geological implications of the 0212 earthquake in 2014 at the tatun volcano group of taiwan synergistic effects of volcanic and faulting activities abstract on february 12 2014 an ml 4 2 earthquake named 0212 eq occurred at the tatun volcano group tvg in northern taiwan seismic data from both the regional broadband array in taiwan and a local dense seismic network in the tvg indicate that the 0212 eq was located at a depth of 4 3 km near shamoshan one of the latest eruptive units in the tvg referring to the aftershocks surrounding the 0212 eq we further found that 1 they formed a linear seismic zone dipping 50 towards the southeast to reach the shanchiao fault that cuts through the tvg 2 focal mechanism of more than half of the larger aftershocks md 1 5 matched this linear seismic zone for a normal faulting and 3 the seismic b value was calculated to be 3 55 they are used to delineate the geometry of the shanchiao fault at the upper crust and to infer that localized geothermal fluid might have affected the activity of aftershocks as manifested by the very high seismic b value the strongly compensated linear vector dipole of the centroid moment tensor suggests the 0212 eq had a non double couple source resulted from the gravitational collapse thus we conclude that the 0212 eq was a combined synergistic effect of a collapsed reservoir filled with volcanic fluids and faulting activities along the shanchiao fault

engineering applications of strong ground motion simulation abstract the formulation validation and application of a procedure for simulating strong ground motions for use in engineering practice are described the procedure uses empirical source functions derived from near source strong motion recordings of small earthquakes to provide a realistic representation of effects such as source radiation that are difficult to model at high frequencies due to their partly stochastic behavior wave propagation effects are modeled using simplified green s functions that are designed to transfer empirical source functions from their recording sites to those required for use in simulations at a specific site the procedure has been validated against strong motion recordings of both crustal and subduction earthquakes for the validation process we choose earthquakes whose source models including a spatially heterogeneous distribution of the slip of the fault are independently known and which have abundant strong motion recordings a quantitative measurement of the fit between the simulated and recorded motion in this validation process is used to estimate the modeling and random uncertainty associated with the simulation procedure this modeling and random uncertainty is one part of the overall uncertainty in estimates of ground motions of future earthquakes at a specific site derived using the simulation procedure the other contribution to uncertainty is that due to uncertainty in the source parameters of future earthquakes that affect the site which is estimated from a suite of simulations generated by varying the source parameters over their ranges of uncertainty in this paper we describe the validation of the simulation procedure for crustal earthquakes against strong motion recordings of the 1989 loma prieta california earthquake and for subduction earthquakes against the 1985 michoacan mexico and valparaiso chile earthquakes we then show examples of the application of the simulation procedure to the estimatation of the design response spectra for crustal earthquakes at a power plant site in california and for subduction earthquakes in the seattle portland region we also demonstrate the use of simulation methods for modeling the attenuation of strong ground motion and show evidence of the effect of critical reflections from the lower crust in causing the observed flattening of the attenuation of strong ground motion from the 1988 saguenay quebec and 1989 loma prieta earthquakes

modelling the effect of time dependent river dune evolution on bed roughness and stage this paper presents an approach to incorporate time dependent dune evolution in the determination of bed roughness coefficients applied in hydraulic models dune roughness is calculated by using the process based dune evolution model of paarlberg et al 2009 and the empirical dune roughness predictor of van rijn 1984 the approach is illustrated by applying it to a river of simple geometry in the 1 d hydraulic model sobek for two different flood wave shapes calculated dune heights clearly show a dependency on rate of change in discharge with time dunes grow to larger heights for a flood wave with a smaller rate of change bed roughness coefficients computed using the new approach can be up to 10 higher than roughness coefficients based on calibration with the largest differences at low flows as a result of this larger bed roughness computed water depths can be up to 15 larger at low flow the new approach helps to reduce uncertainties in bed roughness coefficients of flow models especially for river systems with strong variations in discharge with time

inversion of the rupture process and high frequency radiation of the 2017 jiuzhaigou earthquake northeastern tibetan plateau abstract we studied the low and high frequency source processes of the 2017 jiuzhaigou earthquake and focused on when and where the high frequency 2 0 10 0 hz seismic energy was radiated in relation to the low frequency 0 02 0 5 hz seismic energy the low frequency source processes were jointly inverted using teleseismic p and sh broadband waves combined with near field strong motion data a three dimensional model considering real topography was used to compute the near field green s function the high frequency wave radiation was inversed using the envelope of acceleration seismograms of near field records and the empirical green s function by the differential evolution algorithm the results showed the 2017 jiuzhaigou earthquake was a typical strike slip earthquake with a seismic moment of about 6 9 1018 n m and maximum slip of about 1 5 m during the 2 s following the initial rupture the earthquake radiated large high frequency waves but small low frequency waves then the rupture broke the high stress drop area in the up dip direction of the hypocenter generating an obvious asperity located just above the hypocenter about 60 of the seismic moment of the earthquake was released during about 2 6 s after initiation of the rupture the high frequency radiation areas were mostly located on the lower periphery of the asperity in accordance with the complementary relationship between the distribution of high frequency waves and zones of large slip which might be attributable to both the initiation of the rupture and the breaking of the high stress drop area parts of the high frequency radiation areas overlapped the lower part of the asperity where the high frequency radiation occurred about 2 s earlier than the low frequency radiation the stress drop of the 2017 jiuzhaigou earthquake was considerably lower than average for global intraplate earthquakes but similar to that of the 2013 lushan earthquake

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

sand dune geometry of large rivers during floods the geometry of lower regime bed forms in several large sand bed rivers is investigated during average and flood conditions the van rijn method is revised because it generally underpredicts the dune height of most large rivers around the world during floods in large sand bed rivers upper regime plane bed is not necessarily obtained when t 25 both parameters describing dune height and dune steepness do not decrease as the transport stage parameter t increases in the range 10 t 25 the analysis of bed form data during large floods on the meuse river and the rhine river branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant a reasonable approximation of the wavelength is 6 5 h where h is the flow depth the dune height varies as a function of the depth h and median grain size d50 estimates can be obtained by 2 5 h 0 7d0 350

temporal variations of gas compositions of fumaroles in the tatun volcano group northern taiwan article i nfo he 4 he geochemical monitoring hydrothermal activity is common in the tatun volcano group of northern taiwan helium isotopic compositions of fumarolic samples show that mantle component occupies more than 60 in the previous study along with recent seismic results a magma reservoir is inferred to have existed beneath the area of da you keng where fumarolic venting is the most active in tatun volcano group progressive increases of hcl concentrations and so2 h2s ratio in fumaroles from da you keng have been observed since august 2004 the hcl concentration changed from almost the detection limit to thousands of ppm even up to 30 000 ppm so2 h2s ratios varied from almost 0 to 3 hence so2 became the dominated s species in this area these variations were accompanied by rising temperature of fumaroles in the tatun volcano group especially in the area of da you keng from boiling point to 131 c meanwhile 3

contribution of radar interferometry to a two step inversion of the kinematic process of the 1992 landers earthquake we study the rupture process of the 1992 landers earthquake to limit the trade off between slip amplitude and rupture time that affects solutions using only seismological data we adopt a two step approach we first constrain the slip distribution and its uncertainty by independent geodetic data to recover in the second step the temporal details of the rupture propagation the first step consists of an inversion of interferometric data and global positioning system measurements both independently and together to constrain slip distribution on a three segment fault model along both strike and dip direction we use a genetic algorithm to test the uniqueness of the solution and a least squares formulation to find the model which best fits the data we conclude from the results of these geodetic inversions that interferometric data are rich enough to access the slip distribution in the case of the landers earthquake since the surface deformations are more sensitive to shallow slip in our configuration the slip amplitude is better resolved near the surface than at depth the resulting slip distribution is in agreement with geological observations at the surface and confirms the heterogeneous nature of the landers earthquake most of the slip occurs at shallow depths on the homestead valley fault second segment with a maximum value of around 7 m another high slip zone is observed on the johnson valley fault first segment at 8 km depth in the second step we invert strong motion data with the a priori final slip amplitude and its uncertainty deduced from geodetic data to constrain the time history of the rupture process this second step emphasizes a strong variation of the temporal development of the earthquake fast rupture front velocities appear within high slip zones and the rupture slows when it encounters a resistance along the fault on average the rupture front propagates with velocities close to the s wave velocity and terminates about 20 s after initiation the large variations in both slip amplitude and rupture velocity suggest that the rupture process is better described by successively breaking asperities than by a pulse propagating with constant velocity

