ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

large scale traveling ionospheric disturbances observed by gps total electron content during the magnetic storm of 29 30 october 2003 1 we have investigated the propagation of large scale traveling ionospheric disturbances lstids during the super magnetic storm of 29 30 october 2003 two dimensional total electron content tec perturbation maps over north america were built using tec data provided by the american gps network and the international gnss service three lstid events were observed in the range of 30 degrees n 50 degrees n 60 degrees w 110 degrees w during this period the first two lstids occurred consecutively during 0620 0800 ut on 29 october at the local time of midnight right after the onset of the big substorm the third one was found at noon during the expansion phase of another substorm on 30 october the phase fronts of these lstids passed over the united states and traveled southwestward to the distance of similar to 2000 km with the maximum front width of similar to 4000 km and the duration of less than 2 hours the maximum amplitude of tec perturbations attained 3 total electron content units tecus the results differ from the former observation of afraimovich and voeykov 2004 and afraimovich et al 2006 who reported a solitary lstid propagating southwestward over the united states with the amplitudes of up to 14 tecu on 30 october 2003 we have checked the magnetic h component observed at the geomagnetic observatories in north america and found it is most likely that the auroral westward electrojet was the cause of the lstids on 29 october the source region for these tids was likely to be located several hundred kilometers north of 50 degrees n cross spectral analysis was conducted to obtain the global propagation characteristics of lstids during this superstorm equatorward lstids were found in all the three sectors of north america europe and asia showing high correlation with the occurrence of auroral substorms

statistics of geomagnetic storms and ionospheric storms at low and mid latitudes in two solar cycles 1 the statistics of occurrence of the geomagnetic storms and ionospheric storms at kokubunji 35 7 n 139 5 e 26 8 n magnetic latitude in japan and boulder 40 0 n 254 7 e 47 4 n in america are presented using the dst and peak electron density nmax data in 1985 2005 covering two solar cycles 22 23 when 584 geomagnetic storms dst 50 nt occurred in addition to the known solar cycle and seasonal dependence of the storms the statistics reveal some new aspects 1 the geomagnetic storms show a preference for main phase mp onset at around ut midnight especially for major storms dst 100 nt over 100 excess mp onsets at ut midnight compared to a uniform distribution 2 the number of positive ionospheric storms at kokubunji about 250 is more than double that at boulder and 3 the occurrence of the positive storms at both stations shows a preference for the morning noon onset of the geomagnetic storms as expected from a physical mechanism of the positive storms 4 the occurrence of negative ionospheric storms at both stations follows the solar cycle phases most frequent at solar maximum better than the occurrence of positive storms which agrees with the mechanism of the negative storms

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

aquisgrani terrae motus factus est part 1 the aachen cathedral germany built on weak ground charlemagne charles the great placed the centre of his kingdom during carolingian times in aachen germany aquisgrana this medieval period and his regency are associated with a period of extensive constructions in aachen including the carolingian part of the aachen cathedral the cathedral was the first building in germany to join the unesco world heritage list the foundations and construction ground of the cathedral were excavated during recent archaeological and geotechnical investigations the cathedral is founded on pillars and piles in devonian blue limestone and shale covered by pleistocene loess sediments remains of roman buildings such as thermae are situated below this part of the cathedral the pillars are connected by up to 5 m deep foundation walls and are up to 2 4 m thick even though information about the construction site is important for the assessment of structural health and remediation measures it is often rare for old historical buildings documentations from construction time concentrate on the construction progress and financial aspects detailed descriptions on the foundation ground and techniques are usually not preserved this information is of relevance for assessment of earthquake related structural damages and site effects on construction investigations in the course of remediation measures or archaeological surveys fill this information gap they provide insights in the ancient foundation techniques and can be used for identifying earthquake related phenomena in the construction site furthermore a direct insight into potential seismic effects associated with the ground and building response on seismic shaking becomes possible in the case of the aachen cathedral typical geotechnical investigation methods including drilling and laboratory tests were applied together with gpr measurements to evaluate the construction ground and evaluate potential seismological effects

gps and glonass observations of large scale traveling ionospheric disturbances during the 2015 st patrick s day storm using a comprehensive database of 5300 ground based gnss stations we have investigated large scale traveling ionospheric disturbances lstids during 17 18 march 2015 st patrick s day storm for the first time the high resolution two dimensional maps of the total electron content tec perturbation were made using not only gps but also glonass measurements several lstids originated from the auroral regions in the northern and southern hemispheres were observed simultaneously over europe north america and south america this storm is considered as a two step main phase storm during the first main phase lstids propagated over the whole daytime european region and over high latitudes of north america during the second main phase we report 1 intense lstids propagated equatorward in north america and europe 2 convergence of several lstids originated from the opposite hemispheres in the interference zone over geomagnetic equator in south america 3 super lstids with the wavefront length of more than 10000 km observed simultaneously in north america and europe lstids observed in three sectors had wavelength of 1200 2500 km and wave periods of 50 80 min during the recovery phase on the background of the negative ionospheric storm developed over north america we detect signatures of the stream like structures alongated within the latitudinal range of 29 n 42 n across the usa these structures persisted through the nighttime to the early morning from 04 ut till 13 ut on 18 march 2015 and they were associated with the subauroral polarization streams saps induced nighttime ionospheric flows

fine structure of the landers fault zone segmentation and the rupture process observations and modeling of 3 to 6 hertz seismic shear waves trapped within the fault zone of the 1992 landers earthquake series allow the fine structure and continuity of the zone to be evaluated the fault to a depth of at least 12 kilometers is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent this zone forms a seismic waveguide that extends along the southern 30 kilometers of the landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter another fault plane waveguide disconnected from the first exists along the northern rupture surface these observations in conjunction with surface slip detailed seismicity patterns and the progression of rupture along the fault suggest that several simple rupture planes were involved in the landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane reduction in rupture velocity can tentatively be attributed to fault plane complexity and variations in moment release can be attributed to variations in available energy

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

southern hemisphere ionosphere and plasmasphere response to the interplanetary shock event of 29 31 october 2003 1 we analyze the effects on the southern hemisphere ionosphere and plasmasphere due to the 29 31 october 2003 geomagnetic storms the so called series of halloween storms solar wind data from ace and ionospheric data from the gps global position system ground and leo low earth orbit receivers the topex poseidon altimeter the image fuv camera and the dmsp drift meter are used to understand the ionospheric dynamics as a function of the storm phase the detailed structure of the ionosphere has been obtained using tomographic reconstruction applied to data from both ground and space based gps receivers the tomographic approach using leo observations of signals received from gps satellites above the leo s horizon allows us to investigate the topside ionospheric and plasmaspheric density distribution in more detail than can be obtained using ground based gps receivers this is because with ground based receivers the higher topside ionosphere and plasmasphere contribute only a small fraction to the total electron content tec and so the measurements are dominated by the ionospheric structure at the f2 peak in contrast the australian leo satellite fedsat which has been used for this study orbits at 800 km altitude well above the f2 peak and hence the tec measured is primarily due to the upper topside ionosphere and plasmasphere this paper presents the tomographically reconstructed topside ionosphere and plasmasphere electron density distributions using leo observations the temporal and regional maps of tec and the image fuv data show that the storm that commenced on 29 october dramatically decreased the plasma density in the southern hemisphere middle and high latitudes the region remained depleted of plasma for more than 24 hours until 31 october when the second severe storm began topex poseidon data shows a daytime localized density enhancement occurred above the middle of the pacific ocean these results show large interhemispheric and longitudinally narrow storm time structure in the ionosphere and topside ionosphere plasmasphere

coseismic displacements 1992 landers california earthquake the rupture associated with the 1992 landers earthquake ms 7 5 extended along the west edge of a 60 50 km trilateration network that had been surveyed two months before the earthquake and was resurveyed a month after it the coseismic displacement field within the network was calculated from the changes observed in the trilateration network supplemented by the displacements measured at four gps stations and other less timely trilateration measurements stations near the rupture were displaced by as much as 3 m the observed changes are reproduced reasonably well by dislocation modeling in which the landers rupture is represented by 8 vertical fault segments each extending from the surface to 9 km depth two additional segments represent the big bear and eureka peak faults the average modeled right lateral slip on the landers rupture is about 5 m however the residuals for the best fit slip distribution are about four times greater than expected from measurement error given that uncertainty a broad range of slip models furnish acceptable fits to the data the large residuals are attributed to inelastic deformation principally sympathetic slip on numerous unmodeled faults within the fault blocks assumed to be elastic in the model

the use of geophysical prospecting for imaging active faults in the roer graben belgium as part of a paleoseismological investigation along the bree fault scarp western border of the roer graben various geophysical methods electrical profiling electromagnetic em profiling refraction seismic tests electrical tomography ground penetrating radar gpr and high resolution reflection seismic profiles were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters these geophysical investigations in parallel with geomorphological and geological analyses helped in the decision to locate trench excavations exposing the fault surfaces the results could then be checked with the observations in four trenches excavated across the scarp geophysical methods pointed out anomalies at all sites of the fault position the contrast of physical properties electrical resistivity and permittivity seismic velocity observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change

3 d ground penetrating radar applied to fracture imaging in gneiss three dimensional ground penetrating radar georadar techniques suitable for geological engineering applications have been developed and tested initial experiments were conducted on the floor of a quarry in southern switzerland from which ornamental gneissic rock is extracted during a brief two day period constant offset georadar data were recorded over a 650m2 area with a grid cell size of 0 1 m 0 2 m georadar velocities were estimated from the results of expanding spread surveys all georadar data and associated geometry files were recorded automatically in seismic industry formats the experimental georadar data set was processed image enhanced and interpreted using 3 d seismic reflection software operating on a workstation arbitrary vertical sections time slices 3 d images and animated movies in which the observer travels through the entire data volume were constructed from the resultant migrated georadar data semi automatic tracking routines allowed continuous subhorizontal reflectio

effect of a compliant fault zone on the inferred earthquake slip distribution 1 we present a new semi analytic method to evaluate the deformation due to a screw dislocation in arbitrarily heterogeneous and or anisotropic elastic half plane the method employs integral transformations to reduce the governing partial differential equations to the integral fredholm equation of the second kind dislocation sources as well as spatial perturbations in the elastic properties are modeled using equivalent body forces the solution to the fredholm equation is obtained in the fourier domain using a method of successive over relaxation and is mapped into the spatial domain using the inverse fast fourier transform we apply this method to investigate the effect of a soft damage zone around an earthquake fault on the co seismic displacement field and on the earthquake slip distribution inferred from inversions of geodetic data in the presence of a kilometer wide damage zone with a reduction of the effective shear modulus of a factor of 2 inversions that assume a laterally homogeneous model tend to underestimate the amount of slip in the middle of the seismogenic layer by as much as 20 this bias may accentuate the inferred maxima in the seismic moment release at depth between 3 6 km suggested by previous studies of large strike slip earthquakes

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

integration of sedimentology and ground penetrating radar for high resolution imaging of a carbonate platform ground penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries this article reports the results of an integrated study performed on an upper jurassic outcrop from the south east paris basin where coral bioherms laterally change into prograding depositional sequences ground penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop a ground penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled the excellent penetration depths of the ground penetrating radar 20 m with a monostatic 200 mhz antenna images the carbonate platform geometries ranging between outcrop workscale a few metres and seismic scale several hundreds of metres this study supports recent evidence of icehouse conditions and induced sea level fluctuations controlling the upper jurassic carbonate production

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

altitude adjusted corrected geomagnetic coordinates definition and functional approximations analysis of the functional approximations used to transform between geo graphic and altitude adjusted corrected geomagnetic aacgm coordinates reveals that errors of 50 km can occur in the auroral and polar regions these errors are the result of efforts to better approximate aacgm coordinates near the magnetic equator and the south atlantic anomaly in these regions aacgm coordinates are not defined and alternate coordinates have been used this augmentation and emphasis on the so lution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions in response a new set of spherical harmonic coefficients have been derived that better represent aacgm coordinates in these regions these new aacgm coefficients are limited to below 2000 km in altitude in order to ensure accuracy for altitudes above 2000 km a magnetic field line tracing solution is recommended a software package developed to take advantage of the new aacgm coefficients provides the capability of tracing magnetic field lines at any altitude for improved accuracy in addition linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 present the intent of this work is to provide a more accurate procedure for de termining aacgm coordinates in the auroral and polar regions for the study of mag netospheric and ionospheric processes

revisiting the 1992 landers earthquake a bayesian exploration of co seismic slip and off fault damage existing models for the distribution of subsurface fault slip associated with the 1992 landers ca earthquake m w 7 3 show significant dissimilarities in particular they exhibit different amounts of slip at shallow depths 5 km these discrepancies can be primarily attributed to the ill posed nature of the slip inversion problem and to the use of physically unjustifiable smoothing or regularization constraints in this study we propose a new coseismic model obtained from the joint inversion of multiple observations in a relatively unregularized and fully bayesian framework we use a comprehensive data set including gps terrestrial geodesy multiple sar interferograms and co seismic offsets from correlation of aerial images these observations provide dense coverage of both near and far field deformation to limit the impact of modelling uncertainties we develop a 3 d fault geometry designed from field observations co seismic offsets and the distribution of aftershocks in addition we account for uncertainty in the assumed elastic structure used to compute the green s functions our solution includes the ensemble of all plausible models that are consistent with our prior information and fit the available observations within data and prediction uncertainties using near fault high resolution ground deformation measurements and the density of aftershocks we investigate the properties of the damage zone and its impact on the inferred slip at depth we attribute a part of the inferred slip deficit at shallow depth to our models not including the impact of a damage zone associated with a reduction of shear modulus in the vicinity of the fault

distribution of seismicity across strike slip faults in california 1 the distribution of seismicity about strike slip faults provides measurements of fault roughness and damage zone width in california seismicity decays with distance from strike slip faults according to a power law 1 x2 d2 2 this scaling relation holds out to a fault normal distance x of 3 6 km and is compatible with a rough fault loading model in which the inner scale d measures the half width of a volumetric damage zone and the roll off rate is governed by stress variations due to fault roughness according to dieterich and smith s 2 d simulations approximates the fractal dimension of along strike roughness near fault seismicity is more localized on faults in northern california nocal d 60 20 m 1 65 05 than in southern california socal d 220 40 m 1 16 05 the parkfield region has a damage zone half width d 120 30 m consistent with the safod drilling estimate its high roll off rate 2 30 25 indicates a relatively flat roughness spectrum k 1 versus k 2 for nocal k 3 for socal our damage zone widths the first direct estimates averaged over the seismogenic layer can be interpreted in terms of an across strike fault core multiplicity that is 1 in nocal 2 at parkfield and 3 in socal the localization of seismicity near individual faults correlates with cumulative offset seismic productivity and aseismic slip consistent with a model in which faults originate as branched networks with broad multicore damage zones and evolve toward more localized lineated features with low fault core multiplicity thinner damage zones and less seismic coupling our results suggest how earthquake triggering statistics might be modified by the presence of faults

characterization of complex groundwater flows in the environment of singular buildings by combining hydrogeological and non destructive geophysical ground penetrating radar techniques punta begona galleries getxo spain locating and quantifying groundwater flow in many built up areas are a priority with regard to its complete restoration in this work a hydrogeological survey of the surroundings of the punta begona galleries getxo bizkaia built on a coastal cliff was completed by using ground penetrating radar gpr testing thus the preliminary characterization of soils and rocks in accessible areas of the cliff was first improved by hydrogeological information gathered from a single survey borehole including permeability measurements by low pressure injection tests lpts and continuous water level monitoring as a complementary method the non destructive gpr technique was performed during both dry and wet hydrological periods and in tandem with the injection tests providing more complete spatial and temporal images of water flows specifically gpr allows mapping of flow paths in soils and assessing the continuity of fractures in rock masses altogether this complementary approach provides greater knowledge of complex underground flow dynamics in built environments thus making it easier to make decisions for their management

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

dynamic response of ionospheric plasma density to the geomagnetic storm of 22 23 june 2015 on 21 22 june 2015 three consecutive interplanetary shocks slammed into the earth s magnetosphere immediately after the third shock at 18 36 ut on 22 june marked by an exceptional sudden storm commencement with an amplitude of delta sym h similar to 106 nt a major geomagnetic storm commenced in the present study a multi instrument approach comprising observations data analysis and modeling is used to examine the global ionospheric response results show that enhanced storm time processes produced major total electron content tec variations at different latitudes longitudes and phases of the storm a closer inspection of the tec observations reveals strong longitudinal and hemispherical asymmetry in addition multiple equatorward and poleward propagating traveling ionospheric disturbances tids were detected in the tec data equatorward propagating tids are consistent with vertical neutral winds simulated from thermosphere ionosphere electrodynamics general circulation model however poleward tids were not reproduced in the model we find that a combination of driving processes including enhanced high latitude injection prompt penetration electric fields disturbance dynamo effect neutral winds and composition changes were acting at different stages of the storm

on the use of dispersive apvo gpr curves for thin bed properties estimation theory and application to fracture characterization the presence of a thin layer embedded in any formation creates complex reflection patterns caused by interferences within the thin bed the generated reflectivity amplitude variations with offset have been increasingly used in seismic interpretation and more recently tested on ground penetrating radar gpr data to characterize nonaqueous phase liquid contaminants phase and frequency sensitivities of the reflected signals are generally not used although they contain useful information the present study aims to evaluate the potential of these combined properties to characterize a thin bed using gpr data acquired along a common midpoint cmp survey carried out to assess velocity variations in the ground it has been restricted to the simple case of a thin bed embedded within a homogeneous formation a situation often encountered in fractured media dispersive properties ofthe dielectric permittivity of investigated materials homogeneous formation thin bed are described using a jonscher parameterization which permitted study of the dependency of amplitude and phase variation with offset apvo curves on frequency and thin bed properties filling nature aperture in the second part we discuss and illustrate the validity of the thin bed approximation as well as simplify assumptions and make necessary careful corrections to convert raw cmp data into dispersive apvo curves two different strategies are discussed to correct the data from propagation effects a classical normal moveout approach and an inverse method finally the proposed methodology is applied to a cmp gpr data set acquired along a vertical cliff it allowed us to extract the characteristics of a subvertical fracture with satisfying resolution and confidence the study motivates interest to use dispersion dependency of the reflection coefficient variations for thin bed characterization

continuous penetration of the interplanetary electric field to the equatorial ionosphere over eight hours during intense geomagnetic storms 1 the interplanetary electric field penetrates to the low latitude ionosphere and has significant influence on the ionospheric electrodynamics during intense geomagnetic storms it is critical to understand how much of the interplanetary electric field can penetrate to the ionosphere and how long penetration electric fields can exist in this study we present the defense meteorological satellite program dmsp satellite measurements of the equatorial ionospheric ion vertical velocity in the dusk sector during two intense geomagnetic storms we find that the equatorial ionospheric electric field at dusk is approximately proportional to the interplanetary electric field for 8 10 hours during the storm main phase the penetration efficiency is relatively constant over the entire interval and is 5 at dusk in one storm case the long lasting storm time penetration electric field causes significant redistribution of the ionospheric plasma this study reveals that penetration electric fields can last for 8 10 hours without effective shielding when the magnetic storm activity is strengthening during continuous southward interplanetary magnetic field the result implies that the interplanetary electric field is linearly coupled with the dusk equatorial ionosphere during the entire main phase of intense magnetic storms which is very important for understanding the storm time ionospheric electric field and electrodynamics

multiconfiguration gpr measurements for geometric fracture characterization in limestone cliffs alps rock mass fracturing is a key parameter in rock fall hazard assessment however traditional geologic observations can provide information only about discontinuities at the surface in this case study detailed ground penetrating radar gpr measurements with antennas of 50 mhz 100 mhz 200 mhz and 400 mhz were conducted on a test site using different acquisition configurations deployed on vertical cliff faces conventional 2d profile data common midpoint cmp survey data and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities fractures within a mesozoic limestone massif results showed that the continuity and geometry orientation and dip of the major observed fractures which are crucial parameters for assessing rock stability can be obtained by combining vertical and horizontal profiles measured along the cliff we used 100 mhz antennae and reached a maximum penetration of 20 m which limi

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

finding the buried record of past earthquakes with gpr based palaeoseismology a case study on the hope fault new zealand in places where sedimentation and erosion compete at fast rates part of the record of past earthquakes on faults may be buried hence hidden in the first few metres below the surface we developed a novel form of palaeoseismology of geophysical type based on the use of a dense pseudo 3 d ground penetrating radar gpr survey to investigate such possible buried earthquake traces on a long fast slipping strike slip fault hope fault new zealand at a site terako where marked alluvial conditions prevail we first used lidar data to analyse the ground surface morphology of the 2 km2 site at the greatest resolution nineteen morphological markers were observed mainly alluvial terrace risers and small stream channels that are all dextrally offset by the fault by amounts ranging between 3 and 200 m the measurements document about 10 past earthquake slip events with a mean coseismic slip of 3 3 1 m with the most recent earthquake event having a slip of 3 0 5 m we then investigated a detailed area of the site 400 x 600 m2 with pseudo 3 d gpr we measured 56 similar to 400 m long 510 m spaced gpr profiles 250 mhz parallel to the fault and evenly distributed on either side the analysis revealed the existence of a palaeosurface buried at about 3 m depth corresponding to the top of alluvial terraces of different ages that buried surface is incised by a dense network of stream channels that are all dextrally offset by the fault we measured 48 lateral offsets in the buried channel network more than twice than at the surface these offsets range between 6 and 108 m as observed at the surface yet provide a more continuous record of the fault slip the similarity of the successive slip increments suggests a slip per event averaging 4 4 1 m fairly similar to that estimated from surface data from the total surface and buried 67 offset collection we infer that a minimum of 30 large earthquakes have broken the hope fault at the terako site in the last about 67 kyr with an average coseismic slip of 3 2 1 m a minimum average recurrence time of about 200 yr and a magnitude of at least mw 7 07 4 our study therefore confirms that part of the record of past earthquakes may indeed reside in the first few metres below the surface where it may be explored with geophysical gpr based palaeoseismology developing such a new palaeoseismological tool should provide rich information that may complement surface observations and help to document the past earthquakes on faults

quantifying near field and off fault deformation patterns of the 1992 mw 7 3 landers earthquake coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods e g insar lidar differencing and gps current methods however either fail to capture patterns of near field coseismic surface deformation or lack preevent data consequently the characteristics of off fault deformation and the parameters that control it remain poorly understood we develop a standardized method to fully measure the surface near field coseismic deformation patterns at high resolution using the cosi corr program by correlating pairs of aerial photographs taken before and after the 1992 m w 7 3 landers earthquake cosi corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists for the landers earthquake our measured displacements are systematically larger than the field measurements indicating the presence of off fault deformation we show that 46 of the total surface displacement occurred as off fault deformation over a mean deformation width of 154 m the magnitude and width of off fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system with a weak correlation with the type of near surface materials through which the rupture propagated both the magnitude and width of distributed deformation are largest in stepovers bends and at the southern termination of the surface rupture we find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self affine fractal with dimension of 1 56

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

was magnetic storm the only driver of the long duration enhancements of daytime total electron content in the asian australian sector between 7 and 12 september 2017

ionospheric response at conjugate locations during the 7 8 september 2017 geomagnetic storm over the europe african longitude sector this paper focuses on unique aspects of the ionospheric response at conjugate locations over europe and south africa during the 7 8 september 2017 geomagnetic storm including the role of the bottomside and topside ionosphere and plasmasphere in influencing electron density changes analysis of total electron content tec on 7 september 2017 shows that for a pair of geomagnetically conjugate locations positive storm effect was observed reaching about 65 when benchmarked on the monthly median tec variability in the northern hemisphere while the southern hemisphere remained within the quiet time variability threshold of 40 over the investigated locations the southern hemisphere midlatitudes showed positive tec deviations that were in most cases twice the comparative response level in the northern hemisphere on the 8 september 2017 during the storm main phase on 8 september 2017 we have obtained an interesting result of ionosonde maximum electron density of the f2 layer and tec derived from global navigation satellite system gnss observations showing different ionospheric responses over the same midlatitude location in the northern hemisphere in situ electron density measurements from swarm satellite aided by bottomside ionosonde derived tec up to the maximum height of the f2 layer hmf2 revealed that the bottomside and topside ionosphere as well as plasmasphere electron content contributions to overall gnss derived tec were different in both hemispheres especially for 8 september 2017 during the storm main phase the differences in hemispheric response at conjugate locations and on a regional scale have been explained in terms of seasonal influence on the background electron density coupled with the presence of large scale traveling ionospheric disturbances and low latitude associated processes the major highlight of this study is the simultaneous confirmation of most of the previously observed features and their underlying physical mechanisms during geomagnetic storms through a multi data set examination of hemispheric differences 2020 american geophysical union all rights reserved

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

gpr measurements to assess the emeelt active fault s characteristics in a highly smooth topographic context mongolia to estimate the seismic hazard the geometry dip length and orientation and the dynamics type of displacements and amplitude of the faults in the area of interest need to be understood in this paper in addition to geomorphologic observations we present the results of two ground penetrating radar gpr campaigns conducted in 2010 and 2011 along the emeelt fault in the vicinity of ulaanbaatar capital of mongolia located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes as the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event the fault location and geometry is difficult to determine precisely however by using gpr first a non destructive and fast investigation the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location gpr was performed with a 50 mhz antenna over 2 d lines and with a 500 mhz antenna for pseudo 3 d surveys the 500 mhz gpr profiles show a good consistency with the trench observations dug next to the pseudo 3 d surveys the 3 d 500 mhz gpr imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m this is consistent with a right lateral strike slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6 the 2 d 50 mhz profiles recorded perpendicular to the fault show a strong reflection dipping to the ne which corresponds to the fault plane those profiles provided complementary information on the fault such as its location at shallow depth its dip angle from 23 to 35 and define its lateral extension central asia is known for its high level of seismic hazards especially mongolia which has been one of the most seismically active intracontinental regions in the world with four large earthquakes magnitude around 8 along its active faults in the western part of the country during the last century khilko et al 1985 the deformation in mongolia is located between compressive structures related to the collision and penetration of the indian plate into the eurasian plate and extensive structures in the north of the country related with the baykal rift tapponnier molnar 1979 baljinnyam et al 1993 schlupp 1996 bayasgalan jackson 1999 the seismic activity observed in the vicinity of ulaanbaatar ub capital of mongolia is relatively low compared to the activity observed in western mongolia nevertheless since 2005 the seismic activity around ub not only has increased but is also organized see fig 1 at the west of ub along two perpendicular directions which determine two active faults emeelt fault discovered in 2008 nnw sse direction 25 km long minimum and situated about 10 km w of ub and hustai fault wsw ene direction 80 km long with its ne tip at less than 20 km west of ub their length and morphology indicate that they can produce earthquakes of magnitude 6 5 7 5 schlupp et al 2012 most of the mongolian population 1 2 million over 3 million is concentrated at ub which is the main political and economical centre of the country hence the study of seismic hazard and the estimation of the probability of future destructive earthquakes are of primary importance for the country dugarmaa et al 2006 since the last large earthquake the faults geomorphology has been highly smoothed by erosional processes and the exact location of the fault plane surface rupture is thus hidden within a several metre wide strip the gpr method has been proven to give good and useful results to characterize faults by identifying offsets of radar reflections malik et al 2007 christie et al 2009 yalciner et al 2013 and

dem analysis of rock bridges and the contribution to rock slope stability in the case of translational sliding failures in the presence of joint sets sub parallel to a slope face the stability of the rock mass is assumed to be controlled by the shear strength along the joints if the joints are persistent the shear strength can be assessed according to the mohr coulomb criterion with appropriate values for the cohesion and the friction angle on the associated surface if the joints are non persistent with their continuity being interrupted by the presence of rock bridges their apparent strength increases considerably in this case the contribution of the rock bridges has to be accounted for in the stability analysis jennings formulation is considered to be one of the first rock slope stability analysis that evaluates the resistance to sliding as a weighted combination of both intact rock and joint planes strengths the present study discusses the validity of jennings formulation the progressive failure of a rock slope involving a non persistent joint is numerically investigated based upon simulations performed using a discrete element method specifically enhanced to model jointed rock masses the intact material is represented as an assembly of bonded particles pre existing discontinuities are explicitly included in the model by using a modified contact logic that ensures an explicit and constitutive mechanical behaviour of the joint planes the failure of the rock bridges is simulated through the breakage of the inter particle bonds in addition rock bridges can be spatially distributed along the sliding surface following a prescribed spatial probabilistic distribution the respective contribution of spatial distribution of rock bridges over the main sliding plane the dip angle of that plane and the location of the centre of gravity of the likely unstable block were investigated through a series of numerical simulations and the results systematically compared to jennings predictions the limit of jennings formulation appears as soon as tensile failure becomes predominant and an alternative formulation is proposed to assess the resulting equivalent strength

frequency domain inversion of strong motions application to the 1992 landers earthquake we present a frequency domain inversion in which the observed earthquake strong ground motions are used to constrain the space time dependence of slip on a fault green s functions are numerically evaluated and the parameters describing the rupture are the local slip rupture time and rise time these parameters are simultaneously evaluated without additional constraints this procedure allows for large variations in the local rupture velocity the june 28 1992 landers earthquake mw 7 3 offers an exceptional opportunity to apply this technique to a major strike slip event we model the rupture evolution including local differences in slip durations and variations in rupture velocity our final results are in good agreement with other inversion studies geodetic and surface observations the main discrepancies occurred at depth and at the end of the johnson valley fault we show that a relatively low resolution could be an explanation for these differences rupture velocity and slip are extremely heterogeneous both along strike and with depth a moment of 0 90 1020 n m was found the slip distribution shows that this event consists of a series of regions of high slip subevents separated by regions of relative low slip approximately 50 of the moment was released on the homestead valley fault in this region of large slip the rupture velocity inferred by our inversion is well constrained and is equal to 3 0 km s at depth and 2 5 km s near the surface our inversion favors the hypothesis that the duration of the slip at each point of the fault is of the order of the duration of rupture of each subevent

earthquake deformation cycle on the san andreas fault near parkfield california six moderate earthquakes are thought to have ruptured the parkfield segment of the san andreas fault since 1857 the similar characteristics of the three seismically recorded events together with the quasi regular 22 year recurrence interval have led to the forecast of a similar event in 1988 5 years in this study the potential for the hypothesized earthquake is assessed by estimating the time required for interseismic straining to recover the strain energy released by the most recent june 1966 parkfield earthquake for a simple model of the earthquake cycle this interval is proportional to the ratio of the 1966 seismic moment to the interseismic moment deficit rate baseline lengths measured before and after the 1966 earthquake are inverted to estimate the magnitude and distribution of the combined coseismic and transient postseismic slip although the geodetic data determine only broad spatial averages of the fault slip they do require that slip at depth exceeded the surface offsets measured in 1966 inversions with extreme prior models are calculated to assess the range of seismic moment and moment deficit rates consistent with the available geodetic data inversions assuming only that the slip distributions are to some degree smooth yield strain energy recovery intervals of 14 25 years extreme values range from as little as 6 years to as much as 29 years in comparison historic recurrence intervals of parkfield earthquakes range from 12 to 32 years these results are consistent with the expectation of a magnitude 5 6 earthquake near parkfield by 1993

failure mechanisms and triggering factors in calcareous cliffs of the subalpine ranges french alps in order to enhance the detection of prospective rock falls in calcareous cliffs 25 rock falls have been described in a more detailed way than for an inventory they are representative of middle size rock falls 10 to 100 000 m3 occurring in the french subalpine ranges at an elevation between 200 m and 2 000 m structural conditions of the rock masses morphology of the initial cliff surface and the scar possible failure mechanisms and processes have been studied typical failure configurations have been identified based on the attitude of the failure surface in relation to the bedding planes and the cliff surface irregular cliff morphology appears to be another important susceptibility factor in most cases the classical comparison of the average planes of the main joint sets with the average plane of the slope could not define the potentially unstable masses rather those ones are due to joint planes that deviate from their mean set plane or to irregularities of the cliff surface the proposed investigation method to detect prospective rock falls mainly consists in observing stereoscopic aerial photographs in order to look for critical configurations once a critical mass has been detected its failure probability for a period of the order of one century must be evaluated or its life expectancy the main factor to consider for this purpose appears to be the proportion of rock bridges in the potential failure surface the triggering factors of rock falls in our study area have been investigated by analysing an inventory of 46 rock falls statistical tests have been carried out to study the relation between rock falls and daily rainfall freeze thaw cycles or earthquakes a good correlation has been obtained with freeze thaw cycles a slight correlation with rainfall and no correlation with earthquakes this suggests that ice jacking could the main physical process leading to failure by causing microcrack propagation

on the potential of ground penetrating radar to help rock fall hazard assessment a case study of a limestone slab gorges de la bourne french alps the stability of a potentially unstable rock mass is highly sensitive to the continuity of the joints cutting it the rock fall hazard assessment generally based on surface geological observations and on a simple geomechanical model suffers from the lack of information on the 3d geometry and the properties of the joints this case study investigates the potential of ground penetrating radar gpr measurements regarding hazard assessment in hard rock gpr was used to detect and characterize joints that could cause the failure of an overhanging rock mass located above a road in the gorges de la bourne france gpr data were acquired using high frequency shielded antennae 500 and 800 mhz to assess the extension of these joints and to detect other possible fractures combined with a velocity profile deduced from a common mid point cmp analysis these measurements provided detailed images of the fracture network which were locally consistent with turn rate velocity measurements performed within two horizontal boreholes the rock bridge percentage in the critical joints was estimated from gpr data to be too low to ensure the stability of the overhanging rock mass consequently mining of the rock mass was decided on afterwards a comparison between gpr images and the real joints observed after mining also confirmed the gpr interpretation for the location and the extension of the joints

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

modelling and back analysing failures in steep limestone cliffs abstract the observation of 12 rock fall scars in steep limestone cliffs has shown that the fallen masses were stable as a result of relatively small rock bridges these results demonstrate that consideration of rock bridges is necessary for a realistic evaluation of stability limit equilibrium methods of analysis are presented for sliding and toppling for both isostatic and hyperstatic conditions these methods are illustrated with four case histories the results of nine back analyses of rock falls with volumes between 24 and 3500 m 3 are presented the rock cohesion obtained from back analysis appears to be significantly lower than the cohesion obtained from classical laboratory tests this discrepancy can be attributed to several factors including a spatial and temporal scale effect the oversimplified modelling two dimensional limit equilibrium and some uncertainties affecting the geometrical data when analysing the stability of a cliff with a limit equilibrium method the authors suggest dividing the cohesion by a scale and method factor of 3

nonplanar faults mechanics of slip and off fault damage stress interactions and sliding characteristics of faults with random fractal waviness in a purely elastic medium differ both qualitatively and quantitatively from those of faults with planar surfaces with nonplanar fault models solutions for slip diverge as resolution of the fractal features increases and the scaling of fault slip with fault rupture dimension becomes nonlinear we show that the nonlinear scaling of slip and divergence of solutions arise because stresses from geometric interactions at irregularities along nonplanar faults grow with increasing slip and produce backstresses that progressively impede slip however in real materials with finite strength yielding will halt the growth of the interaction stresses which will profoundly affect slip of nonplanar faults we infer that in the brittle seismogenic portion of the earth s crust off fault yielding occurs on pervasive secondary faults predicted rates of stress relaxation with distance from major faults with random fractal roughness follow a power law relationship that is consistent with reported clustering of background seismicity up to 15 kilometers from faults