models of crustal thickness for south america from seismic refraction receiver functions and surface wave tomography abstract an extensive compilation of crustal thicknesses is used to develop crustal models in continental south america we consider point crustal thicknesses from seismic refraction experiments receiver function analyses and surface wave dispersion estimates of crustal thickness derived from gravity anomalies were only included along the continental shelf and in some areas of the andes to fill large gaps in seismic coverage two crustal models were developed a by simple interpolation of the point estimates and b our preferred model based on the same point estimates interpolated with surface wave tomography despite gaps in continental coverage both models reveal interesting crustal thickness variations in the andean range the crust reaches 75 km in southern peru and the bolivian altiplano while crustal thicknesses seem to be close to the global continental average 40 km in ecuador and southern colombia despite high elevations and along the southern andes of chile argentina elevation lower than 2000 m in the stable continental platform the average thickness is 38 5 km 1 st deviation and no systematic differences are observed among archean paleoproterozoic cratons neoproterozoic fold belts and low altitude intracratonic sedimentary basins an exception is the borborema province ne brazil with crust 30 35 km thick narrow belts surrounding the cratons are suggested in central brazil parallel to the eastern and southern border of the amazon craton and possibly along the transbrasiliano lineament continuing into the chaco basin where crust thinner than 35 km is observed in the sub andean region between the mid plate cratons and the andean cordillera the crust tends to be thinner 35 km than the average crust in the stable platform a feature possibly inherited from the old pre cambrian history of the continent we expect that these crustal models will be useful for studies of isostasy dynamic topography and crustal evolution of the continent

the northeast brazilian rift system the northeast brazilian rift basins provide important data critical to the understanding of continental rifting processes associated with the opening of the south atlantic these basins represent the locus of intersection of the southern and equatorial branches and some basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases similar data are not found in its counterpart in africa especially for the neocomian these early cretaceous rift basins of northeast brazil illustrate key three dimensional geometries of intracontinental rift systems mainly controlled by the basement structural framework during the main rift phase syn rift ii neocomian early barremian extensional deformation was distributed over three main rift axes 1 the gabon sergipe alagoas gsa trend 2 the reconcavo tucano jatoba rtj trend and 3 the cariri potiguar cp trend during this phase extensional deformation jumped west from the easternmost basins gsa trend to a series of ne trending intracratonic basins rtj and cp trends characterized by a set of asymmetric half grabens separated by basement highs transfer faults and or accommodation zones these basins are typically a few tens of kilometers wide and trend ne sw roughly perpendicular to the main extension direction during the neocomian preexisting upper crustal weakness zones like the dominantly ne sw trending shear zones of the brazilian pan african orogeny controlled the development of intracrustal listric normal faults internal transverse structures such as transfer faults and accommodation zones were also controlled by the local basement structural framework the megashear zones of pernambuco brazil and ngaundere africa seem to have behaved like a huge accommodation zone accommodating extensional deformation along the rtj gsa trends with simultaneous extension along the cp trend during the late barremian syn rift phase iii a significant change in rifting kinematics occurred when the cp trend was aborted and major rifting initiated at the equatorial branch during the aptian while the equatorial branch and benue trough africa experienced the main rift phase the rtj trend was aborted and the gsa trend developed a transitional phase between the rift and drift stage the gsa trend and the offshore potiguar basin represent the site of continued evolution into passive margin basins following the main rift episode

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

gravity derived moho for south america crustal structure in south america is one of the least understood among the earth s continental areas variations in crustal thickness are still poorly constrained over large portions of the continent because of scarce or unevenly distributed crustal thickness estimates throughout south america to address this scarce and inhomogeneous data cover we explore the possibility to derive crustal thickness from satellite gravity data in this study we utilize the combined gravity model eigen 6c which is composed of goce and other gravity data the gravity field and steady state ocean circulation explorer goce satellite has a much more uniform spatial resolution than any land based gravity or seismic survey in south america the gravity data inversion is for a simple two layer model with fixed density contrast over the interface the moho the method is not relying on point constraint data and assumes that all of the signal is related to topography of the moho model quality can therefore be assessed by a comparison with point observations on crustal thickness we show that for the stable part of the continent 90 of our estimates are similar within error bounds to seismic observations variations occur in active orogenic zones or regions with suspected non standard moho density contrasts a comparison with seismological models shows a high correlation with the most recent model especially in areas where continental and global models of crustal structure have limitations in terms of wave paths or point constraints the gravity based model provides a unique continuity of crustal structure providing new insights on structure and tectonics and increase our understanding of the earth s structure underneath south america

tectonic evolution of south america during the late proterozoic abstract this paper discusses the evolution and the late proterozoic assembly of the south american continent i e the west gondwana under the light of global tectonics the northern portion of the continent the amazonian craton is a pre brasiliano domain it may be a fragment derived from laurentia this domain behaved as a large continental plate which was accreted to the central and southeastern portions of the continent brasiliano domain the brasiliano domain had a more complex history and composition during the brasiliano cycle middle proterozoic to early paleozoic in the brasiliano domain several late proterozoic continental plates have been identified sao luiz west africa congo kasai sao francisco rio de la plata arequipa antofalla which acted as forelands to the brasiliano orogenic belts that surround and amalgamate these plates smaller fragments of pre brasiliano continental lithosphere are common in the interior of the brasiliano orogenic belts and played diversified roles microplates microcontinents structural highs some of them have acted as true backlands hinterlands flanked by arc magmatism two principal types of brasiliano orogenic belts are recognized between the continental plates a marginal orogenies to the late proterozoic plates with pelitic carbonatic rocks and discrete volcanism which were thrust by collision onto the margin of the plates and which seem to represent final products of previous passive margin sequences b distal orogenics internal belts within the continental masses sometimes a branching system of orogenics that contain varied clastic and minor carbonate sedimentary rocks accompanied by important bimodal volcanism and calc alkaline plutonism for these orogenies a greater variety of basinal scenarios and tectonic settings may be visualized the amalgamation of the continent during the late proterozoic i e the formation of the brasiliano structures indicates the existence of practically synchronous multilateral stresses within lithospheric plates this can be produced by complementary adjustment of the continental plates as a response to major global events elsewhere analogous to modern continental collisions two large and important tectonic zones may be candidates to such a scenario the hijaz mozambique zone site of connection of east and west gondwana and the transbrasiliano lineament which cuts across south america and extends to north africa following the zone of connection between pre brasiliano and brasiliano domains other small ocean openings and closings inside the various brasiliano areas dom feliciano gariep for instance were minor events and complementary to the other two major tectonic zones mentioned above

crustal structure of the eastern borborema province ne brazil from the joint inversion of receiver functions and surface wave dispersion implications for plateau uplift we investigate the crustal structure of the borborema province of ne brazil by developing 44 s wave velocity depth profiles from the joint inversion of receiver functions and fundamental mode rayleigh wave group velocities the borborema province is located in the northeasternmost corner of the south american continent and represents a portion of a larger neoproterozoic mobile belt that formed during the brasiliano pan african orogeny extensional processes in the mesozoic eventually leading to the separation of africa and south america left a number of aborted rift basins in the continental interiors and episodes of diffuse intraplate volcanism and uplift marked the evolution of the province after continental breakup our velocity depth profiles reveal the existence of two crustal types in the province i the thin crustal type which consists of 30 32 5 km thick crust with an upper layer of 3 4 3 6 km s overlying a lower layer of 3 7 3 8 km s and ii the thick crustal type which consists of a 35 37 5 km thick crust with velocities between 3 5 and 3 9 km s down to 30 km depth and a gradational increase in velocity vs 4 0 km s down to upper mantle depths the crustal types correlate well with topography with the thick crustal type being mainly found in the high standing southern borborema plateau and the thin crustal type being mostly found in the low lying sertaneja depression and coastal cuestas interestingly the thin crustal type is also observed under the elevated topography of the northern plateau we argue that the thick crustal type is rheologically strong and not necessarily related to postbreakup mantle processes as it is commonly believed we propose that extensional processes in the mesozoic stretched portions of the brasiliano crust and formed the thin crustal type that is now observed in the regions of low lying topography leaving the rheologically strong thick crust of the southern plateau at higher elevations the crust making the northern plateau would have thinned and subsided during mesozoic extension as part of a greater sertaneja depression to then experience uplift in the cenozoic and achieve its present elevation

improved imaging with phase weighted common conversion point stacks of receiver functions summary broad band array studies frequently stack receiver functions to improve their signal to noise ratio while mapping structures in the crust and upper mantle noise may produce spurious secondary arrivals that obscure or mimic arrivals produced by p to s conversions at large contrasts in seismic impedance such as the moho we use a hilbert transform to calculate phase weights which minimize the constructive stacking of erroneous signal in receiver function data sets we outline this approach and demonstrate its application through synthetic data combined with different types of noise a previously published example of signal generated noise and a large data set from the sierra nevada earthscope project these examples show that phase weighting reduces the presence of signal generated noise in receiver functions and improves stacked data sets

timing and mechanisms for the generation and modification of the anomalous topography of the borborema province northeastern brazil abstract the results of apatite fission track analysis in 14 granitic gneissic samples from two regional transects across the borborema plateau northeastern brazil show evidence for two dominant paleothermal events a late cretaceous cooling event beginning sometime between 100 and 90 ma and a second cooling event in the neogene the distribution of the fission track results suggests that the cooling events have a broad regional expression and are consistent with the geologic record in the araripe basin western borborema province which attests to a post albian uplift of the whole region we hypothesize that the first event is due to the uplift and denudation of regional permanent topography generated after the breakup of brazil and africa such topography is predicted by models of continental margin extension in which continental lithosphere thinning is followed by thickening of the adjacent hinterland lithosphere and crust kusznir n j karner g d 2007 continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins in karner g d manatschal g pinheiro l eds imaging mapping and modeling continental lithosphere extension and breakup special publication 282 geological society london pp 389 419 in northeastern brazil this extension engendered topography may have been amplified by magmatic underplating related to the saint helena and ascension plumes the miocene cooling event 20 0 ma occurred at a time characterized by the transition from carbonate ramp to progradational clastic systems on the pernambuco paraiba margin and the offshore potiguar basin this same stratigraphic response characterizes the neogene stratigraphy of many passive margins and attests to a global increase in the delivery of clastics to margins the simplest explanation of which is a climate change that accentuated erosion of pre existing topography thus the present rugged landscape of northeastern brazil is interpreted to be a product of this younger denudation event a corollary of this study is that the history distribution and delivery of clastics to the northern and northeastern margins of brazil are a function of the regional development of the continental landscape during the late cenozoic

upper crustal earthquake swarms in sao caetano reactivation of the pernambuco shear zone and trending branches in intraplate brazil abstract seismogenic fault reactivation of continental scale structures has been observed in a few intraplate areas but its cause is still a matter of debate the objective of the present study is to analyze two seismic swarms that occurred along the ew trending pernambuco ductile shear zone and in a ne trending branch in 2007 and 2010 in sao caetano county northeastern brazil we studied both epicentral areas using a nine and a seven station network during 180 and 54 days respectively the results indicate that the 2007 swarm correspond to a right lateral strike slip fault with a normal component of slip strike 74 dip 60 and rake 145 and the 2010 swarm corresponds to a normal fault strike 265 dip 79 and rake 91 the former reactivated a ne trending branch whereas the latter reactivated the main e w trending mylonitic belt of the pernambuco shear zone these results are consistent with seismogenic reactivation of this major structure generated by the present day ew trending compression and ns trending extension as observed by previous studies this shear zone was reactivated as rift faults in the cretaceous during the south america africa breakup however our study confirms that the basement fabric such as continental scale ductile shear zones show evidence of crustal weakness outside areas of previous rifting and it reveals the potential for large earthquakes along dormant rift segments associated with major basement shear belts

impulsive radon emanation on a creeping segment of the san andreas fault california radon emanation was continuously monitored for several months at two locations along a creeping segment of the san andreas fault in central california the recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations some of the radon increases were accompanied or followed by earthquakes or fault creep events they were possibly the result of some sudden outbursts of relatively radon rich ground gas sometimes triggered by crustal deformation or vibration

timing of crust formation deposition of supracrustal sequences and transamazonian and brasiliano metamorphism in the east pernambuco belt borborema province ne brazil implications for western gondwana assembly abstract the main structural feature of the central domain of borborema province ne brazil is a network of dextral and sinistral shear zones these shear zones rework an older regionally developed flat lying foliation in orthogneisses and supracrustal belts which in the east pernambuco belt was formed under amphibolite facies conditions this study reports la icp ms u pb zircon ages of metaigneous and metasedimentary rocks aiming to constraint the pre transcurrent tectonothermal evolution in the eastern pernambuco domain ages of 2125 7 and 2044 5 ma in a mafic layer of banded orthogneiss are interpreted as the age of the protolith of the orthogneiss and of high grade transamazonian metamorphism respectively the latter age is consistent with the occurrence of low th u metamorphic zircon xenocrysts dated at 2041 15 ma in the leucosome of a migmatitic paragneiss a granitic orthogneiss dated at 1991 5 ma reflects late to post transamazonian magmatic event a similar age 1972 8 ma was found in rounded zircon grains from a leucocratic layer of banded orthogneiss ages of detrital zircons in a paragneiss sample indicate derivation from sources with ages varying from the archean to neoproterozoic with peak ages at ca 2220 2060 1940 1200 1150 and 870 760 ma detrital zircons constrain the deposition of the supracrustal sequence to be younger than 665 ma magmatic zircons with the age of 626 15 ma are found in the leucosome of a migmatitic paragneiss and constrain the age of the brasiliano high temperature metamorphism a lower intercept age of 619 36 ma from a deformed granodiorite dated at 2097 5 ma and the crystallization age of 625 24 ma of the felsic layer of banded orthogneiss also confirm the late neoproterozoic metamorphism these results show that the present fabric in basement and supracrustal rocks was produced during the brasiliano orogeny paleoproterozoic ages reported in this study are similar to those found in other sectors of the borborema province the cameroon and nigeria provinces and the sao francisco congo craton they show the importance of the transamazonian eburnean event and suggest that these tectonic units may have been part of a larger single continental landmass likewise similarities in post transamazonian metamorphic and magmatic events in the borborema nigeria and cameroon provinces suggest that they shared a common evolution and remained in close proximity until the opening of the atlantic ocean

radon signals related to seismic activity in ecuador march 1987 a radon concentration measurement survey was carried out in ecuador using the ssntd technique the data analysis shows a definite radon anomaly prior to march 6 1987 m 6 9 earthquake anomalies found before october 18 and october 28th mild earthquakes in 1986 could be correlated with these events other anomalies that we cannot correlate with any geophysical event were also found

deep crustal structure of the parana basin from receiver functions and rayleigh wave dispersion evidence for a fragmented cratonic root 1 the deep crustal structure of the parana basin of southern brazil is investigated by analyzing p and pp wave receiver functions at 17 brazilian lithosphere seismic project stations within the basin the study area can be described as a typical paleozoic intracratonic basin that hosts one of the largest large igneous province of the world and makes a unique setting for investigating models of basin subsidence and their interaction with mantle plumes our study consists of 1 an analysis of the moho interaction phases in the receiver functions to obtain the thickness and bulk vp vs ratio of the basin s underlying crust and 2 a joint inversion with rayleigh wave dispersion velocities from an independent tomographic study to delineate the detailed s wave velocity variation with depth the results of our analysis reveal that moho depths and bulk vp vs ratios including sediments vary between 41 and 48 km and between 1 70 and 1 76 respectively with the largest values roughly coinciding with the basin s axis and that s wave velocities in the lower crust are generally below 3 8 km s select sites within the basin however show lower crustal s wave velocities slightly above 3 9 km s suggestive of underplated mafic material we show that these observations are consistent with a fragmented cratonic root under the parana basin that defined a zone of weakness for the initial paleozoic subsidence of the basin and which allowed localized mafic underplating of the crust along the suture zones by cenozoic magmatism

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

spatial and temporal uplift history of south america from calibrated drainage analysis a multi disciplinary approach is used to analyze the cenozoic uplift history of south america residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present day dynamic topography admittance analysis and crustal thickness measurements indicate that the elastic thickness of the borborema and altiplano regions is 10 km with evidence for sub plate support at longer wavelengths a drainage inventory of 1827 river profiles is assembled and used to investigate landscape development linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift erosional parameters are calibrated using observations from the borborema plateau and tested against continent wide stratigraphic and thermochronologic constraints our results predict that two phases of regional uplift of the altiplano plateau occurred in neogene times regional uplift of the southern patagonian andes also appears to have occurred in early miocene times the consistency between observed and predicted histories for the borborema altiplano and patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies finally the predicted pattern of incision across the amazon catchment constrains solid sedimentary flux at the foz do amazonas observed and calculated flux estimates match suggesting that erosion and deposition were triggered by regional andean uplift during miocene times

research on groundwater radon as a fluid phase precursor to earthquakes groundwater radon monitoring work carried out in southern california by the university of southern california since 1974 is summarized here this effort began with a sampling network over a locked segment of the san andreas fault from tejon to cajon and was later expanded to cover part of the southern transverse mountain ranges groundwater samples were brought back weekly to the laboratory for high precision scintillation counting needs for more frequent sampling and less labor prompted the development of an economical and field worthy instrument known as the continuous radon monitor about 10 have been installed in the network since early 1980 the groundwater radon content was found to show anomalous increases mostly at a single station before a number of moderate and nearby earthquakes our work is hampered by a lack of large earthquakes that may have a regional impact on radon anomalies and by the complexity of the underground hydrological regime to circumvent this difficulty we have chosen to monitor only deep artesian wells or hot spring wells

proterozoic history of the borborema province ne brazil correlations with neighboring cratons and pan african belts and implications for the evolution of western gondwana 1 geological and geochronological correlations between borborema province ne brazil and neighboring cratons and brasiliano pan african belts indicate that the amazonian west african and sao francisco congo cratons and the basement of the araguaia borborema nigerian and cameroon provinces were part of the atlantica supercontinent this continent was established at the end of the transamazonian eburnean cycle 2 0 ga and apart from ubiquitous taphrogenesis in the 1 8 1 7 ga interval remained largely unaffected for the following 1 ga around 1 ga an important magmatic event in borborema province correlates with rifting episodes and anorogenic magmatism in the sao francisco congo and amazonian cratons these events are interpreted as failed attempts to break up atlantica which at this time may have been part of the larger rodinia supercontinent renewed extensional conditions in borborema province during the middle and late neoproterozoic are attributed to far field stresses transmitted to the interior of atlantica by outwardly dipping subduction zones that encircled its northern present day coordinates portion the rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the borborema province essentially includes reworked intracontinental domains regional deformation and metamorphism starting at 650 640 ma and shear zone development beginning at 590 595 ma were continuously developed through time and were synchronous throughout most of the borborema araguaia cameroon and nigerian provinces postorogenic conditions were reached 540 530 myr ago while active deformation was still occurring in other belts that accreted around atlantica to form western gondwana

times of increased probability of strong earthquakes m 7 5 diagnosed by algorithm m8 in japan and adjacent territories this paper continues to explore the possibility of identifying the times of increased probability tips of occurrence of a strong earthquake by premonitory intermediate term seismic activation in lower magnitude range as defined in the algorithm m8 a tip refers to a 5 year period and an area whose linear size is several times larger than that of an incipient earthquake in the course of the global test of the algorithm we applied it retrospectively to the data from the national earthquake information center worldwide earthquake catalog since the regional japan meteorological agency catalog was unavailable to authors related to the segment of circum pacific belt between latitudes 20 n and 48 n from the south of kuril arc to the taiwan and izu bonin arc the worldwide catalog allows us to diagnose tips for earthquakes above magnitude 7 5 from 1975 on five out of six earthquakes with m 7 5 occurred within the tips diagnosed by the algorithm m8 with a priori fixed parameters the missed earthquake occurred at the final stage of formation of the corresponding tip altogether the tips occupy less than 20 and times of expectation occupy about 8 of the total space time domain considered there are also current tips covering about half of the territory application of the additional algorithm of localization named mendocino scenario indicates that the southern part of the japan trench is an area deserving particular attention the results obtained here by no means constitute the definitive earthquake prediction but merely outline the territories for more detailed and comprehensive analysis if confirmed by regional data the results may be used for implementation of some safety measures and evaluation of other precursors including short term ones

volcano tectonic segmentation of the northern andes data from landsat images published geologic and geophysical reports and field observations are used to document eight major transverse boundaries that divide the northern andes into segments about 125 km long most of the segment boundaries have no apparent relation to structure on the nazca plate being subducted and may instead represent fundamental and long lasting structures of the continent subduction of the carnegie ridge results in increased uplift of the andes widespread and chemically diverse volcanism and major faulting and seismicity subduction of a highly fractured zone in southern ecuador has led to the formation of a separate platelet with a distinct orientation and to a notable change in volcanic style from andesitic stratovolcanoes to rhyolitic ash flow sheets recognition of the segmented structure of the northern andes provides a framework for interpreting details of the regional geology and illustrates that not all segment boundaries are related to subduction

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

images of crustal variations in the intermountain west 1 we develop a map of crustal thickness variations across the great basin colorado plateau rocky mountain and great plains provinces of the western united states using common conversion point stacking of teleseismic receiver functions below the rocky mountains and high plains in colorado we find the thickest crust in the region at 45 50 km thick beneath the basin and range thinner between 30 and 40 km crust is found thin 30 km thick crust is present in the northern portion of nevada and utah despite elevations similar to those farther south crustal thickness across the colorado plateau can be characterized as a broad transitional region between the thin crust of basin and range to the thicker crust of the rocky mountains the impedance contrast across the mohorovicic discontinuity decreases below the colorado plateau as converted arrivals recorded in this region appear weak compared to surrounding areas variations in vp vs across the region indicate higher values along the western boundary of the basin and range in the rocky mountains and in the western great plains we are not able to characterize vp vs in the colorado plateau we find that crustal thickness does not closely correlate with surface topography within each region or across the region as a whole differences in crustal thickness in each tectonic province indicate the need for a mantle component to support the high elevations across the western united states

radon emanometry in soil gases and activity in ashes from el chichon volcano radon 222em emanation measurements in soil gases are reported in connection with the 1982 eruptions of el chichon volcano 222em detection is performed with lr 115 cellulose nitrate track detectors results show a general decreasing pattern of222em concentration in soil with time after the eruptions activity measurements of radon daughters in ashes show that a large amount of222em and220em was released from magma degassing during the eruptions and that only a fraction of the degassed magma was erupted an important fluid interaction between the magma chamber and the surrounding sedimentary rock is also suggested

upper mantle structure of the borborema province ne brazil from p wave tomography implications for rheology and volcanism data were collected with support of the instituto nacional de ciencia e tecnologia em estudos tectonicos inct et of the centro nacional de desenvolvimento cientifico e tecnologico cnpq grant number 57 3713 2008 01 and the borborema deep electromagnetic and seismic experiment bodes cnpq grant number 400743 2014 0 flsn acknowledges support from the coordenacao de aperfeicoamento de pessoal de nivel superior capes through a 4 yr scholarship to complete his phd at the universidade federal do rio grande do norte ufrn jj thanks cnpq for his research fellowship cnpq grant number 304421 2015 4 ms acknowledges support by brazilian science without border program grant number 40 2174 2012 7

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

crustal architecture of the borborema province ne brazil from receiver function ccp stacks implications for mesozoic stretching and cenozoic uplift abstract we have investigated the crustal architecture of the borborema province of ne brazil by constructing common conversion point ccp receiver function stacks from teleseismic p waveforms recorded at 64 seismic stations in the region the borborema province represents the western portion of a larger neoproterozoic mobile belt that experienced extension in the mesozoic leading to the formation of a number of intra continental rift basins and eventually continental breakup after continental breakup episodes of uplift in the province perhaps related to coeval episodes of cenozoic volcanism helped shape the high topographies of the borborema plateau our receiver function ccp stacks image clear p to s conversions at the crust mantle boundary and confirm independent evidence for a 36 38 km thick crust under the southern portion of the plateau and a thinner 30 32 km thick crust in the surrounding regions including the northern plateau the cross sections also reveal the presence of an intra crustal discontinuity at 9 18 km depth under the regions of thin crust that fades away under the thick southern plateau we argue that the thin crust in the borborema province is the result of mesozoic crustal stretching and that the intra crustal discontinuity represents a low angle detachment zone that helped accommodate extension in the crust the thick crust under the southern plateau would then represent a rheologically stronger portion of the borborema province that resisted deformation by mesozoic extension while the thin crust under the northern plateau would be a portion of formerly depressed thin crust that was uplifted during the cenozoic

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

rayleigh wave group velocity tomography of the borborema province ne brazil from ambient seismic noise ambient seismic noise has traditionally been regarded as an unwanted perturbation that contaminates earthquake data over the last decade however it has been shown that consistent information about subsurface structure can be extracted from ambient seismic noise by cross correlation of noise simultaneously recorded at two seismic stations the empirical green s function for the propagating medium between them can be reconstructed moreover for periods less than 30 s the seismic spectrum of ambient noise is dominated by microseismic energy and because microseismic energy travels mostly as surface waves the reconstruction of the empirical green s function is usually proportional to the surface wave portion of the seismic wavefield in this paper we present 333 empirical green s functions obtained from stacked cross correlations of one month of vertical component ambient seismic noise for different pairs of seismic stations in the borborema province of ne brazil the empirical green s functions show that the signal obtained is dominated by rayleigh waves and that dispersion velocities can be measured reliably for periods between 5 and 20 s the study includes permanent stations from a monitoring seismic network and temporary stations from past passive experiments in the region resulting in a combined network of 34 stations separated by distances between approximately 40 and 1 287 km fundamental mode group velocities were obtained for all station pairs and then tomographically inverted to produce maps of group velocity variation for short periods 5 10 s the tomographic maps correlate well with surface geology with slow velocities delineating the main rift basins potiguar tucano and reconcavo and fast velocities delineating the location of the precambrian sao francisco craton and the rio grande do norte domain for longer periods 15 20 s most of the velocity anomalies fade away and only those associated with the deep tucano basin and the sao francisco craton remain the fading of the rio grande do norte domain fast velocity anomaly suggests this is a supracrustal structure rather than a lithospheric terrain and places new constraints on the precambrian evolution of the borborema province

deep structure of a stretched lithosphere magnetotelluric imaging of the southeastern borborema province ne brazil abstract magnetotelluric data were collected at 25 stations along a nnw sse linear profile deployed perpendicularly to the main structures in the southeastern portion of the borborema province northeast brazil the geotectonic scenario is characterized by a broad range of tectomagmatic events including periods of compressive tectonism associated with amalgamation of lithospheric blocks during the brasiliano orogeny in the late neoproterozoic superimposed by extensional events related to the continental break up and plate drift that led to the formation of the southern atlantic ocean in the early cretaceous strike analysis and distortion decomposition show that most of the data are two dimensional 2d but sensitive to distant off profile structures data fit an ene regional geoelectric strike direction consistent with the geological and tectonic setup a joint 2d inversion of the te and tm modes defined by this strike direction was undertaken and the obtained model exhibits signatures of the different tectonic events in the area the model suggests that the se borborema province is electrically separated into two parts the first comprising the southern domain of the province sergipano belt and pernambuco alagoas block has a highly heterogeneous crust and an anomalously conductive upper mantle the second comprising the transversal domain of the province alto moxoto terrain displays crust and upper mantle predominantly homogeneous and resistive a deep neoproterozoic lithospheric shear zone pernambuco lineament marks the limit between the two contrasting domains also the region where the jatoba basin is located in the southern domain presents a striking conductor at upper to mid crustal depths beneath the basin these results correlate well with seismic refraction data that indicate thicker crust for the transversal domain than for the southern domain with the thinnest crust coinciding with the location of the jatoba basin the data support the conclusion that the lithosphere of the southern domain of the borborema province was significantly stretched in the cretaceous during the opening of the south atlantic ocean allowing refertilization of depleted upper mantle with incompatible elements from enriched deeper mantle material and reactivation of older crustal fabrics the conductivity increase below the jatoba basin is associated with ionic conduction in a currently reactivated fracture zone filled with high salinity fluid apparently the alto moxoto terrain worked as a region of higher resistance to stretching causing the crustal thinning and geoelectric effects to be concentrated to the south of the pernambuco lineament

from rodinia to gondwana a review of the available evidence from south america abstract in this work we will examine the available evidence for the position of the cratonic masses that formed west gondwana in the neoproterozoic such as amazonia west africa sao francisco congo rio de la plata and kalahari some emphasis will be given to south america and the smaller continental masses or microcontinents that are usually forgotten in the exercise of global reconstruction will also be considered among others such tectonic units are the central goias massif the borborema trans saharan block as well as the luiz alves parana and pampia cratonic fragments taking into account the relevant paleomagnetic and geochronological data it is necessary to consider a large time interval for the process of break up of rodinia signals of extension and fracturing are as old as 1000 1100 ma when mafic dyke swarms are observed on the sao francisco congo craton and final break out is reported as young as 750 ma on the other hand the formation of intra oceanic magmatic arcs within the large goias ocean occurred prior to 930 ma ago moreover for the make up of gondwana the first continental collisions are reported at ca 800 ma and the most important accretion episodes are the ones between 650 and 500 ma corresponding to the brasiliano pan african orogenic cycle therefore it is apparent that fragmentation of rodinia is partially synchronous with agglutination of gondwana

gas anomalies at three mineral springs and a fumarole before an inland earthquake central japan conspicuous anomalies in gas compositions were observed at a fumarole and three mineral springs about 1 3 months prior to an inland earthquake of 6 8 magnitude in central japan on september 14 1984 the epicentral distances are 9 km for the fumarole and 50 71 and 95 km for the springs the anomalies in he ar n2 ar and ch4 ar ratios of bubble gases from the springs can be attributed to fluctuations in the emission rate of some deep seated gas due to change in pore pressure which is subjected to crustal stress resulting in the earthquake the anomaly at the fumarole showed an increase in discharge rate of deep volcanic gas under a compressional stress near the focal region since the behavior of subsurface fluids represented by he ar and other ratios is presumably controlled by the change of pore pressure temporal variations in the fluids can be used as a strain gauge for the crust on the other hand the precursory emissions of h2 which were observed after changes in he ar and other ratios had occurred may have resulted from a reaction between groundwater and the surface of newly formed cracks the timing and amplitude of the geochemical anomalies are compatible with the result predicted by a dilatancy model without fluid diffusion although h2 emission may be related to groundwater permeation into newly formed cracks monitoring of several gases with automatic gas chromatographs at several stations may be useful for unraveling earthquake mechanisms and for predicting earthquakes

radon and rilt anomalies detected before the irpinia south italy earthquake of november 23 1980 at great distances from the epicenter some investigators of istitute of physics and istitute of geology of the university of rome are carrying out measurements of tilt and groundwater radon content in sites located in central italy beginning from june to november 1980 anomalous variations in the radon content have been detected in rome and rieti sites water samples for discrete measurements of radon content were drawn periodically from underground strata the amplitude of the anomalies were 25 and 170 compared with the background level from about march 15 a bubble type tiltmeter installed at l aquila site showed a first anomalous tilting with a time scale of about two mounths and an amplitude of 15 rad a second anomalous tilting about 20 rad in amplitude was observed from the middle of may to november the seismicity m 4 0 4 7 within about 100 km of the sites seems to justify only the first anomalous tilting on november 23 1980 a strong m 6 5 earthquake took place in irpinia southern italy at about 250 km from rome rieti and l aquila sites we suggest to assume both the radon content anomalies and the second anomalous tilting as precursors of the irpinia earthquake

enhancement of radon signals in geophysical studies with the track technique the existence of a suspected geological fault has been confirmed using solid state nuclear track detectors ssntds by measuring radon concentration variations in the upper soil above its inferred position the results obtained prompted us to increase the natural radon signal in the soil using an additional radon source this enhancement technique has been experimentally checked with ssntd detectors

crustal structure beneath the eastern part of the coast ranges diablo range of central california from explosion seismic and near earthquake data abstract seismic refraction and near earthquake data of the u s geological survey for central california have been compiled into record sections along profiles and interpreted in terms of crustal structure the profiles are located northeast of the san andreas fault of central california and run parallel to the general structures for the explosion seismic line through the centre of the diablo range an uppermost layer franciscan formation with p velocities of 3 6 5 0 km s 1 decreases in thickness towards the northwest the lower boundaries of layers with constant velocities of 5 75 and 6 8 km s 1 are found at almost constant depths of 12 and 21 km respectively between 21 and 26 km depth a well defined low velocity zone appears whose velocity is estimated as 5 3 km s 1 with the aid of a hedgehog inversion and the calculation of amplitudes this zone is underlain by a layer 3 5 km thick with a velocity of 7 6 km s 1 the upper mantle velocity beneath the moho at 29 30 km depth is 8 2 km s 1 the near earthquake profiles located 20 km southwest and parallel to the explosion seismic line follow more or less the hayward and calaveras fault systems the velocity depth distribution derived for the earthquake data is very similar to that found beneath the diablo range however the low velocity zone at 21 26 km depth does not seem to exist everywhere along the line the moho is not disturbed beneath the calaveras hayward and silver creek faults it rises slightly from the diablo range towards the southwest

upper mantle anisotropy of the borborema province ne brazil implications for intra plate deformation and sub cratonic asthenospheric flow abstract the geological record of the borborema province northeast brazil documents tectonic events that characterised the precambrian formation and mesozoic breakup of gondwana large scale shear zones and associated granitic plutons that developed during the neoproterozoic brasiliano pan african orogeny and major sedimentary basins of mesozoic age indicate significant deformation across the region however whether or not the shear zones resulted from precambrian terrane accretion or are simply the result of episodes of subsequent intra plate deformation is debated also poorly understood is the effect of the thick sao francisco mantle keel on present day asthenospheric flow to address these issues we have performed a teleseismic shear wave splitting study of mantle seismic anisotropy from a new broadband seismograph network centred on the borborema province shear wave splitting parameters t reveal a lack of plate scale anisotropic fabrics associated within the continental interior perhaps supporting models of formation and evolution of the borborema province involving minimal deformation of the lithospheric mantle delamination of anisotropic lithosphere during the development of cenozoic volcanism that eroded older fossil lithospheric fabrics is unlikely because the widespread cenozoic magmatism required to achieve this is absent in the geological record instead the apparently low levels of seismic anisotropy observed in the interior of the borborema province may simply reflect depth dependent anisotropy nulls low t observations may be the subtractive result of orthogonal fast directions in the lithosphere and asthenosphere towards the brazilian coast t 1 s and fast directions are sub parallel to stretching fabrics formed during the opening of the south atlantic this may imply that the mantle lithosphere was deformed but not completely destroyed during gondwana breakup however a more complete backazimuthal coverage of splitting measurements across the region is needed to confirm or refute these hypotheses unambiguously

bulk crustal properties of the borborema province ne brazil from p wave receiver functions implications for models of intraplate cenozoic uplift abstract we investigate variations in crustal thickness and bulk vp vs ratio across the borborema province of ne brazil by analyzing teleseismic p to s conversions recorded at 52 seismic stations in the province the borborema province represents the western portion of a larger neoproterozoic mobile belt that resulted from the assembly of gondwanaland and that split from the african continent during mesozoic times the evolution of the province after continental breakup was marked by episodes of diffuse intraplate magmatism perhaps leading to uplift of the borborema plateau in the cenozoic a number of geodynamic models have been proposed to explain coeval cenozoic magmatism and uplift in the province which invoke either thermal anomalies under the plateau and related mantle upwellings channeling along lithospheric thin spots from a distant mantle plume and small scale convection at the continental edge alternatively plateau uplift might have resulted from thickening of the crust after depth dependent stretching of the continental lithosphere in the mesozoic most of the models imply mafic underplating of the plateau s crust in order to fully explain its elevated topography but the volume of such mafic underplate varies among them our results show that i the crust is 32 40 km thick under the borborema plateau ii the crust is generally thinner about 30 33 km under the lower topographies surrounding the plateau and iii vp vs ratios are in the 1 68 1 80 range for both regions of higher and lower topography no apparent correlation is observed between vp vs ratio and crustal thickness our results suggest that compositional differences between thick and thin crust across the borborema province are minimal and that models of plateau uplift involving a small volume of mafic underplate provide a more plausible explanation for the observed topography of the borborema plateau

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

receiver function analysis of the crust and upper mantle in fennoscandia isostatic implications abstract the mountains across southern norway and other margins of the north atlantic ocean appear conspicuously high in the absence of recent convergent tectonics we investigate this phenomenon with receiver functions calculated for seismometers deployed across southern fennoscandia these are used to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust such parameters are key to understanding crustal isostasy and assessing its role or lack thereof in supporting the observed elevations our study focuses on the southern scandes mountain range that has an average elevation 1 0 km above mean sea level the crust mantle boundary moho is ubiquitously imaged and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal chemical or viscous boundaries in the upper mantle the moho resides at 25 30 km depth below mean sea level in southeastern coastal norway and parts of denmark 35 45 km across the southern scandes and 50 60 km near the norwegian swedish border that section of thickest crust coincides with much of the transscandinavian igneous belt and often exhibits a diffuse conversion at the moho which probably results from the presence of a high wave speed mafic lower crust across inner fennoscandia a zone of thinned crust

the association between ground gas radon variations and geologic activity in hawaii soil gas radon activities have been recorded at 10 stations on kilauea volcano for approximately 5 years long term average radon activities were found to vary substantially among the sites monitored spatial variations appear to be controlled predominantly by 1 near surface hydrothermal activity 2 thickness and permeability of soil cover and 3 the presence of subsurface fracturing temporal changes in radon activity show minor correlation with meteorological changes but a strong correlation with seismic and volcanic events on kilauea magmatic intrusions were associated with contemporaneous changes in radon concentrations whereas seismic events were associated with precursory radon anomalies such changes may be caused by release of trapped radon from rocks by microfracturing under broadly distributed stress changes associated with intrusion events and preceding seismic events

lithospheric structure of the arabian shield from the joint inversion of receiver functions and surface wave group velocities abstract we estimate lithospheric velocity structure for the arabian shield by jointly modeling receiver functions and fundamental mode group velocities from events recorded by the 1995 1997 saudi arabian portable broadband deployment receiver functions are primarily sensitive to shear wave velocity contrasts and vertical travel times and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages so that their combination bridge resolution gaps associated with each individual data set our resulting models correlate well with the observed surface geology the asir terrane to the west consists of a 10 km thick upper crust of 3 3 km s overlying a lower crust of 3 7 3 8 km s in the afif terrane to the east the upper crust is 20 km thick and has an average velocity of 3 6 km s and the lower crust is about 3 8 km s separating the terranes the nabitah mobile belt is made of a gradational upper crust up to 3 6 km s at 15 km overlying an also gradational lower crust up to 4 0 km s the crust mantle transition is found to be sharp in terranes of continental affinity east and gradual in terranes of oceanic affinity west the upper mantle shear velocities range from 4 3 to 4 6 km s temperatures around 1000 c are obtained from our velocity models for a thin upper mantle lid observed beneath station taif and suggest that the lithosphere could be as thin as 50 60 km under this station