frequency dependent attenuation of shear waves in the crust of the southern kanto area japan the attenuation characteristics of shear waves in the crust of the southern kanto area central japan were estimated using strong motion data including acceleration data recorded in the pre tertiary basement rocks by means of downhole observation the quality factor qs f was determined for a range of discrete frequencies from 0 5 to 16 hz from the analysis of data from 13 local earthquakes with focal depths of less than about 50 km that occurred in the philippine sea plate and in the boundary zone between the lower part of the eurasian plate and the upper part of the philippine sea plate the estimated 1 qs f shows a peaked structure in this frequency range on the assumption that the geometrical spreading exponent is 1 body waves the estimated peak 1 qs f is of the order of 10 2 at 0 8 hz

assembling and reactivating the proterozoic capricorn orogen lithotectonic elements orogenies and significance abstract the capricorn orogen was initiated during palaeoproterozoic suturing events that brought together the archaean yilgarn and pilbara cratons to form the west australian craton the orogen comprises palaeoproterozoic plutonic and medium to high grade metamorphic rocks of the gascoyne complex a series of palaeoproterozoic volcano sedimentary and sedimentary basins including the ashburton blair yerrida bryah padbury and earaheedy basins and the deformed margins of the pilbara and yilgarn cratons major pulses of deformation and metamorphism took place during the ca 2200 ma ophthalmian orogeny the 2000 1960 ma glenburgh orogeny the 1830 1780 ma capricorn orogeny and a more localized unnamed event at the end of the palaeoproterozoic 1670 1620 ma the orogen has been the site of repeated intracratonic reactivation with renewed basin formation magmatism and orogeny during the mesoproterozoic and the neoproterozoic the exhumed palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic mesoproterozoic edmund and collier basins bangemall supergroup which have been deformed during the neoproterozoic edmundian orogeny the ophthalmian and glenburgh orogenies affected the northern and southern margins of the orogen respectively the former resulted in the development of a foreland basin along the pilbara craton margin whereas the latter is associated with accretion of an allochthonous element the glenburgh terrane of the gascoyne complex to the northwestern margin of the yilgarn craton effects of the capricorn orogeny extended across the entire orogen and provide a younger limit for amalgamation of the yilgarn and pilbara cratons a number of basins developed along both the northern and southern margin of the orogen during this event and were filled with sediment eroded from the yilgarn craton the gascoyne complex and a presently unexposed early palaeoproterozoic terrane the capricorn orogeny corresponds with a major phase of continental collision both in australia and world wide which appears to mark a major phase of supercontinent assembly mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings including the world class iron orebodies of the hamersley basin

a new appraisal of depositional cyclicity in the neoarchean paleoproterozoic dales gorge member brockman iron formation hamersley basin australia abstract the dales gorge member dgm of the brockman iron formation hamersley basin western australia is a classic banded iron formation bif that was deposited during the archean proterozoic transition just prior to the great oxidation event the goal of this study is to apply modern cyclostratigraphic principles to investigate the possible origins of the characteristic stratigraphic banding in this bif which indicates the influence of quasi regular cyclic processes in the deposition of iron rich and chert rich lithologies a grayscale scan series of the dgm type section 47a drillcore photographs from three cores drilled in the wittenoon gorge vicinity is examined using well established methods of time series analysis complex banding patterns suggest that milankovitch forcing may have taken place with orbital rotational parameters that were significantly modified from the present day due to continuous planetary tidal dissipation over the past 2 5 billion years the banding patterns change systematically and dramatically within the member in response to slowly varying environmental conditions which are interpreted to be related to low frequency sea level changes and or tectonic evolution of the hamersley basin

simultaneous determination of site responses and source parameters of small earthquakes along the atotsugawa fault zone central japan velocity seismograms recorded at nine local stations from 102 small earthquakes on the atotsugawa fault zone central japan with seismic moment from 3 10 17 to 3 10 21 dyne cm are analyzed to obtain the s wave spectra a genetic algorithm is applied to determine the earthquake source parameters and site responses simultaneously the stability of both site responses and source parameters are experimentally tested as well as the effects of different q models the resulting source parameters show that the stress drops appear to vary systematically with the location of earthquakes events located on the mozumi fault or the junction of the mozumi and the atotsugawa faults have higher stress drops than those on the creeping section and southernmost part of the atotsugawa fault the relationship between seismic moment and corner frequency constructed by combining our results and those of iio 1986 for other regions in japan shows that a single scaling relation does not apply in a moment range of 10 10 to 10 25 dyne cm a steplike change in scaling relationship occurs between 5 10 18 and 5 10 20 dyne cm corresponding to corner frequencies between 15 and 25 hz this observation suggests that earthquakes are most likely a multihierarchical system divided by characteristic sizes according to aki9s 1980 model a characteristic source dimension 100 200 meters may represent a critical size of the barriers distributed in the fault zone at which the barrier effects are balanced by the dynamic effect of the source process

a tale of two basins stratigraphy and detrital zircon provenance of the paleoproterozoic turee creek and horseshoe basins of western australia discussion

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

tectonic evolution of the late archaean to early proterozoic mount bruce megasequence set western australia the mount bruce megasequence set formerly the mount bruce supergroup was deposited on the pilbara craton during the late archaean and early proterozoic it comprises two megasequences the chichester range megasequence and the overlying hamersley range megasequence each megasequence comprises three supersequences or supersequence packages whose tectonic history can be explained in terms of phanerozoic style tectonics the basal nullagine supersequence which comprises mostly subaerial basalt and terrigenous sedimentary rock was deposited during an episode of wnw ese directed crustal extension that was initiated at about 2770 ma the overlying mount jope supersequence which comprises mostly basalt and tuff was deposited during the subsequent development of a wnw ese trending rift before about 2690 ma mudrock carbonate sedimentary rock and iron formation in the overlying circa 2690 to circa 2600 ma marra mamba supersequence package were deposited on the ensuing divergent craton margin an unconformity or condensed succession covering a time span of as much as 130 m y separates the top of the chichester range megasequence from the hamersley range megasequence during which time an oceanic island arc is interpreted to have collided with the southern pilbara craton margin subsequently the subducting oceanic plate flipped from southwest dipping to northeast dipping and convergence resulted in the formation of a marginal subduction related orogen with associated arc and backarc volcanism iron formation and distal arc derived tuffs of the brockman supersequence package were deposited on a siliciclastic starved platform in a neutral continental backarc setting at around 2470 ma the overlying circa 2440 ma woongarra supersequence was also deposited in a backarc continental setting and comprises iron formation felsic tuffs and probably coeval mafic rocks the latter two rocks types were derived from a backarc magmatic belt shortening of the southern pilbara craton margin resulted in the development of a backarc compressive cratonic basin in which iron formation and siliciclastic and carbonate sedimentary rock of the turee creek supersequence were deposited and ultimately resulted in a continent continent collision the mount bruce megasequence set and its contained iron formations are preserved in the relatively distal hinterland of this collisional orogen

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

scale dependence of apparent stress for earthquakes along the subducting pacific plate in northeastern honshu japan apparent stress which quantifies the ratio of high frequency spectral amplitude to the direct current level of source displacement spectra is known to reflect the source rupture process whether this parameter depends on the seismic moment has not yet been well established because of the difficulties in the reliable estimation of high frequency source spectra to overcome this problem we estimate s wave source spectra by using site amplification factors and attenuation factor graphic 1 which are systematically measured by the coda normalization method analyzing horizontal components of velocity seismograms recorded at 70 borehole seismic stations of hi net national research institute for earth science and disaster prevention in northeastern honshu japan we estimate site factors and graphic 2 in the 0 5 32 hz frequency band by using these factors we evaluate the source spectra of 225 small to moderate earthquakes that occurred in and around the subducting pacific plate site amplification factors we obtained strongly depend on frequency and the frequency dependence clearly changes with the lithology and geologic age of rock obtained graphic 3 values decrease with frequency in proportion to the reciprocal of frequency the apparent stresses estimated from s wave spectra clearly increase from 104 to 107 pa with the seismic moment increasing which cannot be attributed to the limited frequency band and other artificial causes the power of scale dependence is estimated as 0 39 0 44 for the seismic moment range from 1011 to 1017 n m some of the scale dependence of apparent stress is attributed to the scale dependence of brune s stress drop 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

earthquake stress drops and inferred fault strength on the hayward fault east san francisco bay california we study variations in earthquake stress drop with respect to depth faulting regime creeping versus locked fault behavior and wall rock geology we use the p wave displacement spectra from borehole seismic recordings of m 1 0 4 2 earthquakes in the east san francisco bay to estimate stress drop using a stack and invert empirical green s function method the median stress drop is 8 7 mpa and most stress drops are in the range between 0 4 and 130 mpa an apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4 55 hz there is a trend of increasing stress drop with depth with a median stress drop of 5 mpa for 1 7 km depth 10 mpa for 7 13 km depth and 50 mpa deeper than 13 km we use s p amplitude ratios measured from the borehole records to better constrain the first motion focal mechanisms high stress drops are observed for a deep cluster of thrust faulting earthquakes the correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress we compare the spatial distribution of stress drops on the hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near oakland this also suggests a connection between stress drop and applied shear stress as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher strength material the stress drops do not directly correlate with the strength of the proposed wall rock geology at depth suggesting that the relationship between fault strength and the strength of the wall rock is complex

sedimentology of the paleoproterozoic kungarra formation turee creek group western australia a conformable record of the transition from early to modern earth abstract this paper presents the first detailed sedimentological analysis of the paleoproterozoic kungarra formation the lowermost of three formations comprising the turee creek group in western australia which was deposited across the rise in atmospheric oxygen the great oxidation event or goe and the transition from early to modern earth the data show that the kungarra formation has a gradational conformable lower contact with underlying banded iron formation of the hamersley group and predominantly comprises an upward shallowing succession from deepwater shales and siltstones through rippled fine grained sandstones and stromatolitic carbonates to tidal flat deposits that immediately underlie coastal fluvial deposits of the overlying koolbye formation at the base of the kungarra formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron formation that pass upsection to units of non magnetic shale and ferruginous chert and grey chert reflecting a gradual loss of iron from the world s oceans accompanying the rise of atmospheric oxygen a falling stage systems tract is recognised above this transition in the hardey syncline area capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock two glacio eustatic cycles are recognised within the middle to upper parts of the kungarra formation each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest in contrast to previous models of a north northeastward deepening foreland basin the lack of seismites or internal unconformities within the formation precludes a foredeep setting rather deposition is interpreted as having occurred within an intracratonic basin with detritus sourced from erosion of uplifted bedrock to the southeast

did global tectonics drive early biosphere evolution carbon isotope record from 2 6 to 1 9 ga carbonates of western australian basins the 13 ccarb record of well preserved carbonates in outcrop and core is here examined from the 2 6 to 1 9 ga old basins of western australia these data which are constrained by a well defined stratigraphic and tectonic framework and by u pb zircon ages provide an insight into the variables coincident with the evolution of an oxidative atmosphere and the evolution of the early biosphere in the latest archaean ca 2 6 ga the secular 13 ccarb curve is flat much like that seen in the later palaeoproterozoic basins of northern australia 1 8 ga this implies that photosynthesis was a major component of the biosphere at that time and that the carbon mass balance was stable in the early palaeoproterozoic beginning after 2 5 ga and continuing until at least 1 9 ga the 13 ccarb the curve is much more dynamic with significant positive and negative excursions including a major positive excursion 9 pdb close to 2 2 ga these excursions can be correlated with the lomagundi event identified in africa europe and north america previously published studies of the overlying meso to palaeoproterozoic bangemall basin and of 1 8 1 5 ga old basins in northern australia suggest that the 13 ccarb curve became relatively monotonic again after ca 1 8 ga and remained so for most of the following mesoproterozoic comparisons with data from other ancient cratons especially africa suggest that the secular carbon curve may be even more complex than presently understood and probably comparable to the major excursions seen in the neoproterozoic when the western australian data are placed in their stratigraphic and tectonic framework we find that the monotonic latest archaean curve coincides with a tectonically quiescent period in which carbonates formed in an basinal setting on a craton surrounded by passive margins the data are consistent with an earth in which the carbon mass balance was in equilibrium the 13 ccarb curve began to oscillate following the onset of glaciation as the pilbara and yilgarn cratons began to converge during the capricorn orogeny suggesting periods of rapid carbon burial during continental dispersal however the major positive excursion is preserved in carbonates from back arc basins formed as the ocean closed and subduction began since similar tectonic processes can be recognised not only in northern australia but also on other early cratons it can be argued that the carbon excursions relate to supercontinent cycles and to major periods of mantle overturn and superplume development we explain this coincidence of carbon isotopic excursions

quantifying the spatial distribution of site response by use of the yokohama high density strong motion network we have estimated the spatial variation of site response using three component accelerograms from the yokohama high density strong motion net work 150 surface and 9 borehole accelerometers located in a 20 30 km 2 area the site response is the average from 28 earthquakes 16 were recorded at all borehole stations we inverted data recorded at the boreholes to determine 1 source param eters seismic moment m0 and corner frequency fc for each event 2 q f for the path and 3 frequency dependent site factors for the boreholes the inversion scheme is independent of a reference station that is there are no a priori constraints about site response for events with depths greater than 30 km we find q f almost independent of frequency q f 285f 0 06 for the four shallow events that were analyzed q f 70 f 0 28 having determined m0 fc and q f using the borehole data we computed the site response for each of the 150 surface stations by dividing the observed surface spec trum by the path modified source spectrum we then averaged this ratio for all 24 events to quantify the variability of the site response between sites we introduced a site response ratio that depends on station separation and frequency from this we computed cumulative probability functions for different frequencies for two cases 1 the average vs30 ratio is most similar for two sites with the same separation distance and 2 the average vs30 ratio is least similar when two sites have the most similar vs30 ratio these functions indicate that 95 of the time a frequency dependent site response f 1 hz can be predicted within a factor of two for a site up to 5 km from a site with a known site response and 90 of the time the unknown response is within a factor of three for frequencies 1 10 hz when two sites have the least similar average vs30 ratio the cumulative probability functions have similar shapes for all frequencies above 0 5 hz for frequencies up to 10 hz the site ampli fication can be predicted within a factor of three for 80 of the station pairs separated by as much as 5 km

geologic and geophysical evidence for the influence of deep crustal structures on paleozoic tectonics and the alignment of world class gold deposits north central nevada usa abstract geologic data concur with geophysical and isotopic data that suggest the presence of deep crustal fault zones along the battle mountain eureka bme trend and elsewhere in nevada the fault zones may have originated during proterozoic rifting of the continent and were likely substantially reactivated and modified during paleozoic tectonism five distinct paleozoic structural and stratigraphic domains are defined that demonstrate the complexity of paleozoic tectonic events and also lead to hypotheses about ways in which the margin could have been modified the current locations of these domains adjacent to the geophysically and isotopically defined indicators of the buried continent edge corroborate their interactions with the continental margin during the tertiary preexisting crustal fault zones were intersected and reopened during episodes of extension and served as the conduits for deep sourced gold rich fluids which were disseminated into paleozoic slope facies sedimentary rocks forming sediment hosted carlin type and other deposits multiple factors including the locations of these deep seated structures the original configuration of the lower paleozoic continental margin of nevada and its subsequent reactivation during the paleozoic all were fundamental controls on the location of younger mineral deposits a clearer understanding of the original configuration of the margin and of the effects of subsequent paleozoic and mesozoic tectonic events on the margin would provide insight into the locations of these and other prospective mineral belts

geological history of the early proterozoic paraburdoo hinge zone western australia abstract palinspastic profiles across the paraburdoo hinge zone which forms the southwestern boundary to the hamersley shelf indicate the existence of a fore trough adjacent to the ashburton trough on the edge of the hamersley shelf the fore trough existed during turee creek group and lower wyloo group times of deposition and is characterized by unconformities or shallow water facies on its margins the distribution of mature iron ores in the hamersley group suggests a relationship of this type of ore body to the fore trough margins continual uplift or a gradual migration northeastwards of a geanticline is suggested for the ashburton trough region from post hamersley group times to pre ashburton formation times of deposition

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

earthquake source spectra in eastern north america source spectra for earthquakes of 3 m 7 in eastern north america ena are determined from regional seismograph recordings strong motion records teleseismic data and modified mercalli intensity data the inclusion of mmi data is made possible by the finding that the felt area of an earthquake is an accurate measure of its high frequency spectral level at the source current ground motion relations for ena are based on a brune source model with a stress parameter of 100 bars this model is a poor fit to ena source spectra for events of m 4 at high frequencies 5 to 10 hz observed spectral amplitudes are more nearly matched by a brune stress parameter of 200 bars intermediate frequency amplitudes near 1 hz are matched by a stress parameter of approximately 50 bars an empirical two corner source model is proposed to describe ena source spectra for events of 4 m 7

the mount bruce megasequence set and eastern yilgarn craton examples of late archaean to early proterozoic divergent and convergent craton margins and controls on mineralization abstract the late archaean to early proterozoic mount bruce megasequence set formerly the mount bruce supergroup overlies and is restricted to the pilbara craton and comprises two megasequences which comprise a total of six supersequences or supersequence packages that formed in different but related tectonic settings the chichester range megasequence which is the older of the two megasequences comprises two supersequences overlain by a supersequence package the lower two supersequences are dominated by tholeiitic flood basalt and terrigenous clastic sedimentary rock with only minor placer gold and uranium mineralization these formed during the breakup of a late archaean craton between about 2 77 and 2 70 ga the overlying supersequence package is dominated by mudrock carbonate sedimentary rock iron formation and was deposited in a divergent marginal setting bordering an open ocean between about 2 69 and 2 60 ga the hamersley range megasequence comprises clastic sedimentary rock iron formation carbonate sedimentary rock and felsic volcanic rock was deposited between 2 47 ga and 2 9 ga volcano sedimentary assemblages gold mineralization occurred during the late stages of this orogeny which involved transfer of strain from the eastern yilgarn limited crustal thickening metamorphism and granitoid emplacement accretion into orogenic belts provides the best chance of preserving mineralization formed in deep marine environments such as komatiite associated ni and volcanogenic massive sulphide mineralization and explains the common close spatial association of these deposits with gold mineralization in greenstone belts

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

inversion analysis of site responses in the kanto basin using data from a dense strong motion seismograph array abstract we applied nonlinear inversion analysis to estimate site response in the kanto area using data from 19 moderate sized earthquakes observed at the 843 stations constituting strong motion accelerograph networks of the seismic kanto strong motion network sk net k net and kik net we determined the source parameters seismic moment m 0 corner frequency f c for each event and the quality factor q f for the propagation path based on borehole records we also determined the frequency independent and reference independent site responses the resulting seismic moments are in good agreement with those determined by the national research institute for earth science and disaster prevention nied and are proportional to we found a frequency dependent quality factor for the propagation path q f 107 f 0 52 the site responses averaged over 0 5 1 0 hz correlate well with shear wave velocities for the upper 30 m avs30 correlation coefficient of 0 63 and with depth to the seismic basement the shear wave velocity of which is around 3 0 km sec large site responses are found in areas of unconsolidated sediments such as swampy land the predominant frequencies of our site responses roughly agree with those of the horizontal to vertical h v spectral ratio this indicates that the h v ratio is valid for estimating predominant frequencies of s wave amplification

source retrieval for deep local earthquakes with broadband records abstract body wave data recorded at a small network of broadband seismograph stations are analyzed to investigate local events with focal depths deeper than about 50 km for these events the initial portion of p wave displacement represents well the source time function with a scaler correction for the seismic moment the magnitudes of the analyzed earthquakes range from m w 3 1 to 6 5 it is shown that the seismic moment m 0 and the pulse width are well correlated as m 0 3 constant indicating that the stress drop is largely constant this dynamic similarity seems to be valid for a vast range of earthquake sizes m w 1 8 it is also shown that source complexity such as a multiple shock nature is not a characteristic of only large earthquakes but is often observed even for small earthquakes

u pb detrital zircon geochronology of the turee creek group hamersley basin western australia timing and correlation of the paleoproterozoic glaciations the early paleoproterozoic turee creek group tcg hamersley basin western australia records a continuous siliciclastic dominated sedimentary sequence across the great oxidation event goe and contains at least two glacial horizons showing many similarities with other paleoproterozoic glaciogenic deposits from north america huronian supergroup and south africa transvaal supergroup the correlation between these glacial events is uncertain however because of a lack of geochronological constraints contradictory stratigraphic correlations among di ff erent cratons and the occurrence of numerous sedimentary discontinuities in the transvaal and huronian successions in this study we performed in situ u pb dating of detrital zircons from drill core and surface samples of the tcg the underlying boolgeeda iron formation of the hamersley group and the overlying beasley river quartzite of the lower wyloo group over 1500 zircons analyzed by laser ablation coupled to icp ms yielded major age peaks spanning the archean eon at ca 2 45 ga 2 54 ga 2 68 ga and minor ones at 2 81 ga 2 96 ga and 3 14 ga a younger age of 2340 22 ma obtained at the base of the main glacial deposit of the meteorite bore member represents a maximum age for this glacial event a meter scale level of diamictite has previously been described in the boolgeeda formation at the boundary ridge locality located about 50 km to the east of the meteorite bore member succession and a similar horizon was newly identi fi ed in drill core samples from the hardey syncline area the youngest detrital zircons have an age of ca 2 45 ga in these dia mictites supporting the hypothesis that these horizons represent a di ff erent and older glacial event than the meteorite bore member considering that the tcg and underlying boolgeeda iron formation are in sedimentary continuity these results allow establishing a correlation with the other glaciogenic deposits recorded in the north america and southern africa basins and reconstructing the sequence of redox and climate changes at tending the early paleoproterozoic

