tidal calibration of borehole strain meters removing the effects of small scale inhomogeneity we investigate the estimation of earth strain from borehole strain meter data in a study of tidal calibration of the gladwin borehole tensor strain meter btsm at pinon flat small scale geological inhomogeneity is one of several effects examined that cross couple remote areal shear strain into measured areal shear strain a methodology is developed for incorporating cross coupling into the strain meter calibration using the measured strain tides from the colocated laser strain meter lsm as a reference we show that calibration of the btsm with cross coupling removes systematic errors of up to 30 in the borehole strain meter tides this calibration accurately relates the btsm measurements to strains at the scale length of the lsm about 1 km the calibration technique provides a solution to a major criticism of all short baseline strain measurements namely that tectonic strains are not representatively sampled due to small scale inhomogeneities the technique removes errors potentially greater than 50 in observed strain offsets from fault slip permitting improved constraint of slip mechanisms we show that current theoretical estimates of strain tides in the instrument locality are not yet of sufficient accuracy for cross coupled calibration comparison of theoretical tides with measurements from the lsm suggest that at least half of the error is in the ocean load tide estimates

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

analyses of far field coseismic crustal deformation observed by a new laser distance measurement system summary we have developed a novel absolute distance meter adm for determining coseismic strain steps and analysed far field crustal deformation caused by earthquakes by measuring the optical resonant frequency of a 100 m long optical cavity in relation to an accurate time standard the absolute distance can be determined with a resolution of 2 10 9 10 10 absolute measurements ensure the detection of distance changes before and after an earthquake even when encountering large seismic waves that can often hinder relative distance measurements the proposed system consisting of the adm in combination with a conventional laser strainmeter lsm a relative distance meter having a resolution of 1 10 10 in strain can successfully observe coseismic strain steps ranging from 1 10 10 to 3 5 10 8 we analysed strain steps of 10 earthquakes m 5 8 7 4 and depths of 8 374 km that occurred around the central part of mainland of japan at hypocentral distances of 100 530 km from the kamioka underground observatory the observed strain steps were compared with expected strains calculated using a variety of fault parameters inferred from existing observations both seismic and geodetic assuming two typical models a homogeneous elastic half space case 1 and a spherically symmetric earth model with a modified prem structure case 2 after correcting the estimated rigidity around the source region for calculating a point dislocation from a seismic moment the observations strongly supported case 2 rather than case 1 for deep earthquakes hypocentral depth 20 km on the basis of our analyses we concluded that the distance measurement system could detect coseismic strains with a resolution of 1 10 10 and a wide detection range of at least 3 5 10 8 and could also precisely determine crustal deformation far from the source region the observation constrains dislocation theories especially for the deep region and may geodetically constrain fault parameters on the basis of far field deformation even for deep and ocean earthquakes whose surface deformations are difficult to observe with conventional geodetic methods

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

interaction of low level flow with the western ghat mountains and offshore convection in the summer monsoon abstract seven year averaged values of percent frequency of occurrence of highly reflective cloud for the months june july and august indicate that offshore convection is a major component of the cloudiness of the southwest monsoon principal areas of convection occur off of the western coats of india burma thailand and the philippines this study concentrates on the area upstream of the western ghats mountains of india analysis of a special boundary layer mission flown during the wmo icsu summer monsoon experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection data obtained on this mission allow a large scale momentum budget computation for the subcloud layer which shows pressure deceleration to be significant the budget dominated by advection predicts an increase of average wind speed which is observed the pressure decelera

polarization tomography for p wave velocity structure in southern california we develop a tomographic inversion method that uses teleseismic p wave polarization data to obtain velocity structure polarization inversion has some intrinsic advantages over travel time inversion it is not influenced by source location and origin time errors it is not sensitive to deep mantle velocity structure and can be used iteratively to improve the tomographic result polarization inversion is more sensitive to near station velocity structure and to velocity gradient and is complementary to travel time inversion in this sense the method is applied to california institute of technology u s geological servey southern california array data the result is generally consistent with previous work and also reveals that the high velocity feature beneath the transverse ranges is bounded between 40 and 200 km depths and possibly has a second small piece at about 300 km depth the slow velocity anomaly under the salt on trough is limited to shallow depths less than about 60 km

abnormally strong daily cycle s1 strain tide observation and physical mechanism tidal signals are analyzed in the plate boundary observatory borehole strainmeters in western north america while the extracted diurnal strain tidal constituents except daily cycle s1 respond to the tidal forces in similar proportion the s1 strain tide exhibits an abnormally strong amplitude reaching tens to hundreds times larger than theoretical prediction the s1 strain tide exhibits phase lags and little amplitude correlations with the corresponding s1 barometric pressure tide while no phase lags are observed at the other frequencies between these two observations several mechanisms are examined and are excluded for explaining the strong s1 strain tides including integral effect of barometric pressure loading viscoelastic response to barometric pressure elastic loading of ocean water and hydrological water variation and thermal leakage from the surface to the strainmeter instruments the strong s1 strain tides can be attributed to the results of two physical mechanisms 1 elastic loading of surface barometric pressure and 2 thermoelastic deformation induced by temporally and spatially varying surface temperature the barometric pressure produces a component of elastic strain in phase with the pressure while the surface temperature induces thermoelastic strain exhibiting comparable amplitude with the pressure induced component but with various phase lags as a result the superposition of these two s1 strain tides exhibits a phase difference with respect to the corresponding s1 tides of both barometric pressure and temperature and explains the large s1 strain tides observed in the strainmeter data our results indicate the importance of thermoelastic deformation being a near surface physical process

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

hydrologic effects on water level changes associated with episodic fault creep near parkfield california as part of the parkfield california earthquake prediction experiment water level is monitored in a well 460 m from the main trace of the san andreas fault on middle mountain in the preparation zone of the anticipated parkfield earthquake the well configuration allows water level to be monitored in two fluid reservoirs at depths of 85 and 250 m below land surface during 1987 water level changes were recorded during 12 of the 18 episodes of accelerated fault creep detected by a creep meter spanning the fault trace 750 m northwest of the well the creep related water level changes in the shallow reservoir have durations of less than 1 day whereas in the deeper reservoir the changes persist for as long as 2 months these data suggest that the transient nature of the water level changes in the shallow interval is due to vertical flow to the water table and is not evidence that creep events propagate past the well phase leads of earth tidal constituents in the water level data from the shallow interval relative to the same constituents in the local volume strain tide support the interpretation of significant flow to the water table at periods of 1 day or less the form of the water level changes in the deep interval is affected by horizontal flow to the well bore this effect can be removed from the water level records using a theoretical response curve constrained by the phases of earth tidal constituents in the deep interval relative to the local volume strain tide for the events where the signal in the shallow interval has been large enough to measure the sizes of the simultaneous water level changes in the two reservoirs are consistent with the same amounts of volume strain occurring at both depths

updraft dynamics within a numerically simulated subtropical rainband abstract in this study a three dimensional numerical cloud model is used to examine the early evolution of deep convective rainbands that occur in an environment of weak to moderate buoyancy and directionally varying lower tropospheric vertical wind shear a simulation based on a case observed on 8 june 1987 during the taiwan area mesoscale experiment produced a narrow bow shaped rainband that comprised 1 short lived updrafts along the downshear portion of the weak rain induced cold pool and 2 more persistent updrafts along its southern flank which were highly correlated with vertical vorticity trajectory calculations and an analysis of the dynamic portion of the perturbation pressure field are presented to illustrate the hybrid dynamical character of the simulated rainband the shorter lived updrafts were associated with weak upward directed pressure gradient forces at the leading edge of the surface based cold pool the more persistent updrafts exhibited much stronger upward directed pressure gradie

a box model for non entraining suspension driven gravity surges on horizontal surfaces the propagation of and the deposition from a turbulent gravity current generated by the release of a finite volume of a dense particle suspension is described by a box model the approximate model consists of a set of simple equations a predetermined depth dependent leading boundary condition and one experimentally determined parameter describing the trailing boundary condition it yields predictions that agree well with existing laboratory observations and more complex theoretical models of non eroding non entraining suspension driven flows on horizontal surfaces the essential features of gravity surge behaviour have been observed and are captured accurately by the box model these include the increased rate of downstream loss of flow momentum with increased particle setting velocity the existence of maxima in the thickness of proximal deposits and the downstream thinning of distal deposits our approximation for the final run out distance xr of a surge in deep water is given by xr3 g oq3o w2s 1 5 where g o is the initial reduced gravity of the surge qo the initial two dimensional volume and ws the average settling velocity of the particles in the suspension a characteristic thickness of the resulting deposit is given by oqo xr where oo is the initial volumetric fraction of sediment suspended in the surge our analysis provides additional insight into other features of gravity surge dynamics and deposits including the potential for the thickening of currents with time the maintenance of inertial conditions and the potential for strong feedback in the sorting of particle sizes in the downstream direction at travel distances approaching xr box model approximations for the evolution of gravity surges thus provide a useful starting point for analyses of some naturally occurring turbidity surges and their deposits

borehole strainmeter measurements spanning the 2014 mw6 0 south napa earthquake california the effect from instrument calibration the 24 august 2014 mw6 0 south napa california earthquake produced significant offsets on 12 borehole strainmeters in the san francisco bay area these strainmeters are located between 24 and 80 km from the source and the observed offsets ranged up to 400 parts per billion ppb which exceeds their nominal precision by a factor of 100 however the observed offsets of tidally calibrated strains differ by up to 130 ppb from predictions based on a moment tensor derived from seismic data the large misfit can be attributed to a combination of poor instrument calibration and better modeling of the strain field from the earthquake borehole strainmeters require in situ calibration which historically has been accomplished by comparing their measurements of earth tides with the strain tides predicted by a model although the borehole strainmeter accurately measures the deformation within the borehole the long wavelength strain signals from tides or other tectonic processes recorded in the borehole are modified by the presence of the borehole and the elastic properties of the grout and the instrument previous analyses of surface mounted strainmeter data and their relationship with the predicted tides suggest that tidal models could be in error by 30 the poor fit of the borehole strainmeter data from this earthquake can be improved by simultaneously varying the components of the model tides up to 30 and making small adjustments to the point source model of the earthquake which reduces the rms misfit from 130 ppb to 18 ppb this suggests that relying on tidal models to calibrate borehole strainmeters significantly reduces their accuracy

gradiometry for polarized seismic waves 1 wave gradiometry for a generic point source wave model in cylindrical coordinates is developed to utilize the horizontal components of seismic wavefields attributes of p sv and sh waves such as horizontal slowness and its change the change in geometrical spreading the change in radiation pattern azimuth of propagation and wave polarization can be determined by measuring the horizontal strains and rotations of the wavefield along with three components of displacement gradiometer cells composed of an array of three component seismographs can be used to provide estimates of the wave gradients alternatively a single three component seismograph collocated with an areal strainmeter for p sv waves or a rotation sensor for sh waves can be used to estimate wave polarization and the slowness amplitude behavior of one aspect of the wavefield wave gradients are computed for the 1 april 2007 solomon island earthquake using data from the anza seismic network in southern california and show excellent consistency among stations of the network azimuth and slowness of various long period teleseismic waves are recovered using gradiometry analysis the consistency of strains computed from the broadband array suggests that they may be used to calibrate plate boundary observatory tensor strainmeters in the region

water table effects on the measurement of earth strain abstract forced changes in the water head within a granite penetrating borehole were found to induce anomalously large free surface strains and tilts in the vicinity of the hole this deformation is shown to be due to fluid pressure induced changes in the aperture of a compliant hydraulically conductive fracture at a depth of 100 m and a quantitative analysis of the deformation data is performed to recover fracture characteristics the importance of the effect for secular earth strain measurements is discussed in the light of the ubiquitous nature of both water table fluctuations and fractures in the shallow crust

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

evolution and structure of tropical squall line elements within a moderate cape and strong low level jet environment a three dimensional cloud model is used to simulate the early development and propagation of an arc shaped line element similar to that found in the garp global atmospheric research program tropical atlantic experiment gate 4 5 september 1974 squall line system the simulated squall line element forms in a relatively unexplored environment with moderate convective available potential energy and a strong low level jet bulk richardson number 5 37 associated with an easterly wave the simulated line element develops in a large scale convergence region from an initial cell that splits and elongates in a manner reminiscent of some midlatitude lines simulation features compare favorably with observed characteristics of some of the line elements including line orientation approximately perpendicular to the average wind shear below the low level jet propagation speed 11 m s21 to the southwest length 75 km and maximum precipitation rate 187 mm h21 in addition the simulated line merges with cells that form ahead as observed the simulated arc shaped line element consists of four regions several hours after its initiation the northern region or right flank of the line contains a long lived cell exhibiting three dimensional characteristics similar to midlatitude supercells including long lasting and steady updrafts with midlevel cyclonic rotation and movement to the right of the mean winds although the simulated supercell characteristics cannot be confirmed because of insufficient data from the limited gate 4 5 september observations updrafts with strong vertical vorticity have been observed to occur in other gate rainbands where waterspouts have been seen the region just to the south of this cell is the site where a cell that formed out ahead of the line segment merges with the line and also develops supercell like characteristics farther to the south convection develops with quasi twodimensional characteristics below 3 4 km but breaking into several multicells above a rear inflow jet does not accompany these features and the winds in the downdraft are oblique too and nonuniform along the associated gust front finally on the southernmost or left flank of the line element cells with both long and short lifetimes develop sensitivity tests indicate that once the early line structure has developed its evolution and structure are not seriously altered by the removal of large scale forcing further the formation of the cold pool and gust front between the initial separating splitting cells is crucial to the filling in of the line changes in the thermodynamic profile consistent with nonsquall observations one half day earlier result in only modest differences changes in the wind profile based on the same observations led to significant differences such as the lack of convection between the initial separating cells and the merger taking place to the north of the right flank creating a convective complex in this region

coseismic strains on plate boundary observatory borehole strainmeters in southern california abstract strainmeters can record offsets coincident with earthquakes but how much these represent strain changes from elastic rebound and how much they are contaminated by local effects remains an open question to study this we use a probabilistic detection method to estimate coseismic offsets on nine borehole strainmeters bsms operated by the plate boundary observatory pbo in southern california from 34 earthquakes with a wide range of magnitudes and distances in general the offsets estimated for the bsm data differ substantially from the static strain predicted by elastic dislocation theory which is well supported by other techniques though 10 of the observed offsets agree well with theory for one earthquake the bsm offsets significantly disagree with collocated long base laser strainmeter data comparisons with collocated seismic data provide strong evidence that the absolute errors between the observed and predicted strains scale with the level of seismic energy density but also that relative errors normalized by the model size do not we conclude that apparent strain offsets are induced by seismic waves occurring presumably because of irreversible deformation whether in the rock or cementing materials close to the bsms or in the instruments themselves coseismic offsets seen in pbobsm data should therefore be viewed with caution before being used as a measure of large scale coseismic deformation online material tables of offset estimates and predictions error estimates strike sensitivities and figures of observed versus predicted offsets

measurements of coseismic deformation in southern california 1972 1982 since 1972 a number of static strain changes have been measured at pinon flat observatory southern california as a result of regional faulting as recorded by a collection of long baselength strainmeters and tiltmeters these signals are in good quantitative agreement with the deformation calculated for a dislocation in an elastic half space in contrast colocated short baselength sensors are found to produce spurious results whose size is much larger than expected theoretically and well correlated with peak site acceleration calculations show that the root mean square rms of the coseismic signals from several different instruments at one site or from several sites at known hypocentral distances provide a good estimate of the seismic moment a result confirmed by the observations static moment estimates for the four largest events in this period are imperial valley 1979 m0 9 0 1018nm mexicali valley 1980 m0 6 1 1018nm westmorland 1981 m0 5 3 1017nm and brawley 1979 m0 2 3 1017 nm these estimated moments generally exceed those determined seismically by about 25 which is as expected since they include some postseismic deformation results from the mexicali valley earthquake are particularly interesting indicating an average fault strike approximately 9 different from the historic fault trace several small to moderate earthquakes ml 3 7 5 2 were also well enough recorded to estimate source parameters for the only other detectable events in the period 1972 1982 a total of three others for which the strain change erms was greater than 0 4 ne high accelerations caused most of the instruments at the site to malfunction no precursory signals were evident for any of the earthquakes recorded at this site

noise levels on plate boundary observatory borehole strainmeters in southern california to establish noise levels for the borehole strainmeters of the plate boundary observatory pbo we have analyzed data recorded by eight of these instruments all in the anza region of southern california we determine time varying power spectra for frequencies from 10 3 to 10 hz using a new method that combines multitaper spectrum estimation smoothing by local regression and computation of cumulative distribution functions from about 2 hz to the nyquist frequency of 10 hz the noise floor is set by instrument resolution for frequencies between 0 1 hz and 1 hz it is set by microseisms the lowest noise level is between 0 01 and 0 1 hz with a rapid increase at lower frequencies however in most instruments this low noise range also contains narrowband noise that appears to be caused by power supply fluc tuations we compare these results with noise spectra from other types of strainmeters which suggest two conclusions 1 they are in agreement with results for surficial long baseline instruments and 2 other subsurface strainmeters have lower noise in the seismic band than the pbo instruments do online material noise models and statistical variation

general characteristics of squall lines observed in tamex abstract six cases of prefrontal squall lines were observed over the taiwan strait and western taiwan during the 1987 taiwan area mesoscale experiment tamex the mean propagation speed was 10 m s 1 and the mean life span was 11 4 h for the six squall lines all the lines occurred ahead of the mei yu front and moved away from the front with time the mean environmental conditions associated with the squall lines were analyzed by compositing the six cases the environmental conditions observed during the tamex squall lines were found with characteristics between tropical and midlatitude squall lines the steering level was near 7 km during the mature stage a low level jet at 3 4 km was present with strong vertical shear in the presquall environment below 700 hpa the squall lines were oriented 45 to the shear in the 1 3 km layer like midlatitude cases the cape however is similar to the tropical squall lines the inflow ahead of the squall lines was deeper and stronger below 400 hpa and the cape w

continuous measurements of crustal deformation for the 1992 landers earthquake sequence abstract we describe and attempt to interpret continuous measurements of strains and tilts made at pinon flat observatory pfo before during and after the landers and joshua tree earthquake sequences these data show substantial transient deformation following the landers mainshock with a total amplitude of several percent of the co seismic deformation and a decay time of at least several days comparing data from the many types of instruments at pfo allows us to infer possible sources for this deformation the immediate postseismic transient was nearly the same size on three long base strainmeters suggesting either broadscale deformation or local motion near one part of the observatory the latter can largely be ruled out by the similarity of many other measurements in the area covered by these strainmeters and the observations by others of significant postseismic displacements nearer the source possible mechanisms for broad scale deformation include postseismic fault slip time dependent creep in near surface rocks and elastic or thermal responses to water table changes the first two agree best with the observations from pfo but if postseismic fault slip is the source it must have been distributed differently than the co seismic slip and may have included faults other than those that ruptured seismically if one of the other mechanisms is the main source the pfo data imply that the postseismic slip must have been very much smaller than the seismic slip perhaps 2 or less no significant preseismic deformation was observed at a level of 2 10 3 of the co seismic deformation for the days to minutes before the earthquake

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

coseismic strain steps observed by three component borehole strainmeters abstract thirteen coseismic strain steps were observed by 3 component borehole strainmeters at yasato in the kanto area japan two sets of strainmeters were installed 60 m apart and the observed strain steps were in good agreement with each other corresponding theoretical strain steps were calculated from local mechanisms determined by p wave initial motions or long period seismic waves the calculated strain steps agree with observations within a factor of 2 for amplitudes and within 10 for directions the three component strainmeter can detect steps over 0 3 nanostrain these results demonstrate the high reliability of the three component strainmeter when the network of stations of three component borehole strainmeters is constructed and coseismic steps are observed at several stations it will be possible to determine fault mechanisms including aseismic deformation of the earthquake

tidal calibration of plate boundary observatory borehole strainmeters 1 the plate boundary observatory the geodetic component of the earthscope program includes 74 borehole strainmeters installed in the western united states and on vancouver island canada in this study we calibrate 45 of the instruments by comparing the observed m2 and o1 earth tides with those predicted using earth tide models for each strainmeter we invert for a coupling matrix that relates the gauge measurements to the regional strain field assuming only that the measured strains are linear combinations of the regional areal and shear strains we compare these matrices to those found when constraints are imposed which require the coupling coefficients to lie within expected ranges for this strainmeter design similar unconstrained and constrained coupling matrices suggest the instrument is functioning as expected as no other coupling matrix can be found that better reduces the misfit between observed and predicted tides when the inversion is unconstrained differences imply a coupling matrix with coefficients outside typical ranges gives a better fit between the observed and predicted tides we find that 22 of the strainmeters examined have coupling matrices for which there is little difference between the constrained and unconstrained inversions if we allow a greater divergence in the shear coupling coefficients and consider the possibility that one gauge may not function as expected the discrepancies between the unconstrained and constrained coupling matrices are resolved for a subset of the remaining strainmeters our results also indicate that most of the strainmeters are less sensitive to areal strain than expected from theory

measurements and interpretations of tilt strain gauges in seismically active areas abstract an overview of different aspects of deformation measurements is given an introduction to the general theory of point crustal deformations with an application to the stress strain relations at the earth surface is made the instrumentation used in crustal deformation measurements is briefly explained emphasizing different constructions of tilt and strainmeters the problems connected with the housing of the instruments i e the cavity and topography effects and with the ambient noise factors as the hydrological and pressure effects are discussed the last part of the paper is concerned with the relation between deformation measurements and seismic events both from a theoretical and observational standpoint a number of examples are shown that report on pre co and post seismic and the secular term deformation in different areas of the world

effect of error in theoretical earth tide on calibration of borehole strainmeters 1 since the installation of borehole strainmeters into the ground locally distorts the strain in the rock these strainmeters require calibration from a known source which typically is the earth tide consequently the accuracy of the observed strain changes from borehole strainmeters depends upon the calibration derived from modeling the earth tide previous work from the mid 1970s which is replicated here demonstrate that the theoretical tide can differ by 30 from the tide observed at surface mounted long baseline strainmeters in spite of possible inaccurate tidal models many of the 74 borehole strainmeters installed since 2005 can be calibrated however inaccurate tidal models affect the amplitude and phase of observed transient strain changes which needs to be considered along with the precision of the data from the inherent drift of these borehole instruments in particular the error from inaccurate tidal model dominates the error budget in the observation of impulsive sub daily strain transients

source parameters of the october 1 1987 whittier narrows earthquake from crustal deformation data offsets in the regional strain field generated by the october 1 1987 whittier narrows earthquake were recorded with large amplitudes on two deep borehole dilational strainmeters at distances of 46 7 and 65 5 km from the hypocenter and marginally on instruments at greater distances in the parkfield area and at pinon flat where laser extensometers also recorded small offsets these data are insufficient to solve for the location and physical parameters of the earthquake but by also using the measured elevation changes in the epicentral area we are able to invert for source models consistent with all available observations of crustal deformation the source models obtained indicate that slip extends to a depth of about 30 km well below the recorded aftershock zone the requirement for deeper and presumably aseismic slip derives from the large negative dilatation experienced by the nearest strainmeter pubs but high frequency data from the same site exclude any significant slow component of moment release by ignoring pubs we obtain a moment of about 0 7 1018 n m on a fault that has a strike and dip of about n60 w and 40 down to the north respectively and extends to a depth of about 16 km the most likely reason for the anomalous offset at pubs appears to be sympathetic slip triggered on a nearby fault by the main shock precursive strain during the month prior to the earthquake is not apparent at the nanostrain level in the data from the closest instrument but the event was accompanied by a change in strain rate at the two nearer sites

particulate gravity currents along v shaped valleys this paper extends previous studies of saline gravity currents at high reynolds number flowing along a tank with a v shaped valley we use experiments and a box model to determine the primary features of the flow the particulate gravity currents were initiated by releasing a fixed volume of fluid consisting of pure water mixed with silicon carbide particles from a lock at one end of the tank the resulting motion and deposit pattern differ significantly from those for the propagation of a particulate gravity current along a flat bottomed tank the front of the current seen from above is approximately parabolic with axis parallel to the flow direction in contrast to the current in a flat bottomed tank where it is nearly a straight line perpendicular to the flow this feature mimics the results for pure saline currents when seen in profile the currents do not have a clearly defined raised head which is a feature of the flat bottomed currents the mass deposited per unit area varies nearly monotonically with respect to distance down the tank again in contrast to the case of the flat bottomed tank the exceptions to this are the two experiments which have the highest ratio of lock height to length the mass deposited per unit area across the v shaped valley is much larger in the central part of the valley than it is on the flanks for any position along the valley we find that the results can be described with remarkable accuracy by a box model using a generalization of the equation for sedimentation from a turbulent medium due to martin and nokes our results further show that the factor used in the deposition rate equation which is commonly assumed to be 1 should be smaller typically 0 7

continuous borehole strain and pore pressure in the near field of the 28 september 2004 m 6 0 parkfield california earthquake implications for nucleation fault response earthquake prediction and tremor near field observations of high precision borehole strain and pore pres sure show no indication of coherent accelerating strain or pore pressure during the weeks to seconds before the 28 september 2004 m 6 0 parkfield earthquake minor changes in strain rate did occur at a few sites during the last 24 hr before the earth quake but these changes are neither significant nor have the form expected for strain during slip coalescence initiating fault failure seconds before the event strain is stable at the 10 11 level final prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 10 12 nm m 2 2 and a source size less than 30 m ground displacement data indicate similar constraints localized rupture nucleation and runaway precludes useful prediction of damaging earthquakes coseismic dynamic strains of about 10 microstrain peak to peak were superimposed on volumetric strain offsets of about 0 5 microstrain to the northwest of the epicenter and about 0 2 microstrain to the southeast of the epicenter consistent with right lateral slip observed strain and global positioning system gps offsets can be simply fit with 20 cm of slip between 4 and 10 km on a 20 km segment of the fault north of gold hill m 0 7 10 17 n m variable slip inversion models using gps data and seismic data indicate similar moments observed postseismic strain is 60 to 300 of the coseismic strain indicating incomplete release of accumulated strain no measurable change in fault zone compliance preceding or following the earthquake is indicated by stable earth tidal response no indications of strain change accompany nonvolcanic tremor events reported prior to and following the earthquake

western u s upper mantle structure regional three dimensional inversions of upper mande p wave velocity structure are created from teleseismic p wave travel time residuals recorded by many of the high density high frequency regional arrays operated within the western united states these inversions are adjusted to a global international seismic centre reference and merged to obtain an image of the upper mantle beneath western united states the p wave velocities in the upper mantle are slow on average and the structure is very heterogeneous where resolution is good coherent upper mantle structures are imaged that extend as deep as 200 km the juan de fuca and gorda slabs which penetrate to greater depths are exceptions and deviate from the average velocity at a given depth by as much as 4 lateral resolution of these structures usually is very good although the magnitude of the actual seismic variations is probably greater than that imaged the long wavelength part of the imaged mantle structure defines coherent elongate features with wavelengths of 200 500 km within 250 km of the pacific coast these structures have a wavelength of 250 km and trend parallel to the surface physiography and young tectonic structures beneath the continental interior where use is made of additional seismic studies to infer average structure in regions of poor teleseismic data coverage structures have a wavelength of 500 km and trend northeasterly this northeast orientation is discordant with young tectonic structures but aligns with young volcanic activity

design parameters for borehole strain instrumentation the response of a borehole strain meter to hydrostatic and shear deformations in an isotropic medium is calculated to facilitate optimum instrument design and produce instrument response factors for parameters typically encountered in installed instruments results for an empty borehole are first compared with results for an instrument in intimate contact with the surrounding rock the effects of the grout used to install the instrument are then examined where possible analytic forms for the response factors are given results for typical installations are then presented in graphical form for optimizing instrument design in an environment of known elastic parameters alternatively the results may be applied in the measurement of unknown strain signals to correct for instrument response or to provide in situ estimates of the elastic properties of the environment by examination of observed strain response to known strain signals

tidal calibration of plate boundary observatory borehole strainmeters roles of vertical and shear coupling 1 a multicomponent borehole strainmeter directly measures changes in the diameter of its cylindrical housing at several azimuths to transform these measurements to formation strains requires a calibration matrix which must be estimated by analyzing the installed strainmeter s response to known strains typically theoretical calculations of earth tidal strains serve as the known strains this paper carries out such an analysis for 12 plate boundary observatory pbo borehole strainmeters postulating that each of the strainmeters four gauges responds couples to all three horizontal components of the formation strain tensor as well as to vertical strain orientation corrections are also estimated the fourth extensometer in each pbo strainmeter provides redundant information used to reduce the chance that coupling coefficients could be misleadingly fit to inappropriate theoretical tides satisfactory fits between observed and theoretically calculated tides were obtained for three pbo strainmeters in california where the calculated tides are corroborated by other instrumentation as well as for six strainmeters in oregon and washington where no other instruments have ever recorded earth tidal strain several strainmeters have unexpectedly large coupling coefficients for vertical strain which increases the strainmeter s response to atmospheric pressure vertical coupling diminishes or even changes the sign of the apparent response to areal strain caused by earth tides or deep earth processes because near the free surface vertical strains are opposite in sign to areal strain vertical coupling does not impair the shear strain response however pbo borehole strainmeters can provide calibrated shear strain time series of transient strain associated with tectonic or magmatic processes

in situ calibration of and algorithm for strain monitoring using four gauge borehole strainmeters fgbs 1 borehole strainmeters have proved very useful in geodynamic research because the sensors are imbedded in rock their in situ calibration is of crucial importance the four gauge borehole strainmeter fgbs is a chinese invention to monitor the temporal variation in horizontal strain the four gauges in the fgbs are arranged at 45 intervals to bring about a simple self consistency equation which serves as a means of checking that the measurements obtained from the fgbs are correct the instruments currently used in china are usually placed at depths of several tens of meters to avoid disturbances at the surface while still being sufficiently near the surface for the vertical stress to be regarded as zero the premise on which the theoretical model of this observation is based in this paper an index of data credibility is established based on the self consistency equation to allow evaluation of the observations a relative in situ calibration has been developed to calculate a relative correction factor for each gauge s sensitivity termed the gauge weight and this has proven effective in enhancing data credibility parameters for deriving strain from readings are determined by a concise absolute in situ calibration with the aid of the theoretical earth tide instead of averaging four groups of solutions a simpler comprehensive algorithm is developed to transform readings into strain data from 24 chinese sites of yry 4 type fgbs are processed and evaluated to be fairly good

probing asthenospheric density temperature and elastic moduli below the western united states periodic ocean tides continually provide a cyclic load on earth s surface the response to which can be exploited to provide new insights into earth s interior structure we used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western united states and nearby offshore regions our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers the model indicates that the asthenosphere has a low density anomaly of 50 kilograms per cubic meter a temperature anomaly of 300 c can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli

local effects on tidal strain measurements at esashi japan summary finite element modelling has been used to make a quantitative investigation of local factors affecting the measurement of tidal strain at the esashi earth tide station factors investigated with the approximate magnitude of the perturbation produced by each are topography 12 per cent regional geology 1 per cent inhomogeneity of the elastic properties of the granodiorite from which the strainmeter tunnels were excavated 3 per cent and the cavity effect 2 per cent correction for these factors reduces the average discrepancy between the observed strains observational accuracy 1 per cent and those predicted from the solid earth and ocean loading tide from 23 to 8 per cent after such correction the ratios of observed to modelled amplitudes of the o1 and m2 tides on each strainmeter are in fair agreement but these ratios differ from strainmeter to strainmeter they are about 7 per cent too large on the n s and ne sw strainmeters and 9 per cent too small on the e w instrument these studies illustrate the difficulties involved in relating strains measured in an observatory such as esashi to those representative of the surrounding region and suggest that with the level of detail and sophistication used this relationship cannot be modelled to much better than 10 per cent systematic differences between results from the mid point and free end strainmeters imply that the effects of small scale rock inhomogeneities have not been modelled correctly

co seismic displacements of the 1992 landers earthquake sequence we present co seismic displacement vectors derived from global positioning system gps measurements of 92 stations in southern california these gps results are combined with five well determined gps displacement vectors from continuously tracking stations of the permanent gps geodetic array as well as line length changes from usgs geodolite and two color laser trilateration observations to determine a self consistent set of geodetic data for the earthquake these combined displacements are modeled by an elastic dislocation representation of the primary fault rupture planes on average the model residuals are about twice the estimated measurement errors

long period toroidal earth free oscillations from the great sumatra andaman earthquake observed by paired laser extensometers in gran sasso italy summary strain data recorded by two crossed laser extensometers operating in the gran sasso underground observatory recorded seismic free oscillations excited by the 2004 december 26 sumatra andaman earthquake the main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods t 1000 s we reconstruct the time evolution of selected free oscillations for comparison with synthetic seismograms that include normal mode coupling effects from coriolis force attenuation and ellipticity envelopes estimated for the gran sasso differential data set for free oscillations with period t 1 mhz are approximated adequately by a composite centroid moment tensor cmt source with five subevents and an aggregate mw 9 3 moment magnitude envelopes for several toroidal free oscillations with t 1000 s are predicted less well the amplitude of the rarely observed mode 0t2 is overpredicted at gran sasso by roughly a factor of two and other modes are underpredicted the amplitude discrepancy for 0t2 is confirmed at selected exceptionally low noise seismic stations hypothetical explanations include a slow slip component of the seismic moment release errors in the composite cmt source model unmodelled coupling effects to earth s secular modes and feedback from the sumatra andaman tsunami on indian ocean coastlines of these hypotheses either an extended duration strain release or tsunami feedback seem most plausible the viability of the tsunami feedback mechansim deserves further investigation

revisiting borehole strain typhoons and slow earthquakes using quantitative estimates of precipitation induced strain changes taiwan experiences high deformation rates particularly along its eastern margin where a shortening rate of about 30 mm yr is experienced in the longitudinal valley and the coastal range four sacks evertson borehole strainmeters have been installed in this area since 2003 liu et al 2009 proposed that a number of strain transient events primarily coincident with low barometric pressure during passages of typhoons were due to deep triggered slow slip here we extend that investigation with a quantitative analysis of the strain responses to precipitation as well as barometric pressure and the earth tides in order to isolate tectonic source effects estimates of the strain responses to barometric pressure and groundwater level changes for the different stations vary over the ranges 1 to 3 nanostrain millibar hpa and 0 3 to 1 0 nanostrain hpa respectively consistent with theoretical values derived using hooke s law liu et al 2009 noted that during some typhoons including at least one with very heavy rainfall the observed strain changes were consistent with only barometric forcing by considering a more extensive data set we now find that the strain response to rainfall is about 5 1 nanostrain hpa a larger strain response to rainfall compared to that to air pressure and water level may be associated with an additional strain from fluid pressure changes that take place due to infiltration of precipitation using a state space model we remove the strain response to rainfall in addition to those due to air pressure changes and the earth tides and investigate whether corrected strain changes are related to environmental disturbances or tectonic original motions the majority of strain changes attributed to slow earthquakes seem rather to be associated with environmental factors however some events show remaining strain changes after all corrections these events include strain polarity changes during passages of typhoons a characteristic that is not anticipated from our estimates of the precipitation transfer function that are more readily explained in terms of tectonic origin motions but clearly the triggering argument is now weaker than that presented in liu et al 2009 additional on site water level sensors and rain gauges will provide data critical for a more complete understanding including the currently unresolved issue of why for some typhoons there appears to be a much smaller transfer function for precipitation induced strain changes

runout and fine sediment deposits of axisymmetric turbidity currents we develop a model that describes the runout behavior and resulting deposit of a radially spreading suspension driven gravity current on a surface of negligible slope our analysis considers the separate cases of constant volume and constant flux sources it incorporates expressions for the conservation of volume a froude number condition at the current front and the evolution of the driving suspension due to settling of particles to the underlying bed the model captures the key features of a range of experimental observations the analysis also provides important scaling relationships between the geometry of a deposit and the source conditions for the deposit forming flow as well as explicit expressions for flow speed and deposit thickness as functions of radial distance from the source among the results of our study we find that in the absence of information regarding flow history the geometries of relatively well sorted deposits generated by flows with source conditions of constant volume or constant flux are virtually indistinguishable the results of our analysis can be used by geologists in the interpretation of some geologically important gravity surge deposits using our analytical results we consider three previously studied radially symmetric turbidites of the hispaniola caicos basin in the western atlantic ocean from gross geometry and grain size of the turbidites alone we estimate for the respective deposit forming events that upon entry into the basin the initial sediment concentrations were approximately 3 by volume and the total volumes were roughly between 30 km 3 and 100 kn1 3 each of the suspension driven flows is inferred to have spread into the basin with a characteristic speed of 3 5 m s 1 and reached its ultimate runout length of about 60 75 km while laying down a deposit over a period of about 10 12 hours

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

the effect of confining boundaries on viscous gravity currents newtonian viscous gravity currents propagating along horizontal and inclined channels with semicircular and v shaped boundaries are examined similarity solutions are obtained from the governing mathematical equations and compared with closely matching data from laboratory experiments in which the propagation of glycerine along different channels was recorded geological applications of the results are discussed briefly

gravity currents descending a ramp in a stratified tank this paper describes experiments and numerical simulations of a gravity current flowing down a ramp in a tank stratied in two layers we study the dynamics of the conguration for dierent densities of the gravity current and dierent ramp angles the experiments show that waves of large amplitude can be generated easily and that depending on the density of the gravity current the initial gravity current splits into a gravity current along the interface of the stratied layers and a gravity current along the bottom of the tank we also describe numerical simulations which give results in agreement with the results of the experiments and enable us to study three fluid congurations with wider ranges of density than is possible in the laboratory

a parametrized solid earth tide model and ocean tide loading effects for global geodetic baseline measurements summary an observation model for earth tide displacements in application to very long baseline interferometry and similar precise geodetic techniques is developed it incorporates effects from anelasticity ellipsoidal figure and fluid core resonance based on a harmonic development of the external potential the model follows the familiar love number concept the transfer function of the earth to each harmonic is formulated in terms of coupled harmonics in the space domain and fulfils the causality condition in the time domain solve for parameters can be chosen flexibly the guideline however has been to provide a minimum set of well defined and well resolvable tide response parameters for analysis of observations the aim of accuracy for tide displacements prediction is below 1 mm being the major perturbation of the solid earth tide ocean tide loading effects are computed and the accuracy of the models involved is discussed it appears that the major error source relates to those ocean tide frequencies for which global models are not available these frequencies form a continuum with a power spectrum being largely a result of non linear tide interaction the associated loading effects cannot be reliably interpolated from global tide models which are available only for a few distinct frequencies and which disregard tidal intermodulation thus an accuracy of 1 mm for computed loading tide displacements cannot always be achieved

seismic fracture anisotropy in the earth s crust an overview fluid filled fractures and microcracks are the most stress sensitive component of crustal rock and often determine the pathways and volume of crustal fluid movement if we are to comprehend the role of fractures and fluids in tectonic processes to formulate an accurate hypothesis for phenomena precursory to catastrophic seismic failure or to monitor hydrocarbon and geothermal reservoirs for the presence or absence of major fluid pathways we must understand how seismic waves interact with the fracture crack and microcrack structures within the rock mass a salient feature of fracture related rock structure is the effective seismic anisotropy of aligned fractures and microcracks with the advent of large volume digital seismic data sets it is feasible to use polarized shear waves to explore the anisotropic fracture properties of the crust crustal fracture structures which may be monitored by polarized shear waves range in dimensions from the 10 100 km scale of crustal stress orientation and preseismic stress buildup through the 100 1000 m scale of fluid reservoir structure and characterization and the 1 10 scale of mining and geoengineering rock strain monitoring to millimeter and micrometer or possibly smaller fluid filled inclusions determining the elastic response of the intact rock mass to focus developments in seismic anisotropic studies of crustal fracture phenomena the american geophysical union and the society of exploration geophysicists sponsored a chapman conference on seismic anisotropy in the earth s crust held may 31 to june 4 1988 at the lawrence berkeley laboratory of the university of california this was the third international workshop on seismic anisotropy 3iwsa nineteen conference papers are presented in this special section of the journal of geophysical research

velocity and turbulence structure of density currents and internal solitary waves potential sediment transport and the formation of wave ripples in deep water abstract laser doppler anemometry lda was used to measure the instantaneous downstream and vertical velocities in a series of simple and reflected saline density currents in a lock exchange flume tank all the currents were turbulent and subcritical mean downstream fluid velocities were in excess of the head velocity by up to 30 and instantaneous velocities were greater by up to 50 turbulence intensities were highest within the head and generally greatest in the middle part of the current but did not correspond with the level of highest mean velocities the maximum reynolds stress also occurred within the head large negative values were associated with shear along the upper boundary of the current peaks of turbulence reynolds stress and shear velocity occurred in association with the arrival of reflections in large scale turbidity currents such reflections would be capable of re entraining and resuspending sediment deposited by the forward current some reflections take the form of solitary waves within a residual flow with a velocity vector in the opposite direction in nature these could produce symmetrical ripples in environments below storm wave base

a search in strainmeter data for slow slip associated with triggered and ambient tremor near parkfield california 1 we test the hypothesis that as in subduction zones slow slip facilitates triggered and ambient tremor in the transform boundary setting of california our study builds on the study of peng et al 2009 of triggered and ambient tremor near parkfield california during time intervals surrounding 31 potentially triggering m 7 5 teleseismic earthquakes waves from 10 of these triggered tremor and 29 occurred in periods of ambient tremor activity we look for transient slow slip during 3 month windows that include 11 of these triggering and nontriggering teleseisms using continuous strain data recorded on two borehole gladwin tensor strainmeters gtsm located within the distribution of tremor epicenters we model the gtsm data assuming only tidal and drift signals are present and find no detectable slow slip either ongoing when the teleseismic waves passed or triggered by them we infer a conservative detection threshold of about 5 nanostrain for abrupt changes and about twice this for slowly evolving signals this could be lowered slightly by adding analyses of other data types modeled slow slip signals and gtsm data calibration detection of slow slip also depends on the slipping fault s location and size which we describe in terms of equivalent earthquake moment magnitude m in the best case of the gtsm above a very shallow slipping fault detectable slip events must exceed m 2 and if the slow slip is beneath the seismogenic zone below 15 km depth even m 5 events are likely to remain hidden

high resolution numerical simulations of the convective system observed in the lago maggiore area on 17 september 1999 map iop 2a during intensive observing period iop 2a of the mesoscale alpine programme map a significant convective system developed in the lago maggiore area its evolution is simulated using the meso nh model run over three nested domains with a 2 km horizontal resolution for the finest grid model results are assessed by comparing computed precipitation and model radar reflectivities with observed parameters a control simulation initialized with european centre for medium range weather forecasts analyses and run with the standard microphysical scheme of the model yields fairly realistic results neglecting the ice processes in the microphysical scheme degrades the numerical results whereas significant improvement is obtained when heavy rimed particles are considered to be hail instead of graupel copyright 2003 royal meteorological society