seismic source study of the racha dzhava georgia earthquake from aftershocks and broad band teleseismic body wave records an example of active nappe tectonics summary the racha dzhava earthquake ms 7 0 that occurred on 1991 april 29 at o9 12 48 1 gmt in the southern border of the great caucasus is the biggest event ever recorded in the region stronger than the spitak earthquake ms 6 9 of 1988 a field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity a very precise image of the aftershock distribution is obtained showing an elongated cloud oriented n105 with one branch trending n310 in the western part the southernmost part extends over 80 km with the depth ranging from o to 15 km and dips north the northern branch which is about 30 km long shows activity that ranges in depth from 5 to 15 km the complex thrust dips northwards a stress tensor inversion from p wave first motion polarities shows a state of triaxial compression with the major principal axis oriented roughly n s the minor principal axis being vertical body waveform inversion of teleseismic seismograms was performed for the main shock which can be divided into four subevents with a total rupture time duration of 22s the most important part of the seismic moment was released by a gentle northerly dipping thrust the model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks the focal mechanisms of the three largest aftershocks were also inverted from body wave records the april 29th ms 6 1 and may 5th ms 5 4 aftershocks have thrust mechanisms on roughly e w oriented planes similar to the main shock surprisingly the june 15th ms 6 2 aftershock shows a thrust fault striking n s this mechanism is explai ned by the structural control of the rupture along the eastdipping geometry of the dzirula massif close to the borzhomi kazbeg strike slip fault in fact the orientation and shape of the stress tensor produce a thrust on a n s oriented plane nappe tectonics has been identified as an important feature in the caucasus and the source mechanism is consistent with this observation a hidden fault is present below the nappe and no large surface breaks were observed due to the main shock the epicentral region is characterized by sediments that are trapped between two crystalline basements the dzirula massif which crops out south of chiatoura and the caucasus main range north of oni most if not all of the rupture is controlled by the thrusting of overlapping deformed and folded sediments over the dzirula massif this event is another example of blind active faults with the distinctive feature that the fault plane dips at a gentle angle the racha range is one of the surface expressions of this blind thrust and its growtb is the consequence and evidence of similar earthquakes in the past ii 5

intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

the upper and lower thvera sedimentary geomagnetic reversal records from southern sicily detailed paleomagnetic records of the upper and lower thvera polarity transitions have been determined from pliocenc marine marls in southern sicily the dominant magnetic mineral is fine grained magnetite the two transitions have vgp paths following a great circle passing south america and the west coast of north america there are strong indications that the vgp paths result from smoothing of the non antipodal stable directions before and after the transitions the upper thvera transitional record is preceded by two excursions and followed by a third one the first excursion is a sedimentary artefact caused by post depositional migration of magnetic minerals and the third one by is caused by weathering of the sediment the upper thvera transition from sicily is compared with the record from calabria about 250 km away the two records show similarities as well as differences both transitions have identical vgp paths but in calabria the transition is recorded lower in the sediment the first and third excursions have different characters and the second one is not present apparently the registration of transitions of the earth s magnetic field in sediments is strongly influenced by smoothing and diagenetic processes after deposition

three dimensional attenuation tomography at loma prieta inversion of t for q three dimensional q 1 variations in the aftershock region of loma prieta are derived by tomographic inversion the data set consists of over 4000 aftershock recordings at 22 passcal program for array seismic studies of the continental lithosphere stations deployed after the loma prieta mainshock of 1989 estimates of attenuation are determined from nonlinear least squares best fits to the fourier amplitude spectrum of p and s wave arrivals the linear attenuation inversion is accomplished by using three dimensional velocity variations derived previously in nonlinear velocity inversions low q is observed near the surface and q generally increases with depth the southwest side of the san andreas fault exhibits lower q than does the northeast side and this feature apparently extends to approximately 7 km depth the fault zone as determined by the dipping plane of aftershock activity is characterized by slightly higher qp and lower qs compared to regions immediately adjacent to the fault these correlate with high velocity anomalies associated with seismicity at depth the results are in agreement with earlier observations regarding the association of high velocity anomalies seismicity and fault zone asperities

regional propagation characteristics and source parameters of earthquakes in northeastern north america abstract the vertical components of the s wave trains recorded on the eastern canadian telemetered network ectn from 1980 through 1990 have been spectrally analyzed for source site and propagation characteristics the data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from m 3 to 6 the epicentral distances range from 15 to 1000 km with most of the data set recorded at distances from 200 to 800 km the recorded s wave trains contain the phases s s m s s n and l g and are sampled using windows that increase with distance the acceleration spectra were analyzed from 1 0 to 10 hz to separate the source site and propagation characteristics an inversion for the earthquake corner frequencies low frequency levels and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km the iteration between these two parts of the inversion converges in about 60 steps the average attenuation parameters obtained from the inversion were q 1997 10 and 0 998 0 003 the most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 hz which shallows with increasing frequency and increasing distance out to 200 km the site response spectra obtained for the ectn stations are generally flat the source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events m o 21 dyne cm in the data set whose brune stress drops range from 5 to 150 bars for the five events in the data set with m o 10 23 dyne cm however the source spectra obtained by regressing the residuals suggest that an 2 spectrum is an inadequate model for the spectral shape in particular the corner frequencies for most of these large events appear to be split so that the spectra exhibit an intermediate behavior where u is roughly proportional to

ti in zircon thermometry applied to contrasting archean metamorphic and igneous systems abstract ti in zircon thermometry with shrimp ii multi collector has been applied to two well documented archean igneous and metamorphic samples from southern west greenland zircons from 2 71 ga partial melt segregation g03 38 formed in a small 1000 c yield a low temperature focused normal distribution with a mean of 683 32 c further demonstrated by high resolution ti mapping of two individual grains this distribution is interpreted to represent the temperature of the residual magma at zircon saturation late in the crystallization history of the tonalite hypothetically ti in zircon thermometry on eoarchaean detrital zircons sourced from such a high temperature tonalite would present a low temperature biased image of the host magma which could be misconstrued as being a minimum melt granite multiple analyses from individual zircons can yield complex ti distributions and associated apparent temperature patterns reflecting cooling history and local chemical environments in large magma chambers in addition to inclusions and crystal imperfections which can yield apparent high temperature anomalies zircon surfaces can also record extreme 1000 c apparent ti temperatures in our studies these were traced to 49ti or a molecular isobaric interference contamination derived from the double sided adhesive tape used in sample preparation and should not be assigned geological significance

the effects of attenuation and site response on the spectra of microearthquakes in the northeastern caribbean abstract the spectra of microearthquakes recorded by a seismic network in the northeastern caribbean were analyzed to determine the effects of attenuation and site response on these spectra the ratios of the spectral amplitudes at 5 and 20 hz were measured for several earthquakes at different distances from a fixed receiver to estimate q for p and s waves in the crust and upper mantle the average q p determined from three stations was 380 for epicentral distances between 40 and 200 km the average q s determined from two stations was estimated at 400 spectra of earthquakes closer than 40 km to one station indicate that a high q path q 800 exists for these short distances in the island arc platform the near equivalence of q p and q s observed in this study of the upper lithosphere contrasts with estimates of anderson et al 1965 that q p 9 4 q s in the asthenosphere this finding that q p is approximately equal to q s suggests that the attenuation mechanism in the upper lithosphere differs from that in the asthenosphere the spectra of nearby microearthquakes unaffected by crustal attenuation display corner frequencies which are uniform despite large differences in the seismic moments of the events the corner frequencies of these spectra appear to be characteristic of the receiver site and insensitive to the location and moment of the earthquakes at one station the s wave corner frequency of a nearby blast was identical to the corner frequency of a magnitude 4 8 earthquake derived from the record of a strong motion accelerograph at the same site

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

attenuation structure of coso geothermal area california from wave pulse widths abstract pulse width data are used to invert for attenuation structure in the coso geothermal area california the dataset consists of pulse width measurements of 838 microseismic events recorded on a seismic array of 16 downhole stations between august 1993 and march 1994 the quality factor q correlates well with surface geology and surface heat flow observations a broad region of low q 30 to 37 is located at 0 5 to 1 2 km in depth below devil9s kitchen nicol prospects and coso hot springs a vertical low q 36 in contrast with surrounding rock of 80 region is interpreted as a channel through which hydrothermal energy is transported from depth to the surface the location of the channel is between stations s1 and s4 and its dimension is about 1 km at the deep end of the channel a large broad body of low q is also located at 3 km in depth 2 to 4 km to the southwest of nicol prospects and devil9s kitchen since it lies at the bottom of the target region and beyond the scope of seismicity further research is needed to constrain its extent numerical modeling with a pseudospectral method is also done to investigate the applicability of the inversion scheme to fractured regions a linear relationship between pulse width broadening and travel time is upheld and the proportional constants are estimated

on the robustness of attenuation measurements on teleseismic p waves insights from micro array analysis of the 2017 north korean nuclear test author s bezada mj byrnes j eilon z abstract summary despite their importance as a fundamental constraint on earth properties regional scale measurements of body wave seismic attenuation are scarce this is partially a result of the difficulty in producing robust estimates of attenuation in this paper we focus on measuring differential attenuation on records of teleseismic p waves we examine a unique data set of five records of the north korean nuclear test of 2017 measured at five broad band seismic stations deployed within a few metres of each other but using different installation procedures given their extreme proximity we expect zero differential intrinsic attenuation between the different records however we find that different attenuation measurement methods and implementation parameters in fact produce significant apparent differential attenuation t frequency domain methods yield a wide range of t estimates between stations depending on measurement bandwidth and nuances of signal processing this measurement instability increases for longer time windows time domain methods are largely insensitive to the frequency band being considered but are sensitive to the time window that is chosen we determine that signal generated noise can affect measurements in both the frequency and time domain in some cases the range of results amounts to a significant fraction of the range of differential attenuation across the conterminous united states as determined by a recent study we suggest some approaches to manage the inherent instability in these measurements and recommend best practices to confidently estimate body wave attenuation

complex deformation in the caucasus region revealed by ambient noise seismic tomography abstract cross correlation of 3years of ambient seismic noise recorded at 35 seismic stations deployed in caucasus region yields hundreds of short period surface wave phase speed dispersion curves on inter station paths we inverted these measurements using two techniques to construct tomographic images of the principal geological units of caucasus high resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 5 and 20s and shear velocity tomographic maps between 5 and 30km are generated the resulting maps show a velocity dichotomy between the caucasus region and the surrounding that is interpreted in term of changes in crustal thickness there is also a strong dichotomy in the anisotropic pattern between the eastern part and the western part of the caucasus this difference in both amplitudes and directions of the 2 anisotropy is linked to the tectonic regime changes in the region these observations suggest a good correlation between the tomographic models and the geology of the region it was also possible to identify the early stage of the indentation of the arabian plate into the eurasian plate as well as to detect the possible magma chamber responsible for the javakheti highland

an inversion of lg wave attenuation and site response from seismic spectral ratios in the eastern china region abstract both lg wave attenuation and site responses are determined in the eastern china region the region ranges from 26 n to 33 n and 117 e to 124 e we analyze over 1360 three component seismograms from 92 local and regional earthquakes the seismograms are recorded in the distance range of 100 600 km the earthquakes occurred between 2002 and 2012 in the region and varied in magnitude between 2 0 and 4 7 m l a combined inversion method which can simultaneously estimate attenuation and site response from seismic spectral ratios is implemented in the study modeling errors are determined using a delete j jackknife resampling technique fourier spectral amplitudes are measured from lg phases windowed between the group velocity limits 2 6 and 3 6 km s the inversion are performed in a frequency range of 1 6 hz with an interval of 0 2 hz the frequency dependent quality factor is modeled in the form of q q 0 f the eastern china region displays high q 0 and a weaker frequency dependence characterized by the functions q 335 16 f 0 45 0 02 q 411 21 f 0 26 0 01 and q 432 26 f 0 24 0 01 for vertical north south and east west components respectively the values are similar to the average for other stable regions of the globe site responses from 32 stations are estimated in the region most stations do not show obvious amplification the site responses are mainly smooth flat and less than 5 in the frequency range of 1 6 hz

chapter 7 laboratory techniques for determining seismic velocities and attenuations with applications to the continental lithosphere the interpretation of seismic data is dependent on laboratory investigations of the elastic and anelastic properties of rocks important constraints on the composition of the continental lithosphere have been provided by comparing laboratory and field determined seismic velocities much less is known about the nature of attenuation in the crust and upper mantle furthermore laboratory attenuations have not been studied as extensively as velocities nevertheless the utilization of laboratory attenuation measurements to tie seismic data to the anelastic properties of rocks is promising laboratory velocity measurements are usually obtained with a pulse transmission technique whereas measurements of seismic attenuation in the laboratory are determined by resonance techniques ultrasonic pulse propagation stress strain hysteresis loop analysis and torsion pendulum oscillations velocities in rocks increase with increasing pressure whereas attenuations decrease the greatest changes which occur over the farst 100 mpa are attributed to the closure of microcracks velocities decrease with increasing temperature at temperatures below the boiling point of a rock s volatiles attenuation appears to be temperature independent and above this attenuation decreases increasing pore pressure which lowers compressional and shear wave velocities in sedimentary and crystalline rocks produces a marked increase in poisson s ratio the influence of pore pressure on attenuation in crystalline rocks is at present poorly understood at high pressures velocities are primarily a function of mineralogy whereas mineralogy may only be of secondary importance for attenuation anisotropy which is common in velocities of many crustal and upper mantle rocks may also be an important property of rock attenuation attenuation may vary significantly with frequency for saturated rocks but appears to be frequency independent for dry rocks the effect of frequency on velocity is minimal