coherency characteristics of body waves traveling in a sedimentary layer basement system in the kanto region japan by means of borehole array recordings obtained at six stations from local events we estimated coherency characteristics of body waves that propagate in a sedimentary layer basement system in the kanto region japan the estimated coherence is characterized by an 2 model for p and s waves an important result is that the values of corner frequency become nearly constant 5 6 hz in travel times less than 2 5 sec for sh waves this suggests that bedrock motions recorded in the pre tertiary basement are becoming incoherent in high frequencies also the corner frequency of p waves is approximately twice that for sh waves hence p waves propagate coherently in high frequencies as compared with sh waves

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

spectral analysis of k net and kik net data in japan part ii on attenuation characteristics source spectra and site response of borehole and surface stations abstract in this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the k net and kik net networks in japan in order to derive attenuation characteristics source spectra and site response for this purpose we use a total of more than 67 000 s wave records from 2178 earthquakes m jma 2 7 8 obtained at 1555 stations at the earth s surface and more than 29 000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m attenuation characteristics are investigated in five separate regions showing that crustal q depicts lower values in central compared to southern japan and a significant frequency dependence is observed in every region the source spectra follow the 2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones while strong amplification effects dominate the site contributions for the surface sensors those for the borehole sensors are characterized by smaller variability nevertheless consistent with observations from deconvolution of borehole surface recording pairs downgoing wave effects are visible in the site contributions for many borehole stations finally the site amplification functions obtained at the surface are compared with surface to borehole s b and horizontal to vertical h v spectral ratios showing that the s b ratios generally provide better estimates of the horizontal amplification than the h v ratios due to amplification of the vertical component of ground motion

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

source spectra and rms acceleration of mexican subduction zone earthquakes strong motion sm data of six mexican subduction zone earthquakes 6 4 ms 8 1 recorded near the epicentral zone are analyzed to estimate their far field source acceleration spectra at higher frequencies f 0 3 hz apart from the usual corrections such as geometrical spreading 1 r average radiation pattern 0 6 free surface amplification a factor of 2 and equal partitioning of the energy into two orthogonal horizontal components a factor of 1 sqrt 2 the observed spectra are corrected for a frequency dependentq q 100f a site dependent filter e kf and amplification ofs waves near the surface a factor of about 2 atf 2hz we taker as the average distance from the rupture area to the site if we model the high frequency plateau f 1 hz of the source spectra by a point source 2 model and interpret them in terms of brune s model we obtain between 50 and 100 bars for all earthquakes the low frequency broadband teleseismicp wave spectra corrected witht 1 0 s agrees within a factor of two with sm source spectra near 1 hz the 2 model is inadequate to explain the observed source spectra in a broad frequency range these resemble spectra given bygusev 1983 with some differences

identifying the lithospheric structure of a precambrian orogen using magnetotellurics the capricorn orogen western australia abstract a 300 km long magnetotelluric mt survey was carried out across the capricorn orogen in western australia the capricorn orogen includes reworked crust of the archaean yilgarn and pilbara cratons and the allochthonous latest archaean to palaeoproterozoic glenburgh terrane in the southern gascoyne complex and the palaeoproterozoic northern gascoyne complex the survey aimed to increase our understanding of the juxtaposition of these crustal elements by obtaining information about their electrical structure with depth phase tensor analysis of the data showed that 2d mt inversion could only be carried out for stations in the centre of the profile crossing the gascoyne complex the resulting model showed that there is no electrical distinction between the glenburgh terrane and the northern gascoyne complex suggesting that the glenburgh terrane may form basement to the whole of the gascoyne complex 3d forward modelling was carried out for the entire survey line incorporating the basement blocks as well as the surrounding ocean and sedimentary basins station data are most closely reproduced by a model in which the margin between the glenburgh terrane and the yilgarn craton the errabiddy shear zone dips south with crust of the glenburgh terrane wedged beneath the northern yilgarn craton forward modelling results also suggest that the main boundary between the gascoyne complex and the pilbara craton to the north is a steeply dipping structure beneath the edmund and collier basins that may correlate with the talga fault

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

a tale of two basins stratigraphy and detrital zircon provenance of the palaeoproterozoic turee creek and horseshoe basins of western australia abstract the 2445 2010 ma tectonic evolution of the southwestern pilbara craton is recorded by two depositional basins but considering the time span involved it is pertinent to question whether only two are preserved and others have vanished the first the turee creek basin developed conformably on an 2450 ma back arc volcanic province and was closed long before 2208 ma it was a retroarc basin sited in front of a magmatic fold thrust belt on the southwestern margin of the craton its folded strata were intruded by 2208 ma dolerite sills that are the preserved rock record of a large igneous province the basin and dolerites were deformed by the n verging 2195 2145 ma ophthalmia fold thrust belt the second the horseshoe basin formed at 2050 ma unconformably truncating folded strata of the turee creek basin and the 2208 ma dolerites and was closed prior to intrusion of 2008 ma dolerite dykes it was an intracontinental rift basin sited on the inverted fold thrust belt detrital zircon age spectra for the basins have poor fit to the zircon age spectrum of the pilbara and differ significantly in their youngest modes the youngest mode for the turee creek basin is 2442 ma whereas the youngest mode for the horseshoe basin decreases upwards from 2276 ma to 2206 ma although differing in youngest detrital zircon age modes zircon age spectra of the basins are otherwise similar and broadly match the glenburgh terrane on the southwestern margin of the craton while turee creek sediments were derived from the southwest horseshoe sediments were derived from the north and northeast this conundrum is resolved by the ophthalmia fold thrust belt which tectonically loaded the craton to the north and northeast to form a now vanished ophthalmia foreland basin that derived sediment from the south and southwest thereby emplacing zircon with an exotic age spectrum on the north pilbara inversion of tectonic elements occurred during formation of the horseshoe basin with the fold thrust belt subsiding beneath the rift while the foreland basin was uplifted recycling of the foreland basin inverted its detrital zircon age spectrum explaining why the youngest detrital zircon age mode of the horseshoe basin decreases in age upwards

three dimensional attenuation structure of intrinsic absorption and wide angle scattering of s waves in northeastern japan summary intrinsic absorption and random velocity inhomogeneities are important medium properties for studies on wave propagation at high frequency 1 hz in the lithosphere recent studies have shown that the spatial distribution of random velocity inhomogeneities can be estimated by an inversion analysis of peak delay times where the peak delay time is the time lag between direct wave onset and its maximal amplitude arrival this study estimates the 3 d structure of the s wave attenuation quality factor q 1 after we corrected the maximal amplitude attenuation due to multiple forward scattering on the basis of the markov approximation for parabolic wave equation even though this estimate of q 1 includes both intrinsic absorption and wide angle scattering the contribution of wide angle scattering can be identified by taking into account random inhomogeneities estimated in the peak delay time analysis the estimated q 1 structure in northeastern japan shows weak attenuation q 1 f 10 2 5f 0 5 on the forearc side of the volcanic front and strong attenuation q 1 f 10 2 3f 0 3 beneath the quaternary volcanoes and near the collision zone between the honshu and kuril arcs according to the born approximation the estimated q 1 at 0 40 km depth consists mainly of the intrinsic absorption if the characteristic scale of random inhomogeneities is 5 km or longer beneath the quaternary volcanoes of northeastern japan q 1 f shows weak frequency dependence and the power spectral density functions of random velocity inhomogeneities are characterized by a weak spectral gradient that means rich in small scale inhomogeneities these results demonstrate the importance of the frequency dependence of wave propagation in the lithosphere that is the scale dependence of velocity fluctuation or small scale inhomogeneities is an important property of the lithosphere underlying quaternary volcanoes