rupture history of the 2013 mw 6 6 lushan earthquake constrained with local strong motion and teleseismic body and surface waves 1 the rupture history of the 20 april 2013 mw 6 6 lushan china earthquake is constrained by inverting waveforms of local strong motion teleseismic broadband body waves and long period surface waves this earthquake ruptured a blind thrust fault oriented n210 e along the longmenshan fault zone and dipping 40 to the nw the inverted slip distribution is heterogeneous dominated by a slip patch with a roughly right triangular shape which spans a depth range of 5 20 km and accounts for two thirds of the total seismic moment 8 9 1018 n m the rupture initiated roughly at the middle of the triangle s hypotenuse and during the first 4 s propagated mainly in along strike and downdip directions toward a peak slip of 1 2 m despite a large number of fatalities and economic loss the estimated static and apparent stress drops of the lushan earthquake are 1 5 mpa and 0 35 mpa considerably low with respect to other similar intraplate earthquakes

resolution analysis of finite fault source inversion using one and three dimensional green s functions 2 combining seismic and geodetic data using numerical tests for a prescribed heterogeneous earthquake slip distribution we examine the importance of accurate green s functions gf for finite fault source inversions which rely on coseismic gps displacements and leveling line uplift alone and in combination with near source strong ground motions the static displacements while sensitive to the three dimensional 3 d structure are less so than seismic waveforms and thus are an important contribution particularly when used in conjunction with waveform inversions for numerical tests of an earthquake source and data distribution modeled after the 1994 northridge earthquake a joint geodetic and seismic inversion allows for reasonable recovery of the heterogeneous slip distribution on the fault in contrast inaccurate 3 d gfs or multiple 1 d gfs allow only partial recovery of the slip distribution given strong motion data alone likewise using just the gps and leveling line data requires significant smoothing for inversion stability and hence only a blurred vision of the prescribed slip is recovered although the half space approximation for computing the surface static deformation field is no longer justifiable based on the high level of accuracy for current gps data acquisition and the computed differences between 3 d and half space surface displacements a layered 1 d approximation to 3 d earth structure provides adequate representation of the surface displacement field however even with the half space approximation geodetic data can provide additional slip resolution in the joint seismic and geodetic inversion provided a priori fault location and geometry are correct nevertheless the sensitivity of the static displacements to the earth structure begs caution for interpretation of surface displacements particularly those recorded at monuments located in or near basin environments

preliminary analysis of volcanoseismic signals recorded at the tatun volcano group northern taiwan 1 the tatun volcano group lies at the northern tip of taiwan only 15 km north of the capital taipei a seismic array consisting of 5 stations equipped with both broadband and short period sensors was installed in 2003 in order to monitor the seismic activity of the area it recorded a variety of events including common volcano tectonic earthquakes and volcanoseismic signals like tornillos short duration monochromatic events 10 15 s and long duration spasmodic bursts 15 min an analysis of the complex frequencies of the tornillo monochromatic signals shows that q values are of the order of several hundreds based on the model of a fluid filled crack such q values can result from the oscillations of a crack containing a misty or dusty gas these observations put into doubt the long standing suggestion that the tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area

envelope inversion analysis for high frequency seismic energy radiation from the 2011 mw 9 0 off the pacific coast of tohoku earthquake abstract i study s wave energy radiation in higher frequencies of 1 8 hz from the 2011 m w 9 0 off the pacific coast of tohoku japan earthquake hereafter called the tohoku oki earthquake based on a seismogram envelope inversion method i first evaluate two medium parameters of scattering attenuation and intrinsic absorption for s waves using spatial and temporal distributions of seismic energy from aftershock records which are necessary for calculating green s functions next applying the envelope inversion method to 27 near field strong motion records from the mainshock i estimate the s wave energy radiation from 40 subfaults on the fault of 500 km 250 km each subfault is allowed to rupture for eight consecutive source time windows rupture velocity and the duration of energy radiation for each time window are determined by a grid search to be 2 5 km s and 8 0 s respectively energy radiated from the entire fault is 5 8 10 16 j for 1 2 hz 4 5 10 16 j for 2 4 hz 1 5 10 16 j for 4 8 hz and totaling 1 2 10 17 j in the 1 8 hz range strong energy emanated twice from greater depths of the off miyagi region corresponding to two peaks seen at the northern stations and energy radiation at greater depths off the fukushima ibaraki border is compatible with a single peak found at the southern stations strong high frequency radiations at greater depths strikingly contrast with large slips at shallower depths estimated in lower frequencies this frequency dependent rupture may accord with structural changes along the dip direction online material snapshots of high frequency energy radiation from the fault plane and results of estimating scattering parameters by the multiple lapse time window analysis in 1 2 and 2 4 hz

estimation of high frequency wave radiation areas on the fault plane by the envelope inversion of acceleration seismograms we have developed an inversion method to estimate high frequency wave radiation areas on the fault plane it is very difficult to perform a source inversion for seismic waveforms whose frequencies are higher than 1 hz because of two problems one is the difficulty in obtaining green s functions that are accurate enough for such high frequencies and the other is that involved in doing a waveform inversion for such oscillatory data we overcame these problems by using aftershock records as empirical green s functions and by using the envelopes of acceleration seismograms as the inversion data instead of waveforms envelopes were calculated by smoothing the acceleration seismograms with a running root mean square time window we applied this method to the 1993 kushiro oki japan earthquake mw 7 6 which occurred on a horizontal fault plane inside the pacific plate subducting beneath the north american plate we adopted the mjma 4 9 aftershock as the empirical green s function event we bandpass filtered 2 0 10 0 hz the strong motion acceleration seismograms at three stations and calculated the envelopes by smoothing with a 5 0 s window length the 40 km 60 km fault plane was divided into 4 6 meshes and the acceleration radiation intensity and rupture time of each mesh were obtained by the inversion the results are as follows 1 high frequency waves radiated weakly around the rupture starting point but radiated mainly near the periphery of the fault plane an area with particularly strong radiation intensity of high frequency waves is seen at the edge of the fault plane about 30 km southwest of the rupture starting point its size is about 20 km 20 km 2 the distribution of high frequency radiation intensity and slip distribution are complementary to each other that is the radiation of high frequency waves was strong in those areas where that of low frequency waves was weak

tide driven dune migration and sediment transport on an intertidal shoal in a shallow estuary in devon uk abstract the migration of subaqueous dunes was investigated over a 3 month period on an intertidal shoal near the mouth of the shallow mixed wave tide dominated avon estuary on the channel coast of southwest britain the dunes characterised by heights and lengths of 0 05 0 2 m and 5 10 m respectively migrated 10 20 m over the 3 month period representing an average volumetric sediment transport rate of 0 5 m 3 per unit meter width compared to equilibrium models of dune dimensions based on the water depth the dune height was predicted well but the dune length was under predicted sediment transport on the intertidal shoal was controlled by a distinct tidal asymmetry with maximum flow velocities during flood 0 4 0 5 m s 1 significantly stronger than during ebb 0 2 0 3 m s 1 predicted bedload transport based on theory underestimates the actual transport and this is attributed to the modest flow velocities encountered and perhaps the importance of suspended load transport however when empirically calibrated and related to tide range the transport equation adequately accounts for observed rates using nearby tidal observations the predicted annual volumetric sediment transport rate is 2 6 m 3 per unit meter width this estimate compares favourably with the annual volumetric sediment transport based on dune measurements 2 0 m 3 using the notion that the transport rate decreases on the intertidal shoal in the up estuary direction to zero at its up estuary end a vertical accretion of 0 5 cm yr 1 was predicted the main implication of our study is that accurate and well designed process measurements of dune dynamics and tidal currents can provide useful information on the longer term evolution of intertidal shoals in sandy shallow flood dominant estuaries

focal mechanisms and aftershock locations of the songpan earthquakes of august 1976 in sichuan china the precursory swarm three mainshocks m 7 2 6 7 7 2 and aftershocks of the songpan earthquakes have been reanalyzed using both local and teleseismic data the three mainshocks of this sequence occurred on the huya fault over a 7 day period relocations of the aftershocks using local arrival times show that three fault strands were activated during this sequence each mainshock occurred on a separate strand each one south of the strand activated in the previous mainshock and the aftershock zones of each mainshock appear to abut rather than overlap fault plane solutions determined by matching teleseismic p waveforms at world wide standard seismograph network stations with synthetic seismograms are consistent with the observed aftershock zones the first and third mainshocks m 0 1 3 10 19 and 8 4 10 18 n m respectively showed almost identical senses of motion a combination of reverse and left lateral strike slip motion on parallel strands striking n15 w that were separated by a large rightstepping en echelon offset the second mainshock m 0 4 0 10 18 n m occurred in this offset on a fault at a steep angle 125 to the other two strands and showed almost pure reverse motion differences in the orientations of the slip vectors of the three mainshocks show that the first mainshock increased the normal and shear stresses on the fault segment that moved in the second mainshock and that the second mainshock decreased the normal stress on the fault segment activated by the third mainshock these changes in normal stresses may have given rise to the longer time between the first and second events 5 days as compared with the time between the second and third events 30 hours a precursory swarm that preceded the songpan sequence by 3 years occurred in a volume that surrounded the northernmost part of the planar aftershock zone the time between the start of the swarm and the mainshocks and the magnitude of the largest event in the swarm are similar to those seen for precursory swarms in soviet central asia

