transient seepage model for saturated unsaturated soil systems a geotechnical engineering approach a two dimensional finite element model is proposed to simulate transient seepage for complex groundwater flow systems the complete soil system is treated as a continuum encompassing flow in both saturated and unsaturated zones in the unsaturated zone the air phase is assumed to be continuous and open to atmospheric pressure the coefficient of permeability of the unsaturated soil is assumed to be a function of pore water pressure the governing differential equation is derived within a framework familiar to geotechnical engineers the stress state variables and the constitutive relationships for an unsaturated soil are used in the derivation the finite element solution to the governing differential equation is based on the galerkin weighted residual method the nonlinearity of the equation is solved by iterative procedures the finite element formulation is implemented into a computer model named trasee the model can be applied to a wide variety of problems involving complex boundary conditions and geo

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

preconsolidation pressures in the battleford formation southern saskatchewan canada soft surficial unoxidized till of the battleford formation overlies hard oxidized and unoxidized till of the floral formation the difference in hardness between these two formations is the result of preconsolidation pressures that range from 1500 to 2200 kpa in the floral formation and from 350 to 750 kpa in the lower till unit of the battleford formation the upper till and clay unit of the battleford formation which represents a conformable contact between this formation and the overlying glaciolacustrine clay is normally consolidated preconsolidation of the floral formation apparently took place upglacier where the potentiometric surface for subglacial beds was 170 240 m below the ice surface the lower till unit of the battleford formation was deposited from and consolidated under stagnant ice the upper normally consolidated till and clay unit of the battleford formation was let down upon the lower till unit by ablation the calculated minimum stagnant ice thickness required for consolidation

hydrogeology of two saskatchewan tills i fractures bulk permeability and spatial variability of downward flow groundwater flow patterns were compared and contrasted in two deposits of clayey till of different thicknesses both of which overlie regional aquifers in a flat upland recharge area analysis of 67 field and laboratory hydraulic conductivity determinations indicated that conductive fractures in the unoxidized zone of the thinner till dalmeny site give rise to an isotropic bulk permeability of approximately 5 10 9 ms 1 which is two orders of magnitude greater than the bulk permeability of unoxidized till in the thicker deposit warman site vertical pore water velocities estimated using hydraulic and isotopic evidence vary greatly at dalmeny and appear to be of the order of 8 m in 10 000 yr at warman the association of vertical groundwater flux depth to water table and depth of oxidized zone at a given location is referred to as the flow regime there spatially detailed water level monitoring and test drilling indicated substantial variation of the flow regime at dalmeny on a horizontal scale of tens of meters no such variation exists at warman the differentiation of the flow regime at dalmeny is due to higher till permeability which permits a spatially variable response to microtopographically focussed infiltration of surface water recognition of the causes and symptoms of flow regime variability beneath flat till landscapes has implications for environmental assessment procedures agricultural practices wetland management and waste disposal

evidence for prehistoric earthquakes on the superstition hills fault from offset geomorphic features offset geomorphic features along the superstition hills fault show evidence for at least one slip event prior to the 1987 surface rupture and possibly as many as four to five earlier prehistoric earthquakes we documented several geomorphic features that appeared offset by multiple events by making detailed topographic maps offset features were abundant along reaches of the fault with high topographic relief and large displacement slip distribution for the penultimate event as recorded by offset rills streams and shrub coppice dunes is very similar to the slip distribution from the 1987 earthquake through april 1988 this similarity may prove to be fortuitous if afterslip from the 1987 event continues to increase the total slip for this earthquake but if afterslip associated with the 1987 event ceases in the near future then the past two earthquakes were nearly identical in slip and the superstition hills fault may be expected to produce characteristic earthquakes of roughly magnitude 6

a landslide in clay shale in the north saskatchewan river valley canada abstract a case study of a landslide in heavily overconsolidated clay shale is analyzed to determine shear strength by back analysis the landslide apparently started during deglaciation about 11 000 years b p and is still active the infilling north saskatchewan river alluvium has altered the configuration of the shear zone of the landslide the implications of errors in field data on the results were examined the analysis was most sensitive to modelling the toe configuration and piezometric conditions the effective angle of shearing resistance was estimated at 8 7 degrees assuming zero cohesion

pre earthquake displacement and triggered displacement on the imperial fault associated with the superstition hills earthquake of 24 november 1987 two right lateral slip events about 3 weeks apart in november 1987 broke the surface discontinuously along probably similar nearly 20 km lengths of the northern imperial fault the first displacement at about the beginning of november was accompanied by a surface tilt representing deep vertical motion or distributed strain this movement may have been part of a more regional event that also involved the southern san andreas fault although the evidence there is questionable the later surface offset was triggered probably by the second main shock of the 24 november earthquakes located in the superstition hills about 37 km northwest of the imperial fault the maximum observed displacement was less than 4 cm on both occasions for the triggered movement the maximum slip occurred on a branch strand near the northern extremity of the fault pre earthquake resurveys of short length leveling lines indicated combined surface displacement and an eastward tilt at two locations between surveys 7 1 2 months apart and 13 months apart the tilt at harris road during this pre earthquake interval is modeled as a 1 4 cm vertical component of slip deeper than 100 m on a 70 northeastward dipping fault later resurveys showed a marked reduction of deep movement in the time period including the triggered slip and between december 1987 and january 1988 it had ceased no definite evidence of surface fracturing was found in the brawley fault zone during either period of time when the imperial fault moved remeasurement of leveling lines there indicated small very near surface vertical components of movement in the northern half of the zone elevation changes in the southern part indicated distributed strain and or movement only deeper than about 50 m the brawley zone changes are not fixed in time well enough to clearly relate them to the surface movements on the imperial fault

implications of diverse fault orientations imaged in relocated aftershocks of the mount lewis ml 5 7 california earthquake 1 we use seismic waveform cross correlation to determine the relative positions of 2747 microearthquakes near mount lewis california that have waveforms recorded from 1984 to 1999 these earthquakes include the aftershock sequence of the 1986 ml5 7 mount lewis earthquake approximately 90 of these aftershocks are located beyond the tips of the approximately north striking main shock defining an hourglass with the long axis aligned approximately with the main shock surprisingly our relocation demonstrates that many of these aftershocks illuminate a series of near vertical east west faults that are 0 5 1 km long and separated by as little as 200 m we propose that these structures result from the growth of a relatively young fault in which displacement across a right lateral approximately north striking fault zone is accommodated by slip on secondary left lateral approximately east striking faults we derive the main shock induced static coulomb failure function f on the dominant fault orientation in our study area using a three dimensional 3 d boundary element program to bound viable friction coefficients we measure the correlation between the rank ordering of relative amplitudes of f and seismicity rate change we find that likely friction coefficients are 0 2 0 6 and that the assumed main shock geometry introduces the largest uncertainties in the favored friction values we obtain similar results from a visual correlation of calculated f contours with the distribution of aftershocks viable rate and state constitutive parameters bound the observed relationship between magnitude of f and seismicity rate change and for our favored main shock model a maximum correlation is achieved when f is computed with friction coefficients of 0 3 0 6 these values are below those previously cited for young faults

three dimensional records of surface displacement on the superstition hills fault zone associated with the earthquakes of 24 november 1987 seven quadrilaterals constructed at broadly distributed points on surface breaks within the superstition hills fault zone were repeatedly remeasured after the pair of 24 november 1987 earthquakes to monitor the growing surface displacement changes in the dimensions of the quadrilaterals are recalculated to right lateral and extensional components at millimeter resolution and vertical components of change are resolved at 0 2 mm precision the displacement component data for four of the seven quadrilaterals record the complete fault movement with respect to an october 1986 base these data fit with remarkable agreement the power law u t u f b t 1 b t c where u t is a displacement component at time t after the second main shock and uf b and c are constants this power law permits estimation of the final displacement uf from the data obtained within the period of observation data from one quadrilateral located near the epicenter of the second main shock and northeast trending conjugate faults allow that about 5 cm of right lateral slip may have been associated with the first main shock there data from the other quadrilaterals confirm that the surface faulting on most of the superstition hills fault zone did initiate at the time of the second main shock of the 1987 earthquakes the three dimensional motion vectors all describe nearly linear trajectories throughout the observation period and they indicate smooth shearing on their respective fault surfaces the inclination of the shear surfaces is generally nearly vertical except near the south end of the superstition hills fault zone where two strands dip northeastward at about 70 surface displacement on these strands is right reverse another kind of deformation superimposed on the fault displacements has been recorded at all quadrilateral sites it consists of a northwest southeast contraction or component of contraction that ranged from 0 to 0 1 per cent of the quadrilateral lengths between november 1987 and april 1988

pleistocene stratigraphy of the saskatoon area saskatchewan canada an update pleistocene deposits in the saskatoon area are divided into the sutherland and saskatoon groups the sutherland group is divided into the mennon dundurn and warman formations and the saskatoon group is divided into the floral and battleford formations the floral formation is subdivided into the lower till the riddell member and the upper till each formation is composed of a sequence of deposits including basal proglacial sediment till upper proglacial sediment and nonglacial sediment each formation is defined primarily on the basis of carbonate content and stratigraphic position of its till and commonly it is bounded by weathered zones and or nonglacial sediments the sutherland group is pre illinoian in age and the lower till of the floral formation is illinoian in age the riddell member between the lower and upper tills of the floral formation is late rancholabrean probably sangamon in age radiocarbon ages of sediments lying between the upper till of the floral formation early wis

moment tensor solutions for the 24 november 1987 superstition hills california earthquakes the teleseismic long period waveforms recorded by the global digital seismograph network from the two largest superstition hills earthquakes are inverted using an algorithm based on optimal filter theory these solutions differ slightly from those published in the preliminary determination of epicenters monthly listing because a somewhat different improved data set was used in the inversions and a time dependent moment tensor algorithm was used to investigate the complexity of the main shock the foreshock origin time 01 54 14 5 m b 5 7 m s 6 2 had a scalar moment of 2 3 1025 dyne cm a depth of 8 km and a mechanism of strike 217 dip 79 rake 4 the main shock origin time 13 15 56 4 m b 6 0 m s 6 6 was a complex event consisting of at least two subevents with a combined scalar moment of 1 0 1026 dyne cm a depth of 10 km and a mechanism of strike 303 dip 89 rake 180

coseismic rupture process of the large 2019 ridgecrest earthquakes from joint inversion of geodetic and seismological observations author s liu chengli lay thorne brodsky emily e dascher cousineau kelian xiong xiong

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

the superstition hills california earthquakes of 24 november 1987 the 24 november 1987 superstition hills earthquakes occurred on the conjugate northwest striking right lateral superstition hills fault and a previously unknown northeast striking left lateral structure defined by a lineation of hypocenters extending from the superstition hills fault to the brawley seismic zone master event locations of the earthquakes using caltech usgs seismic network data reveal the following the first main shock 33 4 9 n 115 47 7 h 10 6 km m s 6 2 0154 gmt on the northeast striking structure and its foreshocks co locate events on the northeast structure cluster in space and time and some aftershocks occur in the brawley seismic zone the second main shock 33 0 9 n 115 50 9 w h 1 9 km m s 6 6 1315 gmt on the superstition hills fault was 12 hr after the first main shock and initiated at shallow depth where the two trends join aftershocks of the second main shock lie in a northwest trend between the superstition hills and superstition mountain faults and have a sharply defined western edge the extent of the northwest trend aftershocks is not coincident with surface rupture on the superstition hills fault in general the earthquakes in the northeast trend are deep and the earthquakes in the northwest trend are shallow we compare the earthquake distribution to the distribution of crystalline basement rocks defined from a refraction study of fuis et al 1982 the earthquake locations and extent of aftershock activity appear to be controlled by the presence of crystalline basement rocks

a landslide in till near warman saskatchewan canada little information is available about typical shear strength parameters of tills in southern saskatchewan even though till is the most common earth material used for construction in this region the warman landslide in the south saskatchewan river valley provides some insight into the shear strength characteristics of a till and the results are compared with laboratory tests the till is from the upper till of the sutherland group which has a high clay content relative to the underlying and overlying tills a back analysis of the landslide produced 27 assuming c 0 comparison with laboratory test data and results from a similar landslide near lebret saskatchewan suggests that 22 5 with c 7 kpa may be appropriate residual shear strength parameters a rising water table appears to have been the main contributing factor to instability between 1969 and 1984 there is a possibility however that at the 1 50 return interval for flood levels on the river erosion at the toe of the landslid

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

erratum the gronlid crossing saskatchewan provincial highway no 6 at the saskatchewan river a traffic connection between regina and the northeastern part of saskatchewan required a crossing of the saskatchewan river north of gronlid slope instability developed in lacustrine and deltaic sands on the approaches to a ferry site installed in the early 1960s alternative ferry sites were considered but a river hydraulics study showed that other sites would not offer any improvement the creation of a reservoir by projected dam at nipawin and potential mining development in the area added incentive for the construction of a bridge to replace the original ferry installation valuable information was obtained from the ferry site for locating the new bridge and designing the approach roadways it was possible to locate the bridge and approaches to minimize seepage foundation and slope instability problems in a deposit of over 100 m of saturated interbedded deltaic sand lacustrine silt and clay a major artesian groundwater system was found in the bedrock sand of the swan river group whereas groundwa

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

characterizing an unstable mountain slope using shallow 2d and 3d seismic tomography as transport routes and population centers in mountainous areas expand risks associated with rockfalls and rockslides grow at an alarming rate as a consequence there is an urgent need to delineate mountain slopes susceptible to catastrophic collapse in a safe and noninvasive manner for this purpose we have developed a 3d tomographic seismic refraction technique and applied it to an unstable alpine mountain slope a significant segment of which is moving at 0 01 0 02 m year toward the adjacent valley floor first arrivals recorded across an extensive region of the exposed gneissic rock mass have extraordinarily low apparent velocities at short 0 2 m to long 100 m shot receiver offsets inversion of the first arrival traveltimes produces a 3d tomogram that reveals the presence of a huge volume of very low quality rock with ultralow to very low p wave velocities of 500 2700 m s these values are astonishingly low compared to the average horizontal p wave velocity of 5400 m s determined from labora

a new statistical test for static stress triggering application to the 1987 superstition hills earthquake sequence over the past several years many investigators have argued that static stress changes caused by large earthquakes influence the spatial and temporal distributions of subsequent regional seismicity with earthquakes occurring preferentially in areas of stress increase and reduced seismicity where stress decreases some workers have developed quantitative methods to test for the existence of such static stress triggering but no firm consensus has yet been reached as to the significance of these effects we have developed a new test for static stress triggering in which we compute the change in coulomb stress on the focal mechanism nodal planes of a set of events spanning the occurrence of a large earthquake we compare the statistical distributions of these stress changes for events before and after the mainshock to decide if we can reject the hypothesis that these distributions are the same such rejection would be evidence for stress triggering we have applied this test to the november 24 1987 elmore ranch superstition hills earthquake sequence and find that those post mainshock events that experienced stress increases of at least 0 01 0 03 mpa 0 1 0 3 bar or that occurred from 1 4 to 2 8 years after the mainshocks are consistent with having been triggered by mainshock generated static stress changes

the elmore ranch and superstition hills earthquakes of 24 november 1987 introduction to the special issue on 24 november 1987 two significant earthquakes occurred along the southern san jacinto fault zone and related structural elements in southern california not far from the international border these two events the elmore ranch earthquake m 6 2 at 0154 gmt and the superstition hills earthquake m 6 6 at 1315 gmt both moment magnitudes from sipkin 1989 and their aftershocks have yielded a rich harvest of geological seismological and engineering data pertinent to the cause and effect of earthquakes in this region where the southern san jacinto fault zone enters the salton depression from the peninsula ranges bordering it on the southwest fig 1 this special issue of the bulletin presents 18 geologic and seismologic investigations of these earthquakes a collection of papers born in el centro california on 8 and 9 february 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

waveform modeling of the november 1987 superstition hills earthquakes long period body wave data recorded at teleseismic distances and strong motion data at pasadena for the superstition hills earthquakes of 24 november 1987 are modeled to obtain the source parameters we will refer to the event that occurred at 0153 ut as eq1 and the event at 1316 ut as eq2 at all distances the first earthquake appears to be a simple left lateral strike slip event on a fault striking ne it is a relatively deep event with a source depth of 10 km it has a teleseismic moment of 2 7 10 25 dyne cm the second and more complex event was modeled in two ways by using eq1 as the green s function and by using a more traditional forward modeling technique to create synthetic seismograms the first method indicated that eq2 was a double event with both subevents similar but not identical to eq1 and separated by about 7 5 sec from the synthetic seismogram study we obtained a strike of 305 for the first subevent and 320 for the second both have dips of 80 and rakes of 175 the first subevent has a moment of 3 6 10 25 which is half that of the second we obtain depths of at least 6 km the teleseismic data indicate a preferred subevent separation of 30 km with the second almost due south of the first but the error bounds are substantial this would suggest that the subevents occurred on conjugate faults the strong motion data at pas however imply a much smaller source separation with the sources probably produced by asperities

the petrofka landslide saskatchewan both abutments and all piers of the petrofka bridge are on a landslide the bridge has performed satisfactorily for 23 years indicating the factor of safety of the petrofka landslide is greater than unity this stability is abnormal because landslide slopes on bedrock clays shale in this region are notoriously unstable a dormant landslide is difficult to analyze because the input parameters must represent a condition of limiting equilibrium the petrofka landslide is 70 m high 880 m long 3000 m wide and up to 100 m thick the shear zone is in highly plastic montmorillonitic clays in an unnamed formation of probable tertiary age the upper cretaceous lea park judith river and bearpaw formations and the unnamed formation underly the landslide and are restricted to a collapse structure resulting from dissolution of devonian evaporites a retrogressive mechanism developed as valley downcutting progressed the pore water pressures could be estimated from the hydraulic head in the artesian aquifer of th

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

seismic evidence for conjugate slip and block rotation within the san andreas fault system southern california the pattern of seismicity in southern california indicates that much of the activity is presently occurring on secondary structures several of which are oriented nearly orthogonal to the strikes of the major through going faults slip along these secondary transverse features is predominantly left lateral and is consistent with the reactivation of conjugate faults by the current regional stress field near the intersection of the san jacinto and san andreas faults however these active left lateral faults appear to define a set of small crustal blocks which in conjunction with both normal and reverse faulting earthquakes suggests contemporary clockwise rotation as a result of regional right lateral shear other left lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data many of these structures predate the modern san andreas system and may control the pattern of strain accumulation in southern california geodetic and paleomagnetic evidence confirm that block rotation by strike slip faulting is nearly ubiquitous particularly in areas where shear is distributed and that it accommodates both short term elastic and long term nonelastic strain a rotating block model accounts for a number of structural styles characteristic of strike slip deformation in california including variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults domains of evenly spaced antithetic faults that terminate against major fault boundaries continued development of bends in faults with large lateral displacements anomalous focal mechanisms and differential uplift in areas otherwise expected to experience extension and subsidence since block rotation requires a detachment surface at depth to permit rotational movement low angle structures like detachments of either local or regional extent may be involved in the contemporary strike slip deformation of southern california a block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge bounding faults but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction this behavior coupled with the presence of possible regional detachments accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges although fault displacements along secondary structures associated with block rotations remain small they may still influence the nucleation and the characteristic rupture length of large earthquakes a more complete description of what these structures are and how they interact may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard

ice thrust features and the maymont landslide in the north saskatchewan river valley the battleford glacier created shearing and softening of bedrock clays contributing to widespread slope instability along the valley of the north saskatchewan river the battleford glacier flowed southeastward down the valley of the north saskatchewan river during its final stage in west central saskatchewan it created flutings crevasse fillings folding and faulting in ice thrust ridges and extensive horizontal gouge zones filled with soft malleable clay extensive drilling and testing for the foundations of the maymont bridge provided definitive data outlining at least three gouge zones the shallowest gouge zone at an elevation of 465 m defines the base of the most severe glacial folding and deformation of the bedrock in at least one of the ice thrust ridges the deeper gouge zones are at about 433 and 438 m elevation postglacial landslides slumps along the southern side of the north saskatchewan river are controlled by the gouge zones which are low friction slide surfaces along which large ho

gps velocity and strain fields in sicily and southern calabria italy updated geodetic constraints on tectonic block interaction in the central mediterranean 1 we present an improved rendition of the geodetic velocity and strain fields in sicily and southern calabria obtained through the analysis of 18 years of gps observations from continuous and survey station networks the dense spatial coverage of geodetic data provides precise quantitative estimates of previously established first order active kinematic features including i a narrow east west elongated belt of contraction 1 1 5 mm yr extending offshore northern sicily from ustica to stromboli across the aeolian islands ii a narrow east west trending contractional belt located along the northern rim of the hyblean plateau in southern sicily with shortening at up to 4 4 mm yr iii right motion 3 6 mm yr on the aeolian tindari letojanni fault atlf system a main shear zone extending from the aeolian islands to the ionian coast of sicily with significant transpression and transtension partitioned between discrete sectors of the fault iv transtension 1 mm yr across the sicily channel between sicily and north africa we use geodetic observations coupled to geological constraints to better elucidate the interplay of crustal blocks revealed in the investigated area in particular we focus on the atlf which forms the primary boundary between the sicilian and calabrian blocks the atlf juxtaposes north south contraction between sicily and the tyrrhenian block with northwest southeast extension in northeastern sicily and calabria contraction between sicily and tyrrhenian blocks probably arises from the main europe nubia convergence although sicily has a component of lateral motion away from nubia we found that convergence is not restricted to the northern offshore as commonly believed but is widely accommodated between the frontal belt and the northern rim of the hyblean foreland in southern sicily geodetic data also indicate that active right shear on the atlf occurs to the southeast of the mapped fault array in northern sicily suggesting the fault cuts through till the ionian coast of the island the small geodetic divergence between the hyblean and apulian blocks rimming on both sides the calabria block and subjacent ionian slab coupled with marine geophysical evidences in the ionian sea lends credit to the proposed deep root of the atlf and to a fragmentation of the ionian domain

rupture process of the ms 6 6 superstition hills california earthquake determined from strong motion recordings application of tomographic source inversion abstract we analyze strong motion recordings of the m s 6 6 superstition hills earthquake to determine the timing location spatial extent and rupture velocity of the subevents that produced the bulk of the high frequency 0 5 to 4 hz seismic energy radiated by this shock the earthquake can be characterized by three principal subevents the largest ones occurring about 3 and 10 sec after initiation of rupture timing relationships between pulses on the seismograms indicate that the three subevents are located within 8 km of each other along the northern portion of the superstition hills fault the two largest subevents display different directivity effects we apply a tomographic source inversion to the integrated accelerograms to determine the slip acceleration on the fault as a function of time and distance based on a one dimensional fault model the azimuthal distribution of amplitudes for the second subevent can be largely explained by a rupture that propagated about 2 km to the southeast along the superstition hills fault at a velocity about equal to the p wave velocity an alternative model with rupture propagating to the northeast along a conjugate fault plane can also account for the observed directivity of this subevent but it is not supported by the aftershock distribution the third subevent ruptured to the southeast along an 8 km long portion of the superstition hills fault at about the shear wave velocity this rupture propagation caused the relatively large accelerations and velocities observed in strong motion records for stations southeast of the hypocenter the long time intervals between the subevents and their relative proximity to each other indicate a very slow component to the rupture development the southern half of the superstition hills fault did not generate significant high frequency strong ground motion although it showed substantial co seismic surface displacement the subevents are situated along the same northern portion of the fault where most of the aftershocks are located the locations of the subevents appear to be controlled by bends in the fault mapped at the surface and by changes in basement structure at depth

movement and stability analysis of the beaver creek landslide saskatchewan canada this paper presents a case history of a multiblock landslide where the blocks move at varying rates along a common horizontal slip surface which follows the contact between stratified drift and underlying till movement measurements indicate that the blocks towards the toe move at a higher rate than blocks towards the scarp stability analyses show that the entire slide mass can be analyzed as a single unit as opposed to considering each block separately this finding is compared with the analysis of other multiblock slides the friction angle mobilized along the horizontal slip surface falls within the range of residual values measured in the laboratory key words landslides stability analysis translational slides residual strength

compression characteristics and index properties of tills and intertill clays in southern saskatchewan canada compression characteristics and index properties of unweathered tills and clays from repeated glaciations follow a predictable pattern at 10 sites along a 1300 km transect across southern saskatche

the denholm landslide saskatchewan part ii analysis a procedure incorporating geological evidence with analytical methods was developed for the back analysis of a multiple retrogressive landslide in cretaceous clay shale the slide mass apparently inactive extends 2 km back from the toe at the river and is seated on a shear zone 100 m deep at the main scarp historical evidence of the slope movement was established from radiocarbon dating of the river alluvium over which the landslide moved the geometry of the landslide when the factor of safety was near unity was determined from historic and stratigraphic evidence and sensitivity analyses the stratigraphy of the slide mass showed that the beds are stretched with very little vertical displacement indicating a mainly translational mechanism along a nearly horizontal shear zone apparently movement has taken place at a slow but steady rate over 11 000 years resulting in a horizontal displacement of 390 430 m at the toe the landslide therefore was analyzed as a series of sliding blocks with a common f

fracture permeability and groundwater flow in clayey till near saskatoon saskatchewan field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude such findings are common for weathered till but are rare for unweathered till and have important implications for groundwater recharge and contaminant transport the till in question is 6 m thick and appears to be unweathered and unfractured it is overlain by 12 m of weathered and highly fractured till results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3 5 10 11 m s 1 and a mean specific storage of 1 3 10 4 m 1 results of slug tests yield a horizontal hydraulic conductivity of about 5 10 9 m s 1 drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4 5 10 5m2 s 1 the slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 10

geodetic investigation into the deformation of the salton trough 1 the salton trough represents a complex transition between the spreading center in baja california and the strike slip san andreas fault system and is one of the most active zones of deformation and seismicity in california we present a high resolution interseismic velocity field for the salton trough derived from 74 continuous gps sites and 109 benchmarks surveyed in three gps campaigns during 2008 2009 and previous surveys between 2000 and 2005 we also investigate small scale deformation by removing the regional velocity field predicted by an elastic block model for southern california from the observed velocities we find a total extension rate of 11 mm yr from the mesquite basin to the southern edge of the san andreas fault coupled with 15 mm yr of left lateral shear the majority of which is concentrated in the southern salton sea and obsidian buttes and is equivalent to 17 mm yr oriented in the direction of the san andreas fault differential shear strain is exclusively localized in the brawley seismic zone and dilatation rate indicates widespread extension throughout the zone in addition we infer clockwise rotation of 10 ma consistent with northwestward propagation of the brawley seismic zone over geologic time

the 1987 superstition hills earthquake sequence strains and tilts at pinon flat observatory abstract we describe observations at pinon flat observatory of preseismic co seismic and postseismic strain and tilt changes associated with the superstition hills earthquake sequence of 24 november 1987 the data come from two long base strainmeters one long base tiltmeter and a borehole dilatometer co seismic offsets were seen for the two largest earthquakes these offsets roughly agree with those from a dislocation in a half space though with disagreements at the 30 per cent level suggesting some error in one or more of the co seismic observations for the main shock the moment deduced from the offsets is 5 to 6 10 25 dyne cm less than that found from the seismic data no precursive strain changes were seen for the 8 hr before the main shock any strain changes were less than the instrument noise level 1 per cent of the co seismic strain during the last 1000 sec before this earthquake any precursory strains must be less than 0 5 per cent of the co seismic amount postseismic strain during the 2 hr after the main shock was about 10 per cent of the co seismic strain

teleseismic source parameters and rupture characteristics of the 24 november 1987 superstition hills earthquake long period body waves from the 24 november 1987 superstition hills earthquake are studied to determine the focal mechanism and spatial extent of the seismic source the earthquake is a complex event consisting of two spatially distinct subevents with different focal mechanisms two consistent models of rupture are developed for both models the second subevent begins 8 sec after the initiation of the first subevent and the preferred centroid depth lies between 4 to 8 km model 1 consists of two point sources separated by 15 to 20 km along strike of the superstition hills fault model 2 consists of one point source and one line source with a rupture velocity of 2 5 km sec with moment release distributed along strike of the focal plane at a distance of 10 to 22 km from the epicenter these moment release patterns show that a significant amount of long period energy is radiated from the southern segment of the fault total moment release for both models is approximately 8 10 25 dyne cm both models also suggest a change of dip from near vertical near the epicenter to steeply southwesterly dipping along the southern segment of the fault the difference in rupture characteristics and fault dips seen teleseismically is also reflected in aftershock and afterslip data and crustal structure underlying the two fault segments the northern segment had more aftershocks and a smaller proportion of afterslip than the southern segment the boundary between the two segments lies at a step in the basement that separates a deeper metasedimentary basement to the south from a shallower crystalline basement to the north

a transient analysis of slope stability following drawdown after flooding of a highly plastic clay the stability of slopes at bridge abutments across the carrot river in east central saskatchewan was not influenced significantly by drawdown after flooding in the spring of 1995 traditional metho

movement triggers and mechanisms of two earth slides in the thompson river valley british columbia canada since the construction of the canadian pacific railway and canadian national railway main rail lines in western canada in 1885 and 1905 respectively both companies have had to contend with 11 large translational retrogressive earth slides in the thompson river valley south of ashcroft british columbia the initiation of these slides is associated with the down cutting by the thompson river through the quaternary sediments in its valley the slides move on two subhorizontal weak layers in a glaciolacustrine clay silt unit within this quaternary sediment sequence transient seepage and stability analyses were conducted for two sample slides and the results were in agreement with inclinometer and piezometric data it is concluded that the thompson river triggers the movements in a drawdown mechanism and or erosion mechanism the thompson river affects the stability of these slides in three ways i by changing the pore pressure on the rupture surface ii by changing the supporting force on the toe

recognition of earthquake induced damage in the abakainon necropolis ne sicily results from geomorphological geophysical and numerical analyses seismotectonic activity and slope instability are a permanent threat in the archaeological site of abakainon and in the nearby village of tripi in ne sicily in recent times signs of an ancient earthquake have been identified in the necropolis of abakainon which dating was ascertained to the first century ad earthquake the site is located on a slope of peloritani mts along the tindari fault line and contains evidence for earthquake induced landslide including fallen columns and blocks horizontal shift and counter slope tilting of the tomb basements in this paper we used an integrated geomorphological and geophysical analysis to constrain the landslide the research was directed to the acquisition of deep geological data for the reconstruction of slope process and the thickness of mobilized materials the applied geophysical techniques included seismic refraction tomography and electrical resistivity tomography the surveys were performed to delineate the sliding surface and to assess approximately the thickness of mobilized materials the geophysical and geomorphologic data confirmed the presence of different overlapped landslides in the studied area moreover a numerical simulation of the slope under seismic loads supports the hypothesis of a mobilization of the landslide mass in case of strong earthquakes pga 0 3 g however numerical results highlight that the main cause of destruction for the abakainon necropolis is the amplification of the seismic waves occasionally accompanied by surficial sliding

the hepburn landslide an interactive slope stability and seepage analysis mechanisms of active landslides are continuous processes involving the dynamics of slope failure interacting with the groundwater regime this process is simulated in phases by combining stability calculations interactively with a seepage analysis to determine the factor of safety for a dormant landslide near hepburn saskatchewan the landslide is a multiple retrogressive failure with two parallel slip surfaces at different elevations the slip surfaces are in originally overconsolidated cretaceous and tertiary clays softened by shear from glaciation an artesian aquifer is present at the base of the slip surface causing saline springs at the base of the valley slope a residual effective friction angle of 6 7 with zero cohesion was found to best characterize the shear strength of the clays in the failure zone potential nets and head profiles from the seepage analysis illustrate the strong influence of changing topography on the groundwater flow system the present day factor of safety for the dormant

surface slip subsequent to the 24 november 1987 superstition hills california earthquake monitored by digital creepmeters three creepmeters of new design were operated on the superstition hills fault following the 24 november 1987 earthquake each creepmeter consists of a digital displacement sensor interrogated periodically by a computer at the end of each hour the computer determines a recording rate appropriate to the velocity of the slip on the fault in that hour no data are recorded if the fault is inactive data are recorded at a maximum rate of one sample per minute if slip on the fault is detected the resolution and range of the creepmeters are 10 m and 15 cm respectively fault activity is observed to be confined to periods of episodic slip creep events with mean amplitudes 3 to 6 mm and durations less than 4 hr a total of 80 creep events were recorded during the first week following the earthquake creep events occurred several times each day after 6 months events occurred every 3 weeks this increase in the mean time interval between creep events results in the observed decay in afterslip rate between creep events the fault is inactive although more than 200 microstrain of fault zone deformation may accumulate before each event although creep events were observed to propagate unilaterally in both directions along the fault the most impulsive events appeared to propagate bilaterally from a dilatant offset separating the northern and southern halves of the 24 km long fault zone maximum propagation velocities of 30 m sec were observed aftershocks 2 m 4 7 were observed to occur near the creepmeters following 6 to 9 cm of surface slip on the fault a future aftershock in this region is anticipated in mid 1989 based on afterslip rates in the year following the main shock

recent earthquake sequences at coso evidence for conjugate faulting and stress loading near a geothermal field abstract two recent earthquake sequences near the coso geothermal field show clear evidence of faulting along conjugate planes we present results from analyzing an earthquake sequence occurring in 1998 and compare it with a similar sequence that occurred in 1996 the two sequences followed mainshocks that occurred on 27 november 1996 and 6 march 1998 both mainshocks ruptured approximately colocated regions of the same fault system following a comparison with the background seismicity of the coso region we have detected evidence of stress loading within the geothermal field that appears to be in response to the 1998 earthquakes the m l 5 2 mainshock in the 1998 sequence occurred at 5 47 a m utc and was located approximately 45 km north of the town of ridgecrest in the coso range the mainshock of the 1996 sequence had an m l magnitude of 5 3 there have been no observable surface ruptures associated with either of these sequences though the mainshocks for both sequences were located about 900 m apart and have nearly the same local magnitudes the sequences differ in both their temporal and spatial characteristics an analysis of the fault plane solutions of the mainshocks and the aftershock locations suggests that the two sequences ruptured fault planes that are perpendicular to one another we observe a much faster temporal decay of the 1998 sequence compared to the one in 1996 moreover while the 1996 sequence was not followed by any sizeable i e m l 4 0 aftershocks the 1998 sequence had four such events from an estimate of the tectonic stressing rate on the fault that produced the 1998 sequence we infer a repeat cycle of 135 years for an earthquake of comparable magnitude at coso

deformation of the deer creek bridge by an active landslide in clay shale two parallel concurrently active slip surfaces of a landslide in clay shale of the cretaceous lea park formation are causing deformation of a bridge structure across the north saskatchewan river n

spatial and temporal variations in seismicity in the imperial valley 1902 1984 earthquakes with m l 4 5 that occurred between 1932 and 1973 in the imperial valley region and their related foreshocks and aftershocks are relocated using station delays derived from calibration events that were well recorded at regional distances between 1979 and 1981 the relocated seismicity shows that there was an increase in seismicity in regions northeast of the imperial fault 5 to 6 yr prior to the 1940 m s 7 1 imperial valley earthquake a study of intensity reports for felt earthquakes prior to 1932 also suggests an increase in seismicity in regions surrounding the imperial fault as early as 1917 isoseismal patterns description of the mainshock sequence and patterns of seismicity before and after the 1915 imperial valley earthquakes suggest that the earthquakes occurred off the imperial fault in this case seismicity between 1906 and 1940 would nearly encircle the portion of the imperial fault that ruptured during 1940 in both the 1940 and 1979 imperial valley earthquake sequences aftershocks of m l 4 5 occurred only for 2 months following the mainshock the aftershock sequences were followed by periods of quiescence lasting up to 10 yr in the region within 30 km of the mainshock this is in contrast to m l 6 0 earthquakes occurring near the edges of the imperial valley that had aftershocks of m l 4 5 occurring for up to 4 yr after the mainshock these differences may be related to the high heat flow within the imperial valley

archaeological evidence for a possible first century ad earthquake in the necropolis of abakainon ne sicily abstract the greek necropolis of abakainon ne sicily southern italy was destroyed suddenly some time after the 2nd century bc in order to identify the destruction cause of the necropolis we analyzed geological geomorphological data and site stratigraphy evidence on the site suggests that the observed collapse and deformation may be consistent with a seismic event optically stimulated luminescence dating constrains the age of the collapse to the 1st century ad probably during the time span 14 37 ad when other nearby sites were also damaged by an earthquake as reported by historical sources this study contributes to a better characterization of earthquakes in the area during the first millennium ad and improves knowledge on historical seismicity in ne sicily

slip on the superstition hills fault and on nearby faults associated with the 24 november 1987 elmore ranch and superstition hills earthquakes southern california alignment arrays and creepmeters spanning several faults in southern california recorded slip associated with the 24 november 1987 elmore ranch and superstition hills earthquakes no precursory slip had occurred on the superstition hills fault up to 27 october 1987 when the last measurement before the earthquakes was made about 23 days before the earthquake dextral creep events of about 13 mm and 0 5 mm may have occurred simultaneously on the imperial and southern san andreas faults respectively but the tectonic origin of the smaller event is questionable within 12 hr after the superstition hills earthquake 20 9 cm of dextral slip occurred on the main fault trace at the superstition hills alignment array and 39 8 cm of dextral slip was recorded over the entire 110 m width of the array despite this initial wide distribution of slip nearly all of the postseismic slip is occurring on the main fault trace as of 3 august 1988 the alignment array had recorded a total of 80 2 cm of dextral slip as of 5 days after the earthquakes 65 to 80 per cent of the total slip measured by the alignment array had occurred on discrete mappable fractures in addition the two earthquakes triggered slip on the coyote creek fault the southern san andreas fault and on the imperial fault telemetered data from creepmeters on the southern san andreas and imperial faults indicate that triggered slip began there within 3 min or less of each of the two earthquakes additional triggered slip occurred on the imperial fault beginning 3 5 hr after the second earthquake

flexural slip folding along the eastern elmore ranch fault in the superstition hills earthquake sequence of november 1987 co seismic flexural slip folding of a small anticline along the eastern elmore ranch fault associated with the superstition hills earthquake sequence demonstrates that variations in left lateral slip can be explained locally by folding surface rupture on the eastern branch of the elmore ranch fault was greatest to the northeast of the fold but decreased to zero across the southern limb a kilometer long surface slip gap exists just southwest of the fold being bounded on the northeast with 75 mm of slip and to the southwest with about 60 mm of slip lateral slip continues southwesterly to the faults intersection with the superstition hills fault the gentle to openly folded moderately plunging upright asymmetric anticline experienced left lateral slip on the northern limb and right oblique slip on the southern limb with maximum documented lateral slip along bedding planes of 10 mm slip values were greatest on the limbs and decreased to zero at the fold hinge which is consistent with the flexural slip folding process secondary left lateral faults ruptured both limbs of the anticline and bedding plane slip was not observed hingeward of these faults these data suggest that left lateral strain associated with seismogenic fault rupture was continuous in the subsurface but was accommodated locally by folding at the surface

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

slip on the elmore ranch fault during the past 330 years and its relation to slip on the superstition hills fault abstract the elmore ranch fault is a left lateral fault that strikes northeast within the right lateral transform boundary that strikes northwest through southern california it lies transverse and adjacent to the segment of the superstition hills fault that ruptured in 1987 rupture of the elmore ranch fault m s 6 2 preceded rupture of the superstition hills fault m s 6 6 by about 11 4 hr the elmore ranch fault slipped at the surface in 1987 with left lateral displacements of up to 130 mm geological data indicate that it had slipped prehistorically sometime after about 1660 a d probably in a single event excavations at three sites enable the following comparisons at these sites the only significant component of dip slip down to the southeast was found on the west strand for slip previous to 1987 the superstition hills fault has also been documented to have experienced one slip event between 1660 and 1987 thus these slip events on the elmore ranch and superstition hills faults may have occurred in a sequence similar to that in 1987 neither the main fault nor the cross fault however appear to have exactly duplicated their previous surficial slip previous slip was probably smaller on the superstition hills fault and larger on the elmore ranch fault zone than in the 1987 event because the temporal correlation between previous slip events is not proven rupture sequences other than a doublet in which main fault rupture follows cross fault rupture are possible

new slip along parts of the 1968 coyote creek fault rupture california on 28 and 30 november 1987 we found new surface ruptures along the central break of the coyote creek fault s 1968 rupture mapped slip that may have been triggered by the superstition hills earthquakes of 24 november 1987 was dominantly right lateral and ranged up to 15 mm total length of the new ruptures was about 3 km distributed along two quasi continuous segments of the main fault plus one segment of a secondary fault all of which ruptured in 1968 the longest segment of new rupture followed the northeast side of the ocotillo badlands for 2 3 km newly mapped slip in 1987 occurred along parts of the coyote creek fault that were characterized in 1968 by several features these were large total dextral slip a prominent vertical slip component rupture along single fractures instead of en echelon cracks and large afterslip in the few years following the 1968 earthquake past episodes of triggered slip on the san andreas imperial and superstition hills faults were hypothesized by others to be precursory phenomena the 1987 slip on the coyote creek fault however may be an episode of afterslip this suggestion is supported by the decrease in creep rates since 1968 shown by data from two alinement arrays on the coyote creek fault the correct interpretation of triggered slip events and their value as earthquake precursors therefore depends upon a good knowledge of the slip history of a fault

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

inverting measurements of surface slip on the superstition hills fault we derive and test a set of inversions of surface slip measurements based on the empirical relation u t uf 1 t t c proposed by sharp and saxton 1989 to estimate the final slip uf the power law exponent c and the power law duration t at short times sharp s relation behaves like the simple power law u t u 1 tc where u 1 is the initial slip that is the slip at 1 day after the earthquake at long times the slip approaches the final slip asymptotically the inversions are designed in part to exploit the accuracy of measurements of differential slip that is measurements of surface slip which are made relative to a set of nails or stakes emplaced after the earthquake we apply the inversions to slip measurements made at 53 sites along the superstition hills fault for the 11 months following the m 6 2 and 6 6 earthquakes of 24 november 1987 in general estimates of the initial slip and the power law exponent are well resolved while estimates of the power law durations and the final slip are less well resolved because the durations of the surface slip measurements are often less than the derived power law durations the slip on the three fault strands is a relatively smooth function of position the initial slip and final slip are well correlated the time dependence of surface slip at the 53 sites is roughly similar along the entire fault where the power law exponents are distributed as c 0 14 0 04 and the power law durations range from 100 t 1000 days

multidisciplinary study of the tindari fault sicily italy separating ongoing contractional and extensional compartments along the active africa eurasia convergent boundary abstract the africa eurasia convergence in sicily and southern calabria is currently expressed by two different tectonic and geodynamic domains the western region governed by a roughly n s compression generated by a continental collision the eastern one controlled by a nw se extension related to the south east directed expansion of the calabro peloritan arc the different deformation pattern of these two domains is accommodated by a right lateral shear zone aeolian tindari letojanni fault system which from the ionian sea north of mt etna extends across the peloritani chain to the aeolian islands in this work we study the evidence of active tectonics characterizing this shear zone through the analysis of seismic and geodetic data acquired by the ingv networks in the last 15 years the study is completed by structural and morphological surveys carried out between capo tindari and the watershed of the chain the results allowed defining a clear structural picture depicting the tectonic interferences between the two different geodynamic domains the results indicate that besides the regional n130 e horizontal extensional stress field another one ne sw oriented is active in the investigated area both tension axes are mutually independent and have been active up to the present at different times the coexistence of these different active horizontal extensions is the result of complex interactions between several induced stresses 1 the regional extension nw se related to the slab rollback and back arc extension 2 the strong uplift of the chain 3 the accommodation between compressional and extensional tectonic regimes along the aeolian tindari letojanni faults through a sse nnw right lateral transtensional displacement in these conditions the greater and recurring uplift activity is not able to induce a radial extensional dynamics but under the directing action of the shear system it can only act on the regional extension nw se and produce the second system of extension ne sw

slip along the superstition hills fault associated with the 24 november 1987 superstition hills california earthquake surficial slip along the entire mapped length of the superstition hills fault in southern california occurred in association with the superstition hills earthquake m s 6 6 of 24 november 1987 we made repeated measurements of surface slip at 36 sites along the fault and occupied 64 sites at least once at our sites dextral slip was as high as 48 5 cm 1 day after the earthquake and 71 cm 2 months after the measurements show that slip during the period from hr to several hundred hr following the event is described by a simple power law of time extrapolation to t 1 min indicates that co seismic slippage ranged from 5 to 23 cm at 10 of our best recorded sites suggesting that finite co seismic slippage occurred along the length of the fault these extrapolations are supported by a measurement made at imler road 30 min after the shock measurements are complete through october 1988 at many sites the form of slip rate was decay changed from power law to a function of log time during the interval between 300 and 500 hr after the earthquake logarithmic slip rate decay in time was observed for a period of several yr after the parkfield borrego mountain and imperial valley earthquakes those measurements may have begun too late to resolve power law behavior at early times if current logarithmic behavior of the superstition hills fault persists right lateral slippage will approach 90 cm 10 yr after the rupture changes in the along fault displacement profile correlate well with geometric features including a fault bend and a major fault step moreover slip behavior appears to be correlated to the thickness of sedimentary cover along the fault also the northern half of the fault is bounded by a large block of continental crystalline basement the presence of this block may have contributed to the relatively uniform early slip behavior observed there

behavior of the superstition hills fault during the past 330 years we have investigated the recent prehistoric behavior of the superstition hills fault by examining its effect on the beach deposits of ancient lake cahuilla excavation of these sediments in three dimensions where they are cut by the fault has enabled determination of total offset since the latest highstand of the lake about 330 years ago as of 3 march 1988 total dextral offset was 1106 50 mm about 609 mm of this amount can be attributed to one or more slip events before 1987 the remaining slip occurred during the moderate earthquake of 24 november 1987 and as subsequent aftercreep additional aftercreep here might produce a total of 1210 100 mm for that event thus if afterslip continues according to our prediction slip associated with the penultimate seismic slip event on the superstition hills fault was only about half of the co seismic slip and predicted afterslip associated with the 1987 earthquake this difference established at a single site on the fault may reflect a larger size for the 1987 event than for its predecessor we calculate that the slip rate of the superstition hills fault zone averaged over the past 330 years is between about 2 and at least 6 mm yr at this site during this time the average interval between large surface slip events on the superstition hills fault has been between about 150 and 300 years the pre 1987 slip event documented in our excavations could have occurred at any time between a d 1660 and about a d 1915 these results are significant for understanding earthquake recurrence and patterns of earthquakes in the imperial and coachella valleys

evidence of seismic deformation of the paved floor of the decumanus at tindari ne sicily summary most of the ancient town of tindari ne sicily was settled on a plateau the most surficial layer of which was made of unconsolidated material ongoing excavations at the archaeological site at tindari uncovered a large portion of the decumanus which suffered deformations preliminarily assigned to coseismic effects an analysis of the local dynamic response through the simulation of strong seismic shaking to the bedrock and modelling of spectral ratios of the bedrock soft soil was carried out to verify the susceptibility of superficial terrains of the promontory to coseismic deformations to perform this simulation the finite element method fem was used four accelerometric recordings of three earthquakes of medium high magnitude recorded on rocky sites were chosen to simulate the seismic shaking using a constitutive law for the materials composing the promontory layers both of linear elastic type and of elastoplastic type the analysis of the linear elastic field allowed the definition of the frequencies for which the spectral ratios of the accelerations recorded the highest amplifications in particular the frequency range 31 5 37 2 hz can be combined with deformation of the paved floor of the decumanus the analysis in the elastoplastic field highlighted the zones of promontory more susceptible to suffer plasticization process the results show that the topmost layer of the decumanus is the most susceptible to suffer plasticization therefore the performed analysis lends greater support to the hypothesis that the deformations were produced by seismic shaking

surface faulting along the superstition hills fault zone and nearby faults associated with the earthquakes of 24 november 1987 the m 6 2 elmore desert ranch earthquake of 24 november 1987 was associated spatially and probably temporally with left lateral surface rupture on many northeast trending faults in and near the superstition hills in western imperial valley three curving discontinuous principal zones of rupture among these breaks extended northeastward from near the superstition hills fault zone as far as 9 km the maximum observed surface slip 12 5 cm was on the northern of the three the elmore ranch fault at a point near the epicenter twelve hours after the elmore ranch earthquake the m 6 6 superstition hills earthquake occurred near the northwest end of the right lateral superstition hills fault zone surface rupture associated with the second event occurred along three strands of the zone here named north and south strands of the superstition hills fault and the wienert fault for 27 km southeastward from the epicenter in contrast to the left lateral faulting which remained unchanged throughout the period of investigation the right lateral movement on the superstition hills fault zone continued to increase with time a behavior that was similar to other recent historical surface ruptures on northwest trending faults in the imperial valley region we measured displacements over 339 days at as many as 296 sites along the superstition hills fault zone and repeated measurements at 49 sites provided sufficient data to fit with a simple power law data for each of the 49 sites were used to compute longitudinal displacement profiles for 1 day and to estimate the final displacement that measured slips will approach asymptotically several years after the earthquakes the maximum right lateral slip at 1 day was about 50 cm near the south central part of the north strand of superstition hills fault and the predicted maximum final displacement is probably about 112 cm at imler road near the center of the south strand of the superstition hills fault the overall distributions of right lateral displacement at 1 day and the estimated final slip are nearly symmetrical about the midpoint of the surface rupture the average estimated final right lateral slip for the superstition hills fault zone is about 54 cm the average left lateral slip for the conjugate faults trending northeastward is about 23 cm the southernmost ruptured member of the superstition hills fault zone newly named the wienert fault extends the known length of the zone by about 4 km the southern half of this fault south of new river expressed only vertical displacement on a sinuous trace the maximum vertical slip by the end of the observation period there was about 25 cm but its growth had not ceased photolineaments southeast of the end of new surface rupture suggest continuation of the superstition hills fault zone in farmland toward mexico

interferometric synthetic aperture radar observations of the 1994 double spring flat nevada earthquake m5 9 main shock accompanied by triggered slip on a conjugate fault 1 the 1994 double spring flat dsf earthquake m5 9 was the largest earthquake to strike nevada in more than 30 years it occurred in the sierra nevada basin and range transition zone within a step over region between two major normal faults descending and ascending ers interferograms show a maximum range change of 8 5 cm which is the coseismic ground displacement associated with this normal oblique slip moderatesized earthquake elastic inverse modeling and surface displacements across coseismic ground cracks suggest that two different event sources could account for the observed deformation the first source was the main shock with right oblique slip on the northnorthwest striking dsf fault the second source was normal faulting on a shallow northnortheast striking elongated plane conjugate to the dsf fault these two sources are consistent with the pattern of postevent seismicity and we suggest that the second source represents seismic and aseismic slip triggered by the main shock calculations of changes in coulomb failure stress show that the main shock encouraged normal slip on this plane index terms 1206 geodesy and gravity crustal movements interplate 8155 1241 geodesy and gravity satellite orbits 1242 geodesy and gravity seismic deformations 7205 1299 geodesy and gravity general or miscellaneous 7212 seismology earthquake ground motions and engineering

tectonics and seismicity of the tindari fault system southern italy crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab 1 the tindari fault system southern tyrrhenian sea italy is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab onshore structural data an offshore seismic reflection profile and earthquake data are analyzed to constrain the present geometry of the tindari fault system and its tectonic evolution since neogene including the present seismicity results show that this zone of deformation consists of a broad nnw trending system of faults including sets of right lateral left lateral and extensional faults as well as early strike slip faults reworked under late extension earthquakes and other neotectonic data provide evidence that the tindari fault system is still active in the central and northern sectors and mostly accommodates extensional or right lateral transtensional displacements on a diffuse array of faults from these data a multiphase tectonic history is inferred including an early phase as a right lateral strike slip fault and a late extensional reworking under the influence of the subduction related processes which have led to the formation of the tyrrhenian back arc basin within the present regional geodynamic context the tindari fault system is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments these tectonic compartments relating to the complex processes of plate convergence occurring in the region the tindari fault system might also be included in an incipient oblique extensional transfer zone linking the ongoing contractional belts in the calabrian ionian and southern tyrrhenian compartments

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

seismicity and fault kinematics through the eastern transverse ranges california block rotation strike slip faulting and low angle thrusts hypocentral locations and first motion data from the southern california seismic network are used to infer the present pattern of deformation along the southern san andreas fault the study area lies between the san jacinto fault and desert hot springs and includes the san bernardino mountains and san gorgonio pass this region has some of the deepest earthquakes observed anywhere along the entire san andreas system exhibits a complex surface geology characterized by both right and left lateral faults has high topographic relief as a result of recent uplift and is a potential site for the nucleation of a great earthquake although this area is unusually seismogenic little activity can be directly associated with major throughgoing faults seismicity is also generally absent in the upper 5 km the predominant style of faulting above 10 12 km is oblique slip with a large reverse component the spatial distribution of relocated hypocenters and first motion data suggests the presence of a system of left slip faults striking northeast this pattern of faulting in conjunction with an unusual set of normal and reverse focal mechanisms is interpreted as the clockwise rotation of a small set of crustal blocks subject to regional right lateral shear at depths greater than about 10 km seismicity defines a wedge shaped volume undergoing pervasive internal deformation on a combination of strike slip and low angle thrust faults velocity structures determined from earthquake arrival times suggest a low velocity zone at about 10 km below the san bernardino mountains but not below the san jacinto mountains this is nearly the same depth as the transition between the two layers of different kinematic behavior seen south of the mill creek mission creek branch of the san andreas fault and the maximum depth of seismicity seen north of that fault the low velocity zone and the transition between block rotations and the deeper deformation may thus correspond to a detachment under much of this region and would imply that the overthrust san bernardino mountains are allochthonous the present pattern of seismic deformation in shocks of small to moderate size may only characterize the interval between large earthquakes and may change systematically as the region prepares to accommodate large right lateral displacements

the denholm landslide saskatchewan canada an update the lower block of the denholm landslide has moved 370 m over alluvium deposited by the north saskatchewan spillway and river during the last 11 500 years at an average rate of 32 mm year these values must be considered minimal because erosion of the toe of the landslide is required for the formation of retrogressive landslides the shear strength for the bedrock clay shale of the lea park formation was back calculated to be assuming zero cohesion key words retrogressive landslide clay shale residual strength movement rates geological age inclinometer

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900

surface ruptures on cross faults in the 24 november 1987 superstition hills california earthquake sequence left lateral slip occurred on individual surface breaks along northeast trending faults associated with the 24 november 1987 earthquake sequence in the superstition hills imperial valley california this sequence included the m s 6 2 event on a left lateral northeast trending cross fault between the superstition hills fault shf and brawley seismic zone which was spatially associated with the left lateral surface breaks six distinct subparallel cross faults broke at the surface with rupture lengths ranging from about formula to 10 km and maximum displacements ranging from 30 to 130 mm about half a day after the m s 6 2 event an m s 6 6 earthquake nucleated near the intersection of the cross faults with the shf and rupture propagated southeast along the shf whereas right lateral slip on the shf occurred dominantly on a single trace in a narrow zone the cross fault surface slip was distributed over several stands across a 10 km wide zone also whereas afterslip accounted for a large proportion of total slip on the shf there is no evidence for afterslip on the cross faults we present documentation of these surface ruptures a simple mechanical model of faulting illustrates how the foreshock sequence may have triggered the main rupture displacement on other cross faults could trigger an event on the southern san andreas fault by a similar mechanism in the future