporal pattern of each aftershock sequence and to examine the possibility of predicting the largest aftershock the magnitudes of the main shocks were ml 5 0 the minimum and maximum numbers of aftershocks were 25 and 191 respectively the temporal analysis was performed using the modified omori formula and akaike information criterion first we examine the omori law to see if holds for the whole aftershock sequence second we examine the same data set in order to find out if there is any possibility of distinguishing two aftershock sequences as follows 1 the first must include all the shocks since the occurrence of the main event until the occurrence of the largest aftershock and 2 the second must include all events following the occurrence of the largest aftershock until the end of the aftershock activity in 10 cases out of 12 the model of two different aftershock sequences provides the best fit to the data the aftershock activity prior to the large aftershocks was then examined although the main shocks occurred in different seismogenic regions an almost identical behaviour of aftershock activity was observed the activity shows an appreciable decrease from the level expected from the modified omori formula also in some cases the aftershock activity recovers to a normal level or increases beyond it prior to the occurrence of the main aftershock these results seem to be independent of the magnitude of the large aftershock if the aftershock activity is monitored in real time this observed temporal pattern may be useful in predicting a large aftershock

seismic quiescence at parkfield due to detachment faulting on the san andreas fault near parkfield california rates of seismicity1 2 and geodetic line shortening3 4have been lower since 1986 than before wyss et al 1 3interpret the rate decreases as precursors to an imminent moderate earthquake magnitude m 5 5 6 and estimate the earthquake time to be march 1991 1 yr the earthquake was previously predicted to occur in 1988 5 yr based on five of six similar earthquakes which occurred at intervals 22 yr the last one in 19665 here i present a model that attributes the rate changes to the initiation of slip on a subhorizontal detachment fault under the pending rupture area in this model the slip starts late in the seismic cycle and diminishes the loading rate on the nearby san andreas thus acting as a buffer

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

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

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

on the factors influencing the development of sporadic upwelling in the leeuwin current system cumulates the highest number of upwelling 140 days per year and is characterized by longer events the intensity of intermittent upwelling is influenced by the upwellingfavorable winds the characteristics of the leeuwin current e g onshore geostrophic flow mesoscale eddies and meanders stratification and nitracline and the local topography this suggests that short living nutrient enrichment of variable magnitude may occur at any time of the year at many locations along the wa coast

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

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

numerical modelling of the mean flow characteristics of the leeuwin current system abstract the oceanic circulation of the region between carnarvon 25 s and jurien bay 31 s was examined using observational and remotely sensed data in conjunction with a detailed numerical modelling study the model was validated using in situ adcp and ctd data and the horizontal eddy viscosity parameterization was tested against field observations the results generated using the regional ocean model roms v1 8 simulated the observed mean surface flow s spatial and temporal scales particularly those of the eddy features the modelled results also provided insight into the leeuwin current lc s annually averaged alongshore transport and the leeuwin undercurrent luc s mean flow characteristics analysis of the model results between 26 8 s and 30 8 s revealed the annually averaged alongshore transport across the lc s southern boundary was 5 7 sv of which the northern boundary contributed 3 60 sv or 63 the inflow of water through the western boundary due to geostrophic balance was estimated at 2 1 sv or 37 and found to vary meridionally a geopotential gradient estimated at 1 9 10 7 and acting towards the equator drives the luc located at depths between 250 and 600 m the modelled undercurrent is characterized as an energetic flow with mesoscale variability that is strongly influenced by the more energetic surface current coupling was evident in the region adjacent to the abrolhos islands western boundary 29 s where the offshore movement of lc waters by a surface meander caused the vertical scale of the undercurrent to increase inducing an anticlockwise vorticity response at a depth of 180 m the resulting subsurface eddy grew preferentially downwards before a surface response was observed the model showed that the eddy increased its vertical scale before splitting into two forming a surface and subsurface eddy with a vertical scale characteristic of the two currents the surface eddy intensified detached and moved offshore while the subsurface eddy remained attached to the topography

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

the down stress transition from cluster to cone fabrics in experimentally deformed ice abstract during plastic deformation of polycrystalline ice 1h ice crystals become crystallographically aligned due to dislocation glide primarily on the basal slip system such crystallographic preferred orientation cpo introduces a viscous anisotropy in ice and thus strongly influences the kinematics of the flow of glaciers and ice sheets two key mechanisms exert different controls on cpo in axial compression recrystallization dominated by lattice rotation yields a cluster of c axes parallel to compression and recrystallization dominated by grain boundary migration gbm yields a cone shaped distribution of c axes with the cone axis parallel to compression the transition between these dominant mechanisms of cpo formation has not been well quantified in this study we explore how this transition varies with stress ice deformation experiments were conducted using a high pressure gas medium apparatus to prevent fracturing of samples at relatively high stresses samples were deformed in uniaxial compression at a temperature of 10 c and a confining pressure of 10 mpa fabricated ice samples with starting average grain sizes of either 0 23 mm or 0 63 mm were each deformed to an axial strain of 0 2 at a nominally constant strain rate in the range 1 2 10 6 to 2 4 10 4 s 1 yielding flow stresses of 1 17 to 4 31 mpa high quality electron backscatter diffraction reveal the grain size shape subgrain structure and cpos formed at different stresses all deformed samples have strong non random cpos with c axes concentrated in cones the cone angle and cpo strength are observed to decrease with increasing stress as stress increases the fraction of grains with highly curved or lobate grain boundaries decreases and the fraction of polygonal grains with straight grain boundaries increases based on these observations we propose that a transition in the dominant mechanism of cpo formation occurs with increasing stress from gbm which consumes grains with low schmid factors at low stress to lattice rotation caused by slip primarily on the basal slip system which causes c axes to rotate to become parallel to the shortening direction at high stress mapping out the transition from cluster rotation dominated to cone gbm dominated cpos as a function of stress this study and temperature future studies allows for a robust extrapolation to and a fundamental understanding of the cpos formed at glaciological stresses and temperatures

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

spatiotemporal evolution of upwelling regime along the western coast of the iberian peninsula 1 the spatial and temporal variability of upwelling regime along the western coast of the iberian peninsula ip has been analyzed by means of two different but complementary databases quikscat satellite database which is available from mid 1999 with a high spatial resolution 0 25 0 25 and pacific fisheries environmental laboratory pfel database with a coarser spatial resolution 1 1 but extending back to 1967 the combined use of both databases allows determination of the spatial variability of ekman transport and pumping and identification of temporal trends in upwelling signal upwelling favorable conditions are observed during spring and summer apart from this well known seasonality on upwelling regime along the western coast of the ip some other features have been identified 1 upwelling occurs simultaneously along the entire western coast of the ip but is undoubtedly more complex closer to particular features of the shoreline 2 positive ekman pumping is more intense near capes sao vicente and rocha during spring summer and near cape finisterre all over the year 3 more favorable upwelling conditions have been observed in february and november during the last decade this result is corroborated by sea level pressure composites which show the existence of abnormally high pressures close to the ip during the last decade compared to the historical records 1948 2006 4 the decadal variability of ui is higher in autumn winter than in spring summer 5 monthly upwelling trends indicate a weakening in upwelling intensity during most of the year with the exception of february june and july

relative seismic quiescence before large aftershocks in terms of the modified omori s formula and akaike s information criterion thirteen aftershock sequences have been analysed quantitatively to check if any anomalous change of seismic activity took place before the occurrence of the largest aftershock the analysis follows the method proposed by the epicentre distribution of the main shocks covers the aegean sea greece area and the surrounding regions the earthquakes occurred from 1988 to 1998 although difficulties existed for a quantitative treatment of seismic quiescence the results of the temporal analysis of the aftershock activities seem to be promising in eight of thirteen cases the observed temporal pattern is similar the aftershock activity decreases significantly before the occurrence of the largest aftershock with respect to the level expected according to the modified omori s formula thereafter the activity recovers to its previous level just before or immediately after the occurrence of the main aftershock moreover an estimation of the reliability of the method is made based on the results of this study as well as of previous similar investigations from a total of 41 aftershock sequences which have been analysed following matsu ura s method 29 of them 71 show a remarkable relative quiescence before the occurrence of the main shock although it is difficult to construct a model which explains the precursory pattern the real time monitoring and check for seismic quiescence could at least contribute to a qualitative prediction of the largest aftershock which could at times be as large and disastrous as the main shock

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

seasonal circulation and temperature variability near the north west cape of australia 1 the circulation and temperature variability on the inner shelf near the north west cape of australia off ningaloo reef was investigated using field data obtained from two moorings deployed from 2004 to 2009 the results revealed that alongshore currents on the inner shelf were on average only weakly influenced by the offshore poleward southward leeuwin current flow i e monthly averaged alongshore current velocities were 0 1 m s 1 or less the presence of a consistent summer time wind driven equatorward northward counter flow on the inner shelf referred to in the literature as the ningaloo current was not observed instead the shelf waters were strongly influenced year round by episodic subtidal current fluctuations time scale 1 2 weeks that were driven by local wind forcing analysis of the current profiles showed that periods of strong equatorward winds were able to overcome the dominant poleward pressure gradient in the region leading to upwelling on the inner shelf contrary to prior belief these events were not limited to summer periods the forcing provided by these periodic wind events and the associated alongshore flows can explain much of the observed temperature variability with timescales 1 month that influences ningaloo reef

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

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

linking synoptic forcing and local mesoscale processes with biological dynamics off ningaloo reef 1 a hydrographic survey offshore ningaloo reef north west australia in austral autumn 2010 revealed relatively stable subsurface water masses in the region despite the influence of interannual variability of the leeuwin current lc the surface water mass seems slightly more variable at seasonal time scale probably due to various contributions of the geographically distinct source waters of the lc a subsurface nitrate maximum 110 230 m a prominent feature of the ningaloo area during autumn was consistently observed within different water masses tightly coupled variations of subsurface nitrate and oxygen at small vertical scale suggest it is due to local in situ remineralization of organic matter likely to accumulate along sharp physical interfaces and possibly favored by injections of oxygenated subsurface waters offshore enhanced levels of surface chlorophyll a within the downwelling favorable lc are associated with deeper mixed layer depth eroding the shallow source of nutrients close to the continental shelf these nutrients are observed to be efficiently uplifted within the core of quasi persistent topographically trapped submesoscale cyclonic eddies dominated by nonlinear effects a wind driven coastal upwelling event occurred in autumn and was characterized by a relatively deep source 100 150 m coinciding with the subsurface maximum of nutrients thus promoting coastal productivity locally and farther north by alongshore advection within the ningaloo current

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

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

weak bands within ice stream b west antarctica kilometer scale variations in ice velocity and surface topography are used to investigate the style of glacier deformation in the main body of ice stream b west antarctica the pattern is very different from that reported for other glaciers for the 250 km 2 area studied on ice stream b most of the observed deformation occurs within two narrow bands in which there is large across flow compression and slow lateral shearing the bands underlie valleys in the ice surface topography measured upward displacement of ice adjacent to the rapidly compressing bands appears to be linked to the creation of the ice stream s topography the most likely cause for the observed pattern of strain rates and surface topography and their changes over time is deformation guided by longitudinal bands of ice with an aligned crystal fabric

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

changes of mean magnitude of parkfield seismicity a part of the precursory process the average magnitude of earthquakes produced along the parkfield segment of the san andreas fault was decreased significantly between late 1986 and late 1988 along with the seismic quiescence wyss et al 1990a the change corresponds to an increase of the b value from 1 1 to 1 4 during the last year 1989 however the average magnitude produced was approximately normal again this same phenomenon had been identified before several other mainshocks therefore it may be interpreted as a precursor to the predicted parkfield mainshock

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

seasonality of sporadic physical processes driving temperature and nutrient high frequency variability in the coastal ocean off southeast australia physical processes forced by alongshore winds and currents are known to strongly influence the biogeochemistry of coastal waters combining in situ observations moored platforms hydrographic surveys and satellite data sea surface wind and sea surface height we investigate the transient occurrence of wind driven upwelling downwelling and current driven upwelling events off southeast australia remote sensed indices are developed and calibrated with multiannual time series of in situ temperature and current measurements at two shelf locations based on archives up to 10 years long climatological analyses of these indices reveal various latitudinal regimes with respect to seasonality magnitude duration of events and their driving mechanisms wind or current generally downwelling favorable winds prevail in this region however we demonstrate that up to 10 wind driven upwelling days per month occur during spring summer at 28 33 5 degrees s and up to 5 days in summer further south current driven upwelling upstream of the east australian current separation zone approximate to 32 degrees s occurs twice as often as downstream using independent in situ data sets we show that the response of the coastal ocean is consistent with our climatology of shelf processes upwelling leads to a large range of temperatures and elevated nutrient concentrations on the shelf maximized in the wind driven case while downwelling results in destratified nutrient poor waters the combination of these sporadic wind and current driven processes may drive an important part of the high frequency variability of coastal temperature and nutrient content our results suggest that localized nutrient enrichment events of variable magnitude are favored at specific latitudes and seasons potentially impacting coastal ecosystems key points multisensor analysis of shelf processes combining in situ and satellite data spatio temporal variability of transient wind and current driven up downwelling cold nutrient rich water intrusions favoured at specific locations seasons

eddy formation through the interaction between the leeuwin current leeuwin undercurrent and topography abstract the surface and subsurface circulation off south west australia was simulated using the regional ocean modelling system roms a primitive equation ocean model with terrain following s coordinates the major currents in this region the leeuwin current and leeuwin undercurrent were reproduced by specifying only temperature and salinity distributions from climatology the application of wind stress subsequent to the model reaching a quasi steady state resulted in the generation of the seasonal capes current a northward flowing current on the continental shelf associated with coastal upwelling the simulated currents compared well with the observed current patterns including the location and maximum current speeds shelf topography variations and bottom shear which generated vorticity influenced eddy formation eddies separated from the leeuwin current and the leeuwin undercurrent migrated westward and exited the model domain through merging dissipating or through an open boundary in the model simulations the undercurrent produced mostly cyclonic eddies due to strong negative vorticity where the current flowed against the continental slope the leeuwin current produced anticyclonic warm core eddies initiated from the formation of meanders which were strongest at the surface the eddy field was dominated by anticyclonic eddies at the surface and cyclonic eddies at 500 m the interaction between the leeuwin current and leeuwin undercurrent led to the formation of eddy pairs

environmental drivers of growth in massive porites corals over 16 degrees of latitude along australia s northwest shelf sustained calcification is fundamental for maintaining tropical coral reef ecosystems which are under increasing pressure from global and local changes to the marine environment annual density bands in massive corals provide a robust means to retrospectively monitor growth and identify the environmental drivers we present porites growth characteristics for 60 coral cores from 18 reef sites and five environmental regions off western australia wa over the period 1950 2008 this remote region encompasses diverse coral reef ecosystems and is an economically important natural resource hub despite high variability average calcification is highest in the offshore shelf reefs and lowest in the most southerly reefs the primary environmental drivers of these spatial variations are annual and winter minimum sea surface temperature sst and annual winter minimum photosynthetically active radiation average growth characteristics for wa reefs are comparable to those of australia s great barrier reef calcification rates at the two most southerly wa reefs are anomalously high which may be due to the unusual environmental conditions generated by the leeuwin current variable rates of sst warming across the 18 reefs are however changing the strength of the relationship between sst and calcification we found no evidence to support the contention that annual density banding is driven by environmental seasonality retrospective monitoring of growth rates provides a critical tool for both assessing coral growth responses to ongoing rapid climate change and possible responses to increasing anthropogenic pressures related to natural resource development in the region

decrease in deformation rate as a possible precursor to the next parkfield earthquake crustal deformations along fault zones are monitored because they show the accumulation and possible premonitory release of strain energy before major earthquakes on the parkfield segment of the san andreas fault the next mainshock local magnitude ml 5 7 is expected to occur between 1983 and 1993 based on the relatively regular recurrence of characteristic earthquakes in 1857 1881 1901 1922 1934 and 19661 a concerted monitoring effort is therefore underway at parkfield with the aim of detecting precursory changes in observable quantities that can be measured reliably2 here we report data from two geodetic lines crossing the san andreas fault near parkfield which show that the rate of shortening decreased by 20 starting in august 1986 this change coincided with a rate decrease of 45 for earthquakes of ml 2 1 in the area3 4 both phenomena may have been caused by temporary locking of the fault surface or a decrease in strain accumulation rate and they are interpreted as intermediate term precursors to the next parkfield earthquake