estimation of deep reservoir temperature of co2 rich springs in kangwon district south korea abstract weakly acid to neutral co 2 rich springs ph 5 5 to 6 7 with high concentrations of dissolved ions tds 419 to 3091 mg l and bicarbonate 249 to 2470 mg l occur in kangwon district south korea they are grouped into three chemical types na hco 3 ca na hco 3 and ca hco 3 the na hco 3 type waters correspond to mature or partially equilibrated waters while the other two types show the hydrochemical characteristics of immature waters in this study we examined the applicability of chemical geothermometers and multiple mineral equilibrium approach to estimate potential deep reservoir temperatures the application of silica na k and na k ca thermometers to a representative na hco 3 type water yielded a reasonable temperature estimate 115 157 c for a deep geothermal reservoir the multiple mineral equilibrium approach yielded a similar temperature estimate about 140 160 c on the other hand the ca hco 3 type waters showed a relatively low and wide range of temperature estimates about 60 130 c which suggests that their disequilibrium state is possibly due to surface water mixing we believe that deep reservoir temperatures of co 2 rich groundwaters in kangwon district can be estimated from the chemistry of na hco 3 type waters and possibly approach 140 160 c

magnetotelluric imaging of upper crustal convection plumes beneath the taupo volcanic zone new zealand 1 broadband mt magnetotelluric data were recorded that form an array of measurements at the south eastern margin of the tvz taupo volcanic zone in the central north island of new zealand these array data are used to investigate mechanisms by which the tvz s extraordinarily high heat flux is transported to the surface taken together with seismological data these mt data show compelling evidence that support a model of hydrothermal convection within the brittle upper 6 7 km part of the crust both 2 d and 3 d inversion models of these mt data show vertical low resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle ductile transition

geochemistry of thermal waters in the southern volcanic zone chile implications for structural controls on geothermal fluid composition abstract thermal waters in the southern volcanic zone svz of chile between 36 41 s were studied using major and selected trace element relationships to characterize their geochemistry formation mechanisms and to explore the influence of regional structural controls on fluid composition three sets of waters were identified based on physicochemical characteristics i nacl waters ii acid sulfate waters and iii bicarbonate hco3 waters nacl waters are the most abundant type in the studied region and their chemistry is controlled by significant water rock interaction they are characterized by an alkaline ph 7 2 9 3 generally lower temperatures avg 55 c and relatively high concentrations of cl na b as li and cs acid sulfate waters are typically associated with volcanoes and have a strong magmatic volcanic component due to the absorption of magmatic vapors they are acidic ph 892 ppm in the region and are similar in temperature 6 2 to nacl waters they have elevated concentrations of most cations ca k na mg ba sr as a result of intense shallow cation leaching due to the absorption of co2 rich volcanic vapors on the peripheries of geothermal systems the thermal waters were also characterized according to their spatial relation with the dominant fault systems of the region the nne striking intra arc liquine ofqui fault system lofs and the wnw striking andean transverse faults atf the inherent differences in fault nature between these fault systems constitutes the primary structural control influencing geothermal fluid development in the svz the chemistry of waters spatially associated with the lofs as a whole is defined by high vertical permeability networks and lack magmatic reservoir development therefore these waters tend to have higher cl b ratios and strong correlations between trace alkali metals and cl due to rapid efficient upflow pathways in contrast waters spatially associated with the atf have lower cl b ratios and show no correlation between trace alkali metals and cl due to degassing magma chambers and decreased vertical permeability the relationship between water type and structural domain in cl b ratios and trace metal behavior provides evidence that fault geometry and kinematics exert a fundamental control on geothermal fluid development in the svz of chile

along strike segmentation of the abanico basin central chile new chronological geochemical and structural constraints the andes of central chile are composed mostly of cenozoic volcanic rocks erupted during the opening and subsequent inversion of the intra arc volcano tectonic abanico basin until recently the internal segmentation of this inverted basin was poorly understood based on a combination of u pb geochronology u th he thermochronology whole rock geochemistry and structural data we propose that the abanico basin can be divided into two main segments separated by the nw striking piuquencillo fault and conjugate ne striking faults stratigraphic units defined in the northern segment abanico and farellones formations cannot be correlated with the rocks of the southern segment coya machali formation and teniente volcanic complex in terms of lithofacies depositional ages and geochemistry the northern and southern segments also show temporal differences in their tectonic evolution an early deformation event beginning at 22 ma affected only the northern segment and is associated with the formation of progressive unconformities between the abanico and farellones formations and also with crustal thickening as reflected in the geochemistry of the farellones formation a second stage of crustal thickening and exhumation began at 12 ma as suggested by a sharp increase of the la yb ratios in the northern segment in the southern segment this event is reflected by only a moderate increase of la yb ratios and by the transition between the coya machali formation and the teniente volcanic complex finally a third stage of exhumation and crustal thickening beginning at 7 ma affected both the northern and southern segments this last stage was the main exhumation event affecting the rocks of the andes of central chile and is recorded in the geochemistry of igneous rocks by a sharp increase in the la yb ratios in the southern segment

tectonomagmatic characteristics of the back arc portion of the calama olacapato el toro fault zone central andes 1 post 20 ma magmatism in the central andes is either localized in the magmatic arc or distributed east of it on the altiplano puna plateau here there is a distinct concentration of magmatic centers on nw se trending lineaments such as the calama olacapato el toro cot that extends into the eastern cordillera to the east of the puna understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the central andes we investigated the back arc area of the cot using remote sensing geological structural and petrochemical data our study demonstrates that this portion of the cot consists of nw se striking faults formed under overall left lateral transtension that decreases in activity toward the cot termini deformation on the cot occurred during and after activity of prominent n s striking transpressive fault systems and is coeval with magmatism which is focused on the central cot the most evolved magmatic rocks with an upper crustal imprint are exposed on the central cot whereas more primitive mantle derived mafic to moderately evolved magmatic rocks are found toward the cot termini this points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central cot cot magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle

strain accumulation in the new madrid and wabash valley seismic zones from 14 years of continuous gps observation the mechanical behavior and hence earthquake potential of faults in continental interiors is an issue of critical importance for the resultant seismic hazard but no consensus has yet been reached on this controversial topic the debate has focused on the central and eastern united states in particular the new madrid seismic zone struck by four magnitude 7 or greater earthquakes in 1811 1812 and to a lesser extent the wabash valley seismic zone just to the north a key aspect of this issue is the rate at which strain is currently accruing on those plate interior faults a quantity that remains debated here we address this issue with an analysis of up to 14 6 years of continuous gps data from a network of 200 sites in the central united states centered on the new madrid and wabash valley seismic zones we find that the high quality sites in these regions show motions that are consistently within the 95 confidence limit of zero deformation these results place an upper bound on strain accrual on faults of 0 2 mm yr and 0 6 mm yr in the new madrid and wabash valley seismic zones respectively for the new madrid region where a paleoseismic record is available for the past 5000 years we argue that strain accrual if any does not permit the 500 900 year repeat time of paleo earthquakes observed in the upper mississippi embayment these results together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicate that either tectonic loading rates or fault properties vary with time in the new madrid seismic zone and possibly plate wide

crustal scale structural architecture in central chile based on seismicity and surface geology implications for andean mountain building 1 we document a crustal scale structural model for the central chile andes based on seismicity and surface geology which consists in a major east verging ramp detachment structure connecting the subduction zone with the cordillera the ramp rises from the subducting slab at 60 km depth to 15 20 km below the western edge of the cordillera extending eastward as a 10 km depth flat detachment this structure plays a fundamental role in the andean orogenesis because most of the shortening has been accommodated by structures rooted in it and allows the distribution of crustal thickening in a simple shear deformation mode indeed despite shortening distribution being very asymmetric 16 km versus 70 km in the western and eastern side respectively the western side is higher and thicker than what is expected yield strength envelopes show strong rheological control on this structure vp and vp vs variations in the upper mantle and in the deepest limit of the seismogenic interplate contact mark the intersection of the ramp with the slab which coincides with the blueschist eclogite transition therefore subduction processes would control the depth where the major east verging structure may merge with the slab such a ramp flat structure is observed in other parts of the chilean margin hence it seems to be a first order feature in the andean subduction zone this structure delimitates upward the rocks transmitting part of the plate convergence stress from the plate interface and controls mountain building tectonics thus playing a key role in the andean orogeny

fracture network fluid pathways and paleostress at the tolhuaca geothermal field abstract in this study we examine the fracture network of the tolhuaca geothermal system located in the southern andean volcanic zone that may have acted as a pathway for migration and ascent of deep seated fluids under the far local stress field conditions of the area we collected the orientation slip data and mineralogical content of faults and veins recovered on a ca 1000 m deep borehole tol 1 located in the nw flank of the tolhuaca volcano tol 1 is a non oriented vertical borehole that recovered relatively young 1 axis 083 74 and a subhorizontal ns trending 3 axis 184 03 within the topmost 400 m of the borehole faults and veins are randomly oriented whereas below 400 m depth faults and veins show preferential ne to ew strikes and steep 50 dips the ew striking veins are compatible with the calculated local stress field whereas ne striking veins are compatible with the regional stress field the morphological elongation of volcanic centers alignments of flank vents and dikes orientation our results demonstrate that the paleomagnetic methodology proved to be reliable and it is useful to re orient vertical boreholes such as tol 1 furthermore our data show that the bulk transpressional regional stress field has local variations to a tensional stress field within the ne striking fault zone belonging to the liquine ofqui fault system favoring the activation of both nw and ne striking pre existent discontinuities especially the latter which are favorably oriented to open under the prevailing stress field the vertical 1 and ns trending subhorizontal 3 calculated in the tgs promote the activation of ew striking extensional veins and both ne and nw striking hybrid faults constituting a complex fluid pathway geometry of at least one kilometer depth

imaging the laguna del maule volcanic field central chile using magnetotellurics evidence for crustal melt regions laterally offset from surface vents and lava flows abstract magnetotelluric mt data were collected at the laguna del maule volcanic field ldmvf located in central chile 36 s 70 5 w which has been experiencing unprecedented upward ground deformation since 2007 these data were used to create the first detailed three dimensional electrical resistivity model of the ldmvf and surrounding area the resulting model was spatially complex with several major conductive features imaged at different depths and locations around laguna del maule ldm a near surface conductor c1 0 5 m approximately 100 m beneath the lake is interpreted as a conductive smectite clay cap related to a shallow hydrothermal reservoir at 4 km depth a strong conductor c3 0 3 m is located beneath the western edge of ldm the proximity of c3 to the recent pleistocene to holocene vents in the northwest ldmvf and nearby hot springs suggests that c3 is a hydrous 5 wt h2o rhyolitic partial melt with melt fraction 35 and a free water hydrothermal component c3 dips towards and is connected to a deeper conductor c4 1 m c4 is located to the north of ldm at 8 km depth below surface and is interpreted as a long lived rhyolitic to andesitic magma reservoir with melt fractions less than 35 it is hypothesized that the deeper magma reservoir c4 is providing melt and hydrothermal fluids to the shallower magma reservoir c3 a large conductor directly beneath the ldmvf is not imaged with mt suggesting that any mush volume beneath ldm must be anhydrous 10 km as it moves from the deep magma reservoir c4 to create small ephemeral volumes of eruptible melt c3 it is hypothesized that there may be a north south contrast in physical processes affecting the growth of melt rich zones since major conductors are imaged in the northern ldmvf while no major conductors are detected beneath the southern vents the analysis and interpretation of features directly beneath the lake is complicated by the surface conductor c1 which attenuates low frequency signals the attenuation from c1 does not affect c3 or c4 at 1 km depth directly beneath ldm a weak conductor c2 50 silicic reservoir with 5 wt h2o at 2 to 5 km depth beneath the inflation center is not supported by the mt data however a smaller 10 km3 eruptible volume could go undetected even with relatively high melt fraction 50 the location of large melt regions to the north has important implications for long term volcanic hazards at ldmvf as well as other volcanoes as it raises the possibility that the vent distribution is not always indicative of the location of deeper source regions of melt

