seasonal changes in the hydrological and erosional response of a hillslope under dry mediterranean climatic conditions montes de malaga south of spain the mediterranean eco geomorphological system was analysed at one representative hillslope of the geological unit of montes de malaga province of malaga spain under dry mediterranean climatic conditions the research was divided into two stages first the eco geomorphological pattern of the slope and some physical properties of the soil were analysed second the hydrological and erosional response of the eco geomorphological system was analysed by applying simulated rainfall to the main elements of the system and using closed plots with different lengths this hydrodynamic analysis was carried out during two periods crucial for the mediterranean environment in hydrological terms the end of the dry season or the beginning of the active hydrodynamic season and the middle of the wet season the results show that i the hydrophobic behaviour of soil is the predominant runoff generation mechanism that accounts for sediment movement ii once soil was moistened in the wet season it lost its hydrophobicity and the saturation of soil became a predominant runoff generation mechanism and iii there was high variability in hillslope runoff with evident hydrological disconnections which made the hydrodynamic response of the eco geomorphological system complex due to the absence of a clear predominance of abiotic or biotic factors

permanent deformation caused by subduction earthquakes in northern chile earth s crust is thought to eventually rebound following an earthquake so that deformation is not permanent field analysis in the atacama desert northern chile however identifies numerous large cracks in the crust implying that the crust here has been permanently deformed by thousands of earthquakes that have occurred over the past million years

asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

surface cracks record long term seismic segmentation of the andean margin understanding the long term patterns of great earthquake rupture along a subduction zone provides a framework for assessing modern seismic hazard however evidence that can be used to infer the size and location of past earthquakes is typically erased by erosion after a few thousand years meter scale cracks that cut the surface of coastal areas in northern chile and southern peru preserve a record of earthquakes spanning several hundred thousand years owing to the hyperarid climate of the region these cracks have been observed to form during and or shortly after strong subduction earthquakes are preserved for long time periods throughout the atacama desert demonstrate evidence for multiple episodes of reactivation and show changes in orientation over spatial scales similar to the size of earthquake segments our observations and models show that crack orientations are consistent with dynamic and static stress fi elds generated by recent earthquakes while localized structural and topographic processes infl uence some cracks the strong preferred orientation over large regions indicates that cracks are primarily formed by plate boundary scale stresses namely repeated earthquakes we invert the crack based strain data for slip along the well known iquique seismic gap segment of the margin and fi nd consistency with gravity anomaly based inferences of long term earthquake slip patterns as well as the magnitude and location of the november 2007 tocopilla earthquake we suggest that the meter scale cracks can be used to map characteristic earthquake rupture segments that persist over many seismic cycles which encourages future study of cracks and other small scale structures to better constrain the persistence of asperities in other arid tectonically active regions

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

the erosional response of calcareous soils along a climatological gradient in southeast spain abstract the erosional response of calcareous soils along a climatological gradient in alicante se spain was studied the erosional response was defined in terms of indicators obtained from field rainfall simulation experiments and laboratory studies of soil aggregation measurements were made at seven sites on limestones and marls between benidorm with an annual average rainfall of 400 mm yr 1 and coll de rates annual rainfall 900 mm yr 1 the sites were on matorral vegetation affected to varying intensities by grazing and fire at the seven locations soil aggregation was studied by sieving by the single water drop test and by a microscan particle sizer rainfall simulation experiments were made on circular 55 cm diameter target area plots using the calvo simulator at an intensities between 35 and 59 mm h 1 on limestone it was found that on bare surfaces the coarse soil aggregation increases with depth at the highest sites and decreases at the lower sites the benidorm surface soil has the highest erodibility the least stable soils are at the lower intermediate sites on marls the aggregate stability is generally high in contrast to those under cultivation simulated runoff from the wetter limestone sites is very low the driest areas have the highest runoff and sediment yields trends with climate suggest that the erosional responses of the soils indeed increase with aridity and temperature but local factors have a large effect particularly at intermediate altitudes a clear relationship like that found in israel by lavee on a similar lithology does not exist

comment to nature and tectonic significance of co seismic structures associated with the mw 8 8 maule earthquake central southern chile forearc from arriagada et al 2011

crack formation on top of propagating reverse faults of the chuculay fault system northern chile insights from field data and numerical modelling abstract reverse faults in northern chile have formed 20 300 m high scarps that contain open fractures which occur in a zone of 20 1600 m wide two dimensional numerical models were used to explore the geometrical and mechanical parameters needed to produce extension within a bulk contractional regime all of the mechanical models show the same structure as the field a concentration of cracks predominantly at the top rather than on the forelimbs of the scarps in the field case extension begins as soon as a discrete scarp forms with progressive shortening the scarp height increases producing a broadening of the zone in extension the numerical models show that this broadening stabilizes when a maximum in the scarp height is reached to produce concentration of the extension on top of the scarps the reverse fault needs to be weak 10 the models suggest that distribution of this extensional zone depends on the cross sectional geometry of the fault and on the location of the detachment at depth the main mechanism that produces extension on the top of the reverse scarp is stretching of the topographic surface by folding of the hanging wall at the tip of the fault zone

the mw 8 0 antofagasta northern chile earthquake of 30 july 1995 a precursor to the end of the large 1877 gap abstract an m w 8 0 earthquake occurred on 30 july 1995 in the antofagasta region northern chile the main rupture corresponding to thrust faulting developed from 10 to 50 km in depth along the subduction interface between the nazca and the south american plates the 1995 earthquake took place just south of the large seismic gap where a great earthquake m 9 had occurred in 1877 most of the 1995 rupture was located within a local network consisting of nine short period stations that had been previously installed at the southern end of the 1877 gap and the aftershock sequence could be accurately monitored little destruction resulted from the 1995 earthquake in spite of its large size ground acceleration in antofagasta reached 29 of gravity a tsunami wave 2 to 2 5 m high was observed along the coast from mejillones to taltal one strong foreshock m w 6 2 occurred in the 1995 hypocentral region 6 months before the main event body wave modeling of broadband seismograms from the global network along with the analysis of the aftershock distribution allows us to propose a well constrained model for the whole rupture process some additional details of the rupture were obtained from an accelerometer record at antofagasta the main rupture started as a double even with thrust mechanism below the southern part of the mejillones peninsula and it propagated southward in a n200 e direction with an average velocity of 2 8 km sec it ended near the trench in normal faulting the total rupture area and seismic moment are 185 90 km 2 and 1 2 10 28 dyne cm respectively the aftershock distribution delineates a well defined rupture surface along the subduction interface the distribution of epicenters during the first 20 h of aftershock activity shows a sharp northern boundary beneath the mejillones peninsula hence the 1995 main rupture did not propagate north of the mejillones peninsula into the 1877 gap aftershocks during the following 2 weeks indicate a growth of the initial rupture zone toward the north the mechanisms of the strongest aftershocks are similar to that of the mainshock the down dip termination of the main rupture corresponds to the maximum depth 50 km of the region that had been identified as the locked part of the subduction interface from the analysis of the microseismicity recorded by the local network prior to the 1995 event a well constrained dislocation model is proposed for the 1995 main rupture which produces surface displacements in good agreement with available observations of coastal uplift and gps measurements the dislocation model as well as global positioning system gps measurements indicate that the 1995 earthquake generated e w extension in the coastal region of antofagasta the atacama fault located 40 to 50 km above the 1995 main rupture showed small fresh surface ruptures near sierra remiendos 70 km to the sse of antofagasta with a maximum vertical offset of 20 cm this offset corresponds to normal faulting which is in agreement with the e w co seismic extension the mejillones peninsula appears to be the surface expression of a barrier that interrupted the propagation of the 1995 rupture to the north into the region of the 1877 gap modeling of static stress changes induced by the antofagasta earthquake indicates an increase in compressive stresses along a direction transverse to the trench immediately to the north of the 1995 rupture surface thus the chances for the reactivation of the 1877 gap after this event are greater now

analysis of soil surface component patterns affecting runoff generation an example of methods applied to mediterranean hillslopes in alicante spain abstract spatial patterns of soil surface components vegetation rock fragments crusts bedrock outcrops etc are a key factor determining hydrological functioning of hillslopes a methodological approach to analyse the patterns of soil surface components at a detailed scale is proposed in this paper the methods proposed are applied to two contrasting semi arid mediterranean hillslopes and the influence of soil surface component patterns on the runoff response of the slopes was analysed a soil surface components map was derived from a high resolution photo mosaic obtained in the field by means of a digital camera rainfall simulation experimental data were used to characterise the hydrological behaviour of areas with a specific pattern of soil surface components by means of the parameters of the horton equation plot runoff data were extrapolated at the hillslope scale based on the soil surface component maps and their hydrological characterisation the results show that in both slopes runoff generation is concentrated up and downslope with a water accepting area in the centre of both slopes disrupting the hydrological connectivity at the slope scale this reinfiltration patch at the centre of the slope is related to the type of soil surface component and its spatial pattern herbaceous vegetation and on top rock fragments increase the infiltration capacity of soils at the centre of the slope in contrast embedded rock fragments rock outcrops as well as crusted surfaces located in the upper and lower slopes favour runoff generation in these areas in addition a general pattern of water contribution areas downslope is apparent on both slopes the south facing slope shows a higher hydrological connectivity and more runoff 55 of the surface of the south facing slope produces runoff at the end of a 1 hour rainfall event and 17 3 of the surface is covered by a runoff depth between 0 5 and 1 mm while on the north facing slope only 38 of the surface produces runoff under the same conditions longitudinal connectivity of runoff is higher at the south facing slope where more runoff generating surfaces appear and where the vegetation pattern favours the connectivity of bare areas

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

the mw 7 7 tocopilla earthquake of 14 november 2007 at the southern edge of the northern chile seismic gap rupture in the deep part of the coupled plate interface the slip distribution of the mw 7 7 tocopilla earthquake was obtained from the joint inversion of teleseismic and strong motion data rupture occurred as underthrusting at the base of the seismically coupled plate interface mainly between 35 and 50 km depth from the hypocenter located below the coast 25 km south of the town of tocopilla the rupture propagated 50 km northward and 100 km southward overall the slip distribution was dominated by two slip patches one near the hypo center and the other 70 km to the south where slip reached its maximum value 3 m an additional branch of moderate slip propagated at shallower depth toward the west near the northern tip of the mejillones peninsula rupture velocity remained close to 2 8 km sec with a total rupture duration of 45 sec the first 2 weeks of aftershocks located with a local seismic network display a strong correlation with the slip distri bution the 2007 rupture ended below the mejillones peninsula where the 1995 an tofagasta rupture also ended ruegg et al 1996 delouis et al 1997 pritchard et al 2006 this corroborates the role of barrier played by this structure the downdip end of the seismically coupled zone at 50 km depth evidenced by previous studies for the 1995 event is also confirmed the 2007 tocopilla earthquake contributed only mod erately to the rupturing of the great northern chile seismic gap which still has the capacity for generating a much larger underthrusting event

nonlinearity of ecogeomorphic processes along mediterranean arid transect the study was conducted along a climatic transect extending from the judaean mountains mean annual rainfall 700 mm annual mean temperature 17 c to the dead sea mean annual rainfall 100 mm annual mean temperature 23 c a high correlation was found between climatic conditions and factors and processes of the ecogeomorphological system the values of certain factors and processes such as soluble salt content and overland flow increase with increasing aridity whereas those of others such as soil organic matter content clay content aggregate size and stability and infiltration rate diminish with increasing aridity these trends express the long term effect of the prevailing mean climatic conditions in the research stations conditions that led to the development of various types of soil and of plant communities it was also found that for many of the factors and processes examined such as organic matter content salt concentration aggregate stability infiltration rate and overland flow yield the rates of change with respect to position along the transect are not linear and that a climatic threshold value exists in the zone with a mean annual rainfall of about 300 mm and in which the p t ratio is about 17 which creates a sharp boundary between arid and mediterranean ecogeomorphological systems while in arid systems erosion occurs mainly through physical mechanical processes under mediterranean systems it is governed mainly by chemical and biological processes the significance of the existence of a sharp boundary between the arid and the mediterranean zones is that even a relatively slight increase in the annual mean temperature and or a slight decrease in the mean annual rainfall is liable to shift the boundary towards the mediterranean zone and accelerate desertification processes

deriving indicators of soil degradation from soil aggregation studies in southeastern spain and southern france soil degradation is perceived as a major threat in the mediterranean region due to changes in land use and possible future climate change soil aggregation parameters are used here to demonstrate their potential as a key indicator for land degradation studies the monitoring of these indicators offers a means of establishing the vulnerability and resilience of geo ecosystems soil aggregation stability and distribution were studied on soils with an open shrubby vegetation cover from several places in southeastern spain and southern france by applying drop tests and determining aggregate size distributions aspect and vegetation cover were incorporated in the soil sampling several indices were derived from these analyses to indicate the degree of soil aggregation this was done by referencing to a base level of aggregation bare soil aggregation it was found that soil aggregates were more stable and were often coarser under vegetation when compared to their immediate surrounding bare areas a similar slightly less clear effect was noted on n facing exposed slopes when compared to s facing exposed slopes long term changes were found by studying cultivated land abandoned fields and land covered by semi natural vegetation on comparable substrate and comparable land units it is clear that soil aggregation and aggregate stability increases with time years it is argued that soil aggregation indices can be used as a key indicator for degradation processes at a fine scale with implications for runoff and sediment generating processes at the hillslope scale

using uplifted holocene beach berms for paleoseismic analysis on the santa maria island south central chile major earthquakes m 8 have repeatedly ruptured the nazca south america plate interface of south central chile involving meter scale land level changes earthquake recurrence intervals however extending beyond limited historical records are virtually unknown but would provide crucial data on the tectonic behavior of forearcs we analyzed the spatiotemporal pattern of holocene earthquakes on santa maria island smi 37 degrees s located 20 km off the chilean coast and approximately 70 km east of the trench smi hosts a minimum of 21 uplifted beach berms of which a subset were dated to calculate a mean uplift rate of 2 3 0 2 m ky and a tilting rate of 0 022 0 002 degrees ky the inferred recurrence interval of strandline forming earthquakes is similar to 180 years combining coseismic uplift and aseismic subsidence during an earthquake cycle the net gain in strandline elevation in this environment is similar to 0 4 m per event

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

active faulting in northern chile ramp stacking and lateral decoupling along a subduction plate boundary two large features parallel to the coastline of northern chile have long been suspected to be the sites of young or active deformation 1 the 700 km long coastal scarp with average height above sea level of about 1000 m 2 the atacama fault zone that stretches linearly for about 1100 km at an average distance of 30 50 km from the coastline new field observations combined with extensive analysis of aerial photographs demonstrate that both the coastal scarp and the atacama fault are zones of quaternary and current fault activity little degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes m 7 8 normal fault offsets observed in marine terraces in the coastal scarp at mejillones peninsula require tectonic extension roughly orthogonal to the compressional plate boundary strike slip offsets of drainage observed along the salar del carmen and cerro moreno faults atacama fault system imply left lateral displacements nearly parallel to the plate boundary the left lateral movement observed along the atacama fault zone may be a local consequence of e w extension along the coastal scarp but if also found everywhere along strike left lateral decoupling along the atacama fault zone would be in contradiction with the right lateral component of nazca south america motion predicted by models of present plate kinematics clockwise rotation with left lateral slicing of the andean orogen south of the arica bend is one way to resolve this contradiction the coastal scarp and the atacama fault zone are the most prominent features with clear traces of activity within the leading edge of continental south america the great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth we interpret the coastal scarp to be a west dipping normal fault or flexure and propose that it is located over an east dipping ramp stack at the subduction interface the similar flexure at the western edge of the altiplano may have the same origin ramp stacking along the subduction zone a mechanism disregarded so far may be an important thickening process in the andes and perhaps the basic cause of the uplift of the altiplano

neogene climate change and uplift in the atacama desert chile the relationship between andean uplift and extreme desiccation of the west coast of south america is important for understanding the interplay between climate and tectonics in the central andes yet it is poorly understood here we use soil morphological char acteristics salt chemistry and mass independent fractionation anomalies 17 o values in dated paleosols to reconstruct a middle miocene climatic transition from semiaridity to extreme hyperaridity in the atacama desert paleosols along the southeastern margin of the calama basin change from calcic vertisols with root traces slickensides and gleyed horizons to an extremely mature salic gypsisol with pedogenic nitrate we interpret this transition which occurred between 19 and 13 ma to represent a change in precipitation from 200 mm yr to 20 mm yr this drastic reduction in precipitation likely resulted from uplift of the central andes to elevations 2 km the uplift blocked moisture from the south american summer monsoon from entering the atacama the mid miocene gyp sisol with pedogenic nitrate is located at elevations between 2900 and 3400 m in the cal ama basin significantly higher than modern nitrate soils which occur below 2500 m modern and quaternary soils in this elevation zone contain soil carbonate and lack ped ogenic gypsum and nitrate we infer that 900 m of local surface uplift over the past 10 m y displaced these nitrate paleosols relative to modern nitrate soils and caused a return to wetter conditions in the calama basin by decreasing local air temperatures and creating an orographic barrier to pacific air masses

crustal extensional faulting triggered by the 2010 chilean earthquake the pichilemu seismic sequence 1 we report a sequence of crustal quakes that began after the mw 8 8 thrust subduction maule earthquake that affected the central chile margin on 27 february 2010 this activity lasted by several months having the most important events on 11 march 2010 mw 6 9 and mw 7 0 with normal focal mechanisms seismicity shows a rupture oriented along a nw striking and sw dipping normal fault from the surface down to the interplate contact seismicity can be correlated with neotectonics extensional structures similarly oriented in the region which have coexisted with nne ssw reverse faults since the late pliocene even though both have older periods of activity since the paleozoic this crustal rupture would have been triggered by the high coulomb stress change produced by the maule earthquake enhanced by likely fluid presence along weakened zones of the forearc crust as evidenced by high vp vs ratio the occurrence of relevant neotectonic activity in coincidence with short term deformation suggests a relationship with long term tectonic features of this region which would have been acting as a barrier during the interseismic period increasing the strain accumulation and triggering contractional faulting in the crust as well as producing high slip patches during great subduction ruptures favoring triggering of crustal extensional faulting crustal faulting in pichilemu suggests that this kind of events should be considered in seismic hazard analysis despite the absence of historical crustal seismic activity before the maule earthquake

pervasive cracking of the northern chilean coastal cordillera new evidence for forearc extension despite convergence across the strongly coupled seismogenic interface between the south american and nazca plates the dominant neotectonic signature in the forearc of northern chile is arc normal extension we have used 1 m resolution ikonos satellite imagery to map nearly 37 000 cracks over an area of 500 km2 near the salar grande 21 s these features which are best preserved in a ubiquitous gypcrete surface layer have both nontectonic and tectonic origins however their strong preferred orientation perpendicular to the plate convergence vector suggests that the majority owe their formation to approximate east west extension associated with plate boundary processes such as interseismic loading coseismic and postseismic strain and long term instability resulting from subduction erosion similar structures were formed during or shortly after the 1995 mw 8 0 earthquake near the city of antofagasta south of salar grande and in conjunction with the 2001 mw 8 2 8 4 arequipa peru event cracks such as these may form in other forearcs but remain largely unexposed because of vegetative cover or marked fluvial erosion factors that are absent in northern chile as a result of its hyperarid climate

co seismic slip from the 1995 july 30 mw 8 1 antofagasta chile earthquake as constrained by insar and gps observations summary we analyse radar interferometric and gps observations of the displacement field from the 1995 july 30 mw 8 1 antofagasta chile earthquake and invert for the distribution of slip along the co seismic fault plane using a fixed fault geometry we compare the use of singular value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable separate inversions using only gps data only insar data from descending orbits and insar data from both ascending and descending orbits without the gps data illustrate the complimentary nature of gps and the presently available insar data the gps data resolve slip near gps benchmarks well while the insar provides greater spatial sampling the combination of ascending and descending insar data contributes greatly to the ability of insar to resolve the slip model thereby emphasizing the need to acquire this data for future earthquakes the rake distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions although significant differences do exist gps data projected in the radar line of sight los and corresponding insar pixels have a root mean square rms difference of about 3 cm comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm our inversion and previous results reveal that the location of slip might be influenced by the 1987 mw 7 5 event our analysis further reveals that the 1995 slip distribution was affected by a 1988 mw 7 2 event and might have influenced a 1998 mw 7 0 earthquake that occurred downdip of the 1995 rupture our slip inversion reveals a potential change in mechanism in the southern portion of the rupture consistent with seismic results predictions of the satellite los displacement from a seismic inversion and a joint seismic gps inversion do not compare favourably with the insar observations

great earthquakes and subduction along the peru trench subduction along the peru trench between 9 and 15 s involves both large interplate underthrusting earthquakes and intraplate normal fault earthquakes the four largest earthquakes along the peru trench are from north to south the 1970 m 7 9 intraplate normal fault earthquake and the interplate underthrusting earthquakes in 1966 m 8 0 1940 m 8 and 1974 m 8 0 we have studied the rupture process of these earthquakes and can locate spatial concentrations of moment release through directivity analysis of source time functions deconvolved from long period p wave seismograms the 1966 earthquake has a source duration of 45 s with most of the moment release concentrated near the epicenter two intraplate normal fault events occurred in 1963 m 6 7 and 7 0 at the down dip edge of the 1966 dominant asperity the 1940 earthquake is an underthrusting event with a simple source time function of 30 s duration that represents the rupture of a single asperity near the epicenter the 1974 earthquake has a source duration of 45 50s and two pulses of moment release this earthquake has a bilateral rupture with the first pulse of moment release located northwest of the epicenter and the second pulse of moment release located southeast of the epicenter both pulses of moment release occur on the northern half of the aftershock area the 1970 earthquake is one of the largest intraplate normal fault earthquakes to occur in a subduction zone and has a moment release comparable with many large underthrusting events the aftershocks for the 1970 earthquake form two distinct clusters the smaller cluster near the epicenter has focal mechanisms characterized by down dip tension but the second aftershock cluster located 80 km southeast of the epicenter has focal mechanisms characterized by down dip compression the p waves for the main shock can be modeled as two sources with different focal mechanisms and depths similar to the two clusters of aftershocks the first event has a down dip tensional focal mechanism and is followed 40 s later by a distinct second event located 80 km southeast of the epicenter with a down dip compressional focal mechanism and a somewhat shallower depth than the first event the observable directivity indicates that the second source is located at the second cluster of aftershocks that have down dip compressional focal mechanisms the occurrence of both down dip tensional and compressional focal mechanisms may be explained by extreme unbending stresses associated with the anomalous slab geometry the unusually large size of the 1970 earthquake may also be related to the subduction of the mendana fracture zone the historic earthquake record along the peru trench indicates that the previous event in 1746 was much larger than any of the three underthrusting earthquakes this century the 1746 earthquake may have ruptured the entire segment in a multiple asperity earthquake thus the mode of rupture along the peru coast has changed between successive earthquake cycles

geodetic teleseismic and strong motion constraints on slip from recent southern peru subduction zone earthquakes we use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 november 1996 m w 7 7 and 23 june 2001 m w 8 5 southern peru subduction zone earthquakes as well as two large aftershocks following the 2001 earthquake on 26 june and 7 july 2001 we use all available data in our inversions gps interferometric synthetic aperture radar insar from the ers 1 ers 2 jers and radarsat 1 satellites and seismic data from teleseismic and strong motion stations our two dimensional slip models derived from only teleseismic body waves from south american subduction zone earthquakes with m w 7 5 do not reliably predict available geodetic data in particular we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic teleseismic and two strong motion stations or geodetic insar and gps data the differences might be related to postseismic deformation or more likely the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties the earthquakes studied here follow the pattern of earthquake directivity along the coast of western south america north of 5 s earthquakes rupture to the north south of about 12 s directivity is southerly and in between earthquakes are bilateral the predicted deformation at the arequipa gps station from the seismic only slip model for the 7 july 2001 aftershock is not consistent with significant preseismic motion

overland flow generation mechanisms affected by topsoil treatment application to soil conservation abstract hortonian overland flow is responsible for significant amounts of soil loss in mediterranean geomorphological systems restoring the native vegetation is the most effective way to control runoff and sediment yield during the seeding and plant establishment vegetation cover may be better sustained if soil is amended with an external source four amendments were applied in an experimental set of plots straw mulching sm mulch with chipped branches of aleppo pine pinus halepensis l pm terracottem hydroabsorbent polymer hp and sewage sludge ru plots were afforested following the same spatial pattern and amendments were mixed with the soil at the rate 10 mg ha 1 this research demonstrates the role played by the treatments in overland flow generation mechanism on one hand the high macroporosity of sm and pm together with the fact that soil moisture increased with depth explains weak overland flow and thus low sediment yield due to saturation conditions therefore regarding overland flow and sediment yield ru behaves similarly to sm and pm on the other hand when hp was applied overland flow developed quickly with relatively high amounts this together with the decrease downward in soil moisture along the soil profile proved that mechanisms of overland flow are of the hortonian type

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

paleogene calcareous nannoplankton biostratigraphy of northwestern europe abstract the classic paleogene stages thanetian cuisian lutetian bartonian ludian and stampian defined in the epicontinental deposits of the anglo paris basin s are placed within a standard biostratigraphic framework based on an analysis of their calcareous nannoplankton floras relatively precise biostratigraphic correlations can be made with some chronostratigraphic units e g lutetian while biostratigraphic resolution of others e g ludian is limited important hiatuses are recognized between certain chronostratigraphic units only the base of the lutetian late np14 and bartonian mid np16 stages can be precisely determined in terms of calcareous nannoplankton zones with the recent study of the magnetic polarity history of the paleogene of southern england and recent advances in magnetobiostratigraphic correlations in deep sea cores it is possible to interpret the paleogene history of the anglo paris basin s in a synoptic global framework in which paleomagnetic stratigraphy provides the chronologic and eustatic variations the graphic units of northwestern europe within rather than at the boundaries of i e at dynamic element redefinition of the boundaries of the standard paleogene chronostratigraphic unconformities eustatically controlled depositional cycles would result in more precise correlations in terms of standard calcareous nannoplankton biostratigraphy

the 2010 mw 8 8 maule megathrust earthquake of central chile monitored by gps large earthquakes produce crustal deformation that can be quantified by geodetic measurements allowing for the determination of the slip distribution on the fault we used data from global positioning system gps networks in central chile to infer the static deformation and the kinematics of the 2010 moment magnitude m w 8 8 maule megathrust earthquake from elastic modeling we found a total rupture length of 500 kilometers where slip up to 15 meters concentrated on two main asperities situated on both sides of the epicenter we found that rupture reached shallow depths probably extending up to the trench resolvable afterslip occurred in regions of low coseismic slip the low frequency hypocenter is relocated 40 kilometers southwest of initial estimates rupture propagated bilaterally at about 3 1 kilometers per second with possible but not fully resolved velocity variations

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

the influence of geomorphological position and vegetation cover on the erosional and hydrological processes on a mediterranean hillslope soil erosion and runoff rates are assumed to be highly dependent on slope position however little knowledge exists about the hydrogeomorphological processes at the pedon scale that support this idea in order to assess the hydrological and erosional behaviour of soils at different slope positions simulated rainfall experiments 55 mm was applied during one hour were carried out on a south facing slope with underlying limestone in south east spain in the mean terms the erosion rates 9 g m2 hr 1 and the runoff coefficients 12 were very low at the scale of measurement 0 25 m2 the slope position does not affect erosion rates when the measurements are carried out under extreme dry conditions during summer the low runoff rates found in summer under thunderstorms of high intensity 5 year return period and the runon into surfaces with higher infiltration rates resulted in no detectable direct surface runoff hortonian at the slope scale this implies that erosion as a consequence of surface overland flow will only take place during events of high magnitude 55 mm hr 1 and low frequency 5 years vegetation is the most important factor determining the soil erosion and runoff rates within the slope 1998 john wiley sons ltd

the seismic cycle at subduction thrusts insights from seismo thermo mechanical models 1 the underestimation of the size of recent megathrust earthquakes illustrates our limited understanding of their spatiotemporal occurrence and governing physics to unravel their relation to associated subduction dynamics and long term deformation we developed a 2 d continuum viscoelastoplastic model that uses an eulerian lagrangian finite difference framework with similar on and off fault physics we extend the validation of this numerical tool to a realistic subduction zone setting that resembles southern chile the resulting quasi periodic pattern of quasi characteristic m8 m9 megathrust events compares quantitatively with observed recurrence and earthquake source parameters albeit at very slow coseismic speeds without any data fitting surface displacements agree with gps data recorded before and during the 2010 m8 8 maule earthquake including the presence of a second order flexural bulge these surface displacements show cycle to cycle variations of slip deficits which overall accommodate 5 of permanent internal shortening we find that thermally and stress driven creep governs a spontaneous conditionally stable downdip transition zone between temperatures of 350 c and 450 c ruptures initiate above it and below the forearc moho propagate within it interspersed by small intermittent events and arrest below it as ductile shearing relaxes stresses ruptures typically propagate upward along lithological boundaries and widen as pressures drop the main thrust is constrained to be weak due to fluid induced weakening required to sustain regular subduction and to generate events with natural characteristics fluid pressures of 75 99 of solid pressures the agreement with a range of seismological geodetic and geological observations demonstrates the validity and strength of this physically consistent seismo thermo mechanical approach

invited review paper neogene to quaternary tectonics of the coastal cordillera northern chile abstract the extreme aridity of the northern chilean coastal cordillera enables the complete preservation of permanent deformation related to the coupling between nazca and south america the region between antofagasta and arica is characterized by four types of late cenozoic structures ew striking reverse faults ns striking normal faults sparse wnw and nnw striking right lateral strike slip faults and unimodal and bimodal populations of surface cracks the ew reverse faults occur only between 19 and 21 40 s latitude and have been active since at least 6 ma to present a march 2007 earthquake demonstrates that this deformation can occur during the interseismic phase of the plate boundary seismic cycle the ns normal faults are most abundant near antofagasta and mejillones and diminish in significance northward several of these faults in both the antofagasta and the salar grande area have been reactivated as reverse faults causing minor topographic inversion we suggest that normal faults move during both interseismic and coseismic deformation and are fundamentally very weak surface cracks are ubiquitous throughout the region and form by both non tectonic and tectonic mechanisms a significant proportion forms during coseismic deformation and thus may be used to identify long lived rupture segments on the plate boundary overall forearc deformation is very slow with permanent strain rates of 1 5 nstrain year and fault slip rates less than 0 5 mm year

high interseismic coupling in the eastern makran pakistan subduction zone estimating the extent of interseismic coupling along subduction zone megathrusts is essential for quantitative assessments of seismic and tsunami hazards up to now quantifying the seismogenic potential of the eastern makran subduction zone at the northern edge of the indian ocean has remained elusive due to a paucity of geodetic observations furthermore non tectonic processes obscure the signature of accumulating elastic strain historical earthquakes of magnitudes greater than 7 have been reported in particular the 1945 mw 8 1 earthquake resulted in a significant tsunami that swept the shores of the arabian sea and the indian ocean a quantitative estimate of elastic strain accumulation along the subduction plate boundary in eastern makran is needed to confront previous indirect and contradictory conclusions about the seismic potential in the region here we infer the distribution of interseismic coupling on the eastern makran megathrust from time series of satellite interferometric synthetic aperture radar insar images acquired between 2003 and 2010 applying a consistent series of corrections to extract the low amplitude long wavelength deformation signal associated with elastic strain on the megathrust we find high interseismic coupling i e the megathrust does not slip and elastic strain accumulates in the central section of eastern makran where the 1945 earthquake occurred while lower coupling coincides spatially with the subduction of the sonne fault zone the inferred accumulation of elastic strain since the 1945 earthquake is consistent with the future occurrence of magnitude 7 earthquakes and we cannot exclude the possibility of a multi segment rupture mw 8 however the likelihood for such scenarios might be modulated by partitioning of plate convergence between slip on the megathrust and internal deformation of the overlying actively deforming accretionary wedge

sequence stratigraphic interpretations from palynofacies dinocyst and lithological data of upper eocene lower oligocene strata in southern mississippi and alabama u s gulf coast abstract this paper presents new information on the sequence stratigraphy of the upper eocene lower oligocene strata in southern mississippi and alabama based on palynological and lithological data from five sections by integrating lithological characteristics with palynofacies assemblages several dinocyst paleoecological groups the deflandrea group and the abundance of reworked dinocysts in samples paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area we identified a maximum flooding surface in the middle of the shubuta clay formation in southern mississippi and dated it as latest eocene in southern alabama the eocene oligocene boundary was placed within a condensed section representing about 0 19 ma and it coincided with the shubuta clay vicksburg group contact this condensed section is equivalent to the accumulation of the upper shubuta and red bluff formations in southern mississippi the forest hill mint spring contact which has been interpreted as a sequence boundary that merged with a transgressive surface does not correlate with the tejas a ta 4 3 4 4 sequence boundary of haq et al 1988 the pachuta marl and lower shubuta clay formations are constituents of a late eocene transgressive systems tract in southern mississippi but this systems tract extended to the shubuta clay vicksburg group contact in southern alabama the overlying early oligocene highstand systems tract consisted of the upper shubuta in mississippi and the red bluff bumpnose forest hill formations a thin sandstone in the mint spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern mississippi section in general the mint spring marl and marianna limestone constituted a transgressive systems tract

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

abrupt increase in the coastal uplift and earthquake rate since 40 ka at the northern chile seismic gap in the central andes abstract over long term geological scales the position and vertical movements of the coast are considered to be among the most important effects resulting from first order plate tectonics interactions in the subduction zones however the relationship between short term vertical deformation driven by earthquakes and long term coastal uplift in the andean subduction contact of northern chile has not been thoroughly elucidated to date based on precise radiocarbon dating and geomorphological analysis of littoral deposits in the mejillones peninsula at the southern edge of the major northern chile seismic gap we report a drastic increase in coastal uplift since marine isotope stage 3 mis 3 with uplift rates one order of magnitude more rapid than previously in the late pleistocene geomorphological evidence supplied by holocene littoral deposits and marine terraces shows that this tectonic regime could be operating at present together with new geodetic data following the 2007 mw7 7 tocopilla event these observations indicate that coastal uplift results from cumulative coseismic vertical displacement with low subsequent interseismic subsidence recovery driven by both deep moderate and large megathrust earthquakes we suggest that the accelerated coastal uprising and earthquake rate over the past 44 ka demonstrated in this work results from changes involving the entire subduction contact between the nazca and south american plates in northern chile

the giant coastal landslides of northern chile tectonic and climate interactions on a classic convergent plate margin abstract documented for the first time are an extensive suite of late neogene giant terrestrial coastal landslides along the classic convergent margin of western south america 18 to 24 south these are remarkable in terms of their unusual abundance and atypical setting such failures previously being linked with oceanic volcanic edifices or over steepened glaciated coastlines located within the hyper arid coastal cordillera of the atacama desert of northern chile we report the presence of more than 60 individual large scale landslides with individual volumes up to 9 km 3 developed over a horizontal coastline distance of some 650 km these landslides were emplaced as a combination of rock avalanches and multiple rotational failures the majority terminated directly into the pacific likely generating significant tsunami hazard to the chilean and south peruvian coastline in a region which is today considered to be part of a notorious seismic gap the proliferation and scale of these late neogene giant landslides in this actively uplifting hyperarid terrain suggests they are the main geomorphic agent for relief reduction probably triggered by megathrust earthquakes and potentially providing a unique palaeoseismic archive the temporal and spatial distribution of these giant landslides corresponds with a period of surface steepening of the forearc wedge in the central andes and south to north differential uplift associated with factors such as aseismic ridge subduction the resulting surface gradient increases combined with the persistent climatic aridity of the region have served to limit effective relief reducing geomorphic processes in this oversteepened terrain to large scale landsliding the phenomena documented here geospatially link previously recognised large scale slope failures from the off shore environment and higher altitude areas of the andean forearc suggesting that large scale landsliding is capable of transferring sediment on a regional scale to the off shore peru chile trench this has implications for the friction of the subducting nazca plate and associated seismicity and uplift

evidence for active landscape evolution in the hyperarid atacama from multiple terrestrial cosmogenic nuclides the atacama desert is one of the driest places on earth multiple lines of evidence show that the atacama has been hyperarid since at least the late miocene among these are cosmic ray exposure ages indicating that individual clasts on some surfaces have been preserved for 9 ma and possibly since the oligocene although these remarkably old ages indicate slow landscape evolution it is not clear whether this pace is characteristic of the entire atacama or only of specific regions landforms or landscape elements to address this question we measured cosmogenic 10be 26al and 21ne from a wide variety of landscape elements in a transect across the central atacama where modern precipitation is at an extreme minimum but where the concentration of cosmogenic nuclides in stable landscape elements has not previously been recorded we find that the hyperarid core of the central atacama has substantially slower erosion rates than its eastern and western margins however even the driest part of this transect has erosion rates comparable to those of other deserts ranging from 0 2 0 4 m ma the most stable landscape elements are boulder fields with exposure ages of 1 5 2 6 ma the vast majority of samples in the central atacama desert however have cosmogenic nuclide concentrations corresponding to ages 5 ma documented elsewhere in the atacama were not found in our area and appear to be limited to exceptionally stable boulders or cobbles in either the northern or southern extremes of the atacama desert we suggest that the central atacama has been subject to episodic pliocene and pleistocene rainfall and geomorphic activity perhaps due to intrusion of pacific moisture

normal and reverse faulting driven by the subduction zone earthquake cycle in the northern chilean fore arc 1 despite its location in a convergent tectonic setting the coastal cordillera of northern chile between 21 s and 25 s is dominated by structures demonstrating extension in the direction of plate convergence in some locations however normal faults have been reactivated as reverse faults complicating the interpretation of long term strain in order to place these new observations in a tectonic context we model stress changes induced on these faults by the subduction earthquake cycle our simulations predict that interseismic locking on the plate boundary encourages normal slip on fore arc faults which may result from elastic rebound due to interplate earthquakes or from seismic or aseismic motion that takes place within the interseismic period conversely stress generated by strong subduction zone earthquakes such as the 1995 mw 8 1 antofagasta event provides a mechanism for the reverse reactivation we document here upper plate fault slip in response to the low magnitude stress changes induced by the subduction earthquake cycle suggests that the absolute level of stress on these faults is very low furthermore seismic hazard analysis for northern chile requires consideration of not only the plate boundary earthquake cycle but also the cycle on fore arc faults that may or may not coincide with the interplate pattern though the relationships between permanent strain and deformation calculated using elastic models remain unclear the compatibility of modeled stress fields with the distribution of fore arc faulting suggests that interseismic strain accumulation and coseismic deformation on the subduction megathrust both play significant roles in shaping structural behavior in the upper plate

eco geomorphological system response variability to the 2004 06 drought along a climatic gradient of the littoral betic range southern spain abstract one of the main characteristics of the mediterranean climate is the high frequency of droughts which last for a year or more and the appearance of dry spells within the wet season the littoral betic range in the south of the iberian peninsula shows a significant climatic gradient from the straits of gibraltar 1600 mm year 1 to the cabo de gata 150 mm year 1 these differences in climatic conditions result in variations in the elements of the eco geomorphological system at the hillslope scale this study aimed to analyse the immediate consequences of a two year drought period 2004 06 on several elements of the mediterranean eco geomorphological system on three hillslopes under different climatic conditions sub humid dry mediterranean and semi arid the soil water content the pattern of vegetation and some soil properties organic matter content aggregate stability and permeability were analysed before nov 2003 and during nov 2005 the drought period the most important findings were i a reduction in the soil water content which reached values below the wilting point in the wet seasons affecting negatively the water available for vegetation especially in the wettest sites ii a reduction in vegetation cover and the number of plants especially on semi arid field sites iii changes in the organic matter content which aggravate the loss of stability of soil aggregates a process seen more clearly under more arid conditions and iv a reduction of soil permeability in all situations in the climate gradient studied which supposes a priori an increase in erosive processes due to surface runoff these results indicate increased vulnerability of the eco geomorphological system because of the rainfall drought situation

soil erosion and hydrology of the western mediterranean badlands throughout rainfall simulation experiments a review abstract rainfall simulation experiments are widely used in geomorphological research in badland areas this technique contributed significantly to our understanding of badland geomorphology in the mediterranean belt due to the different types of simulated rainfall applied and the variable size of the plots a review of the state of the art is necessary this study confirmed that rainfall simulations are well suited to i analyse runoff infiltration processes and sediment detachment within badlands and ii to establish the factors determining the hydrological and erosion response at interrill scale in badland areas the hydrological response of badlands is characterized by rapid responses low to moderate infiltration rates ranging from close to 0 to 55 mm h 1 and high runoff coefficients i e 60 positive relationships are observed between antecedent soil moisture content and rainfall intensity on the one hand and runoff coefficients on the other sediment concentration and soil detachment rates are among the highest measured on the mediterranean region i e up to 84 8 g l 1 and 4722 4 g m 2 h 1 results show that rainfall intensity runoff coefficient and slope angle have a positive influence on sediment concentration and sediment detachment in the case of rock fragment cover its influence is variable according to the soil cover percentage rainfall simulations increase our understanding of the temporal and spatial variability of the soil erosion processes however rainfall simulation provides mostly qualitative rather than quantitative information because of the small plot size and the simulated rainfall characteristics due to facility for repeating experiments and recording a high quantity of data in short time however this method allows the comparison amongst different environments and soil conditions as the rainfall properties can be reproduced

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

late pliocene age for the atacama desert implications for the desertification of western south america the atacama desert forms one of the major hyperarid deserts of the world previous studies suggest that desertification commenced at 14 ma during global climate desiccation sedimentologic data from middle miocene to upper pliocene successions in the modern atacama desert indicate that a semiarid climate persisted from 8 to 3 ma punctuated by a phase of increased aridity at ca 6 ma as such hyperaridity did not commence until the late pliocene implications are 1 that the rain shadow generated by the andean cordillera has had a minor influence on climate change and 2 that the upwelling north flowing cold humboldt current although important in establishing the generally arid climate of western south america did not control the shift to hyperaridity the formation of the hyperarid atacama desert in the late pliocene accompanied the development of the current phase of aridification in the sahara and namib deserts and is attributed to a phase of global climate cooling

recent crustal deformation in the antofagasta region northern chile and the subduction process new neotectonic observations along with a detailed aerial photograph analysis allow a new interpretation of the recent tectonic behaviour of the outer forearc in northern chile between 22 5 s and 24 5 s antofagasta region both the coastal cordillera and the mejillones peninsula are under e w extension normal faults dipping east with an almost n s orientation are predominant large scale neogene to recent deformation is characterized by vertical uplift and subsidence related to normal faulting recent kinematics along the atacama fault system including the atacama fault itself are controlled by the regional extensional stress regime and the predominant component of recent displacement along the atacama fault is vertical normal however strike slip components are also observed but with moderate offsets no larger than one to two tens of metres the sense of shear and the ratio between vertical and horizontal offsets vary coherently with the fault azimuth compatible with e w extension oblique slip faulting with normal and left lateral offsets of similar amplitude is observed on the most northeasterly oriented segment of the atacama fault this small left lateral component of displacement and the strike slip motion predicted by models of strain partitioning of the convergence along the atacama fault are in opposite senses this occurs because the stress regime in the coastal region is not compressional but extensional very fresh recent ruptures are numerous especially between 23 s and 24 s and provide clear indications of the occurrence of moderate to large continental earthquakes during the late quaternary as pointed out by several authors indirect lines of evidence suggest active subduction erosion and underplating along the margin of northern chile we propose that part of the long term extension is due to the broad scale flexure of the outer forearc this flexure may be controlled by offshore subsidence caused by subduction erosion near the trench and by onshore uplift related to the underplating of eroded low density material beneath the coastal cordillera neotectonic observations show that the state of stress in the outer forearc remains extensional in a deviatoric sense in the long term however it is proposed that the state of stress has a strong time dependent component which is intimately linked to the subduction seismic cycle the mw 8 0 antofagasta earthquake of 1995 july 30 showed that large subduction earthquakes produce e w extension in the coastal region the overall e w deviatoric extension in the outer forearc should be reduced by interseismic contraction in the period separating two subduction earthquakes this reduction means that continental faults will remain locked and aseismic in the interseismic period of the subduction cycle in agreement with microseismic observations which indicate an absence of shallow crustal seismicity we assume that the amount of extension produced by subduction earthquakes in the coastal area is larger than the cumulative interseismic contraction this occurs because the displacement field generated by subduction earthquakes is concentrated in the outer forearc the e w extension should grow over prepeated subduction seismic cycles and lead to large continental earthquakes occurring within the overriding block simultaneous with large subduction events we show new surface ruptures associated with normal faulting along the atacama fault which were most probably triggered by the 1995 antofagasta subduction earthquake

megathrust and accretionary wedge properties and behaviour in the makran subduction zone this work forms part of the nerc and esrc funded project earthquakes without frontiers and was partially supported by the nerc large grant looking inside the continents from space cp is funded by an nerc studentship the facilities of iris data services and specifically the iris data management center were used for access to waveforms related metadata and or derived products used in this study iris data services are funded through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation under cooperative agreement ear 1261681

constructing forearc architecture over megathrust seismic cycles geological snapshots from the maule earthquake region chile we present new field structural data from the chilean coastal cordillera located above the northern and central parts of the interplate contact ruptured by the a d 2010 m w 8 8 maule earthquake the northern study area contains the northwest striking pichilemu normal fault an intraplate structure reactivated after the megathrust event by crustal earthquakes up to m w 7 0 the structural style of this region is dominated by kilometer scale normal faults that have been active at least throughout the quaternary the orientations of these main faults define three structural systems 1 northeast and 2 northwest striking margin oblique faults and 3 north to north northeast striking margin parallel faults from north to south these three systems vary in their predominant occurrence starting with bimodal orientations of groups 1 and 2 followed by predominantly single north to north northeast orientations of group 3 reverse faults coexist in time and space with the normal structures but are scarce and display variable apparently random orientations the shallow crustal normal faults including the pichilemu fault show a persistent kinematic history probably spanning thousands of subduction seismic cycles though historically smaller in magnitude than those of the triggered normal faults interseismic forearc thrust events were recorded above the rupture area prior to the maule earthquake the quaternary reverse faults identified in our study regions may be preserving interseismic slow strain rate permanent deformation signature in the structural grain analogous observations along the a d 2011 tohoku earthquake rupture in japan imply that such a link between the short and long term deformation patterns of the forearc is not exclusive of the maule earthquake region

oligocene miocene age of aridity in the atacama desert revealed by exposure dating of erosion sensitive landforms the age of onset of hyperaridity in the atacama desert chile which is needed to validate geological and climatological concepts has been heretofore uncertain measurement of cosmogenic 21 ne in clasts from erosion sensitive sediment surfaces in northern chile shows that these surfaces have been barely affected by erosion since 25 ma surface exposure ages of sediment clasts give replicate values at 25 20 and 14 ma and individual values at 37 and 9 ma predominantly hyperarid conditions are required to preserve these oldest continuously exposed surfaces on earth our findings are compatible with the hypothesis that the onset of aridity in the atacama desert could be the reason for rather than the consequence of uplift of the high andes

southern peru desert shattered by the great 2001 earthquake implications for paleoseismic and paleo el nino southern oscillation records in the desert region around the coastal city of ilo the great southern peru earthquake of june 23 2001 8 2 8 4 moment magnitude produced intense and widespread ground failure effects these effects included abundant landslides pervasive ground cracking microfracturing of surficial hillslope materials collapse of drainage banks over long stretches widening of hillside rills and lengthening of first order tributary channels we have coined the term shattered landscape to describe the severity of these effects long term consequences of this landscape shattering are inferred to include increased runoff and sediment transport during postearthquake rainstorms this inference was confirmed during the first minor postearthquake rainstorm there which occurred in june and july of 2002 greater amounts of rainfall in this desert region have historically been associated with el nino events previous studies of an unusual paleoflood deposit in this region have concluded that it is the product of el nino generated precipitation falling on seismically disturbed landscapes the effects of the 2001 earthquake and 2002 rainstorm support that conclusion

runoff generation sediment movement and soil water behaviour on calcareous limestone slopes of some mediterranean environments in southeast spain abstract an interpretation of soil hydrology and erosion data obtained from limestone areas in southeast spain is presented in the framework of recent hypotheses on runoff generation mechanisms in mediterranean environments the main objective is to synthesise and harmonise the data in theoretical concepts or behavioural models of hydrological functioning of mediterranean limestone slopes for this purpose data were collected in a typical limestone area with climatic characteristics ranging from subhumid to semiarid several sites were chosen with comparable slopes vegetation and soils along a transect of 20 km to carry out several research projects the data discussed in this paper consist of information on water redistribution within the soil profiles obtained from long duration up to 5 h rainfall simulation experiments with continuous monitoring of soil moisture at different depths runoff and sediment concentration data were obtained i from rainfall simulation experiments with different antecedent soil moisture conditions and ii as natural results from open gerlach plots on runoff and sediment movement over 4 years three conceptual models of water redistribution during the infiltration process could be observed two of them imply nonuniform water redistribution within the soil profile due mainly to macropore flow caused by specific soil surface characteristics at the plot scale runoff generated in bare patches is mainly hortonian in plots with previously wetted soils or soils with high infiltration capacities the generated runoff implies the saturation of the upper soil both types of runoff are discontinuous through time and space the runoff generation mechanisms at the slope scale have been synthesised into two conceptual models a hortonian discontinuous runoff model that takes place in the most degraded slopes or during high intensity rain events and a mixed runoff generation model in less degraded slopes or in previously wet soils where infiltration excess runoff as well as saturation excess runoff can happen on the same slope in both cases slopes behave as a patchwork of runoff and runon areas the size of the runoff or runon patches is dependent on the climatological conditions these control the hydrological disconnection between different parts of the slopes hortonian and saturation runoff can both be generated and infiltrated downslope

reworked hantkenina specimens at little stave creek alabama abstract abstract the eocene oligocene boundary in mississippi and alabama has been traditionally placed between the shubuta member of the yazoo formation and the overlying red bluff formation or its carbonate facies equivalent the bumpnose formation consequently the presence of eocene planktonic foraminifers in the red bluff and bumpnose has long been attributed to reworking to test the validity of this hypothesis samples were collected on both sides of the boundary from the upper shubuta and bumpnose units at little stave creek alabama and were examined for both calcareous nannofossil and planktonic foraminiferal content the calcereous nannofossil assemblage preserved in the matrix from inside handpicked specimens of hantkenina from both units was demonstrably older than the calcareous nannofossil assemblage from the surrounding sediment thus at least some of the hantkenina specimens in both the shubuta and bumpnose are indeed reworked which not only confirms the original hypothesis regarding reworking within the red bluff and bumpnose but also indicates that the last occurrence of hantkenina the shubuta bumpnose contact and the eocene oligocene boundary in the u s gulf coast may not be equivalent