strain heating in process zones implications for metamorphism and partial melting in the lithosphere abstract since the late 1970s most earth scientists have discounted the plausibility of melting by shear strain heating because temperature dependent creep rheology leads to negative feedback and self regulation this paper presents a new model of distributed shear strain heating that can account for the genesis of large volumes of magmas in both the crust and the mantle of the lithosphere the kinematic geometry and rates frustration associated with incompatible fault junctions e g triple junction prevents localisation of all strain on the major faults instead deformation distributes off the main faults forming a large process zone that deforms still at high rates under both brittle and ductile conditions the increased size of the shear heated region minimises conductive heat loss compared with that commonly associated with narrow shear zones thus promoting strong heating and melting under reasonable rheological assumptions given the large volume of the heated zone large volumes of melt can be generated even at small melt fractions there are clear examples of volcanism correlated with fault complexities that remain enigmatic and that could be related to that mechanism of process zone heating we propose here a simple dislocation model to define the process zones determine off fault strain rates and quantify how much plastic work can be dissipated as heat to provide an example we examine the case of the junction between the east and north anatolian shear zones in eastern turkey this is chosen because the composition and age of emplacement of the quite extensive volcanics are well known as are the rates of motion on the associated strike slip faults the geometry of the system also allows the dislocation method to be easily adopted we conclude that melting of the crust and the lithospheric mantle could start only a few myrs after the onset of deformation conservative assumptions for rheological parameters and melting points can explain both the timing and the bimodal nature of the volcanism predictions of melt volume are within the rheological uncertainties while the current paper is focused on strike slip faults the approach can be applied to kinematic complexities associated with thrust faults as well and maybe more generally to regions in the lithosphere where oblique boundary conditions force deformation to occur partly in a distributed manner while still at high rates

regional strike slip in the eastern continental margin of korea and its tectonic implications for the evolution of ulleung basin east sea sea of japan air gun profiles delineate a large scale strike slip fault system along the eastern continental margin of korea this system comprises two right stepping curvilinear master faults hupo and yangsan faults that are closely associated with en echelon nominal faults and reverse faults and folds these structural features indicate two phases of regional deformation in the earlier phase late oligocene to early miocene the margin experienced extensional shear strain with dextral strike slip movements along the hupo and yangsan faults that guided a pull apart opening of the pohangyoungduk basin the later phase deformation late miocene to early pliocene was governed by shortening strain that induced a convergent strike slip reactivation of the hupo fault as well as widespread contractile faulting and folding the regional deformation in the eastern korean continental margin reflects three stages of tectonic evolution of the ulleung basin 1 pull apart opening stage from late oligocene to early miocene 2 rotational opening stage with a differential rotation of the japanese arc in middle miocene and 3 back arc closing stage from the end of middle miocene to present

small and large earthquakes can have similar starts a long standing question in seismology is whether small and large earthquakes have similar or different onsets an analysis of earthquakes around japan shows that in some cases these onsets are almost identical an analysis of earthquakes along the japan trench

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

local observations of the onset of a large earthquake 28 june 1992 landers california the landers earthquake mw 7 3 of 28 june 1992 had a very emergent onset the first large amplitude arrivals are delayed by about 3 sec with respect to the origin time and are preceded by smaller scale slip other large earthquakes have been observed to have similar emergent onsets but the landers event is one of the first to be well recorded on nearby stations we used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release and to determine the slip function of the 3 sec nucleation process relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2 5 sec three station array analysis of the p wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals indicating that the large amplitude source was several kilometers deeper than the initial onset an ml 2 8 foreshock located close to the hypocenter was used as an empirical green s function to correct for path and site effects from the first 3 sec of the mainshock seismogram the resultant deconvolution produced a slip function that showed two subevents preceding the main energy release an mw 4 4 followed by an mw 5 6 these subevents do not appear anomalous in comparison to simple moderate sized earthquakes suggesting that they were normal events which just triggered or grew into a much larger earthquake if small and moderate sized earthquakes commonly detonate much larger events this implies that the dynamic stresses during earthquake rupture are at least as important as long term static stresses in causing earthquakes and the prospects of reliable earthquake prediction from premonitory phenomena are not improved

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

controls on caldera structure results from analogue sandbox modeling we conducted scaled analogue sandbox models of caldera formation in order to understand the effects of chamber depth and orientation on the spatial and temporal development of calderas dry sand contained in a 1 m diameter cylinder served as a crustal rock analogue and a water filled 0 6 m diameter rubber bladder served as an analogue magma chamber scaling parameters included a length ratio l of 2 5 10 5 and a stress ratio of 1 8 2 4 10 5 in contrast to some previous analogue models the viscosity of the fluid in the chamber and its withdrawal rate were properly scaled generally deformation began with broad sagging followed by an arcuate or linear outward dipping fault that formed on one side of the caldera this fault propagated laterally around the caldera in both directions sometimes joining other faults and typically forming an overall polygonal structure as subsidence continued the caldera grew incrementally outward and progressively formed a series of concentric outward dipping faults lastly a peripheral zone of extension and pronounced sagging and commonly an inward dipping outer fault related to extension developed at the surface as the depth of the chamber increased 1 the area of faulting decreased 2 the symmetry of the caldera was affected and 3 the coherence of the subsiding block decreased tilting the chamber caused highly asymmetric subsidence to occur in this case faults formed first where the bladder was shallowest subsidence then shifted rapidly to where the bladder was deepest producing an elongate trapdoor caldera that was deepest where the bladder was deepest our experiments highlight the roles of sagging and faulting during caldera subsidence surface fault patterns both in our experiments and at natural calderas are frequently not circular the aspect ratio of the block above the magma chamber controls the shape of the caldera which is frequently polygonal the faults at natural calderas determine locations and migration of eruptive vents the degree of subsidence the style of postcal dera resurgent magmatism and the extent of hydrothermal circulation our experiments reveal details of how calderas grow outward incrementally and demonstrate that asymmetric subsidence along linear and arcuate faults is common to many calderas

slip partitioning by elastoplastic propagation of oblique slip at depth oblique motion along tectonic boundaries is commonly partitioned into slip on faults with different senses of motion the origin of slip partitioning is important to structural geology tectonophysics and earthquake mechanics partitioning can be explained by the upward elastoplastic propagation of oblique slip from a fault or shear zone at depth the strain field ahead of the propagating fault separates into zones of predominantly normal reverse and strike slip faulting the model successfully predicts the distribution of fault types along parts of the san andreas and haiyuan faults

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

spatiotemporal variation of stress drop during the 2008 mogul nevada earthquake swarm we estimate stress drops for 148 shallow 6 km earthquakes in the complex 2008 mogul nevada swarm using empirical green s function derived spectral ratios near source temporary broadband seismometers deployed before the mw4 9 main shock provide high quality records of many foreshocks and aftershocks and an ideal opportunity to investigate uncertainties in corner frequency measurement as well as stress drop variation related to space time depth mechanism and magnitude we explore uncertainties related to source model measurement approach cross correlation limit and frequency bandwidth p s wave results range from 0 2 0 15 0 3 0 15 to 36 20 58 7 mpa a variation greater than the error range of each individual estimate although this variation is not explained simply by any one parameter spatiotemporal variation along the main shock fault plane is distinct coherent clusters of high and low earthquakes are seen and high foreshocks correlate with an area of reduced aftershock productivity these observations are best explained by a difference in rheology along the fault plane average s of 3 9 1 1 4 0 1 1 mpa using p s are similar to those found for earthquakes in a variety of settings implying that these shallow potentially fluid driven earthquakes do not have systematically lower than average tectonic earthquakes 4 mpa and therefore have similar or higher due to proximity to the surface expected ground motions compared to typical earthquakes the unprecedented detail achieved for these shallow small magnitude earthquakes confirms that when measured precisely is a valuable observation of physically meaningful fault zone properties and earthquake behavior

tectonic model and fault segmentation of the median tectonic line active fault system on shikoku japan 1 fault segmentation models have been developed by using various types of information about faults including both geological and geophysical data in order to predict the size of future cascade earthquakes in these models however stress conditions within the fault systems have not been considered in sufficient detail major fault systems generally exhibit heterogeneous stress conditions the median tectonic line active fault system mtlafs is the longest and most active arc parallel right lateral strike slip fault system in japan the stress conditions along the mtlafs change from transpression on eastern shikoku island to transtension on kyushu island the change of stress conditions along the fault system is caused by the counterclockwise rotation of the nankai fore arc sliver in response to the relative motion of the philippine sea and eurasian tectonic plates and back arc spreading in the okinawa trough here we propose stress condition segmentation as a concept that deals with the diversity of stress conditions and can be applied in seismic hazard assessment according to this concept the mtlafs is divided into three segments the east shikoku west shikoku and kyushu segments the east shikoku and kyushu segments are under compressional and tensional stress conditions respectively stress in the west shikoku segment which is between the other two segments is transitional from compressional to tensional conditions in particular change in the magnitude of fault normal stresses along strike is one of the key factors that govern the geometry of fault discontinuities rupture propagation and termination and consequently fault segmentation application of our stress condition segmentation concept to the mtlafs suggests that future earthquakes in the west shikoku and kyushu segments will be of lower energy than those in the east shikoku segment

structure of reunion island indian ocean inferred from the interpretation of gravity anomalies abstract reunion is a volcanic edifice whose origin is related to a hot spot in the indian ocean only 3 of its volume is emergent many geological and geophysical studies were carried out on reunion island during the 1980 s but few of them allow study of the internal structure of the edifice several gravity surveys have been carried out on the island since 1976 and we have compiled the available data set the lack of data on the western side of the island led us to conduct a regional survey in 1993 to obtain a more homogeneous distribution of the stations computation of bouguer anomalies for different correction densities accounts for the variable density of the rocks constituting the edifice and provides a distribution of gravity anomalies interpreted as dense bodies of intrusive rocks inside the edifice two very large intrusive complexes can be unambiguously recognised one beneath piton des neiges and one beneath the grand brule area both have been penetrated by geothermal exploration drill holes and the first is also known from outcrop observations 2 5d simple models were constructed to reveal the geometry and extent of the buried intrusives they are deeply rooted extending several kilometres below sea level and extensive 20 25 km long and 10 13 km wide for the piton des neiges complex 12 15 km long and some kilometres wide for the grand brule complex the development of such complexes implies that the activity of the two volcanic centres was long lasting and remained stable while the volcanoes were growing the grand brule complex has been interpreted as relics of an old volcano named alizes volcano the interpretation of the gravity maps suggests the presence of a ridge of dense rocks to the north of the axis joining the centres of piton des neiges and piton de la fournaise volcanoes by analogy with the other structures 2 5d models show that this structure would culminate between 0 and 1 km below sea level and be 15 km wide this complex induces a maximum anomaly in takamaka valley and we thus propose to name it takamaka volcano no geological evidence of the nature of these dense rocks is available but the ridge coincides with structures revealed by magnetic and seismic data interpretation of the bouguer anomaly maps suggests that the inner gravity structure of piton de la fournaise is not characterised by the presence of a voluminous dense body but probably by more restricted concentrations of dense rocks some structures can be recognised along the present ne and se rift zones and in the previous central part of piton de la fournaise to the west of the present summit the recent eastward migration of the centre of activity of piton de la fournaise accounts for the lack of a large positive anomaly beneath the active craters

the san andreas and walker lane fault systems western north america transpression transtension cumulative slip and the structural evolution of a major transform plate boundary abstract relative right lateral pacific north american transform motion across the western us is largely taken up by the san andreas and walker lane fault systems cumulative lateral displacement on active strands of the san andreas system is 3 4 or more times greater than across faults of the walker lane the san andreas system is transpressional while the walker lane system is transtensional the relatively more complex discontinuous and broader system of faults composing the walker lane system is attributed to lower cumulative slip and an attendant extensional component of motion greater slip accompanied by a small component of contraction has yielded the simpler more continuous and generally throughgoing set of faults that comprise the san andreas system with respect to the contrasting amounts of cumulative slip the san andreas is at a more mature stage of structural development than the walker lane despite differences in gross patterns of faulting the systems also share similarities in deformation style slip along each is locally accommodated by clockwise rotation of crustal blocks that has produced structural basins and oblique components of slip are commonly partitioned into subparallel strike slip and dip slip faults

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

japan sea opening history and mechanism a synthesis the respective tectonic effects of back arc spreading and continental collision in asia are considered either as two independent processes or as closely interrelated extrusion tectonics assumes that the opening of the south china sea and the left lateral motion along the red river fault are geometrically linked in a pull apart manner this model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated in the case of the japan sea we can show without ambiguity that back arc opening was controlled by large intracontinental strike slip faults which can be easily understood as effects of the india asia collision far from the indenter the japan sea opened in the early miocene in a broad pull apart zone between two major dextral strike slip shear zones the first one extends from north sakhalin to central japan along 2000 km it has accommodated about 400 km of finite displacement deformation along it varies from dextral transpression in the north to dextral transtension in the south the second is between korea and sw japan and has accommodated a smaller displacement of about 200 km the extensional domain in between lies in the back arc region of japan distributed stretching of the arc crust resulted in the formation of most of the japan sea while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the japan basin the first oceanic crust was formed in a small triangle based on the eastern shear zone and spreading propagated westward inside the pull apart region timing of oceanic crust formation of formation of the dextral shear zones and of block rotation in between as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history this evolution is discussed by comparison to other manifestations of the arc and back arc activity such as the history of sedimentation and volcanism the paper then suggests that the collision of india can have tectonic consequences as far north as japan and sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion

the november 2017 mw 5 5 pohang earthquake a possible case of induced seismicity in south korea the moment magnitude mw 5 5 earthquake that struck south korea in november 2017 was one of the largest and most damaging events in that country over the past century its proximity to an enhanced geothermal system site where high pressure hydraulic injection had been performed during the previous 2 years raises the possibility that this earthquake was anthropogenic we have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks constrain the geometry of this seismic sequence and shed light on its causal factors according to our analysis it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities finally we found that the earthquake transferred static stress to larger nearby faults potentially increasing the seismic hazard in the area

the structure of composite volcanoes unravelled by analogue modelling a review abstract volcanic edifices are unstable accumulations of eruptive and intrusive products with complex internal structures a documentation of these structures facilitates the assessing of the various hazards associated with volcanoes e g flanks instabilities and eruptive events however structures are not easily assessed in the field as volcanoes are regularly covered by eruptive products and are rapidly eroded in the case of recent and active volcanoes internal structures are generally extrapolated from the external morphology of the edifice which can be documented using digital elevation models dem and geodetic data interpretation of such data greatly benefits from analogue models which are idealised representations of reality used to test the impact that various processes may have on the shape of a volcanic edifice this short review focuses on the contribution of analogue models to our comprehension of the internal structure of composite volcanic cones the other volcanic morphologies e g caldera are excluded from this review as they have distinct structure and evolution that have already been thoroughly reviewed the reviewed models were used to investigate the impact that regional faults magma injections and ductile substratum among other processes have on the internal structure and surface morphology of many volcanic edifices these models were also used to locate unstable flanks and eruption sites

cold air incursions over subtropical south america mean structure and dynamics abstract synoptic scale incursions of midlatitude air moving into subtropical south america to the east of the andes cordillera are observed to occur year round with a periodicity of about 1 2 weeks during wintertime they have a profound impact upon the low level temperature field and extreme episodes produce freezing conditions from central argentina to southern brazil and bolivia warm season episodes produce less dramatic variations of temperature but they organize deep convection in the form of synoptic scale bands of convective cloudiness along the leading edge of the cool air on the basis of 17 yr of ncep ncar reanalysis and outgoing longwave radiation fields the mean synoptic scale structure and evolution of these incursions is documented using a simple compositing technique the underlying physical mechanisms responsible for the occurrence of these incursions are also investigated by diagnosing the leading dynamic and thermodynamic forcing of their development

scaling of earthquake rupture growth in the parkfield area self similar growth and suppression by the finite seismogenic layer 1 we propose a new framework on the scaling of earthquake rupture growth time history and we scale the moment rate and the cumulative moment functions of earthquakes over a wide magnitude range mw 1 7 6 0 in parkfield california the moment rate and the cumulative moment functions of the small and medium earthquakes mw 1 7 4 6 are derived by slip inversion analyses with the empirical green s function technique the moment rate functions of the investigated earthquakes except the mw 6 0 event are similar to each other increasing rapidly in the first half growth stage and decelerating in the latter half decline stage in the growth stage the cumulative moment functions are approximated by mo t nm 2 1017 t s 3 independent of the final size of the earthquakes the proportionality of the cumulative moment to the cube of time implies self similarity during earthquake rupture growth in the decline stage the cumulative moment function veers off the common rupture curve the mw 6 0 event also grows along the same rupture curve until 1 s after which the cumulative moment function is proportional to time from the onset itself this is because the finite seismogenic layer limits the vertical extent of dynamic rupture our method and results contribute to our understanding of earthquake source physics especially on earthquake rupture growth processes which may help to improve earthquake early warning techniques

experiments on cauldron formation a polygonal cauldron and ring fractures abstract the sequence of formation of the motojuku type cauldron fujita et al 1970 is summarized as follows 1 doming due to ascent of a magma body 2 development of normal faults which produce a polygonal cauldron and 3 eruption of acidic to intermediate pyroclastic material model experiments on a scale of 1 200 000 reveal that ascent of the magma body which was imitated by a ball of hardened putty produced a polygonal cauldron composed of radial and concentrically arranged short fractures on the roof of a dome no ring fractures were formed this type of cauldron develops near the surface on the other hand emission of magma which was imitated by evaporation of a ball of dry ice in brittle powdered material caused ring faults dipping outward and a circular cauldron without up or downwarping this type of cauldron develops upward from the magma body the former model is equated to the motojuku type cauldron and the latter model to the other types of cauldrons with ring fractures

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

caldera morphology in the western galapagos and implications for volcano eruptive behavior and mechanisms of caldera formation abstract caldera morphology on the six historically active shield volcanoes that comprise isabela and fernandina islands the two westernmost islands in the galapagos archipelago is linked to the dynamics of magma supply to and withdrawal from the magma chamber beneath each volcano caldera size e g volumes 2 9 times that of the caldera of kilauea hawai i the absence of well developed rift zones and the inability to sustain prolonged low volumetric flow rate flank eruptions suggest that magma storage occurs predominantly within centrally located chambers at the expense of storage within the flanks the calderas play an important role in the formation of distinctive arcuate fissures in the central part of the volcano repeated inward collapse of the caldera walls along with floor subsidence provide mechanisms for sustaining radially oriented least compressive stresses that favor the formation of arcuate fissures within 1 2 km outboard of the caldera rim variations in caldera shape depth to diameter ratio intra caldera bench location and the extent of talus slope development provide insight into the most recent events of caldera modification which may be modulated by the episodic supply of magma to each volcano a lack of correlation between the volume of the single historical collapse event and its associated volume of erupted lava precludes a model of caldera formation linked directly to magma withdrawal rather caldera collapse is probably the result of accumulated loss from the central storage system without sufficient recharge and as has been suggested for kilauea may be aided by the downward drag of dense cumulates and intrusives

hyposat an enhanced routine to locate seismic events a program package called hyposat has been under development that attempts to use the maximum information possible to estimate the hypocenter of a seismic source the standard input parameters can be used arrival times of first and later onsets with backazimuths and ray parameters or apparent velocities in addition travel time differences between different phases observed at the same station can be optionally used the observed standard deviations are used to weight all input parameters and the inversion is done with a generalized matrix inversion code

tectonics of strike slip restraining and releasing bends restraining and releasing bends are common but enigmatic features of strike slip fault systems occurring in all crustal environments and at regional to microscopic scales of observation regional scale restraining bends are sites of mountain building transpressional deformation and basement exhumation whereas releasing bends are sites of topographic subsidence transtensional deformation basin sedimentation and possible volcanism and economic mineralization because restraining and releasing bends often occur as singular self contained domains of complex deformation they are appealing natural laboratories for earth scientists to study fault processes earthquake seismology active faulting and sedimentation fault and fluid flow relationships links between tectonics and topography tectonic and erosional controls on exhumation and tectonic geomorphology this volume addresses the tectonic complexity and diversity of strike slip restraining and releasing bends with 18 contributions divided into four thematic sections 1 a topical review of fault bends and their global distribution 2 bends sedimentary basins and earthquake hazards 3 restraining bends transpressional deformation and basement controls on development 4 releasing bends transtensional deformation and fluid flow

chaco low level jet events characterization during the austral summer season 1 previous studies showed a relationship between convection maxima and the convergence of vapor flux over southeastern south america nicolini and saulo 2000 explored the hypothesis of an intensification of this mutual dependency during the chaco jet events they defined these events as extreme cases of low level jets east of the andes that penetrate southernmost to 25 s using eta operative products during the 1997 1998 austral warm season the interest of the present paper centers on the climatic characterization of the chaco jet events cjes and the possibility of researching this hypothesis using the european centre for medium range weather forecasts reanalyses era which cover a 15 year period 1979 1993 the cjes represent a subensemble of low level jet events east of the andes that are infrequent in the era data set their duration varies from 1 to 10 days more frequently extending from 1 to 5 days the outstanding features of the circulation and the thermodynamic field that represent this ensemble are a maximum contrast of air masses in a latitude close to 39 s the presence of a trough centered on 70 w within a baroclinic wave train penetrating from the pacific ocean and a maximum of heat and moisture over northen argentina and paraguay during the cjes there is an important flux of moisture and convergence at low and mid levels that is about 10 times more intense than the summer mean the intensity found in the water vapor flux anomaly reinforces the importance of studying these episodes for the purpose of determining the water balance over southeastern south america the statement that the cjes represent an important characteristic of the southeastern south american climate is founded on the fact that although the cjes only represent 17 of the austral summer days they account for a significant fraction of the precipitation a maximun of 55 over northeastern argentina however it is indispensable to contrast these results with future field experiments to test the hypothesis addressed in this paper

the geological and structural evolution of the cerro tuzgle quaternary stratovolcano in the back arc region of the central andes argentina abstract the aim of our paper is to contribute to a better knowledge of the volcanism in the back arc region of the central andes and its relationships with the basement geology the stress field and the tectonic evolution by studying in detail the stratigraphy and the structure of the quaternary cerro tuzgle stratovolcano in the puna plateau field mapping and remote sensing analysis reveal the stratigraphic architecture the geological evolution and the volcanotectonic interactions in the cerro tuzgle area for the first time in a volcano of the puna plateau synthemic units bounded by unconformity surfaces have been defined unrevealing the temporal and spatial relationships between constructive and destructive phases of the volcano history our study indicates that after the emplacement of a small ignimbrite deposit and of few scattered lava domes the central cerro tuzgle volcano built up throughout three distinct phases of edifice construction the first of these constructive phases ended with a previously unreported destructive event consisting of 0 5 km 3 catastrophic sector collapse of the volcanic edifice whose stratigraphic position and main characteristics have been identified the study suggests that the regional stress regime and the topography of the substrata are the main non magmatic factors controlling the constructive and destructive phases of the volcano including the directions of magmatic intrusions faulting and gravitational sector failure of the volcano the integration of synthemic stratigraphy and volcanotectonic analysis in the study of volcanic edifices showed to be an effective methodological approach for the understanding of the magmatic and tectonic evolution of the puna plateau

internal structure of piton de la fournaise volcano from seismic wave propagation and earthquake distribution abstract arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3 d velocity heterogeneity of piton de la fournaise the lateral heterogeneity of the 2632 m high edifice is resolved as a high velocity plug 1 5 km in diameter surrounded by a low velocity ring which may be interpreted as due to the construction of fournaise on the flank of the older volcano piton des neiges wave mode conversion detected on three component seismograms provides evidence for boundaries of contrasted velocities pre eruptive swarm earthquakes cluster in the high velocity zone under the dolomieu summit crater low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1 3 km radial flow of magma to the vents in enclos fouque beneath the high velocity plug the existence of a body with low velocity for p and even for s waves is well constrained however the walls and base are poorly defined because of the lack of deep earthquakes for sampling the few earthquakes that are located in this depth region usually occur at a depth of around 1 5 km below sea level in the region of the cone this can be considered providing the upper constraint on the lower limit of the aseismic part of the low velocity body the coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low velocity aseismic volume 1 5 km below sea level under the high velocity plug of the cone further down the concentration of seismicity in two swarms between 2 and 4 km under the eastern flank does not allow the structure to be sampled effectively

the 2017 ml 5 4 pohang earthquake sequence korea recorded by a dense seismic network abstract the 2017 ml 5 4 pohang earthquake in southeastern korea which was induced by fluid injection from an enhanced geothermal system and its foreshock aftershock sequence has been recorded by a dense and portable temporary seismic array the hypocentral distribution of the earthquake sequence reveals the reactivation of a complex subsurface fault system that was previously unmapped aftershock seismicity propagated to the southwest and revealed previously unknown fault segments the aftershocks tend to concentrate along the tips of the main rupture with a lack of aftershocks around the mainshock hypocenter this pattern suggests that the stress in the mainshock area was almost completely released during the mainshock and early aftershock phase and that the recurrence of moderate to large earthquakes in the hypocentral area is unlikely compared with the marginal areas a new rupture occurred along the southwestern margin of the main rupture after the largest aftershock ml 4 6

volcano core collapse triggered by regional faulting it has been proposed recently that large scale caldera like structures may result from the viscous lateral spreading of a hydrothermal system located in the central part of volcanic edifices for this to occur an unbutressed boundary resulting in reduced lateral stresses must exist or be created not far from the hydrothermal system different ways to achieve such a weak lateral confinement may be proposed in this paper we show that regional tectonics may provide an unconfined boundary if a normal fault lowers part of the volcanic edifice a natural example is the island of nuku hiva in the marquesas archipelago french polynesia for which geological data strongly suggest that a regional fault oriented n75 e is responsible for the present day shape of the island i e an ellipse cut in the middle by a straight side along which two nested calderas are breached analogue modelling shows the mechanical consistency of the model and reveals that very low velocity faulting is needed for the formation of a caldera like structure

sector collapse forming at casita volcano nicaragua catastrophic sector collapse occurs when a volcano becomes structurally unable to support its own load one process particularly capable of weakening the edifice is hydrothermal activity it can produce high pore pressures and alter strong rock to clays alteration can extend progressively over long periods 100 yr allowing deformation to develop slowly before collapse an important finding is that structures produced by such deformation are recognizable and could permit collapse prediction we present the case of casita nicaragua where hydrothermal activity has been weakening the edifice core causing flank spreading altering original constructional shape and steepening flank slopes one side is slumping outward producing a crescentic scar with a basal bulge we identify this feature as the site of a potential sector collapse with conditions ripe for failure

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

cyclic caldera collapse piston or piecemeal subsidence field and experimental evidence many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution on gran canaria canary islands the miocene tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone sheet swarm obscuring intracaldera structural relations extracaldera radial and circumferential faults and dikes are well exposed we used field data and experiments scaled to the island of gran canaria to clarify the poorly understood structural temporal and genetic relationship of peripheral faults to the central caldera the experimental setup comprises a cone of medium grained sand in which a rubber balloon was repeatedly inflated and deflated balloon inflation resulted in updoming and a dominantly radial fault pattern whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks a complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the tejeda caldera on gran canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes

on large scale circulations in convecting atmospheres the dominant thinking about the interaction between large scale atmospheric circulations and moist convection holds that convection acts as a heat source for the large scale circulations while the latter supply water vapour to the convection we show that this idea has led to fundamental misconceptions about this interaction and offer an alternative paradigm based on the idea that convection is nearly in statistical equilibrium with its environment according to the alternative paradigm the vertical temperature profile itself rather than the heating is controlled by the convection which ties the temperature directly to the subcloud layer entropy the understanding of large scale circulations in convecting atmospheres can therefore be regarded as a problem of understanding the distribution in space and time of the subcloud layer entropy we show that the subcloud layer entropy is controlled by the sea surface temperature the surface wind speed and the large scale vertical velocity in the convecting layer and demonstrate how the recognition of this control leads to a simple physically consistent view of large scale flows ranging from the hadley and walker circulations to the 30 50 day oscillation in particular we argue that the direct effect of convection on large scale circulations is to reduce by roughly an order of magnitude the effective static stability felt by such circulations and to damp all of them

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

forward waveform modelling procedure for 1 d crustal velocity structure and its application to the southern korean peninsula summary we propose a full grid search procedure for broad band waveform modelling to determine a 1 d crustal velocity model the velocity model can be more constrained because of the use of broad band waveforms instead of traveltimes for the crustal phases although only a small number of event station pairs were employed despite the time consuming nature of the full grid search method to search the whole model parameter space the use of an empirical relationship between the p and s wave velocities can significantly reduce computation time the proposed method was applied to a case in the southern korean peninsula broad band waveforms obtained from two inland earthquakes that occurred on 2007 january 20 mw 4 6 and 2004 april 26 mw 3 6 were used to test the method the three layers over half space crustal velocity model of the p and s wave velocities was estimated comparisons of waveform fitness between the final model and previously published models demonstrate advancements in the average value of waveform fitness for the inland earthquakes in addition 1 d velocity models were determined for three distinct tectonic regions namely the gyonggi massif the okcheon belt and the gyeongsang basin which are all located inside the study area a comparison between the three models demonstrates that the crustal thickness of the southern korean peninsula increases from nw to se and that the lower crustal composition of the okcheon belt differs from that of the other tectonic regions

revised stratigraphy and reinterpretation of the miocene pohang basinfill se korea sequence development in response to tectonism and eustasy in a back arc basin margin abstract the miocene pohang basin is a pull apart basin formed along the eastern continental margin of korea ecmk during the back arc opening of the east sea sea of japan the basin is filled by more than 1 km thick nonmarine to deep marine strata these strata show extreme vertical and lateral lithofacies changes and have caused decades long controversies on their nature and stratigraphy previous sedimentological studies suggest that the basinfill was deposited by a series of contemporaneously developed depositional systems including fan delta prodelta slope apron and basin plain detailed mapping and magnetotelluric surveying show however that the basinfill is composed of several packages of strata sequences that are bounded by distinct and laterally persistent stratigraphic discontinuities sequence boundaries this suggests that the depositional systems in the pohang basin developed sequentially rather than contemporaneously six packages of strata are identified in the basin a nonmarine to shallow marine transgressive sequence sequence 1 a gilbert type delta conglomerate sequence 2 and alternations of submarine conglomerates and hemipelagic mudstones sequences 3 6 the conglomerates and hemipelagic mudstones of the latter four sequences are interpreted to represent lowstand depositional systems slope apron submarine fan and high gradient delta and condensed intervals respectively compilation of geochronologic paleomagnetic and biostratigraphic data suggests that sequence 1 formed during the gradual subsidence of the ecmk prior to 17 ma whereas sequence 2 formed in response to abrupt downfaulting of the pohang basin at about 17 ma both sequences are interpreted to have developed in response to the early miocene back arc opening tectonism of the east sea on the other hand sequences 3 6 formed between 17 and about 10 5 ma the pohang basin was subject to only minor tectonism during this period and could record global sea level fluctuations we suggest that the four alternations of conglomerates lowstand systems and hemipelagic mudstones condensed intervals resulted most probably from the 3rd order glacioeustatic cycles during the middle miocene this finding implies that the signatures of global sea level fluctuations can be deciphered from a tectonically active sedimentary basin if the timing of regional tectonic development is well constrained and the global sea level chart of haq et al haq b w hardenbol j vail p r 1987 chronology of fluctuating sea levels since the triassic science 235 1156 1167 haq b u hardenbol j vail p r 1988 mesozoic and cenozoic chronostratigraphy and eustatic cycles in wilgus c k hastings b s posamentier h van wagoner j ross c a kendall c g s c eds sea level changes an integrated approach soc econ paleont mineral spec publ 42 pp 71 108 may serve as a guide to basinfill interpretation even in tectonically active sedimentary basins

oblique slip slip partitioning spatial and temporal changes in the regional stress field and the relative strength of active faults in the basin and range western united states when viewed with stress transformation laws and an idealized physical model observations of oblique slip and slip partitioning in the basin and range western united states are interpreted to show that 1 separate regions with the same net extension direction are not necessarily characterized by the same regional stress field 2 fault systems exhibiting partitioning where one of the faults is near vertical generally do not require temporal changes in the stress field to explain the disparate slip vectors on the adjacent faults and 3 the relative strengths of active fault zones may vary by more than an order of magnitude

moist convective velocity and buoyancy scales abstract velocity buoyancy and fractional area scales for moist convection in statistical equilibrium with large scale forcing are derived using the constraints of global energy and entropy conservation and subcloud layer thermodynamic equilibrium the magnitudes of the velocity and buoyancy in moist convective clouds are shown to depend on cloud microphysical properties and on the vertical distribution but not the magnitude of the large scale forcing comparisons of the theoretically derived scales with velocity and buoyancy values observed in a numerical ensemble cloud model and in a one column radiative convective model show good agreement

monitoring the monsoon in the himalayas observations in central nepal june 2001 abstract the monsoon himalayan precipitation experiment mohprex occurred during june 2001 along the south slopes of the himalayas in central nepal radiosondes were launched around the clock from two sites one in the marsyandi river basin on the eastern footslopes of the annapurna range and one farther to the southwest near the border with india the flights supported rainfall and other hydrometeorological observations including surface winds from the marsyandi network that has been operated in this region since the spring of 1999 the thermodynamic profiles obtained from the soundings support the observed nocturnal maximum in rainfall during the monsoon with total column moisture and instability maximized just before rainfall peaks coinciding with the appearance of a monsoon depression over central india the onset of the monsoon in this region was characterized by a weeklong weakening of the upper level westerlies and an increase in moisture and convective instability the vertical structure of

experimental study of caldera formation scaled experiments have been carried out on caldera collapse mechanisms using silicone as analogue magma and dry sand as analogue rock experiments were carried out in two and three dimensions using a range of roof aspect ratios thickness width 0 2 to 4 5 appropriate for caldera collapse they reveal a general mechanism of collapse only weakly dependent on the shape of the reservoir for low roof aspect ratios 1 subsidence starts by flexure of the roof and the formation of outward dipping reverse ring faults which in turn trigger formation of peripheral inward dipping normal ring faults the subsidence always occurs asymmetrically in cross section the reverse faults delimit a coherent piston bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets the surface depression consists of a nondeformed area piston surrounded by an annular extensional zone tilted strata for high aspect ratios 1 multiple reverse faults break up the roof into large pieces and subsidence occurred as a series of nested wedges 2 d or cones 3 d the extensional zone dominates the surface depression in the case where preexisting regional faults do not play a major role the collapse mechanics of calderas probably depends strongly on the roof aspect ratio calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults the annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant

formation of caldera periphery faults an experimental study changing stresses in multi stage caldera volcanoes were simulated in scaled analogue experiments aiming to reconstruct the mechanism s associated with caldera formation and the corresponding zones of structural weakness we evaluate characteristic structures resulting from doming chamber inflation evacuation collapse chamber deflation and cyclic resurgence inflation and deflation and we analyse the consequential fault patterns and their statistical relationship to morphology and geometry doming results in radial fractures and subordinate concentric reverse faults which propagate divergently from the chamber upwards with increasing dilation the structural dome so produced is characterised bysteepening in the periphery whereas the broadening apex subsides pure evacuation causes the chamber roof to collapse along adjacent bell shaped reverse faults the distribution of concentric faults is influenced by the initial edifice morphology steep and irregular initial flanks result in a tilted or chaotic caldera floor the third set of experiments focused on the structural interaction of cyclic inflation and subsequent moderate deflation following doming caldera subsidence produces concentric faults that characteristically crosscut radial cracks of the dome the flanks of the edifice relax resulting in discontinuous circumferential faults that outline a structural network of radial and concentric faults the latter form locally uplifted and tiltedwedges half grabens that grade into horst and graben structures this superimposed fault pattern also extends inside the caldera we suggest that major pressure deviations in magma chamber s are reflected in the fault arrangement dissecting the volcanoflanks and may be used as a first order indication of the processes and mechanisms involved in caldera formation

plate boundary adjustments of the southernmost queen charlotte fault abstract a revision of the plate boundary configuration offshore southern haida gwaii which is the locus of the 2012 m w 7 8 thrust earthquake is based on a re evaluation of regional geophysical data and leads to recognition of fault segments critical for seismic hazard analysis off western canada the strike slip queen charlotte fault qcf and revere dellwood fault rdf constitute the transpressive plate boundary between the pacific and north american plates the southernmost 80 km of the qcf strikes at the highest angle 20 to the relative plate motion yet geomorphology adjacent to the fault is the most subdued synthesizing geomorphology seismicity sidescan sonar gravity and seismic reflection profiles indicates that the plate boundary is evolving to a less transpressive configuration than previously interpreted the rdf is 100 km longer than previously mapped it has propagated northward and overlaps the qcf by 120 km propagation is defined by strike slip earthquakes 3 9 m w m w 7 8 and the 1949 m 8 1 earthquakes

induced earthquake magnitudes are as large as statistically expected a major question for the hazard posed by injection induced seismicity is how large induced earthquakes can be are their maximum magnitudes determined by injection parameters or by tectonics deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected however if induced earthquakes occur on tectonic faults oriented favorably with respect to the tectonic stress field then they may be limited only by the regional tectonics and connectivity of the fault network in this study we show that the largest magnitudes observed at fluid injection sites are consistent with the sampling statistics of the gutenberg richter distribution for tectonic earthquakes assuming no upper magnitude bound the data pass three specific tests 1 the largest observed earthquake at each site scales with the log of the total number of induced earthquakes 2 the order of occurrence of the largest event is random within the induced sequence and 3 the injected volume controls the total number of earthquakes rather than the total seismic moment all three tests point to an injection control on earthquake nucleation but a tectonic control on earthquake magnitude given that the largest observed earthquakes are exactly as large as expected from the sampling statistics we should not conclude that these are the largest earthquakes possible instead the results imply that induced earthquake magnitudes should be treated with the same maximum magnitude bound that is currently used to treat seismic hazard from tectonic earthquakes

experiments on the indentation process during cryptodome intrusions new insights into mount st helens deformation scaled experiments were carried out to study the deformation of a volcanic edifice by forcible intrusion of a cryptodome as the magma analogue is injected vertically into a sand cone asymmetric deformation is caused by the formation of a curved major shear fault which dips inward from one side of the cone to the opposite edge of the intrusion the path of the ascending silicone deviates to follow the trajectory of the fault and a lateral bulge grows slowly from the footwall of the fault the oblique push makes the bulge migrate outward causing extension upslope to form an asymmetric graben in the hanging wall of the major shear fault we suggest that the pattern of internal deformation within mount st helens prior to the may 18 1980 eruption was similar to that observed in our scaled models

isolating the role of surface evapotranspiration on moist convection along the eastern flanks of the tropical andes using a quasi idealized approach abstractthe contribution of surface evapotranspiration et to moist convection cloudiness and precipitation along the eastern flanks of the tropical andes eads was investigated using the weather research and forecasting wrf model with nested simulations of selected weather conditions down to 1 2 km grid spacing to isolate the role of surface et numerical experiments were conducted using a quasi idealized approach whereby at every time step the surface sensible heat effects are exactly the same as in the reference simulations whereas the surface latent heat fluxes are prevented from entering the atmosphere energy balance analysis indicates that surface et influences moist convection primarily through its impact on conditional instability because it acts as an important source of moist entropy in this region the energy available for convection decreases by up to approximately 60 when the et contribution is withdrawn in contrast when convective motion is not thermally driven or under condit

detection of microearthquakes and identification of their causative structures in the eastern offshore region of south korea abstract a matched filter has been applied to continuous seismic records from the eastern offshore region of south korea to identify small earthquakes undetected by routine processing the resulting density of the regional earthquake catalog has increased by a factor of five relative to the detections reported by the korea meteorological administration high precision locations of newly identified microearthquakes and previously located earthquakes cluster into streaks that delineate structures responsible for the seismicity associated with the hupo fault offshore of the southern korean peninsula microearthquakes in the northern and southern segments of the fault zone exhibit different behaviors earthquakes in the northern segment occur at a regular temporal interval while those in the southern segment occur in bursts the identified fault system dips steeply to the west at shallow

elliptical calderas in active tectonic settings an experimental approach abstract caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber many field theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults in the simplest theoretical scenario circular magma chambers produce circular calderas many calderas however are elliptical in shape particularly those in extensional and compressive tectonic settings several factors may explain elliptical calderas the first is the presence of an elliptical magma chamber established by for instance preferential intrusion along pre existing basement structures or differential spalling of the magma chamber walls the second is the overlap nesting of several discrete calderas to form a single larger elliptical structure the third is asymmetric subsidence the fourth is variable pre collapse topography a fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation a sixth factor is the post collapse distortion of the caldera structure due to continued regional deformation to better understand relationships between caldera surface expression reservoir geometry and regional tectonic stresses we conducted scaled analogue experiments these experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs circular rubber balloons of known dimensions and depths the results show that in principle calderas produced in compression extension experiments are elongated parallel to the direction of minimum horizontal compressive stress despite the chamber beneath being circular in plan view as a consequence model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress to shallower dips where striking parallel to the minimum horizontal regional compressive stress this leads us to suggest that the influence of a regional stress field on caldera fault orientation during and or after caldera formation may be significant in the development of elliptical calderas in addition such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions

caldera subsidence in areas of variable topographic relief results from analogue modeling calderas form in volcanic areas commonly associated with topographic relief pre existing topography plays an important role in the style of the caldera subsidence topography increases the load and affects the principle stress trajectories located between the roof of the magma chamber and the surface the morphology internal structure and temporal evolution of calderas are therefore sensitive to the local topography we carried out scaled analogue experiments to investigate the effect of pre existing topographic relief on caldera subsidence by modeling the presence of stratocones and plateaus of variable mass diameter and positions prior to collapse we induced collapse in sandbox experiments by withdrawing water from a rubber bladder to simulate caldera collapse into a large shallow reservoir deformation was first manifested by sagging of the sand at the surface followed by the upward propagation of a set of subsidence controlling faults from the bladder in experiments with no topography these faults usually reached the surface near the centre of the cylinder as evacuation and incremental growth progressed a second outer set of subsidence controlling faults developed this outer set dominated the subsidence by increasing the topographic load by 6 the subsidence efficiency increased producing calderas up to approximately 20 deeper the inner set of subsidence controlling faults steepened and controlled most of the collapse by contrast to the experiments without topography adding load also reduced outward growth of peripheral sagging and development of extensional faults leading to a diameter of sagging 20 smaller than with no topography a comparative analysis of our results with mount mazama at crater lake oregon and glass mountain at long valley california supports the interpretation that the addition of topographic load modifies the evolution of the major caldera faults

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

the parametrization of surface fluxes in large scale models under free convection this paper investigates the idea of formulating free convection in large scale models as a special case of forced convection in free convection the wind speed in the surface transfer law is related to the velocity of the large eddies in the mixed layer and is proportional to the convection velocity scale the empirical coefficient is estimated with the help of large eddy simulation data by sykes et al 1993 and the resulting formulation is compared with field data by stull 1994 this concept is shown to be applicable to smooth ocean surfaces as well as rough land surfaces it is argued that within this framework free convection is a natural extension of forced convection and only needs a minor modification of traditional transfer laws

sar revealed slip partitioning on a bending fault plane for the 2014 northern nagano earthquake at the northern itoigawa shizuoka tectonic line abstract by applying conventional cross track synthetic aperture radar interferometry insar and multiple aperture insar techniques to alos 2 data acquired before and after the 2014 northern nagano central japan earthquake a three dimensional ground displacement field has been successfully mapped crustal deformation is concentrated in and around the northern part of the kamishiro fault which is the northernmost section of the itoigawa shizuoka tectonic line the full picture of the displacement field shows contraction in the northwest southeast direction but northeastward movement along the fault strike direction is prevalent in the northeast portion of the fault which suggests that a strike slip component is a significant part of the activity of this fault in addition to a reverse faulting clear displacement discontinuities are recognized in the southern part of the source region which falls just on the previously known kamishiro fault trace we inverted the sar and gnss data to construct a slip distribution model the preferred model of distributed slip on a two plane fault surface shows a combination of reverse and left lateral fault motions on a bending east dipping fault surface with a dip of 30 in the shallow part and 50 in the deeper part the hypocenter falls just on the estimated deeper fault plane where a left lateral slip is inferred whereas in the shallow part a reverse slip is predominant which causes surface ruptures on the ground the slip partitioning may be accounted for by shear stress resulting from a reverse fault slip with left lateral component at depth for which a left lateral slip is suppressed in the shallow part where the reverse slip is inferred the slip distribution model with a bending fault surface instead of a single fault plane produces moment tensor solution with a non double couple component which is consistent with the seismically estimated mechanism

frequent observations of identical onsets of large and small earthquakes every gigantic earthquake begins as a tiny rock failure at almost a point followed by successive slip of the complex fault system before radiating strong shaking from a vast rupture area extending over hundreds of kilometres whether the growth process of the rupture of a large earthquake is predictable and whether it produces observable signatures different from that of smaller events1 5 are fundamental questions related to the potential for earthquake early warning and probabilistic forecasting inspired by a recent discovery that large earthquakes might have seismic waves and probably rupture processes that are almost identical to those of smaller events6 8 we show that such similarity characterized by large cross correlation is a common feature of earthquakes in the tohoku hokkaido subduction zone japan a systematic comparison of 15 years of high sensitivity seismograph records for approximately 100 000 events reveals 80 extremely similar and 390 very similar pairs of large moment magnitude m 4 5 and small m 4 0 earthquakes co located within about 100 metres an extremely high similarity is observed for pairs of subduction type earthquakes 170 of 899 large events separated by a long period of up to 15 years whereas for pairs of other types of large earthquakes only the foreshocks and aftershocks are similar this frequently occurring similarity between different sized subduction type earthquakes suggests repeated cascading rupture processes in a widespread hierarchical structure9 12 along the plate interface and indicates a specific but probabilistically limited predictability of the final size of the earthquake that is the location and a set of possible sizes of an earthquake are well predicted but its final size is not at all well constrained analysis of a dataset of high sensitivity tohoku hokkaido seismograph records shows that pairs of subduction type earthquakes of different sizes have very similar initial characteristics implying that the final size of an earthquake cannot be reliably predicted from these

analogue models of collapse calderas and resurgent domes collapse calderas and resurgent domes are a common association related to inflation deflation processes in volcanic systems the structure of calderas and domes depends upon the permitted relative movements of crustal volumes at depth the so called space problem in order to study the structures of collapse calderas and resurgent domes and to take the space problem into account several analogue models were made dry quartz sand was used to simulate the rheology of the brittle crust while newtonian silicone putty located at the base of the sand pack simulated the ductile behaviour of the magma a piston moved the silicone putty downward or upward inducing collapse and doming within the sand three separate sets of experiments simulated 1 caldera collapse 2 resurgence and 3 superimposition of resurgence on collapse and vice versa collapse experiments are characterized by the development of two concentric depressions the first formed depression is bordered by outward dipping reverse ring faults the subsequent outer concentric depression is bordered by inward dipping normal ring faults the deformation pattern during resurgence is a function of the overburden thickness t and the dome diameter d for higher t d ratios a dome forms bordered by inward dipping high angle reverse ring faults outward dipping normal ring faults develop at late stages for lower t d ratios the dome shows at late stages a crestal depression accompanied by radial fractures subsequently an apical extrusion of silicone occurs the superimposition of resurgence over collapse and vice versa is characterized by the complete reactivation with opposite kinematics of all the pre existing ring faults during inversion both in caldera and resurgence reverse ring faults form in the early stages due to differential uplift extensional structures subsequently form to accommodate gravitational collapse during the activity of the reverse faults the experiments and the overall similarities with nature suggest that the activity of both reverse and normal faults constitutes a possible solution to the space problem during major collapses or resurgences

high resolution simulation of tropical storm ivan 2004 in the southern appalachians role of planetary boundary layer schemes and cumulus parametrization the weather research and forecasting wrf model was used to simulate the evolution of tropical storm ivan 2004 in the southeast united states using both the yonsei university ysu and mellor yamada janjic myj boundary layer parametrizations in contrast to tropical cyclone tc simulations over the ocean the effect of the surface layer becomes secondary for a dissipating hurricane along its terrestrial track although these two schemes can reproduce ivan reasonably well our results suggest that the mixing properties for damped mechanical turbulent conditions weakly stable are strongly underestimated by both parametrizations this underestimation impacts the thermodynamic properties of the storm leading to significant differences in the storm areal extent and the simulated precipitation fields suggestions for further improvements are provided an evaluation of the impact of using or not using a convective parametrization specifically the kain fritsch kf scheme at 3 km grid spacing shows marginal impact on storm coverage intensity and precipitation except for the presence of widespread light rainfall in the piedmont east of the mountains when the kf is employed analysis of the thermal structure of the simulated storm indicates that in the inner storm region the kf is either not activated or primarily produces parametrized shallow convection as a result the net heating tendency associated with adiabatic and diabatic processes is almost unaltered inside the storm together with a nearly equivalent surface momentum sink leading to similar storm areal extent and intensity light rainfall to the east of the mountains can be due to the trigger mechanism of kf which depends on boundary layer convergence forcing parametrized deep convection near the coast where surface roughness changes enhance convergence

large scale relocation of two decades of northern california seismicity using cross correlation and double difference methods 1 we simultaneously reanalyzed two decades 1984 2003 of the digital seismic archive of northern california using waveform cross correlation cc and double difference dd methods to improve the resolution in hypocenter locations in the existing earthquake catalog generated at the northern california seismic network ncsn by up to three orders of magnitude we used a combination of 3 billion cc differential times measured from all correlated pairs of events that are separated by less than 5 km and 7 million p wave arrival time picks listed in the ncsn bulletin data were inverted for precise relative locations of 311 273 events using the dd method the relocated catalog is able to image the fine scale structure of seismicity associated with active faults and revealed characteristic spatiotemporal structures such as streaks and repeating earthquakes we found that 90 of the earthquakes have correlated p wave and s wave trains at common stations and that 12 are colocated repeating events an analysis of the repeating events indicates that uncertainties at the 95 confidence level in the existing network locations are on average 0 7 km laterally and 2 km vertically correlation characteristics and relative location improvement are remarkably similar across most of northern california implying the general applicability of these techniques to image high resolution seismicity caused by a variety of plate tectonic and anthropogenic processes we show that consistent long term seismic monitoring and data archiving practices are key to increase resolution in existing hypocenter catalogs and to estimate the precise location of future events on a routine basis

normal faults and thrusts reactivated by deep fluids the 6 april 2009 mw 6 3 l aquila earthquake central italy 1 on 6 april 2009 a mw 6 3 earthquake occurred in the central apennines italy damaging the city of l aquila and the surrounding country we relocate the october 2008 to 6 april 2009 foreshocks and about 2000 aftershocks occurred between 6 and 30 april 2009 by applying a double difference technique and determine the stress field from focal mechanisms the events concentrate in the upper 15 km of the crust three main nw se to nnw sse striking 30 45 and 80 90 dipping faults were activated during the seismic sequence among these a normal fault and a thrust were reactivated with dip slip movements in response to ne sw extension the structural maturity of the seismogenic fault system is lower than that displayed by other systems in southern apennines because of the lower strain rate of the central sector of the chain with respect to the southern one vp vs increases progressively from october 2008 to the 6 april 2009 main shock occurrence along a nw se strike because of an increment in pore fluid pressure along the fault planes pore pressure diffusion controls the space time evolution of aftershocks a hydraulic diffusivity of 80 m2 s 1 and a seismogenic permeability of about 10 12 m2 suggest the involvement of gas rich co2 fluids within a highly fractured medium suprahydrostatic high fluid pressure about 200 mpa at 10 km of depth within overpressurized traps bounded by preexisting structural and or lithological discontinuities at the lower upper crust boundary are required to activate the april 2009 sequence traps are the storage zone of co2 rich fluids uprising from the underlying about 20 km deep metasomatized mantle wedge these traps easily occur in extensional regimes like in the axial sector of apennines but are difficult to form in strike slip regimes where subvertical faults may cross the entire crust in the apennines fluids may activate faults responsible for earthquakes up to mw 5 6 deep fluids more than tectonic stress may control the seismotectogenesis of accretionary wedges

on the origin of the bolivian high and related circulation features of the south american climate abstract the climatological structure in the upper tropospheric summertime circulation over south america is diagnosed using a gcm with and without south american topography a linear model and observational data emphasis is placed on understanding the origin of observed features such as the bolivian high and the accompanying nordeste low to the east results from the linear model indicate that these two features are generated in response to precipitation over the amazon basin central andes and south atlantic convergence zone with african precipitation also playing a crucial role in the formation of the nordeste low the direct mechanical and sensible heating effects of the andes are minimal acting only to induce a weak lee trough in midlatitudes and a shallow monsoonal circulation over the central andes in the gcm the effects of the andes include a strengthening of the bolivian high and northward shift of the nordeste low primarily through changes in the precipitation field the position of

impact of amazonian evapotranspiration on moisture transport and convection along the eastern flanks of the tropical andes the weather research and forecasting wrf model was used to investigate the impact of amazonian evapotranspiration et on moisture transport and convection along the eastern flanks of the andes eads to isolate the role of surface et quasi idealized simulations down to 1 2 km grid spacing were conducted where over the amazon lowlands amzl and at every time step the surface sensible heat effects are identical to the realistic reference runs while surface latent heat fluxes are prevented from entering the atmosphere the results show that without surface et daily precipitation within the amzl decreases by as much as 75 but nearly doubles over the surrounding mountainous regions this dramatic influence is attributed to a dipole structure of convergence divergence anomalies over the amzl primarily due to the considerable cooling of the troposphere associated with suppressed convection further examination of moist static energy evolution indicates that the net decrease in convective available potential energy over the amzl is due to the removal of surface et that is only partially compensated by related regional circulation changes because of the concave shape of the andean mountain range enhanced low level divergence promotes air mass accumulation to the east of the central eads this perturbation becomes sufficiently strong around nightfall and produces significant eastward low level pressure gradient force rendering stronger winds away from the andes moisture convergence and convection over the eads vary accordingly strengthened in the day but attenuated at night nocturnal convective motion is however more widespread analytical solutions of simplified diagnostic equations of convective fraction suggest that reduction of lower troposphere evaporation is the driving mechanism additional exploratory experiments with varied surface et magnitude demonstrate that the connection between the amzl et and eads precipitation is robust

partitioned fault movement and aftershock triggering evidence for fault interactions during the 2017 mw 5 4 pohang earthquake south korea

slip partitioned surface breaks for the mw 7 8 2001 kokoxili earthquake china slip partitioned fault breaks have been mapped for a 70 km stretch of the 450 km surface rupture of the 14 november 2001 kokoxili earthquake simultaneous dip slip and strike slip motion on parallel faults has been proposed before but the new observations demonstrate unequivocally that it can occur in a single earthquake and allows the mechanical processes to be scrutinized observed normal fault offsets were between 0 5 and 1 m and strike slip offsets were 3 5 m the partitioned stretch of faulting has a strike that differs by 2 3 from the pure strike slip faulting to the east and west this allows a horizontal opening vector of 0 25 m to be determined for the partitioned region the distance between the two faults is greatest 2 km at the center of the partitioned portion and diminishes toward the ends the faulting is modeled to result from strains due to a buried oblique slip fault dipping at 80 to the south the depth to the top of the buried fault is shown to vary commensurately with the separation of the surface faults clear surface rupture is observed where the predicted model mechanisms are colinear and where substantial faults can develop into a kinematically stable partitioned system in a few interesting examples fragmentary oblique surface ruptures occur where the predicted mechanisms are not colinear but they are not associated with long term surface faulting the proposed mechanism for slip partitioning requires that rupture propagates upward from depth for the kokoxili surface breaks this is a consequence of coseismic dynamic rupture traveling faster at depth than near the surface leaving the surface deformation to catch up while the mechanism we propose requires slip weakening and localization to create faults or shear zones it does not require that faults with different mechanisms have different frictional behavior

assessing whether the 2017 mw 5 4 pohang earthquake in south korea was an induced event the moment magnitude m w 5 4 pohang earthquake the most damaging event in south korea since instrumental seismic observation began in 1905 occurred beneath the pohang geothermal power plant in 2017 geological and geophysical data suggest that the pohang earthquake was induced by fluid from an enhanced geothermal system egs site which was injected directly into a near critically stressed subsurface fault zone the magnitude of the mainshock makes it the largest known induced earthquake at an egs site

cenozoic deformation history of the area around yangnam yangbuk se korea and its tectonic significance abstract detailed mapping and structural analysis were carried out to establish the cenozoic deformation history of the yangnam yangbuk area se korea all structural elements were analyzed to establish the chronological sequence based on the classification of the fracture systems and the ages of the rocks two detailed grid maps represent the deformation history based on the cross cutting relationship between deformation fabrics we established the cenozoic deformation history in the studied area by synthesizing the analysis of structural elements in rocks of different ages and observing cross cutting relationships on grid maps results using these two approaches with two independent data sets are consistent the deformation history is comparable to that proposed from previous studies restoration of the structural elements suggests tilting and rotation in this area there is clear evidence of tectonic inversion which was observed in a previous trench study of the eupchon fault this implies that normal faults related to the right lateral yangsan fault associated with opening of the east sea japan sea may have been reactivated as thrust faults in the quaternary period

from steep slope volcano to flat caldera floor 1 most laboratory experiments of caldera collapse have dealt with reservoir emptying below a flat lying overburden without an overlying analogue volcanic edifice on top the overload and the role of topography are then neglected so that the final flat floor within the caldera is directly linked to the initial one in addition caldera subsidence is commonly attributed to the collapse of the top of a magma chamber linked to eruptions delivering large amounts of volcanic products analogue experiments show that the deformation of a weak clay rich core resulting from the hydrothermal alteration in a volcanic edifice can in certain conditions reproduce the structures of a caldera in particular it is a way to explain the flat floor of a caldera when resurfacing resulting from new eruptions or destructive processes seems unlikely

complete gravity study of piton de la fournaise volcano reunion island abstract we present an interpretation of all available gravity data on piton de la fournaise volcano including a new set collected in the summit area using a linear programming inversion method we determine the extension of the grand brule ultramafic body drilled in 1985 and we propose to interpret it as a frozen magma chamber related to a disappeared volcano we also present evidence for superficial mass excess under the enclos fouque and plaine des sables calderas that we link to the present piton de la fournaise volcanism the detailed gravity survey of the summit area allows us to emphasize the great importance of dyke complexes associated with the ne and se rift zones and with the shallow magma chamber a negative anomaly in the summit area is interpreted as a relative minimum between the positive anomaly of grand brule and those of the western part of the enclos fouque and plaine des sables calderas

scaling relation between earthquake magnitude and the departure time from p wave similar growth we introduce a new scaling relation between earthquake magnitude m and a characteristic of initial p wave displacement by examining japanese k net data averaged in bins partitioned by mw and hypocentral distance we demonstrate that the p wave displacement briefly displays similar growth at the onset of rupture and that the departure time tdp which is defined as the time of departure from similarity of the absolute displacement after applying a band pass filter correlates with the final m in a range of 4 5 mw 7 the scaling relation between mw and tdp implies that useful information on the final m can be derived while the event is still in progress because tdp occurs before the completion of rupture we conclude that the scaling relation is important not only for earthquake early warning but also for the source physics of earthquakes

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

complex spatiotemporal evolution of the 2008 mw 4 9 mogul earthquake swarm reno nevada interplay of fluid and faulting after approximately two months of swarm like earthquakes in the mogul neighborhood of west reno nv seismicity rates and event magnitudes increased over several days culminating in an mw 4 9 dextral strike slip earthquake on 26 april 2008 although very shallow the mw 4 9 mainshock had a different sense of slip than locally mapped dip slip surface faults we relocate 7 549 earthquakes calculate 1 082 focal mechanisms and statistically cluster the relocated earthquake catalog to understand the character and interaction of active structures throughout the mogul nv earthquake sequence rapid temporary instrument deployment provides high resolution coverage of microseismicity enabling a detailed analysis of swarm behavior and faulting geometry relocations reveal an internally clustered sequence in which foreshocks evolved on multiple structures surrounding the eventual mainshock rupture the relocated seismicity defines a fault fracture mesh and detailed fault structure from approximately 2 6 km depth on the previously unknown mogul fault that may be an evolving incipient strike slip fault zone the seismicity volume expands before the mainshock consistent with pore pressure diffusion and the aftershock volume is much larger than is typical for an mw 4 9 earthquake we group events into clusters using space time magnitude nearest neighbor distances between events and develop a cluster criterion through randomization of the relocated catalog identified clusters are largely mainshock aftershock sequences without evidence for migration occurring within the diffuse background seismicity the migration rate of the largest foreshock cluster and simultaneous background events is consistent with it having triggered or having been triggered by an aseismic slip event