foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

activity of the offshore newport inglewood rose canyon fault zone coastal southern california from relocated microseismicity an offshore zone of faulting approximately 10 km from the southern california coast connects the seismically active strike slip newport inglewood fault zone in the los angeles metropolitan region with the active rose canyon fault zone in the san diego area relatively little seismicity has been recorded along the offshore newport inglewood rose canyon fault zone although it has long been suspected of being seismogenic active low angle thrust faults and quaternary folds have been imaged by seismic reflection profiling along the offshore fault zone raising the question of whether a through going active strike slip fault zone exists we applied a waveform cross correlation algorithm to identify clusters of microseismicity consisting of similar events analysis of two clusters along the offshore fault zone shows that they are associated with nearly vertical north northwest striking faults consistent with an offshore extension of the newport inglewood and rose canyon strike slip fault zones p wave polarities from a 1981 event cluster are consistent with a right lateral strike slip focal mechanism solution manuscript received 23 july 2003

strong shaking in los angeles expected from southern san andreas earthquake 1 the southernmost san andreas fault has a high probability of rupturing in a large greater than magnitude 7 5 earthquake sometime during the next few decades new simulations show that the chain of sedimentary basins between san bernardino and downtown los angeles form an effective waveguide that channels love waves along the southern edge of the san bernardino and san gabriel mountains earthquake scenarios with northward rupture in which the guided wave is efficiently excited produce unusually high long period ground motions over much of the greater los angeles region including intense localized amplitude modulations arising from variations in waveguide cross section

late quaternary evolution of the la cantera fault system central precordillera argentina a morphotectonic and paleoseismic analysis abstract the la cantera fault system lcfs is the most active quaternary structure in the central precordillera of san juan in central western argentina the system extends for 47 km along the intermountain valley that separates the sierra de la cantera and la invernada north of the san juan river the average fault trend is 20 it dips at angles varying between 15 and 30 w in the northern section to approximately 40 w in the central section and up to 60 w in the southern section the fault affects holocene to recent alluvium deposits in the western piedmont of the sierra de la cantera and is defined by a series of landforms found in compressive tectonic environments including simple and compound counterslope fault scarps staircased alluvial terraces sag ponds flexural scarps aligned springs broom shaped drainage patterns river diversions beheaded channels changes in incision depths sinuosity and a river gradient along channels trench investigations indicated that at least three events occurred in the past 1 1 10 1 ky the topographic profiles of the selected channels and interfluves cutting across the northern and central trace of the fault were analyzed using a stonex vector gps differential system to establish the relationship between the topography and slope of the rivers this morphometric analysis of scarps indicates that active tectonics have played an essential role in controlling the drainage pattern in the piedmont leading the rivers to adjust to these slope variations based on the analyzed geomorphologic stratigraphic and structural characteristics the lcfs is considered to be a relevant seismogenic source in the intraplate portion of southern south america with a recurrence interval of at least 2000 500 years for moderate magnitude earthquakes during the last 11 000 years

shear wave velocity characteristics of geological units throughout tehran city iran abstract one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity vs in the shallow subsurface to classify materials we used the average shear wave velocity to a depth of 30 m v s 30 to develop site categories for tehran this parameter can further be used for modifying a calculated ground motion to account for site conditions the national earthquake hazard reduction program nehrp classification was used to group sites into different classes our classification was based on v s 30 values measured in 188 seismic profiles and on the assumption of similar values for similar geological materials for each geological unit characteristics of shear wave velocity distribution including histograms of shear wave velocity and variation of vs versus depth were calculated and shown this study reveals that the v s 30 of the mountainous zones fall into categories a and b of nehrp site classification but in the tehran plain the northern alluvium tends to have v s 30 values which fall into range of category c of the nehrp site classification whereas those in the southern alluvium would be categorized as nehrp d

nature and timing of the solonker suture of the central asian orogenic belt insights from geochronology and geochemistry of basic intrusions in the xilin gol complex inner mongolia china the solonker suture zone of the central asian orogenic belt caob records the final closure of the paleo asian ocean the nature and timing of final collision along the solonker suture has long been controversial partly because of an incomplete record of isotopic ages and differing interpretations of the geological environments of key tectonic units the xilin gol complex consisting of strongly deformed gneisses schists and amphibolites is such a key tectonic unit within the caob lenticular or quasi lamellar amphibolites are dispersed throughout the complex intercalated with biotite plagioclase gneiss both rock types experienced amphibolite facies metamorphism the protolith of the amphibolite is a basic rock that intruded into the biotite plagioclase gneiss at 319 4 ma based on la icpms zircon u pb dating the basic intrusion was sourced from a modified magma that experienced crystal fractionation and was admixed with slab derived fluids the slab derived fluids which formed during early paleozoic oceanic subduction along the north dipping sonidzuoqi xilinhot subduction zone mixed with the magma source and produced subduction related geochemical signatures superimposed on volcanic arc chemistry after early paleozoic oceanic subduction and arc continent collision a transient stage of extension occurred between 313 and 280 ma in the sonidzuoqi xilinhot area deformation and recrystallization during the switch from compression to extension and reheating by the later magmatic intrusions reset the isotope systems of minerals in the xilin gol complex recorded by a 312 2 1 5 ma biotite 40ar 39ar age from biotite plagioclase gneiss a 309 12 ma zircon intercept age and a 307 5 3 5 ma hornblende 40ar 39ar age from amphibolites in the complex there was an arc forearc related marine basin at the southern margin of the xilin gol complex during the permian the closure of the oceanic basin led to late paleozoic middle triassic north dipping subduction beneath the xilin gol complex and induced the amphibolite facies metamorphism of the complex the final suturing of the solonker zone occurred from 269 to 231 ma this latest amphibolite facies metamorphism with pressures of 0 31 0 39 gpa and temperatures of 620 660 c was recorded at 263 4 1 4 ma to the xilin gol complex as indicated by the hornblende 40ar 39ar age from the amphibolites as well as several zircon ages of 260 3 231 3 ma the xilin gol complex documented the progressive accretion of a single long lived subduction system at the southern margin of the south mongolian microcontinent from the early paleozoic 452 ma to middle triassic 231 ma the caob shows protracted collision prior to final suturing

shakeout d ground motion estimates using an ensemble of large earthquakes on the southern san andreas fault with spontaneous rupture propagation 1 we simulate ground motion in southern california from an ensemble of 7 spontaneous rupture models of large mw7 8 northwest propagating earthquakes on the southern san andreas fault shakeout d compared to long period spectral accelerations from the next generation attenuation nga empirical relations shakeout d predicts similar average rock site values i e within roughly their epistemic uncertainty but significantly larger values in los angeles and ventura basins due to wave guide focusing effects the shakeout d ground motion predictions differ from those of a kinematically parameterized geometrically similar scenario rupture 1 the kinematic rock site predictions depart significantly from the common distance attenuation trend of the nga and shakeout d results and 2 shakeout d predictions of long period spectral acceleration within the basins of the greater los angeles area are lower by factors of 2 3 than the corresponding kinematic predictions we attribute these differences to a less coherent wavefield excited by the complex rupture paths of the shakeout d sources

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

frictional properties of shale reservoir rocks 1 we performed laboratory friction experiments on shale samples from three hydrocarbon reservoirs to assess compositional controls on fault slip behavior accompanying hydraulic stimulation the samples span a range of clay and total organic content from 10 to 60 by weight and demonstrate fine scale heterogeneity within each reservoir friction measurements demonstrate strong dependence of strength and rate state constitutive properties on shale composition shale samples with clay and organic content above 30 by weight show coefficient of friction 0 4 and consistently velocity strengthening behavior while those below this threshold show increased strength and velocity weakening behavior this transition in frictional strength and stability suggests a change in the shale grain packing framework from rigid clast supported to clay mineral and organic matter supported measurements of gouge dilatancy further support these relationships showing a negative correlation with clay and organic content critical slip evolution distance exhibits similar dependence on composition implying common micromechanical mechanisms for the observed transition in frictional behavior we performed microstructural characterization of the experimental samples and observe changes in the gouge load bearing framework and shear localization features consistent with these mechanical data while these results can be applied generally to infer slip stability on faults in clay bearing sedimentary rock we employ the experimental data to place constraints on microearthquake magnitudes and the occurrence of slow shear slip on preexisting faults during hydraulic stimulation in shale reservoirs

source related variations of ground motions in 3 d media application to the newport inglewood fault los angeles basin summary deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation our aim is to calculate a substantial number of different finite source scenarios embedded in a 3 d structure for a particular fault or fault system by pre calculating numerical green s functions ngfs a large seismic fault is divided into subfaults of appropriate size for which synthetic green s functions at the surface are calculated and stored consequently ground motions from arbitrary kinematic sources can be simulated for the whole fault or parts of it by superposition to illustrate this approach and its functionalities we simulate m 7 up to 0 5 hz scenario earthquakes for a simplified model of the newport inglewood ni fault in the los angeles la basin we quantify the variations of surface ground motion e g peak ground velocity pgv and synthetic seismograms due to source parameters e g hypocentre location and corresponding slip history the results show a complex behaviour with dependence of absolute pgv and its variation on asperity location source directionality and local structure and demonstrate the necessity to combine 3 d structural and finite source effects to quantify ground motion characteristics and their variations

nonlinear and linear site response and basin effects in seattle for the m 6 8 nisqually washington earthquake we used recordings of the m 6 8 nisqually earthquake and its m l 3 4 aftershock to study site response and basin effects for 35 locations in seattle washington we determined site amplification from fourier spectral ratios of the recorded horizontal ground motions referenced to a soft rock site soft soil sites generally national earthquake hazard reduction program nehrp class e on artificial fill and young alluvium have the largest 1 hz amplifications factors of 3 7 for both the mainshock and aftershock these amplifications are correlated with areas of higher damage from the mainshock to major buildings and liquefaction there are several indications of nonlinear response at the soft soil sites for the mainshock ground motions despite relatively modest peak accelerations in the s waves of 15 22 g first the mainshock spectral ratios do not show amplification at 2 8 hz as do the aftershock spectral ratios spectral peaks at frequencies below 2 hz generally occur at lower frequencies for the mainshock spectral ratios than for the aftershock ratios at one soft soil site there is a clear shift of the resonant frequency to a lower frequency for the mainshock compared with the aftershock the frequency of this resonance increases in the coda of the mainshock record indicating that the site response during the weaker motions of the coda is more linear than that of the initial s wave three of the soft soil sites display cusped one sided mainshock accelerograms after the s wave these soft soil sites also show amplification at 10 20 hz in the s wave relative to the rock site that is not observed for the aftershock the cusped waveforms and 10 20 hz amplification are symptomatic of nonlinear response at the soft soil sites these sites had nearby liquefaction the largest amplifications for 0 5 hz occur at soft soil sites on the southern portion of the seattle basin stiff soil sites nehrp classes d and c on pleistocence age glacial deposits display similar spectral amplification for the mainshock and aftershock indicating approximately linear response the stiff soil sites generally have moderate amplification factors of 1 1 2 4 at 0 5 and 1 hz amplifications at 1 and 5 hz for all sites generally increase with decreasing shear wave velocity measured in the top 30 m v s 30 however larger amplifications at 0 5 and 1 hz for sites with similar v s 30 values are observed for sites in the seattle basin illustrating the amplification from the deeper 30 m sediments and the contribution from basin surface waves record sections for the mainshock and aftershock show that basin surface waves produce the peak velocities for many of the sites in the seattle basin and often dominate the amplitude at 1 hz and lower frequencies

broadband simulations for mw 7 8 southern san andreas earthquakes ground motion sensitivity to rupture speed using the high performance computing resources of the southern california earthquake center we simulate broadband 0 10 hz ground motions for three m w 7 8 rupture scenarios of the southern san andreas fault the scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0 96 0 89 and 0 84 times the local shear wave velocity consistent with previous simulations a southern hypocenter efficiently channels energy into the los angeles region along the string of basins south of the san gabriel mountains however we find the basin ground motion levels are quite sensitive to the prescribed rupture speed with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15 these results have important implications for estimating seismic hazards in southern california and emphasize the need for improved understanding of earthquake rupture processes

source characterization of the san juan argentina crustal earthquakes of 15 january 1944 mw 7 0 and 11 june 1952 mw 6 8 abstract the backarc region of the andes in the vicinity of san juan argentina is one of the most seismically active fold and thrust belt regions in the world four large damaging crustal earthquakes 1894 1944 1952 and 1977 occurred during the last 111 yr between 30 s and 32 s we have determined the source parameters for two of these important earthquakes the 1944 and 1952 events using historic seismic records the earthquake on 15 january 1944 had an epicentral location between the eastern thin skinned precordillera fold and thrust belt and the thick skinned sierras pampeanas basement cored uplifts the 11 june 1952 earthquake occurred in the eastern precordillera about 35 km southwest of the 1944 epicenter location the p wave first motions long period teleseismic p waveform modeling and sv sh amplitude ratio indicate a thrust focal mechanism for the 1944 event strike n45 e dip 35 to the southeast and rake 110 with m0 3 01 1019 n m and mw 7 0 the 1952 earthquake focal mechanism solution indicates a more oblique mechanism strike n40 e dip 75 to the southeast and rake 30 with m0 2 20 1019 n m and mw 6 8 both the 1944 and 1952 earthquakes have focal depths

upper plate deformation measured by gps in the coquimbo gap chile abstract since the mw 7 3 punitaqui earthquake in 1997 the area between 30 s and 32 s coquimbo illapel section of the chilean subduction has been the locus of a decennial seismic swarm a dense network of 30 benchmarks have been installed in this area and surveyed six times with high precision gps over the last 3 years surface deformation here is compatible with elastic loading due to partial locking on the subduction interface at depth here we show that in this area only 40 45 of the total convergence rate between nazca and south america plates gives way to accumulation of elastic deformation in the upper plate the remaining 60 55 being dissipated by free or aseismic slip the cumulative slip due to the seismic swarm explaining no more than 1 3rd to 1 4th of it we also find that the accumulation decreases northward to reach almost zero around 30 s la serena tongoy whether this is a steady state or only a transient pattern a steady decrease of coupling is not clear since our measurements span only 3 years and since early measurements 10 years ago were sparse and differ only marginally from ours

estimating deep s wave velocity structure in the los angeles basin using a passive surface wave method this article summarizes a passive surface wave method that uses only two sensors and its application to the estimation of deep s wave velocity structure three dimensional s wave velocity structure to a depth of several kilometers has a large effect on long period ground motion in tectonic basins such as the los angeles la basin recent studies of long period ground motion in the la basin e g hatayama and kalkan 2012 show that observed ground motion in some areas cannot be explained by the s wave velocity models in current use most studies of basin velocity structure rely on geologic information surface and borehole geophysical data and observed earthquake records to deduce or measure seismic velocities geophysical data and seismic stations commonly used for velocity analysis are sparsely distributed and most well data are too shallow to characterize deep s wave velocity structure to establish more accurate basin velocity structure there is a need for more densely distributed deep s wave vel

seismotectonics of thin and thick skinned deformation in the andean foreland from local network data evidence for a seismogenic lower crust local network data from san juan argentina provides new information about crustal seismicity in the andean foreland above a horizontal segment of the subducted nazca plate the authors find two areas of foreland seismicity one associated with the sierras pampeanas basement uplifts and the other beneath but not within the precordillera foreland fold thrust belt the precordillera seismicity provides direct evidence for basement deformation beneath the sediments of the thrust belt and supports the idea that its eastern part is significantly modified by underlying basement deformation in both areas events are concentrated between 15 and 35 km depth and have volumetric rather than planar fault like distributions the depth distribution is usually deep for intraplate earthquakes and suggests a brittle ductile transition near 30 35 km it also suggests the upper plate may have a geotherm similar to stable cratonic regions rather than a steeper one that may be expected due to a lithospheric thinning implied by the location of the subducted plate this can be understood as a transient effect of a neogene flattening of the dip of the subducted plate where a rapid thinning of the upper plate was followed with underplating by the cool subducted plate leaving the upper plate geothermmore unchanged while producing a thinned mechanically weaker lithosphere finally a spatial correlation of upper plate seismicity and structures with subducted plate seismicity raises the possibility that a major lithospheric structure cutting across the strike of the foreland near 31 degree s may be related to subduction of the juan fernandez ridge less

cybershake derived ground motion prediction models for the los angeles region with application to earthquake early warning real time applications such as earthquake early warning eew typically use empirical ground motion prediction equations gmpes along with event magnitude and source to site distances to estimate expected shaking levels in this simplified approach effects due to finite fault geometry directivity and site and basin response are often generalized which may lead to a significant under or overestimation of shaking from large earthquakes m 6 5 in some locations for enhanced site specific ground motion predictions considering 3 d wave propagation effects we develop support vector regression svr models from the scec cybershake low frequency 415 000 finite fault rupture scenarios 6 5 m 8 5 for southern california defined in ucerf 2 0 we use cybershake to demonstrate the application of synthetic waveform data to eew as a proof of concept being aware that these simulations are not yet fully validated and might not appropriately sample the range of rupture uncertainty our regression models predict the maximum and the temporal evolution of instrumental intensity mmi at 71 selected test sites using only the hypocentre magnitude and rupture ratio which characterizes uni and bilateral rupture propagation our regression approach is completely data driven where here the cybershake simulations are considered data and does not enforce pre defined functional forms or dependencies among input parameters the models were established from a subset 20 per cent of cybershake simulations but can explain mmi values of all 400 k rupture scenarios with a standard deviation of about 0 4 intensity units we apply our models to determine threshold magnitudes and warning times for various active faults in southern california that earthquakes need to exceed to cause at least moderate strong or very strong shaking in the los angeles la basin these thresholds are used to construct a simple and robust eew algorithm to declare a warning the algorithm only needs to locate the earthquake and to verify that the corresponding magnitude threshold is exceeded the models predict that a relatively moderate m6 5 7 earthquake along the palos verdes newport inglewood rose canyon elsinore or san jacinto faults with a rupture propagating towards la could cause very strong to severe shaking in the la basin however warning times for these events could exceed 30 s

nonlinearity at california generic soil sites from modeling recent strong motion data the average strong to weak motion amplification ratios during the 1989 loma prieta and 1987 whittier narrows earthquakes in california are estimated by modeling strong ground motions at soil sites in the linear response assumption and comparing the simulated and observed records the linear amplification function used to synthesize ground motions is the generic transfer function developed for california soil the database consists of 22 and 80 soil stations for the loma prieta and whittier narrows events respectively a statistically significant at 95 confidence reduction in amplification for the loma prieta event within 40 km from the fault is observed between approximately 1 and 3 hz examining individual strong to weak motion amplifications as a function of peak acceleration at the base of soil within this frequency range shows that detectable reduction in amplification occurs at accelerations above about 200 cm sec2 the strong motion amplification is reduced by a factor of 1 7 2 on average relative to a generic weak motion response the results of this study suggest the magnitude of the reduction in amplification caused by soil nonlinearity at large strain that can be expected on average at california soil sites

plate reconstructions aseismic ridges and low angle subduction beneath the andes low angle subduction segments beneath peru and chile are believed to represent interaction of the subduction zone with the aseismic nazca and juan fernandez ridges on the basis of symmetric sea floor spreading models and plate hotspot reconstructions predicted continuations of the relatively buoyant ridges correspond well with the limits of the low angle subduction segments further the history of interaction of the aseismic ridges with the subduction zone as predicted by plate reconstructions is not inconsistent with available information on volcanic episodes of the andes if the contemporary correlation of volcanic gaps and low angle subduction is also applicable to the rest of the late cenozoic the occurrence of deep seismicity beneath the eastern flanks of the andes is also believed to reflect the effects of low angle subduction the deep seismic segments are adjacent to segments which are presently or were recently experiencing low angle subduction thus the deep seismicity is interpreted as representative of remnants of normal oceanic lithosphere subducted before interaction of aseismic ridges with the subduction zone other geologic phenomena are associated with low angle subduction beneath south america including landward shift in loci of tectonism surficial subsidence and laramide style deformation the aseismic ridge buoyancy hypothesis appears to be a valuable predictive tool for the interpretation of such geologic effects

chronology of motion in a complete thrust belt the precordillera 30 31 s andes mountains in the precordillera thrust belt of west central argentina faulted rotated and onlapping relations of piggyback basin units and foreland basin units yield an accurate but imprecise chronology of thrust motion addition of data from provenance history strata accumulation rates and presence of thick conglomerate units in the bermejo foreland basin results in a thrust chronology that is more precise but not entirely independent of assumptions about foreland basin dynamics seven new radiometric dates allow substantial revision of the interpreted age of first deformation in the precordillera at about 30 south units previously assigned to the paleozoic and mesozoic are of oligocene and miocene ages a redbed unit that began before 21 6 pm 0 8 ma appears to have pre dated thrusting deposits in the early bermejo foreland basin were dominated by eolian sandstones unlike the younger fluvial and alluvial units an andesitic volcanic center within the miocene foreland basin had long term effects on sub

a transect of 200 shallow shear velocity profiles across the los angeles basin this study assesses a 60 km north northeast south southwest transect along the san gabriel river for shallow shear velocities in san gabriel valley and the los angeles basin of southern california we assessed a total of 214 sites 199 along the transect at 300 m spacing during a one week field campaign with the refraction microtremor remi technique the transect9s maximum 30 m shear velocity vs30 occurs in coarse alluvium of san gabriel valley where the san gabriel river exits the san gabriel mountains at 730 m sec upper national earthquake hazards reduction program nehrp site class c much of the northeast section of the transect in san gabriel valley is also nehrp class c or near the cd class boundary the section of the transect south from whittier narrows to seal beach shows nehrp d velocities in active alluvium the transect9s lowest vs30 230 m sec at the alamitos bay estuary is also classed as nehrp d an increase toward the nehrp cd class boundary occurs at the shoreline beach outside alamitos bay confirmed by additional measurements on seal beach our measured vs30 values generally show good correlation with published site classification maps and existing borehole data sets there is no evidence in our data for an increase in velocity predicted by wills et al 2000 at their cd to bc site classification boundary at the san gabriel mountains front nor for any decrease at their d to de class boundary at alamitos bay very large vs30 variations exist in soil and geologic units sampled by our survey the vs30 variations we measured are smaller than vs30 variations of 30 or more we found between closely spaced

thick skinned and thin skinned thrusting in the la ramada fold and thrust belt crustal evolution of the high andes of san juan argentina 32 sl abstract the cenozoic structural evolution of the la ramada fold and thrust belt in the high andes of argentina between 32 00 s and 32 30 s shows in time and space the interaction of thin skinned and thick skinned deformations based on geometric and kinematic constraints three different deformation stages have been recognized the first began with thin skinned nnw trending structures detached in upper jurassic gypsum in the second stage the basement was involved by tectonic inversion of triassic normal faults producing a thick skinned fold and thrust belt this inversion combined with the ductile rheology of the jurassic gypsum resulted in refolding of older structures the uplift of the basement by high angle reverse faults at the ramada espinacito massif produced a sticking point in the foreland propagation of the thrust belt this was responsible for the third stage of deformation characterized by thin skinned nnw out of sequence thrusts developed in the westernmost sector the total andean shortening calculated in the area was 21 24 km near 30 the structure of the la ramada fold and thrust belt was integrated into a crustal scale cross section at 32 s latitude based on gravimetric models and surface geology a crustal model is proposed for the andes of chile and argentina a shortening of 180 km was calculated between the chile trench and the sierra de pie de palo this implies a mean deformation rate of 2 8 mm year 1 during cenozoic times an initial crustal thickness of ca 33 km was computed a two layer model with a middle detachment level is proposed to explain the spatial decoupling between maximum shortening at the surface and maximum crustal thickening the upper layer was balanced based on surface structural information the lower layer is interpreted to have been constructed by an imbricate thrust system controlled by the mercedario rift master shear and the precordillera chilenia suture

expected seismic shaking in los angeles reduced by san andreas fault zone plasticity computer simulations of large m 7 8 earthquakes rupturing the southern san andreas fault from se to nw e g shakeout widely used for earthquake drills have predicted strong long period ground motions in the densely populated los angeles basin due to channeling of waves through a series of interconnected sedimentary basins recently the importance of this waveguide amplification effect for seismic shaking in the los angeles basin has also been confirmed from observations of the ambient seismic field by simulating the shakeout earthquake scenario based on a kinematic source description for a medium governed by drucker prager plasticity we show that nonlinear material behavior could reduce the earlier predictions of large long period ground motions in the los angeles basin by up to 70 as compared to viscoelastic solutions these reductions are primarily due to yielding near the fault although yielding may also occur in the shallow low velocity deposits of the los angeles basin if cohesions are close to zero fault zone plasticity remains important even for conservative values of cohesions suggesting that current simulations assuming a linear response of rocks are overpredicting ground motions during future large earthquakes on the southern san andreas fault

nonlinear attenuation of s waves and love waves within ambient rock we obtain scaling relationships for nonlinear attenuation of s waves and love waves within sedimentary basins to assist numerical modeling these relationships constrain the past peak ground velocity pgv of strong 3 4 s love waves from san andreas events within greater los angeles as well as the maximum pgv of future waves that can propagate without strong nonlinear attenuation during each event the shaking episode cracks the stiff shallow rock over multiple events this repeated damage in the upper few hundred meters leads to self organization of the shear modulus dynamic strain is pgv divided by phase velocity and dynamic stress is strain times the shear modulus the frictional yield stress is proportional to depth times the effective coefficient of friction at the eventual quasi steady self organized state the shear modulus increases linearly with depth allowing inference of past typical pgv where rock over the damaged depth range barely reaches frictional failure still greater future pgv would cause frictional failure throughout the damaged zone nonlinearly attenuating the wave assuming self organization has taken place estimated maximum past pgv within greater los angeles basins is 0 4 2 6 m s 1 the upper part of this range includes regions of accumulating sediments with low s wave velocity that may have not yet compacted rather than having been damaged by strong shaking published numerical models indicate that strong love waves from the san andreas fault pass through whittier narrows within this corridor deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double pgv of love waves reaching downtown los angeles

structural evolution of the argentine precordillera the rio san juan section abstract the argentine precordillera ap represents a high level fold and thrust belt which was formed during the andean tertiary crustal shortening in a w e transect studied mostly e directed imbrications are combined with folding and involve a pile of cambrian to tertiary sediments the thrust belt is detached above a main decollement within the ordovician to lower devonian strata to the east it is bounded by a back thrust zone directed westwards restored sections allow an estimate of crustal shortening and also provide insight into the structural development during pre tertiary times carbonate platform sequences of cambrian to ordovician age grade into a volcani clastic succession with transitional melanges representing deposits along a western continental slope in the western and easternmost parts of the ap cambrian to silurian deposits are affected by a first folding which to the west is combined with a slight metamorphic overprint during carboniferous to permian times intensified mobility along the eastern rim and in the western parts of the ap leads to crustal extension which partly was triggered by the formation of synsedimentary normal faults in the central ap no angular unconformities at the base of carboniferous permian deposits were found there was no field evidence found to postulate a terrane boundary within the ap area and an onset of thrust tectonics during cretaceous to early tertiary times

tectonic and magmatic responses to the subduction of high bathymetric relief subduction of high bathymetric relief such as aseismic ridges and magmatic plateaus is considered to be responsible for dramatic changes in the dynamics and kinematics of the subduction zone for example the buoyancy of high bathymetric relief is thought to flatten the dip of the subducting slab modifying the structural and magmatic evolution of the overriding plate and terminating arc volcanism in addition the effect of ridge subduction in retreating plate boundaries can inhibit subduction rollback a process that could locally pin the subduction hinge and lead to the development of cusps and slab tearing here we discuss the tectonic response to subduction of high bathymetric relief using examples from the circum pacific subduction systems we demonstrate that flattening of the subduction dip angle is only significant in the eastern pacific where the average slab dip angle is relatively shallow in the western pacific in contrast the average subduction dip angle is steeper and there is no significant flattening of the dip angle in areas of ridge subduction subduction of high bathymetric relief in the circum pacific is commonly associated with reduced arc volcanism and in many cases the area of ridge subduction coincides with a volcanic gap in the overriding plate ridge subduction is associated with pronounced changes in the style of deformation involving uplift reactivation of basement thrusts development of orogen perpendicular tear faults and block rotations leading to oroclinal bending the discussed characteristic patterns associated with ridge subduction provide important guidelines for reconstructing past plate tectonic processes and could help constraining the geodynamics of ancient subduction systems

dynamic triggering of high frequency bursts by strong motions during the 2004 parkfield earthquake sequence high pass filtering 20 hz of acceleration records from the usgs parkfield dense seismograph array upsar reveals a series of bursts that occur only during strong shaking from the 2004 mw6 parkfield california earthquake and its immediate aftershocks because there is no correlation between these high frequency bursts observed at closely spaced stations we hypothesize that they are associated with dynamically triggered events occurring within 20 meters of the stations in the highly fractured shallow crust the triggering threshold was found to be 0 02 mpa consistent with a previous estimate based on a similar analysis of high frequency bursts observed in strong motion data from the 1999 chi chi earthquake in taiwan fischer et al 2008 the consistent observation of high frequency bursts at both parkfield and taiwan suggest that they may be a common phenomenon associated with strong motion in the very shallow crust

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

geometry and brittle deformation of the subducting nazca plate central chile and argentina summary we use data from the chile argentina geophysical experiment charge broad band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the south american subduction zone between 30 s and 36 s this region contains a zone of flat slab subduction where the subducting nazca plate flattens at a depth of 100 km and extends 300 km eastward before continuing its descent into the mantle we use a grid search multiple event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the wadati benioff zone these contours reflect slab geometries from previous studies of intermediate depth seismicity in this region with some small but important deviations our hypocentres indicate that the shallowest portion of the flat slab is a

magnetic anomaly interpretation across the southern central andes 32 34 s the role of the juan fernandez ridge in the late tertiary evolution of the margin marine and terrestrial magnetic surveys have been integrated to study the tectonic structure of the convergent margin of chile between 32 34 s three magnetic domains have been identified oceanic continental margin and subaerial the oceanic domain has seafloor spreading anomalies 16 37 ma to 18 39 5 ma disturbed by anomalies of the juan fernandez hot spot chain in the continental margin the most prominent fabric are e w anomalies in the upper slope corresponding to onshore e w anomalies of large intrusive bodies onshore a n s lineament of short wavelength anomalies defines the roots of a cretaceous volcanic arc a resembling lineament offshore indicates a submerged older volcanic arc and that continental basement extends to 50 km landward of the trench absolute cenozoic plate motion for nazca and south american plates and dating of the juan fernandez chain provide a kinematic model of ridge continent collision the reconstruction indicates rapid southward migration of the collision point along 1400 km of the margin from 20 to 11 ma 20 cm yr 1 from 11 ma to present the collison point has migrated at a slower rate along 375 km of the margin 3 5 cm yr 1 the predicted location of the subducted portion of the juan fernandez chain coincides with the south edge of the southward migrating flat slab segment of the subducted lithosphere and with a cluster of deep earthquakes indicating a causal relationship in the last 10 myr the ridge has separated a sediment starved trench to the north where subduction erosion may dominate from a sediment filled trench to the south where recent sediment accretion dominates these observations indicate that subduction of the juan fernandez chain plays a major role in arc forearc tectonics

shallow s wave well logs as an indicator of past strong shaking from earthquakes on the newport inglewood fault numerical calculations assuming linear elasticity by bose et al 2014 indicate that an m w 7 75 earthquake on the newport inglewood fault would cause 5 m s of horizontal peak ground velocity pgv within the los angeles basin however the dynamic strain from this event would take much of the uppermost few hundred meters of basin rock beyond its frictional elastic limit stiff quartz rich beds within the basin are fragile geological features that would fail and crack before the rest of the clay rich rock mass repeated cracking would reduce the shear modulus of the quartz rich beds to the level that cracking barely occurred during strong events when interpreted in this way data from such stiff beds near the los angeles international airport indicate past pgv of 1 6 m s comparable with near field records from the strike slip 2002 denali and 1992 landers earthquakes numerical calculations capable of representing nonlinear failure within shallow bedded rocks are warranted online material digital rosrine s wave borehole logs

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

geomorphic and sedimentary response of rivers to tectonic deformation a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings abstract rivers are extremely sensitive to subtle changes in their grade caused by tectonic tilting as such recognition of tectonic tilting effects on rivers and their resultant sediments can be a useful tool for identifying the often cryptic warping associated with incipient and smaller scale epeirogenic deformation in both modern and ancient settings tectonic warping may result in either longitudinal parallel to floodplain orientation or lateral normal to floodplain orientation tilting of alluvial river profiles alluvial rivers may respond to deformation of longitudinal profile by 1 deflection around zones of uplift and into zones of subsidence 2 aggradation in backtilted and degradation in foretilted reaches 3 compensation of slope alteration by shifts in channel pattern 4 increase in frequency of overbank flooding for foretilted and decrease for backtilted reaches and 5 increased bedload grain size in foretilted reaches and decreased bedload grain size in backtilted reaches lateral tilting causes down tilt avulsion of streams where tilt rates are high and steady down tilt migration combing where tilt rates are lower each of the above effects may have profound impacts on lithofacies geometry and distribution that may potentially be preserved in the rock record fluvial sedimentary evidence for past tilting is traditionally based on the assumption that depositional features reminiscent of modern fluvial tectonic effects are evidence for past tectonic effects where it is closely associated with historically active structures or where non tectonic causes cannot be invoked however caution must be exercised when using these effects as criteria for past or current tectonic warping as these effects may be caused by non tectonic factors these non tectonic causes must be eliminated before tectonic interpretations are made

basement seismicity beneath the andean precordillera thin skinned thrust belt and implications for crustal and lithospheric behavior data from a digitally recording seismic network in san juan argentina provide the first images of crustal scale basement faults beneath the precordillera this seismicity is near the boundary between the precordillera a thin skinned thrust belt and the sierras pampeanas a region of thick skinned basement deformation two seismically active tectonic provinces of the andean foreland the seismicity data support models for this region in which crustal thickening rather than magmatic addition or thermal uplift plays the dominant mountain building role the precordillera seismicity occurs in three segments distributed north to south the southern segment is an area of diffuse activity extending across the precordillera and eastward into the sierras pampeanas that shows no patterns in map or cross section the northern and central segments have well defined dipping planes that define crustal scale faults extending from 5 to 35 km depth it is clear from the relative fault geometries that the overlying precordillera is not simply related to the basement activity the seismicity here may result from reactivation of an ancient suture between the precordillera and pampeanas terranes or be occurring in basement of unknown affinity west of the suture the seismicity provides the first constraints on basement fault geometries and we present models integrating this information with the surface geology these basement faults may have been responsible for the 1944 ms 7 4 earthquake that destroyed the city of san juan the imaging of these faults suggests that seismic risk estimates for san juan made on the basis of surface geologic studies may be too low

regional relative tectonic activity of structures in the pampean flat slab segment of argentina from 30 to 32 s abstract the pampean flat slab segment of the central andes in argentina is a broad active deformation zone subject to both plate boundary related and intraplate deformation to the west plate boundary related deformation is dominated by thin skinned fold and thrusts of the precordillera while to the east intraplate deformation involves thick skinned reverse faults of the sierras pampeanas gps data and absolute dating of displaced geomorphic features suggest that most of the active permanent deformation occurs between these two regions at the andean orogenic front and that there is a west to east trend of decreasing shortening rates however gps stations and sites with geomorphic slip rate measurements are currently too sparse and cover too short a time period to make reliable inferences about the longer term distribution and relative rates of deformation mountain range scale geomorphic indices on the other hand reflect tectonic activity since at least the pleistocene in this study we measured geomorphic indices hypsometric integral and curves basin elongation ratio basin volume to area ratio valley floor width to height ratio mountain front sinuosity and normalized steepness indices of rivers from 10 different n s striking range bounding faults that span both the precordillera and sierras pampeanas regions from west to east we use these data to assess the regional relative tectonic activity of major quaternary deformation features in the pampean segment of the central andes even when variations in climate and geology are considered mean values for each geomorphic index suggests uplift rates for the 10 mountain range bounding faults display local trends that are closely associated with the structural style and tectonic evolution of these structures although vertical uplift rates vary little horizontal shortening rates are higher for the precordillera fold and thrusts in the west than the thick skinned reverse faults of the sierras pampeanas in the east due to shallower fault dips for precordilleran structures the similarity with decadal slip rate gradients from gps studies could possibly indicate that the stress field has been constant since at least the pleistocene but further slip rate studies over broader time intervals in the late quaternary are necessary to confirm this variations observed in relative uplift rates along each fault point to sites that warrant further detailed study of slip rates and evaluation of associated seismic hazards

multiple geophysical methods examining neotectonic blind structures in the maradona valley central precordillera argentina abstract a high resolution superficial geophysical study was carried out in an area of the retroarc region of the andes mountains located in the southwest of san juan province 31 45 s 68 50 w central precordillera of argentina the main objectives of this study were to confirm the presence of blind neotectonic structures and characterize them by observing variations in magnetic susceptibility density and p wave velocities geological evidence demonstrates the existence of a neotectonic fault scarps affecting quaternary alluvial deposits in eastern piedmont of de las osamentas range in addition to direct observation of the cinematic of this feature in several natural exposures the maradona valley is characterized by the imbricated eastern vergence maradona fault system that uplifts neogene sedimentary rocks albarracin formation over quaternary late pleistocene holocene alluvial deposits the combined application of different geophysical methods has allowed the characterization of a blind fault geometry also identified on a natural exposure the magnetic data added to the gravimetric model and its integration with a seismic profile clearly shows the existence of an anomalous zone interpreted as uplifted blocks of miocene sedimentary rocks of formation albarracin displaced over quaternary deposits the application and development of different geophysical methods together with geological studies allow to significantly improving the knowledge of an area affected by quaternary tectonic activity finally this multidisciplinary study applied in active blind structures is very relevant for future seismic hazard analysis on areas located very close to populated centers

distribution of landslides along the andean active orogenic front argentinean precordillera 31 33 s abstract as one of the main environmental effects of earthquakes the distribution of landslides could reflect regional neotectonic activity to that end we carried out an inventory of landslides along the precordillera range 31 33 s comprising the most seismically active region of argentina main quaternary deformation is concentrated in this western central part of the country associated with active faults linked to intense shallow seismic activity

seismically damaged regolith as self organized fragile geological feature 1 the s wave velocity in the shallow subsurface within seismically active regions self organizes so that typical strong dynamic shear stresses marginally exceed the coulomb elastic limit the dynamic velocity from major strike slip faults yields simple dimensional relations the near field velocity pulse is essentially a love wave the dynamic shear strain is the ratio of the measured particle velocity over the deep s wave velocity the shallow dynamic shear stress is this quantity times the local shear modulus the dynamic shear traction on fault parallel vertical planes is finite at the free surface coulomb failure occurs on favorably oriented fractures and internally in intact rock i obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock extending all the way to the surface the imposed dynamic shear strain in stiff rock causes coulomb failure at shallow depths and leaves cracks in it wake cracked rock is more compliant than the original intact rock cracked rock is also weaker in friction but shear modulus changes have a larger effect each subsequent event causes additional shallow cracking until the rock becomes compliant enough that it just reaches coulomb failure over a shallow depth range of tens to hundreds of meters further events maintain the material at the shear modulus as a function where it just fails the formalism provided in the paper yields reasonable representation of the s wave velocity in exhumed sediments near cajon pass and the san fernando valley of california a general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking this process causes transient changes in s wave velocity but not strong nonlinear attenuation of seismic waves wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock

dynamic driving of small shallow events during strong motion abstract high pass filtering 20 hz of acceleration records from the 1999 chi chi taiwan and 2004 parkfield california earthquakes reveals a series of bursts that occur only during strong shaking initially interpreted as originating from asperity failure on the chelungpu fault bursts observed during the chi chi earthquake were subsequently determined to be a local effect within about 1 km of the seismic stations similar bursts were observed at the u s geological survey parkfield seismic array during the parkfield earthquake and were constrained to originate less than 20 m from the instruments such small shallow events cannot result from the triggered release of stored elastic energy because rate and state friction rules out stick slip instability on such small shallow patches our hypothesis is that the bursts are not triggered but are driven by simultaneous shear and tensile stresses near the surface during the strong motion at 2 hz sv to p wave mode conversion at the free surface produces tensile stresses to depths of 70 m where standard triggering releases stored elastic energy and adds to the incident wave field this new driving mechanism takes energy out of the 2 hz strong motion and reradiates it at high frequencies it is thus an attenuation mechanism that we estimate can contribute 3 to the net attenuation in the very shallow crust

horizontal subduction zones convergence velocity and the building of the andes we discuss the relationships between andean shortening plate velocities at the trench and slab geometry beneath south america although some correlation exists between the convergence velocity and the westward motion of south america on the one hand and the shortening of the continental plate on the other hand plate kinematics neither gives a satisfactory explanation to the andean segmentation in general nor explains the development of the bolivian orocline in paleogene times we discuss the cenozoic history of horizontal slab segments below south america arguing that they result from the subduction of oceanic plateaus whose effect is to switch the buoyancy of the young subducting plate to positive we argue that the existence of horizontal slab segments below the central andes during eocene oligocene times and below peru and north central chile since pliocene resulted 1 in the shortening of the continental plate interiors at a large distance from the trench 2 in stronger interplate coupling and ultimately 3 in a decrease of the trenchward velocity of the oceanic plate present day horizontal slab segments may thus explain the diminution of the convergence velocity between the nazca and south american plates since late miocene

paleoseismicity of the north branch of the newport inglewood fault zone in huntington beach california from cone penetrometer test data abstract application of cone penetrometer testing cpt is a promising method for studying subsurface fault zones in stratified unconsolidated sediment where trenching is not feasible analysis of data from 72 cpts spaced 7 5 to 30 0 m apart and 9 borings indicates that the north branch fault the active strand of the newport inglewood fault zone nifz in huntington beach has generated at least three and most likely five recognizable surface ruptures in the past 11 7 0 7 ka additional smaller earthquakes similar to the m w 6 4 1933 long beach earthquake may also have occurred but would not be recognizable with this method the minimum right lateral holocene slip rate of the nifz in the study area is estimated to be 0 34 to 0 55 mm yr the actual slip rate may be significantly higher

morphotectonic and neotectonic control on river pattern in the sierra de la cantera piedmont central precordillera province of san juan argentina article i nfo the drainagepattern on the western piedmontof thesierra de lacantera isdivergent typical of alluvialfansand showing anomalies that are directly related to the trace of la cantera thrust in previous studies two types of anomalies were identified upstream of the fault scarp rivers have a broom shaped pattern while downstream in the hanging block streams become denser more sinuous and incised in this contribution these morphotectonic aspects were analyzed in detail making direct and indirect analysis to quantify the relationship between theseanomaliesandthe faults affectingalluvialfans inaddition theinfluenceofneotectonicactivityon smaller water course patterns in the alluvial fan areas was investigated in order to find indicators of on going vertical movements since the spatial arrangements of these piedmont channels are determined by slope and structure where active faults cause diversions or anomalies topographic profiles in two selected channels cutting across the trace of the fault were performed using a differential gps in order to establish the relationship between the sinuosity and slope of these rivers the results obtained allow us to state that the most sinuous channels have lower slopes and are located in the hanging wall of the fault morphometric analysis of scarps stated that active tectonics have played an essential role in controlling the drainage pattern in the piedmont leading the rivers to adjust to these slope variations finally based on the geomorphologic stratigraphic structural and seismological characteristics and parameters analyzed la cantera thrust is considered a seismogenic source of significance to the nearby towns n700 000 inhabitants and also to the large scale dams built downstream along the san juan river published by elsevier b v