structure of the vakhsh fold and thrust belt tadjik ssr geologic mapping on a landsat image base an enhanced landsat image of the northeastern tadjik depression in the soviet union was combined with field data to produce a 1 250 000 geologic map of the vakhsh fold and thrust belt and adjacent autochthon mapping of the relatively continuous geologic structure in this region first required recognizing marker beds and contacts at or near the resolution of the landsat sensor and then defining mappable units satellite image mapping was complemented by field study which was necessary in this recently deformed area both to verify the image mapping and to obtain more accurate structural dips deformation of the cretaceous and tertiary strata of the fold and thrust belt is in the western half of the mapped area conspicuously absent north of a buried basement fault that marks the hinge zone of the late mesozoic passive margin in the eastern half of the mapped area however the major thrusts displacing rocks northward have moved coherent sheets over the block fault these sheets now lie flat atop the autochthon to the north tectonically these observations indicate that 1 the crustal structure inherited from the mesozoic extensional phase has strongly influenced the late cenozoic pattern of deformation 2 the thrust sheets that are displaced over the paleo hinge zone actively load the basement rocks to the north and 3 the development of the fold and thrust belt which is markedly asymmetric has included the progressive overlapping of thrusts the later thrusts apparently formed internal to the older thrusts and subsequently overrode them

earthquakes faulting and stress in the los angeles basin since 1920 fourteen moderate sized m l 4 9 6 4 earthquakes have been reported in the los angeles basin these events are associated with both mappable surficial faults and concealed faults beneath the basin sediments to determine the style of faulting and state of stress in the basin single event focal mechanisms for 244 earthquakes of m 2 5 that have occurred during 1977 1989 have been calculated fifty nine percent of the events are strike slip and are mostly located near two of the major northwest striking right lateral strike slip faults in the basin the newport inglewood fault and the palos verdes fault the 1988 pasadena and the 1988 upland earthquakes showed left lateral strike slip on northeast striking faults numerous small earthquakes in the eastern part of the basin show left lateral strike slip faulting and form a northeast trend near yorba linda thirty two percent of the events have reverse mechanisms and are distributed along two broad zones the first the elysian park fold and thrust belt coincides with anticlines along the eastern and northern flank of the los angeles basin extending into santa monica bay the second the torrance wilmington fold and thrust belt coincides with anticlines mapped on the southwest flank of the basin and extends from offshore newport beach to the northwest into santa monica bay oblique faulting that could be inferred by the merging of strike slip and compressional tectonics does not occur in the basin instead the coexistence of zones of thrusting and large strike slip faults in the basin suggests that the thrust and strike slip movements are mostly decoupled a few normal faulting mechanisms appear to be related to faulting orthogonal to the axes of plunging anticlines the trend of the maximum horizontal stress varies from n1 w to n31 e across the basin and consistently forms high angles with the fold axes the stress field that exists along the flanks of the basin has a vertical minimum stress axis this stress field and ongoing folding and thrusting suggest that tectonic deformation is concentrated along the flanks of the deep central basin today the deformation of the basin consists of uplift and crustal thickening and lateral block movement to accommodate the north south compression across the basin

1 fβ fluctuations and self similarity in earthquake dynamics observational evidences in southern italy abstract recently it has been determined that many statistical features of earthquakes are scale invariant with universal values for exponents the analysis of scaling laws has led to the development of a wide variety of physical models of seismogenesis involving nonlinear dynamics and it can be used to better characterize the seismicity pattern in this work the presence of scale invariance properties in the seismicity of a selected area of the southern appennine chain is revealed 1 f fluctuations are detected from the analysis of earthquake sequences using the counting statistics and at the spatial scale a self similar structure in the epicentre aggregate is determined by the estimation of its fractal dimension finally correlations between temporal exponent fractal dimension and b value variations are described

spatial distribution of earthquakes in aftershock zones of the garm region soviet central asia summary we examined the spatial distribution of earthquakes in aftershock zones of eight m4 5 to m6 3 earthquakes that occurred during the period january 1969 february 1987 in the garm region of soviet central asia this seismically active region is a part of the collisional plate boundary between the indian and eurasian plates spatial patterns in earthquake distribution were studied using the technique of pair analysis which is based on a quantitative comparison between observed and randomly simulated distributions of interevent distances similar to our previous findings from other seismically active areas of various scales and tectonic settings we show that the spatial distribution of earthquakes in all of the aftershock zones studied is characterized by significant non random features most prominent of the spatial patterns observed is spatial clustering at short interevent distances the degree of non randomness is usually higher for the aftershocks than for the background seismicity i e the remainder of the catalogue after space time clusters have been removed in some of the study areas the spatial distribution of aftershocks appears to be self similar in magnitude but in most cases is not self similar with respect to the size of the study areas more specifically the seismic activity in the smallest subareas of only few kilometres in size exhibits a higher degree of spatial clustering than the activity in larger subareas furthermore some of the spatial patterns observed change systematically in time one such change is the gradual increase of the degree of pre shock clustering as the main event approaches other temporal features are observed during the aftershock sequences themselves when the degree of spatial non randomness often increases to a peak value and then gradually decreases reaching a reduced background level at some time after the sequences are over some of the temporal changes observed are similar to patterns previously identified in central california aftershock areas

a geodynamic model of the southern apennines accretionary prism the apennines comprise a neogen quaternary accretionary prism that shows several anomalies with respect to classic alpine type mountain belts namely i low elevation ii a shallow new moho below the core of the belt iii high heat flow in the internal parts iv mainly sedimentary cover involved in the prism v a deep foredeep and vi a fully developed back arc basin the suction exerted by a relatively eastward migrating mantle can determine the eastward retreat of the subduction zone and an asthenospheric wedging at the retreating subduction hinge heat flow geochemical and seismological data support the presence of a hot mantle wedge underlying the western side of the apenninic accretionary prism a thermal model of the belt with foreland dipping isotherms fits with deepening of the seismicity toward the east mantle volatiles signatures are also widespread in springs along the apennines

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

earthquake prediction an empirical approach abstract earthquake precursor data so far accumulated in japan have shown that the larger the main shock magnitude the larger the distance between the epicenter and an observation point where a precursor is observed it is possible to empirically establish an approximate relationship between maximum detectable distance d max and main shock magnitude m the relationship being different from discipline to discipline of precursor when a number of precursors are observed we may draw circles with a radius equal to d max peculiar to each precursor discipline centered at the respective observation points on the condition that m takes on a certain value in that case the epicenter of a future earthquake should be located in the area which is common to all of the circles if m is too small some of the circles do not overlap if it is too large an epicentral area which is too wide to be realistic must be assumed in this way an approximate epicenter location and a rough value of the main shock magnitude can be assessed applying the procedure to the precursors of the izu oshima kinkai m 7 0 1978 and the niigata m 7 5 1964 japan earthquakes remarkable success is achieved probabilities of an earthquake occurring in a specified time interval can be evaluated as a function of time when a precursor is observed for such an evaluation we rely either on the log t m relationship with a prescribed value of m or on the frequency distribution of log t which is empirically obtained depending on precursor disciplines t being the precursor time when a number of precursors are observed one by one changes in synthetic probability of earthquake occurrence can be estimated according to the existing formula utsu 1977 as an example such probability changes with time are estimated making use of the precursor data for the izu oshima kinkai earthquake it turns out that the synthetic probability generally increases as time goes on when a long term precursor happens to be observed however the probability drops discontinuously being followed by a gradual rise again the temporal change in probability therefore shows considerable fluctuations this is especially so when a short interval for probability evaluation is specified because of uncertain preliminary probability involved in the evaluation and an unknown rate of false precursor signals against true ones the absolute value of probability thus evaluated may not be perfectly reliable even so the temporal change in probability may provide some clues for the actual publication of earthquake prediction

tropical extratropical geopotential height teleconnections during the northern hemisphere winter abstract simultaneous and lagged correlation statistics have been calculated between time series of seasonal height anomalies at selected stations and extratropical grid point anomalies in both hemispheres the tropical stations in two major tropical precipitation zones the indo china maritime continent and africa are well correlated with each other these stations are also correlated with stations in the north pacific and australia but the coefficients are smaller the correlations between height anomalies at any of these stations and northern hemisphere height anomalies show a well defined global pattern depending upon the location of the stations the pattern is either a pacific north american pna a tropical northern hemisphere tnh pattern or a mixed pattern having both elements all three patterns pna tnh and wpo western pacific oscillation have been linked to tropical variations the correlations between height anomalies at these well correlated stations and the southern hemisphere heig

evidence for an increase in cosmogenic 10be during a geomagnetic reversal reversals in the geomagnetic field which occur every few hundred thousand years represent a dramatic change in the earth s environment although there is no satisfactory theory for such reversals it is generally accepted that the dipole field intensity decreases to 20 of its normal value for a few thousand years during the change in direction1 because the galactic and solar cosmic rays which impinge on the earth s atmosphere are charged a significant fraction about half of them are deflected by the geomagnetic field2 at the time of a reversal this magnetic shielding is greatly reduced and it has been suggested that the increased flux of high energy particles could have effects on evolutionary3 or climatic4 processes for example the statistically significant coincidence in levels of some marine faunal extinctions and reversal boundaries in ocean sediments5 could be caused directly or indirectly by the decreased geomagnetic intensity during the reversal we report here evidence in marine sediments for an increase in cosmogenic 10be production in the earth s atmosphere during the brunhes matuyama reversal 730 000 yr ago in addition to confirming an increase in cosmogenic isotope production the results provide information on the magnitude and duration of the geomagnetic intensity decrease during such an event and the depth at which rmanent magnetism is acquired in marine sediments

the application of the magnetotelluric impedance tensor to earthquake prediction research in greece continuous short period 0 1 3600 s measurements of the magnetotelluric field components were conducted simultaneously at two sites in greece for a period of 5 weeks the estimation of the impedance tensor elements from 8 hr windows of recorded data at each station is found to describe the local electromagnetic induction with great accuracy the computation of the residual electric field obtained as the difference between the observed and estimated inductive part of the electric fields clearly improves the detection of any local electric field anomaly this method was used in an attempt to detect precursory sci smic electrical signals ses that have been reported to precede earthquakes in greece the results indicate the success of this method in resolving ambiguities about the nature of the reported ses i e whether it has an external or internal source although during the recording period no large earthquake occurred five with a magnitude of between ml 4 0 and ml 4 3 occurred within a radius of 150 km from one of the stations the magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the ses precursors to these events were analysed in some detail in two of the cases it was found that the sources could not be related to earthquake processes in the other three cases the nature of the source of the suspected ses although electric could not be established with certainty these results indicate that for earthquakes of small magnitude ml 4 3 or of large epicentral distance r 100 km the detection of a ses is extremely difficult

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

fractal analysis of ulf geomagnetic data associated with the guam earthquake on august 8 1993 this paper presents a fractal analysis of the ulf electromagnetic data obtained at guam observatory during a strong ms 8 0 earthquake occurred on august 8 1993 near the guam island we have already reported the presence of seismogenic ulf emissions for this quake hayakawa et al grl 1996 the chosen period covered four months before and two months after the earthquake it was found that the spectrum of emissions at noon exhibited a power law behavior f which is typical for self organized critical dynamics the slope of the spectrum in the noon sector fluctuates in a range from 2 5 to 0 7 with a tendency to gradually decrease during the process of the earthquake preparation we consider this to be a candidate for a precursory signature the similar effect was found for the night sector we suggest that the focal zone was at the critical stage of self organized criticality process before the quake related to active microfracturing processes followed by the generation of ulf emissions as we detected

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

quantification of variability in bedform geometry we analyze the variability in bedform geometry in laboratory and field studies even under controlled steady flow conditions in laboratory flumes bedforms are irregular in size shape and spacing also in case of well sorted sediment our purpose is to quantify the variability in bedform geometry we use a bedform tracking tool to determine the geometric variables of the bedforms from measured bed elevation profiles for each flume and field data set we analyze variability in 1 bedform height 2 bedform length 3 crest elevation 4 trough elevation and 5 slope of the bedform lee face each of these stochastic variables is best described by a positively skewed probability density function such as the weibull distribution we find that except for the lee face slope the standard deviation of the geometric variable scales with its mean value as long as the ratio of width to hydraulic radius is sufficiently large if the ratio of width to hydraulic radius is smaller than about ten variability in bedform geometry is reduced an exponential function is then proposed for the coefficients of variation of the five variables to get an estimate of variability in bedform geometry we show that mean lee face slopes in flumes are significantly steeper than those in the field the 95 and 98 values of the geometric variables appear to scale with their standard deviation the above described simple relationships enable us to integrate variability in bedform geometry into engineering studies and models in a convenient way

seismic domains within the gissar kokshal seismic zone soviet central asia by evaluating seismological data from the belt of shallow intraplate seismicity known as the gissar kokshal seismic zone in soviet central asia in conjunction with recent data on the shallow crustal structure and longer term geologic deformation we show that certain size classes of earthquakes are characteristic of adjacent and in some places overlapping geologic tectonic settings we call these settings seismic domains they are both geologically and seismologically distinct i e they contain different rocks and structures and have different frequency magnitude relationships for example in terms of number of events gissar kokshal seismicity is dominated by the microearthquakes that have occurred within the sedimentary rocks of the vakhsh fold thrust belt these are all shallow and have occurred mostly within the frontal portions of the thrust sheets more rarely moderate size m 5 5 earthquakes have ruptured the thrust ramps on the other hand the major strain release in this region has accompanied the large 5 5 m 8 1 shallow earthquakes on basement faults in the southern gissar range adjacent to the fold thrust belt within these ranges there is relatively little microearthquake activity that dichotomy indicates that a significantly different seismic hazard is associated with each of these areas but the seismological distinction is obscured along the front of the fold thrust belt where the domain of small shocks in the sedimentary rocks overlaps the domain of large earthquakes on basement faults to explain the localization of the large basement events along the southern flank of the fold thrust belt adjacent to the fold thrust belt we hypothesize a mechanism of thrust sheet loading thrust loads are greatest in this region since thrust sheets have overridden large basement block uplifts beneath the illiac and peter the first range faults

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

monitoring resistivity change in parkfield california 1988 1995 continuous electric field measurements from 1988 1995 with a telluric array straddling the san andreas fault in parkfield california have been analyzed for changes in electrical resistivity associated with the four largest mb 4 0 local earthquakes and three larger but more distant california earthquakes 1989 loma prieta 1992 landers 1994 northridge treatment of the propagation of errors through the analysis process yields formal estimates of the uncertainties in the results and thus a definition of anomalous variations based on statistical confidence statistically significant variations of the telluric coefficients were associated with none of the four local earthquakes and none of the california earthquakes an obvious but mistaken conclusion from this disappointing result is that resistivity changes do not occur prior to earthquakes previous observations in both the field and laboratory have shown that they do occur a more likely explanation of the current result is that the telluric array is not sufficiently sensitive to resistivity changes associated with such small earthquakes the next parkfield earthquake while overdue should be of sufficient magnitude to test this explanation results from this experiment have shown the need for continuous redundant measurements in precursory monitoring studies

the lithosphere of the earth as a nonlinear system with implications for earthquake prediction the lithosphere of the earth can be viewed as a hierarchy of volumes from tectonic plates to grains of rock their relative movement against the forces of friction and cohesion is realized to a large extent through earthquakes the movement is controlled by a wide variety of independent processes concentrated in the thin boundary zones between the volumes a boundary zone has a similar hierarchical structure consisting of volumes separated by boundary zones etc altogether these processes transform the lithosphere into a large nonlinear system featuring instability and deterministic chaos from this background some integral grossly averaged empirical regularities emerge indicating a wide range of similarity collective behavior and the possibility of intermediate term earthquake prediction

present day geodynamics and seismicity in the garm test area tadjikistan abstract data are presented relating to the tectonics seismicity and horizontal movements in the garm test area situated in the transition region between the pamirs and tien shan an upper crustal structure is suggested for the region in hand two hypotheses are proposed for the causes of tectonogenesis and a method is suggested for a possible combination of the two

comparison of orientations of stress and strain tensors based on fault plane solutions in kaoiki hawaii the stress tensor orientation was estimated based on inversion from 238 first motion fault plane solutions of earthquakes with mostly m 3 5 0 6 located in the 10 km radius kaoiki crustal volume separate inversions for subvolumes containing 20 50 events yielded the same results in several adjacent volumes suggesting that the stress tensor is homogeneous in those parts of the kaoiki area and that the inversion results are stable and meaningful five spatial subsets of the data were found for which the orientation of at least one of the principal axes was different from that in the other sets by 20 80 and at confidence levels exceeding 95 the volcano summits of kilauea and mauna loa and their rift systems are identified as the source of stress in the kaoiki crust because the greatest principal stress points to kilauea and mauna loa in addition the strain tensor due to energy released by these 238 earthquakes was computed for the kaoiki area and several subvolumes of it by summing the moment tensors the moment tensor of each earthquake was constructed from the individual fault plane solutions and from an estimate of the scalar moment derived from the moment magnitude relationship a comparison of the directions of strain and stress tensors showed close agreement for subvolumes with predominantly strike slip faulting in these volumes the inversion process for stress directions led to misfits of approximately equal size for the conjugate near vertical nodal planes these observations are interpreted to show that in the strike slip regime of the upper part of the crust neither of the nodal planes is preferred for faulting rupture probably occurs along the nw and along the nh striking nodal planes in separate earthquakes subvolumes with more decollement faulting showed significant differences of 30 40 between the principal strain and stress directions in these volumes the near horizontal nodal planes showed noticeably smaller misfits in the inversion for the stress directions these facts are interpreted to indicate that the decollement plane is weak allowing slip on it even if the principal stresses are inclined at a large angle to it it is proposed that comparison of strain and stress tensor calculations may be able to differentiate between tectonic regimes uniform in strength no well developed fault plane and regimes in which a fault with low frictional strength dominates as a function of time significant rotations of the strain tensor by approximately 45 can be observed which seem to be related to the occurrences of kaoiki mainshocks during three background periods of about 7 years each the average strain tensor showed an orientation typical for predominant decollement faulting while two premainshock periods of 2 5 years each showed an orientation closer to strike slip faulting it is proposed that this pattern may be repeated before the next kaoiki mainshock the strain released seismically is less than the geodetically observed strain by approximately an order of magnitude stress strain fault plane solutions hawaii

geoelectric signals in china and the earthquake generation process we present original apparent resistivity records for stations located in the chinese provinces of hebei and sichuan along with seismicity patterns fault maps and limited hydrologic data these records are part of a 30 year database of geoelectric signals that have been recorded in china by a nationwide network of more than 100 stations set up by the state seismological bureau of the people s republic of china the database includes the time period during which the m 7 8 1976 tangshan and m 7 2 1976 songpan earthquakes occurred resistivity data recorded in and around the epicentral region of the tangshan event show coherent changes both temporal and in areal distribution years and months before and after the earthquakes a regional change in water table occurred more than 3 years prior to the tangshan earthquake the resistivity and water table signals appear to correlate in the 2 to 3 year period prior to the earthquake rainfall records from the region around tangshan extending to the cities of beijing and tianjin do not appear to account for the resistivity changes regional seismicity and active fault patterns in north china indicate that deformation occurs mainly along the borders of large tectonic blocks the source region for the geoelectric signals appears to lie within a large shear zone at the edge of a tectonic block undergoing rotation the tangshan epicentral area is thus only part of a larger zone of deformation we suggest that dilational strain associated with the opening of fractures may lower resistivity and water table for shallow crustal depths such as those monitored by the chinese geoelectric network dilation and resistivity changes are expected to begin at stress levels well below the peak values of the seismic cycle our study suggests that in some cases the areal extent of geoelectric signals may be significantly larger than that of the eventual earthquake source dimension the chinese geoelectric database offers an opportunity to improve our understanding of possible geoelectric precursors to earthquakes

precursory seismicity changes preceding moderate and large earthquakes in the garm region central asia this study reports on variations in seismic activity preceding moderate and large earthquakes in a highly active portion of the india eurasia collision zone the study is based on the catalog of earthquake locations from the complex seismic expedition cse network in the garm region central asia the local seismic network was established in the mid 1950s and recorded and located over 85 000 earthquakes from 1955 to 1988 two main approaches were used to evaluate variations in seismic activity associated with 12 moderate to large magnitude ml 5 0 to 6 3 mainshocks that occurred in the study area 1 a qualitative approach involving examination of maps cross sections space time plots and earthquake histograms for the area identified as the rupture area of the mainshock and 2 a quantitative approach based on magnitude frequency relations estimated for small space time windows within the seismic network in addition to temporal variations in seismicity three long term gaps were identified 1 in the western peter the first range near the city of garm 2 in the central peter the first range and 3 in the northeastern part of the study area approximately coinciding with a gap identified by other authors using different approaches the potential magnitude of future gap filling events is estimated to be in the range 6 7 to 7 0 evidence of precursors has been found to varying extent for 9 out of the 12 mainshocks studied these include quiescence or low activity before the mainshock foreshock activity before the mainshock and a sequence of low activity high activity quiescence before the mainshock for the quantitative analysis the level of seismic activity in small space time windows is quantified by the parameter a 2 defined as the a value at magnitude 2 in the gutenberg richter magnitude frequency relation log n a bm the a 2 values were calculated for 30 12 12 minute spatial cells with a moving time window of five years from this analysis only one earthquake the m 6 3 dzhirgital earthquake of 26 october 1984 shows a significant decrease by a factor of 45 in activity level a 2 the results of the quantitative analysis also show strong spatial variations the central portion of the study area which includes the peter the first range fold thrust belt shows high but relatively stable seismic activity the tien shan basement uplift in the north has a tendency of decreasing activity and the northeastern part of the study area shows increasing activity the october 1984 earthquake is located near the transition between the two tendencies

paleomagnetic evidence for cenozoic block rotations in the tadjik depression central asia this paper presents results of a paleomagnetic study of oligo miocene red beds of the tadjik depression in central asia we sampled about 530 cores at 69 sites and six localities across the depression and along the western border of the pamirs samples were thermally demagnetized and high temperature components appear to predate folding of upper tertiary age throughout the depression paleomagnetic inclinations are consistent with those observed on the stable turan platform at the western margin of the depression however they are shallower by about 30 than the inclination predicted from the reference apparent polar wander path this appears to indicate a 23 difference in latitude which is incompatible with paleogeographic reconstructions for the tertiary a sound interpretation of this anomaly would require a better constrained tertiary paleomagnetic reference for asia inside the tadjik depression paleomagnetic declinations are all significantly rotated counterclockwise with respect to those measured on the turan platform the eastern part of the depression is a domain of large rotation 52 13 to 46 15 whereas smaller amounts of rotation have occurred in the western part 27 14 to 14 15 the similarity between tertiary and cretaceous data available for the area shows that rotations have occurred since the miocene little or no paleomagnetic rotations are observed in the ranges bordering the northern and western parts of the depression paleomagnetic and structural data suggest that block rotations in the tadjik depression are associated with indentation of the pamirs into stable asia at a larger scale observed rotations are compatible with a model of regional sinistral wrenching along a strip running from the gulf of oman to lake baikal

structural and seismic evidence for intracontinental subduction in the peter the first range central asia this paper examines the stratigraphy structure and seismicity of the peter the first range an actively deforming foreland basin in soviet tadjikistan the range represents a highly deformed segment of a large intracontinental basin the tadjik depression which is being shortened in response to the cenozoic convergence between two orogenic massifs the pamir and the tien shan ranges the late jurassic to paleogene stratigraphy of the peter the first range includes more than 2 000 m of shallow marine to nonmarine sediments deposited under relatively quiescent conditions close to sea level in contrast the correlative units of the northernmost pamir directly south of the peter the first range show evidence of proximity to a major uplifted source area to the south these mesozoic early cenozoic strata are overlain by thick sequences of alluvial sandstone and conglomeratic units that coarsen upward through the neogene and record the progressive uplift of the pamir shortening within the peter the first range is recorded by kilometer scale isoclinal upright to over turned folds and imbricate north verging thrusts that emerge near the northern edge of the range and mark the active tectonic boundary with the tien shan most of the deformation appears to postdate the accumulation of the mio pliocene molasse the stratigraphy and structure of the region are best explained by a model of the mesozoic tadjik depression as an intracontinental foreland basin developed in a back arc position with respect to the active andean or collisional orogens located in northern afghanistan and the pamir seismicity in the region is dominated by earthquakes extending from the surface to 12 km depth apparently occurring within the deformed sediments of the peter the first range a subhorizontal zone of relatively low activity at this depth may mark the location of a basal detachment that underlies a structurally thickened sedimentary section this aseismic zone is in turn underlain by a south dipping belt of seismicity that extends from about 17 to 35 km depth and which can be traced updip to the seismogenic crystalline basement of the tien shan range to the north we interpret this south dipping structure as a zone of intracontinental subduction that may be an updip continuation of the enigmatic intermediate depth wadati benioff zone beneath the pamir range to the south

co seismic geoelectric potential changes observed in japan co seismic signals of geoelectric potential have been observed for several earthquakes eqs in japan it has been argued that if there are precursory changes stronger signals should be at the time of eq our results prove that co seismic signals do exist but they start with the arrival of seismic waves and not at the origin time of eqs their amplitude does not scale with the dipole length both facts indicate that the changes are local effects of passing seismic waves and not due to electric signals emitted from the seismic source observed changes contain two components oscillatory and offset decay ones the former is synchronized with seismic waves whereas the latter with a rise time of a few seconds and a decay time of 0 1 1 hour is suspected to be related to eq induced subsurface hydrological change in both cases the origin of electric potential variations may be electrokinetic

detailed study of the potentino seismic zone in the southern apennines italy abstract most relevant macroseismic and instrumental data concerning past and current seismic activity of the potentino southern italy have been collected in order to study the seismic behaviour of this area ten among the most important recent and historical earthquakes occurred in the area from 1826 to 1990 have been studied by means of macroseismic methodologies macroseismic fields for all the events indicate a general isoseismal lengthening in the direction of the apennines chain northwest southeast a rapid attenuation of intensity westward of the studied area and a strong propagation eastwards this configuration is strongly dependent on the source mechanisms of the seismic events and the geological dishomogeneities of the concerned areas as regards earthquakes which have been instrumentally recorded in the campania basilicata area from 1980 to 1991 more than 1300 accurate hypocentral locations have been computed for events with m d 2 5 using data from osservatorio vesuviano o v and istituto nazionale di geofisica i n g seismic networks special emphasis is put on the potenza may 5 1990 earthquake m s 5 4 neic national earthquake information center i vii msk which was the strongest recent event in the area and was felt in a large sector of southern italy as regards the seismic sequence following this event about 110 aftershocks with m d 1 9 have been located very close to the town of potenza northeast of it with a clustering type space distribution the occurrence of the events is strongly time concentrated in so defining a main shock aftershocks typical sequence moreover the macroseismic investigation of the main event has allowed to map out isoseismal lines bounding vii vi v and iv msk areas the isoseismals pattern shows that attenuation and amplification of intensity are observed in the same areas as for the previous events beginning from may 26 1991 an increase of seismicity initiated by an earthquake of m l 4 7 neic and i vi vii msk was observed nearly in the same area as the 1990 sequence accurate locations of 84 events with m d 1 9 have been computed however this sequence seems to have a slightly different character from the 1990 one in that events are scattered in time and seismic energy release is comparable to a swarm type seismic sequence as regards the previous sequences fault plane solutions for the highest magnitude events and for appropriate groups of events have been worked out the mechanisms indicate normal faulting motion with t axes oriented orthogonal to the apenninic chain in conclusion detailed analyses on the historical and recent seismicity of the potentino area and adjacent ones have allowed to identify at least four seismogenic zones which show activity with different features such zoning represents a contribution to the seismic hazard assessment in the southern apennines on a regional scale

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

anomalies in the magnitude frequency relation of earthquakes in the garm region soviet central asia we examine magnitude frequency relations for earthquakes in the garm region of soviet central asia using 17 years of data gathered by the complex seismological expedition cse network earthquakes in most of the region obey the linear magnitude frequency gutenberg richter relation however when we focus on the highly active area in the western portion of the peter the first range we observe a significant departure from the g r relation in the form of an excess in the number of earthquakes with magnitudes in the range of 3 5 to 5 5 we show there is less than a 5 per cent probability that this anomaly is due to random chance we speculate that this anomalous behavior may be related to the fact that the peter the first range is an active fold and thrust belt in which the deformation is dominated by moderate sized events on imbricate thrust planes the linear portion of the magnitude frequency relation at smaller magnitudes represents the self similar response of the fault system on smaller scale structures

earthquake focal mechanisms deformation state and seismotectonics of the pamir tien shan region central asia this paper presents a review of the seismotectonics of the pamir tien shan collision zone in the garm region tajikistan based on geological structure seismicity and focal mechanism solutions the region is dominated by horizontal compression manifested by imbricate low angle thrust faults that separate the upper crust into a series of tectonic sheets these thrust systems verge northward from the tajik depression toward the southern tien shan and southward toward the northern pamir the pattern of seismicity across the region suggests that similar low angle thrust faults exist within the crystalline basement as well in order to reconstruct the present day stress strain state of the region we used data from over 15 000 earthquake focal mechanism solutions for small earthquakes m 1 0 gathered over the 27 year period 1963 1989 the method of reconstruction of the seismotectonic deformation std field involves dividing the data set into small spatial windows and summing the individual focal mechanism solutions to form an average earthquake mechanism tensor for each cell the std state of that cell can then be represented by the orientation of the principal axes of compression and tension the intensity or relative uniformity of the average mechanism and the lode nadai coefficient which defines the relation between the magnitudes of the principal strain components we observe throughout the study area a general predominance of subhorizontal compression manifested in a mixture of thrust and strike slip deformation normal fault deformation is observed in only two small portions of the study area the orientation of principal compression varies from nearly n s in the northern pamir and the southern tien shan to nw se in the peter the first range in general the std field has a clearly developed mosaic structure defined by spatial groupings of nearly uniform orientations of compression and tension axes the boundaries of these groups cannot in most cases be directly correlated with known geological contacts the std structure also shows some variation with depth with more or less uniform std orientation in the upper crust 0 14 km depth changing significantly at greater depths examination of various subsets of the focal mechanism catalog shows the spatial structure of the std field to be largely stable with respect to both time and magnitude the reliability of the reconstructed std field was verified using three approaches 1 comparison of individual focal mechanism determinations for a large subset of the data using both soviet and u s algorithms 2 comparison of std reconstruction results using the two independent focal mechanism catalogs and 3 examination of the effect of spatial sampling on the results the dominance of generally north oriented subhorizontal compression is interpreted to be primarily the result of convergence between the pamir and tien shan ranges in turn caused by the ongoing collision of india and eurasia

velocity structure and seismicity of the garm region central asia summary we have examined arrival time data from two seismic networks operating within the pamir tien shan region of central asia in order to evaluate crustal structure and earthquake distribution in one of the most seismically active zones in the region the data are from two networks surrounding the soviet earthquake prediction laboratory at garm tadjikistan a 15 station local network operated by the soviet complex seismological expedition cse since the mid l950s and a dense telemetered network nested within the larger cse network operated jointly by the us geological survey usgs and the cse since 1975 a simultaneous inversion procedure was used to calculate l d layered velocity models and station corrections independently for each of the two networks using a variety of data subsets and starting models we obtained stable estimates of the velocity structure independent of the initial velocity models for both the cse and the usgs network data the velocities of two upper crustal layers proved to be indistinguishable from a model with a single layer over a half space for the cse network the best p wave velocity model comprises an 8 km thick upper crustal layer of 5 2 km sk overlying a 5 9 km sk half space using data from the usgs network alone a similar velocity model was obtained with the exception of a significantly higher velocity v 6 3 km sk for the mid crustal half space these results contradict previously published velocity models featuring anomalously low or high seismic velocities in the upper to mid crust hypocentral parameters were redetermined for approximately 26 000 events occurring during the period 1975 82 using the newly obtained velocity models and station corrections most of the seismicity in the study area is associated with active deformation of the sedimentary rocks of the peter the first range the distribution of hypocentres within the range suggests the presence of a southeastdipping zone of seismicity that can be traced updip to the petrovsky thrust fault beneath this upper crustal seismicity at a depth of 12 17 km is an aseismic zone that may be related to the presence of low strength evaporites at the base of the sedimentary section this aseismic zone is in turn underlain by anomalously deep crustal seismicity at a depth of 17 30 km the deeper seismicity appears to be associated with a southeast dipping feature approximately 10 km in thickness this dipping seismic zone is interpreted as a zone of intracontinental subduction whose surface expression is the vakhsh thrust fault at the frontal edge of the peter the first range

linear and nonlinear dynamics in electrical precursory time series implications for earthquake prediction abstract the time dynamics of geoelectrical precursory time series has been investigated using autoregressive models the approach used here allows us to obtain information on the geophysical system producing the electrical phenomena in seismic active areas when the only information about the time series comes from the time series themselves it is based on two forecasting approaches the global autoregressive approximation and the local autoregressive approximation the first approach views the data as a realization of a linear stochastic process whereas the second approach considers the data points as the results of a deterministic process supposedly nonlinear the comparison of the predictive skills of the two techniques is a strong test to distinguish between low dimensional chaos and random dynamics our findings give us insight in the inner dynamics of the geophysical process under study an estimate of the number of degrees of freedom of the dynamical system governing the electrical phenomena is obtained the stochastic nature of the electrical precursory signals has been highlighted and the possible implications for the earthquake prediction problem are discussed the processed time series are geoelectrical measurements recorded by an automatic station located in tito southern italy which is one of the most seismic areas of the mediterranean region we found that the global linear approach is superior to the local one and the physical system governing the phenomena of electrical nature is characterized by a large number of degrees of freedom the results are confirmed by the presence of rich scaling properties in the power spectra of the processed electrical signals

1 fα fluctuations in geoelectrical signals observed in a seismic area of southern italy abstract recent studies have shown that many natural systems display temporal fluctuations with long range power law correlations suggesting a fractal geometry of the underlying dynamical system four geoelectrical time series measured in a seismic area of southern italy are investigated by means of spectral tools in order to evidence the existence of power law correlations results show the scaling behaviour for all the signals recorded pointing to the presence of fractal features expressing a long term correlation with scaling exponents which indicate stabilizing mechanisms furthermore our findings suggest an observational evidence of correlations between the variation of parameters describing the temporal fluctuations of geoelectrical signals and earthquakes that occurred in the area investigated

arctic oscillation or north atlantic oscillation abstract the definition and interpretation of the arctic oscillation ao are examined and compared with those of the north atlantic oscillation nao it is shown that the nao reflects the correlations between the surface pressure variability at its centers of action whereas this is not the case for the ao the nao pattern can be identified in a physically consistent way in principal component analysis applied to various fields in the euro atlantic region a similar identification is found in the pacific region for the pacific north american pna pattern but no such identification is found here for the ao the ao does reflect the tendency for the zonal winds at 35 and 55 n to anticorrelate in both the atlantic and pacific regions associated with the nao and pna because climatological features in the two ocean basins are at different latitudes the zonally symmetric nature of the ao does not mean that it represents a simple modulation of the circumpolar flow an increase in the ao or nao implies stro

a new approach to investigate the correlation between geoelectrical time fluctuations and earthquakes in a seismic area of southern italy we propose a new approach to investigate the possible correlation between electrical signals and earthquakes good correlation has been found between the spectral power law exponent of geoelectrical signals and the hurst exponent of the seismicity of the area investigated a tendency of both parameters to converge toward unity typical of self organized critical dynamics is evident before the occurrence of the major event recorded in the area during the observation period

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

land use can offset climate change induced increases in erosion in mediterranean watersheds the aim of this paper is to assess the impacts of projected climate change on a mediterranean catchment and to analyze the effects of a suite of representative land use practices as an adaptation tool to reduce climate change driven erosion and hydrologic extremes relevant climatic variables from the era interim global atmospheric reanalysis of the european centre for medium range weather forecasts ecmwf were downscaled for the study area and perturbed with the anomalies of 23 global circulation models for three emission scenarios b1 a1b and a2 both a projected daily rainfall time series for the period 2010 2100 and a single precipitation event with a one hundred year return period were used to assess the impact of climate change the downscaled data were fed into a distributed hydro sedimentary model tetis with five land use configurations representative of future demographic tendencies geographical characteristics and land management policies e g european union cap the projected changes showed a general decrease in runoff and sediment production by the end of the century regardless of land use configuration sediment production showed a positive relationship with an increase in agricultural land and a decrease in natural land under present day agricultural management according to our simulations some conservation practices in agriculture can effectively reduce net erosion while maintaining agricultural production as such they can play a critical role as an adaptation tool to reduce climate change impacts in the 21st century

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

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

characteristics of electromagnetic noise in the ioannina region greece a possible origin for so called seismic electric signal ses the study of electromagnetic noise in the ioannina region nw greece shows the existence of long transient electric signals duration 10 s without measurable correlated magnetic signals as is the case for seismic electric signal ses observed in the van network of short term earthquake prediction our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the ioannina region this origin can be clearly ascertained from simultaneous observation at stations in direct sight of the transmitters of four electromagnetic components two electric and two magnetic in a broad band of frequencies 10 3 10 hz relying on these observations it is proposed that the april 18 and 19 1995 electric signals interpreted by the van group as ses precursors to the may 13 kozani earthquake are due to some transmitter located far to the north of the ioa station of the van network the transmitters of this area would be of digital type as is increasingly common in radio telecommunication networks we believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals

ulf electromagnetic precursors for an earthquake at biak indonesia on february 17 1996 ulf electromagnetic emissions associated with a large earthquake occurred at biak island indonesia at 5h 59m ut on february 17 1996 magnitude mw 8 2 and depth 20 km from usgs catalog have been investigated on the basis of ulf magnetic observations at two stations biak and darwin in australia about 1 200 km apart though a simple analysis of magnetic field intensity horizontal and vertical magnetic field components at both stations was found to be closely correlated with geomagnetic kp activity a detailed analysis of the difference of h and z components at the two stations the polarization analysis z h and fractal analysis frequency spectrum slope at these two stations has yielded that the ulf emissions in the frequency range from 5 mhz to 30 mhz about 1 5 1 0 months before the quake are likely to be a precursory signature of the quake with its intensity on the order of 0 2 0 3 nt

time dependent seismicity in china precise zonation of the territory of china has been performed based on the active known faults type of faulting and seismicity level one hundred and forty seven seismogenic regions were defined forming 10 larger seismic areas and the seismotectonic characteristics in each one of them were investigated in detail after checking for data accuracy and completeness of the shallow earthquakes h 60 km the regional time and magnitude predictable model was applied and the model parameters were estimated based on the model applicability in the studied area probabilities for the occurrence of strong m 6 0 earthquakes during the next 10 years were calculated for each seismogenic region statistical tests have been used proving the superiority of the model in comparison with the time independent one as well as in comparison with the actual earthquake occurrence q 2001 elsevier science ltd all rights reserved

an analysis of daily maximum wind speed in northwestern europe using generalized linear models abstract the basic climatological pattern and recent trends in daily maximum wind speed dmws for the region 47 5 65 n and 12 5 w 22 5 e are studied using gamma distributions within a generalized linear model between 1958 and 1998 dmws has increased over the ocean in winter but weakened over continental europe in summer large scale circulation changes such as those of the north atlantic oscillation nao and arctic oscillation ao account for the strengthening wind over the ocean global warming may have impacted the regional wind climate in particular southern hemisphere temperature exhibits a significant effect on the distinct oceanic and continental trends in dmws it is suggested that the steady warming of the southern hemisphere during the last few decades may have forced the north atlantic storm track to shift in such a way that storms are enhanced toward the northwestern oceanic area but weakened throughout most of the european continent

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

seismic strain rates in the central and eastern united states seismic strain rates for the entire central and eastern united states are estimated from historical seismicity and from several seismicity models typical strain rates are estimated to be the on the order of 10 12 to 10 11 per year except near historical sites of large earthquakes where higher rates pertain uncertainties in strain rates are large deformation caused by strain rates less than 10 10 yr 1 is very small compared to average denudation rates denudation and deposition may control the rate of earthquake occurrence in some parts of the central and eastern united states by modifying the vertical stress due to load a simple quantitative model predicts the earthquake occurrence rate in the appalachian mountains from an estimate of the regional denudation rate

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

seismicity and s wave velocity structure of the crust and the upper mantle in the baikal rift and adjacent regions abstract correlations between seismicity seismotectonic deformation std field and velocity structure of the crust and the upper mantle in the baikal rift and the adjacent areas of the siberian platform and the mongol okhotsk fold belt have been investigated the 3d s wave velocity structure up to the depths of 500 km has been modeled using a representative sample of rayleigh wave group velocity dispersion curves about 3200 paths at periods from 10 to 250 s the std pattern has been reconstructed from mechanisms of large earthquakes and is in good agreement with gps and structural data analysis of the results has shown that most of large shallow earthquakes fall in regions of low s wave velocities in the uppermost mantle western mongolia and areas of recent mountain building in southern siberia and in zones of their relatively high lateral variations northeastern flank of the baikal rift in the first case the dominant std regime is compression manifested in a mixture of thrust and strike slip deformations in the second case we observe a general predominance of extension