the yavapai mazatzal boundary a long lived tectonic element in the lithosphere of southwestern north america a seismic reflection profile crossing the jemez lineament in north central new mexico images oppositely dipping zones of reflections that converge in the deep crust we interpret these data as a paleoproterozoic bivergent orogen centered on the jemez lineament that formed during original proterozoic crustal assembly by collision of mazatzal island arcs with yavapai proto north american continent at ca 1 68 1 65 ga the two major sets of reflections within the yavapai mazatzal transition boundary dip at 15 20 and we interpret them as part of a south dipping thrust system and as a north dipping crustal scale duplex that formed synchronously with the thrust system the upper crust shows structures recording a succession of tectonic and magmatic events from the paleoproterozoic to the holocene notable among these structures is a system of nappes that formed during development of the bivergent orogen elements of the nappe system are exposed in rocky mountain uplifts and have been dated as having formed at 1 68 ga at depths of 10 km and at temperatures of 500 c we also see continuous bright reflections in the upper part of the middle crust that we associate with basaltic sills that postdate accretion the data show that the yavapai mazatzal suture is low angle 20 an observation that explains why the boundary between the provinces has previously been so hard to define in the surface geology the jemez lineament overlies the root of this bivergent orogen that we also suggest is a paleoproterozoic zone of weakness that has subsequently acted as a conduit for magmas and a locus of tectonism

regional variation of the ω upper bound magnitude of giii distribution in hindukush pamir himalaya and the adjacent regions a perspective on earthquake hazard the upper bound magnitude or maximum magnitude in 28 seismogenic source zones in the hindukush pamir himalaya and the adjacent regions have been computed with the help of a complete and homogeneous earthquake catalogue during the period 1900 2010 to estimate the earthquake hazards in the region the gumbel s third asymptotic distribution giii of extreme value method is used to estimate this parameter in this study a comparison of maximum magnitude obtained by giii distribution is carried out with kijko sellevoll method it is observed that the maximum earthquake magnitudes estimated by kijko sellevoll and giii methods are comparable to each other and the average of differences of their values is only 0 13 the results also estimate the most probable earthquake magnitude that can be expected in next 100 years m100 in all 28 seismogenic source zones an effort is made to make regression relations between and maximum magnitude estimated by kijko sellevoll method mmax ks and and maximum observed magnitude mmaxobs the estimated values exceeded the value of 7 00 in 15 and 8 00 in 5 of the 28 seismogenic source zones the geographical distribution of and m100 in 28 seismogenic source zones of the study region is visualized to analyze the localized seismicity parameters it is observed that earthquake hazard level varies spatially from one zone to another which suggests that examined region have high crustal heterogeneity and seismotectonic complexity

unbedded diatreme deposits reveal maar diatreme forming eruptive processes standing rocks west hopi buttes navajo nation usa diatremes provide partial records of how dyke delivered magma periodically interacting with water produces the largest known cylindrical conduit structures of any volcano type we address how pre eruptive country rock is disrupted and redistributed to form the diatreme structure during an eruption by establishing the internal architecture of the unbedded diatreme at standing rocks west and the volumes and sources of wall rock within the diatreme and in a complementary tephra ring at teshim both in the hopi buttes volcanic field the unbedded diatreme is dominantly exposed as a massif comprising multiple subvertical columns interpreted as ephemeral conduit deposits of well mixed poorly sorted composite and juvenile pyroclast rich deposits that truncate marginal layered deposits plus a peripheral heterolithic country rock breccia wall rock clasts are scarce in the massif and were mainly sourced from 75 to 245 m depth below the paleosurface by contrast the tephra ring has abundant wall rock fragments dominantly from the upper 75 m of the pre eruptive sedimentary sequence the diatreme structure is interpreted to have been formed by many small volume explosions fed by a low flux of basaltic magma late stage explosive activity was rooted mostly within pyroclastic debris at shallow to intermediate depths within the diatreme structure this resulted in damped and shifting intra diatreme explosions and jets that facilitated gradual mixing recycling and remobilization of debris in the diatreme with incremental addition of juvenile material and possibly a local rise in the crater floor

seismic discontinuities beneath the southwestern united states from s receiver functions abstract s receiver functions along the colorado plateau rio grande rift great plains transect known as la ristra in the southwestern united states have been utilized to map seismic discontinuities beneath this tectonically active region individual receiver functions were stacked according to ray piercing points with moveout corrections in order to improve the signal to noise ratio of the converted s to p phases a mantle discontinuity which is interpreted as the lithosphere asthenosphere boundary lab is observed along the profile with depth ranging from 80 km beneath the rio grande rift rgr to 100 km beneath the great plains gp and 120 180 km beneath the colorado plateau cp the shallow lab beneath the rio grande rift is indicative of lithosphere extension and asthenosphere upwarp the lab deepens sharply at the rgr cp and rgr gp boundaries providing evidence for edge driven small scale mantle convection beneath la ristra two local discontinuities beneath the southeastern colorado plateau are imaged at 250 km and 300 km and could be the top and base of the eroded lithosphere respectively the s receiver function images suggest that edge driven small scale convection is probably the mantle source for recent extension and uplift in the rio grande rift and the colorado plateau

maps of titan s surface from 1 to 2 5 μm abstract we have acquired resolved images of titan with the adaptive optics systems pueo kir at the cfht hawaii and naos conica at the vlt chile we report here on images and maps when data at several orbital phases are available of titan s surface from observations taken during the last 4 years 2001 2004 in all the methane windows between 1 and 2 5 m namely at 1 08 1 28 1 6 and 2 m we present the only complete maps of titan currently available at 1 3 m a spectral window where titan appears particularly bright in spectroscopy with a resolution of about 200 km at best on the ground our surface maps show the bright and dark regions sharing titan s landscape with as much detail as possible from the ground and with high contrast in most cases from the information gathered by comparing the maps at different wavelengths we derive constraints on the ground s composition our results could complete optimize the return of the cassini huygens mission

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

a probabilistic assessment of earthquake hazard parameters in nw himalaya and the adjoining regions the maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of nw himalaya and the adjoining regions for this purpose we have prepared a reliable homogeneous and complete earthquake catalogue during the period 1500 2010 the technique used here allows the data to contain either historical or instrumental era or even a combination of the both in this study the earthquake hazard parameters which include maximum regional magnitude mmax mean seismic activity rate the parameter b or b log e of gutenberg richter g r frequency magnitude relationship the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900 2010 the uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters the earthquake hazard in the whole nw himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level tectonics and focal mechanism the annual probability of exceedance of earthquake activity rate of certain magnitude is also calculated for all seismogenic source zones the obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters it is observed that seismic hazard level is high in quetta kirthar sulaiman region in pakistan hindukush pamir himalaya region and uttarkashi chamoli region in himalayan frontal thrust belt the source zones that are expected to have maximum regional magnitude mmax of more than 8 0 are quetta southern pamir caucasus and kashmir himanchal pradesh which have experienced such magnitude of earthquakes in the past it is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity

assessment of earthquake hazard in the tokyo area japan abstract the probability of occurrence of an inland earthquake originating beneath the tokyo area is evaluated for a 10 year period from 1991 on the basis of an earthquake catalogue containing some 40 earthquakes which caused some damage to edo now tokyo over a period of 400 years the parameters of the weibull and lognormal probability distributions applied to recurrence interval statistics are estimated with these parameters it is concluded that an earthquake directly beneath the capital the magnitude of which is equal to or greater than 6 0 occurs with a probability of 0 40 for the period in question when the magnitude threshold is assumed as 6 4 and 7 0 the probabilities become 0 17 and 0 049 respectively these probability evaluations are extended to those for the seismic intensity at typical sites in the area although no accurate evaluation is possible because the exact focal depths of historical earthquakes are not known on the assumption that these earthquakes occur near the upper surface of the down going philippine sea plate however a typical depth of 30 km or so is suggested should an earthquake having a mean magnitude of 6 4 say and at a mean location of past earthquakes occur the probability of seismic intensity at typical sites in the capital area exceeding 5 on the japan meteorological agency jma scale would amount to 0 17 the possibility of having a highly damaging earthquake of intensity 6 on the jma scale also cannot be ruled out judging from earthquake disasters in the past although the probability does become lower to summarize it may be said that the probability of japan s capital area being hit by a damaging earthquake in the foreseeable future is not particularly low

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

late pleistocene and holocene large magnitude earthquakes along himalayan frontal thrust in the central seismic gap in nw himalaya kala amb india abstract the himalayan frontal thrust hft forms the southernmost active tectonic mountain front of the himalaya to understand the ongoing tectonics further paleoseismological study has been carried out in the vicinity of the hft system along the himalayan front near kala amb india the trench excavation survey conducted across an explicit surface exposure of the hft exhibits two distinct faults considered to be associated with the reactivation of the hft where the middle siwalik rocks late miocene have repeatedly thrust over the late pleistocene and holocene sediments presence of large sized coseismically induced sand injection feature and its disposition recognized in the trench also suggest occurrence of large magnitude earthquakes in this region an uplifted and upwarped strath terrace 3 to 5 m thick alluvium resting over the 15 m high middle siwaliks abruptly truncated by the hft indicates its latest activity optically stimulated luminescence dating techniques were employed to constrain the chronology of events the long term slip rate of the abandoned terraces due to the activity of the hft is estimated to be 3 4 mm yr or greater since late holocene the paleoseismological investigations have provided unambiguous evidences of at least two large magnitude earthquakes occurred in this region where an earthquake with 12 m or larger surface displacement and magnitude 7 5 or greater hit this region in the period between 29 3 ka and 17 ka in the late pleistocene and another great earthquake recurred with 20 22 m or more surface displacement and magnitude of 7 7 or greater between 5 8 ka and 2 ka in the holocene the present study is the first time report of multiple large magnitude paleoearthquakes in the northwestern part of the frontal himalaya during late pleistocene and holocene the repeated reactivation of hft substantiates high seismic potential of the frontal himalaya and calls for more extensive study of paleoearthquakes of this vastly populous mountainous region

development of a velocity model for black mesa arizona and the southern colorado plateau from multiple data sets during the summer of 2003 a consortium of scientific institutions conducted a set of seismic experiments on black mesa arizona in the southern colorado plateau to determine the velocity structure and crustal thickness below the mesa we detonated a series of explosions which were recorded by 130 near source vertical component sensors and 25 broadband seismometers the broadband stations deployed in a linear array to the south of the mesa also recorded earthquakes at regional and teleseismic distances during the duration of the deployment prior to the explosion series we conducted a shallow refraction study at the site by using 20 three component geophones we utilized the multiple data sets recorded by the experiment to develop a new velocity model for black mesa we analyzed the shallow refraction and explosion data to generate p and s velocity models for the upper crust the p velocities were determined by examining first arrival times as a function of distance from the source in addition we performed ground roll and surface wave studies to develop a shear wave velocity structure for the upper crust the results indicate an upper crustal velocity structure that consists of very slow velocity sediments and respectively for the deeper crustal and upper mantle velocity we used refraction data from broadband stations and inverted surface wave dispersion data we were not able to confidently determine the depth of the moho as our results indicate it to be between 37 and 46 km the velocity model developed for black mesa was validated using comparisons between observed and synthetic waveforms and small ground truth explosion location studies

probabilistic assessment of earthquake hazards in the north east indian peninsula and hindukush regions the himalayan region is one of the most seismic prone areas of the world the north east ne indian peninsula and the hindukush regions mark the zone of collision of the indian and eurasian plates the probability of the occurrence of great earthquakes with magnitude greater than 7 0 during a specified interval of time has been estimated on the basis of four probabilistic models namely weibull gamma lognormal and exponential for the ne indian peninsula and hindukush regions the model parameters have been estimated by the method of maximum likelihood estimates mle and the method of moments mom the cumulative probability is estimated for a period of 40 years from 1964 and is ranging between 0 881 to 0 995 by the year 1995 using all four models for the ne indian peninsula the conditional probability is also estimated and it is concluded that the ne indian peninsula would expect a great earthquake at any time in the remaining years of the present century for the hindukush region the cumulative probability has already crossed its highest value but no earthquake of magnitude greater than 7 0 has occurred after 1974 in this area it may attribute to the occurrence of frequent shocks of moderate size as seventeen earthquakes of magnitude greater than 6 0 including four greater than 6 4 have been reported until 1994 from this region

probabilistic assessment of tsunami recurrence in the indian ocean the indian ocean is one of the most tsunamigenic regions of the world and recently experienced a mega tsunami in the sumatra region on 26 december 2004 m w 9 2 earthquake with tsunami intensity i soloviev imamura intensity scale equal to 4 5 causing heavy destruction of lives and property in the indian ocean rim countries in this study probabilities of occurrences of large tsunamis with tsunami intensities i 2 0 and i 3 0 average wave heights h 2 83 m and h 5 66 m respectively during a specified time interval were calculated using three stochastic models namely weibull gamma and lognormal tsunami recurrence was calculated for the whole indian ocean and the special case of the andaman sumatra java asj region excluding the 1945 makran event from the main data set for this purpose a reliable homogeneous and complete tsunami catalogue with i 2 0 during the period 1797 2006 was used the tsunami hazard parameters were estimated using the method of maximum likelihood the logarithm of likelihood function ln l was estimated and used to test the suitability of models in the examined region the weibull model was observed to be the most suitable model to estimate tsunami recurrence in the region the sample mean intervals of occurrences of tsunamis with intensity i 2 0 and i 3 0 were calculated for the observed data as well as for the weibull gamma and lognormal models the estimated cumulative and conditional probabilities in the whole indian ocean region show recurrence periods of about 27 30 years 2033 2036 and 35 36 years 2039 2040 for tsunami intensities i 2 0 and i 3 0 respectively while it is about 31 35 years 2037 2041 and 41 42 years 2045 2046 for a tsunami of intensity i 2 0 and i 3 0 respectively in the asj region a high probability 0 9 of occurrence of large tsunamis with i 2 0 in the next 30 40 years in the indian ocean region was revealed

seismic evidence for widespread serpentinized forearc upper mantle along the cascadia margin petrologic models suggest that dehydration and metamorphism of subducting slabs release water that serpentinizes the overlying forearc mantle to test these models we use the results of controlled source seismic surveys and earthquake tomography to map the upper mantle along the cascadia margin forearc we find anomalously low upper mantle velocities and or weak wide angle reflections from the top of the upper mantle in a narrow region along the margin compatible with recent teleseismic studies and indicative of a serpentinized upper mantle the existence of a hydrated forearc upper mantle wedge in cascadia has important geological and geophysical implications for example shearing within the upper mantle inferred from seismic reflectivity and consistent with its serpentinite rheology may occur during aseismic slow slip events on the megathrust in addition progressive dehydration of the hydrated mantle wedge south of the mendocino triple junction may enhance the effects of a slab gap during the evolution of the california margin

determining moho depth beneath sedimentary basins using regional pn multiples the study of the moho beneath thick sedimentary basins involving natural earthquakes is challenging as low velocity materials often cause strong reverberations that mask moho signals here we develop a method to determine the depth of the moho by taking advantage of the presence of the sediments the method utilizes the first pn crustal multiple from regional earthquakes pnpn and its differential travel time with respect to pn pnpn is usually weak in amplitude thus it is difficult to identify in regions without a sedimentary cover however pnpn is significantly amplified in the presence of low velocity sediments because of an increase in the near surface p to p reflection coefficient the arrival time amplitude and wave shape of pnpn if normalized by the reference pn are insensitive to earthquake source parameters such as focal mechanism and focal depth we demonstrate the potential of this method using both 1d and 2d waveform simulations synthetic waveforms suggest that pmppn and pnpmp one pn leg merges to pmp near the source or the receiver largely contribute to the pnpn amplitudes which depend on the near surface structure at their free surface p to p reflection points we further validate the method with two field examples in the imperial valley one is near the united states mexico border and the other is in oklahoma in the central united states both examples suggest that the method can be used to study the moho either near the source or the receiver

estimation of strong ground motion from a great earthquake mw 8 5 in central seismic gap region himalaya india using empirical green s function technique in the present study ground motions for a mw 8 5 scenario earthquake are estimated at 13 sites in kumaun garhwal region using the empirical green s function technique the recordings of 1991 uttarkashi earthquake of mw 6 8 at these sites are used as an element earthquake a heterogeneous source model consisting of two asperities is considered for simulating the ground motions the entire central seismic gap csg can expect acceleration in excess of 100 cm s2 with nw portion in excess of 400 cm s2 and se between 100 and 200 cm s2 the central portion can expect peak ground acceleration pga between 200 and 400 cm s2 it has been observed from simulation of strong ground motion that sites located near the rupture initiation point can expect accelerations in excess of 1g in the present analysis bhatwari and uttarkashi can expect ground accelerations in excess of 1g the estimates of the pga are compared with earlier studies in the same region using different methodologies and it was found that the results are comparable this has put constrains on the expected pgas in this region the obtained pga values can be used in identifying the vulnerable areas in the central himalaya thereby facilitating the planning design and construction of new structures and strengthening of the existing structures in the region

vs and density structure beneath the colorado plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data 1 the colorado plateau is a physiographic province in the western us with an average elevation of 1 9 km where in contrast to neighboring provinces there is little evidence of large scale tectonic deformation or magmatism recent availability of earthscope usarray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau s uplift and relative stability using phase velocities for fundamental mode rayleigh waves and p receiver functions we perform over 800 joint inversions for 1 d shear wave velocity vs profiles sampling the plateau and surrounding regions down to 150 km depth we image a sharp change in crustal thickness at the western edge of the colorado plateau with a more gradual increase eastward moving into the rocky mountains a relatively thick 100 km lithosphere beneath the plateau extends into the rocky mountains to the north we use empirical scaling relations to estimate densities from our vs results and predict the associated gravity anomalies which are inconsistent with the observed distribution of the bouguer gravity anomalies we somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant while there is some evidence for small scale convection and lithospheric removal at its edges the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the farallon slab we conclude that the lithospheric root is key to the long term stability of the colorado plateau leading to a colder stronger crust

modelling of active lineaments for predicting a possible earthquake scenario around dehradun garhwal himalaya india abstract the doon valley which consists of the doon gravels and siwalik rocks is surrounded by the main boundary thrust mbt in the north the main frontal thrust mft mohand thrust and bhimgoda thrust in the south the ganga tear fault in the east and the yamuna tear fault in the west lineaments identified from the aerial photographs show that a few of them trend parallel to the himalayan orogen and the others are transverse to it the effect of the neotectonic activity is clearly reflected in the doon valley implying that the doon valley is tectonically unstable today and that the possibility of earthquakes in this region cannot be ruled out the ruptures along identified active lineaments are modelled three dimensionally peak accelerations are obtained by using a methodology based on the semi empirical method of irikura which was used by midorikawa the efficacy of this modelling technique for the himalayan region is established by simulating peak ground accelerations for the uttarkashi earthquake of 20 october 1991 and comparing it with recorded one a seismic study of the region shows that it is prone to moderate as well as great earthquakes the technique of midorikawa has been applied for the preparation of zonation maps in this seismically active region two different zonation maps showing respectively the effects of moderate as well as great earthquakes in this region are presented in this paper the zonation map for moderate earthquakes shows that the region can experience peak ground accelerations around 310 cm s2 this value is close to the peak ground acceleration of 304 cm s2 recorded for the uttarkashi earthquake ms 7 1 at uttarkashi station which is about 60 km north of dehradun the prepared map shows that among all identified active lineaments rupture along four lineaments can cause major damage in the region among these four three lineaments are transverse to the major tectonic zones viz the mft and mbt in the region and one extends along the mft lying south of dehradun the zonation map for great earthquakes m 8 has been prepared by modelling a rupture in the central gap region of the himalaya seven different possibilities of rupture nucleation within the rupture plane are modelled and a zonation map containing three different zones is prepared the prepared zonation map for this worst possible scenario shows that cities like tehri uttarkashi srinagar deoprayag pauri and dehradun fall within zone 1 and can experience ground accelerations bigger than 600 cm s2 the region like hardwar and rishikesh fall within zone 2 and can experience ground accelerations around 300 cm s2 the zonation map shows that tehri can experience accelerations up to 0 84g and this value is comparable with that obtained by other researchers this study confirms that for very long periods the destruction in the region will be dominantly affected by ruptures having longer lengths and least effected by shorter ruptures therefore special consideration about the longer ruptures should be taken while considering effect of earthquake hazards in this region

a new ground motion prediction model for northeastern india nei crustal earthquakes in this study a stochastic point source model is used to develop a ground motion prediction model for northeastern india nei crustal earthquakes calibrated using region specific source path and site parameters the nei strong ground motion database is too limited to derive an empirical ground motion prediction model valid for all magnitudes and distances in the present study we simulated 30 000 ground motions to develop the horizontal ground motion prediction model for nei these simulations are for 1000 earthquakes of moment magnitudes m w 4 8 5 and epicentral distances of 1 300 km in simulating ground motions quality factor stress drop and kappa derived from available nei strong motion records have been used the model has been validated by comparing it with the available but sparse database of recorded events the best fit between the model and observed strong ground motion records indicate that the new model is consistent with the available data and can be used in seismic hazard analyses until more data are collected and the model is improved

support of high elevation in the southern basin and range based on the composition and architecture of the crust in the basin and range and colorado plateau toexplorethenatureofhowthestructureandphysicalpropertiesofthecrustvaryfromextendedtorelativelyunextendeddomains we present teleseismic receiver functions which measure crustal thickness shear wavespeed structure and the vp vs ratio at 12 seismic stations in eastern arizona the crustal thickness is 28 km increases slightly eastward and remains nearly uniform beneath the varying elevations in the southern basin and range the observed vp vs ratio in the basin and range 1 78 exceeds the global average the southern colorado plateau exhibits thicker crust 40 km and a slightly greater observed vp vs 1 81 a discrete region in the colorado plateau generates an unusually high vp vs ratio 1 90 and contains low wavespeed zones which serve as evidence of partial melt related to quaternary volcanism the metamorphic core complexes in the southern basin and range likewise exhibit anomalously high vp vs values 1 79 1 87 and lack locally compensating crustal roots density models show that 85 kg m 3 lighter crust or 35 kg m 3 lighter mantle than that of the surrounding basin and range helps these metamorphic core complexes maintain their high elevation compositional modeling of intrusive bodies exposed throughout the catalina rincon metamorphic core complex indicates that the observed high vp vs ratio and modeled low density could result from substantial amounts of a plagioclase rich quartz poor rock these vp vs data are evidence that significant compositional heterogeneity of the crust can occur over a short distance and provide a clue as to how these areas that underwent significant tertiary extension may have been preconditioned for orogenic collapse

probabilistic models for forecasting earthquakes in the northeast region of india northeast india and its adjoining areas are characterized by very high seismic activity according to the indian seismic code the region falls under seismic zone v which represents the highest seismic hazard level in the country this region has experienced a number of great earthquakes such as the assam 1950 and shillong 1897 earthquakes that caused huge devastation in the entire northeast and adjacent areas by flooding landslides liquefaction and damage to roads and buildings in this study an attempt has been made to find the probability of occurrence of a major earthquake m w 6 in this region using an updated earthquake catalog collected from different sources thereafter dividing the catalog into six different seismic regions based on different tectonic features and seismogenic factors the probability of occurrences was estimated using three models the lognormal weibull and gamma distributions we calculated the logarithmic probability of the likelihood function ln l for all six regions and the entire northeast for all three stochastic models a higher value of ln l suggests a better model and a lower value shows a worse model the results show different model suits for different seismic zones but the majority follows lognormal which is better for forecasting magnitude size according to the results weibull shows the highest conditional probabilities among the three models for small as well as large elapsed time t and time intervals t whereas the lognormal model shows the lowest and the gamma model shows intermediate probabilities only for elapsed time t 0 the lognormal model shows the highest conditional probabilities among the three models at a smaller time interval t 3 15 yrs the opposite result is observed at larger time intervals t 15 25 yrs which show the highest probabilities for the weibull model however based on this study the indoburma range and eastern himalaya show a high probability of occurrence in the 5 yr period 2012 2017 with 90 probability

role of static stress transfer in earthquake occurrence in the himalaya abstract coulomb failure hypothesis suggests that earthquake interaction can lead to earthquake sequences and clustering this implies that the phenomenon should be considered a fundamental feature in any description of seismicity and evaluation of the seismic hazard and risk of a region we translate this idea to the himalaya and investigate how significantly the past earthquakes of the region may have influenced the present day seismicity and seismic hazard potential along its different segments for this we estimate separately the change in coulomb failure stress at the source of the most recent moderate magnitude earthquake along the kumaon garhwal segment the march 29 1999 chamoli earthquake due to two possible major sources these are i the process of subduction of the indian plate beneath the himalaya and ii some selected preceding moderate and small earthquakes in and around the region during their post seismic phase our results indicate that the change due to the former source completely overshadows that due to the latter the implication of our calculations is that the plate subduction processes in the himalaya i actively promote large moderate and small earthquake activity and ii also indirectly influence the regional seismicity through the occurrence of the past earthquakes

seismic characteristics and seismic hazard assessment source region of the 2015 nepal earthquake mw 7 8 in central himalaya seismicity and seismic characteristics like b value fractal dimension energy release and recurrence period are assessed for the region 80 e 89 e and 26 n 31 n which includes the 2015 large nepal earthquake mw 7 8 in central himalaya the international seismological centre isc catalogue of earthquakes with mb 3 8 for the period august 1964 january 2013 are used the b values are estimated using the maximum likelihood and least square methods the fractal dimension is estimated using the correlation integral method the events are also used for estimating radiated energy in the region the probability of occurrence of moderate earthquakes mb 5 0 using isc data and mw 6 0 using usgs data for the period 1964 2015 during a specified interval of time is estimated on the basis of three probabilistic models namely weibull gamma and lognormal the model parameters are estimated by the maximum likelihood estimates it is found that there is a 99 probability for occurrence of at least one earthquake mb 5 0 in this region in a time window of 2 3 years from the year 2013 and in 20 30 years for an earthquake mw 6 0 from the year 2015 the b value maps identified variable stressed zones and the fractal dimension maps fractal characteristics of the active fault zones the energy release map identified the zones of higher and lower energy release the percent probability maps prepared using the poisson distribution identify the zones of higher and lower probability earthquakes and thus indicate the areas of future probable earthquakes

a deterministic seismic hazard map of india and adjacent areas a seismic hazard map of the territory of india and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases the input data set consists of structural models seismogenic zones focal mechanisms and earthquake catalogues there are few probabilistic hazard maps available for the indian subcontinent however this is the first study aimed at producing a deterministic seismic hazard map for the indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation the level of seismicity and wave propagation in anelastic media synthetic seismograms at a frequency of 1 hz have been generated at a regular grid of 0 2 x 0 2 by the modal summation technique the seismic hazard expressed in terms of maximum displacement d m a x maximum velocity v m a x and design ground acceleration dga has been extracted from the synthetic signals and mapped on a regular grid over the studied territory the estimated values of the peak ground acceleration are compared with the observed data available for the himalayan region and are found to be in agreement many parts of the himalayan region have dga values exceeding 0 6 g the epicentral areas of the great assam earthquakes of 1897 and 1950 in northeast india represent the maximum hazard with dga values reaching 1 2 1 3 g the peak velocity and displacement in the same region is estimated as 120 177 cm s 1 and 60 90 cm respectively

crustal structure and evolution beneath the colorado plateau and the southern basin and range province results from receiver function and gravity studies over the past several decades contrasting models have been proposed for the physical and chemical processes responsible for the uplift and long term stability of the colorado plateau cp and crustal thinning beneath the basin and range province brp in the southwestern united states here we provide new constraints on the models by modeling gravity anomalies and by systematically analyzing over 15 500 p to s receiver functions recorded at 72 usarray and other broadband seismic stations on the southwestern cp and the southern brp our results reveal that the brp is characterized by a thin crust 28 2 0 5 km a mean vp vs of 1 761 0 014 and a mean amplitude r of p to s converted wave relative to that of the direct p wave of 0 181 0 014 that are similar to a typical continental crust consistent with the model that the thin crust was the consequence of lithospheric stretching during the cenozoic the cp is characterized by the thickest crust 42 3 0 8 km largest vp vs 1 825 0 009 and smallest r 0 105 0 007 values in the study area in addition many stations on the cp exhibit a clear arrival before the p to s converted phase from the moho corresponding to a lower crustal layer of about 12 km thick with a mafic composition we hypothesize that the lower crustal layer which has an anomalously large density as revealed by gravity modeling and high velocities in seismic refraction lines contributed to the long term stability and preuplift low elevation of the colorado plateau

xenolithic evidence for proterozoic crustal evolution beneath the colorado plateau tertiary diatremes of the navajo volcanic field brought a wide variety of proterozoic xenoliths to the surface of the colorado plateau examination of crustal xenoliths from the navajo volcanic field diatremes permits reconstruction of proterozoic pressure temperature p t histories beneath the colorado plateau diatremes from the northwest part of the navajo volcanic field carry the greatest variety of xenoliths including metasedimentary rocks amphibolites felsic gneisses mafic granulites and crustally derived eclogites these rock types show variable degrees of hydrous alteration and evidence for complex reaction histories in contrast diatremes from the southeast part of the navajo volcanic field contain primarily mafic and felsic granulites that show fewer reaction textures and less alteration metasedimentary and eclogitic xenoliths are absent in these diatremes the p t paths from the northwest xenoliths are counterclockwise and reach temperatures as high as 850 c and pressures equal to or greater than 10 kbar later hydrous alteration occurred around 500 c and 8 12 kbar xenoliths from the southeast diatremes preserve little evidence of their p t evolution but paths involve heating and or decompression the differing rock types p t paths and alteration histories of the northwest and southeast populations suggest that proterozoic tectonism juxtaposed two distinct crustal blocks beneath the colorado plateau previous workers have postulated that the boundary between the proterozoic yavapai and mazatzal provinces occurs in the region our data support the existence of a northeast trending boundary beneath the four corners area if the eclogitic metamorphism and hydrous alteration are proterozoic in age their restricted occurrence beneath the northwest part of the plateau suggests that subduction was northwest dipping during proterozoic accretion of the mazatzal province onto north america