earthquake of 1987 off chiba central japan and possible triggering of eastern tokyo earthquake of 1988 abstract a moderate earthquake m 6 7 occurred off eastern chiba central japan on december 17 1987 as a consequence of the internal deformation of the philippine sea plate this event helped in clarifying the geometry of the easternmost part of the philippine sea plate as well as the mode of earthquake occurrence in this region three months later another moderate earthquake m 6 0 took plate beneath eastern tokyo this event was generated at the slab slab collision zone at about 90 km depth and is considered to be triggered by the former earthquake a similar phenomenon was observed for the izu m 6 7 of june 29 1980 and the mid chiba m 6 1 of september 25 1980 earthquake pair and the off ibaraki m 7 0 of july 23 1982 and the southern ibaraki m 6 0 of february 27 1983 earthquake pair these are the only three earthquake pairs of m 6 which occurred in the tokyo metropolitan area since 1974 thus over these 15 years all m 6 interplate earthquakes in this specific region are preceded by nearby m 7 earthquakes this suggests that m 7 shallow events enhance stress in the deeper plate collision zone beneath the tokyo metropolitan area and trigger m 6 interplate events

late archaean crustal extension sedimentary basin formation flood basalt volcanism and continental rifting the nullagine and mount jope supersequences western australia abstract the mount bruce megasequence set formerly the mount bruce supergroup is a succession of volcanic and sedimentary rocks that was deposited on the pilbara craton of western australia in the late archaean to early proterozoic its history can be described and explained in terms of modern style sequence stratigraphy and of phanerozoic style plate tectonics the megasequence set comprises the chichester range megasequence that was deposited on a rifted to divergent continental margin and the overlying hamersley range megasequence that was deposited on a convergent continental margin the chichester range megasequence comprises in order of superposition the nullagine and mount jope supersequences and the marra mamba supersequence package the nullagine and mount jope supersequences are each the rock record of one phase of a protracted two phase late archaean 2770 2700 ma continental break up the nullagine supersequence consists of the mount roe sequence which comprises mostly subaerial basalt and the overlying hardey sequence package which comprises mostly terrigenous sedimentary rocks that were deposited in extensional sedimentary basins the mount jope supersequence consists of in order of superposition the kylena sequence which comprises mostly basalt the tumbiana sequence which comprises mostly tuff and tuffaceous rocks and the maddina sequence package which comprises mostly basalt the nullagine supersequence was deposited during an episode of wnw ese directed crustal extension that possibly led to the development of a rift to the west of the present pilbara craton the mount jope supersequence was deposited during the subsequent development of a wnw ese trending rift the position of which approximates the present southern craton margin regional scale uplift was associated with the development of both supersequences particularly with the nullagine supersequence basement strike slip faults were reactivated as dip slip structures during crustal extension and controlled the locations of some hardey sequence package extensional sedimentary basins nullagine supersequence and mount jope supersequence rifting led to a divergent continental margin bordering an ocean along the south and probably the far west of the craton post rift thermal subsidence was accompanied by the accumulation of mudrock carbonate sedimentary rock and iron formation of the marra mamba supersequence package in a shelf setting the implications of these interpretations are that at 2800 ma the pilbara craton was significantly larger than at present and that it had a sufficiently thick subcontinental lithosphere that divided it in a manner analogous to the break up of phanerozoic continents the nullagine and mount jope supersequences contain three stacked flood basalt successions which were erupted over a time period of between of 55 and 80 m y stacked flood basalt successions covering such a long time period are not known in the phanerozoic and are tangible evidence of a hotter late archaean mantle

scaling relations of earthquakes that occurred in the upper part of the philippine sea plate beneath the kanto region japan estimated by means of borehole recordings acceleration source spectra of sh waves for 94 interplate and 74 intraplate earthquakes with a moment range of m 0 10 13 10 18 n m are investigated using 634 strong motion records obtained at 27 borehole and 7 surface hard rock stations installed in the kanto region central japan different scaling relations control the estimated acceleration source spectra for interplate and intraplate events the estimated acceleration source spectra of interplate events are similar to the spectra expected from the barrier model and those of intraplate events show a characteristic bump around the corner frequency the amplitude of acceleration source spectrum of interplate events is on the whole larger than that of intraplate events for the same seismic moment seismic moment m 0 corner frequency f c and seismic energy e are evaluated from the estimated acceleration source spectrum for each earthquake the seismic moment m 0 is nearly proportional to f c 3 the ratio of seismic energy to seismic moment is e m 0 1 15 12 9 10 5 for all events without a significant difference between interplate and intraplate earthquakes this means that the estimated velocity source spectra for interplate and intraplate events with the same seismic moment are nearly identical the dependence of apparent stress a e m 0 on seismic moment is weak and depends on tectonic setting apparent stress drop 2 a is almost proportional to the brune9s stress drop