source parameters of loma prieta aftershocks and wave propagation characteristics along the san francisco peninsula from a joint inversion of digital seismograms abstract aftershock recordings from 10 digital seismographs deployed along the axis of the san francisco peninsula from the epicenter of the 18 october 1989 loma prieta earthquake to san francisco provide the data for a joint inversion for source wave propagation and site effects the inversion procedure is a least squares method using the singular value decomposition algorithm and is done in two parts the first solves only for the source and attenuation terms for all events and the second projects the residuals from the first inversion onto the site terms the coefficient of geometrical spreading is solved for as part of the model of attenuation residuals plotted versus distance and frequency provide a check on the appropriateness of the attenuation model the earthquakes are all located near the san andreas fault mostly in the aftershock zone of the loma prieta mainshock but some area near daly city on the peninsula the data set provided by geos recorders consists of 148 digital seismograms for 33 events from 10 sites that form a linear profile from the epicentral region to the city of san francisco a distance of approximately 100 km strong motion accelerograms are also available for the larger events body wave spectra are fit surprisingly well by our model especially at distances beyond about 20 km where differences due to radiation pattern effects and changes in angle of incidence become less important results from the inversion show that estimates of moment are only 1 higher for the p waves compared to the s waves apparently there are no major biases in the estimates as each is determined independently of the other p wave corner frequencies are 1 5 times higher than s wave corner frequencies on average stress drops with an average of 176 bars for events that range in magnitude from 1 7 to 4 2 are higher than those found in previous studies where site and path were not explicitly taken into account the exponents of geometrical spreading are very close to one 1 019 for p waves and 1 017 for s waves for this data set which extends to about 100 km the whole path q assumed to be frequency independent was about 800 for both p and s waves specifically 790 for p waves and 830 for s waves the average p wave attenuation at all sites is quantified by a t of 0 020 sec which compares to 0 03 sec for s waves t determined for each site range from a low of 0 008 sec at san bruno mountain a hard rock site to a high of 0 065 sec at corralitos in the epicentral area residuals of the model fits which are distance dependent show larger amplitudes near the epicenter but fall off with a minimum at about 30 km where amplitudes are about 30 to 60 lower than average at distances farther than 30 km amplitudes rise out to the limit of the data at about 105 km where amplitudes are about average at frequencies less than 10 hz but are slightly above average for higher frequencies the location of this low in amplitude can be explained as the boundary between the amplitude decay of direct arrivals and the emergence of wide angle reflections from the lower crust and moho which increase in amplitude beyond 30 km these amplitudes correlate with damage patterns from the mainshock as less damage was observed along the peninsula but appeared to increase towards san francisco even when damage in the marina and china basin districts of san francisco are not included in the damage census

p wave attenuation structure in the fault area of the 1995 kobe earthquake the three dimensional 3 d p wave attenuation structure in the kobe epicentral area is determined using aftershock records from the 1995 kobe hyogo ken nanbu earthquake waveform data from both permanent seismic networks and portable stations set up following the kobe mainshock were used the observed p wave amplitude spectra were inverted for the spectral plateau value the source corner frequency and a frequency independent t operator assuming an 2 type source model the calculated t operators were subsequently used for the computation of the 3 d absorption structure using a 3 d velocity model only high quality amplitude spectra were used for the estimation of reliable attenuation parameters resulting in a final data set of 4100 t operators two regions of high absorption were found in the upper part of the crust one is below the northern part of awaji island and reaches down to a depth of 5 km the other region northeast of kobe city is along the arima takatsuki tectonic line and extends along the rokko kashiodani and yamada faults it extends northward to the hokusetsu sanchi area in both regions a high density of fault lineations is mapped and high poisson ratios are known this suggests that partially saturated cracks cause the observed high attenuation

comparison of seismic body wave and coda wave measures of q measurements of seismic attenuation q 1 can vary considerably when made from different parts of seismograms or using different techniques particularly at high frequencies these discrepancies may be methodological or may reflect earth processes to investigate this problem we compare body wave with coda q 1 results utilizing three common techniques i parametric fit to spectral decay ii coda normalization of s waves and iii coda amplitude decay with lapse time q 1 is measured from both body and coda waves beneath two mountain ranges and one platform from recordings made at seismic arrays in the caucasus and kopet dagh over paths 4 long if q is assumed frequency independent spectral decay fits show q s and q coda near 700 800 for both mountain paths and near 2100 2200 for platform paths similar values are determined with the coda normalization technique however frequency dependent parameterizations fit the data significantly better with q s 1 hz and q coda l hz near 200 300 for mountain paths and near 500 600 for platform paths lapse decay measurements are close to the frequency dependent values showing that both spectral and lapse decay methods can give similar results when q has comparable parameterizations above 6 hz coda measurements suggest some enrichment relative to body waves perhaps due to scattering but intrinsic absorption appears to dominate at lower frequencies all approaches show sharp path differences between the eurasian platform and adjacent mountains and all are capable of resolving spatial variations in q

propagation characteristics of short period sn and lg in the middle east abstract we present propagation characteristics of the short period regional seismic phases sn and lg for the middle east digital waveform data from the iranian long period array ilpa and the global seismic network gsn stations abkt alibek turkmenistan anto ankara turkey keg kottamya egypt and kiv kislovodsk georgia were used in this study three component rotated seismograms were bandpass filtered 0 5 to 5 0 hz and examined for the presence and strength amplitude of sn and lg relative to the pn and pg phases the short period sn and lg waveforms show great variability sn propagates efficiently for paths crossing the mediterranean black and caspian seas as well as for paths passing north of the greater caucasus alborz and kopet dag mountains generally sn is not observed or propagates inefficiently for paths with segments beneath the turkish plateau and northern iranian plateau consistent with a previous study by kadinsky cade et al 1981 this study finds that the zone of inefficient sn propagation coincides with a zone of low pn velocities pn tomography lg is consistently not observed for paths crossing the mediterranean black and caspian seas lg propagates efficiently for paths crossing the northern arabian shield generally lg propagates efficiently for paths contained within the turkish iranian plateau paths in the middle east greater than about 2000 km consistently show no or little lg energy the correspondence of zones of inefficient sn propagation and low pn velocities suggests that high temperatures and partial melt lie at shallow depths in the upper mantle beneath the turkish plateau and northern iranian plateau the presence of water presumably due to subduction of hydrated oceanic crust lowers the solidus temperature and enhances partial melt lg is blocked by oceanic crustal structures as well as by structural and topographic variations associated with tectonic boundaries

earthquake source parameters and the frequency dependence of attenuation at coalinga mammoth lakes and the santa cruz mountains california least squares best fits were calculated to the fourier amplitude spectra of p and s waves of locally recorded earthquakes attenuation amplification and earthquake source parameters were calculated from parameters of the fits approximately 8200 spectra were fit at 39 sites at coalinga mammoth lakes and the santa cruz mountains california typically the spectra were fit from 2 to 45 hz for p waves and 2 to 20 hz for s waves the source spectral falloff of p waves was limited to be no greater than f 2 5 f is frequency by low attenuation sites in the sierra nevada attenuation was measured through t the travel time divided by q attenuation was considered to be frequency dependent according to t to f which is equivalent to q qof negative values of were found to minimize the sum of squared residuals at most of the sites studied attenuation and amplification varied from site to site systematically with site geology source parameters were determined for individual earthquakes by averaging fit parameters from between four and 18 spectra depending on the earthquake seismic moments ranged from roughly 5 1012 to 1015 nm at coalinga and mammoth lakes moments ranged from 2 1011 to 3 1014 nm in the santa cruz mountains when the fits were determined using negative values of a the seismic moments trended approximately as fc 3 fc is the corner frequency for 0 5 stress drops varied from roughly 0 2 to 50 mpa at coalinga and mammoth lakes stress drops were lower in the santa cruz mountains ranging from approximately 0 05 to 8 mpa

anomalous seismic attenuation along the plate collision boundary in southeastern taiwan observations from a linear seismic array abstract lateral variations of seismic attenuation are investigated using data from a linear seismic array deployed across southern taiwan the attenuation parameter t is obtained by fitting the amplitude spectra of p and s waves with a theoretical spectrum using an 2 model the observed t data are then plotted against the travel time back azimuth and focal depth respectively to explore the spatial variations of t for p and s waves significant lateral variations of seismic attenuation are found between the eastern mountainous and western plain areas of taiwan large attenuation contrast with depth in the east indicates that an anomalously high attenuation zone is located in a shallower area north of the array in southeastern taiwan a 2d raytracing method is applied to show that the probable depth of the anomalous zone is at about 15 20 km this anomalous attenuation zone coincides with an area marked by low p and low s velocities as well as a total absence of seismicity the area is also marked by other prominent manifestations of active collision between the eurasian and philippine sea plates for example high mountain ranges rapid uplift and high heat flows

azimuthal anisotropy of lg attenuation in eastern tibetan plateau 1 the q of seismic phase lg is measured to approach the crustal q which can be used to infer crustal rheology a reverse two station event method is used to measure the interstationqlg which theoretically eliminates effects from the source and site response strong azimuthal anisotropy of 1 qlg in northern tibet is observed which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic s waves both the intrinsic and scattering attenuation contribute the isotropic q whereas the anisotropic q may be associated with the fractures and faults in the crust strong 1 qlgis observed in the northwestern songpan ganzi fold belt where the high qdirections correspond with the orientations of major strike slip faults intrinsic and scatteringq values are estimated for different tectonic terranes in eastern tibetan plateau the intrinsic qvalues are approximately 500 in the northern tibetan plateau which suggests a hot 700 c crust consistent with low seismic velocity measurements our result suggests that the crust of northwestern songpan ganzi fold belt may be hotter than that of the qiangtang terrane which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost tibet

intrinsic qp seismic attenuation from the rise time of microearthquakes a local scale application at rio antirrio western greece we determine the attenuation structure of a three dimensional medium based on first pulse width measurements from microearthquake data ninety five microearthquakes from a seventy stations local network were considered in this study measurements of the first half cycle of the wave the so called rise time r were carried out on high quality velocity seismograms and inverted to estimate the p waves intrinsic quality factor q p the results of this investigation indicate that first pulse width data from a local microearthquake network permit retrieval with sufficient accuracy of the heterogeneous q p structure the inferred attenuation variability corresponds to the known geological formations in the region

the shape of ground motion attenuation curves in southeastern canada the shape of the attenuation curve of the fourier spectrum of acceleration is established for southeastern canada from empirical data the dataset is comprised of 1200 digital vertical component seismograms from 100 earthquakes recorded on 30 stations of the eastern canada telemetered network the distance range of the observations is 10 to 1700 km focal depths are from 5 to 30 km results indicate that the attenuation curve has three distinct sections at distances less than 70 km corresponding to attenuation of the direct wave amplitudes decay slightly more rapidly than 1 r r 1 1 between 70 and 130 km where the direct wave is joined by sms spectral amplitudes are approximately constant beyond 130 km corresponding to the lg phase amplitudes decay at a rate that is consistent with r 0 5 and q 670 f 0 33 the findings support the hypothesis of burger et al 1987 that postcritical reflections from the moho discontinuity play an important role in determining the shape of the attenuation curve however the influence of sms is subtle allowing the shape to be approximated by simple functional forms for example the commonly assumed bilinear form r 1 r 0 5 with frequency dependent q fits well if the transition from direct wave to lg spreading is placed at approximately 60 km a linear form r 1 over all distances with constant q 2000 also provides a satisfactory fit overall we find little evidence for the dependence of attenuation on focal depth or tectonic province

evidence of a highly attenuative aseismic zone in the active collision orogen of taiwan abstract seismic attenuation across an aseismic zone in the southeastern central range of taiwan is investigated in terms of t data with inverted q models the t data are obtained by fitting the observed spectra of p and s waves with an 2 source model using broadband records of a 25 station linear array deployed across southern taiwan both tp and ts data at the eastern stations show remarkable decreasing trends with depth down to 40 km in contrast to the western stations the inverted qp and qs profiles across southern taiwan reveal a high attenuation zone qp 288 qs 219 at depth about 20 km beneath the eastern stations traversing the southeastern central range high temperature and possible presence of fluids in the high attenuation zone are derived from the q models this high attenuation zone happens to coincide with the aseismic zone suggesting that the aseismic zone may be due to high geothermal and partial melting effects of a very active collision orogeny the area is also marked by other geological and geophysical indicators in support of this interpretation

geophysical constraints on geodynamic processes at convergent margins a global perspective abstract convergent margins being the boundaries between colliding lithospheric plates form the most disastrous areas in the world due to intensive strong seismicity and volcanism we review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure seismicity and geometry of subducting slab we present global maps of free air and bouguer gravity anomalies heat flow seismicity seismic vs anomalies in the upper mantle and plate convergence rate as well as 20 profiles across different convergent margins a global analysis of these data for three types of convergent margins formed by ocean ocean ocean continent and continent continent collisions allows us to recognize the following patterns 1 plate convergence rate depends on the type of convergent margins and it is significantly larger when at least one of the plates is oceanic however the oldest oceanic plate in the pacific ocean has the smallest convergence rate 2 the presence of an oceanic plate is in general required for generation of high magnitude m 8 0 earthquakes and for generating intermediate and deep seismicity along the convergent margins when oceanic slabs subduct beneath a continent a gap in the seismogenic zone exists at depths between ca 250 km and 500 km given that the seismogenic zone terminates at ca 200 km depth in case of continent continent collision we propose oceanic origin of subducting slabs beneath the zagros the pamir and the vrancea zone 3 dip angle of the subducting slab in continent ocean collision does not correlate neither with the age of subducting oceanic slab nor with the convergence rate for ocean ocean subduction clear trends are recognized steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate with slab rotation towards a near vertical dip angle at depths below ca 500 km at very high convergence rate 4 local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs however near isostatic equilibrium may exist in broad zones of distributed deformation such as tibet 5 no systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation magmatic activity crustal faulting horizontal heat transfer and also due to low number of heat flow measurements across many margins 6 low upper mantle vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels

upper mantle shear structure beneath the colorado rocky mountains a tomographic inversion of teleseismic shear wave delays has been performed using data collected in the 1992 program for array seismic studies of the continental lithosphere rocky mountain front experiment the shear wave residuals used as data were corrected for known crustal sediment and topographic differences and thus were sensitive to mantle shear velocity variations beneath the colorado array large differences in shear wave travel time are observed across colorado and into western kansas with a maximum difference of near 5 sec between the central rockies in colorado and a station in western kansas the shear wave residuals were inverted for shear wave velocity variations in the upper 350 km of the mantle beneath colorado and kansas large differences in mantle shear velocity are found between the rockies and the kansas great plains the average shear velocity in the upper 200 km is about 9 greater beneath kansas than beneath the rockies at greater depths lateral variations are far smaller and not as well correlated with surface tectonics in a qualitative sense there appear to be three mantle structures present beneath the study area beneath the rockies the upper mantle is extremely slow both to the west and east of the rockies we find intermediate mantle shear velocity there is then an abrupt increase in mantle shear velocity near the colorado kansas border we interpret the abrupt increase in mantle shear velocity near the colorado kansas border to mark the boundary of cratonic lithosphere the slow velocity zone beneath the rockies appears to be upwelled asthenosphere as is seen beneath the rio grande rift to the south to match the seismic contrast between the mantle beneath kansas and the colorado rockies requires a temperature contrast of at least 350 c as well as partial melt beneath the rockies the hot mantle beneath the rockies implies that the mantle density is low and the high topography of the rockies is at least partially due to buoyant mantle