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

small scale convection at the edge of the colorado plateau implications for topography magmatism and evolution of proterozoic lithosphere the colorado plateau of the southwestern united states is characterized by a bowl shaped high elevation late neogene quaternary magmatism at its edge large gradients in seismic wave velocity across its margins and relatively low lithospheric seismic wave velocities we explain these observations by edge driven convection following rehydration of colorado plateau lithosphere a rapidly emplaced cenozoic step in lithosphere thickness between the colorado plateau and adjacent extended rio grande rift and basin and range province causes small scale convection in the asthenosphere a lithospheric drip below the plateau is removing lithosphere material from the edge that is heated and metasomatized resulting in magmatism edgedriven convection also drives margin uplift giving the plateau its characteristic bowl shape the edge driven convection model shows good consistency with features resolved by seismic tomography

transition zone between the upper diatreme and lower diatreme origin and significance at round butte hopi buttes volcanic field navajo nation arizona round butte is a small but complex miocene diatreme that crops out 190 m below the pre eruptive surface in the southeastern part of the hopi buttes volcanic field erosional remnants consist of a diatreme 170 190 m in diameter of which the central 130 150 m is well exposed in a massif featuring 20 30 m high sub vertical cliffs and a 50 cm thick basanite dike field mapping allowed us to define three main groups of pyroclastic rocks in the diatreme undisturbed beds disturbed beds and non bedded rocks pyroclastic rocks range in grain size from coarse tuff to tuff breccia and in componentry from juvenile rich to lithic rich with a dominance of heterolithic lapilli tuffs rocks from the undisturbed bedded pyroclastic group are present above an unconformity found all around the massif whereas the disturbed bedded and the non bedded pyroclastic groups are always found below it this unconformity was previously understood as the contact between the upper and the lower diatremes the undisturbed beds above the unconformity indeed compose the upper diatreme but the assemblage of non bedded rocks invasive columns and disturbed beds residual columns below it is not typical of the lower diatreme instead they represent a transition zone between the upper and lower diatremes such a transition zone also occurs in other diatremes it is important genetically and we propose to add it to the general model of maar diatreme volcanoes

probabilistic appraisal of earthquake hazard parameters deduced from a bayesian approach in the northwest frontier of the himalayas a straightforward bayesian statistic is applied in five broad seismogenic source zones of the northwest frontier of the himalayas to estimate the earthquake hazard parameters maximum regional magnitude mmax value of g r relationship and seismic activity rate or intensity for this purpose a reliable earthquake catalogue which is homogeneous for mw 5 0 and complete during the period 1900 to 2010 is compiled the hindukush pamir himalaya zone has been further divided into two seismic zones of shallow h 70 km and intermediate depth h 70 km according to the variation of seismicity with depth in the subduction zone the estimated earthquake hazard parameters by bayesian approach are more stable and reliable with low standard deviations than other approaches but the technique is more time consuming in this study quantiles of functions of distributions of true and apparent magnitudes for future time intervals of 5 10 20 50 and 100 years are calculated with confidence limits for probability levels of 50 70 and 90 in all seismogenic source zones the zones of estimated mmax greater than 8 0 are related to the sulaiman kirthar ranges hindukush pamir himalaya and himalayan frontal thrusts belt suggesting more seismically hazardous regions in the examined area the lowest value of mmax 6 44 has been calculated in northern pakistan and hazara syntaxis zone which have estimated lowest activity rate 0 0023 events day as compared to other zones the himalayan frontal thrusts belt exhibits higher earthquake magnitude 8 01 in next 100 years with 90 probability level as compared to other zones which reveals that this zone is more vulnerable to occurrence of a great earthquake the obtained results in this study are directly useful for the probabilistic seismic hazard assessment in the examined region of himalaya

flat versus normal subduction zones a comparison based on 3 d regional traveltime tomography and petrological modelling of central chile and western argentina 29 35 s

aftershocks of the march 1999 chamoli earthquake and seismotectonic structure of the garhwal himalaya the aftershocks of the chamoli earthquake m b 6 3 of 28 march 1999 are analyzed to understand the seismotectonic structure of the garhwal himalaya the permanent as well as temporary microearthquake network data are used the mainshock occurred on the basement thrust by thrust faulting the aftershocks on the other hand are triggered at the seismogenic faults to the south of the main central thrust mct by thrust faulting as well as by strike slip faulting and all the events occurred above the plane of detachment basement thrust the mct is not the seismogenic fault

surface motions and continental deformation in the indian plate and the india eurasia collision zone the collision of the indian plate with eurasia has played a major role in controlling the dynamics of central asia leading to the world s largest continental deformation zone in order to study the deformation within the indian plate as well as the india eurasia collision zone we model the lithospheric stress field by calculating the two primary sources of stress one arising due to topography and shallow lithospheric structure estimated by gravitational potential energy differences and the other arising from basal tractions derived from density driven mantle convection we use several tomography models to calculate horizontal tractions using the convection code hc for two radially varying viscosity structures we also take into account lateral viscosity variations in the lithosphere model arising from stiff cratons weak plate boundaries and strength variations due to old and young oceanic lithosphere we do a quantitative comparison of our predicted deviatoric stresses strain rates and plate velocities with surface observables and find that the regional tomography model of singh et al 2014 embedded in the global s wave model s40rts does a remarkable job of fitting the observations of gps velocities and strain rates as well as intraplate stress field from the world stress map

preservation of proterozoic terrane boundaries within the colorado plateau and implications for its tectonic evolution abstract during the proterozoic the north american continent grew by the accretion of arcs onto the archean craton subsequent tectonic events affected much of the lithosphere of western north american resulting in the destruction of many of the features that reflect continental growth the colorado plateau which is centrally located within the tectonically active western portion of north america experienced only minor amounts of volcanism during subsequent magmatic events and has undergone comparatively little internal deformation during the remainder of the precambrian and phanerozic despite the occurrence of some significant tectonic events because the lithosphere of the plateau has not been significantly reworked by tectonic events it may have retained structures since accretion that give insight into processes of continental growth the crust of the southeastern portion of the colorado plateau revealed here through seismic data recorded by the temporary spe and la ristra arrays is greater than 40 km thick and possesses distinct changes in intercrustal layering and the character of the moho the moho appears quite dim towards the center of the plateau and much brighter along its southeastern margins connecting changes in crustal features that are common between the two arrays indicates a northeastern structural trend that matches the pattern of gravity anomalies in the region differences in crustal structures between terranes extend across much of the crust suggesting that entire distinct crustal columns align with terrane boundaries it is unlikely that extensive crustal flow as required by some models of plateau evolution could have traversed across the entire colorado plateau without producing features that cross cut these boundaries

the crustal structure of the arizona transition zone and southern colorado plateau from multiobservable probabilistic inversion the arizona transition zone is a narrow band that separates two of the main and most contrasting tectonic provinces in western us namely the southern colorado plateau and the southern basin and range provinces as such the internal crustal structure and physical state of this transitional zone hold clues for understanding i the amalgamation of these provinces ii the partitioning of deformation due to both past and present day stress fields and iii the role of thermal versus compositional effects in controlling surface observables here we employ and expand a novel multiobservable probabilistic inversion method and jointly invert fundamental mode rayleigh phase velocities receiver functions surface heat flow geoid height and absolute elevation to obtain an internally consistent 3 d model of the temperature density vs and vp of the arizona transition zone and the southern portions of the colorado plateau and basin and range our results confirm a significant crustal thickening from 28 km in the sw of the arizona transition zone and southern basin and range to 48 km beneath the southern colorado plateau inverted temperatures agree well with the location of recent volcanism and indicate that the lithosphere asthenosphere boundary is not deeper than 70 km in most of the region we find that major pre cambrian surface structures and or shear zones separate crustal domains with distinct bulk properties suggesting that the juxtaposed crustal blocks still retain at least in part their original characteristics however widespread intrusions of significant volumes of mafic magmas have affected these blocks at different depths locally overprinting their original compositions and creating highly heterogeneous crustal sections a dominant and large scale internal crustal pattern of sw dipping planes structures is evident in our models coinciding with the orientation of deep faults previously inferred from earthquake focal mechanisms while we cannot categorically corroborate the presence of melt or aqueous fluids within the crust our results are compatible with these scenarios beneath some parts of the basin and range the mogollon datil and springerville volcanic fields

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

southern limits of major earthquake ruptures along the himalaya between longitudes 75 and 90 e the ruptures responsible for major earthquakes along the himalayan convergent plate margin hcpm occur in a strikewise oriented zone of frictional failure and relative slip in a buried detachment along the upper surface of the indian shield rocks subducting under the himalaya the southern limit of the rupture zone is a geotectonic lineament whose geographic location is important in assessing risk due to earthquakes a major part of this article is taken up in arguing that the available macroseismic and instrumental evidence for the 1934 bihar nepal earthquake is consistent with the view that the rupture which caused it occurred in the detachment mostly under the lesser himalaya northward from the vicinity of the surface trace of the main boundary thrust mbt since a similar location has been inferred by others for the 1905 kangra earthquake rupture a basis arises for postulating that over more than half of the length of the hcpm between 75 and 90 e longitudes the ruptures responsible for major earthquakes lie in the detachment with their southern limits geographically similarly close to the surface trace of the mbt this includes the nearly 700 km long seismic gap between the 1905 and 1934 ruptures

spatial distribution of earthquake potential along the himalayan arc abstract to determine the spatial distribution of earthquake potential along the active himalayan arc we utilize gps measurements and earthquake data we derive horizontal velocity field and 2 d strain rates from a new set of 41 regional gps stations along with 446 published velocities we convert these strain rate tensors to geodetic moment rate build up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years the geodetic to seismic moment rate ratio an indicator of stored strain energy varies from below unity to more than 50 in different segments the estimated geodetic moment rate ranges from 1 7 1018 nm yr to 10 2 1018 nm yr whereas the seismic moment rate ranges from 3 7 1016 nm yr to 5 1 1019 nm yr this variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of 1 15 1017 nm yr to 7 97 1018 nm yr along various segments of the study region the above moment deficit rate provides an equivalent earthquake potential of magnitude 5 7 8 2 in different segments specifically the higher earthquake potential mw 8 0 corresponds to the segments in the central seismic gap and the northeast part of himalaya whereas the lower earthquake potential mw

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

probabilistic assessment of earthquake hazards in the indian subcontinent the indian subcontinent is one of the most seismic prone areas of the world the himalayan mountains in the north mid oceanic ridges in the south and earthquake belts surrounding the indian plate all show that the subcontinent has undergone extensive geological and tectonic processes in the past the probability of the occurrence of earthquakes with magnitude 6 m b 7 during a specified interval of time has been estimated on the basis of four probabilistic models namely lognormal weibull gamma and exponential distribution for the indian subcontinent the seismicity map has been prepared using the earthquake catalogue from the period 1963 1994 and six different zones have been identified on the basis of clustering of events the model parameters have been estimated by the method of maximum likelihood estimates mle and method of moments mom a computer program package has been developed for all four models which represents the distributions of time intervals fairly well the logarithmic of likelihood ln l is estimated for testing the models and different models have been found to be plausible the probability of different magnitude thresholds has been evaluated using the gutenberg richter formula log n a bm for magnitude distribution the constants a and b have been computed for each region and found to be varying between 5 46 8 53 and 0 87 1 34 respectively

developing local to near regional explosion and earthquake discriminants abstract we develop local to near regional 0 200 km amplitude discriminants using earthquakes single fired explosions and delayed fired explosions we use the source phenomenology experiment spe broadband data collected across the colorado plateau during the summer of 2003 which recorded explosions in hard and soft rock mines we optimized a local surface wave magnitude scale derived from a stable regional surface wave magnitude russell 2006 for the sources however the magnitude of the source and the distance to the station limit the surface wave energy which can cause instability in the surface wave magnitudes magnitude scales for the local phases pg lg sg and rg were also tested and compared when an azimuthal station correction was applied to each magnitude scale there was an average reduction of standard deviation by 16 58 regional and teleseismic discrimination techniques were optimized for local distance and our results show that lithology of the source is a critical component in discriminating events at local distances we also found that magnitude and amplitude ratios are effectively used to discriminate between small earthquakes and explosions at local distances with each performing the best in the hard rock lithology furthermore the ratio techniques perform equally in both lithologies if multiple stations are used to establish the ratio values we find that an average of four or five stations will generally have a 90 or better correct identification for both types of ratios finally we find that the source lithology local site effects and large scale geologic features control most of the variability in the amplitude measurements

a probabilistic estimate of the most perceptible earthquake magnitudes in the nw himalaya and adjoining regions nw himalaya and its neighboring region 25 40 n and 65 85 e is one of the most seismically hazardous regions in the indian subcontinent a region that has historically experienced large to great damaging earthquakes in the present study the most perceptible earthquake magnitudes mp are estimated for intensity i vii horizontal peak ground acceleration a 300 cm s2 and horizontal peak ground velocity v 10 cm s in 28 seismogenic zones using the two earthquake recurrence models of kijko and sellevoll bulletin of the seismological society of america 82 1 120 134 1992 and gumbel s third asymptotic distribution of extremes giii both methods deal with maximum magnitudes the earthquake perceptibility is calculated by combining earthquake recurrence models with ground motion attenuation relations at a particular level of intensity acceleration and velocity the estimated results reveal that the values of mp for velocity v 10 cm s show higher estimates than corresponding values for intensity i vii and acceleration a 300 cm s2 it is also observed that differences in perceptible magnitudes calculated by the kijko sellevoll method and giii statistics show significantly high values up to 0 7 0 6 and 1 7 for intensity acceleration and velocity respectively revealing the importance of earthquake recurrence model selection the estimated most perceptible earthquake magnitudes mp in the present study vary from mw 5 1 to 7 7 in the entire zone of the study area results of perceptible magnitudes are also represented in the form of spatial maps in 28 seismogenic zones for the aforementioned threshold levels of intensity acceleration and velocity estimated from two recurrence models the spatial maps show that the quetta of pakistan the hindukush pamir himalaya the caucasus mountain belt and the himalayan frontal thrust belt kashmir kangra uttarkashi chamoli regions exhibit higher values of the most perceptible earthquake magnitudes mw 6 0 these spatially distributed values indicate good agreement with high seismic hazard zones in previously published hazard maps based on seismicity maximum expected earthquake magnitudes during specific time intervals and maximum expected acceleration these maps have useful implications in preparing earthquake selection criteria for the anti seismic design of non critical structures in the study region

the use of velocity spectrum for stacking receiver functions and imaging upper mantle discontinuities summary in order to improve the signal to noise ratio of receiver function data it is typical to stack receiver functions calculated from events at similar distances and back azimuths we have adapted the velocity spectrum stacking vss technique used extensively in reflection seismology to the receiver function method in order to stack data with different ray parameters thereby improving further the signal to noise ratio perhaps more importantly by producing the velocity spectrum stacks we take advantage of the differences in the shapes of the moveout curves of converted phases and reverberations to identify and separate the various phases and to infer velocity structure by comparison of velocity spectrum stacks produced from the observed data at the iris ida broad band station at obninsk russia obn with those produced from prem synthetics we have identified ps phases from the 400 and 670 km discontinuities the p to s ps converted phase from the 400 km discontinuity observed at obn is much larger compared with that of the 670 km discontinuity than is predicted by prem this suggests a higher velocity contrast at 400 km than in prem by adapting a bootstrap method to assess the depth and velocity estimates determined by vss we find that the ps phase from the 670 km discontinuity is best imaged with higher than prem upper mantle p and s velocities and at a depth of 663 3 km we find no evidence of a 220 km discontinuity beneath obn in these data

titan s north south asymmetry from hst and voyager imaging comparison with models and ground based photometry abstract new measurements of titan s hemispheric brightness asymmetry from hst images from 260 to 1040 nm show that the contrast is strongest near 450 nm blue and with the opposite sign at 889 nm methane band comparison with a full titan year of disk integrated albedo data indicates that the seasonal cycle in asymmetry is smooth but is insufficient to explain the variation in albedo and a twice per year global albedo enhancement 50 larger than the hemispheric asymmetry amplitude is required as noted by other workers we also report measurements of limb darkening strongest at red wavelengths and note that the transition zone between the hemispheres lies in the northern brighter hemisphere at present comparison of models to the hst data set indicates that a change in aerosol number density above 70 km and largely below 120 km is the likely mechanism and is probably driven by aerosol transport by meridonal and vertical winds

modeling earthquake recurrence in the himalayan seismic belt using time dependent stochastic models implications for future seismic hazards interest in and pertinent studies related to the seismic hazard in the himalayan region have increased significantly since the instrumental era and each damaging earthquake encourages its reestimation in the work presented herein the non poissonian probabilities of exceedance of magnitudes in a specified time in the future were investigated for different elapsed times based on the recurrence time intervals of past earthquakes in the himalaya using the weibull log normal gamma and inverse gaussian stochastic models the whole himalayan arc is divided into four seismogenic source zones viz the northwestern himalayas zone 1 the central seismic gap region zone 2 the eastern nepal and sikkim zone 3 and the eastern himalayas zone 4 by considering approximately 380 years of seismological data the suitability of each stochastic model for each zone was estimated using the kolmogorov smirnov k s test to describe the different physical processes responsible for earthquake occurrence the results show that the gamma inverse gaussian log normal and inverse gaussian models were most suitable for zones 1 4 respectively for m 6 0 the cumulative probability of recurrence intervals reaches up to 90 in 30 years for zones 1 and 2 49 years for zone 3 and 41 years for zone 4 the estimated conditional probability reaches 90 in 30 years in zone 1 35 years in zone 2 and 50 years in zones 3 and 4 the most suitable models for m 7 0 were found to be the log normal for zones 1 2 and 3 and gamma for zone 4 the cumulative probability for m 7 0 reaches 90 in 85 years in zone 1 86 years in zone 2 93 years in zone 3 and 148 years in zone 4 the estimated conditional probabilities reach 90 in 80 years in zone 1 90 years in both zone 2 and 3 and 150 years in zone 4 it is strongly recommended that model suitability be evaluated in complex regions such as the himalaya before proceeding with seismic hazard assessments the heterogeneous and complex tectonics of the himalayas differentiated plate motions different stress release patterns spatially and temporally and locking unlocking of faults thrusts are some of the reasons responsible for the different probabilistic models describing the earthquake occurrence phenomena in these four zones

rocky mountain evolution tying continental dynamics of the rocky mountains and deep probe seismic experiments with receiver functions 1 in this study we have determined the crustal structure using three different receiver function methods using data collected from the northern transect of the continental dynamics of the rocky mountains cd rom experiment the resulting migrated image and crustal thickness determinations confirm and refine prior crustal thickness measurements based on the cd rom and deep probe experiment data sets the new results show a very distinct and thick lower crustal layer beneath the archean wyoming province in addition we are able to show its termination at 42n latitude which provides a seismic tie between the cd rom and deep probe seismic experiments and thus completes a continuous north south transect extending from new mexico into alberta canada this new tie is particularly important because it occurs close to a major tectonic boundary the cheyenne belt between an archean craton and a proterozoic terrane we used two different stacking techniques based on a similar concept but using two different ways to estimate uncertainties furthermore we used receiver function migration and common conversion point ccp stacking techniques the combined interpretation of all our results shows 1 crustal thinning in southern wyoming 2 strong northward crustal thickening beginning in central wyoming 3 the presence of an unusually thick and high velocity lower crust beneath the wyoming province and 4 the abrupt termination of this lower crustal layer north of the cheyenne belt at 42n latitude

images of crustal variations in the intermountain west 1 we develop a map of crustal thickness variations across the great basin colorado plateau rocky mountain and great plains provinces of the western united states using common conversion point stacking of teleseismic receiver functions below the rocky mountains and high plains in colorado we find the thickest crust in the region at 45 50 km thick beneath the basin and range thinner between 30 and 40 km crust is found thin 30 km thick crust is present in the northern portion of nevada and utah despite elevations similar to those farther south crustal thickness across the colorado plateau can be characterized as a broad transitional region between the thin crust of basin and range to the thicker crust of the rocky mountains the impedance contrast across the mohorovicic discontinuity decreases below the colorado plateau as converted arrivals recorded in this region appear weak compared to surrounding areas variations in vp vs across the region indicate higher values along the western boundary of the basin and range in the rocky mountains and in the western great plains we are not able to characterize vp vs in the colorado plateau we find that crustal thickness does not closely correlate with surface topography within each region or across the region as a whole differences in crustal thickness in each tectonic province indicate the need for a mantle component to support the high elevations across the western united states

lithospheric and upper mantle structure of central chile and argentina summary the tectonics of central chile and argentina have been greatly affected by the shallow dips of the subducting nazca plate which controlled patterns of magmatism and deformation nearly 1000 km away from the plate boundary we calculate receiver functions from data recorded by the charge array which transected the andes and sierras pampeanas in central chile and argentina to better constrain the crustal structure of this region beneath the northern transect of the charge array where the nazca slab flattens near 100 km we find the crust is over 60 km thick beneath the andes and thin to the east the thick crust however extends 200 km to the east of the high elevations estimates of vp vs obtained from receiver functions vary along ancient terrane boundaries exhibiting higher values to the west interestingly we observe that the amplitude of the phase corresponding to the moho on receiver functions diminishes to the west complicating our images of crustal structure we proposed that the observations presented here of thickened crust within a region of low elevations diminished receiver function arrivals and reports of high shear wave speeds atop of the mantle wedge overlying the shallowly subducted nazca slab can be explained by partial eclogitization of the lower crust the moho appears simpler across the southern transect where it can be identified near 50 km depth at its deepest point beneath the andes and shallows eastwards volcanism remains active near the latitudes of our southern transect and we observe multiple crustal lowvelocity zones indicative of regions of partial melt near the centres of volcanism signals related to the nazca slab remain more elusive suggestive of a small impedance contrast between the slab and overlying mantle

upper mantle structure beneath the eastern colorado plateau and rio grande rift revealed by bouguer gravity seismic velocities and xenolith data 1 the lithospheric architecture of the colorado plateau rio grande rift transition zone reflects a narrow corridor of active tectonism and magmatism between the tectonically stable colorado plateau and the stable interior of north america in this paper we analyze bouguer gravity data crustal thickness variations xenolith data and seismic wave speed structure to argue that the rio grande rift and southeastern colorado plateau is underlain by a low density upper mantle province that does not trend along upper crustal tectonic boundaries but rather is correlated with regions of middle to late tertiary magmatism we model uppermost mantle density contrasts using bouguer gravity along five parallel profiles across the colorado plateau and validate our models by converting modeled density contrasts to seismic velocity variations for comparison with regional seismic data as well as comparing modeled densities to calculated densities from xenoliths we find that upper crustal features and crustal thickness variations do not explain long wavelength 200 km variations in bouguer gravity across the colorado plateau rio grande rift a large 200 440 km wide region of low uppermost mantle density is modeled beneath the eastern colorado plateau margin jemez lineament rio grande rift and parts of the westernmost great plains this region has a density contrast of 90 to 30 kg m3 relative to the adjacent colorado plateau and great plains provinces and coincides with previously imaged regions of low upper mantle seismic velocities in situ densities inferred from xenolith data in the colorado plateau support the modeled upper mantle density variations and support the idea that the eastern and western margins of the plateau have been significantly modified by metasomatism we suggest that the region of low upper mantle density likely reflects some combination of temperature variations partial melt contents and compositional variations related to tertiary magmatic activity and or thinned lithosphere the relationship of this zone of modified upper mantle to extension in the rio grande rift remains enigmatic however particularly given the lack of spatial correlation between the trends of upper mantle structures and surficial extensional structures

earthquake recurrence in nw and central himalaya abstract in this study we compare himalayan seismic moment release estimates derived from strain rate observations with those derived from large historical earthquakes and to this end we use a reassessed catalogue of historical earthquakes from western and central himalaya since the beginning of the 16th century we have computed seismic moment rates within six contiguous segments along the himalayan arc and compared these using kostrov s formula with moment rates computed from recent global strain rate estimates and regional studies while the ratios between strain based moment rate estimates and those inferred from observed seismicity vary significantly between the segments we find on the average consistently larger strain based values by about a factor of two based on seismicity from the last 515 years the moment rate ratio is however significantly reduced when shorter catalogues are used to 1 28 for the last 215 years and to 1 05 for the last 115 years which is an almost perfect match the possible inclusion of afterslip in the model would further improve the 515 year match this is indicating that a significant part of the difference possibly most of it is likely to be caused by incompleteness of the longer earthquake catalogue possibly combined with underestimated magnitudes the difference between geodetic and seismic estimates for the more complete part of the catalogue is smaller than previously reported along the western himalayan frontal thrust in fact the only region where a significant moment rate difference is found in our study is in se himachal pradesh in terms of seismic hazard it is found that the moment rate reduction of about a factor of two when going from 115 to 515 years leads to a reduction in the 475 year pga of about 26 it is also found that using 50 years of usgs seismicity data between 1963 and 2012 leads to a 40 lower hazard as compared to using moment release for the last 115 years

imaging crustal and upper mantle structure beneath the colorado plateau using finite frequency rayleigh wave tomography a new 3 d shear velocity model of the crust and upper mantle beneath the colorado plateau and surrounding regions of the southwestern united states was made with finite frequency rayleigh wave tomography using earthscope usarray data the goal of our study is to examine the colorado plateau lithospheric modification that has resulted from cenozoic tectonism and magmatism we have inverted for the isotropic vs model from a grid of rayleigh wave dispersion curves obtained by a modified two plane wave method for periods from 20 to 167 s we map the lithosphere asthenosphere boundary under the colorado plateau by identifying the middle of the shallowest upper mantle negative vs gradient the depths of the lithosphere asthenosphere boundary inferred here agree well with receiver function estimates made independently the strong lateral heterogeneity of shear velocity can be mainly attributed to 200 400 k variations in temperature together with 1 partial melt fraction in the shallow upper mantle the resulting vs structures clearly image the upper mantle low velocity zones under the colorado plateau margins that are associated with magmatic encroachment these upper mantle low velocity zones resulted from the convective removal of the colorado plateau lithosphere that had been rehydrated by subduction released water refertilizing and destabilizing it this convective erosion by the asthenosphere at the low viscosity part of the lithosphere is driven by the large step in lithospheric thickness and the thermal gradient across the boundary between the plateau and the extended basin and range since the mid cenozoic at a rate similar to that of magmatic migration into the plateau from the southeast south and northwest moreover the rayleigh wave tomography model images parts of a high velocity drip in the western colorado plateau and thus provides additional seismic evidence for ongoing convective downwelling of the lithosphere that was initially suggested by receiver functions and body wave tomography the widespread edge convective erosion which the regional delamination style downwelling processes are a 3 d manifestation of could provide additional buoyancy sources to support the excess uplift at the margins of the plateau

seasonal photometric variability of titan 1972 2006 abstract measurements at lowell observatory of titan in the b 472 nm and y 551 nm filters of the stromgren photometric system at thirty four consecutive apparitions 282 nights from 1971 72 to 2006 show a 10 sinusoidal variation that lags seasonal extremes by about 1 8 of a titan year the seasonal variations are asymmetric the autumn lightcurve maxima of the northern and southern hemispheres differ significantly as do the spring lightcurve minima changes also occur from one titan year to the next titan was 3 fainter in b and 1 fainter in y following the 2002 southern summer solstice than it was one titan year earlier in 1973 these changes appear to be intrinsic to titan s atmosphere and cannot be explained by instrumental effects and changing geometries orbital variations visible in recent hubble space telescope images at 673 nm and voyager orange images 590 640 nm may have a small 0 002 0 001 mag counterpart in the b y photometric record eastern elongation brighter consistent with the cassini near infrared albedo map

through thick and thin a new model for the colorado plateau from seismic refraction data from pacific to arizona crustal experiment we have constructed a model for the crust and uppermost mantle beneath the colorado plateau by combining newly acquired seismic refraction wide angle reflection data from the 1989 pacific to arizona crustal experiment pace cross profile with data collected by roller 1965 a combination of forward modeling methods was used to model travel times and relative amplitudes of crustal and upper mantle phases the salient features of the model for the colorado plateau hereafter referred to as the plateau are 1 an upper crust having an average velocity of 6 1 km s with a low vertical velocity gradient 2 midcrustal discontinuities at depths of 30 to 38 km beneath the plateau 3 a lower crust that varies in thickness 5 to 16 km and has an average velocity of 6 8 km s 4 a transitional lower crust upper mantle boundary and 5 a crustal thickness of 45 3 km a comparison of our new model for the colorado plateau with recent models for the basin and range shows that the upper crusts of the two provinces are similar but that the lower crust of the plateau is thicker particularly in the plateau s central region these observations are consistent with the idea that the basin and range could have formed from crust like that of the colorado plateau

a geophysical model for the origin of volcano vent clusters in a colorado plateau volcanic field variation in spatial density of quaternary volcanic vents and the occurrence of vent clusters correlate with boundaries in proterozoic crust in the springerville volcanic field svf arizona usa inverse modeling using 538 gravity measurements shows that vent clusters correlate with gradients in the gravity field due to lateral variation in crustal density these lateral discontinuities in the crustal density can be explained by boundaries in the north american crust formed during proterozoic accretion spatial density of volcanic vents is low in regions of high density proterozoic crust high in areas of relatively low density proterozoic crust and is greatest adjacent to crustal boundaries vent alignments parallel these boundaries we have developed 2d and 3d numerical models of magma ascent through the crust to simulate long term average magma migration that led to the development of vent clusters in the svf assuming that a viscous fluid flow through a porous media is statistically equivalent to magma migration averaged over geological time in the full field scale the location and flux from the uniform magma source region are boundary conditions of the model changes in model diffusivity associated with changes in the bulk properties of the lithosphere can simulate preferential magma migration paths and alter estimated magma flux at the surface implying that large scale crustal structures such as inherited tectonic block boundaries influence magma ascent and clustering of volcanic vents probabilistic models of volcanic hazard for distributed volcanic fields can be improved by identifying crustal structures and assessing their impact on volcano distribution with the use of numerical models

titan s smile and collar hst observations of seasonal change 1994 2000 we observed titan with the hubble space telescope in november 2000 using the wide field plane tary camera wfpc2 and the space telescope imaging spectrograph stis considerable change is apparent be tween these and observations in 1994 1997 in particular the north south asymmetry at visible wavelengths has re versed with the southern hemisphere brighter as during the voyager epoch the asymmetry shows considerable varia tion with wavelength in the near infrared in the 889nm methane band the asymmetry which formerly resembled a smile has reversed in the last 3 years while at 953nm the southern limb is still bright a south polar collar dark at ultraviolet wavelengths is apparent some five years after equinox

probabilistic assessment of earthquake hazard in gujarat and adjoining region of india the gujarat and adjoining region falls under all four seismic zones v iv iii and ii of the seismic zoning map of india and is one of the most seismically prone intracontinental regions of the world it has experienced two large earthquakes of magnitude m w 7 8 and 7 7 in 1819 and 2001 respectively and several moderate earthquakes during the past two centuries in the present study the probability of occurrence of earthquakes of m 5 0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely weibull gamma and lognormal a complete earthquake catalogue has been used covering the time interval of 1819 to 2006 the whole region has been divided into three major seismic regions saurashtra mainland gujarat and kachchh on the basis of seismotectonics and geomorphology of the region the earthquake hazard parameters have been estimated using the method of maximum likelihood the logarithmic of likelihood function ln l is estimated and used to test the suitability of models in three different regions it was found that the weibull model fits well with the actual data in saurashtra and kachchh regions whereas lognormal model fits well in mainland gujarat the mean intervals of occurrence of earthquakes are estimated as 40 455 20 249 and 13 338 years in the saurashtra mainland gujarat and kachchh region respectively the estimated cumulative probability probability that the next earthquake will occur at a time later than some specific time from the last earthquake for the earthquakes of m 5 0 reaches 0 9 after about 64 years from the last earthquake 1993 in saurashtra about 49 years from the last earthquake 1969 in mainland gujarat and about 29 years from the last earthquake 2006 in the kachchh region the conditional probability probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake is also estimated and it reaches about 0 8 to 0 9 during the time interval of about 57 to 66 years from the last earthquake 1993 in saurashtra region 31 to 51 years from the last earthquake 1969 in mainland gujarat and about 21 to 28 years from the last earthquake 2006 in kachchh region

titan s surface revealed by hst imaging we present for the first time relative albedo maps of titan s surface the maps were made from images taken by the hubble space telescope s planetary camera 295 km per pixel through atmospheric windows at 940 and 1080 nm coverage at all longitudes and between 45 s and 60 n was obtained with 14 orbits from 4 18 october 1994 each image is characterized by haze with both limb effects brightening and a large north south contrast subtracting an averaged image from each frame removes haze effects and reveals surface features of 10 maximum contrast many features are clearly visible in multiple images and in both filters but the surface map is dominated by a large bright roughly rectangular feature centered at 110 w 10 s and elongated in an east west direction 4000 2500 km2 this feature and others indicate the diversity of titan s surface we consider the origin of the bright feature in an otherwise dark landscape and suggest that highland washing by methane rainfall is a likely mechanism

probabilistic assessment of earthquake recurrence in northeast india and adjoining regions northeast india and adjoining regions 20 32 n and 87 100 e are highly vulnerable to earthquake hazard in the indian sub continent which fall under seismic zones v iv and iii in the seismic zoning map of india with magnitudes m exceeding 8 7 and 6 respectively it has experienced two devastating earthquakes namely the shillong plateau earthquake of june 12 1897 mw 8 1 and the assam earthquake of august 15 1950 mw 8 5 that caused huge loss of lives and property in the indian sub continent in the present study the probabilities of the occurrences of earthquakes with magnitude m 7 0 during a specified interval of time has been estimated on the basis of three probabilistic models namely weibull gamma and lognormal with the help of the earthquake catalogue spanning the period 1846 to 1995 the method of maximum likelihood has been used to estimate the earthquake hazard parameters the logarithmic probability of likelihood function ln l is estimated and used to compare the suitability of models and it was found that the gamma model fits best with the actual data the sample mean interval of occurrence of such earthquakes is estimated as 7 82 years in the northeast india region and the expected mean values for weibull gamma and lognormal distributions are estimated as 7 837 7 820 and 8 269 years respectively the estimated cumulative probability for an earthquake m 7 0 reaches 0 8 after about 15 16 2010 2011 years and 0 9 after about 18 20 2013 2015 years from the occurrence of the last earthquake 1995 in the region the estimated conditional probability also reaches 0 8 to 0 9 after about 13 17 2008 2012 years in the considered region for an earthquake m 7 0 when the elapsed time is zero years however the conditional probability reaches 0 8 to 0 9 after about 9 13 2018 2022 years for earthquake m 7 0 when the elapsed time is 14 years i e 2009

revisiting the 1991 uttarkashi and the 1999 chamoli india earthquakes implications of rupture mechanisms in the central himalaya abstract the central himalaya has attracted much attention due to its potential to host a great earthquake an inference based on the history of earthquakes and the geodetic slip estimates the largest and earliest historically documented earthquake in the central himalaya occurred in 1803 m 7 7 near uttarkashi on its western part much before the great event of 1934 mw 8 2 located farther to the east both of which were felt severely in the gangetic plain south of the mountain front the seismotectonic model by seeber and armbruster 1981 predicts that large great earthquakes originate on the main himalayan thrust mht and their ruptures propagate southward to the main frontal thrust mft the rupture of the april 25 2015 mw 7 8 gorkha nepal earthquake however was southeast directed with a southwest directed slip and its mw 7 3 aftershock on may 12 also showed a similar slip direction post 2015 we revisited the 1991 uttarkashi mw 6 7 and the 1999 chamoli mw 6 5 earthquakes in india both of which had originated on the mht flat but show ssw directed slips as reported in this study ruptures of both these earthquakes fell short of reaching the mft just as the historically documented 1803 earthquake but their shaking effects were felt in the southern plains these observations compel us to conclude that the varying rupture modes exhibited by the himalayan earthquakes are controlled primarily by the geometry of the flat ramp flat system

genesis and implication of soft sediment deformation structures in high energy fluvial deposits of the alaknanda valley garhwal himalaya india abstract valley fill terraces and fluvio lacustrine sediment successions were investigated for the nature and type of soft sediment deformation structures ssds in the alaknanda valley of the garhwal himalaya based on their morphologies sediment characteristics and comparison with existing data on ssds these features are classified into seismic and aseismic categories the study indicates that despite the terrain being in the seismically active domain of the central himalaya the majority of the deformation structures seem to have been generated aseismically we attribute their genesis to uneven loading slope failure and most importantly turbulent flow and sudden loading by flash floods the study suggests that a cautious approach is needed before assigning a seismic origin to deformation structures in sediments deposited in high energy fluvial systems

homogenization of earthquake catalog for northeast india and adjoining region a catalog for northeast india and the adjoining region for the period 1897 2009 with 4 497 earthquakes events is compiled for homogenization to moment magnitude m w gcmt in the magnitude range 3 8 7 relations for conversion of m b and m s magnitudes to m w gcmt are derived using three different methods namely linear standard regression inverted standard regression isr and orthogonal standard regression osr for different magnitude ranges based on events data for the catalog period 1976 2006 the osr relations for m s to m w gcmt conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported in other studies since the number of events with magnitude 7 for this region is scanty we therefore considered whole india region to obtain the regression relationships between m w gcmt and m s isc a relationship between m w gcmt and m w neic is also obtained based on 17 events for the range 5 2 magnitude 6 6 a unified homogeneous catalog prepared using the conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast india and the adjoining region

the moho of north america a brief review focused on recent studies abstract recent national programs in canada lithoprobe and the u s earthscope are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution more modest but significant results are also being produced in and about mexico this paper primarily focuses on results published since 2005 and presents an updated moho map of north america this overview of crustal structure does reveal a number of interesting observations for example two buried distinct crustal blocks have been discovered in the past 20 years one was caught in a precambrian suture zone in canada and the other is buried under the gulf coast region and is still of unknown origin the precambrian assembly of the continent has been documented by the mapping of numerous suture zones and shallow portions of subducted slabs have been preserved in several cases not surprisingly the internal structure of these suture zones is complex and highly variable isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations specifically the correlation of crustal thickness with elevation is only approximate at best several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast vp 7 0 km s rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the mid continent rift system to the broad region of extension in the basin and range province crustal structure along the active modern western margin of north america is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism we clearly still have a lot to learn about the structure and evolution of this continent

isotopic evidence for preservation of cordilleran lithospheric mantle during the sevier laramide orogeny western united states it has been inferred that sevier laramide flat subduction imparted a large basal shear traction force to the overriding north american plate resulting in laramide rocky mountain foreland deformation and significant thinning of cordilleran lithosphere additional inferred consequences include regional refrigeration of cordilleran crust and suppression of synorogenic extensional collapse nd isotopic data from cenozoic mafic volcanic rocks indicate that normal thickness lithospheric mantle was preserved beneath the cordilleran craton from precambrian to late cenozoic time therefore cordilleran lithosphere was not thinned significantly and extensional collapse of orogenically thickened crust was not suppressed by refrigeration analogy with the south american cordillera suggests that flat subduction does not apply significant shear stress to the base of overriding plate lithosphere beyond the fore arc region and therefore does not mechanically thin overriding plate lithosphere except in the fore arc region the principal result of flat subduction was enhanced mechanical coupling between the underriding and overriding plates along the fore arc region this increased the horizontal end load due to relative plate convergence placed on the north american plate horizontal end load stress was transmitted laterally across both 1 a hinterland that had attained maximum crustal thickness and 2 the rigid colorado plateau into the laramide rocky mountain foreland early tertiary waning of plate convergence rates then allowed radial extensional collapse of the southern cordilleran region to drive the colorado plateau block northward resulting in late laramide rocky mountain foreland deformation

spatial mapping of earthquake hazard parameters in the hindukush pamir himalaya and adjacent regions implication for future seismic hazard abstract the study deals spatial mapping of earthquake hazard parameters like annual and 100 years mode along with their 90 probability of not being exceeded nbe in the hindukush pamir himalaya and adjoining regions for this purpose we applied a straightforward and most robust method known as gumbel s third asymptotic distribution of extreme values giii a homogeneous and complete earthquake catalogue during the period 1900 2010 with magnitude mw 4 0 is utilized to estimate these earthquake hazard parameters an equal grid point mesh of 1 longitude x 1 latitude is chosen to produce detailed earthquake hazard maps this performance allows analysis of the localized seismicity parameters and representation of their regional variations as contour maps the estimated result of annual mode with 90 probability of nbe is expected to exceed the values of mw 6 0 in the sulaiman kirthar ranges of pakistan and northwestern part of the nepal and surroundings in the examined region the 100 years mode with 90 probability of nbe is expected to exceed the value of mw 8 0 in the hindukush pamir himalaya with caucasus mountain belt the sulaiman kirthar ranges of pakistan northwestern part of the nepal and surroundings the kangra himanchal pradesh and kashmir of india the estimated high values of earthquake hazard parameters are mostly correlated with the main tectonic regimes of the examined region the spatial variations of earthquake hazard parameters reveal that the examined region exhibits more complexity and has high crustal heterogeneity the spatial maps provide a brief atlas of the earthquake hazard in the region

dikes sills and stress regime evolution during emplacement of the jagged rocks complex hopi buttes volcanic field navajo nation usa abstract the dikes and related intrusions formed below small volcanoes in volcanic fields are remnants of the simplest volcanic plumbing systems their geometry is controlled by interaction of magma driven cracks with country rock and reveals regional structural and stress patterns at the time of their emplacement the shallow stress field however may change during the time an intrusion complex is emplaced in response to addition or removal of magma and country rock during associated surface eruptions the jagged rocks complex in the miocene hopi buttes volcanic field navajo nation arizona is exposed 300 350 m below the pre eruptive surface it comprises a group of generally nw se striking dikes punctuated in places by buds a saucer like intrusion larger pyroclastic massifs and a diatreme we made measurements of 13 dikes divided into 172 segments with thicknesses from 8 to 122 cm mean 43 cm and lengths of 60 to 780 m several sills and inclined sheets in places are thicker than dikes having mean thicknesses of 48 cm and 73 cm respectively dikes typically show straight parallel and en echelon patterns while sills and inclined sheets are curved the northwestern dikes differ from the rest in containing large mafic crystals and are inferred to have been emplaced after the others we find that the strike of the overall complex dikes and other sheets elongate massifs and aligned sub cylindrical bodies reflects a crystalline basement control that is evident throughout hopi buttes over the period of the complex s emplacement local stress patterns were not stable we infer that excavation of deep maar craters and perhaps the construction of a scoria cone at the surface modified the local stress patterns to favor emplacement of sills and en echelon dikes later in the complex s evolution in contrast to simple straight dikes as the complex first formed