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

crustal lineament control on magmatism and mineralization in northwestern argentina geological geophysical and remote sensing evidence abstract the relationship between long lived deep crustal lineaments and the locations of magmatic centers and associated mineral deposits has been investigated in the puna region of northwestern argentina through the analysis of regional aeromagnetic surveys landsat images and geological information the good exposure and excellent preservation of basement and supracrustal geology in this region makes it particularly suitable for such a study at a regional scale several contrasting magnetic domains are recognized which correlate with crustal geology two basement domains are separated by a nne trending boundary which is believed to correlate with a paleozoic suture zone between the pampia to the southeast and arequipa antofalla terranes to the northwest locally overlying these basement terranes is the cenozoic magmatic domain which is best developed in the n s trending volcanic arc at the western edge of the puna the cordillera occidental in addition four southeast trending volcanic zones extend for several hundred kilometers across the puna many important mineral deposits and areas of hydrothermal alteration are associated with these volcanic breakouts and we have selected three such areas for more detailed study bajo de la alumbrera argentina s largest porphyry copper deposit cerro galan the largest ignimbrite caldera in argentina with associated hydrothermal alteration zones and el queva a historic polymetallic district located within a major volcanic range a comparison of lineament maps generated from aeromagnetic and landsat tm images reveals broad correlation between these different remote sensing techniques which respectively highlight subsurface magnetic and surface geological features in addition the locations of magmatic and hydrothermal centers can be related to the interpreted structural framework and are seen to occur near the intersections of major lineament zones it is suggested that in three dimensions such intersection zones form trans lithospheric columns of low strength and high permeability during transpressional or transtensional tectonic strain and may thereby serve as conduits for magma ascent to the shallow crust pooling of large volumes of deeply derived magma in shallow crustal magma chambers may then result in voluminous devolatilization and the formation of hydrothermal mineral deposits it is important to note that in this model structural intersections serve as facilitators for magma ascent and volatile exsolution but do not in themselves cause this process other factors such as magma supply rate and tectonic stress are essential primary ingredients and local magmatic and volcanic processes affect the ultimate potential for ore formation nevertheless we suggest that lineament analysis provides a valuable framework for guiding the early stages of mineral exploration other regional and local geological considerations must then be applied to identify priority targets within this framework

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

chemical and isotopic features of cold and thermal fluids discharged in the southern volcanic zone between 32 5 s and 36 s insights into the physical and chemical processes controlling fluid geochemistry in geothermal systems of central chile abstract the principal cordillera of central chile is characterized by two belts of different ages and lithologies i an eastern mesozoic belt consisting of limestone and gypsum rich sedimentary rocks at the border between central chile and argentina where the active volcanic arc occurs and ii a western belt of cenozoic age containing basaltic to andesitic volcanic and volcanoclastic sequences this distinctive geological setting controls water chemistry of cold and thermal springs in the region which are fed by meteoric water that circulates through deep regional structures in the western sector of principal cordillera water rock interaction processes produce low tds slightly alkaline hco3 dominated waters although dissolution of underlying mesozoic evaporitic rocks occasionally causes so42 and cl enrichments in this area few na hco3 and na so42 waters occurred being likely produced by a ca2 na exchange during water rock interactions differently the chemical features of ca2 cl waters was likely related to an albitization chloritization process affecting basaltic to andesitic rocks outcropping in this area addition of na cl brines uprising from the eastern sector through the west verging thrust faults cannot be excluded as suggested by the occurrence of mantle he 19 in dissolved gases in contrast in the eastern sector of the study region mainly characterized by the occurrence of evaporitic sequences and relatively high heat flow mature na cl waters were recognized the latter being likely related to promising geothermal reservoirs as supported by the chemical composition of the associated bubbling and fumarolic gases their relatively low 3he 4he ratios up to 3 9 ra measured in the fumaroles on this area evidenced a significant crustal contamination by radiogenic 4he the latter was likely due to i degassing from 4he rich magma batches residing in the crust and or ii addition of fluids interacting with sedimentary rocks this interpretation is consistent with the measured 13c co2 values from 13 2 to 5 72 vs v pdb and the co2 3he ratios up to 14 6 1010 which suggest that co2 mostly originates from the limestone rich basement and recycling of subducted sediments with an important addition of sedimentary organic derived carbon whereas mantle degassing contributes at a minor extent according to geothermometric estimations based on the na k mg2 and ca2 contents the mature na cl rich waters approached a chemical equilibrium with calcite dolomite anhydrite fluorite albite k feldspar and ca and mg saponites at a broad range of temperatures up to 300 c in the associated gas phase equilibria of chemical reactions characterized by slow kinetics e g sabatier reaction suggested significant contributions from hot and oxidizing magmatic gases this hypothesis is consistent with the 13c co2 rc ra co2 3he values of the fumarolic gases accordingly the isotopic signatures of the fumarolic steam is similar to that of fluids discharged from the summit craters of the two active volcanoes in the study area tupungatito and planchon peteroa these results encourage the development of further geochemical and geophysical surveys aimed to provide an exhaustive evaluation of the geothermal potential of these volcanic hydrothermal systems

reactivation of fault systems by compartmentalized hydrothermal fluids in the southern andes revealed by magnetotelluric and seismic data in active volcanic arcs such as the andean volcanic mountain belt magmatically sourced fluids are channeled through the brittle crust by faults and fracture networks in the andes volcanoes geothermal springs and major mineral deposits have a spatial and genetic relationship with nne trending margin parallel faults and margin oblique nw trending andean transverse faults atf the tinguiririca and planchon peteroa volcanoes in the andean southern volcanic zone svz demonstrate this relationship as their spatially associated thermal springs show strike alignment to the nne oriented el fierro thrust fault system we constrain the fault system architecture and its interaction with volcanically sourced hydrothermal fluids using a combined magnetotelluric mt and seismic survey that was deployed for 20 months high conductivity zones are located along the axis of the active volcanic chain delineating fluids and or melt a distinct wnw trending cluster of seismicity correlates with resistivity contrasts considered to be a reactivated atf seismicity occurs below 4 km suggesting activity is limited to basement rocks and the cessation of seismicity at 9 km delineates the local brittle ductile transition as seismicity is not seen west of the el fierro fault we hypothesize that this structure plays a key role in compartmentalizing magmatically derived hydrothermal fluids to the east where the fault zone acts as a barrier to cross fault fluid migration and channels fault parallel fluid flow to the surface from depth increases in fluid pressure above hydrostatic may facilitate reactivation this site specific case study provides the first three dimensional seismic and mt observations of the mechanics behind the reactivation of an atf

a magnetotelluric study of mount ruapehu volcano new zealand summary mt ruapehu is an active andesite cone volcano which marks the southern termination of the kermadec volcanic arc results from 40 broad band magnetotelluric soundings have been analysed using the phase tensor this approach provides a way of determining dimensionality allowing for distortion removal and visualizing data in a 3 d situation the phase tensor analysis suggests that the shallow resistivity structure is largely 1 d in character but that the deeper structure requires a 3 d interpretation 1 d inversions show that at sites on ruapehu a shallow conductive layer lies between a high resistivity layer of a few hundred metres thickness and higher resistivity layer corresponding to basement greywacke the low resistivity layer is contiguous with the waters of the highly acidic crater lake and thus is believed to be the hydraulically controlled upper limit of a zone of acid alteration overlain by dry volcanic rock and ash to the southwest of the volcano the conductive layer merges with a surface conductor associated with tertiary sediments following initial 2 d inversions the deep resistivity structure has been derived through 3 d inversion of data from 38 sites this indicates the existence of a dyke like low resistivity zone that persists to at least 10 km depth and extends from beneath the summit of ruapehu to the northeast where it appears to connect to a poorly constrained region of high conductivity which lies outside the network of measurement sites the low resistivity dyke like feature may be identified with a volcanic feeder system which also supplies the other volcanoes of the tongariro volcanic centre and marks the conduit by which hot gases and occasionally magma reach the surface

geochemistry of fluid discharges from peteroa volcano argentina chile in 2010 2015 insights into compositional changes related to the fluid source region s abstract this study presents the first geochemical data of fluid discharges collected from february 2010 to march 2015 from the planchon peteroa azufre volcanic complex ppavc located in the transitional southern volcanic zone tsvz at the border between argentina and chile during the study period from january 2010 to july 2011 peteroa volcano experienced phreatic to phreatomagmatic eruption possibly related to the devastating maule earthquake occurred on february 27 2010 the compositional dataset includes low temperature from 43 2 to 102 c gas discharges from i the summit of peteroa volcano and ii the se flank of azufre volcano both marked by a significant magmatic fluid contribution as well as bubbling gases located at the foothill of the peteroa volcanic edifice which showed a chemical signature typical of hydrothermal fluids in 2012 strong compositional changes affected the peteroa gases from the summit area the acidic gas species especially so 2 increased suggesting an input of fluids from magma degassing nevertheless the r ra and 13 c co 2 values decreased which would imply an enhanced contribution from a meteoric hydrothermal source in 2014 2015 the chemical and isotopic compositions of the 2010 2011 gases were partially restored the anomalous decoupling between the chemical and the isotopic parameters was tentatively interpreted as produced by degassing activity from a small batch of dacitic magma that in 2012 masked the compositional signature of the magmatic fluids released from a basaltic magma that dominated the gas chemistry in 2010 2011 this explanation reliably justifies the observed geochemical data although the mechanisms leading to the change in time of the dominating magmatic fluid source are not clear at this regard a geophysical survey able to provide information on the location of the two magma batches could be useful to clarify the possible relationships between the compositional changes that affected the peteroa fluid discharges and the 2010 2011 eruptive activity

transtension driving volcano edifice anatomy insights from andean transverse to the orogen tectonic domains abstract dykes and minor eruptive vents are not randomly distributed within tectonically controlled volcanic arcs which is reflected in the resulting morphology of stratovolcanoes as a first order approach regional stress field controls the spatial distribution and geometry of dykes and minor eruptive vents however favourably oriented pre existing weakness zones such as inherited fault systems parallel or close to parallel to the orogen scale shortening axis may reactivate and be the loci for magma migration within the upper crust in intra arc regions field mapping and satellite image analyses were used to establish the callaqui stratovolcano csv structural setting in the andean southern volcanic zone central southern chile geometrical and morphometric analyses of intravolcanic dykes and minor eruptive vents respectively yields a consistent model of dykes propagating and erupting into either 1 n 60 e 5 oriented inherited pre existing fractures in central portions of the volcanic edifice and or 2 regional stress controlled n 70 e 10 self propagating fractures at distal zones a wing crack like structural array of the intra volcanic dyke swarm documents a local right lateral transtensional setting driving the late pleistocene to holocene volcano building up process the latter plays a fundamental role in the progressive shaping of the csv elongated anatomy in space and time parallel dyking and fissural eruptions contribute to successive volcanic output in a predominant ene orientation on the other hand a prominent elongated relief enhances normal to the volcano elongation flank instability developing steeper flanks that could trigger sector collapses this may promote an increase in the extensional component reinforcing further parallel dyking and subsequent eruptions these results improve the understanding of the tectonic role in magma migration processes within the upper crust which is crucial to understand geothermal systems and to minimize hazards related to volcano instability

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

three dimensional resistivity image of the magmatic system beneath lastarria volcano and evidence for magmatic intrusion in the back arc northern chile lazufre volcanic center located in the central andes is recently undergoing an episode of uplift conforming one of the most extensive deforming volcanic systems worldwide but its magmatic system and its connection with the observed uplift are still poorly studied here we image the electrical resistivity structure using the magnetotelluric method in the surroundings of the lastarria volcano one of the most important features in the lazufre area to understand the nature of the magmatic plumbing the associated fumarolic activity and the large scale surface deformation results from 3 d modeling show a conductive zone at 6 km depth south of the lastarria volcano interpreted as the magmatic heat source which is connected to a shallower conductor beneath the volcano showing the pathways of volcanic gasses and heated fluid a large scale conductive area coinciding with the area of uplift points at a magma intrusion at midcrustal depth

tectonic role of margin parallel and margin transverse faults during oblique subduction in the southern volcanic zone of the andes insights from boundary element modeling obliquely convergent subduction margins develop trench parallel faults shaping the regional architecture of orogenic belts and partitioning intra plate deformation however transverse faults also are common along most orogenic belts and have been largely neglected in slip partitioning analysis here we constrain the sense of slip and slip rates of differently oriented faults to assess whether and how transverse faults accommodate plate margin slip arising from oblique subduction we implement a forward 3d boundary element method bem model of subduction at the chilean margin evaluating the elastic response of intra arc faults during different stages of the andean subduction seismic cycle ssc our model results show that the margin parallel nne striking liquine ofqui fault system lofs accommodates dextral reverse slip during the interseismic period of the ssc with oblique slip rates ranging between 1 7 mm yr nw striking faults exhibit sinistral reverse slip during the interseismic phase of the ssc displaying a maximum oblique slip of 1 4 mm yr ene striking faults display dextral strike slip with a slip rate of 0 85 mm yr during the ssc coseismic phase all modeled faults switch their kinematics ne striking fault become sinistral whereas nw striking faults are normal dextral because coseismic tensile stress changes on nw faults reach 0 6 mpa at 10 15 km depth it is likely that they can serve as transient magma pathways during this phase of the ssc our model challenges the existing paradigm wherein only margin parallel faults account for slip partitioning transverse faults are also capable of accommodating a significant amount of plate boundary slip arising from oblique convergence

characterization of the hydrothermal system of the tinguiririca volcanic complex central chile using structural geology and passive seismic tomography abstract a structural characterization of the hydrothermal volcanic field associated with the tinguiririca volcanic complex had been performed by combining passive seismic tomography and structural geology this complex corresponds to a 20 km long succession of n25 e oriented of eruptive centers currently showing several thermal manifestations distributed throughout the area the structural behavior of this zone is controlled by the el fierro el diablo fault system corresponding to a high angle reverse faults of oligocene miocene age in this area a temporary seismic network with 16 short period stations was setup from january to april of 2010 in the context of the msc thesis of lira 2010 covering an area of 200 km 2 that corresponds with the hydrothermal field of tinguiririca volcanic complex tvc central chile southern central andes using p and s wave arrival times a 3d seismic velocity tomography was performed the preliminary locations of 2270 earthquakes have first been determined using an a priori 1d velocity model afterwards a joint inversion of both the 3d velocity model and final locations have been obtained high vp vs ratios are interpreted as zones with high hot fluid content and high fracturing meanwhile low vp vs anomalies could represent the magmatic reservoir and the conduit network associated to the fluid mobility based on structural information and thermal manifestations these anomalies have been interpreted in order to visualize the relation between local geology and the velocity model the volume associated with the magma reservoir and the fluid circulation network has been delimited using an iso value contour of vp vs equal to 1 70 the most prominent observed feature in the obtained model is a large v shaped low velocity anomaly extending along the entire study region and having the same vergency and orientation as the existing high angle inverse faults which corroborates that el fierro el diablo fault system represents the local control for fluid mobility this geometry coincides with surface hydrothermal manifestations and with available geochemical information of the area which allowed us to generate a conceptual model of fluid circulation in the volcanic hydrothermal system as well as define the location of the magmatic reservoir

subsidence at southern andes volcanoes induced by the 2010 maule chile earthquake large earthquakes in subduction zones can affect nearby volcanoes analysis of ground deformation following the 2010 earthquake in maule chile shows that some volcanoes subsided by up to 15 cm probably because of quake triggered release of hydrothermal fluids

first seismic record for intra arc strike slip tectonics along the liquine ofqui fault zone at the obliquely convergent plate margin of the southern andes a temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike slip liquine ofqui fault zone lofz in southern chile seventy five shallow crustal events with magnitudes up to m tief w 3 8 and depths shallower than 25 km were observed in an 11 month period mainly occurring in different clusters those clusters are spatially related to the lofz to the volcanoes chaiten michinmahuida and corcovado and to active faulting on secondary faults further activity along the lofz is indicated by individual events located in direct vicinity of the surface expression of the lofz focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike slip mechanisms indicating a ne sw direction of the p axis for the lofz at this latitude the seismic activity reveals the present day activity of the fault zone the recent m tief w 6 2 event near puerto aysen southern chile at 45 4 s on april 21 2007 shows that the lofz is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region

time variable deformation in the new madrid seismic zone new geodetic measurements show that the new madrid is currently deforming too slowly if at all to account for large earthquakes in the region over the past 5000 years this result together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors indicates that either tectonic loading rates or fault properties vary over a few thousand years

tectonics magmatism and paleo fluid distribution in a strike slip setting insights from the northern termination of the liquine ofqui fault system chile this study addresses the interplay between strain stress fields and paleo fluid migration in the southern andean volcanic zone svz the svz coexists with the margin parallel liquine ofqui fault system lofs and with nw striking andean transverse faults atf to tackle the role of different fault fracture systems on deformation distribution and magma fluid transport we map the nature geometry and kinematics of faults veins and dikes at various scales fault slip data analysis yields stress and strain fields from the full study area data base regional scale and fault zones representative of each fault system local scale regional scale strain analysis shows kinematically heterogeneous faulting local strain analyses indicate homogeneous deformation with ne trending shortening and nw trending extension at nne striking liquine ofqui master fault zones strain axes are clockwise rotated at second order fault zones with ene trending shortening and nnw trending stretching the atf record polyphasic deformation conversely stress field analysis at regional scale indicates a strike slip dominated transpressional regime with n64 e trending 1 and n30 w trending 3 deformation is further partitioned within the arc through nne striking dextral reverse faults ne striking dextral normal faults and nw striking sinistral reverse faults with normal slip activation the regional tectonic regime controls the geometry of ne striking dikes and volcanic centers ne striking faults record local stress axes that are clockwise rotated with respect to the regional stress field nne and ne striking faults are favorably oriented for reactivation under the regional stress field and show poorly developed damage zones conversely nw striking fault systems misoriented under the regional stress field show multiple fault cores wider damage zones and dense vein networks deformation driven by oblique subduction is partially partitioned into strike slip and shortening components the trench parallel component is mostly accommodated by ns striking right lateral faults of the lofs trench perpendicular shortening is accommodated by sinistral reverse atf and dextral reverse nne striking faults we conclude that the svz records a deformation history coeval with magma fluid migration

arc oblique fault systems their role in the cenozoic structural evolution and metallogenesis of the andes of central chile abstract the evolution of the main cordillera of central chile is characterized by the formation and subsequent inversion of an intra arc volcano tectonic basin the world s largest porphyry cu mo deposits were emplaced during basin inversion statistically the area is dominated by ne and nw striking faults oblique to the n striking inverted basin margin faults and to the axis of cenozoic magmatism this structural pattern is interpreted to reflect the architecture of the pre andean basement stratigraphic correlations syn extensional deposits and kinematic criteria on fault surfaces show several arc oblique structures were active as normal faults at different stages of basin evolution the geometry of syn tectonic hydrothermal mineral fibers in turn demonstrates that most of these structures were reactivated as strike slip reverse faults during the middle miocene early pliocene fault reactivation age is constrained by 40 ar 39 ar dating of hydrothermal minerals deposited during fault slip the abundance and distribution of these minerals indicates fault controlled hydrothermal fluid flow was widespread during basin inversion fault reactivation occurred under a transpressive regime with e to ene directed shortening and was concentrated around major plutons and hydrothermal centers at the margins of the former intra arc basin deformation was largely accommodated by reverse faulting whereas in its central part strike slip faulting was predominant

why earthquake hazard maps often fail and what to do about it abstract the 2011 tohoku earthquake is another striking example after the 2008 wenchuan and 2010 haiti earthquakes of highly destructive earthquakes that occurred in areas predicted by earthquake hazard maps to be relatively safe here we examine what went wrong for tohoku and how this failure illustrates limitations of earthquake hazard mapping we use examples from several seismic regions to show that earthquake occurrence is typically more complicated than the models on which hazard maps are based and that the available history of seismicity is almost always too short to reliably establish the spatiotemporal pattern of large earthquake occurrence as a result key aspects of hazard maps often depend on poorly constrained parameters whose values are chosen based on the mapmakers preconceptions when these are incorrect maps do poorly this situation will improve at best slowly owing to our limited understanding of earthquake processes however because hazard mapping has become widely accepted and used to make major decisions we suggest two changes to improve current practices first the uncertainties in hazard map predictions should be assessed and clearly communicated to potential users recognizing the uncertainties would enable users to decide how much credence to place in the maps and make them more useful in formulating cost effective hazard mitigation policies second hazard maps should undergo rigorous and objective testing to compare their predictions to those of null hypotheses including ones based on uniform regional seismicity or hazard such testing which is common and useful in similar fields will show how well maps actually work and hopefully help produce measurable improvements there are likely however limits on how well hazard maps can ever be made because of the intrinsic variability of earthquake processes

volcanism in compressional tectonic settings is it possible 1 this study presents the first field evidence of emplacement of a huge stratovolcano within contractional tectonics in spite of the widely accepted idea that volcanism can develop only in extensional or transcurrent tectonic settings el reventador volcano ecuador started to grow 0 32 ma bp and is still active during pre el reventador times its substratum has been affected by n s to nne striking reverse faults during late pleistocene holocene some reverse faults with the same orientations were still active locally with a component of right lateral strike slip motions seismicity shows widespread events with intensity up to 6 9 mw and compression some of these faults cut the volcano creating differential uplift along n s to nne trending tectonic blocks hypocenter swarms and field data indicate east vergent basal thrusting under the volcano and n s trending fault propagation folds to the east a model for magma migration in this setting is proposed suggesting that similar cases of volcanism within a dominantly contractional tectonic regime may be more frequent than previously thought

probabilistic earthquake locations of induced seismicity in the groningen region the netherlands the groningen gas reservoir situated in the northeast of the netherlands is western europe s largest producing gas field and has been in production since 1963 the gas production has induced both subsidence and seismicity seismicity is detected and located using the koninklijk nederlands meteorologisch instituut shallow borehole array for the period 2015 2017 incorporating the back projection techniques of quakemigrate and the nonlinear location procedure to constrain earthquake locations and depths the uncertainties on the estimated depths are estimated taking into account velocity model changes in station array geometry and uncertainties in the measurement of arrival times of the p and s waves we show that the depth distribution of seismicity is consistent with nucleation within the reservoir 28 per cent or in the overburden 60 per cent within 500 m from the top of the reservoir earthquakes with hypocentres in the overburden likely originate from overlying zechstein anhydrite caprock based on their depth distribution it seems like the earthquakes are primarily driven by the elastic strain in the reservoir and overburden induced by the reservoir compaction we estimate the probability of earthquakes nucleating beneath the reservoir in the underlying carboniferous limestone and basement to be no more than 12 per cent

inversion of an oligocene volcano tectonic basin and uplifting of its superimposed miocene magmatic arc in the chilean central andes first seismic and gravity evidences abstract a new structural model is presented for the cenozoic part of the main range east of santiago a chain made up of thick miocene ignimbrites and andesitic lavas overlying primitive oligocene volcanoclastics deposited on a thin continental crust because the latter coya machali formation locally show tight folding close to the margins of the miocene volcanics they had previously been described as deformed prior to construction of the arc our field observations analysed along two profiles at 33 and 34 15 s however support the conclusion hinted at by ongoing geochronological and geochemical studies deformation of both formations is synchronous and related to late miocene inversion of the coya machali intra arc basin uplift of the rigid arc rocks and part of its volcanoclastic basement took place mainly along two northward shallowing boundary structures that seem to share a lower decollement the eastern fierro out of sequence thrust and a series of western back thrusts that resemble triangle zones seismic data obtained from el teniente porphyry copper mine 34 s rockbursts and two gravimetric profiles at the western end of the southern profile are compatible with a decollement located at that locality 2 3 km under the surface

coalescence microseismic mapping earthquakes are commonly located by linearized inversion of discrete arrival time picks made from signals recorded at a network of seismic stations if mis picks are made these will contribute to the location therefore causing potential bias for data recorded by a dense seismic array direct imaging methods can be applied instead we describe the coalescence microseismic mapping method which is a bridge between the two approaches and will operate with seismic data recorded continuously on a sparse array by continuously mapping scalar signals derived from the envelope of seismic arrivals we derive robust estimates of the spatio temporal coordinates of the origins of seismic events noisy data are migrated away from the correct origin so do not contribute to errors in location the method is rooted in a bayesian formulation of event location traveltime inversion allows imaging of source locations and has the capacity to handle errors in modelled traveltimes it has the advantage of working with any 3 d velocity model which therefore may include anisotropy it also automatically incorporates both p and s wave data a multiresolution grid search leads to an efficient implementation with a search over a larger domain including joint inversion for location and velocity structure possible where warranted by the data quality we discuss the theory and implementation of this method and illustrate it with real data from microseismic events in iceland caused by melt intrusion in the crust

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

oblique plate motion and continental tectonics three dimensional deformation is necessarily associated with oblique plate convergence and commonly results in partitioning of deformation between contractional and transcurrent components along plate margins kinematic models of strike slip partitioning for transpression and transtension allow the exact relation among three critical parameters plate motion instantaneous strain axes and degree of strike slip partitioning to be calculated application to two end member tectonic environments characterized by a low south island new zealand and high central california degree of strike slip partitioning demonstrates a remarkable consistency among the three parameters suggesting that strike slip partitioned transpression is a valid model for deformation in these regions the extreme degree of strike slip partitioning in wrench dominated systems such as central california is tentatively associated with a fundamental misorientation of finite and instantaneous strain axes

comment on why earthquake hazard maps often fail and what to do about it by s stein r geller and m liu stein et al 2012 contends that the occurrence of some recent destructive earthquakes in areas mapped as low hazard in some probabilistic seismic hazard maps illustrates limitations of earthquake hazard mapping this statement is fundamentally incorrect these instances illustrate that short term observations such as recent seismicity do not characterize the hazard from faults with long recurrence time earthquakes this is not an inherent limitation in the methodology of probabilistic seismic hazard assessment psha they repeat arguments made in their previous articles one of them recent stein et al 2011 and others on the new madrid region of the central united states that were published and commented on several years ago e g frankel 2003 2004 stein et al 2003 stein et al 2012 makes three major points 1 the inputs to seismic hazard maps should include long term geologic data in addition to historical and instrumental seismicity 2 uncertainties in hazard values should be estimated and communicated to users and 3 seismic hazard maps need to be objectively tested the first two points have long been recognized and practiced in the seismic hazard mapping community in the united states and elsewhere the third point has also been the subject of substantial work e g stirling and petersen 2006 this comment points out problems

intra arc crustal seismicity seismotectonic implications for the southern andes volcanic zone chile we examine the intra arc crustal seismicity of the southern andes volcanic zone svz our aim is to resolve inter seismic deformation in an active magmatic arc dominated by both margin parallel liquine ofqui fault system lofs and andean transverse faults atf crustal seismicity provides information about the schizosphere tectonic state delineating the geometry and kinematics of high strain domains driven by oblique subduction here we present local seismicity based on 16 months data collected from 34 seismometers monitoring a 200 km long section of the southern volcanic zone including the lonquimay and villarrica volcanoes we located 356 crustal events with magnitudes between mw 0 6 and mw 3 6 local seismicity occurs at depths down to 40 km in the forearc and consistently shallower than 12 km beneath the volcanic chain suggesting a convex shape of the crustal seismogenic layer bottom focal mechanisms indicate strike slip faulting consistent with ene wsw shortening in line with the long term deformation history revealed by structural geology studies however we find regional to local scale variations in the shortening axes orientation as revealed by the nature and spatial distribution of microseismicity within three distinctive latitudinal domains in the northernmost domain seismicity is consistent with splay faulting at the northern termination of the lofs in the central domain seismicity distributes along ene and wnw striking discrete faults spatially associated with hitherto seismic atf the southernmost domain in turn is characterized by activity focused along a n15 e striking master branch of the lofs these observations indicate a complex strain compartmentalization pattern within the intra arc crust where variable strike slip faulting dominates over dip slip movements

three dimensional electrical resistivity image of the south central chilean subduction zone abstract based on isotropic 3 d inversion we re interpret long period magnetotelluric data collected across the geotectonic structures of the south central chilean continental margin at latitudes 38 41 s and summarize results of long period magnetotelluric mt investigations performed between 2000 and 2005 the new 3 d conductivity image of the south central chilean subduction zone basically confirms former 2 d inversion models along three profiles and complete the previous results the models show good electrical conductors in the tip of the continental crustal beneath the pacific ocean the frequently observed forearc conductor at mid crustal levels a highly conductive zone at similar levels slightly offset from the volcanic arc and a not well resolved conductor in the argentinian backarc the subducted nazca plate generally appears as a resistive but discontinuous feature unlike before we are now able to resolve upper crustal conductors interpreted as magma reservoirs beneath active lonquimay villarrica and llaima volcanoes which were obscured in 2 d inversion data fit is rather satisfactory but not perfect we attribute this to large scale crustal anisotropy particularly beneath the coastal cordillera which we cannot include into our solution for the time being

correlation of electrical conductivity and structural damage at a major strike slip fault in northern chile 1 large scale strike slip fault zones are often imaged as electrically conductive structures in the brittle crust however the relationship of conductivity and internal architecture of the fault zone remains largely unclear this paper presents results of a study designed to compare the record of structural deformation across a fault zone with its electrical conductivity image two high resolution magnetotelluric profiles trend perpendicularly across the west fault a branch of the precordilleran fault system in northern chile the magnetotelluric and geomagnetic response functions in the frequency range from 1000 hz to 0 1 hz clearly image a fault zone conductor fzc about 350 m wide and 1500 m deep trending along the surface trace of the fault the position of the fzc and its geometric properties width dip correlate with a region of intense fluid alteration and the orientation of fault related damage elements minor faults fractures according to estimates of fluid salinity and rock porosity the conductivity anomaly results from meteoric water penetrating into a permeable zone this suggests that the increase in electrical conductivity is causally related to a mesh of minor faults and fractures acting as a pathway for fluids the fzc reflects the central and most fractured part of the damage zone in view of similar published magnetotelluric studies we infer a dependency of a fault s state of activity and the characteristics of the fzc such as its conductance width and depth extent ongoing deformation is the controlling factor for maintaining a permeable and electrically conductive fracture network

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

segmentation of megathrust rupture zones from fore arc deformation patterns over hundreds to millions of years arauco peninsula chile 1 this work explores the control of fore arc structure on segmentation of megathrust earthquake ruptures using coastal geomorphic markers the arauco nahuelbuta region at the south central chile margin constitutes an anomalous fore arc sector in terms of topography geology and exhumation located within the overlap between the concepcion and valdivia megathrust segments this boundary however is only based on 500 years of historical records we integrate deformed marine terraces dated by cosmogenic nuclides syntectonic sediments published fission track data seismic reflection profiles and microseismicity to analyze this earthquake boundary over 10 2 10 6 years rapid exhumation of nahuelbuta s dome like core started at 4 1 2 ma coeval with inversion of the adjacent arauco basin resulting in emergence of the arauco peninsula here similarities between topography spatiotemporal trends in fission track ages pliocene pleistocene growth strata and folded marine terraces suggest that margin parallel shortening has dominated since pliocene time this shortening likely results from translation of a fore arc sliver or microplate decoupled from south america by an intra arc strike slip fault microplate collision against a buttress leads to localized uplift at arauco accrued by deep seated reverse faults as well as incipient oroclinal bending the extent of the valdivia segment which ruptured last in 1960 with an mw 9 5 event equals the inferred microplate we propose that mechanical homogeneity of the fore arc microplate delimits the valdivia segment and that a marked discontinuity in the continental basement at arauco acts as an inhomogeneous barrier controlling nucleation and propagation of 1960 type ruptures as microplate related deformation occurs since the pliocene we propose that this earthquake boundary and the extent of the valdivia segment are spatially stable seismotectonic features at million year scale

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

tectono stratigraphic evolution of the andean orogen between 31 and 37 s chile and western argentina fil charrier reynaldo universidad de chile facultad de ciencias fisicas y matematicas departamento de geologia chile universidad andres bello chile

the role of preexisting geologic architecture in the formation of giant porphyry related cu au deposits examples from new guinea and chile development of giant porphyry related copper and or gold deposits in new guinea and northern and central chile occurred during tertiary magmatic events that overprinted earlier extensional tectonic settings the earlier tectonic settings consisted of a mesozoic passive margin in new guinea a jurassic cretaceous back arc basin in northern chile and an oligocene intra arc basin in central chile the preexisting architecture of the basement rocks the fault systems and the stratigraphic packages associated with these settings played a strong role in controlling development of the giant deposits although the extensional tectonic settings in these terranes were different they share a number of elements that were used during formation of the tertiary ore deposits these were the presence of coupled systems of deeply detached listric synsedimentary faults and steep transverse faults and the presence of a relatively flat lying heterogeneous volcano sedimentary rock package during tertiary collision the deeply detached listric faults were inverted and strongly focused uplift exhumation and associated overpressuring induced failure and fluid flow in addition steep transverse faults were activated to form wrench systems with attendant steep deeply tapping pathways for magma and or fluid associated with dilatant jogs flexures or fault intersections ore deposits are commonly located in the hanging wall of the thrust faults under compression associated with collision the competent units of flat lying stratigraphic packages formed plates overlying the folded weaker units underneath and separated by a detachment or otherwise faulted contact examples of the competent upper units include the darai mendi limestone or equivalents in new guinea and the lavas of the farellones formation in central chile these plates appear to have impeded magma ascent and formed a cap on a magma and or fluid system pressurized by collision and orogenesis this geometry provided an ideal location for focusing of magmas and magmatic hydrothermal fluids from these three example terranes a set of exploration indicators have been constructed to highlight belts that are prospective for giant porphyry cu systems these indicators include 1 the presence of magmatic arcs that migrated into preexisting extensional architectures 2 coupled systems of deeply detached listric synsedimentary faults and steep transverse faults 3 rigid basement blocks that could form regional stress field perturbations and 4 fold belts with a major plate to 50 km wide of competent relatively undeformed or gently folded stratigraphy overlying more complexly folded and faulted parts of the sequence

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile