loading of the san andreas fault by flood induced rupture of faults beneath the salton sea the southern san andreas fault terminates in a stepover zone several small faults that separate major fault segments beneath the salton sea analysis of movements on the stepover zone faults indicates that periodic flooding of the palaeo salton sea during the late holocene could have triggered earthquakes on the san andreas fault

volcanism and faulting of the campania margin eastern tyrrhenian sea italy a three dimensional visualization of a new volcanic field off campi flegrei by means of information technology 3d digital geologic models are increasingly the best methods of constraining interpretations of geology at depth visualization in three dimensions has allowed us to develop solutions that explain the stratigraphic and structural complexity of the campania margin of the eastern tyrrhenian sea especially the lateral relationships among volcanoes and underlying normal faults using seismic and sequence stratigraphy and structural geology approaches in a dedicated gis environment we interpreted a seismic grid and investigated a subsurface volcanic field in gaeta bay off campi flegrei located within the campania margin the gaeta bay basin fill is characterized by several volcanic units that were analyzed using 2d structure contour maps and isochron maps these volcanoes are comparable in size to the edifices of campi flegrei vesuvius and the submerged volcanoes of the bay of naples their age spans from the lower pleistocene for the isolated v0 volcano sited in central gaeta bay to 0 4 0 1 ma for the volcanic field of southern gaeta bay the study of the interplay between volcanic units and faults allowed us to distinguish 1 the oldest fault buried by the lower pleistocene v0 volcano in central gaeta bay 2 a normal fault swarm ne sw that in the middle pleistocene gave rise to a half graben filled by the v1 v5 volcanic field in southern gaeta bay and 3 post 0 4 ma normal faults that downthrow the v1 and v3 volcanoes we correlated the 1 500 m thick late quaternary volcanoes of southern gaeta bay to the buried lava volcanoes interlayered with volcanoclastic deposits drilled at campi flegrei geothermal wells

relationships among seismic velocity metamorphism and seismic and aseismic fault slip in the salton sea geothermal field region the salton sea geothermal field is one of the most geothermally and seismically active areas in california and presents an opportunity to study the effect of high temperature metamorphism on the properties of seismogenic faults the area includes numerous active tectonic faults that have recently been imaged with active source seismic reflection and refraction we utilize the active source surveys along with the abundant microseismicity data from a dense borehole seismic network to image the 3 d variations in seismic velocity in the upper 5 km of the crust there are strong velocity variations up to 30 that correlate spatially with the distribution of shallow heat flow patterns the combination of hydrothermal circulation and high temperature contact metamorphism has significantly altered the shallow sandstone sedimentary layers within the geothermal field to denser more feldspathic rock with higher p wave velocity as is seen in the numerous exploration wells within the field this alteration appears to have a first order effect on the frictional stability of shallow faults in 2005 a large earthquake swarm and deformation event occurred analysis of interferometric synthetic aperture radar data and earthquake relocations indicates that the shallow aseismic fault creep that occurred in 2005 was localized on the kalin fault system that lies just outside the region of high temperature metamorphism in contrast the earthquake swarm which includes all of the m 4 earthquakes to have occurred within the salton sea geothermal field in the last 15 years ruptured the main central fault mcf system that is localized in the heart of the geothermal anomaly the background microseismicity induced by the geothermal operations is also concentrated in the high temperature regions in the vicinity of operational wells however while this microseismicity occurs over a few kilometer scale region much of it is clustered in earthquake swarms that last from hours to a few days and are localized near the mcf system

u th he zircon and archaeological ages for a late prehistoric eruption in the salton trough california usa u th and u th he zircon geochronology redefines the timing of volcanic activity in the salton trough southern california usa the subaerial extension of the incipiently oceanic gulf of california u series disequilibrium corrected u th he zircon analyses for a granophyre ejecta clast from the red island rhyolite dome indicate an eruption age of 2480 470 a calendric dates between 0 and 940 before common era bce error at 95 confidence this eruption age is supported by u th zircon crystallization ages for two obsidian bearing lavas red island the host for the granophyre and obsidian butte a prehistoric quarry for obsidian that is widely distributed in southern california and northern mexico archaeological sites lavas and granophyre display overlapping zircon crystallization age distributions that support field and compositional evidence that they are cogenetic and contemporaneous the u th he eruption age is younger and significantly more precise than previous ages for these volcanoes and is the first indication that the eruption of obsidian flows coincided with human presence in the region a late prehistoric eruption age agrees with the absence of the obsidian butte lithic source among early prehistoric cultural artifacts previously attributed to submergence of the quarry location during hypothesized persistent flooding by ancient lake cahuilla

the seismogenic thickness of the southern california crust the average seismogenic thickness measured from the surface down to maximum depth of earthquake rupture for the southern california crust is 15 0 km 1 2 1 1 km we determine the seismogenic thickness using the depth distribution of the seismic moment release of 19 years of seismicity we calibrate the depth distribution of moment release from background seismicity by comparing the maximum depth of rupture during moderate to large magnitude earthquakes to the premainshock background seismicity of the respective mainshock region the calibration shows that the depth above which 99 9 of the moment release of background seismicity occurs reliably estimates the maximum depth of rupture during moderate to large earthquakes locally the seismogenic thickness is highly variable ranging from less than 10 km in the salton trough to greater than 25 km at the southwestern edge of the san joaquin valley similarly the seismogenic thickness along the major strike slip faults can vary significantly along strike changes in seismogenic thickness along strike do not correspond to the mapped surface segmentation of the major southern california strike slip fault systems in the future such estimates of the seismogenic thickness can be used to refine existing seismic hazard estimates for southern california

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

the colli albani mafic caldera roma italy stratigraphy structure and petrology new results for the colli albani volcano roma italy surveyed for the geological map of italy at 1 50 000 scale carg project integrated with previous data provide insights on caldera evolution the colli albani a quiescent volcano became active at 600 ka eruptive compositions are consistently mafic 50 km 3 deposits forming the villa senni eruption unit ignimbrites at ca 355 ka two edifices were built within the caldera 1 the horseshoe shaped tuscolano artemisio ta composite edifice or lithosome consists of coalescing peri caldera fissure related scoriae cones interbedded with lava flows the fissure system forms two segments controlled by regional fractures 2 the steep sided faete stratovolcano 949 m a s l filled the caldera the ta and faete lithosomes partly interfinger and were emplaced at 350 260 ka their products indicate reduced eruption rates relative to the vl period and a change to effusive and mildly explosive eruptions the most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano collectively named via dei laghi composite lithosome the colli albani caldera is poly phase 1 a piecemeal caldera is associated with large volume ignimbrites of the vl edifice the present shape of the caldera is related to the villa senni eruption 2 the ta composite edifice erupted from peripheral caldera fissures is unrelated to explosive phases of caldera collapse the ta final products cover a morphologically stable caldera wall the peripheral fractures feeding the ta composite edifice are interpreted as volcano tectonic structures activated during the late stage downsag of the caldera reduced eruption rates during the ta and the faete stages 10 1 km 3 1 ka respect to 10 0 km 3 1 ka for the vl edifice suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures by this interpretation the ta edifice represents the surface expression of ring dykes at depth the absence of similar fissure structures along the western caldera rim may relate to the deep geometry of the ring faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence by contrast the following and still active phreatomagmatic phase that has emplaced the via dei laghi composite edifice is located right on the western side of the caldera and may therefore relate to resurgent conditions classical petrological and pers pearce elements ratios analyses indicate that lavas are co genetic and show a differentiation trend up through stratigraphy driven by

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

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

co2 release variations during the last 2000 years at the colli albani volcano roma italy from speleothems studies abstract the colli albani is the quiescent volcano that dominates the southwestern skyline of roma italy the last eruption occurred during the holocene from the eccentric albano maar along its western slope the volcano is presently affected by cyclic seismic swarms ground uplift and diffuse co 2 degassing the degassing has caused several deadly incidents during the last years and constitutes a major civil protection concern as the volcano slopes are densely inhabited nevertheless the volcano does not have a permanent monitoring network and the background level and anomalous co 2 levels the relationship between the gas release and the seismic and ground deformation activity at the colli albani are still to be defined the aim of this work is to define the historical record of co 2 release evidences of deep co 2 periodic release during the last 2000 years in the area of colli albani volcano roma italy are offered from speleothems studies a roman age stone mine now used for mushroom cultivation is decorated with actively growing speleothems characterised by depositional hiatuses different levels of four stalactites separated by depositional unconformities and several samples from a single depositional cycle belonging to a stalagmite have been dated by u th method and analysed for their o and c isotopic composition eight cycles of deposition have been identified from 90 110 a d to 1350 1370 a d some of which are recognised across different speleothems the age gap dividing different growth layers is in the order of one to few hundred years giving a temporal span for periodic interruption of speleothems deposition o and c isotopic analyses performed on the samples collected from a single cycle the oldest have shown that the composition of the mother solutions was initially mainly meteoric and that a progressive increase in the input of a deep component rich in co 2 up to a proportion of 20 30 occurred just before the interruption of the speleothem deposition this could be due to a progressive increase of the acidity of the water solutions that caused the undersaturation of fluids if we extrapolate this mechanism to the other cycles of deposition being characterised by analogue isotopic compositions we can hypothesise periods of deposition interrupted by episodes of co 2 release which in the colli albani volcano are often recorded in coincidence with earthquakes therefore we have correlated the hiatuses with some of the largest historical earthquakes interesting to the city of rome

san andreas fault earthquake chronology and lake cahuilla history at coachella california the southernmost 100 km of the san andreas fault has not ruptured historically it is imperative to determine its rupture history to better predict its future behavior this paleoseismic investigation in coachella california establishes a chronology of at least five and up to seven major earthquakes during the past 1100 yr this chronology yields a range of average recurrence intervals between 116 and 221 yr depending on assumptions with a best estimate average recurrence interval of 180 yr the most recent earthquake occurred c 1690 more than 300 yr ago suggesting that this stretch of the fault has accumulated a large amount of tectonic stress and is likely to rupture in the near future assuming the fault follows a stress renewal model this study also establishes the timing of the past 5 6 highstands of ancient lake cahuilla since a d 800 we found that earthquakes do not tend to occur at any particular stage in the lake cycle

pulsed strain release on the altyn tagh fault northwest china abstract earthquake recurrence models assume that major surface rupturing earthquakes are followed by periods of reduced rupture probability as stress rebuilds although purely periodic time or slip predictable rupture models are known to be oversimplifications a paucity of long records of fault slip clouds understanding of fault behavior and earthquake recurrence over multiple ruptures here we report a 16 kyr history of fault slip including a pulse of accelerated slip from 6 4 to 6 0 ka determined using a monte carlo analysis of well dated offset landforms along the central altyn tagh strike slip fault atf in northwest china this pulse punctuates a median rate of 8 1 1 2 0 9 mm a and likely resulted from either a flurry of temporally clustered mw 7 5 ground rupturing earthquakes or a single large mw 8 2 earthquake the clustered earthquake scenario implies rapid re rupture of a fault reach 195 km long and indicates decoupled rates of elastic strain energy accumulation versus dissipation conceptualized as a crustal stress battery if the pulse reflects a single event slip magnitude scaling implies that it ruptured much of the atf with slip similar to or exceeding the largest documented historical ruptures both scenarios indicate fault rupture behavior that deviates from classic time or slip predictable models

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

geology of proximal small volume trachyte trachyandesite pyroclastic flows and associated surge deposits roccamonfina volcano italy abstract this paper describes the 232 ka b p mttt trachyte trachyandesite pyroclastic succession of roccamonfina volcano this small volume proximal sequence crops out along mulino di sotto paratone and pisciariello ravines in the southwest sector of the central caldera and covers a minimum extent of 3 5 km2 area it is made up of seven pyroclastic flows and pyroclastic surge units consisting of trachytic ash matrix containing juvenile trachyandesitic scoria and dense lava fragments pumice clasts of uncertain trachyandesite and a foreign trachyandesitic lithic facies two stratigraphic markers allow correlation of the units no paleosoils and plinian fallout have been observed at the base and within the succession some lateral grading of scoria and lithic clasts suggests that mttt derived from three distinct source vents the sequence consists of a basal ash flow passing laterally to laminated surge deposits unit a this is overlain by a reversely graded scoria and pumice lapilli flow unit b which is in turn overlain by a thinly cross stratified scoria lapilli surge unit c unit c is capped by a prominent ash and scoria flow unit d a ground layer marker mk1 divides unit d from a massive ignimbrite which grades upcurrent to sand wave surge deposits unit e another ground layer marker mk2 separates unit e from unit f this unit consists of a basal ignimbrite passing laterally to bedded surge deposits with convolute structures subunit fl and grading upcurrent to a subhorizontally plane laminated ash cloud subunit f2 containing near the top a layer of millimetric lithic clasts embedded in fine ash the succession is closed by the pyroclastic flow unit g surge unit c can be interpreted in terms of vertical gradients in turbulence particle concentration and velocity during flowage whereas the bedded surge parts present in the massive deposits of units a and e f1 can be related to abrupt changes of velocity down the steep slopes of ravines reverse grading in unit b is probably due to grain dispersive pressures the convolute structures within fl are related to zones of diagenetic cementation associated with groundwater finally the laminated fine grained nature of subunit f2 is interpreted as due to ash clouds elutriated from the basal part of unit f stratigraphic markers mk1 mk2 are ground layer breccias formed by settling of lithic and scoria clasts from overlying units e and f respectively vesiculation and morphologies of glass shards of the mttt succession suggest that eruptions were essentially driven by magmatic explosions which had an appreciable hydromagmatic component

pre seismic electromagnetic phenomena in the framework of percolation and fractal theories abstract understanding the electromagnetic response to geodynamic processes occurring in the earth s upper crust in particular pre seismic and seismic processes is a challenging task in modern geophysics there is increasing evidence that seismo electromagnetic sem phenomena are difficult to describe quantitatively by linear models using averaged parameters of the medium such as electrical and hydraulic conductivities because the upper crust is highly inhomogeneous at all scales porous and can be fully or partially water saturated the most natural way to describe its parameters is via fractal theoretic and percolation theoretic models recent studies indicate that the electrokinetic effect is the most likely driving mechanism for the various types of sem signals here we considered the hydraulic electric and electrokinetic conductances of a porous water saturated medium as a function of porosity and moisture content utilizing a percolation fractal approach we show that the electric conductivity and electrokinetic current in such a medium are both proportional to c 2 and c 2 where c and c are the critical values of porosity and moisture content respectively this behavior admits the possibility of a relatively large change in the respective electric and electrokinetic parameters due to a small change in the mechanical strain field this is significant because it may account for the appearance of some types of sem signals at large distances from the earthquake origin which is the main deficiency of most models indeed the anticipated strain changes related to pre earthquake processes is usually very small except near the focal area the expected averaged electromagnetic response also would be very small unless a local underground water system exists not necessarily near the focal area but which is close to critical point s we discuss the conditions under which electrotelluric and geomagnetic variations can accompany mechanical disturbances in the earth s crust

geophysical evidence for a san andreas subparallel transtensional fault along the northeastern shore of the salton sea abstract the southern san andreas fault ssaf accommodates a significant amount of strain between the pacific and north american plates thus the fault represents a major geohazard to the populated areas of southern california in particular the larger los angeles metropolitan area paleoseismic chronology of ruptures along the ssaf segment suggests this fault is near the end of its interseismic period 180 years because it has not ruptured in historic times 320 years a recent active source seismic experiment performed in the salton sea west of the ssaf provides evidence for extensional deformation along the northeastern shore of the salton sea this study posits that the extensional deformation is due to a previously unmapped fault here named the salton trough fault stf the seismic reflection data image a divergent sediment package that dips toward the northeast with thicknesses up to at least 2 km refraction inversion produces a southwestward dipping velocity discontinuity that crops out east of the ssaf surface trace consistent with the existence of a southwest to northeast gradient in lithology if present the existence of the stf has scientific and societal relevance first the stf appears to control the recent salton trough architecture north of bombay beach second from a seismological hazards perspective the presence of this structure could alter the current understanding of stress transfer and rupture dynamics in the region as well as community fault models and ground motion simulations on the ssaf online material uninterpreted seismic reflection profiles

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake crustal deformation processes occur with relative rapidity when short term precursors appear at the final preparatory stage of a tectonic earthquake this paper contains calculations of crustal bulk strain before an earthquake based on the model of a rigid inclusion the data give initial conditions for the problem of fluid percolation in a two phase medium accompanied by electrokinetic effects the solution provides a description of systems of currents arising in the vicinity of the source region an analysis of this theoretical evidence yields information on the behaviour of short term precursors in telluric currents and the geomagnetic field

geomorphological features of the archaeological marine area of sinuessa in campania southern italy abstract submarine surveys carried out since the 90s along the coastland of sinuessa allowed us to draw up a geomorphological map with archaeological findings along the sea bottom 650 m off and 7 m depth a campanian ignimbrite bedrock was detected dated 39 kyr bp its position is incompatible with the current sea level towards the northern edge of the shoal a depressed area with 24 cubic elements in concrete was surveyed these artefacts pilae are typical of roman maritime structures widespread along the southernmost phlegrean coast beachrocks and accessory landforms at the same depth of bedrock suggest that this was emerging and attended by man in roman times even for activities related to port facilities submerged palaeo channels in alignment of current watercourses on the mainland dissect the shoal these channels were moulded in subaerial environment during wurm glaciation following the tuff deposition and then were drowned by sea level rise the northernmost channel next to the pilae likely allowed transit and manoeuvring of roman ships the discovery along the seabed of a large stump of lead anchor hundreds of roman amphorae and fragments as well as of a depression of millstone confirm this finding probably the sinuous physiography favored the choice of this site for the docking of sinuessa as sheltered from storms

geomorphological evidence of recent tilting in the central amazonia region abstract geomorphometric techniques applied to remote sensing data represent powerful tools as an aid for detecting terrain features produced by recent vertical crustal movements in a variety of landscapes in this work geomorphometric analysis of the central amazonia drainage network using shuttle radar topography mission srtm data was carried out to determine surface water loading and tectonic influence on the development of the uatuma and urubu river basins since the miocene the main objective was to detect geomorphological domains of lateral stream migration and channel sinuosity changes that could indicate recent vertical crustal movement to achieve this the transverse topographic symmetry factor and sinuosity index were applied to analyze the study area drainage network comparison of the geomorphological domains with structural field data and records of seismicity suggests that they are influenced by subsurface fault reactivation which coincides in space with faults mapped in outcrops that have activated since the miocene this interpretation is corroborated by the spatial correspondence between these faults with domain boundaries and shapes by river sinuosity change when crossing these boundaries and by a high concentration of seismic activity along one of these limits the crustal movement caused by hydrological loading can also influence such geomorphological features such is the case of lateral stream migrations of a domain in the opposite sense to the amazon river flow this may be a consequence of the more pronounced expression of hydrological loading in the negro and solimoes river confluence region

shallow drilling in the salton sea region the thermal anomaly during two shallow thermal drilling programs thermal measurements were obtained in 56 shallow 76 2 m and one intermediate 457 3 m depth holes located both onshore and offshore along the southern margin of the salton sea in the imperial valley california these data complete the surficial coverage of the thermal anomaly revealing the shape and lateral extent of the hydrothermal system the thermal data show the region of high thermal gradients to extend only a short distance offshore to the north of the quaternary volcanic domes which are exposed along the southern shore of the salton sea the central thermal anomaly has an arcuate shape about 4 km wide and 12 km long across the center of the anomaly the transition zone between locations exhibiting high thermal gradients and those exhibiting regional thermal gradients is quite narrow thermal gradients rise from near regional 0 09 c m to extreme 0 83 c m in only 2 4 km the heat flow in the central part of the anomaly is greater than 600 mw m2 and in the two local anomalies exceeds 1200 mw m2 the shape of the thermal anomaly is asymmetric with respect to the line of volcanoes previously thought to represent the center of the field with its center line offset south of the volcanic buttes there is no broad thermal anomaly associated with the magnetic high that extends offshore to the northeast from the volcanic domes the salton sea thermal anomaly can be described as three nested thermal features superimposed on the regional salton trough heat flux a broad region of elevated conductive heat flow with constant temperature gradients of about 0 1 c m a central anomaly of high 0 4 c m near surface gradients observed through a conductive thermal cap underlain by a nearly isothermal zone of hydrothermal circulation and two local anomalies with shallow temperature gradients as high as 0 8 c m superimposed on the central geothermal system these observations of the thermal anomaly provide important constraints for models of the circulation of the hydrothermal system thermal budgets based on a simple model for this hydrothermal system indicate that the heat influx rate for local hot spots in the region may be large enough to account for the rate of heat flux from the entire salton trough

the palos verdes fault offshore southern california late pleistocene to present tectonic geomorphology seascape evolution and slip rate estimate based on auv and rov surveys the palos verdes fault pvf is one of few active faults in southern california that crosses the shoreline and can be studied using both terrestrial and subaqueous methodologies to characterize the near seafloor fault morphology tectonic influences on continental slope sedimentary processes and late pleistocene to present slip rate a grid of high resolution multibeam bathymetric data and chirp subbottom profiles were acquired with an autonomous underwater vehicle auv along the main trace of pvf in water depths between 250 and 600 m radiocarbon dates were obtained from vibracores collected using a remotely operated vehicle rov and ship based gravity cores the pvf is expressed as a well defined seafloor lineation marked by subtle along strike bends right stepping transtensional bends exert first order control on sediment flow dynamics and the spatial distribution of holocene depocenters deformed strata within a small pull apart basin record punctuated growth faulting associated with at least three holocene surface ruptures an upper shallower landslide scarp a buried sedimentary mound and a deeper scarp have been right laterally offset across the pvf by 55 5 52 4 and 39 8 m respectively the ages of the upper scarp and buried mound are approximately 31 ka the age of the deeper scarp is bracketed to 17 24 ka these three piercing points bracket the late pleistocene to present slip rate to 1 3 2 8 mm yr and provide a best estimate of 1 6 1 9 mm yr the deformation observed along the pvf is characteristic of strike slip faulting and accounts for 20 30 of the total right lateral slip budget accommodated offshore southern california

using t z plots as a graphical method to infer lithological variations from growth strata the t z plot method consists of plotting the throw of sedimentary horizons across a growth fault versus their depth in the hanging wall this method has been initially developed for the analysis of growth fault kinematics from seismic data a brief analytical examination of such plots shows that they can also provide valuable information about the evolution of fault topography when growth is a continuous process stages of topography creation fault scarp and filling of the space available in the hanging wall are related to non dynamic draping mud prone pelagic settling and dynamic sand prone dynamically deposited sedimentation respectively in this case the t z plot analysis becomes a powerful tool to predict major lithological variations on seismic profiles in faulted settings q 2004 elsevier ltd all rights reserved

origin of the calderas and evolution of roccamonfina volcano roman region italy abstract the roccamonfina volcano consists of a volcanic fluvial succession dated 549 ka bp paleoauruncus overlain by a 546 ka bp stratacone main cone formed by leucite bearing lava and tephra the main cone was dissected by four nested calderas a ring fracture concentric with and outside of the central caldera is also present detailed mapping of the volcano inspection of landsat satellite images and radiometric dating establish that the gli stagli and northern calderas subsided between respectively 546 474 and 403 374 ka bp and that the summit part collapsed between 546 and 446 ka bp to form the central caldera a chronologically intermediate state dated in the range 376 323 ka bp was identified between the 549 374 ka bp leucite bearing high k series hks stage i and the 317 96 ka bp leucite free low k series lks stage ii this stage is made up of concurrent hks lks rocks stage ics the central gli stagli and northern calderas are older than blt and wtt as supported by the strong discrepancies between calculated volumes of these pyroclastic rocks and the volume of the caldera also caldera collapses due to sector sliding are improbable as tested by the absence of rock slide avalanche deposits the collapses occurred incrementally through repetitive draining of the magma chamber s resulting from a succession of moderate sized volcanic events gli stagli caldera was infilled by a lake early after collapse so that sediments alternated with leucite tephrite lava flows and tephra within the lake the sequence was overlain by a thick succession of young pyroclastic rocks downfaulting downsagging cut the flat lying gli stagli filling sequence resulting in the old valle caldera successive pyroclastic and debris flows derived by updoming of the central caldera deposits infilled the last structure and downfaulted part of the valle fill producing the young valle caldera

late holocene forest dynamics in the gulf of gaeta central mediterranean in relation to nao variability and human impact abstract a new high resolution pollen record spanning the last five millennia is presented from the gulf of gaeta tyrrhenian sea central italy with the aim of verifying if any vegetation change occurred in the central mediterranean region in relation to specific well known global and or regional climate events including the 4 2 ka event the medieval climate anomaly mca and the little ice age lia and to detect possible vegetation changes related to still under investigated climate signals for example the so called bond 2 cold event around 2 8 ka bp the vegetation dynamics of the gaeta record shows a recurrent pattern of forest increase and decline punctuating the mid and late holocene when the timing of these patterns is compared with the climate proxy data available from the same core planktonic foraminifera assemblages and oxygen stable isotope record and with the nao north atlantic oscillation index it clearly appears that the main driver for the forest fluctuations is climate which may even overshadow the effects of human activity we have found a clear correspondence between phases with negative nao index and forest declines in particular around 4200 cal bp a drop in ap arboreal pollen confirms the clearance recorded in many sites in italy south of 43 n around 2800 cal bp a vegetation change towards open conditions is found at a time when the nao index clearly shows negative values between 800 and 1000 ad a remarkable forest decline coeval with a decrease in the frequencies of both castanea and olea matches a shift in the oxygen isotope record towards positive values indicating cooler temperatures and a negative nao between 1400 1850 ad in the time period chronologically corresponding to the lia little ice age the gaeta record shows a clear decline of the forest cover particularly evident after 1550 ad once again in correspondence with negative nao index

40ar 39ar and k ar dating of k rich rocks from the roccamonfina volcano roman comagmatic region italy abstract roccamonfina is the northernmost volcano of the campanian area of the k rich roman comagmatic region of italy it erupted a huge amount of pyroclastics and lavas belonging to both the leucite basanite and leucitite series lbls and the shoshonite series ss spread over an area of about 300 km2 the above series correspond to the high k series hks and low k series lks of appleton 1972 respectively 40ar 39ar and k ar dating of samples from both series gave ages ranging from 0 656 to 0 096 ma for the ss and from 1 03 to 0 053 ma for the lbls these results indicate that the products of the two series were outpoured together at least between 0 7 and 0 1 ma ago i e during both the so called pre caldera phase and the post caldera phase of activity the latest products of the volcanism at roccamonfina were erupted just before the deposition of the grey campanian ignimbrite which erupted from vents located about 50 km to the south in the phlegrean fields near naples and has an age of about 33 000 years taking into account all the available radiometric data we conclude that roccamonfina was active between 1 5 and 0 05 ma ago in excellent agreement with the stratigraphie evidence in this same time span is concentrated the activity of all the centers of the roman region north of naples

aftershocks and triggered events of the great 1906 california earthquake the san andreas fault is the longest fault in california and one of the longest strike slip faults in the world yet little is known about the aftershocks following the most recent great event on the san andreas the m w 7 8 san francisco earthquake on 18 april 1906 we conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake we examined existing catalogs and historical documents for the period april 1906 to december 1907 compiling data on the first 20 months of the aftershock sequence we grouped felt reports temporally and assigned modified mercalli intensities for the larger events based on the descriptions judged to be the most reliable for onshore and near shore events a grid search algorithm derived from empirical analysis of modern earthquakes was used to find the epicentral location and magnitude most consistent with the assigned intensities for one event identified as far offshore the event s intensity distribution was compared with those of modern events in order to constrain the event s location and magnitude the largest aftershock within the study period an m 6 7 event occurred 100 km west of eureka on 23 april 1906 although not within our study period another m 6 7 aftershock occurred near cape mendocino on 28 october 1909 other significant aftershocks included an m 5 6 event near san juan bautista on 17 may 1906 and an m 6 3 event near shelter cove on 11 august 1907 an m 4 9 aftershock occurred on the creeping segment of the san andreas fault southeast of the mainshock rupture on 6 july 1906 the 1906 san francisco earthquake also triggered events in southern california including separate events in or near the imperial valley the pomona valley and santa monica bay in western nevada in southern central oregon and in western arizona all within 2 days of the mainshock of these triggered events the largest were an m 6 1 earthquake near brawley and an m 5 0 event under or near santa monica bay 11 3 and 31 3 hr after the san francisco mainshock respectively the western arizona event is inferred to have been triggered dynamically in general the largest aftershocks occurred at the ends of the 1906 rupture or away from the rupture entirely very few significant aftershocks occurred along the mainshock rupture itself the total number of large aftershocks was less than predicted by a generic model based on typical california mainshock aftershock statistics and the 1906 sequence appears to have decayed more slowly than average california sequences similarities can be drawn between the 1906 aftershock sequence and that of the 1857 m w 7 9 san andreas fault earthquake

post collapse volcanic history of calderas on a composite volcano an example from roccamonfina southern italy roccamonfina part of the roman potassic volcanic province is an example of a composite volcano with a complex history of caldera development the main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the brown leucitic tuff blt around 385 000 yr bp the campagnola tuff the youngest ignimbrite of the blt however drapes the caldera margin and must postdate at least the initial stages of collapse during the subsequent history of the caldera there were several major explosive eruptions the largest of these was that of the galluccio tuff at about 300 000 yr bp it is likely that there was further collapse within the main caldera associated with these eruptions it is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr bp early in the history of roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera one of the youngest major events on roccamonfina occurred at the head of this northern caldera with explosive activity producing the conca ignimbrite and associated caldera there is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

continental rupture and the creation of new crust in the salton trough rift southern california and northern mexico results from the salton seismic imaging project a refraction and wide angle reflection seismic profile along the axis of the salton trough california and mexico was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting from the northern salton sea to the southern imperial valley the crust is 17 18 km thick and approximately one dimensional the transition at depth from colorado river sediment to underlying crystalline rock is gradual and is not a depositional surface the crystalline rock from 3 to 8 km depth is interpreted as sediment metamorphosed by high heat flow deeper felsic crystalline rock could be stretched preexisting crust or higher grade metamorphosed sediment the lower crust below 12 km depth is interpreted to be gabbro emplaced by rift related magmatic intrusion by underplating low upper mantle velocity indicates high temperature and partial melting under the coachella valley sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement mafic rock does not exist at 12 18 km depth as it does to the south and a weak reflection suggests moho at 28 km depth structure in adjacent mexico has slower midcrustal velocity and rocks with mantle velocity must be much deeper than in the imperial valley slower velocity and thicker crust in the coachella and mexicali valleys define the rift zone between them to be 100 km wide in the direction of plate motion north american lithosphere in the central salton trough has been rifted apart and is being replaced by new crust created by magmatism sedimentation and metamorphism

alteration and remelting of nascent oceanic crust during continental rupture evidence from zircon geochemistry of rhyolites and xenoliths from the salton trough california abstract rhyolite lavas and xenoliths from the salton sea geothermal field southern california provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust salton buttes rhyolite lavas contain xenoliths that include granophyres fine grained altered rhyolites felsite and amphibole bearing basalts zircon is present in lavas and xenoliths surprisingly even in the basaltic xenoliths where it occurs in plagioclase rich regions interpreted as pockets of crystallized partial melt zircons in the xenoliths are exclusively late pleistocene holocene in age and lack evidence for inheritance u th isochron ages are 20 5 1 2 1 2 ka granophyres 18 3 3 5 3 6 ka felsite 30 1 12 4 14 1 ka and 9 2 6 6 7 0 ka basalts all errors 1 the dominant zircon population in the rhyolite lavas yielded u th ages between 18 and 10 ka with few pre quaternary xenocrysts present 18ozircon values are lower than typical crustal basement values thus ruling out rhyolite genesis by melting of continental crust moreover 18ozircon values are 0 5 1 0 lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid ocean ridge basalt suggesting that basaltic crust and silicic plutons in the subsurface of the salton sea geothermal field isotopically exchanged with meteoric waters this is evidence for deep reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma

modulation of the earthquake cycle at the southern san andreas fault by lake loading 1 changes in the level of ancient lake cahuilla over the last 1500 years in the salton trough alter the state of stress by bending the lithosphere in response to the applied lake load and by varying the pore pressure magnitude within the crust the recurrence interval of the lake is similar to the recurrence interval of rupture on the southern san andreas and san jacinto faults both of which are partially covered by the lake at its highstand furthermore four of the last five ruptures on the southern san andreas fault have occurred near a time of substantial lake level change we investigate the effect of coulomb stress perturbations on local faults due to changing level of lake cahuilla to determine a possible role for the lake in affecting the timing of fault rupture coulomb stress is calculated with a three dimensional model of an elastic plate overlying a viscoelastic half space plate thickness and half space relaxation time are adjusted to match observed vertical deformation since the last lake highstand the lake cycle causes positive and negative coulomb stress perturbations of 0 2 0 6 mpa on the southern san andreas within the lake and 0 1 0 2 mpa on the southern san andreas outside the lake these coulomb stress perturbations are comparable to stress magnitudes known to have triggered events at other faults along the north america pacific plate boundary

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

an assessment of 40 ar 39 ar dating of incompletely degassed xenoliths the possibility of measuring the age of eruption of pleistocene lavas by 40 ar 39 ar analysis of entrapped ancient potassic xenoliths is demonstrated by a study of model systems upon inclusion in the hot magma such xenoliths are commonly only partially degassed of radiogenic 40 ar which has accumulated in them since their original crystallization the residual 40 ar will increase the apparent k ar age of the xenolith however if a xenolith is of cretaceous age or younger then a plateau in its 40 ar 39 ar age spectrum giving the age of eruption is expected to extend over 25 50 of the total 39ar released if degassing of the xenolith in the magma exceeded 90 and if the phases in the xenolith are characterized by sufficiently different diffusion dimensions or activation energies if diffusion was from a bimodal population of spheres then the radii must differ by a factor of 10 or more or the diffusion coefficients by a factor of 100 or more or if the spheres were equal in size and in diffusion coefficients then the activation energies must differ by a factor of at least 1 5 that such requirements may be realized in real xenoliths containing k feldspars is expected from published activation energies for microcline and from data determined on a granitic xenolith which was degassed in an early pleistocene basalt flow the experimental results appear to establish that old xenoliths may contain ar in distinctive phases which degas at sufficiently different temperatures as to permit determination of the age of degassing or eruption

temporal evolution of the roccamonfina volcanic complex pleistocene central italy abstract the roccamonfina volcanic complex rvc in southern italy is an early to middle pleistocene stratovolcano sharing temporal and morphological characteristics with the somma vesuvius and the alban hills both being associated with high volcanic hazard for the cities of naples and rome respectively the rvc is important for the understanding of volcanic evolution in the roman and campanian volcanic provinces we report a comprehensive study of its evolution based on morphological geochemical and k ar geochronological data the rvc was active from c a 550 ka to 150 ka its evolution is divided into five stages defining a volcanic pulse recurrence time of c a 90 100 kyr the two initial stages consisted in the construction of two successive stratovolcanoes of the tephrite phonolite namely high k series the first stage was terminated by a major plinian eruption emplacing the trachytic rio rava pumices at 439 9 ka at the end of the second stage the last high k series stratovolcano was destroyed by a large sector collapse and the emplacement of the brown leucitic tuff blt at 353 5 ka the central caldera of the rvc is the result of the overlapping of the rio rava and of the blt explosions the plinian eruption of the blt is related to the emptying of a stratified deep seated hks magma chamber during the upwelling of k series ks magma marking a major geochemical transition and plumbing system re organization the following stage was responsible for the emplacement of the lower white trachytic tuff at 331 2 ka and of basaltic trachytic effusive products erupted through the main vent the subsequent activity was mainly restricted to the emplacement of basaltic shoshonitic parasitic cones and lava flows and of minor subplinian deposits of the upper white trachytic tuff between 275 and 230 ka the northern crater is most probably a maar that formed by the phreatomagmatic explosion of the yellow trachytic tuff at 230 ka the latest stage of activity featured the edification of the central shoshonitic domes at c a 150 ka

evolution of seismicity near the southernmost terminus of the san andreas fault implications of recent earthquake clusters for earthquake risk in southern california three earthquake clusters that occurred in the direct vicinity of the southern terminus of the san andreas fault saf in 2001 2009 and 2016 raised significant concern regarding possible triggering of a major earthquake on the southern saf which has not ruptured in more than 320 years these clusters of small and moderate earthquakes with m 4 8 added to an increase in seismicity rate in the northern brawley seismic zone that began after the 1979 m w 6 5 imperial valley earthquake in contrast to the quiet from 1932 to 1979 the clusters so far triggered neither small nor large events on the saf the mostly negative coulomb stress changes they imparted on the saf may have reduced the likelihood that the events would initiate rupture on the saf although large magnitude earthquake triggering is poorly understood the relatively rapid spatial and temporal migration rates within the clusters imply aseismic creep as a possible driver rather than fluid migration

clay formation and pedogenetic processes in tephra derived soils and buried soils from central southern apennines italy abstract volcanic activity in central southern italy produced pyroclastic deposits that covered large areas of the apennine mountains the major volcanic centres include roccamonfina campi flegrei phlegraean fields and somma vesuvius the properties of six soils formed in volcanic tephras in the matese massif were analysed to shed light on processes that lead to different expressions of andic properties in a mountain environment andosols at 1600 m a s l at campitello matese are strongly acidic and rich in organic carbon not only in the subsurface horizons but also in buried horizons these pedons have horizons that meet all the criteria for non allophanic andosols and have modest contents of gibbsite and short range ordered fe minerals such as ferrihydrite pedons at lower altitudes of 830 m a s l at colle santa croce developed on different pyroclastic materials and contain well crystallized secondary minerals and have clay contents up to 30 the general sequence of pyroclastic deposits and distribution of upland andosols in the matese massif suggests that volcanic ash and possibly neapolitan yellow tuff are the main soil parent materials in the upper mountains by contrast the andosols developed at lower altitude at colle santa croce were most likely influenced by geomorphologic deformation of a sequence of relict of lacustrine deposits related to old volcanic activity at roccamonfina that occurred 437 1 9 ka buried horizons of these pedons lack andic properties and contain sepiolite that originated from weathering in an alkaline lacustrine environment mineralogical and chemical data for the colle santa croce pedons suggest that andosols developed as non allophanic aluandic andosols and as a result contain mainly al and fe humus complexes with poorly crystalline active al and fe phases buried soil horizons at campitello matese contain gibbsite which suggests that these horizons weathered at the soil surface for relatively long periods before being buried by subsequent ash falls over the past 39 ka soils formed in volcanic ash may be more widespread in the apennine mountains than currently believed and they may be more widespread in other mountainous areas of italy as well

geodetic investigation into the deformation of the salton trough 1 the salton trough represents a complex transition between the spreading center in baja california and the strike slip san andreas fault system and is one of the most active zones of deformation and seismicity in california we present a high resolution interseismic velocity field for the salton trough derived from 74 continuous gps sites and 109 benchmarks surveyed in three gps campaigns during 2008 2009 and previous surveys between 2000 and 2005 we also investigate small scale deformation by removing the regional velocity field predicted by an elastic block model for southern california from the observed velocities we find a total extension rate of 11 mm yr from the mesquite basin to the southern edge of the san andreas fault coupled with 15 mm yr of left lateral shear the majority of which is concentrated in the southern salton sea and obsidian buttes and is equivalent to 17 mm yr oriented in the direction of the san andreas fault differential shear strain is exclusively localized in the brawley seismic zone and dilatation rate indicates widespread extension throughout the zone in addition we infer clockwise rotation of 10 ma consistent with northwestward propagation of the brawley seismic zone over geologic time

laboratory measurements anomalous 0 1 0 5 hz streaming potential under geochemical changes implications for electrotelluric precursors to earthquakes streaming potentials resulting from flow of various salt solutions in rock were measured on saturated sediments fontainebleau sandstones the streaming potential v was found to be proportional to the driving pore pressure p pulses of amplitude 15 40 mv in the frequency range of 0 1 to 0 5 hz were observed when the conductivity of the injected water was decreased and the fluid flow rate was relatively low corresponding to a darcian velocity of 17 to 30 cm h the amplitudes of these pulses are 47 to 133 of the corresponding steady components of the v values such geochemically induced effects may possibly be responsible for the frequency signals from 0 1 to 0 5 hz that were sometimes observed before an earthquake

abrupt along strike change in tectonic style san andreas fault zone san francisco peninsula seismicity and high resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10 to 15 km wide zone along the san andreas fault on the san francisco peninsula and offshore from the golden gate this 100 km long section of the san andreas fault includes the hypocenter of the mw 7 8 1906 san francisco earthquake as well as the highest level of persistent microseismicity along that 470 km long rupture we define two distinct zones of deformation along this stretch of the fault using well constrained relocations of all post 1969 earthquakes based a joint one dimensional velocity hypocenter inversion and a redetermination of focal mechanisms the southern zone is characterized by thrust and reverse faulting focal mechanisms with ne trending p axes that indicate fault normal compression in 7 to 10 km wide zones of deformation on both sides of the san andreas fault a 1 to 2 km wide vertical zone beneath the surface trace of the san andreas is characterized by its almost complete lack of seismicity the compressional deformation is consistent with the young high topography of the santa cruz mountains coast ranges as the san andreas fault makes a broad restraining left bend 10 o through the southernmost peninsula a zone of seismic quiescence 15 km long separates this compressional zone to the south from a zone of combined normal faulting and strike slip faulting focal mechanisms including a m l 5 3 earthquake in 1957 on the northernmost peninsula and offshore on the golden gate platform both linear pseudo gravity gradients calculated from the aeromagnetic data and seismic reflection data indicate that the san andreas fault makes an abrupt 3 km right step less than 5 km offshore in this northern zone a similar right stepping dilatational geometry is also observed for the subparallel san gregorio fault offshore persistent seismicity and extensional tectonism occur within the san andreas right stepover region and at least 15 km along strike both to the se and nw the 1906 san francisco earthquake may have nucleated within the san andreas right stepover which may help explain the bilateral nature of rupture of this event our analysis suggests two seismic hazards for the san francisco peninsula in addition to the hazard associated with a m 7 to 8 strike slip earthquake along the san andreas fault the potential for a m 6 normal faulting earthquake just 5 8 km west of san francisco and a m 6 thrust faulting event in the southern peninsula

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

recent and long term behavior of the brawley fault zone imperial valley california an escalation in slip rate the brawley fault zone bfz and the brawley seismic zone constitute the principal transfer zone accommodating strain between the san andreas and im perial faults in southernmost california the bfz ruptured along with the imperial fault in the 1940 mw 6 9 and the 1979 mw 6 4 earthquakes although in each case only minor slip apparently occurred on the bfz several other episodes of slip and creep have been documented on the bfz historically until this study it has been unclear whether the past few decades reflect average behavior of the fault two trenches were opened and a series of auger holes were bored across three strands of the bfz at harris road to compare the amount of slip observed historically with the displacements observed in the paleoseismic record evidence is presented across the westernmost strand of the bfz and across the entire bfz at harris road to show that both the average vertical slip rate observed in modern times since 1970 and the vertical creep rate excluding coseismic slip observed during the 1970s are sig nificantly higher than the long term average across the westernmost strand the long term vertical rate is 1 2 1 5 0 5 mm yr and the average rate since about a d 1710 is determined to be no greater than 2 0 mm yr in contrast the average vertical rate between 1970 and 2004 across that strand was at least 4 3 mm yr and the 1970s vertical aseismic creep rate was 10 mm yr likewise across the entire bfz the long term vertical rate is 2 8 4 1 1 4 mm yr whereas the rate between 1970 and 2004 was at least 7 2 mm yr and the 1970s aseismic creep rate was 10 mm yr the long term strike slip rate cannot be determined across any strands of the bfz but may be significant in contrast to the commonly accepted higher sedimentation rates inferred for the entire imperial valley we find that the average sedimentation rate on the downthrown side of the bfz adjacent to mesquite basin in the millennium preceding the onset of agricultural influences was at most 3 5 mm yr finally a creep event occurred on the bfz during our study in 2002 and is documented herein online material appendices 1 and 2 trench logs and color versions of figures 7 8 and 10

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

results of ultra low frequency magnetic field measurements during the guam earthquake of 8 august 1993 we report the results of measurements of ultra low frequency magnetic noise during a large earthquake ms 7 1 at guam of 8 august 1993 depth 60 km the ulf observing system is located in the guam island about 65 km from the epicenter several distinct features of this analysis are summarized 1 we have proposed rather sophisticated statistical analyses monthly mean standard deviation in order to estimate the wave intensity and polarization i e ratio z h 2 a comparison between the ulf wave activity and kp is useful in distinguishing between the space geomagnetic pulsations and non space emissions 3 then the use of the ratio z h is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves 4 the statistical analysis of the temporal evolution of this ratio has yielded that it shows a broad maximum only about one month before the earthquake and this suggests that the emissions during this period are very likely to be magnetic precursors 5 the temporal variation of z component is similar to that for the loma prieta earthquake such that it shows a broad maximum ten days two weeks before the earthquake and another increase a few days before the earthquake 6 the emissions presumably associated with the earthquake are of noise like nature and their main frequency is 0 02 0 05 hz with maximum intensity 0 1 nt

kinematic analysis of secondary faults within a distributed shear zone reveals fault linkage and increased seismic hazard abstract complex multifault earthquake ruptures involving secondary faults emphasize the necessity to characterize their seismogenic potential better and study their relationship with major faults to improve the seismic hazard assessment of a region high resolution geophysical data were interpreted to make a detailed characterization of the averroes fault and the north averroes faults which are poorly known secondary right lateral strike slip faults located in the central part of the alboran sea western mediterranean these faults appear to have evolved since the pliocene as part of a distributed dextral strike slip shear zone in response to local strain engendered by the diverging movement of the carboneras fault to the north and the yusuf and alboran ridge faults to the south in addition the architecture of these faults suggests that the averroes fault may eventually link with the yusuf fault thus leading to a higher seismogenic potential therefore these secondary faults represent a hitherto unrecognized seismogenic hazard since they could produce earthquakes up to moment magnitude mw 7 6 our results highlight the importance of the role played by secondary faults in a specific kinematic framework their reciprocal linkage and their mechanical relationship with the main faults could lead to future complex fault ruptures this information could improve fault source and earthquake models used in seismic and tsunami hazard assessment in this and similar regions

an integrated stratigraphical approach to the middle pleistocene succession of the sessano basin molise italy abstract an integrated stratigraphical approach was applied to the sessano sedimentary succession molise investigated through an 80 m core and an 11 m trench section the lithostratigraphical study allowed reconstruction of the palaeoenvironmental conditions during the existence of a palaeo marsh based on tephrostratigraphical analysis the significant volcanoclastic inputs recorded along the sessano succession were correlated to the explosive activity of the nearby roccamonfina volcano and in particular to the high k series hks period of activity lasted from 546 to 364 ka the 40 ar 39 ar age of 437 9 1 9 ka obtained at the base of the trench section which stratigraphically overlaps the core succession confirms the tephrostratigraphical model and indicates that the marsh dried up during the glacial phase of marine isotope stage mis 12 on this basis the glacial interglacial cycle recognised in the core through pollen analysis was ascribed to mis 14 and 13 while the interglacial phase identified at the core base was tentatively ascribed to mis 15 the duration of the marshy phase was estimated between 130 and 150 ka the floral composition of the pollen spectra shows a more modern character with respect to coeval pollen records from campania confirming that the heterochronous disappearance of the last subtropical elements from italy had a latitudinal character

tectonic evolution of the salton sea inferred from seismic reflection data the salton sea is an evolving pull apart basin located between the san andreas and imperial faults in southern california seismic and geological data reveal a rapidly subsiding southern sub basin that is bounded by a hinge zone to the north and northwest dipping normal faults to the south oblique extension across strike slip faults causes subsidence and leads to the formation of pull apart basins such as the salton sea in southern california the formation of these basins has generally been studied using laboratory experiments or numerical models1 2 3 4 here we combine seismic reflection data and geological observations from the salton sea to understand the evolution of this nascent pull apart basin our data reveal the presence of a northeast trending hinge zone that separates the sea into northern and southern sub basins differential subsidence 10 mm yr 1 in the southern sub basin suggests the existence of northwest dipping basin bounding faults near the southern shoreline which may control the spatial distribution of young volcanism rotated and truncated strata north of the hinge zone suggest that the onset of extension associated with this pull apart basin began after 0 5 million years ago we suggest that slip is partitioned spatially and temporally into vertical and horizontal domains in the salton sea in contrast to previous models based on historical seismicity patterns5 the rapid subsidence and fault architecture that we document in the southern part of the sea are consistent with experimental models for pull apart basins1

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

40ar 39ar and rb sr age determinations on quaternary volcanic rocks 40 ar 39 ar and rb sr ages have been measured on separated minerals from the potassic volcanics of the roman comagmatic region to test the ability of these methods to accurately data quaternary geological events the very high k and rb contents of the roman magmas present particularly favorable situations in which the very high concentrations of the radioactive nuclides 40 k and 87 rb result in well resolved in situ enrichments of the daughter isotopes despite the very young ages six leucite separates contained ar with very high bulk 40 36 ratios above 1000 and in which the 40 ar and the 39 ar were very well correlated yielding well defined ages averaging 3 38 0 08 10 5 years two leucites contained ar with lower bulk 40 36 ratios 400 and in at least two release steps from these leucites the 40 ar 36 ar ratio was significantly lower than atmospheric despite the uncertainty in the composition of the trapped component these two leucites have ages that do not differ significantly from the ages of the other leucites for the biotites it was not possible to obtain through stepwise degassing a good separation of in situ radiogenic 40 ar from trapped 40 ar and therefore the calculated ages are not as precise as those of the leucites in three cases the biotite age agrees with the age of the cogenetic leucite but in the remaining two cases discordant ages are obtained suggesting caution when using biotites as quaternary age indicators rb sr measurements on leucite biotite and pyroxene separates hand picked from each of three tuff samples yielded a dispersion in 87 sr 86 sr as large as 16 parts in 10 4 and 87 rb 86 sr as high as 218 for leucites and permitted the determination of internal isochron ages the ages obtained range from 3 8 0 2 10 5 to 3 3 0 2 10 5 years and are in good agreement with the 40 ar 39 ar ages on the leucites the data for each tuff sample yield a well defined uniform initial 87 sr 86 sr however different tuffs show small differences in initial 87 sr 86 sr pointing to distinct sources or to assimilation of different materials during the extrusion of the tuffs these measurements demonstrate the possibility of dating quaternary materials by both the 40 ar 39 ar method and the rb sr method the observation of concordant ages with a precision of a few percent represents a powerful tool in quaternary stratigraphy

holocene event record of aysen fjord chilean patagonia an interplay of volcanic eruptions and crustal and megathrust earthquakes in the first months of 2007 the aysen region in southern chile was affected by a crustal seismic swarm its largest earthquake m w 6 2 occurred in april and had its epicenter in aysen fjord seismic intensities became so high that hundreds of onshore mass movements were triggered several of which entered into the fjord resulting in mass transport deposits mtds preserved at the fjord bottom here we present a holocene record of paleo earthquakes in the previously unstudied patagonian fjordland based on mtd stratigraphy high resolution seismic data retrieved using two different seismic systems sparker and topas reveal multiple older mtds on different stratigraphic levels correlation of the seismic stratigraphy with sedimentological data obtained from a long calypso core md07 3117 allows conclusion on the seismic origin of these deposits additionally radiocarbon dating permits constructing an age model validated by tephrochronology providing an age for the different mtd levels we thus present a highly detailed paleoseismological history of the aysen region including at least six major holocene earthquakes one of which is likely related to a known megathrust earthquake other earthquakes are related to activity of the liquine ofqui fault zone lofz forming the main source of seismic hazard in the area we can infer a general average recurrence time for lofz earthquakes of 2 100years in the vicinity of aysen fjord with clustered events during the early and late holocene finally we argue that cascading events causal link between volcanic and seismic events may be a frequent phenomenon along the lofz

volcanology of trachytic and associated basaltic pyroclastic deposits at roccamonfina volcano roman region italy abstract the 274 ka basalt trachytic tuff of tuoripunzoli tbtt from roccamonfina volcano roman region italy consists of a basaltic scoria lapilli fall unit a overlain by a trachytic sequence formed by a surge unit b repetitive pumice lapilli and ash rich layers both of fallout origin unit c and a pyroclastic flow deposit unit d the tbtt is widespread 40 km 2 in the northern sector of the volcano but limited to a small area on the southern slopes of the main cone interpolation between the northern deposits and the latter one yields a minimum depositional area of 123 km 2 and an approximate bulk volume of 0 2 0 3 km 3 isopach and isopleth maps are consistent with a source vent within the main caldera of roccamonfina unit a shows a fairly good sorting and a moderate grain size glass fragments are cuspate and vesicular unit b is fine grained and poorly sorted shards are blocky and nonvesicular pumice lapilli of unit c are moderately sorted and moderately coarse grained glass shards are equant and vesicular lithic clasts are strongly comminuted to submillimetric sizes by contrast the ash rich internal divisions are very fine grained and poorly sorted they consist of a mixture of equant shards which are prevailingly blocky and poorly vesicular unit d is a massive poorly sorted moderately coarse grained deposit glass fragments are nearly equant and slightly or nonvesicular the tbtt is interpreted as due to eruption of a basaltic magma followed in rapid succession by one trachyte magma unit a formed by subplinian fallout of a moderate purely magmatic column interaction between a trachyte magma and water resulted in eruption of surge unit b a high standing eruption column erupted alternating fallout pumice lapilli and fallout ashes pumice lapilli originated prevailingly from the inner part of the eruption column whereas magma water interaction on the external parts of the column resulted in ash fallout the uppermost pyroclastic flow unit d is interpreted as due to final collapse of the eruption column

forestepping backstepping stacking pattern of volcaniclastic successions roccamonfina volcano italy abstract we use unconformity bounded stratigraphie units ubsu to reconstruct the chronostratigraphy of volcaniclastic deposits of roccamonfina volcano southern italy significant discontinuities of different hierarchical order in the stratigraphic succession of the volcano have allowed us to identify the ubsu supersynthems synthems and subsynthems the hierarchical order has been determined by the importance and duration of the discontinuities bounding such units and by their geographic distribution supersynthems are bounded by regional scale unconformities that may correspond to important tectonic events changes in the style of eruptive activity or volcano tectonic collapses synthems are bounded by unconformities marked by paleosols that are representative of considerable hiatus and extended all over the synthem they are composed of complex sequences of depositional units at roccamonfina the synthems reveal cyclical eruptive activity unconformities bounding the subsynthems have been recognized through a detailed facies analysis more than 100 stratigraphic sections have been analyzed and correlated restoring them to single successive datum planes it has been possible to reconstruct the original stratigraphic relationships the geometry of the units and the effects of syn eruptive tectonic activity this procedure revealed that the unconformity surfaces bounding depositional units show different physical expression in the proximal medial and distal areas a erosive surfaces may become amalgamation surfaces b amalgamation of several depositional units can locally produce a single lithostratigraphic unit in this case the unconformity surfaces bounding the units can be identified by the presence of discontinuous pumice and lithic concentration zones c non depositional surfaces in proximal areas bypassing surfaces or in interfluve areas may correspond to downslope deposits d unconformity surfaces can bound different lithostratigraphic units that are the result of down current facies variation the pyroclastic units at roccamonfina are organized as forestepping backstepping sequences we interpret this organization as resulting from waxing waning processes associated with eruption and emplacement in fact the internal geometry of each synthem indicates a forestepping phase until the maximum eruption rate is achieved as it later declines deposition occurs upslope backstepping this mechanism is also reproduced at smaller scale within each subsynthem the forestepping backstepping organization of the deposits provides an explanation for the variability of physical chemical and sedimentological parameters observed in the roccamonfina volcaniclastic deposits

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

late quaternary tephra layers along the cilento coastline southern italy abstract the results of stratigraphic and tephrostratigraphic analyses of several pyroclastic levels collected along the coastal sector of the cilento region southern italy are presented some of these levels are here described for the fist time others already known in literature were reconsidered in order to better understand their stratigraphic position and to point out the possible volcanic sources the main outcrops are located along the southern coast of the campania region cilento coast all pyroclastic layers are interbedded within coastal or continental successions younger than the substage 5e of the last interglacial the results of sem eds analyses on well preserved glass fragments indicate a composition falling between the trachyte and phonolite fields of the tas plot as typical of phlaegrean fields products by comparing their composition with those of the main tephra marker layers recorded in southern italy the correlation of the cilento pyroclastic layers with well known eruptive episodes was hypothesised in summary four different eruptions were recognised the first one is testified by a pyroclastic layer not correlated with a terrestrial counterpart covered by a middle pleistocene alluvial fan the second one is the eruptive event emplacing the x 6 marker tephra layer and dates around 107 ka the third is the campanian ignimbrite eruption 39 ka and the last one is testified by the layers correlated with the y 3 tephra about 30 ka these pyroclastic layers can be useful tools for stratigraphic correlations of late quaternary successions in southern italy

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

rb sr and k ar ages on minerals at temperatures of 300 400 c from deep wells in the larderello geothermal field italy rb sr and k ar ages have been obtained on six biotites two muscovites and one hornblende from samples of micaschist gneiss and amphibolite of lower paleozoic to precambrian age at a depth exceeding 2 000 m in basement rocks of the larderello travale geothermal region most of the data cluster in the range 2 5 3 7 ma revealing the existence of a pliocene thermal event to which the origin of the field may be attributed the resulting duration of the larderello geothermal field is unexpectedly long in the basement levels of the two wells examined unstabilized minimum temperatures of 290 and 380 c were measured all the biotites show almost complete 40ar and 87sr retention at the measured well temperatures petrologic evidence stilpnomelane stability and experimental data activation energies and diffusion coefficients also favour a closure temperature above 400 c for rb sr and k ar in biotites in agreement with recent direct experimental determinations

sea level induced seismicity and submarine landslide occurrence the temporal coincidence between rapid late pleistocene sea level rise and large scale slope failures is widely documented nevertheless the physical mechanisms that link these phenomena are poorly understood particularly along nonglaciated margins here we investigate the causal relationships between rapid sea level rise flexural stress loading and increased seismicity rates along passive margins we find that coulomb failure stress across fault systems of passive continental margins may have increased more than 1 mpa during rapid late pleistocene early holocene sea level rise an amount sufficient to trigger fault reactivation and rupture these results suggest that sea level modulated seismicity may have contributed to a number of poorly understood but widely observed phenomena including 1 increased frequency of large scale submarine landslides during rapid late pleistocene sea level rise 2 emplacement of coarse grained mass transport deposits on deep sea fans during the early stages of marine transgression and 3 the unroofing and release of methane gas sequestered in continental slope sediments

recurrence of volcanic activity along the roman comagmatic province tyrrhenian margin of italy and its tectonic significance 1 the roman comagmatic province rcp developed along the nw se striking extensional tyrrhenian margin of italy since middle pleistocene and includes ultrapotassic small eruptive centers and large volcanic districts by means of a review and statistical analysis of a large data set of radiometric ages we demonstrate that in the rcp major eruptive cycles occurred at different volcanic districts almost simultaneously and with an almost constant recurrence time our analysis started with the alban hills volcanic district where a detailed 40ar 39ar chronology of the eruptive cycles has been recently achieved and then extended to include a database of 264 radiometric ages of the rcp volcanics published since 1980 statistical treatment of the data set shows a marked non poissonian behavior of volcanic activity through the whole magmatic province with climax of each major eruptive cycle occurring simultaneously at the different districts approximately every 48 kyr the concomitant eruption of many volcanic districts spreading over a 250 km long chain implies a control mechanism acting at a regional scale after discussing the possible relationship between tectonics sea level changes and volcanic activity we hypothesize that constant rates of slab retreat during middle pleistocene could have been a key factor controlling the rate of magma upwelling and the major cycles of recharge of the magma chambers as a working hypothesis we propose that the duration of the cycles may be related to 1 progressive weakening of the crust due to magma underplating or 2 cyclic injection of convective plumes into the mantle wedge

geophysical applications of electrokinetic conversion in volume 1 of geophysics 1936 r r thompson of humble oil and refining company proposed that the coupling of seismic and electrical energy can be used as an exploration tool subsequent efforts were directed toward using electric field antennas as geophones small scale studies concluded that antennas are not as sensitive as conventional geophones and their response is highly variable depending on the local soil conditions by 1959 martner and sparks of pan american petroleum reported in geophysics a systematic study of seismoelectric coupling using explosives at various depths their results were the first to show that the conversion of seismic to electromagnetic energy at the water table could be detected using surface antennas no studies have systematically explored the full potential of electroseismic methods using the same level of experimental sophistication used in seismic exploration

a 90 000 200 000 yrs marine tephra record of italian volcanic activity in the central mediterranean sea abstract a detailed tephrochronological study was undertaken in three deep sea cores collected in the tyrrhenian and ionian seas the age and the origin of the marine tephra were inferred from oxygen isotope records of foraminifera and from major element compositions of glass shards seventy one eruptions were detected in the time interval 90 000 200 000 yrs during which the volcanoes of the roman and campanian regions and of the southern italy were in activity this is attested by the consistency of the geochemical compositions of both marine and terrestrial deposits most of the marine tephra consisted in trachytes and phonolites characterizing a roman and campanian origin several tephra were proposed as key horizons for proximal and distal sediments among them one tephra originating from mount etna 149 300 yrs and five tephra from pantelleria island 130 000 yrs 163 600 yrs 192 500 yrs 197 400 yrs and 198 400 yrs were northerly dispersed several other key horizons originated from the campanian or roman provinces were detected as far as 1000 km from the vents

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

plausibility of long distance electrotelluric precursors to earthquakes a systematic analysis of the plausibility of different classes of models which could account for low frequency precursory electrotelluric signals observable at large distances from a large earthquake is carried out first we consider linear models for which either a stationary electrical field is generated by a current dipole in the source volume or a static deformation field results from a precursory strain in the source volume linearly inducing a streaming potential effect near the electrode in the former case only the conjunction of very favorable circumstances may lead to an electrical field larger than 10 mv km at more than 100 km with the constraint that no anomaly exceeds a few volts per kilometer in the source area it indeed requires a powerful electrical dipole current 104 a length 1 km which might be produced by a streaming potential effect associated with the connection of nonhydrostatic fluid reservoirs pore pressure difference up to 100 mpa a two dimensional channeling of the electrical currents from the source to the electrode area which would result from high conductivity horizontal layers and finally a local amplification factor of typically 100 near the electrodes which might be produced by a narrowing of the conductive channel for an elastic long distance interaction an electric field of 10 mv km at a distance 10 times the source length 100 km away from a m 6 earthquake requires a precursory deformation larger than the coseismic deformation if no strong local amplification is considered alternatively nonlinear models are proposed and discussed assuming that the crust is stuffed with small scale local instabilities fractures and nonhydrostatic fluid reservoirs among which a number are close to their instability threshold these instabilities may follow their own evolutionary process inducing sporadic fluid flow and hence streaming potential effect in the vicinity of the electrodes without any relation to a remote tectonic activity however these instabilities may be sensitive to very small changes in the stress field and hence be triggered by the elastic precursory deformation of a remote seismic source this requires that the precursory deformation near the instability is at least larger than the tidal strain 10 7 this necessary condition is met at a distance of up to 10 times the source dimension when the precursory strain source is only 10 of the coseismic deformation provided that the strain source is double the size of the seismic fault itself this model could account for the absence of self potential anomalies related to the earthquake itself as a large proportion of the available instabilities could have been swept away by the precursory strain furthermore with such a model a precursory strain in the source area could induce a detectable change in the background seismic activity over a vast area which may give a new interpretation of the times of increased probability observations for short distances the triggering of fluid instabilities by strain perturbation and the associated streaming potential effect may well be a promising model for explaining low frequency electric and magnetic precursors

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

ocean loading effects on stress at near shore plate boundary fault systems 1 changes in eustatic sea level since the last glacial maximum create a differential load across coastlines globally the resulting plate bending in response to this load alters the state of stress within the lithosphere within a half flexural wavelength of the coast we calculate the perturbation to the total stress tensor due to ocean loading in coastal regions our stress calculation is fully 3 d and makes use of a semianalytic model to efficiently calculate stresses within a thick elastic plate overlying a viscoelastic or fluid half space the 3 d stress perturbation is resolved into normal and shear stresses on plate boundary fault planes of known orientation so that coulomb stress perturbations can be calculated in the absence of complete paleoseismic indicators that span the time since the last glacial maximum we investigate the possibility that the seismic cycle of coastal plate boundary faults was affected by stress perturbations due to the change in sea level coulomb stress on onshore transform faults such as the san andreas and alpine faults is increased by up to 1 1 5 mpa respectively promoting failure primarily through a reduction in normal stress these stress perturbations may perceptibly alter the seismic cycle of major plate boundary faults but such effects are more likely to be observed on nearby secondary faults with a lower tectonic stress accumulation rate in the specific instance of rapid sea level rise at the black sea the seismic cycle of the nearby north anatolian fault was likely significantly advanced

earthquake hazards rivers rifts and ruptures the southern san andreas fault is due for a large earthquake seismic images of sediments deposited in an ancient lake overlying the southern end of the fault indicate that episodic flooding may have triggered earthquakes in the past

the effect of sea level changes on fault reactivation potential in portugal abstract the aim of this study is to assess the impact of sea level changes on both the stress field and the potential of fault reactivation in west iberia the analysis is applied to a set of five active faults distributed across portugal selected for representing predominant fault directions and for being seismically active the results show that the rise of sea level since the last glacial maximum has produced flexural effects with distinct impacts on different faults the coulomb stress changes induced by the sea level rise along the s marcos quarteira south portugal and the horseshoe offshore sw iberia faults are found to be extremely small independently of the elastic plate thickness these faults are thus unaffected by flexural effects related to ocean loading and are unlikely to possess any paleoseismic record of this phenomenon in contrast the eustatic sea level rise during the late pleistocene could have raised the coulomb stress by 0 5 1 mpa along the manteigas vilarica braganca north portugal and lower tagus valley lisbon area fault systems such stress perturbations are probably sufficient to impact the seismic cycle of the manteigas vilarica braganca fault bringing it closer to failure and possibly triggering the earthquake clusters that have been observed in previous paleoseismologic studies