3 d structure of the rio grande rift from 1 d constrained joint inversion of receiver functions and surface wave dispersion the southern terminus of the rio grande rift region has been poorly defined in the geologic record with few seismic studies that provide information on the deeper rift structure in consequence important questions related to tectonic and lithospheric activity of the rio grande rift remain unresolved to address some of these geological questions we collect and analyze seismic data from 147 earthscope transportable array usarray and other seismic stations in the region to develop a 3 d crust and upper mantle velocity model we apply a constrained optimization approach for joint inversion of surface wave and receiver functions using seismic s wave velocities as a model parameter in particular we compute receiver functions stacks based on ray parameter and invert them jointly with collected surface wave group velocity dispersion observations the inversions estimate 1 d seismic s wave velocity profiles to 300 km depth which are then interpolated to a 3 d velocity model using a bayesian kriging scheme our 3 d models show a thin lower velocity crust anomaly along the southeastern rio grande rift a persistent low velocity anomaly underneath the colorado plateau and basin and range province and another one at depth beneath the jemez lineament and the southern rgr

geophysical constraints on the crustal structure of the southern rio grande rift abstract evidence of geologic activity still occurring in the rio grande rift rgr includes quaternary faulting seismicity and widening at a small rate we map the crustal thickness and seismic velocity ratio to generate constrained crustal model cross sections that highlight the regional extension of the southern rgr srgr specifically we computed receiver functions and receiver function stacks for 147 stations from earthscope usarray transportable array and previously collected data in the southwestern united states and interpolated the crustal and velocity results using a kriging interpolation scheme we include a new optimized gravity inversion approach using the receiver function results as a constraint for inverted density profiles we produce constrained crustal models that characterize the srgr as showing a shallower moho 30 km in the region of the srgr which is thicker than previously suggested the crust appears to be delaminated west of the rgr in the basin and range province and thicker east of the rgr toward the great plains with a denser lower crustal layer we also find that the delaware basin shows a significant geophysical anomaly likely due to thick saturated sediments given that there is no deep mantle anomaly determined from other studies in this region we suggest that rifting could be the result of small scale convection of the uppermost mantle and we conclude that the rgr is at a minimum the boundary between the basin and range province and the great plains perhaps reflecting the terminus of flat slab subduction

a study of source parameters site amplification functions and average effective shear wave quality factor qseff from analysis of accelerograms of the 1999 chamoli earthquake himalaya the accelerograms of the 1999 chamoli earthquake and nine of its aftershocks which occurred in uttaranchal himalaya have been analyzed to investigate their source parameters the site amplification functions and the average effective shear wave quality factor qseff in the region the fault plane solution of the main shock is obtained using the spectral amplitudes of sh waves approximated by transverse components of accelerograms of the high energy packets observed in the accelerograms of the main shock it is found to be comparable with the reported solutions in other studies similarly the other source parameters viz seismic moment 5 03 1 7 1025 dyne cm stress drop 65 bars source duration 5 2 s and moment magnitude 6 4 estimated for the main shock are consistent with the values obtained in other studies the stress drops estimated for the aftershocks vary from 23 bars to 153 bars and the seismic moment from 1 4 1023 dyne cm to 2 9 1023 dyne cm the average estimated values of the effective shear wave quality factor qseff vary from 655 359 in the uttaranchal sector of himalaya and 1475 130 in the delhi region in general the qseff value increases with an increase in the epicentral distance reflecting the penetration of the waves into deeper layers of the crust as the epicentral distance of the observation point increases these values of qseff indicate that in general the curst is at low temperatures that will promote brittle behavior and conditions for episodic failure as compared to creep under the accumulated strains from plate collision at the himalaya plate boundary the site amplification characteristics at sites have been identified from the frequency bands of significant amplification observed in the spectral ratios of the horizontal to the vertical component records the decay of peak ground acceleration pga values with distance has been investigated using the empirical regression curves vis a vis the site amplification factors

crustal structure of the northwestern basin and range province from the 1986 program for array seismic studies of the continental lithosphere seismic experiment the basin and range province of the western united states is characterized by active east west extension at strain rates of 1 cm yr 1 high regional heat flow of 90 mw m 2 and widespread late cenozoic bimodal rhyolitic basaltic magmatism the 1986 program for array seismic studies of the continental lithosphere basin and range seismic experiment imaged a portion of northwestern nevada to determine the crustal structure and to assess reported differences between refraction versus reflection determinations of moho depth and how the crustal composition and structure has been influenced by volcanic and extension mechanisms our interpretation of the refraction wide angle reflection data suggests that the crust is fairly uniform in thickness and varies by less than 5 km over the 280 km east west profile and 3 km over its 220 km north south length we characterize the velocity structure by five layers 1 an upper most crust composed of sedimentary rocks and basement that has an average velocity of 5 7 km s i 2 a middle crust that extends to a depth of 18 22 with an average velocity of 6 1 km s 1 3 a 10 12 km thick lower crust with an average velocity of 6 6 km s 1 4 a 2 5 km thick transitional crust mantle boundary defined by a 7 6 km s l velocity and 5 an upper mantle with an average pn velocity of 7 9 8 0 km s 1 these data show a uniformily thick crust of 28 km 5 km beneath northwestern nevada and a lack of evidence for significant low velocity crustal layers in general the entire crustal column exhibits uniform positive velocity gradients of 0 02 0 04 s the midcrustal discontinuity is interpreted as a small velocity increase of 0 2 km s l at 18 km depth the absence of a significant midcrustal reflection and the presence of large velocity gradients throughout the crust arises either from 1 a systematic increase in mafic composition with depth or 2 possibly high lower crustal pore pressure that acts to decrease the velocity contrast across the midcrustal boundary our interpreted seismic velocity structure is consistent with a broad range of bulk compositions for the crust upper crustal velocities are consistent with bulk compositions that range from metasediments and granites at shallow depth to diorites at midcrustal levels while lower crustal velocities suggest bulk compositions that range from diorites and amphibolities at midcrustal depths to mafic granulites and gabbros at the base of the crust the uniform crustal thickness of 30 34 km in northwestern nevada is close to the crustal average for the basin and range province but is thin when compared to surrounding regions such as the sierra nevada and colorado plateau where crustal thickness is greater than 40 kin similarily northwestern nevada pn velocities of 7 9 8 0 km s 1 are near the province wide average of 7 9 km s l temperature corrected pn velocities from a 90 mw m 2 geotherm for the basin and range to 60 mw m 2 for the stable interior of the united states are within one standard deviation of the continental average of 8 05 km s i and suggest a uniform upper mantle composition across the basin and range in addition to these observations the homogeneity of the velocity structure beneath the western basin and range argues for a youthful moho and crust that has been reworked by province wide late cenozoic extension episodic magmatism and underplating

on the possibility of reservoir induced seismicity in the garhwal himalaya chander r 1991 on the possibility of reservoir induced seismicity in the garhwal himalaya eng geol 30 393 399 it is argued from a brief review of available evidence that the possibility of reservoir induced seismicity ris in the himalaya as a whole cannot be ruled out at the present time on the other hand a review of recent local investigations of small earthquakes mb less than 5 and teleseismic investigations of moderate earthquakes mb between 5 and 6 mainly occurring in the garhwal segment of the alpide himalayan seismic belt provides evidence that ris in the region can be anticipated while their epicentral belts coincide geographically the estimated focal depths of small and moderate earthquakes of the garhwal himalaya are in the ranges of 0 14 and 10 20 km respectively small earthquakes occur by reactivation of strike slip and reverse faults and moderate earthquakes occur on thrust faults elsewhere in the world ris has been observed most often in the crust at the depths where small earthquakes have been observed in the garhwal himalaya in addition ris has been experienced during the impoundment of reservoirs in strike slip and reverse fault environments while theoretical analyses indicate that if suitably located in relation to the reservoir even a thrust fault may be destabilised by impoundment

luminescence studies on neotectonic events in south central kumaun himalaya a feasibility study abstract results of a feasibility study on luminescence dating of neotectonic events as recorded in fault gouges and buried soils formed on landslide debris are reported it is suggested that clay mineralogical data on illite and chlorite can provide a reasonable estimate on the thermal excursion and hence on resetting of the luminescence clock during faulting the thermoluminescence ages are consistent with the available radiocarbon ages and have been used to infer that naini lake was formed at ca 40 50 ka

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

transverse tectonics structures in the garhwal himalaya corridor inferred from 3d inversion of magnetotelluric profile data in the garhwal himalayan corridor ghc we recorded the magnetotelluric mt data at 40 sites in three phases out of these 40 sites useful tipper or vertical magnetic field transfer function vtf data was available only at 19 sites the resistivity model obtained from 3d inversion of the mt data is used to investigate the existence of transverse tectonic structures in the garhwal himalaya through a synthetic inversion experiment on scattered data over a profile like our ghc profile we have demonstrated that the mt data can be used to qualitatively infer about the off profile resistivity structures within about 20 km from the profile we carried out several 3d inversion experiments using different subsets of full impedance tensor and vtf responses individually and jointly to arrive at the final resistivity model the 2d profile section of our 3d resistivity model explains the thrust tectonic and flat ramp flat geometry of the main himalayan thrust mht furthermore the inverted model delineated delhi haridwar ridge dhr as a highly resistive 1000 m feature beneath the low resistive 50 m sediments of the indo gangetic plain igp the dhr continues up to the inner lesser himalayan region and it is bounded by two conductive 10 m fluid saturated fractured zones situated off profile and these run nearly parallel to the dhr from the electrical image of the dhr and of the associated conducting feature which have the geoelectric strike of n13 e we inferred that these features are transverse to the main himalayan arc

contrasting lithospheric signatures across the western united states revealed by sp receiver functions abstract to explore how lithospheric structure varies between tectonic and magmatic terranes of the western united states we use observations of shear to compressional wave conversions across lithospheric velocity interfaces with a newly developed automatic method designed to take advantage of the earthscope transportable array and other broadband seismic arrays deployed across the region and an optimized deconvolution technique based on the extended time multi taper method we map variations in the depth to the seismic moho lithosphere asthenosphere boundary lab and mid lithospheric discontinuities mlds beneath areas that have undergone substantial extension in the neogene including the eastern great basin the southern basin and range and the southern rio grande rift we detect strong sp conversions across a relatively shallow 60 80 km seismically defined lab we detect sp conversions across an 80 90 km depth discontinuity beneath the high rockies which we interpret as the seismically defined lab beneath areas that have remained relatively undeformed including the wyoming craton and the great plains craton we detect sp conversions in the 90 140 km depth range that are substantially weaker and more distributed in depth than those beneath less stable regions beneath the colorado plateau sp ccp stacks show that lithospheric thinning has accompanied magmatic encroachment and the lab beneath the margins of the plateau is indistinguishable from the lab of the surrounding extensional provinces in contrast beneath central and northern colorado plateau weaker sp conversions are observed in the 90 140 km depth range the observed variations in lithospheric structure across structural blocks with different magmatic and deformational histories imply that 1 both mechanical thinning and magmatic and thermal erosion have likely contributed to the thin lithosphere observed in the basin and range and southern rio grande rift 2 at the margins of the colorado plateau and beneath the high rockies where extension has been relatively minor strong and shallow seismic labs indicate magmatic alteration of the lithosphere 3 mlds seen in comparatively thick stable lithosphere produce weaker sp conversions and are often more distributed in depth than seismically observed labs in regions of thin lithosphere 4 mlds and weak deep phases consistent with a seismic lab are sometimes observed together

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard