sea land breeze development during a summer bora event along the north eastern adriatic coast the interaction of a summer frontal bora and the sea land breeze along the north eastern adriatic coast was investigated by means of numerical simulations and available observations available measurements in situ radiosonde satellite images provided model validation the modelled wind field revealed several regions where the summer bora weaker than 6 m s 1 allowed sea breeze development in the western parts of the istrian peninsula and rijeka bay and along the north western coast of the island of rab along the western istrian coast the position of the narrow convergence zone that formed depended greatly on the balance between the bora jets northward and southward of istria in the case of a strong northern trieste bora jet the westerly istrian onshore flow presented the superposition of the dominant swirled bora flow and local weak thermal flow it collided then with the easterly bora flow within the zone with weakening of the trieste bora jet the convergence zone was a result of the pure westerly sea breeze and the easterly bora wind in general during a bora event sea breezes were somewhat later and shorter with limited horizontal extent the spatial position of the convergence zone caused by the bora and sea breeze collision was strongly curved the orientation of the head of the thermally induced flow was more in the vertical causing larger horizontal pressure gradients and stronger daytime maximum wind speed than in undisturbed conditions except for the island of rab other lee side islands in the area investigated did not provide favourable conditions for the sea breeze formation within a bora wake near the island of krk onshore flow occurred as well although not as a sea breeze flow but as the bottom branch of the lee rotor that was associated with the hydraulic jump like feature in the lee of the velika kapela mountain copyright 2010 royal meteorological society

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

moment tensor solutions of the 1994 to 1996 double spring flat nevada earthquake sequence and implications for local tectonic models abstract the 12 september 1994 m w 5 8 double spring flat nevada earthquake initiated at the intersection of a northeast and northwest striking set of conjugate faults within an overlapping zone between the genoa and antelope valley fault zones of the eastern sierra nevadan range frontal fault system the mainshock ruptured on the northeast striking fault plane eight days after the mainshock the aftershock activity migrated from the mainshock fault plane to the northwest striking conjugate fault over the next 2 years aftershocks migrated southward onto another set of conjugate faults and then onto the antelope valley fault zone the focal mechanisms of 17 m 4 aftershocks were estimated from a time domain moment tensor inversion using regional broadband data the t axis minimum stress direction is oriented east west n80 e to n100 e for the m 4 events as is commonly observed along the eastern sierra nevadan range front in northwestern nevada from these results we make some general points that can be considered in seismic hazard assessment the maximum magnitude in overlapping normal fault zone is limited to the size of the overlapping zone this makes small to moderate size m m 7 earthquakes the seismicity within this overlapping zone may indicate interseismic strain accumulation from east west extension mainly through strike slip deformation the apparent scarcity of modern normal faulting earthquakes along the sierran range front faults suggests a characteristic model while a gutenberg and richter model for the recurrence behavior of earthquakes applies to the overlap zones between the normal faults the pattern of seismicity and principle stress directions from the aftershock fault plane solutions suggest a tectonic model of changing fault geometry for the overlapping zone between the genoa and antelope valley fault zones two plausible long term tectonic outcomes may develop with this model a normal fault growth model where the overlapping segments of the genoa and antelope valley faults eventually become hard linked form a throughgoing fault or a normal fault growth model where the overlapping segment of the genoa fault system grows southward while the antelope valley fault is isolated in the formation of new basins and ranges

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

consistency of precariously balanced rocks with probabilistic seismic hazard estimates in southern california abstract the overturning fragility of a freestanding block such as a precariously balanced rock pbr has been parameterized as a function of a vector of ground motion intensity measures methodologies are outlined to estimate the failure probabilities of such objects given their residence times for deterministic seismic hazard analyses dshas a pbr is exposed to the scenario earthquakes that occur during its exposure time providing an estimate of the probability that the pbr survives the ensemble of events for probabilistic seismic hazard analyses pshas the pbr overturning fragility is multiplied by the ground motion occurrence rate from a vector valued probabilistic seismic hazard analysis vpsha yielding the marginal overturning rate for each ground motion bin summing the marginal rates over all ground motion bins produces the total overturning rate for time independent poisson based psha estimates the probability of block failure can be easily calculated as a function of exposure time this latter method is used to test vpsha estimates similar to the 2002 u s geological survey usgs national seismic hazard maps via pbr residence times pbr overturning fragilities are estimated at sites in southern california near the san andreas fault between the san jacinto and elsinore faults and near the white wolf fault the resulting failure probabilities for several of the pbrs are very high suggesting that they are inconsistent with the 2002 usgs ground motions an investigation of the hazard calculated with zero aleatory variability in the ground motion prediction equations gmpes suggests that the median ground motions or the earthquake rupture rates are too high at certain pbr sites

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

observations of bora events over the adriatic sea and black sea by spaceborne synthetic aperture radar abstract bora events over the adriatic sea and black sea are investigated by using synthetic aperture radar sar images acquired by the advanced sar asar on board the european satellite envisat it is shown that the sea surface roughness patterns associated with bora events which are captured by sar yield information on the finescale structure of the bora wind field that cannot be obtained by other spaceborne instruments in particular sar is capable of resolving 1 bora induced wind jets and wakes that are organized in bands normal to the coastline 2 atmospheric gravity waves and 3 boundaries between the bora wind fields and ambient wind fields quantitative information on the sea surface wind field is extracted from the envisat asar images by inferring the wind direction from wind induced streaks visible on sar images and by using the c band wind scatterometer model cmod ifr2 to convert normalized cross sections into wind speeds it is argued that spaceborne sar images acquired over the east c

eigenoscillations and stability of rocking stones the case study of the hus pulpit in the central bohemian pluton stability of precariously balanced rocks is employed in seismic hazard estimates standard toppling models of these rocks are based on a rigid body motion i e this approximation assumes that their eigenfrequencies are infinite in any position of a rock this assumption is however questionable in the case of rocking stones oscillating with lowest eigenfrequencies of only several hertz when resonance effects facilitating rolling wobbling due to a seismic signal cannot be a priori excluded an example demonstrating existence of such low frequencies is the hus pulpit rocking stone located in the central bohemian pluton 49 568n 14 363e the observed lowest frequencies recorded by a guralp cmg 40t seismometer located on the top of this rocking stone are 3 7 and 9 hz with the quality factors of 60 55 and 77 respectively using the comsol multiphysics software package we model the oscillations of this rocking stone numerically and demonstrate that these observed low frequencies and their dampings can be explained by a force interaction between the stone base and the bedrock that can formally be interpreted as the damped elastic response of the bedrock to its surface deformation by the stone we also numerically study stability of the stone under the presence of such an interaction and conclude that beginning of toppling requires very high horizontal pgv pga for input seismic frequencies even at the resonance frequencies however different numerical models where the seismic displacements are considered as the direct input at the rock base can result in rock instabilities under a presence of an hbox m 7 earthquake at a distance of about 150 km

aerial observations of the yugoslavian bora abstract the first aircraft observations of the bora in yugoslavia were accomplished during the alpex project in 1982 data from all five alpex bora flights have been analyzed in a comparative study of bora structure although the bora varies considerably in depth in the strength of the incoming low level flow and in the direction of the winds aloft several common features are evident these include upstream descent and acceleration beginning where the mountains rise an approximate coincidence between the depth of the uppermost descending streamline and the wind reversal level upstream when a reversal exists a decoupling of the flow aloft associated with a splitting of the inversion and the formation of a thick mixed layer downstream a narrow region of intense turbulence and an ascending jet just downstream of the plunging bora the bora structure is similar in many respects to the boulder windstorm internal hydraulic theory taking into account the decoupling effect of the intermediate layer a

precarious rock constraints on ground motion from historic and recent earthquakes in southern california new examples of precarious rocks are presented these rocks provide constraints on ground motion for historical and recent large earthquakes an approximate field calibration of the precarious rock methodology was provided by the m 7 1 hector mine earthquake of 16 october 1999 previously documented rocks at granite pass near kelso california brune 1996 were overturned by the earthquake and a nearby strong motion station indicated ground motions of about 0 2 g consistent with the toppling accelerations estimated in the published article the time of the last earthquake for the section of the fault nearest the precarious rocks has recently been determined to be more than 10 ka consistent with previously estimated ages for precarious rocks this first example of an actual earthquake field test lends strong support to the precarious rock methodology the other rocks discussed here give constraints on ground motions for historic earthquakes such as the 1812 and 1857 san andreas fault earthquakes the 1899 and 1912 san jacinto fault earthquakes the 1952 kern county earthquake and possibly recent but prehistoric earthquakes on the banning and garlock faults the ground motion constraints for these earthquakes are lower than predicted by some recent ground motion attenuation curves which are extrapolations to near fault distances from a data set dominated by data from larger distances but are generally consistent with peak ground accelerations observed from the recent large turkey and taiwan earthquakes and provide important additional information for seismic hazard analysis on the other hand there are areas where precarious rocks would be expected on the basis of previous studies but are apparently not found this suggests possible earthquakes on previously unrecognized or only recently recognized faults one such area is in northwestern san diego and southwestern orange county between the elsinore and newport inglewood faults the lack of precarious rocks in this area might be attributed to recent earthquakes on the blind thrust faults proposed in the area by grant et al 1999 2002 and rivero et al 2000

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

rocking and overturning of precariously balanced rocks by earthquakes abstract precariously balanced rocks in seismically active regions may be used to provide constraints on probabilistic estimates of strong ground motion a computer program is developed to study the rocking response of models of precariously balanced rocks when subjected to various levels of ground accelerations the computer code validated by comparing the numerical and experimental results for simple shaped rigid blocks is used to study the rocking response of rectangular blocks with various aspect ratios to the el centro strong ground motion recording of the 18 may 1940 imperial valley earthquake results show that during earthquakes the horizontal components of ground motion play a dominant role in overturning rocking objects the rederived and corrected housner9s equation 1963 could be used to estimate the minimum overturning acceleration of precarious rocks at different frequencies by measuring the quasi static toppling acceleration in the field

on the onset of bora and the formation of rotors and jumps near a mountain gap this study investigates the onset phase of a strong adriatic bora windstorm that occurred on 4 april 2002 the target area is a gap about 20 km wide embedded in the coastal mountain barrier of the dinaric alps that favours strong jet like winds airborne aerosol back scatter lidar measurements on board the dlr falcon research aircraft together with surface and upper air observations are used to verify high resolution numerical experiments conducted with the mesoscale atmospheric model rams and a single layer shallow water model swm especially during the breakthrough phase of the bora the flow at the gap exit exhibits a complex spatial structure and temporal evolution on a transect through the centre of the gap a hydraulic jump forms this is located close to the coast throughout the night and starts to propagate downstream in the early morning on a transect through the edge of the gap a lee wave induced rotor becomes established due to boundary layer separation it starts to propagate downstream about two hours after the jump this flow evolution implies that the onset of strong winds at the coast occurs several hours earlier downstream of the centre of the gap than downwind of the edge of the gap consequently the wind field in the vicinity of rijeka airport located downwind of the gap is strongly inhomogeneous and transient and represents a potential hazard to aviation measured bora winds at the surface exceed 20 ms 1 and the simulated wind speed in the gap wind layer exceeds 30 ms 1 the simulated turbulent kinetic energy exceeds 10 m2 s 2 rams indicates that wave breaking near a critical level is the dominant mechanism for the generation of the windstorm gap jets can be identified downstream of several mountain passes the simulated wave pattern above the dinaric alps the wave decay with height due to directional wind shear and the strong flow descent on the leeward side of the barrier are supported by measured back scatter intensities basic bora flow features including gap jets and jumps are remarkably well reproduced by swm simulations the rams reference run captures observed flow phenomena and the temporal flow evolution qualitatively well a cold low level bias an overestimated bora inversion strength and a slightly too early bora onset are probably related to insufficient turbulent mixing in the boundary layer the amplitude of trapped gravity waves the time of the bora breakthrough and the inversion strength are found to be quite sensitive to the turbulence parametrization copyright 2008 royal meteorological society

methodology for using precarious rocks in nevada to test seismic hazard models abstract fields of precariously balanced rocks indicate that strong earthquake motions have not occurred at that site since the precarious rocks developed these fields can be characterized with an estimate of the peak acceleration that would be sufficient to topple the rocks and an estimate of how long the rocks have been precarious this article uses this information to test the input to probabilistic seismic hazard analysis the fundamental assumption is that the probability of exceeding a ground motion capable of toppling a precarious rock during a time period equal to the age of the rock is equal to the confidence level at which the inputs to the probabilistic seismic hazard analysis can be rejected we performed a probabilistic seismic hazard analysis for 26 sites of observed precarious rocks in nevada using preliminary estimates of the toppling acceleration and the age of the features two standard models are rejected with over 95 confidence by most of the precarious rock observations we consider several possible explanations for the inconsistency a probabilistic seismic hazard analysis that eliminates the area sources and only includes faults is consistent with the precarious rock observations at most of the sites spatial clustering of small magnitude events could maintain this effect without contradicting the precarious rock observations however it may not be necessary to completely reject the area sources from our probabilistic seismic hazard analysis the physics of rock stability may allow increasing the minimum magnitude to 6 0 in the area sources because the short duration of high frequency accelerations in smaller events may not topple all precarious rocks the precarious rocks could generally have small site effects attenuation models may overestimate ground motions on the foot wall of normal faults and a different attenuation model in general might decrease the ground motion predictions the ergodic assumption that is made in estimating the uncertainty in attenuation models may be contributing to overestimate the hazard individually each of these effects might allow more of the precarious rock sites to be consistent with the area source zones

precariously balanced rocks and ground motion maps for southern california groups of precariously balanced rocks are effectively low resolution strong motion seismoscopes that have been operating on solid rock outcrops for thousands of years and once the methodology has been developed can provide important information about seismic risk in one zone near victorville only 30 km from the nearest point on the san andreas fault more than 50 precarious rocks have been documented widespread rock varnish suggests that many of these rocks have been in their current unstable positions for thousands of years we have established the mechanical basis for rough estimates of the horizontal accelerations necessary to topple these rocks using field observations and numerical and physical modeling to verify that zones of precarious rocks do not occur near historic earthquakes searches using binoculars were made along roads with occasional foot surveys near large earthquakes based on these reconnaissance searches we conclude that no precarious rock zones are found within 15 km of zones of high energy release of historic large earthquakes to document the occurrence of precarious rocks in southern california road surveys were carried out along major roads four zones of precarious rocks and seven other zones of somewhat less precarious rocks have been documented published probabilistic ground motion maps for southern california are compared with the occurrence of zones of precarious and semi precarious rocks the results are encouraging and suggest that eventually studies of precarious rocks will provide important constraints on the assumptions on which the maps are based results from studies of precarious rocks may eventually provide important information for siting and design of sensitive structures such as hospitals and power plants precarious rocks give a direct indication of past ground shaking in contrast to the indirect inference provided by fault trenching studies which may be subject to uncertainties in the actual time history of slip due to the fault e g fault creep slow earthquakes or unknown dynamic stress drop it is concluded that precarious rocks warrant further study and quantitative analysis

investigation of upstream boundary layer influence on mountain wave breaking and lee wave rotors using a large eddy simulation abstract interactions between a turbulent boundary layer and nonlinear mountain waves are explored using a large eddy simulation model simulations of a self induced critical layer which develop a stagnation layer and a strong leeside surface jet are considered over time wave breaking in the stagnation region forces strong turbulence that influences the formation and structure of downstream leeside rotors shear production is an important source of turbulence in the stagnation zone and along the interface between the stagnation zone and surface jet as well as along the rotor edges buoyancy perturbations act as a source of turbulence in the stagnation zone but are shown to inhibit turbulence generation on the edges of the stagnation zone surface heating is shown to have a strong influence on the strength of downslope winds and the formation of leeside rotors in cases with no heating a series of rotor circulations develops capped by a region of increased winds weak heating disrupts this system an

wave breaking induced surface wakes and jets observed during a bora event 1 an observational and modeling study of a bora event that occurred during the field phase of the mesoscale alpine programme is presented research aircraft in situ measurements and airborne remote sensing observations indicate the presence of strong low level wave breaking and alternating surface wakes and jets along the croatian coastline over the adriatic sea the observed features are well captured by a high resolution coamps simulation analysis of the observations and modeling results indicate that the long extending wakes above the boundary layer are induced by dissipation associated with the low level wave breaking which locally tends to accelerate the boundary layer flow beneath the breaking farther downstream of the high peaks a hydraulic jump occurs in the boundary layer which creates surface wakes downstream of lower terrain passes the boundary layer flow stays strong resembling supercritical flow

terrain types and local scale stratigraphy of grooved terrain on ganymede grooved terrain is subdivided on the basis of pervasive morphology into 1 groove lanes elongate parallel groove bands 2 grooved polygons polygonal domains of parallel grooves 3 reticulate terrain polygonal domains of orthogonal grooves and 4 complex grooved terrain polygons with several complexly cross cutting groove sets detailed geologic mapping of select areas employing previously established conventions for determining relative age relations reveals a general three stage sequence of grooved terrain emplacement first dissection of the lithosphere by throughgoing grooves and pervasive deformation of intervening blocks second extensive flooding and continued deformation of the intervening blocks third repeated superposition of groove lanes concentrated at sites of initial throughgoing grooves this sequence is corroborated by crater density measurements dominant orientations of groove sets are parallel to relict zones of weakness that probably were reactivated during grooved terrain formation groove lane morphology and development consistent with that predicted for passive rifts suggests a major role of global expansion in grooved terrain formation

ambiguities in direct dating of rock surfaces using radiocarbon measurements an attempt was made to date rock surfaces with accelerator mass spectrometry ams radiocarbon measurements of rock varnishes or rock weathering rinds in two case studies samples pretreated in the laboratory of dr ronald dorn prior to ams analysis have been found to contain significant quantities of carbon rich materials of two distinct classes type i material resembles bituminous coal whereas type ii material resembles pyrolized wood charcoal fragments in samples where these type i and type ii materials were separated and ams radiocarbon dated they were found to have widely differing radiocarbon ages in these cases the measurement of the radiocarbon age of the entire sample would yield results that are at best ambiguous neither type i nor type ii materials were found in comparable samples that were independently prepared

locating distributed faulting contributions from insar imaging to probabilistic fault displacement hazard analysis pfdha abstract prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment currently the best practice involves the applications of probabilistic fault displacement hazard analysis pfdha whose results fit sufficiently well real data in the near range of the primary fault but show considerable inaccuracies in the far range we believe that this inaccuracy descends from the biased earthquake databases used for regression analysis whose data relative to old earthquakes were largely collected only by field surveys focused close to the primary fault i e near range remotely sensed data i e interferometric radar imaging insar offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting we analyze the l aquila earthquake case study 29th april 2009 mw 6 3 and explore the correlation between location and slip on distributed faulting and insar derived deformation field we find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field in spite of the distance from the primary fault moreover distributed faults tend to occur within the area deformed by the earthquake as imaged by insar data and whose extent is directly proportional to the earthquake magnitude mw according to a dataset of 30 recent earthquakes we then propose that these observations have to be incorporated into the present pfdha practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field based and remotely data collection have to be implemented following strong earthquakes

the response of bora type flow to sea surface temperature a non linear two dimensional hydrostatic incompressible numerical model with a higher order turbulence closure scheme is used to study the effect of sea surface temperature on the severe downslope wind called bora at the adriatic coast a non linear large amplitude mountain wave is generated and is broken beneath and within its critical layer due to resonant tuning between the initially single layer atmosphere and the terrain the tuning is governed by the froude number a qualitative and sometimes quantitative analogy exists between the wave breaking unsteady stratified flow and the hydraulic jump steady two layer flow it is also known that the strongest adriatic bora appears during the winter season when the sea surface temperature is typically larger than the ground surface temperature firstly a relatively higher lower sea surface temperature means an additional distortion moderation of the mountain wave and consequently a larger smaller area with bora wind maxima for a relatively higher sea surface temperature a propagating hydraulic jump occurs typically bora maxima are about three to four times larger than the related geostrophic wind 8 m s 1 secondly the presence and importance of the inertial oscillation are indicated since the wave breaking is the vital component of the strongest bora cases there is a relatively large elevated area i e the critical layer with substantial flow decelerations and generally low wind speeds the wave breaking area has a rossby number o 1 hence the earth s rotation appears to be an important part of bora evolution the simulations presented consider generalized bora cases which may pertain to other similar orographic flows

studies on precarious rocks in the epicentral area of the ad 1356 basle earthquake switzerland summary for the first time precarious rocks have been analysed in the epicentral area of the ad 1356 basle earthquake in northern switzerland several cliff sites in flat lying thickly bedded upper jurassic coral limestones in the jura mountains were investigated seven blocks are regarded as precarious with respect to earthquake strong ground motions the age of these precarious rocks could not be determined directly as for instance by radiometric dating methods however based on slope degradation processes it can be concluded that the formation of these blocks predates the ad 1356 basle earthquake the acceleration required to topple a precarious rock from its pedestal is estimated using geometrical data for individual block sections and earthquake strong motion records from stations on rock sites in the european strong motion database as input data for the computer program rocking v1 0 from the seismological laboratory university of nevada reno the calculations indicate that toppling of a precarious rock largely depends on earthquake strength but also on the frequency spectrum of the signal although most investigated precarious rocks are surprisingly stable for ground motions similar to those expected to have occurred during the ad 1356 basle earthquake at least two blocks are clearly precariously balanced with peak toppling accelerations lower than 0 3 g possible reasons why these blocks did not topple during the ad 1356 basle earthquake include incomplete separation from their base sliding of precarious rocks their size lower than assumed ground accelerations and or duration of shaking

lee wave resonances over double bell shaped obstacles lee wave resonance over double bell shaped obstacles is investigated through a series of idealized highresolution numerical simulations with the nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps model using a free slip lower boundary condition the profiles of wind speed and stability as well as terrain derive from observations of lee wave events over the sierra nevada and inyo mountains from the recently completed terrain induced rotor experiment t rex numerical experiments show that double bell shaped obstacles promote trapped lee waves that are in general shorter than those excited by an isolated ridge while the permissible trapped lee wave modes are determined by the upstream atmospheric structure primarily vertical wind shear the selected lee wave wavelengths for two obstacles that are close or equal in height are dictated by the discrete terrain spectrum and correspond to higher harmonics of the primary orographic wavelength which is equal to the ridge separation distance the exception is the smallest ridge separation distance examined one that corresponds to the owens valley width and is closest to the wavelength determined by the given upstream atmospheric structure for which the primary lee wave and orographic wavelengths were found to nearly coincide the influence two mountains exert on the overall lee wave field is found to persist at very large ridge separation distances for the nonlinear nonhydrostatic waves examined the ridge separation distance is found to exert a much stronger control over the lee wave wavelengths than the mountain half width positive and negative interferences of lee waves which can be detected through their imprint on wave drag and wave amplitudes were found to produce appreciable differences in the flow structure mainly over the downstream peak with negative interference characterized by a highly symmetric flow pattern leading to a low drag state

high resolution mapping of bora winds in the northern adriatic sea using synthetic aperture radar 1 the adriatic sea is regularly subjected to strong bora wind events from the northeast during winter the events have a strong effect on the oceanography in the adriatic driving basin scale gyres that determine the transport of biogeochemical material and extracting large amounts of heat the bora is known to have multiple surface wind jets linked to the surrounding orography and have been the focus of many studies but it has not been possible to describe the detailed spatial structure of these jets by in situ observations using high resolution spaceborne radarsat 1 synthetic aperture radar sar images collected during an active bora period 23 january 16 february 2003 we created a series of high resolution 300 m maps of the wind field the obtained winds show reasonable agreement with several in situ wind observations with an rms wind speed error of 3 6 m s slightly higher than the 2 3 m s errors reported in previous studies these sar images reveal the spatial structure of the bora wind in unprecedented detail showing several new features in the senj region of croatia several images show rhythmic structure with wavelengths of 2 3 km that may reflect bora pulsation seen at fixed locations by previous investigators along the italian coast several images show a wide 20 30 km band of northwesterly winds that abruptly change to the northeasterly bora winds further offshore meteorological model results suggest that these northwesterly winds are consistent with those of a barrier jet forming along the italian apennine mountain chain

classification of cyclone tracks over the apennines and the adriatic sea abstract cyclones that appear in the adriatic sea basin strongly influence the climate and weather conditions in the area in particular apart from the usually mild climate cyclone activity in the adriatic and the central mediterranean sea provide both the main hydrological forcing and the trigger mechanisms for a range of extreme weather phenomena therefore a basic understanding of the cyclogenesis over the adriatic sea is essential in particular the classification of different types of cyclogenesis in the area is fundamental because it will help the understanding and prediction of the relevant weather phenomena in this study based on the analysis of the 4 yr 2002 05 operational european centre for medium range weather forecasts t511 dataset various types of cyclone tracks are classified and the mesocyclogenesis areas in the vicinity of the adriatic basin are isolated this analysis indicates that the following four types of cyclogenesis over the adriatic sea can be identified 1 type a cycl

the intense lee wave rotor event of sierra rotors iop 8 abstract a large amplitude lee wave rotor event observationally documented during sierra rotors project intensive observing period iop 8 on 24 26 march 2004 in the lee of the southern sierra nevada is examined mountain waves and rotors occurred over owens valley in a pre cold frontal environment in this study the evolution and structure of the observed and numerically simulated mountain waves and rotors during the event on 25 march in which the horizontal circulation associated with the rotor was observed as an opposing easterly flow by the mesonetwork of surface stations in owens valley are analyzed the high resolution numerical simulations of this case performed with the coupled ocean atmosphere mesoscale prediction system coamps run with multiple nested grid domains the finest grid having 333 m horizontal spacing reproduced many of the observed features of this event these include small amplitude waves above the sierra ridge decoupled from thermally forced flow within the valley and a l

constraints on probabilistic seismic hazard models from unstable landform features in new zealand we undertake the first new zealand based pilot study to investigate the use of ancient precariously balanced rocks rocks that are unstably balanced on top of a pedestal as a criteria for testing estimates of earthquake shaking from probabilistic seismic hazard models for long return periods to date research to test seismic hazard models in new zealand has been restricted to the short historical record of earthquakes our survey of five sites in the south island of new zealand has yielded a total of 28 precariously balanced rocks which on the basis of established methodology are used to provide estimates of the maximum ground motions that could have occurred at the sites since the rocks became precarious age estimates for the precariously balanced rocks 40 400 to 55 300 years for central otago schist rocks and 77 300 years for northwest nelson granitic rocks are made from a limited number of cosmogenic dates obtained from bedrock removed from the pedestals of the rocks comparisons of the maximum peak ground accelerations and ages of the precariously balanced rocks with seismic hazard curves derived from the new zealand national seismic hazard model show that the rocks indicate considerably lower hazard than the seismic hazard model at sites located within 5 km of active faults whereas the agreement is favorable for sites located away from active faults the variability about the median estimates of peak ground acceleration for the fault sources and or the median accelerations for the fault sources assumed in the seismic hazard model may therefore be overestimated for the sites near active faults

precarious rock evidence for low ground shaking on the footwall of major normal faults preliminary interpretations of precarious rock observations suggest relatively low near fault 3 km footwall ground motions for normal faults relative to strike slip faults as reported for a dynamic foam rubber normal fault model by brune and anooshehpoor 1999 since for large normal fault earthquakes there are no instrumental data at such close distances from the fault trace precarious rocks may provide important data for estimating the ground motion for these earthquakes use of empirical curves in the literature based mainly on strike slip data may lead to overestimates of seismic hazard for the near fault footwall of normal faults these preliminary results may warrant more comprehensive and more quantitative followup studies

complex bora flow in the lee of southern velebit the complexity of bora flow in the lee of southern velebit croatia is investigated by means of high resolution numerical simulations carried out with the us naval research laboratory s nrl coupled ocean atmosphere mesoscale prediction system coamps model the aim of this study is to identify reasons for the strong spatial variability of bora in the wider zadar region and the uncharacteristically weak bora in the city of zadar the primary focus is put on the severe bora episode of 20 december 2004 during which a sodar sonic detection and ranging system was operated at zemunik airport numerical results are verified against the available surface and upper air observations upstream conditions governing dynamics of this particular bora event are characterized by the presence of a mean state critical level at 3 4 km above mean sea level amsl defining the upstream bora layer low level airflow over zadar peninsula during this event displays marked temporal variability during the morning a highly three dimensional and unsteady wake i e region of reduced wind speed is established over zadar peninsula downstream of a hydraulic jump that forms in the lee of but not collocated with highest portions of the southern velebit terrain during its most extensive phase the wake scales the entire length of zadar peninsula in the horizontal and extends up to the critical level in the vertical a wake vortex develops as the flow reverses along the wake centreline in the evening hours an undular bore forms in the same location with large amplitude waves on top of it inducing boundary layer separation and rotors wake flow is affected both by changes in the upstream atmospheric structure and diurnal boundary layer evolution sensitivity experiments show that the influence of velebit s height is particularly strong governing the onset and strength of bora the terrain of zadar peninsula exerts a strong influence on the characteristics of the developed bora flow particularly when non hydrostatic effects are significant boundary layer separation is particularly sensitive to downstream orography copyright 2012 royal meteorological society

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

the 1356 basel earthquake an interdisciplinary revision summary within historical times one of the most damaging events in intra plate europe was the 1356 basel earthquake given its significance for assessing regional seismic hazard in central europe an interdisciplinary project was launched in 2005 to re explore this event our effort aimed to incorporate techniques from history seismology archaeology paleoseismology and engineering new and reinterpreted historical data from basel and its surroundings plus archaeological findings on buildings that survived the event and still exist enabled this macroseismic assessment palaeoseismological studies combined with historical evidence provided additional data for the surrounding areas archaeology offers sparse information on some castles and churches sometimes supported by historical records a contemporary source allows some reconstruction of the stronger fore and aftershocks this expanded information base improves our sense of the event s damage and consequences for the city of basel the relatively abundant archaeological data allowed us to assess statistically the macroseismic intensity at ix although the pattern of damage was scattered data points for the expected area of damage around basel are not distributed regularly the absence of historical and archaeological findings for southern germany might be due to archival problems future investigation may improve this situation our results confirm that the basel earthquake was the most destructive known for central europe intensities up to viii are found within a radius of about 30 km analysing the macroseismic field confirms our former assessment of the event and shows an epicenter located about 10 km south of basel the most probable range for the moment magnitude mw is between 6 7 and 7 1

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

dating precariously balanced rocks in seismically active parts of california and nevada precariously balanced boulders that could be knocked down by strong earthquake ground motion are found in some seismically active areas of southern california and nevada in this study we used two independent surface exposure dating techniques rock varnish microlamination and cosmogenic 36 cl dating methodologies to estimate minimum and maximum limiting ages respectively of the precarious boulders and by inference the elapsed time since the sites were shaken down the results of the exposure dating indicate that all of the precarious rocks are 10 5 ka and that some may be significantly older at victorville and jacumba california these results show that the precarious rocks have not been knocked down for at least 10 5 k y a conclusion in apparent conflict with some commonly used probabilistic seismic hazard maps at yucca mountain nevada the ages of the precarious rocks are 10 5 to 27 0 ka providing an independent measure of the minimum time elapsed since faulting occurred on the solitario canyon fault

history of modern earthquake hazard mapping and assessment in california using a deterministic or scenario approach modern earthquake ground motion hazard mapping in california began following the 1971 san fernando earthquake in the los angeles metropolitan area of southern california earthquake hazard assessment followed a traditional approach later called deterministic seismic hazard analysis dsha in order to distinguish it from the newer probabilistic seismic hazard analysis psha in dsha seismic hazard in the event of the maximum credible earthquake mce magnitude from each of the known seismogenic faults within and near the state are assessed the likely occurrence of the mce has been assumed qualitatively by using late quaternary and younger faults that are presumed to be seismogenic but not when or within what time intervals mce may occur mce is the largest or upper bound potential earthquake in moment magnitude and it supersedes and automatically considers all other possible earthquakes on that fault that moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships and for calculating ground motions as in neo dsha zuccoloet al 2008 the first deterministic california earthquake hazard map was published in 1974 by the california division of mines and geology cdmg which has been called the california geological survey cgs since 2002 using the best available fault information and ground motion attenuation relationships at that time the california department of transportation caltrans later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists seismologists and engineers for many years some engineers involved in the siting process of large important projects for example dams and nuclear power plants continued to challenge the map s the second edition map was completed in 1985 incorporating more faults improving mce s estimation method and using new ground motion attenuation relationships from the latest published results at that time cdmg eventually published the second edition map in 1992 following the governor s board of inquiry on the 1989 loma prieta earthquake and at the demand of caltrans the third edition map was published by caltrans in 1996 utilizing gis technology to manage data that includes a simplified three dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map the spatial relationship of fault hazards with highways bridges or any other attribute can be efficiently managed and analyzed now in gis at caltrans there has been great confidence in using dsha in bridge engineering and other applications in california and it can be confidently applied in any other earthquake prone region earthquake hazards defined by dsha are 1 transparent and stable with robust mce moment magnitudes 2 flexible in their application to design considerations 3 can easily incorporate advances in ground motion simulations and 4 economical dsha and neo dsha have the same approach and applicability the accuracy of dsha has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment in the final analysis dsha is a reality check for public safety and psha results although psha has been acclaimed as a better approach for seismic hazard assessment it is dsha not psha that has actually been used in seismic hazard assessment for building and bridge engineering particularly in california

bora driven potential vorticity banners over the adriatic a case study is presented of the secondary potential vorticity pv banners over the northern adriatic that occurred in an early stage of a bora on 7 november 1999 during the mesoscale alpine programme map special observation period the dynamics and structure of the lee side and cross mountain flow past the dinaric alps were investigated using data collected in a dual aircraft ncar electra and noaa p 3 map intensive observing period 15 mission over the adriatic and high resolution numerical simulations the observational study employs flight level dropsonde and scanning aerosol backscatter lidar data the observed flow structure is compared with simulations results of the coamps model run at a horizontal resolution of 3 km the dinaric alps the north west south east oriented coastal mountain range of croatia has an irregular ridge line with a number of peaks in the range of 1 5 2 km with several prominent mountain passes the identified jet and wake structure within the east north easterly bora over the adriatic was found to be well correlated with the upwind distribution of mountain passes and peaks the wake flow structure was found also to be in excellent agreement with the climatological profile of the bora strength along the croatian coast the attendant secondary pv banners separating individual jets and wakes diagnosed by computing pv from the flight level data were found to have a characteristic horizontal scale of 10 25 km and a maximum amplitude of up to 6 pvu within the boundary layer over the open sea the thickness of the boundary layer within which the east north easterly bora also achieved its maximum strength was approximately 1 km detailed comparison with the numerical model results shows that at the horizontal resolution of 3 km the coamps model reproduces well the overall flow structure the coamps simulated pv field was found to be in good agreement with the pv derived from observations the differences in substructure between simulated and experimentally derived pv profiles derive from minor differences between modelled and observed velocity and potential temperature profiles which are subsequently accentuated by computing differentiated quantities such as vorticity and potential temperature gradients the high predictability and steadiness of the pv banners and a good correlation with the geometry of the upwind topography support the orographic generation mechanism of pv with dissipation in hydraulic jumps and gravity wave breaking regions as the likely main source of pv copyright 2004 royal meteorological society

age of unstable bedrock landforms southwest of yucca mountain nevada and implications for past ground motions we determine minimum exposure ages for unstable outcrops at three sites in amargosa desert southwestern nevada including a site at the southern end of yucca mountain varnish microlamination dating techniques provide minimum exposure ages of 12 5 36 k y for the unstable outcrops of welded tuff including a 24 k y age for the south yucca mountain site the youngest exposure age 12 5 k y is found at the site located only 10 km from the death valley furnace creek fault suggesting outcrops may be more frequently modified when close to major active earthquake sources a simplistic stability assessment of the south yucca mountain outcrops suggests peak ground accelerations pgas may not have exceeded about 1 g uncertainty bounds 0 5 2 g in at least 24 k y a pga of 1 g is consistent with the predicted 24 k y return period pgas from the near decade old yucca mountain probabilistic seismic hazard psh model except for the ninety fifth percentile and above we gain confidence in our interpretations by additionally observing 1 minimal damage to the south yucca mountain outcrops from a recent moderate earthquake that is estimated to have produced a pga of less than 0 1 g there i e motions less than 0 5 g do not significantly damage the outcrops and 2 severe damage to similar volcanic outcrops associated with pgas of the order 0 5 1 g near a nuclear blast site from the 1960s these observations support our suggestion that pgas greater than 0 5 1 g have not occurred at the south yucca mountain site for a time period of at least 24 k y significant seismic events that substantially modify the outcrops and produce associated rubble fields may therefore occur on longer time scales