volcanism and aseismic slip in subduction zones the spatial and temporal relationship of volcanism to the occurrence of large earthquakes and convergent plate motion is examined the number of volcanic eruptions per year in a convergent zone is found to be linearly related to the aseismic slip component of plate motion if the aseismic slip rate is low coupling between converging plates is strong then the primary manifestation of tectonic activity is the occurrence of large earthquakes with only infrequent volcanic activity if however the aseismic slip rate is high coupling is weak then there are few large earthquakes and volcanism is the principal manifestation of tectonic activity this model is consistent with the spatial distribution of large earthquakes and active volcanoes in the circum pacific area it is tested by examining the extent of volcanic activity in the rupture zones of the 1952 1973 sequence of earthquakes in the japan kurile islands area the number of volcanic euptions along these zones during the interval between large earthquakes is used to compute the aseismic slip rates for these segments based on the relationship developed in this study the aseismic slip rates so computed agree with those determined from the earthquake history of the area and rates of plate motion themore agreement suggests that in the interval between large earthquakes the aseismic plate motion is manifested in a specific number of volcanic eruptions therefore in areas with adequate historial data it should be possible to use the model developed in this study to monitor volcanic eruptions for long term prediction of large earthquakes less

how to remove the seasonal atmospheric effect an application on a surface volcanic temperature at nisyros active volcano hellenic volcanic arc abstract surface temperature at a volcanic system is the result of a mixture of two heat sources originating one from above and another from below the ground surface the atmosphere significantly affects the surface s temperature of the volcano and removal of the atmospheric effect is required for meaningful interpretations prior to any characterization of anomalous volcanic activity time series of meteorological data were acquired from the closest weather station to nisyros volcano and surface volcanic temperature from the southern part of nisyros caldera were analyzed time series analysis took place at different time scales through a decomposition method the decomposition of the time series into long seasonal and short term components was performed by the application of the kolmogorov zurbenko kz filter to separate the noise that appears on the obtained data the time series regression tsr model was applied in all time scales the long and the short term components of the surface volcanic temperature show no significant correlation with the atmospheric variables while the seasonal term indicates a very strong association with an r2 equal with 99 after the removal of the atmospheric effect our model indicates that there is a normal activity of the seasonal heat emission in nisyros with no anomalous signals in the temperature residuals during our survey this methodology may facilitate the process of filtering a seasonal atmospheric effect and better comprehend the heat emission of a volcano hydrothermal system from temperature surface readings

large intermediate depth shocks and volcanic eruptions in the hellenic arc during 1800 1985 abstract the most reliable and complete seismological data have been utilized to define three seismic energy highs associated with large m 7 5 intermediate depth earthquakes h 70 km in the hellenic arc during 1800 1985 these highs were correspondingly followed by the three eruption cycles which occurred on the volcano of santorini during the same time interval the time lag is of the order of 15 years the distance between santorini and the epicentre of the shocks ranges from about 60 to 200 km these results agree with those found in other island arcs of the world possible geodynamic correlation between deep seismicity and magma formation along the upper surface of the descending slab is discussed

the early holocene sea level rise the causes anatomy and consequences of the early holocene sea level rise ehslr are reviewed the rise of ca 60m took place over most of the earth as the volume of the oceans increased during deglaciation and is dated at 11 650 7000 cal bp the ehslr was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams the patterns of ice sheet decay and the evidence for meltwater pulses are reviewed and it is argued that the ehslr was a factor in the ca 8470 bp flood from lake agassiz ojibway patterns of relative sea level changes are examined and it is argued that in addition to regional variations temporal changes are indicated the impact of the ehslr on climate is reviewed and it is maintained that the event was a factor in the 8200 bp cooling event as well as in changes in ocean current patterns and their resultant effects the ehslr may also have enhanced volcanic activity but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated the rise probably influenced rates and patterns of human migrations and cultural changes it is concluded that the ehslr was a major event of global significance knowledge of which is relevant to an understanding of the impacts of global climate change in the future

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

two mica granites of northeastern nevada the field settings are described and analytical data are presented for six two mica granites from north eastern nevada high 18o and 87sr 86sr values indicate that all are s type granites derived from continental crust the major element chemistry and accessory mineral contents of these rocks also are characteristic of s type granites chemical x ray and other data are presented for the micas recovered from these granites the muscovites are notably high in fe2o3 feo and mgo except for one hydrobiotite each of the biotites has an mgo content near 6 0 weight percent two different types of two mica granites are recognized in the area of this study one type is distinguished by the presence of many biotite euhedra within muscovite phenocrysts and by an unusual suite of accessory minerals completely devoid of opaque oxides this type probably resulted from anatexis of late precambrian argillites under conditions of relatively low oxygen fugacity along a line that roughly coincides with the westward disappearance of continental basement in the other textural type of two mica granite the micas are equigranular and there is a greater variety of accessory minerals the magmatic evolution of this type also appears to reflect the influence of late precambrian argillites there may be age differences between the two types of two mica granites

spatial changes in volcanic and seismic activity prior to great earthquakes spatial relationship between volcanism and seismicity prior to the occurrence of several great interplate earthquakes in the circum pacific area has been examined in order to understand the process of underthrusting in detail the locations of the epicenters of the great earthquakes have been examined in terms of locations of concentrated volcanic and seismic activity in a short time period in order to determine if there is any relationship between these activities and whether such relationships can be used to refine the underthrusting model the study shows that in most cases 1 there is no volcanic activity in the vicinity of the epicenter of the great earthquake and 2 maximum volcanic activity is localized i e volcanoes adjacent to one another exhibit considerable activity in a short time period very little systematic spatial relationship between these three parameters is observed although in most cases there is no volcanic activity at the time of maximum earthquake activity locations of active volcanoes and earthquake activity during the five years prior to the occurrence of the great earthquake do not appear to be a guide to the epicenter of the great earthquake this study therefore suggests that although there is temporal relationship between the occurrence of maximum volcanic and seismic activity and the occurrence of great earthquake there appears to be no systematic spatial relationship between these three parameters

an inhomogeneous fault model for gaps asperities barriers and seismicity migration we develop a model for a fault in which various areas of the fault plane have different stress slip constitutive laws the model is conceptually simple involving nonlinear algebraic equations which can easily be solved by a graphical method of successive iterations application is made to the problem of explaining seismicity patterns associated with great earthquakes the model quantitatively explains phenomena associated with seismic gaps asperities and barriers

main environmental changes since the weichselian glaciation in the danish waters between the north sea and the baltic sea as reflected in the molluscan fauna abstract the danish waters forming the transition zone between the north sea and the baltic sea are described through changes in the molluscan fauna and bottom communities during the holocene the major change in the fauna at the pleistocene holocene boundary is thought to be caused by changes in the palaeocurrents at this time a sudden sea level rise marked by floodwaters is recorded at the levels from 24 5 to 4 0 m between ca 8600 and 7800 cal years bp corresponding to a sea level rise of around 3 5 m every 100 years an expiring tide is identified in the early subboreal affecting the prolific fjord faunas of the atlantic time

a tilt and seismicity episode in the new hebrides vanuatu island arc tilt and seismicity have been monitored in the central new hebrides island arc since 1978 using bench mark arrays long tube water tiltmeters borehole tiltmeters and a local seismometer network releveling of the bench mark array on efate island in late november 1986 revealed a 10 rad tilt up to the nnw since the previous leveling in april 1986 the tilt event was preceded by a magnitude 5 9 thrust event that occurred on october 25 1986 at a depth of 48 km and about 11 km nw of the tiltmeter instruments six days later a shallow 20 km swarm of earthquakes occurred 12 km nnw of the tiltmeter instruments and 5 km north of the epicenter of the magnitude 5 9 earthquake closely coincident in time with the swarm a 5 rad tilt up to the nnw that occurred over a period of 5 days was recorded on both the 100 m baseline water tube tiltmeter and the borehole bubble level tiltmeter a composite focal mechanism of 191 earthquakes selected from the swarm indicates a thrust mechanism with some component of strike slip calculations show that the seismic slip associated with a swarm of this magnitude is apparently inadequate to cause the observed surface deformation two similar shallow swarms in november 1987 and july 1988 have occurred within 15 km of the 1986 swarm but with no apparent surface deformation the most likely explanation supported by simple modeling is that the swarm and tilt are the result of a magmatic intrusion from island arc volcanism an alternate hypothesis is that both the seismicity and the tilt are due to an episode of largely aseismic creep in the upper crust

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

patterns of seismicity associated with asperities in the central new hebrides island arc in the central part of the new hebrides island arc efate malekula region 16 s 18 6 s a sequence of moderate sized earthquakes their aftershock sequences and other clusters of small earthquakes together form an intricate but coherent time space pattern that probably reveals a major asperity complex along the interplate boundary of the subduction zone this pattern is determined by study of data from a local network the sequences including one event with magnitude mw 7 1 eight events with magnitudes mw between 5 8 and 6 3 and nearly 13 000 smaller events occurred during the six year period 1978 1984 the seismicity is very unevenly distributed in space a sharply defined east west line near 17 2 s separates the very active efate region to the south where nearly 10 500 earthquakes occurred from the less active malekula region to the north where less than 2 500 earthquakes occurred during the six year period in the efate region several spatial patterns are highlighted first the seismic regimes of the updip and the downdip part of the interplate boundary are different the updip part is characterized by a low background activity and main shocks with large aftershock zones while the downdip part is characterized by a very high level of background activity and main shocks with much smaller aftershock zones or no aftershocks this difference in seismic regimes suggests that asperities are located in the updip part of the interplate boundary while the downdip part may slip predominantly by creep a creep episode may have been responsible for the tilt signal observed by periodic relevelings of a l km aperture network of benchmarks on efate island second specific locations along the interplate boubdary are identified either as sites of very intense and repeatedly activated concentrations of hypocenters or as sharp boundaries limiting the spatial development of aftershock zones two areas of concentrated activity particularly stand out one located in the updip part of the interplate boundary and the other in the downdip part most of the clustered activity that occurred during the six years of observation is concentrated in these two areas four boundaries limiting the spatial development of aftershock zones are located in the updip part of the interplate boundary one of these boundaries coincides with one of the areas of intense activity epiceniers of moderately large events that occurred in the region since 1960 are also concentrated along the boundaries the zones of concentrated activity and the boundaries limiting the development of aftershock zones can be interpreted either as locations of penties or as edges of asperities an alternative interpretation is that a giant asperity is located in the ylekula region with the different spatial patterns observed in the efate region being interpreted as the southern edge of that asperity a transition zone between a locked part to the north and normal i subduction to the south study of the temporal patterns of the seismicity shows that the main shocks in tbe downdip part of the interplate boundary are not preceded by obvious long term months to year nor short term days to week precursory activity in the updip part of the interplate boundary short term fipreshocks preceded each main shock but only one of these foreshock sequences is outstanding although no clear cyclic pattern related to the main shocks is evident clustered activity that occurred in the two zones of concentrated activity and two other zones located in the back arc region are correlated ih time with the occurrence of the major sequences located in the updip part of the interplate boundary activation of these four zones always follows the sequences in the updip part of the interplate boundary qith varying time intervals days to months these four zones are also sometimes activated before sequences in the updip part of the interplate boundary in particular one of the zones of concentrated a ctivity shows possibly repeated long term few months precursory activity this phenomenon could b e an indicator of increasing probability of occurrence of main events in the updip part of the interplate b oundary i tuk ukiis lmcui l ilu tl6aj2 qfiztqf

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

fine structure of the dipping seismic zone and subduction mechanics in the shumagin islands alaska microearthquake data from a permanent telemetered array have been used to elucidate the structure and tectonics of the subduction zone in the shumagin islands alaska the shallow microseismicity is characterized by active interplate thrusting in the 25 45 km depth range arcward of this interplate activity microearthquakes in the overlying plate have a strike slip mechanism the near horizontal p axis of this mechanism is oriented in the direction of plate convergence suggesting that the plate interface at shallow depths is currently efficiently coupled below 45 km depth the dipping seismic zone appears to be double planed the upper plane dips at 32 from 45 to 100 km depth where it exhibits a kneelike bend below the volcanic front the lower plane begins at about 65 km depth where it is separated from the upper plane by some 25 km and appears to converge with the upper plane at about 120 km depth the inferred geometry of the plate interface suggests that the double planed portion of the dipping seismic zone is a product of elastic unbending of the subducted plate a composite fault plane solution for events in the upper plane indicates however that downdip tension is currently present rather than the downdip compression that would be expected from unbending it is proposed that because of locking of the plate interface at shallower depths slab pull is currently overprinting the unbending stresses which predominate at times when the plates are unlocked this model is consistent with previous interpretations that there is a high probability of a great earthquake in the shumagin islands seismic gap within the next decade or two

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

holocene sea level changes and glacio isostasy in the gulf of finland baltic sea abstract shoreline displacement in the eastern part of the gulf of finland during the past 9000 radiocarbon years was reconstructed by studying a total of 10 isolated lake and mire basins located in virolahti in southeastern finland and on the karelian isthmus and in ingermanland in russia study methods were diatom analyses sediment lithostratigraphical interpretation and radiocarbon dating in southeastern finland the marine litorina transgression maximum occurred ca 6500 6200 14 c yr bp 7400 7100 cal yr bp in areas of the slower land uplift rate on the karelian isthmus and in ingermanland the transgression maximum occurred ca 6400 6000 14 c yr bp 7300 6800 cal yr bp the highest litorina shoreline is located at ca 23 m above present sea level in southeastern finland whereas in the eastern part of the karelian isthmus near st petersburg it is located at ca 8 m above present sea level the amplitude of the litorina transgression in virolahti area is ca 4 m whereas on the karelian isthmus and in ingermanland the amplitude has varied between 5 and 7 m the regional differences between areas are solely due to different glacio isostatic land uplift rates the seven basins studied in this research were connected to the baltic sea basin during the litorina sea stage and their diatom and lithostratigraphical records indicate a single smooth litorina transgression

seismicity associated with the great colombia ecuador earthquakes of 1942 1958 and 1979 implications for barrier models of earthquake rupture abstract we have relocated earthquakes along the colombia ecuador coast with the method of joint hypocenter determination in order to examine the nature of fault heterogeneities that controlled northward propagation of plate boundary rupture from the source region of the earthquake of 14 may 1942 to the source region of the 19 january 1958 earthquake and eventually to the source region of the earthquake of 12 december 1979 the entire region of the 1942 1958 and 1979 shocks had previously ruptured in the single great earthquake of 31 january 1906 the relocated hypocenters lie on the same plane to within the approximately 20 km uncertainty of the focal depths also the main shocks nucleated at nearly the same distance from the colombia trench these observations suggest that the heterogeneities between the 1942 and 1958 ruptures and between the 1958 and 1979 ruptures do not correspond to a major distortion of the downgoing slab but rather to either minor distortions of the slab or to regions of high friction or low available strain energy on a continuous fault surface in particular the heterogeneity between the 1958 and 1979 rupture zones seems to have been a high strength barrier with dimensions much smaller than the dimensions of either of the rupture zones the 1942 and 1958 earthquakes had source dimensions no larger than the 1979 main shock but they had stronger aftershock sequences than the 1979 earthquake this observation suggests that the arrest of earthquake rupture in 1979 left the plate boundary segment that had ruptured in 1906 in a state of lower stress than it had been following the 1942 and 1958 earthquakes long term seismicity in the decades preceding the 1979 earthquake occurred mostly outside or on the boundaries of the rupture area defined by the distribution of 1979 aftershocks the intense aftershock activity that followed the 1958 main shock within tens of kilometers of the eventual 1979 hypocenter may correspond to a long term precursory seismic swarm for the 1979 earthquake

seismicity changes prior to several great earthquakes in the circum pacific area abstract spatio temporal variation in earthquake activity prior to several post 1950 earthquakes with magnitude 8 0 in the circum pacific area has been examined in order to identify a common precursory pattern strain energy e released in the rupture zone of these great earthquakes was computed for every year between 1910 and the time of the great earthquake an examination of strain energy release as a function of time shows that maximum strain energy e b is released in the rupture zone at a time which depends on the magnitude m of the subsequent great earthquake the ratio of strain energy e m released in the great earthquake to the strain energy e b varies between 3 and 30 i e this burst of activity is equivalent to a single earthquake of magnitude between 1 2 to 2 units less than the magnitude of the great earthquake the amount of maximum deformation and the time at which it occurs appears to depend on the magnitude of the great earthquake

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

spatial seismicity variations and asperities in the new hebrides seismic zone the term asperity has been used in many recent studies to describe sections of faults with higher strength than the surrounding zones the level of background seismicity expected in such zones is unclear they may appear as quiet zones because of high strength or active zones because of high stress in this work the problem of seismicity levels in asperities is addressed by identifying regions of anomalously high or low seismicity and comparing the locations of these regions with the locations of asperities as determined from other observations the regions of anomalously high or low seismicity are identified using a quantitative technique which relies on spatial rate comparisons done with the z test for a difference between two means this technique allows the determination of the significance of spatial rate differences and the uniqueness of zones of outstanding seismicity four active zones which make up 10 and eight quiet zones which make up 16 of the length of the new hebrides seismic zone were recognized using this technique asperities in the new hebrides seismic zone were identified using characteristics which include large event initiation and stopping clusters of aftershocks and moderate events foreshock activity and earthquake stress drops eight regions which showed two or more of these characteristics were identified they make up 34 of the length of the seismic zone the overlap between the asperities and the active and quiet regions provides a test of possible relationships between these zones thirty four percent of the asperity area is active as opposed to the 10 expected and 6 of the asperity area is quiet as opposed to the 16 expected this suggests that in the asperities in the new hebrides seismic zone stress concentration overcomes increased strength and that phenomena other than increased strength can cause seismic quiescence nearly all of the asperities in the new hebrides seismic zone show high background seismicity or high stress drops which suggests that likely zones of mainshock initiation can be identified using background seismicity

drumlins subglacial meltwater floods and ocean responses drumlins and erosional marks in bedrock give evidence for broad subglacial meltwater floods that have discharge rate estimates of about 10 6 m 3 s similar discharge rates are obtained for other late glacial catastrophic floods the total volume of meltwater that is thought to have formed the livingstone lake saskatchewan drumlin field is estimated at 8 4 x 10 4 km 3 this volume is equivalent to a eustatic rise of 0 23 m in global sea level meltwater release and roughly contemporaneous formation of drumlin fields in north america and europe could have involved several metres of sea level rise in a few years the implications of such floods for the generation of myths and the interpretation of the oxygen isotopic record of the oceans are discussed high meltwater discharges are of potential importance to the generation of a lid of cold fresh water over the north atlantic and its effects on late glacial climate

spatial and temporal variations in seismicity in the imperial valley 1902 1984 earthquakes with m l 4 5 that occurred between 1932 and 1973 in the imperial valley region and their related foreshocks and aftershocks are relocated using station delays derived from calibration events that were well recorded at regional distances between 1979 and 1981 the relocated seismicity shows that there was an increase in seismicity in regions northeast of the imperial fault 5 to 6 yr prior to the 1940 m s 7 1 imperial valley earthquake a study of intensity reports for felt earthquakes prior to 1932 also suggests an increase in seismicity in regions surrounding the imperial fault as early as 1917 isoseismal patterns description of the mainshock sequence and patterns of seismicity before and after the 1915 imperial valley earthquakes suggest that the earthquakes occurred off the imperial fault in this case seismicity between 1906 and 1940 would nearly encircle the portion of the imperial fault that ruptured during 1940 in both the 1940 and 1979 imperial valley earthquake sequences aftershocks of m l 4 5 occurred only for 2 months following the mainshock the aftershock sequences were followed by periods of quiescence lasting up to 10 yr in the region within 30 km of the mainshock this is in contrast to m l 6 0 earthquakes occurring near the edges of the imperial valley that had aftershocks of m l 4 5 occurring for up to 4 yr after the mainshock these differences may be related to the high heat flow within the imperial valley

volcanic activity and large earthquakes abstract several investigators have noted an increase in volcanic activity prior to several large interplate earthquakes in the circum pacific area from these data i have examined the temporal relationship between the beginning of this increased volcanic activity and the occurrence of large earthquakes i find that the time year of the beginning of enhanced volcanic activity depends on the magnitude of the subsequent large earthquake for earthquakes with magnitude 7 5 the volcanoes which exhibit this enhanced activity are situated on the landward side of the rupture zone of the large earthquake and this study therefore suggests a casual physical relationship between the two phenomena i also find that this increase in volcanic activity occurs a few years before an increase in the occurrence of smaller earthquakes noted by several invesigators in the rupture zones of large earthquakes

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

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

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

the 1968 tokachi oki and the 1969 kurile islands earthquakes variability in the rupture process the may 16 1968 tokachi oki mw 8 2 and the august 11 1969 kurile islands mw 8 2 shallow thrust earthquakes occurred along the japan kurile arc about 500 km apart and possess similar static fault parameters their dynamic source processes were investigated using the observable directivity in the source time functions deconvolved from long period p waves the rupture processes of both earthquakes can be understood in terms of a combination of the end member asperity and barrier models of earthquake rupture the 1969 kurile islands earthquake ruptured in the sense of the asperity model one region of the fault plane radiated most of the seismic moment i e the asperity and is surrounded by the rupture zones of large precursor events the rupture process of the 1968 tokachi oki earthquake contains elements of both end member rupture models a dominant asperity is bounded to the south by a region of the fault plane ruptured by a large precursor event and is bounded to the north by a geometric barrier where the plate margin changes direction this geometric feature is responsible for the abrupt termination of the rupture front it appears that the tectonic setting plays a vital role in determining the rupture mode earthquakes that occur along linear trenches where no geometric or topographic complications exist seem to rupture in the sense of the asperity model whereas earthquakes that occur in the vicinity of such complications are more likely to possess rupture processes intermediate between the two end member models

relative sea level change and evidence for the holocene storegga slide tsunami from a high energy coastal environment cocklemill burn fife scotland uk a site in the cocklemill burn valley on the north shore of the firth of forth scotland provides evidence of relative sea level changes during the holocene from ca 7970 to ca 5090 radiocarbon years bp and of the holocene storegga slide tsunami dated here as having taken place after ca 7215 radiocarbon years bp marine sediments associated with two shorelines widely present in mainland scotland the main postglacial shoreline and the blairdrummond shoreline are recorded the holocene storegga slide tsunami deposits are unique here in the record of such sediments in eastern scotland in that they occur within marine sands of which the upper horizons are intertidal sandflat deposits the tsunami deposits probably accumulated shortly after a period of accelerated relative sea level rise the pattern and timing of which could have played a role in triggering the holocene storegga slide

the oxygen isotope composition of granitoid and sedimentary rocks of the southern snake range nevada six diverse intrusive igneous types are exposed as discrete outcrops within an area of 900 km2 in the southern snake range white pine county nevada the previously recognized variety among these igneous types is reflected in the wide range of 18o values 1 1 to 13 4 permil found in these rocks this range of 18o values probably results from differences in source material and post crystallization history of the different intrusive types

effects of fault interaction on moment stress drop and strain energy release solutions for collinear shear cracks are used to examine quantitatively the effects of fault slip zone interaction on determinations of moment stress drop and static energy release two models the barrier model and the asperity model are considered in the asperity model the actual distribution of strengths on a fault plane is idealized as a combination of two limiting cases areas which slip freely at a uniform value of a residual friction stress and unbroken ligaments or asperities across which slip occurs only at the time of a seismic event in the barrier model slip zones separated by unbroken ligaments barriers are introduced into a uniformly stressed medium to approximate the nonuniform fault propagation proposed by das and aki the strain energy change due to introducing collinear slip zones or due to breaking the asperities between them is shown to be given by the usual formula for an isolated slip zone with the stress drop replaced by the effective stress significant interaction between slip zones occurs only if the length of the asperity is less than half the length of the slip zones for the case of two collinear slip zones fracture of the asperity between them is shown to cause a large moment primarily because of the additional displacement which is induced on the adjacent slip zones for example if the asperity length is 0 05l where l is the length of each adjacent slip zone then fracture of the asperity causes a moment almost 1 8 times the moment caused by introducing a slip zone of length l for two collinear slip zones the local stress drop due to fracture of the separating asperity is shown to become unbounded as the asperity length goes to zero but in the same limit the stress drop averaged over the entire fault length is approximately equal to the apparent stress drop inferred for an isolated fault of the same moment and total fault length this apparent stress drop is approximately equal within a factor of 2 or 3 to the effective stress and hence can be used in the usual formula to give a good estimate of the strain energy change for the barrier model numerical results are given for the ratio of the stress drop calculated on the assumption of an isolated slip zone to the true stress drop for example in the case of two collinear slip zones of length l separated by a barrier of length 0 2l this ratio is 0 5 whereas for a barrier length equal to that of the adjacent slip zones the ratio is 0 24 stress drop estimates become worse with increasing number of fault segments