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany i sedimentology and morphology the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine germany bed sediments dune geometry bedform migration rates and the internal structure of dunes are considered in this paper hydrodynamic and sediment transport data are considered in a companion paper the pebbles and cobbles d50 of 10 mm of the flat lag layer are rarely entrained dunes consist of well sorted medium to coarse sand d50 of 0 9 mm small pebbles move over the dunes by overpassing but there is a degree of size and shape selectivity populations of ripples in sand d50 0 6 mm and small and large dunes are separated by distinct breaks in the bedform length data in the regions of 0 7 1 m and 5 10 m ripples and small dunes may have sinuous crestlines but primarily exhibit two dimensional planforms in contrast large dunes are primarily three dimensional barchanoid forms ripples on the backs of small dunes rarely develop to maximum steepness small dunes may achieve an equilibrium geometry either on the gravel bed or as secondary dunes within the boundary layer on the stoss side of large dunes secondary dunes frequently develop a humpback profile as they migrate across the upper stoss slope of large dunes diminishing in height but increasing in length as they traverse the crestal region however secondary dunes more than 5 m in length are rare the dearth of equilibrium ripples and long secondary dunes is probably related to the limited excursion length available for bedform development on the parent bedforms large dunes with lengths between 20 m and 100 m do not approach an equilibrium geometry a depth limitation rather than a sediment supply limitation is the primary control on dune height dunes rarely exceed 1 m high in water depths of 4 m dune celerity increases as a function of the mean flow velocity squared but this general relationship obscures more subtle morphodynamics during rising river stage dunes tend to grow in height owing to crestal accumulation which slows downstream progression and steepens the dune form during steady or falling stage an extended crestal platform develops in association with a rapid downstream migration of the lee side and a reduction in dune height these diminishing dunes actually increase in unit volume by a process of increased leeside accumulation fed by secondary dunes moving past a stalled stoss toe a six stage model of dune growth and diminution is proposed to explain variations in observed morphology the model demonstrates how the development of an internal boundary layer and the interaction of the water surface with the crests of these bedload dominated dunes can result in dunes characterized by gentle lee sides with weak flow separation this finding is significant as other studies of dunes in large rivers have attributed this morphological response to a predominance of suspended load transport

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

statistical characterization of bed roughness due to bed forms a field study in the elbe river at aken germany 1 bed form geometry and dynamics in a straight section of the elbe river in germany is analyzed considering the measured bed surfaces as two dimensional random fields of bed elevations statistically derived roughness parameters are evaluated from high resolution digital elevation models which were available for a range of flow rates from low flows to floods the key results relate to the identification of characteristic scaling regions in the bed surface spectra and to observed relationships between water discharge and both the standard deviation and a factor of the 3 spectral law of bed elevations two dimensional second order structure functions of bed elevations are also analyzed to gain further insight into the spatial structure of sand wave beds in addition the interrelations between flow rate hysteresis and the statistical structure of bed forms as well as effects of channel modification by groynes are highlighted and discussed the reported results demonstrate that statistical parameters of bed forms may be used for characterization and prediction of flow dependent sand bed roughness

insar and gps derived coseismic deformation and fault model of the 2017 ms7 0 jiuzhaigou earthquake in the northeast bayanhar block abstract on 8 august 2017 a ms7 0 earthquake stroke the city of jiuzhaigou sichuan china the jiuzhaigou earthquake occurred on a buried fault in the vicinity of three well known active faults and this event offers a unique opportunity to study tectonic structures in the epicentral region and stress transferring here we present coseismic displacement field maps for this earthquake using descending and ascending sentinel 1a interferometric synthetic aperture radar insar data deformation covered an area of approximately 50 50 km with a maximum line of sight los displacement of 22 cm in ascending and 14 cm in descending observations on the west side of the source fault based on insar and global positioning system gps measurements both separately and jointly we constructed a one segment model to invert the coseismic slip distribution and dip angle of this event our final fault slip model suggests that slip was concentrated at an upper depth of 15 km there was a maximum slip of 1 3 m and the rupture was dominated by a left lateral strike slip motion the inverted geodetic moment was approximately 6 75 1018 nm corresponding to a moment magnitude of mw6 5 consistent with seismological results the calculated static coulomb stress changes indicate that most aftershocks occurred in stress increasing zones caused by the mainshock rupture the jiuzhaigou earthquake has brought the western part of the tazang fault 0 1 0 4 mpa closer to failure indicating an increasing seismic hazard in this region the coulomb stress changes caused by the 2008 mw7 8 wenchuan earthquake suggest that stress loading from this event acted as a trigger for the jiuzhaigou earthquake

did the 2008 mw 7 9 wenchuan earthquake trigger the occurrence of the 2017 mw 6 5 jiuzhaigou earthquake in sichuan china

integrated seismic source model of the 2015 gorkha nepal earthquake we compared spatiotemporal slip rate and high frequency around 1 hz radiation distributions from teleseismic p wave data to infer the seismic rupture process of the 2015 gorkha nepal earthquake for these estimates we applied a novel waveform inversion formulation that mitigates the effect of green s functions uncertainty and a hybrid backprojection method that mitigates contamination by depth phases our model showed that the dynamic rupture front propagated eastward from the hypocenter at 3 0 km s and triggered a large slip event centered about 50 km to the east it also showed that the large slip event included a rapid rupture acceleration event and an irregular deceleration of rupture propagation before the rupture termination heterogeneity of the stress drop or fracture energy in the eastern part of the rupture area where aftershock activity was high inhibited rupture growth high frequency radiation sources tended to be in the deeper part of the large slip area which suggests that heterogeneity of the stress drop or fracture energy there may have contributed to the damage in and around kathmandu

coseismic deformation of the 2001 mw 7 8 kokoxili earthquake in tibet measured by synthetic aperture radar interferometry the 14 november 2001 m w 7 8 kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left lateral kunlun fault in northern tibet interferometric synthetic aperture radar data from descending orbits along four adjacent tracks covering almost the entire rupture and 1 m pixel ikonos satellite images are used to map the rupture geometry and the surface displacements produced by the event interferograms are then inverted to solve for coseismic slip on the fault at depth the radar data show that the rupture connected the heituo fault where the earthquake initiated to the main kunlun fault cutting across a pull apart trough in between the two strike slip faults the fault model includes two vertical sections extending to a depth of 20 km and discretized into 5 km 5 km patches using a nonnegative least squares method that includes an appropriate degree of smoothing we solve for the left lateral slip on each fault patch our solution shows that the largest slip occurred at depths between 0 and 5 km reaching 8 m in two areas 200 and 250 km east of the earthquake epicenter significant slip took place below 10 km at both ends of the rupture slip appears to have been highly variable along the fault defining six sections of major moment release these sections correspond to six subsegments of the kunlun fault system defined from the surface morphology of the fault this suggests that fault geometry exerted a predominant influence on controlling the rupture propagation

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

compositions and flux of soil gas in liu huang ku hydrothermal area northern taiwan abstract soil co 2 flux has been considered a useful proxy to remotely monitor volcanic activity in a hydrothermal area within a safe distance the liu huang ku lhk area which is close to the taipei basin and many existing active fumaroles and hot springs was chosen for the first systematic soil gas study in a hydrothermal area of taiwan in 2004 and 2006 the soil co 2 flux was measured by the closed chamber method with a non dispersive infrared detector soil co 2 emission rate was estimated 19 8 0 2 t day 1 and 582 t km 2 day 1 in 2004 and 22 4 0 2 t day 1 and 659 t km 2 day 1 in 2006 respectively these values are close to those reported for other active high co 2 flux hydrothermal areas of the world it implies that magmatic gases are actively degassing from subsurface in northern taiwan helium and carbon isotopic data reveal that soil gas in lhk is mainly derived from the mantle and is mixed with a small amount of crustal and air components the abundance of soil co 2 shows a positive correlation with the 3 he 4 he ratios and total sulfur contents which are considered as magmatic sensitive indicators for the fumarolic samples therefore soil co 2 could be used as a good proxy for future monitoring of magmatic activity in this area

mapping of the high frequency source radiation for the loma prieta earthquake california waveform inversion has been successfully applied to map the spatial distribution of earthquake fault slip from strong motion records but its application has been restricted to a relatively lower frequency range of the data 5 hz generation is incoherent between neighboring patches on the fault we formulated an analytical model for calculating the envelope time history of the squared high frequency displacement seismogram this envelope time history is found through the line integration of the squared energy radiation intensity over the isochron using a recursive stochastic inversion scheme we determined both the lower frequency slip distributions from the low pass filtered strong motion displacement data and the higher frequency energy radiation intensity from the envelope of the squared high frequency displacement data on an extended fault for the 1989 loma prieta earthquake respectively our resulting lower frequency slip model shows that there are two main slip patches and little slip directly updip of the hypocenter one major slip zone located 10 km northwest of the hypocenter with predominant dip slip and the other located 12 km southeast of the hypocenter with predominant oblique slip our preliminary results of the high frequency energy radiation intensity inversion indicate three large high frequency sources and few smaller ones located on the outer periphery of the large slip zones this suggests that the high frequency energy sources are located along or near the boundaries of large slip zones which is consistent with the theoretical consideration that high frequencies are primarily generated from the rupture stopping areas or places with large slip variation

spatio temporal distribution of fault slip and high frequency radiation of the 2010 el mayor cucapah mexico earthquake 1 earthquake slip history and moment release are best resolved using long period seismic waves but details in the rupture process such as sharp changes in rupture velocity or direction can be imaged more clearly using higher frequency waves here we investigate the slip and the high frequency radiation histories of the 2010 el mayor cucapah baja california mexico earthquake mw 7 2 the slip distribution inferred from inversion of strong motion data between 0 02 and 0 25 hz indicates northwest propagating rupture followed by bilateral rupture for 40 s the sources of high frequency radiation between 0 3 and 2 hz inferred from back projection analysis using teleseismic data are adjacent to but not within the high slip patches from the finite slip model in time and space this implies relatively smooth rupture during the times and regions of maximum moment release as theoretical models have predicted high frequency radiation seems mostly associated with changes in rupture velocity or slip magnitude strong high frequency radiation is also found where the rupture propagated to a branch fault 50 km northwest of the hypocenter complementary constraints on both fault slip and high frequency radiation provide increased understanding of earthquake rupture mechanics and may help improve strong motion evaluation at high frequencies

effects of realistic surface topography on seismic ground motion in the yangminshan region of taiwan based upon the spectral element method and lidar dtm we combine light detection and ranging lidar digital terrain model dtm data and an improved mesh implementation to investigate the effects of high resolution surface topography on seismic ground motion based upon the spectral element method in general topography increases the amplitude of shaking at mountain tops and ridges whereas valleys usually have reduced ground motion as has been observed in both records from past earthquakes and numerical simulations however the effects of realistic topography on ground motion have not often been clearly characterized in numerical simulations especially the seismic response of the true ground surface here we use lidar dtm data which provide two meter reso lution at the free surface and a spectral element method to simulate three dimensional 3d seismic wave propagation in the yangminshan region in taiwan incorporating the effects of realistic topography a smoothed topographic map is employed beneath the model surface in order to decrease mesh distortions due to steep ground surfaces numerical simulations show that seismic shaking in mountainous areas is strongly affected by topography and source frequency content the amplification of ground motion mainly occurs at the tops of hills and ridges whilst the valleys and flat topped hills experience lower levels of ground shaking interaction between small scale to pographic features and high frequency surface waves can produce unusually strong shaking we demonstrate that topographic variations can change peak ground accel eration pga values by 50 in mountainous areas and the relative change in pga between a valley and a ridge can be as high as a factor of 2 compared to a flat surface response this suggests that high resolution realistic topographic features should be taken into account in seismic hazard analysis especially for densely populated moun tainous areas

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

low frequency submarine volcanic swarms at the southwestern end of the okinawa trough 1 a low frequency lf submarine volcanic swarm has been first observed at the southwestern end of the okinawa trough where some submarine volcanoes have recently been identified a swarm of more than 24 earthquakes was recorded at land seismic stations in taiwan between september 1st and september 4th 2006 these earthquakes without clear s arrivals were substantially different from other abundant tectonic earthquakes in the area the dominant frequency of around 1 or 2 hz recorded at all stations shows that the lf seismograms were generated by neither path nor site effects but directly from the source these lf earthquakes can be characterized as b type volcanic earthquakes which have been observed in some active volcanoes before significant eruptions the observations of these lf volcanic earthquakes beneath submarine volcanic cones and seamounts are strong indicator that some submarine volcanoes are still active at the southwestern end of the okinawa trough

a major hydrothermal reservoir underneath the tatun volcano group of taiwan clues from a dense linear geophone array a dense linear geophone array is deployed across the tatun volcano group tvg at the northern tip of taiwan where more than 7 million residents live in the taipei metropolis the array is composed of 50 geophones with a station spacing of 200 m in average and it is designed for striking in the nw se direction to record the many earthquakes in eastern taiwan where the philippine sea plate subducted beneath the eurasia plate the detailed examination of felt earthquakes shows consistent p wave delays are recorded at particular stations of the array the further forward modeling indicates there is a low velocity zone lvz at depths between 0 5 and 2 5 km beneath the major fumarole sites combining this preliminary result with previous studies including clustering seismicity volcanic earthquakes low resistivity zone strong degassing processes and shallow velocity structures we suggest that the lvz might be associated with the major hydrothermal reservoir at the tvg the identification of the hydrothermal reservoir by the lvz not only implies a potential volcanic threat such as phreatic eruptions in the future but also provides the possibility of sustainable geothermal resources for replacing traditional nuclear and fossil fuel power plants detailed images of the lvz and other volcanic structures will be obtained soon when dense geophone arrays with more than 600 geophones are deployed from 2020 to 2022

the 1994 northridge california earthquake investigation of rupture velocity risetime and high frequency radiation a hybrid global search algorithm is used to solve the nonlinear problem of calculating slip amplitude rake risetime and rupture time on a finite fault thirty five strong motion velocity records are inverted by this method over the frequency band from 0 1 to 1 0 hz for the northridge earthquake four regions of larger amplitude slip are identified one near the hypocenter at a depth of 17 km a second west of the hypocenter at about the same depth a third updip from the hypocenter at a depth of 10 km and a fourth updip from the hypocenter and to the northwest the results further show an initial fast rupture with a velocity of 2 8 to 3 0 km s followed by a slow termination of the rupture with velocities of 2 0 to 2 5 km s the initial energetic rupture phase lasts for 3 s extending out 10 km from the hypocenter slip near the hypocenter has a short risetime of 0 5 s which increases to 1 5 s for the major slip areas removed from the hypocentral region the energetic rupture phase is also shown to be the primary source of high frequency radiation 1 15 hz by an inversion of acceleration envelopes the same global search algorithm is used in the envelope inversion to calculate high frequency radiation intensity on the fault and rupture time the rupture timing from the low and high frequency inversions is similar indicating that the high frequencies are produced primarily at the mainshock rupture front two major sources of high frequency radiation are identified within the energetic rupture phase one at the hypocenter and another deep source to the west of the hypocenter the source at the hypocenter is associated with the initiation of rupture and the breaking of a high stress drop asperity and the second is associated with stopping of the rupture in a westerly direction

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

gravity monitoring of tatun volcanic group activities and inference for underground fluid circulations abstract the tatun volcano group tvg located on the northern coast of taiwan adjacent to the city of taipei experiences active hydrothermalism but has no historical record of volcanic eruption yet recent studies suggest that tvg is dormant active rather than extinct to monitor mass transfers and to gain further understanding of this volcanic area gravity variations have been recorded continuously since 2012 using a superconducting gravimeter and once every few months since 2005 using absolute gravimeters we analyze the continuous gravity time series and propose a model that best explains the gravity variations due to local groundwater redistribution by correcting these variations we identify gravity changes as large as 35 gal that occurred concomitantly to fluid pressure induced earthquakes and changes in the gas composition at dayoukeng one of tvg s fumaroles over 2005 2007 we examine several fluid movements that can match the gravity observations yet too few additional constraints exist to favor any of them in particular no significant ground displacements are observed when these gravity variations occurred on the other hand the model of gravity changes due to local groundwater redistribution can be routinely computed and removed from the ongoing time gravity measurements in order to quickly identify any unusual mass transfer occurring beneath tvg

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

high frequency radiation process during earthquake faulting envelope inversion of acceleration seismograms from the 1993 hokkaido nansei oki japan earthquake we investigate the process of high frequency 1 to 10 hz radiation on the fault plane of the 1993 hokkaido nansei oki japan earthquake mw 7 5 from the envelope inversion of strong motion acceleration seismograms for the analysis empirical green s functions are used because theoretical approach is not available for such high frequencies the source is modeled with two fault planes with different strike angles the rupture process of this earthquake is very complex in terms of high frequency wave generation the rupture which started on the northern fault plane had a delay of about 10 sec or propagated very slowly between the northern and southern fault planes high frequency wave radiation is large at the northern and southern edges of the source region deceleration of rupture is also observed there this is interpreted to be associated with stopping of rupture another high frequency wave radiation area is found at the center of the northern fault plane where discontinuity in the depth distribution of aftershocks suggests an existence of a barrier the areas of high and low frequency wave radiation are not correlated this is considered to result from the complexity of rupture process we cannot distinguish between westward and eastward dip of the southern fault plane because of one sided station distribution

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

dunes and associated sand transport in a tidally influenced sand bed channel fraser river british columbia dunes form annually on the sand bed of the tidally influenced south arm of fraser river british columbia bathymetric surveys along the center of the main channel throughout a snow melt freshet provided measurements of dune geometry and migration dune length height and steepness all increase with river discharge however lag between the highest flow conditions and development of the largest steepest dunes reflects the influence of antecedent flow conditions on dune geometry population averages of dune height and steepness ratio change more rapidly than dune length whilst coefficients of variation of dune height length and steepness ratio indicate high variability in dune geometry within the estuarine reach during periods of dune growth and decay unlike dune geometry dune migration rates display little lag with flow conditions the largest coefficients of variation for dune migration occur during periods of rapid change in discharge and tidal fall corresponding to the onset of rapid change in

effect of non migrating bars on dune dynamics in a lowland river as dunes and larger scale bed forms such as bars coexist in rivers the question arises whether dune dynamics are influenced by interaction with the underlying bed topography the present study aims to establish the degree in which dune characteristics in two and three dimensions are influenced by an underlying topography dominated by non migrating bars as a case study a 20km stretch in the waal river in the netherlands is selected which represents a sand bed lowland river at this location longitudinal training dams ltds have recently been constructed to ensure sufficient navigation depth during periods with low water levels and to reduce flood risk by using data covering two year long periods before and after ltd construction the robustness of the results is investigated before ltd construction dune characteristics show large variability both spatially and temporally with dunes being longer lower less steep and having a lower lee side angle when they are located on bar tops the correlation between dune characteristics and the underlying bed topography is disrupted by unsteady conditions for which the dunes are in a state of transition the bar pattern causes tilting of dune crest lines which may result from a transverse gradient in bed load sediment transport as a result of ltd construction the hydraulic and morphological conditions have changed significantly despite this the main conclusions still hold which strengthens the validity of the results

rupture history of the 2008 mw 7 9 wenchuan china earthquake evaluation of separate and joint inversions of geodetic teleseismic and strong motion data an extensive data set of teleseismic and strong motion waveforms and geodetic offsets is used to study the rupture history of the 2008 wenchuan china earthquake a linear multiple time window approach is used to parameterize the rupture because of the complexity of the wenchuan faulting three separate planes are used to represent the rupturing surfaces this earthquake clearly demonstrates the strengths and limitations of geodetic teleseismic and strong motion data sets geodetic data static offsets are valuable for determining the distribution of shallower slip but are insensitive to deeper faulting and reveal nothing about the timing of slip teleseismic data in the distance range 30 90 generally involve no modeling difficulties because of simple ray paths and can distinguish shallow from deep slip teleseismic data however cannot distinguish between different slip scenarios when multiple fault planes are involved because steep takeoff angles lead to ambiguity in timing local strong motion data on the other hand are ideal for determining the direction of rupture from directivity but can easily be over modeled with inaccurate green s functions leading to misinterpretation of the slip distribution we show that all three data sets are required to give an accurate description of the wenchuan rupture the moment is estimated to be approximately graphic 1 with the slip characterized by multiple large patches with slips up to 10 m rupture initiates on the southern end of the pengguan fault and proceeds unilaterally to the northeast upon reaching the cross cutting xiaoyudong fault rupture of the adjacent beichuan fault starts at this juncture and proceeds bilaterally to the northeast and southwest 1 embed inline graphic 1 gif

the combined inversion of seismic and geodetic data for the source process of the 16 october 1999 mw 7 1 hector mine california earthquake we investigate the source process of the m w 7 1 hector mine earthquake by inverting broadband regional and local seismic displacement waveforms com bined with global positioning system gps and synthetic aperture radar interfer ometry insar geodetic measurements we find that the three data sets individually produce remarkably similar slip distributions over a multisegment fault a simulta neous inversion of the three data sets is presented and the sensitivity of the combined inversion to the weighting of the three independent data sets is examined the results indicate that the overall length of the fault that slipped is 42 km with a peak slip of 5 50 m and total scalar seismic moment of 6 8 10 19 n m the majority of slip is located on the western branch of the lavic lake fault to the northwest of the hypo center although the overall rupture is bilateral with appreciable slip on the bullion fault to the southeast some slip is located on an eastern branch of the lavic lake fault an apparent bifurcation which is also evident from aftershock locations the average slip and stress drops are 2 70 1 62 1 60 m and 78 36 and 55 bars for the western lavic lake the eastern lavic lake and bullion faults respectively the results also indicate that the overall rupture process is relatively slow which is char acterized by a several second delay before the onset of significant slip a 1 8 km sec rupture velocity of the primary asperity and long spatially variable dislocation rise times

quantification of bedform dynamics and bedload sediment flux in sandy braided rivers from airborne and satellite imagery images from specially commissioned aeroplane sorties manned aerial vehicle mav repeat unmanned aerial vehicle uav surveys and planet cubesat satellites are used to quantify dune and bar dynamics in the sandy braided south saskatchewan river canada structure from motion sfm techniques and application of a depth brightness model are used to produce a series of digital surface models dsms at low and near bankfull flows a number of technical and image processing challenges are described that arise from the application of sfm in dry and submerged environments a model for best practice is presented and analysis suggests a depth brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low turbidity and shallow 2 m deep water the aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18 km reach and three 1 km long reaches respectively dune and unit bar migration rates are highly variable in response to local variations in planform morphology sediment transport rates for dunes and unit bars obtained by integrating migration rates from uav with the volume of sediment moved from dsms using mav imagery show near equivalence in sediment flux hence reach based sediment transport rate estimates can be derived from unit bar data alone moreover it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2d imagery including from satellite images so long as informed assumptions are made regarding average bar shape and height with recent availability of frequent repeat satellite imagery and the ease of undertaking repeat mav and uav surveys for the first time it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low turbidity rivers that currently have sparse information on bedload sediment transport rates

fault scarp features and cascading rupture model for the mw 7 9 wenchuan earthquake eastern tibetan plateau china on 12 may 2008 the m w 7 9 wenchuan earthquake ruptured two northeast striking imbricated reverse faults and one northwest striking reverse fault along the middle longmen shan thrust belt at the eastern margin of the tibetan plateau the morphology of the coseismic scarp varies drastically along strike we distinguish eight different categories 1 simple thrust scarp 2 hanging wall collapse scarp 3 simple pressure ridge 4 dextral pressure ridge 5 fault related fold scarp 6 backthrust pressure ridge 7 local normal fault scarp and 8 pavement suprathrust scarp the coseismic surface ruptures confirm that the wenchuan earthquake is dominated by reverse faulting with some right lateral component that varies from site to site the surface rupture can be divided into two parts the yingxiu segment and the beichuan segment when the earthquake is split into two subevents accordingly they correspond to an m w 7 8 event and an m w 7 6 event respectively these two segments can in turn be divided into four second order subsegments which are equivalent to four subevents of m w 7 5 m w 7 7 m w 7 0 and m w 7 5 respectively the segmentation of the rupture is consistent with a cascading rupture pattern responsible for the total 110 s of the earthquake rupture in addition to surface ruptures the focal mechanisms determined for the aftershocks recorded by the local seismic network are used to constrain the fault geometry of the subsegments they show that the dip of the fault responsible for the earthquake varies along strike and the fault tends to flatten at depth in addition the fault plane gets steeper northward enabling the fault to accommodate a larger strike slip component along a lateral ramp this major earthquake confirms that crustal shortening could be the main driving force for the growth of high topography along the eastern margin of the tibetan plateau and that lower crustal flow is not required

shallow crustal velocities and volcanism suggested from ambient noise studies using a dense broadband seismic network in the tatun volcano group of taiwan abstract the tatun volcano group tvg is situated adjacent to the taipei metropolis and was active predominantly around 0 8 0 2 ma pleistocene various recent lines of evidence suggest that the tvg is a potentially active volcano and that future volcanic eruptions cannot be ruled out geothermal activities are largely constrained to faults but the relationship between volcanism and detailed velocity structures is not well understood we analyzed ambient seismic noise of daily vertical components from 2014 using a dense seismic network of 40 broadband stations we selected a 0 02 grid spacing to construct 2d and 3d shallow crustal phase velocity maps in the 0 5 3 s period band two s wave velocity profiles transect chishingshan mt cs in the shallow 3 km crust are further derived the footwall of the shanchiao fault is dominated by low velocity which may relate to tertiary bedrock buried under andesitic lava flows dozens to hundreds of meters thick the hanging wall of the shanchiao fault is the location of recent major volcanic activities low velocity zones in the southeast of dayoukeng dyk may be interpreted as hydrothermal reservoirs or water saturated tertiary bedrock related to cenozoic structures in the shallow crust high velocities conspicuously dominate the east of the tvg where the earliest stages of volcanism in the tvg are located but where surface hydro geothermal activities were absent in recent times between the shanchiao fault and kanchiao fault high velocities were detected which converge below mt cs and may be related to early stages of magma conduits that gradually consolidated these two faults may play a significant role with the tvg the submarine volcanism adjacent to the keelung coastline also requires further attention

time space variation of volcano seismic events at la fossa vulcano aeolian islands italy new insights into seismic sources in a hydrothermal system we investigated the relationship between volcano seismic events recorded at la fossa crater of vulcano aeolian islands italy during 2004 2006 and the dynamics of the hydrothermal system during the period of study three episodes of increasing numbers of volcano seismic events took place at the same time as geothermal and geochemical anomalies were observed these geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids three classes of seismic events long period high frequency and monochromatic events characterised by different spectral content and various similarity of the waveforms have been recognised these events clustered mainly below la fossa crater area at depths of 0 5 1 1 km b s l were space distributed according to the classes based on their features we can infer that such events at vulcano are related to two different source mechanisms 1 fracturing processes of rocks and 2 resonance of cracks or conduits filled with hydrothermal fluid in the light of these source mechanisms the increase in the number of events at the same time as geochemical and geothermal anomalies were observed was interpreted as the result of an increasing magmatic component of the hydrothermal fluids implying an increase of their flux indeed such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids increased pore pressures gave rise to fracturing processes while the increased fluid flux favoured resonance and vibration processes in cracks and conduits finally a gradual temporal variation of the waveform of the hybrid events one of the subclasses of long period events was observed likely caused by heating and drying of the hydrothermal system

joint inversion of insar gps teleseismic and strong motion data for the spatial and temporal distribution of earthquake slip application to the 1999 izmit mainshock the space time distribution of slip of the 17 august 1999 izmit earthquake is investigated by inverting synthetic aperture radar sar interferometry and global positioning system gps data together with teleseismic broadband and near field strong motion records surface offsets are used as an added constraint special emphasis is given to analysis of the resolution of the different data sets we use a four segment finite fault model and a nonlinear inversion scheme allowing slip to vary in amplitude direction and duration as well as variable rupture velocity from the inversion of synthetic data we find that the best spatial resolution can be expected in the upper half of the fault model above 12 km where coverage of the interferometric sar data is good western half of the rupture and near the gps and strong motion stations teleseismic data are found to have a lower resolution that is more evenly distributed over the fault model the joint inversion of all the data sets has an increased resolving power compared with the separate inversions and gives a more robust description of the space and time distribution of slip our study shows the importance of resolution tests in evaluating the reliability of earthquake kinematic models and it confirms that an excellent fit of a single kind of data does not necessarily imply a good retrieval of the kinematic properties of an earthquake the izmit rupture which is almost pure right lateral strike slip faulting is dominated by the bilateral breaking of a central asperity located between 29 7 e about 10 km west of the city of golcuk and 30 4 e eastern margin of sapanka lake with slip reaching 6 8 m in the depth range 6 12 km the western termination of the rupture is found near the city of yalova but large slip ends around 29 7 e about 10 km east of hersek delta a second area of large slip is required by all the data sets further east toward the city of duzce between 30 7 e and 31 1 e karadere and duzce faults this eastern slip zone which is separated from the main central asperity by an area of greatly reduced slip is less well constrained by the data however a strong motion station near the city of duzce helps to locate a high slip patch near 31 1 e in the depth range 6 12 km the total seismic moment resulting from the joint inversion is 2 4 1027 dyne cm most of the energy release occurred in a short time less than 15 sec corresponding to the bilateral breaking of the central asperity rupture propagation is relatively uniform and fast toward the west with a rupture velocity close to 3 5 km sec propagation of large slip toward the east is initially slower but it accelerates during a short time interval about 10 sec after rupture nucleation eastward progression then slows down to less than 2 km sec after 15 sec and rupture almost vanishes in amplitude ca 20 sec after initiation rupture propagation then proceeds on the easternmost karadere and duzce fault segments east of 30 7 e from 22 to ca 50 sec supershear rupture propagation is not required for modeling the waveforms considered in this study the hypocenter of the duzce earthquake which occurred 3 months later 12 november 1999 m w 7 2 is located in the immediate vicinity of the easternmost slip patch of the izmit earthquake manuscript received 28 july 2000

high resolution backprojection at regional distance application to the haiti m7 0 earthquake and comparisons with finite source studies a catastrophic m w7 earthquake ruptured on 12 january 2010 on a complex fault system near port au prince haiti offshore rupture is suggested by aftershock locations and marine geophysics studies but its extent remains difficult to define using geodetic and teleseismic observations here we perform the multitaper multiple signal classification music analysis a high resolution array technique at regional distance with recordings from the venezuela national seismic network to resolve high frequency about 0 4 hz aspects of the earthquake process our results indicate westward rupture with two subevents roughly 35 km apart in comparison a lower frequency finite source inversion with fault geometry based on new geologic and aftershock data shows two slip patches with centroids 21 km apart apparent source time functions from usarray further constrain the intersubevent time delay implying a rupture speed of 3 3 km s the tips of the slip zones coincide with subevents imaged by backprojections the different subevent locations found by backprojection and source inversion suggest spatial complementarity between high and low frequency source radiation consistent with high frequency radiation originating from rupture arrest phases at the edges of main slip areas the centroid moment tensor cmt solution and a geodetic only inversion have similar moment indicating most of the moment released is captured by geodetic observations and no additional rupture is required beyond where it is imaged in our preferred model our results demonstrate the contribution of backprojections of regional seismic array data for earthquakes down to m 7 especially when incomplete coverage of seismic and geodetic data implies large uncertainties in source inversions

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

tornillo type seismic signals at galeras volcano colombia 1992 1993 abstract unusual low frequency seismic events called tornillos screws at the observatorio vulcanologico y sismologico de pasto ovsp have been observed at galeras volcano during 1992 1993 of six eruptions that occurred between july 1992 and june 1993 five were preceded by episodes of tornillo signals these signals are characterized by 1 a waveform having a homogeneous distribution of frequencies 2 a long coda lasting up to several minutes 3 a small amplitude compared to the duration and 4 a slow decay of the coda the tornillo signals have been grouped into thirteen principal forms the 1992 1993 tornillos showed four main periods of occurrence each of which was followed by an eruption episode i occurred from 11 to 16 july 1992 and consisted of nine events episode ii lasted from 23 december 1992 to 14 january 1993 with twenty events episode iii was observed from 13 february to 23 march 1993 with 74 events episode iv lasted from 10 april to 7 june 1993 with 109 events the seismic activity at galeras in april may 1993 was characterized mainly by the occurrence of tornillo signals the behavior of these signals was similar to that before previous episodes ending with eruptions these observations permitted us to forecast the 7 june 1993 eruption several days to weeks beforehand the occurrence of tornillos is the most important criterion for determining the probability of an eruption at galeras in the current period of reactivation the maximum daily number of tornillos and the longest duration of individual events occur near the end of each episode within an individual episode the durations of single events increase progressively near to the point of eruption a positive correlation is observed between the total number of pre eruptive tornillo signals during an episode and the volume of material ejected by the eruption these observations may suggest that the presence of tornillos is an indication of variations in the physical conditions between the fluid and the surrounding solid material within the volcano and they constitute an important tool for forecasting future eruptions at galeras

seismogram envelope inversion for the spatial distribution of high frequency energy radiation from the earthquake fault application to the 1994 far east off sanriku earthquake japan incoherency of high frequency seismic waves leads to the idea to analyze seismogram envelopes disregarding phase information for the source study we develop an inversion method for estimating high frequency above 1 hz energy radiation from the earthquake fault and site amplification factors from observed mean square s wave seismogram envelopes the inversion is executed by using the s wave envelope green function from the onset to coda for a point shear dislocation source in a scattering medium which is formulated based on an extended version of the radiative transfer theory the use of the envelope green function enables us to estimate the spatial distribution of high frequency energy radiation on a fault plane this has been difficult by conventional waveform inversion methods the rupture velocity and the duration time of energy radiation on each subfault are also estimated by grid search method we apply this new method to the 1994 far east off sanriku northeastern japan earthquake mw 7 7 which ruptured a 90 km segment of the plate boundary along the japan trench inverting observed seismogram envelopes at 10 strong motion stations in japan it is concluded that above 90 of the high frequency energy was radiated from the western half of the fault with the largest energy radiation near the deep side edge the rupture velocity is estimated to be 2 7 km s the estimated site amplification factors ranging between 0 3 and 15 are consistent with those independently estimated by the coda normalization method

dynamics of nonmigrating mid channel bar and superimposed dunes in a sandy gravelly river loire river france abstract a field study was carried out to investigate the dynamics during floods of a nonmigrating mid channel bar of the loire river france forced by a riffle and renewed by fluvial management works interactions between the bar and superimposed dunes developed from an initial flat bed were analyzed during floods using frequent mono and multibeam echosoundings acoustic doppler profiler measurements and sediment grain size analysis when water left the bar terrestrial laser scanning and sediment sampling documented the effect of post flood sediment reworking during floods a significant bar front elongation spreading on margins and swelling was shown whereas a stable area no significant changes was present close to the riffle during low flows and falling limbs of floods intense sediment reworking on the top of the bar and lateral scouring occurred hydrological variations controlled the sediment supply in terms of phasing quantity and grain size delivered by surrounding channels during floods and thus superimposed dune development their development was also linked to the sediment availability armor layers riffle proximity their relatively constant height highlights a preferential adaptation on dune length during floods the role of each morphological forcing parameters riffle vs channel widening and curvature on the bar dynamics and evolution is stage dependent the shape dynamics and long term morphological evolution of the bar and of the river reach surrounding islands channel translation mainly depends on the presence of the natural riffle

parameterization of multichromatic tornillo signals observed at galeras volcano colombia in the past decade several of the ash eruptions at galeras volcano colombia have been preceded by tornillos these unusual tremor wavelets have quasi sinusoidal waveforms with screw like envelope profiles and can last up to several minutes a swarm of tornillos occurred at galeras volcano between 8 december 1999 and 12 february 2000 these tornillos appear to be more complex than those previously recorded with the broadband instruments or with the short period network of the observatorio vulcanologico y sismologico in pasto they are multichromatic with a varying number of narrow spectral peaks between 1 and 20 hz we describe a procedure for parameterizing the tornillo signals in the time and frequency domains to determine signal parameters in addition to wavelets like the tornillos the procedure can be applied to random signals such as volcanic tremor we derive distribution and correlation functions for the signal parameters determined from the swarm these provide along with the signal signature constraints for modelling variations of the source process from these observations we derive qualitative conclusions about the characteristics of differential equations which describe the underlying processes and excitation mechanisms as forced or self excited oscillators

elucidating the geometry of the active shanchiao fault in the taipei metropolis northern taiwan and the reactivation relationship with preexisting orogen structures the shanchiao fault is an active normal fault with documented paleoearthquakes in the taipei metropolis taiwan while posing direct seismic threat on the multimillion population its crustal scale fault plane configuration has not been constrained this study presents the first attempt to resolve the fault plane dip changes of the shanchiao fault within the upper crust by forward modeling late quaternary deformation tectonic subsidence over the last 23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline a 2 d profile across the shanchiao fault is chosen for elastic half space dislocation modeling and the results suggest that the fault is listric in the shallow crust with an abrupt change from subvertical ramp 85 75 to near horizontal flat 10 15 at 3 4 km depth consistent with an origin from the inversion of an orogen related thrust detachment given the presence of rift related fabrics in the underthrust chinese continental margin basement beneath the taiwanese orogenic wedge listric ramp flat ramp models with a second deeper bend to 60 dip are also tested reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth which correlates with the hypocentral location of a moderate earthquake in 2004 joint reactivation of preexisting thrust and rift faults by the shanchiao fault is therefore plausible with implications for seismic hazard in the taipei area

bedform migration and bed load transport in some rivers and tidal environments reliable field data obtained by directly measuring bed load transport of fine to coarse grained bed material are extremely scarce mainly because of the difficulty of sampling accurately therefore the verification of bed load transport formulae is largely based on flume experiments which refer to unrealistic shallow water conditions in this study some bed load transport formulae were tested against data from natural environments as an alternative to ascertaining the bed load transport rate by sampling the bed load the transport rate was deduced from data on bedform height and bedform celerity for this purpose 43 sets of data from rivers representing a wide range of bed material bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings two formulae were used for the prediction of the bed load transport the formula of van rijn 1981 and the kalinske 1947 formula as approximated by elzerman frijlink 1951 and in the present study slightly modified for application to tidal waters both the bed load function of van rijn and the modified formula of kalinske frijlink require data which are easily obtained and that can be measured accurately at those stages of the flow when bed load transport was high the van rijn function tended to overestimate that transport for flow stages when bed load transport was low the opposite was true the modified kalinske frijlink function gave consistently good results 86 of the transport rates predicted using the river data were within 0 5 2 0 times the values actually measured

bar and dune development during a freshet fraser river estuary british columbia canada bi weekly multi track sonar surveys collected along a 2 km reach of the estuarine south arm of the fraser river british columbia canada during seasonal high flows document the initiation development and interaction of dune and bar morphologies bedforms of several scales developed in well delineated fields bedforms that appear to fit accepted equilibrium depth scaling developed in the main channel during rising discharge when there was little local aggradation during the rising stage a bar also formed along the tidal shelf of the channel migrated downstream and expanded into the main channel dunes that formed along the bar crest a region of rapid deposition lagged flow conditions and were larger than expected based on depth scaling relations the larger dunes developed simultaneously although bar growth lagged dune development and was initially partially obscured by the more rapidly developing dune field it appears that rapid deposition enhances dune development along the channel tidal shelf to dimensions larger than would be expected by simple depth scaling rules smaller dunes that fit equilibrium depth scaling relations re established themselves throughout the study area during falling discharge when there was again little or no aggradation bed material transport rates estimated from the migration rates of the large dunes suggest that at high flows the dunes transport the majority of the material found within the bar

high frequency earthquakes at white island volcano new zealand insights into the shallow structure of a volcano hydrothermal system abstract volcano tectonic earthquakes at white island are concentrated in a single seismically active zone southeast of the active vents and at depths of less than 1 km a few deeper earthquakes also occur beneath the active vents a composite focal mechanism indicates that the stress regime in the shallow seismic zone is n s extensional shallow seismicity occurs within the main volume of the volcano hydrothermal system that underlies the main crater floor and we interpret this as a region where the rocks have been weakened by past magmatic intrusions elevated pore fluid pressure and physico chemical effects of acid volcanic fluids thereby allowing preferential seismic failure brittle seismic failure within this region requires a temperature less than about 400 c and implies high horizontal temperature gradients close to the active craters and fumaroles spasmodic bursts events are also a result of brittle failure but occur close to zones of significant permeability in response to changes in local fluid pressure

rupture process during the 2015 illapel chile earthquake zigzag along dip rupture episodes we constructed a seismic source model for the 2015 mw 8 3 illapel chile earthquake which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the green s function together with the hybrid backprojection method enabling us to track the spatiotemporal distribution of high frequency 0 3 2 0 hz sources at high resolution by using globally observed teleseismic p waveforms a maximum slip amounted to 10 4 m in the shallow part of the seismic source region centered 72 km northwest of the epicenter and generated a following tsunami inundated along the coast in a gross sense the rupture front propagated almost unilaterally to northward from the hypocenter at 2 km s however in detail the spatiotemporal slip distribution also showed a complex rupture propagation pattern two up dip rupture propagation episodes and a secondary rupture episode may have been triggered by the strong high frequency radiation event at the down dip edge of the seismic source region high frequency sources tends to be distributed at deeper parts of the slip area a pattern also documented in other subduction zone megathrust earthquakes that may reflect the heterogeneous distribution of fracture energy or stress drop along the fault the weak excitation of high frequency radiation at the termination of rupture may represent the gradual deceleration of rupture velocity at the transition zone of frictional property or stress state between the megathrust rupture zone and the swarm area

volcano hydrothermal activity detected by precise levelling surveys at the tatun volcano group in northern taiwan during 2006 2013 abstract precise levelling surveys were conducted from 2006 to 2013 on three levelling routes in the tatun volcano group tvg located approximately 15 km northeast of taipei to detect deformation in relation to the volcano hydrothermal activities of the tvg uplift was detected around the most active fumarole tayoukeng fumarole throughout the period 2007 to 2011 the uplift rate throughout the period from march 2009 to march 2011 was reduced in comparison to the rate between 2007 and 2009 following this a dormant state or a small amount of subsidence was detected in the period march 2011 to march 2013 and throughout the period from june 2006 to march 2013 subsidence was centred on an area 0 5 km east of the summit of mt cising the highest peak in the tvg a model of two spherical sources was therefore estimated from the deformation recorded from august 2007 to march 2011 using a genetic algorithm a deflation source was obtained about 0 5 km northeast of mt cising at a depth of 2 km and an inflation source was situated approximately 1 km south of the tayoukeng fumarole at a depth of 0 7 km based on previous seismic and amt studies the estimated sources are interpreted as being hydrothermal reservoirs because almost all the benchmarks around mt cising show subsidence at a constant speed we conclude that the deeper hydrothermal reservoir at a depth of 2 km may have been releasing hydrothermal fluid at a constant rate throughout the period from 2006 to 2013 however it was suggested that in 2011 the shallower hydrothermal reservoir at a depth of 0 7 km changed from an inflation state to a dormant state or small deflation based on temporal vertical changes around tayoukeng fumarole a possible model for the volcano hydrothermal system is therefore proposed it is considered that the hydrothermal fluid may be supplied intermittently from the magma chamber to the deeper hydrothermal reservoir at a depth of 2 km although this type of fluid input event may not have occurred during our research period and that the hydrothermal fluid upwelling between mt cising and tayoukeng fumarole flows transversally into a highly cracked and fluid saturated area that continues to tayoukeng fumarole the existence of a shallower hydrothermal reservoir at a depth of 0 7 km in the highly cracked and fluid saturated area is therefore plausible

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

alternate bars in a sandy gravel bed river generation migration and interactions with superimposed dunes a field study was carried out to investigate the development of alternate bars in a secondary channel of the loire river france as a function of discharge variations we combined frequent bathymetric surveys scour chains and stratigraphical analysis of deposits with measurements and modelling of flow dynamics the channel exhibited migrating bars non migrating bars and superimposed dunes possible mechanisms of bar initiation were found to be chutes associated with changes of bank direction and instability resulting from interactions between existing bars during the fall in water level after floods we propose that the reworking of bar sediments during low flows high width to depth ratio reinforced by high values of the shields mobility parameter can explain the formation or re generation of new alternate migrating bars during a subsequent flood the migration pattern of the bars was found to be cyclic and to depend mainly on i channel layout and ii the dynamics of superimposed dunes with heights and lengths depending on location and discharge value for instance the hysteresis affecting the steepness of dunes influences the flow resistance of the dunes as well as the celerity of migrating bars during flood events we compare the findings from the field with results from theoretical studies on alternate bars this gives insight in the phenomena occurring in the complex setting of real rivers but it also sheds light on the extent to which bar theories based on idealized cases can predict those phenomena copyright 2014 john wiley sons ltd

the morphodynamics of fluvial sand dunes in the river rhine near mainz germany ii hydrodynamics and sediment transport the dynamics of large isolated sand dunes moving across a gravel lag layer were studied in a supply limited reach of the river rhine during daylong surveys suspended sediment concentration bedload transport rate water depth flow velocity turbulence intensity near bed shear stress and water temperature were recorded over individual isolated dunes this paper considers the hydrodynamic environment and sediment transport over the dunes a companion paper details the sedimentology and morphology of the dunes flow over the flat gravel lag upstream of large dunes is more uniform than that over dunes and gravels are rarely entrained by in bank discharges unsteady and non logarithmic velocity profiles are common within the boundary layer above the stoss side of large dunes and the near bed flow demonstrates evidence of large scale coherent low frequency flow structures these may reflect stacked sequences of separated boundary layers generated by secondary dunes however the low amplitude morphology of large dunes does not affect the statistical properties of turbulence production over the stoss sides bed roughness and near bed shear stress commonly increase steadily over the stoss of dunes but may decrease near the crest especially where a crestal platform exists that is devoid of secondary bedforms bed roughness scales with the physical size of bed roughness elements however variability in roughness lengths is large owing to the composite nature of bed roughness bedload transport over stoss slopes is spatially variable but often shows an increase with increasing bed shear stress over the stoss well formed wakes only develop downstream of lee slopes which are close to the angle of repose otherwise separation is weak and suspension and settling of fine sediments is of little consequence to dune evolution wake flow is characterized by turbulence production one order of magnitude greater than over the stoss side which may be related to vortex shedding from the dune however wake current speeds are extremely low and variable in direction reverse flow is not sustained and no retrogressive bedforms occur in the lee of large dunes near bed shear stress and bed roughness are usually low within the wake reflecting low current speeds weak wake flow reattachment occurs at a variable distance downstream up to several times the duneform height a two dimensional numerical model for flow over dune topography calibrated using average parameter values provided a reasonable description of the flow upstream and over the backs of large dunes as far as the crestal region wake flow could not be modelled however the temporal and spatial complexity of natural three dimensional flow over the dunes resulted in variance in parameter estimates this variance precluded modelling of flow and bedload transport consequently it was not possible to model dune evolution in a deterministic sense

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

probable dynamic triggering of phreatic eruption in the tatun volcano group of taiwan abstract on 16 march 2014 utc a small phreatic eruption occurred in the tatun volcano group tvg of taiwan although it was not reported until analysis of both seismic and acoustic data revealed that the source was in the vicinity of the hsiaoyukeng fumarole a replay of the acoustic data accelerated 60 fold reveals that the gradual decrease in frequency that was recorded produces a volcanic whistle similar to the jet of steam released from a heating kettle the phreatic eruption may have been dynamically triggered by a m6 7 earthquake in chile a similar phenomenon occurred on 5 january 2015 when a phreatic eruption was recorded in the tvg immediately after the generation of dynamic seismic waves by an m5 0 earthquake in japan this is the first scientific report of a phreatic eruption detected in the tvg indicating that these volcanoes are still active as a result it is important to monitor their volcanic activity and identify volcanic reservoirs beneath the tvg to mitigate future possible volcanic impact

response of low angle dunes to variable flow current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments there are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides as a consequence the ability to predict bedform response to variable flow is rudimentary using high resolution multibeam bathymetric data this study explores the dynamics of a dune field developed by tidally modulated fluvially dominated flow in the fraser river estuary british columbia canada the dunes were dominantly low lee angle features characteristic of large deep river channels data were collected over a field ca 1 0 km long and 0 5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet yielding the most comprehensive characterization of low angle dunes ever reported the data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs then increasing as the tide rises and the flow velocities decrease bedform lengths do not appear to respond to the changes in velocity caused by the tides changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity indicating that changes in the bedform geometry lag changes in the flow the data reveal that lee angle slope responds directly to suspended sediment concentration supporting previous speculation that low angle dune morphology is maintained by erosion of the dune stoss and crest at high flow and deposition of that material in the dune trough