a three dimensional stationary model of the thermal and thermoelastic fields of the caucasus abstract three dimensional geothermal and thermoelastic models of the caucasus have been produced application of the three dimensional approach to regions as complex as the caucasus has been justified the model calculations were made excluding the surface heat flow and could therefore be used to test the validity of the model the theoretical heat flow agreed well with the experimental model over the black and caspian sea areas and over the whole rioni kura depression as was expected areas of young volcanism presented exceptions charts of temperature and thermoelastic displacement were plotted for the granitic conrad and mohorovicic discontinuities

deep structures along the boundary of a collisional belt attenuation tomography of p and s waves in the greater caucasus summary seismic attenuation q 1 o fp and s waves shows a major discontinuity from the russian platform to the tectonically active greater caucasus broadband records show this boundary over paths 4 long as revealed by the decay of amplitude spectra from a digital seismic network flanking the greater caucasus we measure attenuation from individual spectra using a non linear least squares procedure to determine an attenuation parameter t simultaneously with source parameters at frequencies between 1 and 15 hz the t measurements are then inverted for spatial variations of q 1 with parametrizations of varying complexity model variance for heterogeneous structures improves by more than 30 per cent compared with homogeneous parametrizations site corrections also significantly improve the fit in these inversion results mountainous regions exhibit q values 2 3 times lower q s 775 75 than do the adjacent shields q s 2060 315 showing that the discontinuity is large for both regions q p is roughly equal to q s comparison of body wave to coda spectra indicates that intrinsic absorption rather than scattering dominates the q 1 measurements at least beneath the mountains hence q 1 variations may give a reasonable proxy for temperature if so then temperature beneath the mountains exceeds that beneath the shield by 70 400 c these temperature increases may not be high enough to generate widespread partial melting beneath the mountains but could produce regional metamorphism and could contribute substantially to isostatic compensation of the mountains whatever their origin the boundary in seismic attenuation is abrupt and large between stable craton and an adjacent mountain belt demonstrating that q 1 is a sensitive indicator of tectonic process

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

electrical conductivity temperatures and fluids in the lower crust we have compiled both laboratory and worldwide field data on electrical conductivity to help understand the physical implications of deep crustal electrical profiles regional heat flow was used to assign temperatures to each layer in regional electrical conductivity models we avoided those data where purely conductive heat flow suggested temperatures more than about 1000 sup 0 c substantially higher than solidus temperatures and outside the range of validity of heat flow models the resulting plots of log conductivity sigma versus 1 t demonstrate that even low conductivity layers lcl have conductivities several orders of magnitude higher than dry laboratory samples and that the data can be represented by straight line fits in addition tectonically active regions show systematically higher conductivities than do shield areas because volatiles are usually lost in laboratory measurements and their absence is a principal difference between laboratory and field conditions these materials probably account for the relatively higher conductivities of rocks in situ in the crust free water in amounts of 0 01 0 1 in fracture porosity could explain crustal conductivities other possibilities are graphite hydrated minerals in rare instances and sulfur in combination with other volatiles as most of the temperatures are less than 700 sup 0 c partial melting seems likely onlymore in regions of highest heat flow where the conductive temperature profiles are inappropriate another result is that at a given temperature crustal high conductivity layes hcl are more conductive by another order of magnitude and show more scatter than do lcl s less

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

three dimensional attenuation variations in southern california seismic attenuation 1 q in southern california varies substantially over distances of tens of kilometers these variations are apparent in high frequency spectral decay of body waves we measure the spectral decay from earthquake seismograms at regional distances by estimating a frequency independent decay parameter t for both p and s waves for frequencies of 0 5 25 hz and invert the resulting 1138 t values to show spatial 1 q variations in the crust and upper mantle the p and s results agree closely with each other and both correlate with regional tectonics the upper crust 0 5 14 km depth exhibits high 1000 q 2 0 q 500 in the los angeles basin and transverse ranges compared to low 1000 q 1 0 q 1000 in the mojave desert high 1 q of the los angeles basin probably reflects high porosity in basin sediments the lower crust exhibits areas of high 1 q beneath the salton trough 1000 qp 1 5 and 1000 qs 2 3 or qp 700 and qs 400 and beneath the san gabriel mountains 1000 qp 2 2 and 1000 qs 1 7 values 2 4 times larger than other areas high 1 q beneath the salton trough may reflect elevated temperature or partial melt resulting from active rifting the high 1 q beneath the san gabriel mountains may represent elevated temperature associated with active mountain building as seen in similar tectonic settings elsewhere attenuation varies less in the mantle perhaps because resolution is poorer relatively high qp qs 1 5 beneath the salton trough may similarly indicate high temperatures these measurements show large variation in 1 q across the region relevant to any complete model for ground shaking in southern california

postseismic deformation following the 1991 racha georgia earthquake 1 the 1991 ms 7 0 racha earthquake is the largest ever recorded in the caucasus mountains approximately three months after this thrust faulting earthquake a gps network was set up to measure postseismic surface deformation we present an analysis of these data which indicate accelerated postseismic motions at several near field sites we model this deformation as either afterslip on the rupture surface or viscoelastic relaxation of the lower crust we find that the postseismic motions are best explained by shallow afterslip on the earthquake rupture plane the minimum postseismic moment release is estimated at 6 0 1018 n m which is over 200 times the moment released by aftershocks in this same period and about 20 of the coseismic moment we also show that the effective viscosity of the lower crust in the western greater caucasus region exceeds 1018 pa s

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

the origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

seismic wave dispersion and attenuation in aheim dunite an experimental study summary a machine has been developed which provides for the study of both shear modulus dispersion and internal friction in geological materials through the observation of forced torsional oscillations of low frequency 10 1000 mhz and strain amplitude 1000 c the eventual goal is an understanding of the dispersion and attenuation of seismic shear waves in the earth s upper mantle measurements have been made on cylindrical specimens of an olivine rich rock from aheim norway which contains in addition to olivine about 10 per cent pyroxene and 5 10 per cent of hydrous silicate phases dominantly clinochlore serpentine and talc in order to separate aspects of the mechanical behaviour associated with the olivine aggregate from those attributable to the hydrous phases and or their dehydration products the specimens were either previously fired under controlled oxygen fugacity at 1200 c for 24 hours in order to effect complete dehydration within the olivine stability field or simply oven dried at 110 c linearity of the mechanical behaviour has been demonstrated by the amplitude independence of the results for the strain amplitude range 10 8 10 6 and by the quantitative consistency between the observed modulus dispersion and that calculated from the measured internal friction through the kramers kronig relations of linear theory both the pressure dependence at room temperature and the temperature dependence at 300 mpa of the shear modulus and internal friction have been investigated much of the variation of the shear modulus is attributed to changes of crack porosity associated with changes in pressure and temperature and with in situ dehydration temporal evolution of q 1 towards a lower asymptotic value over periods of hours of exposure to given conditions of high pressure and temperature is tentatively attributed to the gradual diminution of enhanced anelastic relaxation associated with regions of decaying stress concentration at asperities on cracks and or grain boundaries at the highest pressures and temperatures achieved in this study 300 mpa and 1000 c marked dispersion of the shear modulus amounting to 5 per cent between periods of 3 and 100 s and concomitant strong internal friction varying with oscillation period to approximately as 0 011to1 6 are observed the energy dissipation appears to be concentrated within rather than at the boundaries between the olivine grains these results provide the clearest indication yet that solid state probably intragranular anelastic relaxation in ultramafic rocks gives rise to losses comparable with those observed seismologically in the earth s upper mantle although the mechanistic basis for the observed anelasticity remains to be established

attenuation models qp and qs in three dimensions of the southern california crust inferred fluid saturation at seismogenic depths we analyze high dynamic range waveform spectra to determine t values for both p and s waves from earthquakes in southern california we invert the t values for three dimensional 3 d frequency independent q p and q s regional models of the crust the models have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth and extend from the u s mexico border to the coast ranges in the south and sierra nevada in the north in general qp and qs increase rapidly with depth consistent with crustal densities and velocities the 3 d q p and q s models image the major tectonic structures and to a much lesser extent the thermal structure of the southern california crust the near surface low q p and q s zones coincide with major sedimentary basins such as the san bernardino chino san gabriel valley los angeles ventura and santa maria basins and the salton trough in contrast at shallow depths beneath the peninsular ranges southern mojave desert and southern sierras we image high q p and q s zones which correspond to the dense and high velocity rocks of the mountain ranges several clear transition zones of rapidly varying q p and q s coincide with major late quaternary faults and connect regions of high and low q p and q s at midcrustal depths the q p and q s exhibit modest variation in slightly higher and lower qp or qs zones which is consistent with reported crustal reflectivity in general for the southern california crust q s q p is greater than 1 0 suggesting partially fluid saturated crust a few limited regions of q s q p less than 1 0 correspond to areas mostly outside the major sedimentary basins including areas around the san jacinto fault suggesting a larger reduction in the shear modulus compared to the bulk modulus or almost complete fluid saturation

lithospheric temperature estimates from seismic attenuation across range fronts in southern and central eurasia seismic attenuation 1 q changes abruptly between the stable eurasian craton and adjacent mountain belts associated with the alpine himalayan collision new attenuation measurements on local body and coda waves provide quantitative constraints on this contrast near the caucasus kopet dagh and tien shan mountains the 1 q estimates from all range fronts are similar the mountains being two to three times more attenuative than adjacent stable platforms these 1 q variations are a reasonable proxy for temperature variations and reveal crustal heating on the order of 100 c but probably not melting beneath the mountain ranges attenuation 1 q is high wherever high topography is seen implying that active mountains are typically hot hence processes that generate or transport heat dominate advective cooling due to lithospheric thickening even over the 10 20 m y lifetimes of these young mountain belts

defect microdynamics in minerals and solid state mechanisms of seismic wave attenuation and velocity dispersion in the mantle the propagation of seismic waves in the earth s mantle can be significantly affected by relaxation processes causing attenuation and velocity dispersion reduction this paper reviews the solid state mechanisms of relaxation processes based on the theory of defect microdynamics in solids together with some experimental observations on defects in minerals particularly in olivine for a given mechanism to have a significant effect on seismic wave propagation both the density and the mobility of the defects must be in an appropriate range the examination of the densities and geometry and mobilities of defects in olivine shows that dislocation and or grain boundary mechanisms can have a significant effect on seismic wave propagation although wide distributions of geometrical factors such as spacing of pinning points and of mobilities are required to explain all available data point defect mechanisms however are unlikely to be important because their densities are too small and or their mobilities are too large since the dislocation density and or grain size are determined in most cases by the long term tectonic stress seismic wave attenuation and velocity dispersion reduction involving these defects are likely to depend on the magnitude of the tectonic stress as well as the temperature theoretical considerations suggest a wide range of dependence of seismic wave attentuation and velocity dispersion on the long term tectonic stress this is particularly the case for dislocation mechanisms and warrants careful experimental investigation dislocations and or grain boundaries cause anelastic behavior relaxation peaks when they are pinned or blocked at some points pinning or blocking becomes ineffective at high temperatures and or low frequencies causing a transition to viscoelastic behavior both laboratory and seismological observations of internal friction are dominated by the high temperature background where internal friction increases monotonically with temperature which can be interpreted as a gradual transition to viscoelastic behavior or to a wide distribution of relaxation times however in most experimental studies to date the dislocation densities or the grain sizes were not well controlled making it difficult to identify the attenuation mechanisms and preventing any quantitative applications to earth the need for better characterization of defect microstructures in experimental specimens is emphasized

magnetostratigraphy based astronomical tuning of the early pliocene lacustrine sediments of ptolemais nw greece and bed to bed correlation with the marine record continental deposits from the early pliocene lacustrine ptolemais basin in nw greece display rhythmical alternations of lignite and marl beds three parallel sections from this area are studied using magnetostratigraphy and cyclostratigraphy the presence of the greater part of the gilbert chron enables the recognition of astronomical periodicities in the succession especially the precessional influence is evident as it determines the lithological cycles the continental ptolemais composite section is correlated to the most recent astronomical time scale and thus to the marine reference section the rossello composite from sicily c g langereis f j hilgen the rossello composite a mediterranean and global reference section for the early to early late pliocene earth planet sci lett 104 1991 211 225 on a bed to bed scale it is concluded that lignite corresponds to an insolation minimum beige layer in the rossello composite and marl to an insolation maximum grey layer in the rossello composite this implies a precipitation increase during insolation maxima in early pliocene continental greece 1998 elsevier science b v all rights reserved

seismic attenuation and mantle wedge temperatures in the alaska subduction zone 1 anelastic loss of seismic wave energy or seismic attenuation 1 q provides a proxy for temperature under certain conditions the q structure of the upper mantle beneath central alaska is imaged here at high resolution an active subduction zone where arc volcanism is absent to investigate mantle thermal structure the recent broadband experiment across the alaska range beaar provides the first dense broadband seismic coverage of this region the spectra of p and sh waves for regional earthquakes are inverted for path averaged attenuation operators between 0 5 and 20 hz along with earthquake source parameters these measurements fit waveforms significantly better when the frequency dependence of q is taken into account and in the mantle frequency dependence lies close to laboratory values inverting these measurements for spatial variations in q reveals a highly attenuating wedge with q 500 assuming frequency dependence comparison with p results shows that attenuation in bulk modulus is negligible within the low q wedge as expected for thermally activated attenuation mechanisms bulk attenuation is significant in the overlying crust and subducting plate indicating that q must be controlled by other processes the shallowest part of the wedge shows little attenuation as expected for a cold viscous nose that is not involved in wedge corner flow overall the spatial pattern of q beneath alaska is qualitatively similar to other subduction zones although the highest wedge attenuation is about a factor of 2 lower the q values imply that temperatures exceed 1200 c in the wedge on the basis of recent laboratory based calibrations for dry peridotite these temperatures are 100 150 c colder than we infer beneath japan or the andes possibly explaining the absence of arc volcanism in central alaska

attenuation of high frequency shear waves in the crust measurements from new york state south africa and southern california we compare the attenuation of high frequency 3 30 hz shear waves for crustal paths in new york state south africa and southern california over source receiver distances of about 10 400 km the data consist of digital recordings of s waves 5 100 km and lg waves 100 400 km produced by earthquakes we use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the s and lg waves over the entire distance range studied 10 400 km the amplitude decay of 3 hz shear wave energy is considerably less for the tectonicaily stable areas of new york and south africa than for the tectonicaily active region of southern california high frequency 30 hz s wave attenuation is significantly less for new york and south africa than for southern california for distances between 15 and 90 km we parameterize the decay with distance r of coda normalized shear wave amplitudes with a frequency independent q and geometrical spreading exponent where geometrical spreading is proportional to r for new york state the s wave amplitude decay 3 30 hz is well described by a frequency independent q of 2100 330 490 and of 1 3 0 1 the decay of lg wave amplitudes from 3 to 15 hz in the new york state region is fit with a frequency independent q of 1600 280 330 of 0 70 0 2 the s wave amplitudes 3 30hz in south africa yield a q of 1500 190 380 and of 1 3 0 1 fixing the geometrical spreading at r 0 5 produces an lg wave q estimate at 3 hz in south africa of 360 50 80 this lg wave q is low considering that south africa is a cratonic tectonicaily stable area the s wave amplitudes from southern california are described with a frequency independent q of 800 150 240 and a large geometrical spreading exponent of of 1 9 0 2 we find an lg wave q at 3 hz of 260 30 for southern california after constraining the geometrical spreading at r 0 5

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

energy flux model of seismic coda separation of scattering and intrinsic attenuation a new model of seismic coda is presented based on the balance between the energy scattered from the direct wave and the energy in the seismic coda this energy flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic anelastic attenuation of the medium this formula is valid for both weak and strong scattering and implicitly includes multiple scattering the model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity some of the simulations also included intrinsic dissipation the energy flux model explains the coda decay and amplitude observed in the synthetics for random media with a wide range of scattering q in contrast the single scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation scattering q less than or equal to 150 the simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate as predicted by the energy flux model the coda decay rate is sensitive however more to the intrinsic q of the medium the ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation thus analysis of the decay rate and amplitude of the coda can in principle produce separate estimates for the scattering and intrinsic q values of the crust we analyze the coda from two earthquakes near anza california intrinsic q values determined from these seismograms using the energy flux model are comparable to coda q values found from the single scattering theory the results demonstrate that coda q values are at best measures of the intrinsic attenuation of the lithosphere and are unrelated to the scatteing q less

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

seismic structure of the crust and uppermost mantle beneath caucasus based on regional earthquake tomography abstract we present a new seismic model of the crust beneath the caucasus based on tomographic inversion of p and s arrival times from earthquakes occurred in the region recorded by regional seismic networks in the caucasian republics the resulting p and s velocity models clearly delineate major tectonic units of the study area a high velocity anomaly in transcaucasian separating the great and lesser caucasus possibly represents a rigid crustal block corresponding to the remnant oceanic lithosphere of tethys another high velocity pattern coincides with the southern edge of the scythian plate strongly deformed areas of great and lesser caucasus are mostly associated with low velocity patterns representing thickened felsic part of the crust and strong fracturing of rocks most cenozoic volcanic centers of caucasus match to the low velocity seismic anomalies in the crust for example the kazbegi volcano group is located above an elongated low velocity anomaly squeezed between high velocity segments of transcaucasian and scythian plate we propose that mantle part of the arabian and eurasian plates has been delaminated due to the continental collision in the caucasus region as a result overheated asthenosphere appeared nearly the bottom of the crust and facilitated melting of the crustal material that caused the origin of recent volcanism in great and lesser caucasus

analysis of short period regional phase path effects associated with topography in eurasia propagation of regional seismic phases is highly dependent on path effects but we have a limited understanding of these effects and no general procedure for accounting for path variation influence on regional waveforms thus there is strong regional variability in the effectiveness of regional wave discriminants used to identify small earthquakes and nuclear explosions motivated by many observations of correlation between surface geology and regional phase behavior we empirically explore the relationship between short period regional and upper mantle distance signal energy and statistics of topography along different travel paths using data for underground nuclear explosions at semipalatinsk kazakhstan we find strong linear correlations of the logarithmic rms amplitude ratio sn lg and to a lesser extent p lg with mean altitude rms roughness rms slope and skewness of topography along the paths to receivers in eurasia this indicates that energy partitioning in the regional wave field is controlled by wave guide structure and attenuation variations that are manifested in surface topography this suggests that it is feasible in many cases to directly calibrate regional discriminants for path effects in terms of observable surface topography as a surrogate for overall path properties the relationships also help to understand the nature of regional phase propagation

high temperature experiments on the elastic and anelastic behaviour of magmatic rocks measurements of the complex shear modulus have been performed on various ultrabasic and basic rocks dunite peridotite gabbro and basalts and a synthetic forsterite at temperatures between 600 and 1500 c depending on the sample material and in the frequency range from 0 003 to 30 hz under forced torsional oscillations the maximum shear stress was 0 3 mpa and the strains were of the order 5 10 6 to 5 10 5 measurements of the electrical resistivity as a function of temperature have been carried out together with the mechanical experiments to indicate the beginning of partial melting the absolute values of the shear modulus below tm are comparable with the results of other authors the onset of melting shows up in a rapid decrease of both shear modulus and electrical resistivity at high temperatures t 0 8 tm the absorption factor q 1 follows a power law q 1 exp a rt with 0 15 0 30 and a between 100 and 200 kj mol 1 towards lower temperatures this high temperature background is superimposed by a flat absorption peak which shifts from high to low frequencies with falling temperature this peak can often be described by a lognormal distribution of simple relaxation processes with a standard deviation of about three and a mean relaxation time exp a rt with a 400 600 kj mol 1 above tm a third contribution to q 1 is observed that can be regarded as independent of frequency between 1 and 30 hz this last component which contributes 50 to the total absorption is attributed to the melt phase in the samples an explanation for the high temperature background and the peak is proposed which is based on the relaxation of pinned dislocation lines by some coupling mechanism via the reorganisation of the stress field with increasing deformation this process may be responsible for both features at very high temperatures and low frequencies a small influence of steady state flow on q 1 is observed and below t 0 6 tm thermal cracking or thermoelastic losses may contribute to q 1 the influence of lithostatic pressure on q 1 is estimated and the extrapolation of the experimental data to the p t conditions of the uppermost mantle are in good agreement with published earth models an attempt is made to establish a general q t relationship from the experimental data

mechanisms of seismic attenuation in the crust scattering and anelasticity in new york state south africa and southern california the envelopes of high frequency seismograms from earthquakes in new york state south africa and southern california are analyzed to determine how much of the observed attenuation of shear waves in the crust is caused by anelasticity and how much is produced by scattering from small scale heterogeneities for seismograms from new york and south africa there is a systematic enrichment of high frequency energy that develops in the coda relative to the direct s or l sub g waves the author uses the growth with source receiver distance of the high frequency energy in the coda relative to the direct wave to estimate the scattering attenuation of the crust and the relative time decay of high frequency energy in the coda to determine the anelastic attenuation using the estimate of l sub g wave q as a constraint he finds that the scattering q in the crust of new york is either independent of frequency or increases with frequency f slower than f sup 0 3 a similar analysis for south africa indicates that scattering is the major cause of the observed s wave attenuation of high frequency energy 30 hz at local distances 100 km for southern california the extent of the scattering attenuation is unclear from the data more although the relatively steep coda decay of southern california implies that anelastic attenuation is stronger there than in new york or south africa for southern california and new york state the 3 hz coda q taken from the late coda 50 110 s is comparable to the l sub g wave q however the 3 hz coda q for south africa over these lapse times is about 5 times the estimated l sub g wave q for all three areas the frequency dependence of the coda q does not match the frequency dependence of the s wave q and for new york and south africa it changes with lapse time less

inferring water infiltration in the longtan reservoir area by three dimensional attenuation tomography summary high resolution 3 d qp and qs models at depths of 0 14 km in the longtan reservoir area which were used to further infer the water infiltration around the reservoir were constructed by the local earthquake tomography technique the inversion used t values measured from velocity spectral amplitudes of 16 134 p wave and 17 027 s wave observations of 2828 events recorded by 23 digital seismic stations in the longtan reservoir area 3 d qp and qs tomographic images suggest a close relation between the attenuation models and water infiltration low qp and qs exist down to 4 7 km depths beneath the main rivers in the reservoir area whereas high qp and qs are found both at deep layers and at shallow layers in regions other than the main river area we inferred that the rocks beneath the main rivers are infiltrated by substantial water and water infiltration reaches 4 7 km deep and the ranges of water infiltration vary by region specifically the zone of high water content is estimated to extend up to 10 km away from the buliu river in the reservoir dam area where water depth in the reservoir reaches maximum and the extent of water infiltration in rocks can only be about 5 km around from the hongshui river and the youla river low qp and high qs indicate that the carbonate rocks in the east of the bala fault area may be saturated with water earthquake clusters are mainly concentrated on the low qp and low qs zones indicating that water infiltration beneath the main rivers possibly plays an important role in inducing earthquakes in the longtan reservoir area

regional compensation of the greater caucasus mountains based on an analysis of bouguer gravity data abstract teleseismic and geological observations of the continent continent collision zone in the greater caucasus mountains of the southwestern soviet union indicate that the range is presently being underthrust primarily from the south since the onset of alpide deformation tectonic activity has been concentrated along the southern slope of the mountains but ongoing deformation along the northern slope in the eastern part of the range may be associated with thrusting of the mountains northward over the scythian platform in this area to understand the present day plate interactions in the caucasian region and the mode of compensation of the greater caucasus mountains we analyze bouguer gravity anomaly data using both spectral coherence and admittance calculations and traditional spatial domain forward modeling techniques as a whole the range appears to be in regional isostatic equilibrium with compensation by flexure of an elastic plate of approximately 40 km thickness d 6 10 23 nm loaded strongly from the bottom as well as the top subsurface loads corresponding to stacking of thrust sheets uplifts of basement rocks active volcanic zones and thick sequences of basin sediments play an important role in improving the fit between observed and calculated bouguer values closer examination of the individual tectonic provinces which make up the range yields results consistent with support by a 40 50 km thick plate in the eastern and central parts of the greater caucasus mountains and by a plate with no flexural rigidity in the western part of the range coupled with the active volcanism and the relative lack of seismicity in the western part of the greater caucasus region these results indicate the presence of hot thermally altered lithosphere in this area contrasting to the colder more brittle and more elastic lithosphere of the seismically active eastern region

modelling short period crustal phases at regional distances for the seismic source parameter inversion abstract waveforms of short period crustal phases observed at regional distances are modelled in an attempt to retrieve the source parameters of small earthquakes for a simple shield type crustal structure the synthetic seismograms calculated for elementary source mechanisms show that the waveforms of crustal phases are quite distinct for different source mechanisms and suggest that these features can be used to constrain the source mechanisms waveforms of the crustal phases are also strongly affected even by small variations in the crustal thickness as well as in the focal depth a generalized linearized waveform inversion technique is used to invert the regional crustal phases for a deviatoric moment tensor source the inversion technique is applied to regional short period records from a small earthquake in central sweden for determining its source parameters the waveform inversion which mainly used lg waves produced a satisfactory fit between the observed and synthetic records suggesting that the source mechanism and focal depth estimates were reasonable the focal depth of 40 km obtained for the event studied suggests the occurrence of a deep crustal earthquake and demonstrates the usefulness of crustal phases in studying small intraplate earthquakes

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

active thrust front of the greater caucasus the april 29 1991 racha earthquake sequence and its tectonic implications although fault bounded thrust sheest are common in the geological record seismic evidence for their motion is sparse the april 29 1991 racha earthquake m s 7 0 the largest instrumentally recorded earthquake in the greater caucasus is one of the largest recent earthquakes in continental thrust belts and provides evidence on mechanisms of thrust sheet motion using data from a deployment of program for array seismic studies of the continental lithosphere passcal digital seismographs and various other instrumental we locate 1952 aftershocks occurring between may 7 and june 30 1991 the aftershocks form a zone 70 km long and 10 25 km wide striking e w following the racha ridge at the southern boundary of the greater caucasus thrust system teleseismic body waves are inverted for source parameters of the mainshock and the two largest aftershocks the solutions show thrust faulting with centroid depths of 3 10 km comparable to depths of locally recorded aftershocks 2 12 km the shallow dipping nodal plane the aftershock distribution and surface geology demonstrate that the main event was caused by faulting on a thrust system dipping nne at 20 o 31 o bounding the southern slope of the greater caucasus this fault system thrusts the greater caucasus structures south over the dzhirula basement massif the inferred fault geometry suggests that the active fault is either a detachment between sediments and dzhirula basement or cuts through the basement at shallow depths the 1500 m high racha ridge overlies the aftershock zone and is a likely consequence of repeated similar earthquakes hence the 1991 earthquake sequence shows that the western greater caucasus is accommodating plate convergence at a rate possibly comparable to the eastern greater caucasus a few millimeters per year along strike geological discontinuities above and below the thrust surface correspond to the eastern end of the mainshock rupture area no strong evidence for transfer structures could be found along strike suggesting that differences in collisional style between the western and eastern greater caucasus may reflect differences in mechanical properties rather than differences in convergence rate a june 15 1991 event and its aftershocks southeast of the primary aftershock zone along strike show fault planes and slip vectors rotated 41 o clockwise from the mainshock this rotation is consistent with an along strike change in direction of the thrust front near 44 o e longitude and demonstrates strong local structural or topographic control on slip direction the rotation requires along strike shortening within the greater caucasus thrust system at a rate comparable to the rate of thrusting

strong along arc variations in attenuation in the mantle wedge beneath costa rica and nicaragua attenuation structure in the central american subduction zone was imaged using local events recorded by the tomography under costa rica and nicaragua array a 20 month long deployment july 2004 until march 2006 of 48 seismometers that spanned the fore arc arc and back arc regions of nicaragua and costa rica p and s waveforms were inverted separately for the corner frequency and moment of each event and for the path averaged attenuation operator t of each event station pair assuming attenuation is slightly frequency dependent 0 27 then tomographic inversions were performed for s and p attenuation q s 1 and q p 1 since p wave amplitudes reflect both shear and the bulk moduli tomographic inversions were also performed to determine shear and bulk attenuation q s 1 and q 1 the loss of energy per cycle owing to shearing and uniform compression respectively damping and other inversion tomographic parameters were systematically varied as is typical in subduction zone attenuation studies a less attenuating slab upper plate and wedge corner and a more attenuating mantle wedge were imaged in addition first order differences between the mantles beneath nicaragua and costa rica were observed the slab in nicaragua is more attenuating than the slab in costa rica a larger zone of higher shear attenuation also characterizes the nicaraguan mantle wedge within the wedge maximum attenuation values at 1 hz correspond to qs 38 73 beneath nicaragua and qs 62 84 beneath costa rica and average values are qs 76 78 and qs 84 88 respectively attenuation variations correlate with along arc trends in geochemical indicators that suggest that melting beneath nicaragua occurs at more hydrated conditions and possibly to greater extents and depths relative to northern costa rica shear attenuation dominates over bulk attenuation in the well resolved regions of the wedge the more extensive zones of greater shear attenuation observed in the nicaraguan wedge could be explained by higher temperatures and or greater hydration but comparison with petrological data suggests that hydration variations play a larger role average wedge attenuation values are comparable to estimates for the andes and japan greater than those for alaska and less than those for tonga lau