paleoseismology along the 1980 surface rupture of the irpinia fault implications for earthquake recurrence in the southern apennines italy the irpinia fault was the source of the ms 6 9 1980 irpinia earthquake and produced the first unequivocal historical surface faulting in italy trenching of the 1980 fault scarp at piano di pecore a flat intermontane basin about 5 km south of the 1980 instrumental epicenter provides the first data on earthquake recurrence intervals slip per event and slip rate on a major normal fault in the southern apennines fault zone the trenches exposed evidence of four pre 1980 paleoearthquakes that occurred during the past 8600 years a best estimate average recurrence interval is 2150 years although the time interval between individual events varies by as much as a factor of 2 each paleo earthquake is similar to the 1980 surface rupture in amount of slip and style of deformation which suggests that the 1980 event is characteristic for the irpinia fault slip per event values average 61 cm the net vertical displacement of 2 12 2 36 m since 8600 cal year b p observed in the trenches gives a vertical slip rate of 0 25 0 35 mm yr a dip slip rate of 0 29 0 40 mm yr and an extension rate of 0 14 0 20 mm yr although fault behavior data are only available for the irpinia fault they provide a starting point for evaluating earthquake recurrence and rates of deformation in southern apennines they suggest that 1 fault specific earthquake recurrence intervals based on the historical seismic record overestimates the occurrence of large magnitude m7 earthquakes and 2 the holocene rate of extension across the apennines is 1 mm yr the 1980 earthquake and the paleoseismologic observations show that repeated and localized surface faulting occurs in southern apennines and leaves subtle but distinct geomorphic evidence that can be detected with detailed and careful investigation

geoelectric investigations of a fault system in quaternary deposits geoelectric soundings were used to investigate the younger fault activity middle and early pleistocene of the southwestern fault margin area of the central graben and extension of the rhine graben in the southern netherlands and northern belgium some effects of this fault activity can still be observed in the present geomorphology and hydrography investigations have been concentrated on the uppermost 20 30 m consisting mainly of middle and early pleistocene fluviatile deposits marshy clays and loams are most conductive they alternate with large sand beds and gravelly gully infillings characterized by high specific resistivities problems in the interpretation of the geoelectric data caused by the variability of the deposits are partially solved by in situ resistivity measurements mini electric measurements in spite of the lithologic inhomogeneity a few marker horizons allow the geologic structure to be determined some new tectonic boundaries have been traced the movements along the faults during the quaternary are very small less than 10 m therefore the network of soundings has to be very dense and a very intensive analysis of the soundings is necessary the results also have a hydrogeologic significance this project illustrates the possibility of locating small tectonic structures in relatively inhomogeneous deposits by a detailed and carefully designed geoelectric survey

late quaternary earthquake related soft sediment deformation along the belgian portion of the feldbiss fault lower rhine graben system abstract trench investigations along the bree fault scarp in belgium in the framework of a first paleoseismological experience in the area of the lower rhine graben system have not only demonstrated the existence of seismogenic faults almost extending to the present ground surface but also exposed several types of soft sediment deformation affecting sandy sediments and soils of inferred late weichselian to holocene age the observed features include asymmetric folding small scale normal faulting possible sand intrusions and small water escape or load structures establishing a seismic origin for the individual features is not always possible based on their sedimentary characteristics only particularly due to the potential confusion with periglacial phenomena but their abundance the close association of different deformational styles and their vicinity to a known active fault all seem to be compatible with an earthquake induced scenario the features are to some extent comparable to those generated during the recent ms 5 3 roermond earthquake at the opposite side of the roer valley graben stratigraphical and mutual geometrical relationships suggest the occurrence of at least three distinct deformational events since probably 30 000 years and one event before that time since nothing is yet known about their regional distribution however estimating the associated paleomagnitudes from these soft sediment deformations is premature

investigation of the yellow river buried fault in the wuhai basin northwestern ordos block china using deep shallow seismic reflection and drilling techniques abstract studying the faults in wuhai basin which is located in the northwestern corner of the ordos block in china can not only guide earthquake safe construction in the region but also provide a greater understanding of the structure of the wuhai basin and the dynamic environment of northwestern ordos block in this study we effectively detected the yellow river buried fault yrf which we believe currently presents a risk to human life in the area first we laid out a deep seismic reflection profile dsrp in the north of the wuhai basin and found that the yrf is composed of two subparallel faults the east branch of the yellow river buried fault eyf and the west branch of the yellow river buried fault wyf which formed a y type graben in the section we then used 25 shallow seismic exploration profiles to find out how the faults are distributed finally we used drillings and quaternary dating methods to certify their existence and obtain their activity parameters we used the sequence stratigraphy method to compare sediment strata and identified paleo earthquake events by finding the unequal thickness layers utls on both sides of the fault the drillings revealed that four earthquakes occurred on the yrf around 25 6 0 11 ka bp 39 5 0 45 41 7 0 57 ka bp 58 25 7 13 ka bp and 111 1 21 ka bp since the last activity on the yrf occurred much longer ago than its estimated recurrence cycle we believe that the fault yrf currently presents a dangerous risk our study confirms that the yrf is a normal fault graben and that the wuhai bain is an extensional basin formed by the relative movement of the tibetan plateau the alashan block and the ordos block

active faulting and paleoseismology along the bree fault lower rhine graben belgium paleoseismic analysis of the 10 km long bree fault scarp in the lower rhine graben yields numerous lines of evidence of earthquake activity in the holocene and late pleistocene this active normal fault a part of the feldbiss fault system dips 70 ne and is expressed at the surface by a prominent nw se trending 7 to 20 m high scarp formed since the deposition of the maas river main terrace 700 kyr b p trenches and geophysical prospecting show that the fault which is known to have 100 m of vertical offset since the late pliocene breaks late pleistocene and holocene deposits ground penetrating radar seismic refraction and electric tomography suggest that at shallow depth the amount of displacement is larger than the youngest vertical offset visible in the trenches and corresponds to cumulative fault displacements the analysis of 36 leveling profiles across the scarp indicates that its height can be classified into three groups likely corresponding to different events a morphologic dating gives approximate ages of 2 1 5 kyr b p 14 5 kyr b p and 41 6 kyr b p for the past three surface faulting earthquakes analysis of faulted stratigraphy and earthquake induced deformation structures exposed in trenches suggests the occurrence of three large earthquakes during the past 45 l03 years and yields 0 07 mm yr of relative vertical deformation rate the most recent seismic event occurred between a d 610 and 890 the first identification of an active fault with surface ruptures in the lower rhine graben area emphasizes that large earthquake sources exist within intraplate europe and that at least some of these events are preserved in the geologic record

late quaternary evolution of the feldbiss fault roer valley rift system the netherlands based on trenching and its potential relation to glacial unloading abstract the most important tectonic structure in the southern part of the netherlands is the roer valley rift system rvrs the main border fault zones of the rvrs the peel boundary and the feldbiss fault zones have been active during the quaternary and are still active today as indicated by the occurrence of earthquakes in this paper we present the results of a trench across the feldbiss fault part of the feldbiss fault zone this trench provided no evidence for earthquakes along this segment of the fault zone fluidization structures were not encountered a sudden increase in the average fault displacement rate was inferred for the period around 15 ka b p in a trench nearby across the geleen fault of the same fault zone the limited age control cannot exclude that such an acceleration also occurred at the feldbiss fault during the second half of the 1990 s several paleoseismological trenching studies have been carried out in the rvrs the compilation of the results of these studies reveals that the main border faults possibly experienced an increase in fault activity around 10 15 ka b p the timing of this increased activity and results from glacial rebound modelling indicate that glacial unloading of the crust can have triggered this increase in fault activity

geological and geophysical evidence for large palaeo earthquakes with surface faulting in the roer graben northwest europe from the analysis of geological geodetic and geophysical data we provide clear evidence of seismogenic faults capable of producing large earthquakes in intraplate europe previous studies paulissen vandenberghe gullentops 1985 van den berg et al 1994 geluk et al 1994 have yielded some constraints on the rate of crustal deformation along the roer valley a graben structure crossing the netherlands belgium and germany and have allowed us to address the fundamental questions can intraplate earthquakes rupture the surface in this part of stable continental europe and if so what is their return period detailed palaeoseismic investigations have been carried out in belgium along a 10 km long fault scarp which is the morphological expression of the feldbiss fault the southwestern border fault of the roer graben camelbeeck meghraoui 1996 the scarp is multiple and the frontal fault scarp offsets young deposits and alluvial terraces field investigations using geological and geomorphological methodologies combined with geophysical prospecting provide evidence of holocene seismic surface faulting from 14c dating it is suggested that the last earthquake along the fault scarp occurred between 610 ad and 890 ad levelling profiles across the scarp suggest that it produced a vertical coseismic displacement of 0 5 1 m along the scarp if we suppose that the last surface faulting earthquake ruptured the whole seismogenic layer 17 km thickness over a minimum length 10 km corresponding to the length of the bree scarp with an average slip of 0 6 m its seismic moment was at least 3 1 1018 n m mw 6 3 for an average rigidity 3 1010 pa by estimating the offset of the main terrace of the maas river by slippage along the feldbiss fault we calculate the average late pleistocene vertical deformation rate as 0 08 0 04 mm yr 1 palaeoseismic information combining the trench and geomorphic observations suggests the occurrence of two surface faulting earthquakes during the last 20 kyr a third dates before 28 35 kyr bp then if the time distribution of earthquakes is uniform a return period of 12 5 ka and a vertical deformation rate of 0 06 0 04 mm yr 1 are inferred

active normal faulting in the upper rhine graben and paleoseismic identification of the 1356 basel earthquake we have identified an active normal fault in the epicentral area of the basel switzerland earthquake of 18 october 1356 the largest historical seismic event in central europe the event of 1356 and two prehistoric events have been characterized on the fault with geomorphological analysis geophysical prospecting and trenching carbon 14 dating indicates that the youngest event occurred in the interval 610 to 1475 a d and may correspond to the 1356 basel earthquake the occurrence of the three earthquakes induced a total of 1 8 meters of vertical displacement in the past 8500 years for a mean uplift rate of 0 21 millimeters per year these successive ruptures on the normal fault indicate the potential for strong ground movements in the basel region and should be taken into account to refine the seismic hazard estimates along the rhine graben

imaging the structural style of an active normal fault through multidisciplinary geophysical investigation a case study from the mw 6 1 2009 l aquila earthquake region central italy firb abruzzo high resolution analyses for assessing the seismic hazard and risk of the areas affected by the 2009 april 6 earthquake no rbap10zc8k 005

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

intraplate deformation in western europe deduced from an analysis of the international terrestrial reference frame 1997 itrf97 velocity field although tectonic deformation in western europe is essentially concentrated in the appenines and alpine alps pyrenees mountain ranges several large historical and instrumentally recorded earthquakes m 6 are known in the supposedly stable part of europe because of its accuracy and internal consistency at a global scale the international terrestrial reference frame 1997 itrf97 velocity field allows testing of intraplate rigidity in western europe at a millimeter per year level using the full statistical information available on the itrf97 velocities we identify a subset of sites located in central europe that satisfies a rigid cap rotation with residual velocities 1 mm yr and therefore provide a stable europe reference frame serf in this reference frame we find residual velocities at european itrf sites that are consistent with known active tectonic features we identify a northward motion at sites located in italy with internal deformation of the adriatic block rather than rigid plate motion and a westward motion of the westernmost part of europe of the order of 1 2 mm yr relative to central europe the relative motion of the adriatic block and western europe agrees with the current extension known in the tyrrhenian sea and the apennines in central europe we find active deformation 1 mm yr in the eastern alps and western carpathians in the alpine range our results indicate e w extension across the western alps and n s compression across the central and eastern alps in agreement with the strain regime deduced from seismotectonic observations in belgium and the netherlands we find residual velocities of 1 1 5 mm yr to the northwest at all the sites most likely accommodated along the upper and lower rhine graben structures an important outcome of this study is the identification of internal deformation of the order of 1 2 mm yr in an area usually interpreted as stable europe this result should be further checked as new denser and more accurate space geodetic data sets with longer observation time spans become available for europe

episodic activity of a dormant fault in tectonically stable europe the rauw fault ne belgium abstract our knowledge about large earthquakes in stable continental regions comes from studies of faults that generated historical surface rupturing earthquakes or were identified by their recent imprint in the morphology here we evaluate the co seismic character and movement history of the rauw fault in belgium which lacks geomorphological expression and historical present seismicity this 55 km long normal fault with known neogene and possibly early pleistocene activity is the largest offset fault west of the active roer valley graben its trace was identified in the shallow subsurface based on high resolution geophysics all the layers within the late pliocene mol formation 3 6 to 2 59 ma are displaced 7 m vertically without growth faulting but deeper deposits show increasing offset a paleoseismic trench study revealed cryoturbated but unfaulted late glacial coversands overlying faulted layers of mol formation in between those deposits the fault tip was eroded along with evidence for individual displacement events fragmented clay gouge observed in a micromorphology sample of the main fault evidences co seismic faulting as opposed to fault creep based on optical and electron spin resonance dating and trench stratigraphy the 7 m combined displacement is bracketed to have occurred between 2 59 ma and 45 ka the regional presence of the sterksel formation alluvial terrace deposits limited to the hanging wall of the rauw fault indicates a deflection of the meuse rhine confluence 1 0 to 0 5 ma by the fault s activity suggesting that most of the offset occurred prior to at this time interval in the trench sterksel formation is eroded but reworked gravel testifies for its former presence hence the rauw fault appears as typical of plate interior context with an episodic seismic activity concentrated between 1 0 and 0 5 ma or at least between 2 59 ma to 45 ka possibly related to activity variations in the adjacent continuously active roer valley graben

role of transverse structures in paleoseismicity and drainage rearrangement in rift systems the case of the valdecebro fault zone teruel graben eastern spain the e w trending nearly pure extensional valdecebro fault zone is a transverse structure at the central sector of the n s teruel graben it was activated by the late ruscinian early pliocene ca 3 7 ma giving rise to structural rearrangement of the graben margin until the late pleistocene it has accommodated a net slip ca 205 m with slip rate of 0 055 mm a paleoseismicity has been analysed in a 29 m long 5 m deep trench excavated through a fault branch that offsets a pleistocene pediment surface the paleoseismic succession includes a minimum of 6 7 events occurred since ca 142 ka bp although a model with 12 events could be more realistic the following paleoseismic parameters have been inferred assuming a minimum of 6 and a maximum of 12 events average coseismic slip 58 117 cm recurrence period 8 4 28 4 ka potential moment magnitude mw 5 8 5 9 the recorded displacement since ca 142 ka bp totalizes 7 0 m with slip rate of 0 05 0 07 mm a slip on the transverse valdecebro fault zone has critically contributed to bulk deformation under a prevailing multidirectional extensional regime drainage patterns have been rearranged recurrently switching between westward and southward directions as a consequence of diverse slip episodes at the valdecebro fault zone e w and the neighbouring la hita n s and concud nw se faults the ultimate westward drainage of the valdecebro depression incised and dismantled a southward sloping pleistocene pediment sourced at the valdecebro mountain front representing a capture by the alfambra river occurred between 124 and 22 ka bp

the roer valley graben earthquake of 13 april 1992 and its seismotectonic setting a moderately sized pure normal dip slip earthquake occurred in the roer valley graben rvg near roermond the netherlands on 13 april 1992 at 1h 20m utc this contribution presents an overview of the locations fault plane solutions and magnitudes obtained for the mainshock and the aftershocks by the different scientific groups involved in their analysis the observed maximum intensity of vii is compared with that of other earthquakes in the region to illustrate the relatively low level of damage caused by the mainshock using sh and lg waves recorded at seven local and regional broadband stations we determine a seismic moment of 1 4 1017 nm a static stress drop of 9 7 mpa and an average displacement of 33 cm over a rupture surface of approximately 11 km2 the seismotectonics of the region extending from the rvg to the city of liege including the western part of the rhenish massif wrm and the eastern part of the brabant massif ebm is analysed based on the roermond earthquake studies and data collected since 1985 by the belgian seismic network the geographical distribution of focal mechanism reveals four different seismotectonic regimes in this area from stress tensor inversion we find that s3 coincides with the minimum horizontal stress component in the rvg the wrm and possibly in the ebm while in the liege region s3 is approximately vertical the minimum horizontal stress component shows a 30 rotation to the north in the wrm and the liege region and possibly 50 in the ebm when compared with the minimum horizontal stress component in the rvg

thin section analysis as a tool to aid identification of palaeoearthquakes on the slow active geleen fault roer valley graben abstract we analyzed thin sections from two palaeoseismic trenches across the low slip rate geleen fault in the belgian maas river valley to help identifying the most recent large palaeoearthquake on this fault segment in the first trench we sampled silty sediment below and above a prehistoric stone pavement that was supposedly at or near the surface at the time of the event and subsequently thrown down the samples below show a well developed in situ argillic bt soil horizon in parent sediment containing remnants of stratification whereas the sediment above is a structureless colluvium reworked at least partly from bt horizon material below the stone pavement we also found evidence of contorted stratification which is in agreement with macroscopic observations of both the sediment and the stone pavement itself and which is attributed to co seismic soft sediment deformation in the second trench we sampled a sequence of vaguely discernible soil horizons in the hanging wall interpreted as a buried soil profile bt e and possibly a horizons overlain by a featureless deposit thin section analysis supports the colluvial nature of the latter and also provides evidence that both the base of this layer and the top of the poorly developed a horizon below have occupied a shallow position in a soil profile a sample from the same depth in the footwall is composed of very different material instead of colluvium we find patches of bt soil most likely representing the same pedogenic level as the in situ bt horizon at larger depth in the hanging wall but displaced and subsequently degraded furthermore thin sections confirm that vertical structures cutting this bt horizon are sand dykes these dykes could be traced macroscopically upward to the base of the colluvium in both trenches we have thus identified a stratigraphic boundary in the hanging wall close to the surface separating an in situ soil below from colluvium above we interpret this limit and the overlying colluvium as the event horizon and the colluvial wedge respectively of a surface rupturing palaeoearthquake in addition in both cases we found evidence of soft sediment deformation related to liquefaction contemporaneous with the event within the stratigraphic resolution

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

introduction to special section paleoseismology a proverb of confucius states study the past if you would divine the future if we could learn about the past history of earthquakes on a specific fault then we could serve society well by better forecasting the future earthquake behavior of that fault for most of the world the period of historical records is short about 200 years in california and less than that in new zealand oregon and other parts of the world and even where the historical record is thousands of years long such as in north central china or the eastern mediterranean region it is commonly difficult to correlate a major historical earthquake with a specific active fault even if this correlation could be made without ambiguity the recurrence intervals for many faults are longer than even a historical record of several thousand years for these reasons the history of large earthquakes on faults must for the most part be learned from the geological record

paleoseismology in venezuela objectives methods applications limitations and perspectives abstract the privileged location of venezuela along an active interplate deformation belt despite of being a so called developing country has led to a long paleoseismic tradition as attested by 45 trench assessments since 1968 since then a first 2 trench study was carried out by the american woodward clyde company across the oca fault at sinamaica since 1980 all further paleoseismic studies have been performed by funvisis and the uribante caparo hydroelectric project southern merida andes became their first assessment where 22 huge trenches were bulldozer dug except for these compania anonima de administracion y fomento electrico cadafe financed trenches and two others all other assessments were for petroleos de venezuela s a pdvsa in this paper geographic and geologic factors as well as logistic limitations conditioning success in paleoseismic studies by trenching shall be discussed based on the venezuelan experience developed over the years the scientific contribution of this approach refer to confirmation of holocene fault activity slip per event and average slip rate of a given fault or segment seismic potential repeat of maximum credible earthquakes of known faults fault segmentation fault interaction as consequence of stress loading by stick slip on contiguous faults time space distribution of seismic activity along a given tectonic feature seismotectonic association of historical earthquakes and landscape evolution on the short term and its implications on the long term evolution poorly discussed since this is really part of the field of neotectonics in recent years since 1999 a new approach has been introduced in venezuela consisting in complementing the seismic history derived from trenching studies with the evaluation of seismically induced perturbations in the continuous quaternary sedimentary record of either active or fossil lakes the future of this discipline in venezuela heads to more trenching and lake coring in order to gather more data on the previously mentioned aspects other paleoseismic approaches have been developed very little in venezuela since either climate or the geodynamic setting do not favor their application

the 1993 killari latur central india earthquake an example of fault reactivation in the precambrian crust the september 30 1993 killari event in central india is a rare incidence of an earthquake occurring within a precambrian craton a pertinent question concerning seismicity in such regions is whether a preexisting fault exists and if so what is its reactivation interval ourstudiesinthe1993rupturezonesuggestthatthekillariearthquakeoccurred in a region of previous seismic activity older thrust sheets and fault gouge presumably formedduringpreviousepisodes wereexposedinadeeptrench thestudiesalsoindicated an obsequent fault line scarp aligned with the current rupture zone the morphological features in the area suggest mass removal of the upper part of the hanging wall on the southwestern side of the rupture existence of a prominent northwest striking structure passing through the epicentral zone is revealed in the digital landsat data these data together with the spatial trend of historic earthquakes along the northwest striking structure reinforce the argument that the earthquake at killari is related to the reactivation of a preexisting fault

recent height changes in the central segment of the rhinegraben and its adjacent shoulders abstract zippelt k and malzer h 1981 recent height changes in the central segment of the rhinegraben and its adjacent shoulders in j h illies editor mechanism of graben formation tectonophysics 73 119 123 the height changes in the central segment of the rhinegraben its shoulders included are computed from first order levelling data the network for investigation with regard to recent vertical crustal movements extends the graben segment between karlsruhe and worms and overlaps the shoulders of the pfalzer wald in the west and the kraichgau in the east the investigated area is characterized by negative height changes subsidence in its eastern shoulder and by positive values uplift in its western one in the graben positive height changes were found in its western part but in the eastern part negative values dominate over thick unconsolidated pleistocene sediments tectonically controlled ground motions cannot be separated from atectonic processes like subsidence as caused by changing groundwater levels

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

active faulting in the western pyrenees france paleoseismic evidence for late holocene ruptures abstract we have identified a 50 km long active fault scarp called herewith the lourdes fault between the city of lourdes and arette village in the french pyrenees this region was affected by large and moderate earthquakes in 1660 io viii ix msk 64 in 1750 io viii msk 64 and in 1967 md 5 3 io viii msk 64 most earthquakes in this area are shallow and the few available focal mechanism solutions do not indicate a consistent pattern of active deformation field investigations in active tectonics indicate an east west trending and up to 50 m high fault scarp in average made of 3 contiguous linear fault sub segments to the north the fault controls quaternary basins and shows uplifted and tilted alluvial terraces deviated and abandoned stream channels of the southern block are likely due to the successive uplift of the northern block of the fault paleoseismic investigations coupled with geomorphic studies georadar prospecting and trenching along the fault scarp illustrate the cumulative fault movements during the late holocene trenches exhibit shear contacts with flexural slip faulting and thrust ruptures showing deformed alluvial units in buried channels 14c dating of alluvial and colluvial units indicates a consistent age bracket from two different trenches and shows that the most recent fault movements occurred between 4221 bc and 2918 bc fault parameters and paleoseismic results imply that the lourdes fault and related sub segments may produce a mw 6 5 to 7 1 earthquake fault parameters imply that the lourdes fault segment corresponds to a major seismic source in the western pyrenees that may generate earthquakes possibly larger than the 1660 historical event

using the aster global dem to derive empirical relationships among triangular facet slope facet height and slip rates along active normal faults abstract the advent of global dems provided a uniform elevation dataset for studying geomorphic parameters in a variety of settings in this paper aster dem data 30 m pixel size are used to derive empirical relationships between triangular facet attributes and slip rates along active normal faults we sampled 232 triangular facets along 10 normal faults in greece and bulgaria that slip with rates from 0 1 mm yr up to 1 3 mm yr the studied normal faults accumulate quaternary tectonic strain in well known extensional provinces such as central greece crete and sw bulgaria the normal fault footwalls analyzed herein have been developed under similar long term climatic conditions it is suggested that two key geometrical features of the youngest generation of triangular facets slope angle and height can provide useful metrics to assess rates of deformation when seismological and geodetic data are lacking or not found in sufficient quantity to make reasonable assessments our derived empirical relation between slip rate and facet slope angle is y 0 057 x 1 where y is the fault slip rate mm yr and x is the facet slope angle degrees with an r 2 0 728 it is envisaged that our analysis may be helpful in assessing seismic hazard along normal faults with similar facet characteristics in other extensional settings

seismic hazard assessment for a characteristic earthquake scenario an integrated probabilistic deterministic method probabilistic seismic hazard analysis psha is classically performed through the cornell approach by using a uniform earthquake distribution over the source area and a given magnitude range this study aims at extending the psha approach to the case of a characteristic earthquake scenario associated with an active fault the approach integrates psha with a high frequency deterministic technique for the prediction of peak and spectral ground motion parameters in a characteristic earthquake the method is based on the site dependent evaluation of the probability of exceedance for the chosen strong motion parameter the latter is obtained from the statistical analysis of the synthetic waveform database produced for a large number of possible rupture histories occurring on the characteristic earthquake fault the method has been applied to a hazard evaluation in the umbria region where the threat is represented by a fault having the same geometry and mechanism as the 26 september 1997 colfiorito earthquake central italy moment magnitude m w 6

neotectonics and intraplate continental topography of the northern alpine foreland research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues the accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years which on geological time scales is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity more reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on going intraplate deformation the alpine orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that deformation of the northern alpine foreland is still on going and will continue in the future this has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area we examine relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland and their implications for tectonically induced topography for the environmental tectonics project entec the upper and lower rhine graben urg and lrg and the vienna basin vb were selected as natural laboratories the vienna basin developed during the middle miocene as a sinistral pull apart structure on top of the east alpine nappe stack whereas the upper and lower rhine grabens are typical intracontinental rifts the upper rhine graben opened during its late eocene and oligocene initial rifting phase by nearly orthogonal crustal extension whereas its neogene evolution was controlled by oblique extension seismic tomography suggests that during extension the mantle lithosphere was partially decoupled from the upper crust at the level of the lower crust however whole lithospheric folding controlled the mid miocene to pliocene uplift of the vosges black forest arch whereas thermal thinning of the mantle lithosphere above a mantle plume contributed substantially to the past and present uplift of the rhenish massif by contrast oblique crustal extension controlling the late oligocene initial subsidence stage of the lower rhine graben gave way to orthogonal extension at the transition to the neogene the entec project integrated geological geophysical geomorphologic geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations the response of europe s intraplate lithosphere to late neogene compressional stresses depends largely on its thermo mechanical structure which in turn controls vertical motions topography evolution and related surface processes

complexity of intracontinental seismic faultings the gazli uzbekistan sequence reconnaissance of scismic activity in the area of the three ms 7 gazli earthquakes 8 april and 17 may 1976 and 19 march 1984 was carried out during may through june 1991 as part of a collaborative program between the university of grenoble and the academy of sciences of the uzbek republic more than 300 events 0 3 ml 4 0 recorded by at least six stations were located using an array of 16 seismic stations we study this 70 50 km area using 1 seismic activity recorded for the 15 yr following the 1976 ms 7 sequence and 7 yr after the last mainshock 2 the rupture planes of the three mainshocks deduced from geodetic data 3 fault patterns deduced from satellite images and 4 location by the uzbek network of the main aftershock activity and the available focal mechanisms the seismicity recorded in 1991 is located mainly at shallow depth but both 1991 hypocenter locations and geodetic fault planes appear to be bounded by a critical 20 to 25 km depth i e the thickness we propose for the local brittle crust most of the earthquakes located by the 1991 dense seismic survey were located southward of the 1984 geodetically determined rupture plane and this seismic activity does not exhibit any link with the 1976 mainshocks since the onset of the sequence on april 1976 the seismicity has unilaterally migrated 90 km along a n240 e direction there are no simple mechanisms to explain this overall migration even taking into account the potential role of the exploitation of a local gas field the direction defined by the epicenters of the largest events of the 1976 to 1993 period is correlated with the direction of one of the main structural populations we propose that this seismic fault population represents a structurally immature fault zone that could explain both the occurrence of three major earthquakes and the variety of seismic fault plane orientations within the immature fault network within such an immature fault network energy partitioning for three m 7 earthquakes appears as a more efficient system than the energy release by a single m 7 3 mainshock

application of ground penetrating radar to investigation of near surface fault properties in the san francisco bay region abstract in many geologic environments ground penetrating radar gpr provides high resolution images of near surface earth structure gpr data collection is nondestructive and very economical the scale of features detected by gpr lies between those imaged by high resolution seismic reflection surveys and those exposed in trenches and is therefore potentially complementary to traditional techniques for fault location and mapping sixty two gpr profiles were collected at 12 sites in the san francisco bay region results show that gpr data correlate with large scale features in existing trench observations can be used to locate faults where they are buried or where their positions are not well known and can identify previously unknown fault segments the best data acquired were on a profile across the san andreas fault traversing pleistocene terrace deposits south of olema in marin county this profile shows a complicated multi branched fault system from the ground surface down to about 40 m the maximum depth for which data were recorded

localization and characterization of an active fault in an urbanized area in central guatemala by means of geoelectrical imaging article i nfo article history the polochic and motagua faults define the active plate boundary between the north american and caribbean plates in central guatemala a splay of the polochic fault traverses the rapidly growing city of san miguel uspantan that is periodically affected by destructive earthquakes this fault splay was located using a 2d electrical resistivity tomography ert survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built ert images show the fault as a 50 m wide near vertical low resistivity anomaly bounded within a few meters by high resistivity anomalies forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location geometry and internal structure of the fault zone as well as the affected lithologies our results indicate that the city is constructed on a 20 m thick surficial layer consisting of poorly consolidated highly porous water logged pumice this soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking the electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might at least in part be fed by water rising along the fault therefore the potential threat posed by this fault splay may not be limited to its seismic activity per se but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments the results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of san miguel uspantan and illustrate the potential of ert surveying for paleoseismic studies

late quaternary changes in amazonian ecosystems and their implications for global carbon cycling abstract the current role of amazonia in the terrestrial carbon budget is the focus of intensive scientific interest in large part due to its potential to accelerate global warming however its role in mediating co2 changes over millennial time scales since the last glacial maximum lgm has generally been overlooked and is the subject of speculation recent advances in our understanding of the late quaternary history of amazonian ecosystems offers an opportunity to make more informed inferences about late quaternary changes in the magnitude of amazon carbon storage than has hitherto been possible therefore in this paper we reconstruct changes in the magnitude of amazon carbon storage over the last 21 000 years since the lgm by reference to recently published palaeohydrological and palaeoecological data and compare these data with results from simulations using a process based terrestrial ecosystem model for the mid holocene and the lgm building on these results further we interpret changes in tropical forest biomass in the context of late quaternary polar ice core records of atmospheric methane and carbon dioxide concentrations palaeo data and model simulations show that amazonia was predominantly forested at the lgm although there is evidence for savanna expansion near the margins of the basin and southern amazonia may have been covered by deciduous semi deciduous dry forests rather than evergreen rain forests we estimate amazon c storage at the lgm to be only 135 gt c 50 smaller than today but find that its proportion of the entire terrestrial carbon store was almost twice that of today the model shows that between the lgm and the mid holocene there is a significant increase in evergreen broad leaf forests at the expense of deciduous forests and a 67 increase in total amazon c storage attributable to rising temperatures and atmospheric co2 levels although our results indicate that the amazon basin was dominated by rain forests throughout the holocene rain forest cover expanded in the late holocene at the expense of savannas and total amazon carbon storage is simulated to have risen by 22 between the mid holocene 225 gt c and the present day pre industrial 225 gt c comparison of these amazon carbon fluxes with palaeo data from other parts of the world suggests that contrary to previous hypotheses the terrestrial biosphere acted as a net carbon sink throughout the holocene and that the observed co2 rise from 260 to 285 ppmv between 8 and 1 ka bp revealed by the antarctic taylor dome ice core record may have been driven by release of carbon from the oceans rather than land

climatic warming glacier recession and runoff from alpine basins after the little ice age maximum records of discharge of rivers draining alpine basins with between 0 and 70 ice cover in the upper aare and rhone catchments switzerland for the period 1894 2006 have been examined together with climatic data for 1866 2006 with a view to assessing the effects on runoff from glacierized basins of climatic warming coupled with glacier recession following the little ice age maximum annual runoff from ice free basins reflects precipitation variations rising from minima between 1880 and 1910 to maxima between the late 1960s and early 1980s the more highly glacierized the basin the more runoff mimicked mean may september air temperature during two periods of warming runoff increased gradually from the 1900s rapidly in the 1940s before decreasing to the late 1970s rising runoff levels during the second warming period failed to exceed those attained during the first despite higher summer temperatures although temperatures continued to rise discharge from glacierized basins declined after reaching maxima in the late 1980s to early 1990s in the first warming period rising specific melt rates augmented by increasing precipitation opposed the impact of declining glacier area on runoff although melt continued to increase in the second period enhanced melting even in the exceptionally warm summer of 2003 appears to have been insufficient to offset reducing glacier surface area exposed to melt low or reducing levels of precipitation and increasing evaporation thus runoff from glacierized basins peaked in the late 1940s to early 1950s

earthquake induced flooding and paleoseismicity of the el asnam algeria fault related fold late quaternary activity of the el asnam thrust fault responsible for the october 10 1980 ms 7 3 earthquake and 36 km coseismic faulting is explored through diverse paleoseismological field methods we trenched through the main and secondary 1980 coseismic scarps made an analysis of earthquake induced flood deposits conducted a geomorphic study of leveling profiles and offset geological units across thrust and normal scarps and considered the geomorphology of the active fold twenty five radiocarbon ages from colluvial and alluvial deposits along with conventional fossils and artefacts dating of geological units show the timing of successive net vertical displacements on the thrust related fold and bending moment faults previous work showed that eight pre 1980 earthquakes occurred in clusters during the late holocene cumulative net vertical slip that amounts to 3 times the 1980 displacement is observed on multiple thrust fault scarps and offsets of geological units on bending moment faults maximum cumulative vertical displacements which are visible in different zones along the fault segments can reach 10 to 25 times the 1980 coseismic displacements the late quaternary uplift rate on the el asnam fault is 0 6 mm yr and taking into account slip variation along the fault this rate may range between 0 25 1 6 mm yr from which we obtain a shortening rate of 0 17 1 2 mm yr because the tell atlas mountains exhibit comparable seismogenic fault related folds with parallel and sequential structures of active faults a total average shortening rate of 2 05 mm yr during the late quaternary represents part of the convergence accommodated along the africa eurasia plate boundary

the 1989 ms 6 3 ungava quebec earthquake a complex intraplate event on 25 december 1989 the largest earthquake ms 6 3 in northern quebec in at least 60 yr occurred in the ungava peninsula this earthquake was unique in that it marked the first time surface faulting could be confirmed for a historical eastern north american earthquake field observations indicated a combination of thrust and strike slip motion waveforms modeled in this study show that the earthquake consisted of two subevents a thrust subevent on a ne sw striking plane followed by a larger strike slip subevent on a nne ssw striking plane the surface waves give an equivalent double couple moment of 1 3 1025 dyne cm the sum of the subevent moments is greater than the simple source moment by almost a factor of 2 both subevents occurred at a depth of 3 km they were separated by 0 9 sec in time with the second subevent occurring 5 2 km southwest of the first the source parameters determined by modeling and those inferred from the ground observations generally agree but there are some differences with respect to the subevent offset these may be reconciled if the strike slip motion was distributed among the several small faults at the southwestern end of the rupture or if the complete surface rupture was not found the stress orientation nw compression inferred from the fault plane solution is consistent with the focal mechanisms of many other recent northeastern canadian events the ungava earthquake and many intraplate events from several continents share a number of characteristics including shallow hypocenters source complexity and occurrence on faults that showed no evidence for previous ruptures

integrated study on the topographic and shallow subsurface expression of the grote brogel fault at the boundary of the roer valley graben belgium abstract the grote brogel fault gbf is a major wnw ese striking normal fault in belgium that diverges westward from the nw se striking western border fault system of the roer valley graben the gbf delimits the topographically higher campine block from the subsiding roer valley graben and is expressed in the digital terrain model dtm by relief gradients or scarps by integrating dtm electrical resistivity tomography ert cone penetration test cpt and borehole data we studied the quaternary activity of the gbf and its effects on local hydrogeology in the shallow subsurface

relationship of late quaternary fault scarps to subjacent faults eastern great basin utah high resolution seismic reflection profiles in the sevier desert basin in western utah help clarify the relationship between some late quaternary fault scarps and subjacent faults a profile crossing the clear lake fault confirms that holocene displacement has occurred on a high angle normal fault that is directly connected to the sevier desert detachment if detachment faults can act as seismogenic source zones then the young movement on the normal fault suggests that the sevier desert detachment may be unstable and perhaps the source of future earthquakes a swarm of late quaternary scarps near the drum mountains overlies a network of steep faults in competent rock that have had recurrent movement many subsurface faults are not associated with scarps suggesting that selected faults ruptured during the last episode of surface faulting

scarp degraded by linear diffusion inverse solution for age under the assumption that landforms unaffected by drainage channels are degraded according to the linear diffusion equation a procedure is developed to invert a scarp profile to find its diffusion age diffusion age having dimension length 2 is the product of diffusivity times chronological age the second moment of scarp slope grows linearly with age this fact together with an assumption about initial scarp shape allows the inverse determination of diffusion age age found assuming a vertical initial scarp is termed apparent age any nonvertical initial scarp profile has a nonzero initial apparent age true diffusion age differs from apparent age by a fraction of scarp offset squared the inverse procedure applied to synthetic data yields the following rules of thumb evidence of initial scarp shape has been lost when apparent age reaches twice its initial value if a scarp is formed by two events the inversion gives their offset weighted mean age with an error that is a fraction of offset squared a scarp that appears to have been formed by one event may have been formed by two with an interval between them as large as apparent age after scarps of two fault traces have diffused to appear as one the error in inferred age may be as large as half the apparent age variation of apparent age along strike would indicate multiple fault traces the simplicity of scarp profile measurement and this inversion makes profile analysis attractive if linearity of the flow law time for a free face to be reduced to the angle of repose and variation of diffusivity with climate and material could be established profile analysis would become a reliable dating technique

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

slip rate and mode of the feldbiss normal fault roer valley graben after removal of groundwater effects abstract the feldbiss fault is the main active fault bounding to the southwest the roer valley graben of nw europe in order to investigate the reasons of the discrepancy between its short and long term slip rate estimates we have repeatedly surveyed a 2 3 km long line by levelling at sittard the netherlands from april 2001 to december 2004 simultaneously three superposed aquifers were monitored on both sides of the fault the across fault differential groundwater variations are shown to be responsible for a seasonal 0 87 mm m vertical motion of the fault mainly through the effect of pore pressure changes in confined aquifers after removal of this effect i get a residual trend of 0 60 0 11 mm yr for the relative motion of the hangingwall this trend was disturbed in the summer of 2002 by transient millimetre level up and down motions temporally associated with the small eschweiler earthquake that occurred on july 22 2002 on the feldbiss fault at a distance of 35 km from sittard i explain this as a creep event triggered by the passage of trapped seismic waves the subsisting discrepancy between the long term slip rate of 0 06 mm yr and short term rates of 1 5 mm yr from 1962 to 2001 and 0 6 mm yr from 2001 to 2004 is tentatively interpreted as resulting from the current occurrence of a decade long episode of aseismic slip involving a large part of the fault plane occasionally associated with minor seismicity this aseismic slip event could betray a thickening of the transitional region located below the upper crustal zone of stable sliding it causes a total fault slip of 5 10 cm in a few tens of years releasing smoothly all or a great part of the strain accumulated during the previous 1 2 ky of fault quiescence

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

ground penetrating radar investigation of active faults along the dead sea transform and implications for seismic hazards within the city of aqaba jordan abstract ground penetrating radar gpr was used in an effort to locate a major active fault that traverses aqaba city jordan measurements over an exposed trenched cross fault outside of the city identify a radar signature consisting of linear events and horizontal offset flexured reflectors both showing a geometric correlation with two known faults at a control site the asymmetric linear events are consistent with dipping planar reflectors matching the known direction of dip of the faults however other observations regarding this radar signature render the mechanism generating these events more complex and uncertain gpr measurements in aqaba city were limited to vacant lots seven gpr profiles were conducted approximately perpendicular to the assumed strike of the fault zone based on regional geological evidence a radar response very similar to that obtained over the cross fault was observed on five of the profiles in aqaba city although the response is weaker than that obtained at the control site the positions of the identified responses form a near straight line with a strike of 45 although subsurface verification of the fault by trenching within the city is needed the geophysical evidence for fault zone location is strong the location of the interpreted fault zone relative to emergency services military bases commercial properties and residential areas is defined to within a few meters this study has significant implications for seismic hazard analysis in this tectonically active and heavily populated region

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected