observing earthquakes triggered in the near field by dynamic deformations we examine the hypothesis that dynamic deformations associated with seismic waves trigger earthquakes in many tectonic environments our analysis focuses on seismicity at close range within the aftershock zone complementing published studies of long range triggering our results suggest that dynamic triggering is not confined to remote distances or to geothermal and volcanic regions long unilaterally propagating ruptures may focus radiated dynamic deformations in the propagation direction therefore we expect seismicity triggered dynamically by a directive rupture to occur asymmetrically with a majority of triggered earthquakes in the direction of rupture propagation bilaterally propagating ruptures also may be directive and we propose simple criteria for assessing their directivity we compare the inferred rupture direction and observed seismicity rate change following 15 earthquakes m 5 7 to m 8 1 that occurred in california and idaho in the united states the gulf of aqaba syria guatemala china new guinea turkey japan mexico and antarctica nine of these mainshocks had clearly directive unilateral ruptures of these nine seven apparently induced an asymmetric increase in seismicity rate that correlates with the rupture direction the two exceptions include an earthquake preceded by a comparable magnitude event on a conjugate fault and another for which data limitations prohibited conclusive results similar but weaker correlations were found for the bilaterally rupturing earthquakes we studied although the static stress change also may trigger seismicity it and the seismicity it triggers are expected to be similarly asymmetric only if the final slip is skewed toward the rupture terminus for several of the directive earthquakes we suggest that the seismicity rate change correlates better with the dynamic stress field than the static stress change manuscript received 1 march 2002

spatial and temporal deformation along the northern san jacinto fault southern california implications for slip rates the san timoteo badlands is an area of uplift and erosional dissection that has formed as a result of late quaternary uplift along a restraining bend in the san jacinto fault of the san andreas fault system in southern california this bend currently is located in a region where late quaternary deposits and associated surfaces have formed in lower san timoteo canyon we have used morphometric analysis of these surfaces in conjunction with computer modeling of deformational patterns along the san jacinto fault to reconstruct spatial and temporal variations in uplift along the bend morphometric techniques used include envelope subenvelope map ping a gradient length index along channels and denudation values age control is determined using a combination of thermoluminescence tl and near infrared op tical simulation luminescence dating irosl and correlation of soil development indices these approaches are combined with an elastic half space model used to determine the deformation associated with the fault bend the region of modeled uplift has a similar distribution as that determined by morphometric techniques luminescence dates and soil correlation age estimates generally agree based on soil development surfaces within the study area were stabilized at approximately 300 700 ka for q3 43 67 ka for q2 and 27 5 67 ka for q1 luminescence ages both tl and irosl for the formation of the younger two surfaces are 58 to 94 ka for q2 and 37 to 62 ka for q1 ages reported to 1r uncertainty periods of uplift were determined for the surfaces in the study area resulting in approximate uplift rates of 0 34 to 0 84 m ka for the past 100 ka and 0 13 to 1 00 m ka for the past 66 ka comparison of these rates of uplift to those generated by the model support a higher rate of lateral slip along the san jacinto fault than commonly assumed greater than 20 mm yr as compared to 8 12 mm yr commonly cited this higher slip rate supports the proposal that a greater amount of slip has transferred from the san andreas fault to the san jacinto fault than generally held the san jacinto fault may have accommodated a significant portion of the plate boundary slip during the past 100 ka

comparison of warm and wet and cold and icy scenarios for early mars in a 3 d climate model we use a 3 d general circulation model to compare the primitive martian hydrological cycle in warm and wet and cold and icy scenarios in the warm and wet scenario an anomalously high solar flux or intense greenhouse warming artificially added to the climate model are required to maintain warm conditions and an ice free northern ocean precipitation shows strong surface variations with high rates around hellas basin and west of tharsis but low rates around margaritifer sinus where the observed valley network drainage density is nonetheless high in the cold and icy scenario snow migration is a function of both obliquity and surface pressure and limited episodic melting is possible through combinations of seasonal volcanic and impact forcing at surface pressures above those required to avoid atmospheric collapse 0 5 bar and moderate to high obliquity snow is transported to the equatorial highland regions where the concentration of valley networks is highest snow accumulation in the aeolis quadrangle is high indicating an ice free northern ocean is not required to supply water to gale crater at lower surface pressures and obliquities both h2o and co2 are trapped as ice at the poles and the equatorial regions become extremely dry the valley network distribution is positively correlated with snow accumulation produced by the cold and icy simulation at 41 8 obliquity but uncorrelated with precipitation produced by the warm and wet simulation because our simulations make specific predictions for precipitation patterns under different climate scenarios they motivate future targeted geological studies

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

small scale stress heterogeneity in the anza seismic gap southern california focal mechanism inversions reveal significant lateral variations in stress orientations along the anza segment of the san jacinto fault zone the most notable stress anomaly is within the 20 km aseismic seismic gap portion of the fault zone where 1 the maximum compressive stress is nearly horizontal and is oriented at 74 13 relative to the fault strike this contrasts with orientations ranging from 62 11 to 49 7 along the more seismically active portions of the fault zone immediately to the northwest and southeast of the seismic gap regional stress results found by inverting all focal mechanisms simultaneously indicate that 1 is horizontal and trends north south while 3 is horizontal and trends east west approximately 15 km west of the seismic gap in the off fault cahuilla swarm area 1 and 3 solutions are rotated clockwise by about 25 relative to the regional model roughly 10 km southeast of the seismic gap near the buck ridge fault 1 and 3 are rotated counterclockwise by about 10 relative to the regional solution northwest of the seismic gap along the fault zone 3 plunges about 30 from the horizontal correlating with a local increase in reverse faulting between the hot springs and san jacinto faults southeast of the seismic gap 1 plunges about 45 from the horizontal correlating with a local increase in normal faulting in the trifurcation region of the buck ridge clark and coyote creek faults we propose a simple mechanical model in which a block rotation superimposed on the dominant right lateral strikeslip motion of the fault zone satisfies the first order observations of stress orientation faulting and horizontal surface strain under this model the anza seismic gap is the region of zero convergence between the northeast and southwest sides of the fault and the fault zone strength within the seismic gap is either comparable to or exceeds the fault zone strength adjacent to the gap

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

local displacement of diapir contacts and its importance to pluton emplacement study abstract the extent to which mid crustal plutons have grown by diapirism cannot be deduced from the horizontal shortening of ductilely deformed host rocks and associated displacement of lateral intrusive contacts by contrast the vertical shortening above plutons and upward displacement of their roof contacts may provide a good measure of the diapiric component of pluton emplacement this is related to the vertical bulk translation of buoyant material in immature diapirs and associated escape flow of overlying rocks the length change of a vertical material line situated above the crest of an immature upright diapir corresponds to the upward displacement of the local contact the length change of horizonal material lines situated at lateral contacts of model diapirs however differs markedly from the contact displacement this is related to the absence of horizontal symmetry planes in the finite strain field about upright diapirs of any shape and the importance of vertical shear at the lateral contacts the host rock strain held of a hypothetical pluton grown in situ by spherical expansion ballooning has an infinite number of symmetry planes the strain held is characterized by large volume losses but the length change of all radial lines corresponds to the local magnitude of contact displacement this precludes the possibility of differentiating in ductile host rocks above plutons between vertical diapirism and spherical expansion unless gauges of volume change are available

mars outflow channels a reappraisal of the estimation of water flow velocities from water depths regional slopes and channel floor properties methods used so far to assess the flow velocities of the water commonly assumed to be responsible for forming the major outflow channel systems on mars have relied widely on various versions of the manning equation this has led to problems in allowing for the difference between the accelerations due to gravity on mars and earth and for the differences of scale between martian floods and most river systems on earth we reanalyze the problem of estimating water flow velocities in martian outflow channels using equations based on the darcy weisbach friction factor instead of the manning n factor we give simplified formulae appropriate to mars for the darcy weisbach friction coefficient as a function of bedrock size distribution for a given channel floor slope and water flood depth similar mean flow velocities are implied for a wide range of values of the ratio of bed roughness to water depth relevant to martian outflow channels using a recent rederivation of manning s equation based on turbulence theory we obtain a new value of 0 0545 s m 1 3 for the manning n coefficient appropriate to martian channels and show that previous analyses have generally overestimated though in some cases underestimated water flow velocities on mars by a factor of order two combining the consequences of this flow velocity overestimate with likely overestimates of flow depth from assuming bank full flow we show that discharges may have been overestimated by a factor of up to 25 leading to corresponding overestimates of subsurface aquifer permeabilities rates of filling of depressions with water and grain sizes of sediments on channel floors despite the availability of an improved value for the manning n coefficient for mars we strongly recommend that modified forms of the original version of the manning equation should be replaced by the modern form or preferably by the darcy weisbach equation in future work

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

earthquake depths and the relation to strain accumulation and stress near strike slip faults in southern california earthquakes in the major fault zones are predominantly deep earthquakes in the crustal blocks bounding the fault zones are predominantly shallow in the san jacinto fault zone maximum earthquake depths correlate with surface heat flow these relations together with focal mechanisms geodetic strain measurements and fault zone models are consistent with the following ideas 1 interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes 2 the aseismic slip in a narrow fault zone in the brittle plastic transition region concentrates strain at the base of the brittle fault zone 3 deep earthquakes occur in thelower part of the brittle fault zone due to stick slip failure of highly stressed patches 4 background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding deep and stick slip shallow regions of the fault zone furthermore the difference in seismicity between the san jacinto and southern san andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases 5 shear stress may be lessmore in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks 6 in the stress field produced by plate motion and slip in the deep fault zone the upper brittle fault zone is not oriented favorably for shear failure lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation less

precise location of san andreas fault tremors near cholame california using seismometer clusters slip on the deep extension of the fault 1 we examine a 24 hour period of active san andreas fault saf tremor and show that this tremor is largely composed of repeated similar events utilizing this similarity we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake lfe master template located using p and s wave arrivals to be 26 km deep to compensate for low signal to noise we estimate event pair differential times at clusters of nearby stations rather than at single stations we find that the locations form a near linear structure in map view striking parallel to the saf and near the surface trace therefore we suggest that at least a portion of the tremor occurs on the deep extension of the fault likely reflecting shear slip similar to subduction zone tremor if so the saf may extend to the base of the crust 10 km below the deepest regular earthquakes on the fault

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

incipient sediment motion across the river to debris flow transition sediment transport in mountain channels controls the evolution of mountainous terrain in response to climate and tectonics and presents major hazards to life and infrastructure worldwide despite its importance we lack data on when sediment moves in steep channels and whether movement occurs by rivers or debris flows we address this knowledge gap using laboratory experiments on initial sediment motion that cross the river to debris flow sediment transport transition results show that initial sediment motion by river processes requires heightened dimensionless bed shear stress or critical shields stress with increasing channel bed slope by as much as fivefold the conventional criterion established for lowland rivers beyond a threshold slope of 22 the channel bed fails initiating a debris flow prior to any fluvial transport and the critical shields stress within the debris flow regime decreases with increasing channel bed slope combining theories for both fluvial and debris flow incipient transport results in a new phase space for sediment stability with implications for predicting fluvial sediment transport rates mitigating debris flow hazards and modeling channel form and landscape evolution

late quaternary rate of slip along the san jacinto fault zone near anza southern california the anza section of the san jacinto fault southern california has not experienced a groundbreaking earthquake since at least 1918 and probably since before 1899 leading previous workers to designate this 20 km long fault segment as a seismic gap study of displaced pleistocene and holocene alluvial fan and fluvial deposits across the san jacinto fault near anza california dated using 14c and soil development age control indicates a minimum right lateral slip rate of 9 2 2 mm yr since 9 5 ka and a slip rate of 11 9 5 mm yr since 14 ka 12 9 5 mm yr since 17 ka and 13 10 6 mm yr since 50 ka these estimates agree with a previously determined 700 ka to present minimum slip rate of 10 2 mm yr based on an estimated average slip rate of 12 mm yr from the longer term slip rate estimates about 0 8 m of potential slip has accumulated if the 1918 earthquake broke the anza segment over 1 1 m of potential slip has accumulated if the last earthquake occurred prior to 1899 these data attest to the potential for an earthquake m6 5 for this section of the fault

infrequent triggering of tremor along the san jacinto fault near anza california we examine the conditions necessary to trigger tremor along the san jacinto fault sjf near anza california where previous studies suggest triggered tremor occurs but observations are sparse we investigate the stress required to trigger tremor using continuous broadband seismograms from 11 stations located near anza california we examine 44 mw 7 4 teleseismic events between 2001 and 2011 these events occur at a wide range of back azimuths and hypocentral distances in addition we included one smaller magnitude regional event the 2009 mw 6 5 gulf of california earthquake because it induced extremely high strains at anza we find the only episode of triggered tremor occurred during the 3 november 2002 mw 7 8 denali earthquake the tremor episode lasted 300 s was composed of 12 tremor bursts and was located along sjf at the northwestern edge of the anza gap at approximately 13 km depth the tremor episode started at the love wave arrival when surface wave particle motions are primarily in the transverse direction we find that the denali earthquake induced the second highest stress 35 kpa among the 44 teleseismic events and 1 regional event the dominant period of the denali surface wave was 22 8 s at the lower end of the range observed for all events 20 40 s similar to periods shown to trigger tremor in other locations the surface waves from the 2009 mw 6 5 gulf of california earthquake had the highest observed strain yet a much shorter dominant period of 10 s and did not trigger tremor this result suggests that not only the amplitude of the induced strain but also the period of the incoming surface wave may control triggering of tremors near anza in addition we find that the transient shear stress 17 35 kpa required to trigger tremor along the sjf at anza is distinctly higher than what has been reported for the well studied san andreas fault

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

dynamic triggering of microearthquakes in three geothermal volcanic regions of california geothermal volcanic regions are most susceptible to local earthquake triggering by regional and remote earthquakes transient stresses caused by surface waves of these earthquakes can activate critically stressed faults though earthquakes can be triggered in geothermal volcanic regions it is less understood how these regions differ in their triggering responses to distant earthquakes we conduct a systematic survey of local earthquakes triggered by distant earthquakes in three geothermal volcanic regions of california long valley caldera coso geothermal field and geysers geothermal field we examine waveforms of distant earthquakes with magnitudes 5 5 occurring between 2000 and 2012 and compute statistics to confirm the significance of our findings we find that long valley coso and geysers vary in triggering frequency 2 0 3 8 and 6 8 in the 12 year period respectively and when compared to the triggering of deep tectonic tremors along the parkfield cholame section of san andreas fault 9 2 in the 12 year period stress triggering thresholds vary among the regions with long valley having the highest of 5 kpa and 1 kpa for the other regions because dynamic stresses from distant earthquakes are similar in these three regions the varying triggering behavior likely reflects faults having a tendency to be at or near failure this is compatible with geysers having a higher a value in the gutenberg richter relationship and higher geothermal productivity than the other two regions the observation of more frequent triggering of tremor than microearthquakes is consistent with recent laboratory studies on increasing triggerability with lower effective stress

deep creep as a cause for the excess seismicity along the san jacinto fault earthquakes are far more common along the san jacinto fault in california than the nearby southern san andreas fault an analysis of seismic and geodetic data suggests that the excess seismicity along the san jacinto fault is due to a creeping motion along the deeper parts of the fault

segmentation of the northern san jacinto fault zone southern california accurate forecasting of large earthquakes in the san jacinto fault zone depends on the correct determination of fault segmentation we have searched for discontinuities in the fault zone using as data geological maps of the fault traces relocated earthquake hypocenters focal mechanisms slip rates and historic large earthquake rupture zones we identify nine principal discontinuities in the northern san jacinto fault zone these are characterized as structural discontinuities bends steps branches intersections geodetic discontinuities slip rate and lithologic discontinuities most of the discontinuities have more than one defining characteristic we also analyzed the local strain field orientation along the fault zone significant lateral discontinuities in the strain field orientation are coincident with many of the structural and geodetic discontinuities we identify segment lengths defined from the data vary from about 7 to 35 km this range of segment lengths is consistent with the lengths of large historical earthquake ruptures however evidence from small earthquake hypocenter patterns suggests the possibility that in some areas large earthquakes may rupture multiple adjacent segments in these cases maximum magnitudes may be larger than those observed historically because of the short historic record and the sparse paleoseismic record probabilistic estimates of earthquake recurrence for this fault zone have depended heavily on assumed characteristic lengths of individual rupture segments ours and previous delineations of segment lengths have varied considerably indicating that assumed segment length is a major source of uncertainty in the recurrence calculations this source of uncertainty should be taken into account in calculations of the reliability of the probabilistic hazard estimates

triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes the passage of radiating seismic waves generates transient stresses in the earth s crust that can trigger slip on faults far away from the original earthquake source the triggered fault slip is detectable in the form of earthquakes 1 3 and seismic tremor 4 7 however the significance of these triggered events remains controversial 8 9 in part because they often occur with some delay long after the triggering stress has passed here we scrutinize the location and timing of tremor on the san andreas fault between 2001 and 2010 in relation to distant earthquakes we observe tremor on the san andreas fault that is initiated by passing seismic waves yet migrates along the fault at a much slower velocity than the radiating seismic waves we suggest that the migrating tremor records triggered slow slip of the san andreas fault as a propagating creep event we find that the triggered tremor and fault creep can be initiated by distant earthquakes as small as magnitude 5 4 and can persist for several days after the seismic waves have passed our observations of prolonged tremor activity provide a clear example of the delayed dynamic triggering of seismic events fault creep has been shown to trigger earthquakes 10 12 and we therefore suggest that the dynamic

aureole deformation by flattening around a diapir during in situ ballooning the cannibal creek granite the cannibal creek granite a foliated pluton within a strongly deformed aureole shows several diagnostic features of a diapir the intensity of the aureole deformation diminished away from the contact the aureole foliation is continuous with that of the granite and forms closed elliptical trend lines and the contact metamorphic minerals are synkinematic with regard to the aureole foliation the pluton deformed its aureole in three stages involving initially brittle then ductile and finally brittle deformation styles initial intrusion of a low strength magma stoped kinked and flexed aside its overburden crystallization of the magma prevented further rise and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact this the major stage of aureole deformation records no evidence of vertical movement of the pluton or of progressive simple shear along its margin during this stage the magma may have been theologically a high strength bing

comparisons of triggered tremor in california abstract we conduct a visual inspection of deep nonvolcanic tremor triggered by large teleseismic earthquakes around the calaveras fault in northern california nc and the san jacinto fault in southern california sc out of the 42 large m w 7 5 earthquakes between 2001 and 2010 only the 2002 m w 7 9 denali fault earthquake triggered clear tremor in these two regions this is in marked contrast with the parkfield cholame section of the san andreas fault in central california cc where 12 earthquakes have triggered tremor in that region the amplitude of the triggered tremor correlates with that of the triggering surface waves in cc and is consistent with the clock advance model the lack of widespread triggered tremor in nc and sc is not simply a consequence of their different background noise levels from cc but rather reflects different background tremor rates in these regions online material tables of parameters for triggered nontriggered teleseismic earthquakes and triggered tremors and figures of band pass filtered seismograms maximum vertical pgvs versus median amplitude of band pass filtered envelope functions tremor amplitude versus pgv and s wave spectra and corresponding noise of local selected earthquakes

seismic wave triggering of nonvolcanic tremor episodic tremor and slip and earthquakes on vancouver island 1 we explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on vancouver island british columbia during and immediately after the arrival of large amplitude seismic waves from 30 teleseismic and 17 regional or local earthquakes we identify tremor triggered by four of the teleseismic earthquakes the close temporal and spatial proximity of triggered tremor to ambient tremor and aseismic slip indicates that when a fault is close to or undergoing failure it is particularly susceptible to triggering of further events the amplitude of the triggering waves also influences the likelihood of triggering both tremor and earthquakes such that large amplitude waves triggered tremor in the absence of detectable aseismic slip or ambient tremor tremor and energy radiated from regional local earthquakes share the same frequency passband so that tremor cannot be identified during these smaller more frequent events we confidently identify triggered local earthquakes following only one teleseism that with the largest amplitude and four regional or local events that generated vigorous aftershock sequences in their immediate vicinity earthquakes tend to be triggered in regions different from tremor and with high ambient seismicity rates we also note an interesting possible correlation between large teleseismic events and episodic tremor and slip ets episodes whereby ets events that are late and have built up more stress than normal are susceptible to triggering by the slight nudge of the shaking from a large distant event while ets events that are early or on time are not

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

interior channels in martian valleys constraints on fluvial erosion by measurements of the mars express high resolution stereo camera 1 in high resolution stereo camera hrsc images of the mars express mission a 130 km long interior channel is identified within a 400 km long valley network system located in the lybia montes ages of the valley floor and the surroundings as derived from crater counts define a period of 350 myrs during which the valley might have been formed based on hrsc stereo measurements the discharge of the interior channel is estimated at 4800 m3 s corresponding to a runoff production rate of 1 cm day mass balances indicate erosion rates of a few cm year implying the erosion activity in the valley to a few thousand years for continuous flow or one or more orders of magnitude longer time spans for more intermittent flows therefore during the hesperian relatively brief but recurring episodes of erosion intervals are more likely than sustained flow

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

surface wave potential for triggering tectonic nonvolcanic tremor corrected abstract source processes commonly posed to explain instances of remote dynamic triggering of tectonic nonvolcanic tremor by surface waves include frictional failure and various modes of fluid activation the relative potential for love and rayleigh wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike slip faults under the coulomb griffith failure criteria as a function of incidence angle are anticorrelated over the 15 to 30 km depth range that hosts tectonic tremor love wave potential is high for strike parallel incidence on low angle reverse faults and null for strike normal incidence the opposite holds for rayleigh waves love wave potential is high for both strike parallel and strike normal incidence on vertical strike slip faults and minimal for 45 incidence angles the opposite holds for rayleigh waves this pattern is consistent with documented instances of tremor triggered by love waves incident on the cascadia megathrust and the san andreas fault saf in central california resulting from shear failure on weak faults apparent friction is 0 2 documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan however are associated primarily with rayleigh waves this is consistent with the tremor bursts resulting from mixed mode failure crack opening and shear failure facilitated by near lithostatic ambient pore pressure low differential stress with a moderate friction coefficient 0 6 on the nankai subduction interface rayleigh wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process except perhaps for an indirect role on the saf in sustaining tremor into the rayleigh wave coda that was initially triggered by love waves

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

dynamic strains at regional and teleseismic distances abstract we develop formulas for the size of dynamic strains caused by seismic waves from an earthquake of given magnitude and distance these formulas include peak strain peak dissipated power and total dissipated energy and they are applicable at regional and teleseismic distances the formulas are fits to data from 89 large 6 5 m w 9 0 shallow earthquakes with source distances between 500 and 16 000 km recorded between 1977 and 2013 by three long base laser strainmeters at pinon flat observatory in southern california these strainmeters provide uniquely well calibrated measurements of tensor strain the residuals to the fits suggest that strain values can usually be predicted to within a factor of 2 these data also show that the strain tensor can be substantially different from that expected for plane waves in particular the extension perpendicular to the back azimuth which should be zero is always 20 or more of the extension along that azimuth how much the strains resemble those for plane waves depends on their path perhaps because inhomogeneities along different paths produce different amounts of multipathing the observed strains are systematically 10 30 larger at nearby laser strainmeter sites in the salton trough suggesting local amplification from inhomogeneous crustal structure online material tables of earthquake catalogs and dynamic strain analysis and figures of earthquake magnitude distance distributions and time delays of maximum strain

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

bursting the bubble of ballooning plutons a return to nested diapirs emplaced by multiple processes a popular model for the emplacement of roughly spherical plutons is that of ballooning or in situ inflation of a magma chamber in a common version of this model magma ascends until loss of heat or buoyancy causes the outermost magma to crystallize and cease ascent while the hotter tail of magma continues to rise and expand the already crystallized outer margin this expansion forms a concentric gneissic to mylonitic foliation and flattening type strain in the outer margin of the pluton by means of subsolidus deformation and pushes aside the surrounding country rock to form a dynamothermal aureole that postdates regional structures our reexamination of three supposedly ballooned plutons ardara ireland cannibal creek australia papoose flat california and evaluation of published descriptions of many others indicate that this model is largely incorrect deflections of country rock structures strains and porphyroblast matrix relationships indicate that only minor to moderate expansion usually 30 or less occurred during emplacement that other emplacement mechanisms must have occurred and that regional deformation continued during and after emplacement internal structures indicate that when magma chamber expansion did occur it did so by flow of magma that magmatic foliations and lineations formed late in the magma chamber evolution that enclave shapes are neither good strain markers nor indicators of the magnitude of expansion and that only minor internal subsolidus deformation results from emplacement this study indicates that many plutons previously interpreted as post tectonic ballooning plutons are better viewed as syntectonic nested diapirs emplaced by a variety of country rock material transfer processes this nested diapir model implies that magma ascent may occur by rise of large magma batches instead of transport in dikes followed by ballooning that magma chamber dynamics differ from that in the ballooning model and that normally zoned plutons may form by intrusion of several pulses of magma rather than by in situ crystal fractionation from a single parent melt

remote triggering of non volcanic tremor around taiwan summary we perform a systematic survey of triggered deep non volcanic tremor beneath the central range cr in taiwan for 45 teleseismic earthquakes from 1998 to 2009 with mw 7 5 and epicentral distance 1000 km to the broad band station tpub triggered tremors are visually identified as bursts of high frequency 2 8 hz non impulsive and long duration seismic energy that are coherent among many seismic stations and modulated by the teleseismic surface waves out of the 45 earthquakes we identified nine teleseismic events associated with nine tremor sources in the southern and five in the northern cr most of the tremor sources are located within the depth range of 15 25 km in the lower crust above the moho we find that the amplitudes of the surface waves play an important role in determining the triggering potential and the apparent triggering threshold is 0 1 cm s 1 or 7 8 kpa however such threshold is partially controlled by the background noise level which could prevent weaker tremor triggered by surface waves with smaller amplitudes from being identified the amplitudes of the triggered tremor show a positive correlation with the amplitudes of the triggering surface waves consistent with the predictions by the clock advance model in addition to amplitudes other factors such as frequency contents and incidence angles also affect the triggering potential we find that intermediate period 30 10 s surface waves could trigger modulate tremors suggesting that long period 30 s surface waves are not always required in long range triggering tremors appear to be triggered by both love and rayleigh waves when the incidence angles are parallel to the strike of the cr all six events triggered tremor primarily during the rayleigh waves for strike normal incidence only the 2001 mw7 8 kunlun earthquake showed predominant love wave triggering this observation can be qualitatively explained by a simple coulomb failure for a left lateral shear on the low angle detachment fault beneath the southern cr

s wave triggering of tremor beneath the parkfield california section of the san andreas fault by the 2011 tohoku japan earthquake observations and theory the dynamic stresses that are associated with the energetic seismic waves generated by the m w 9 0 tohoku earthquake off the northeast coast of japan triggered bursts of tectonic tremor beneath the parkfield section of the san andreas fault saf at an epicentral distance of 8200 km the onset of tremor begins midway through the 100 s period s wave arrival with a minor burst coinciding with the shsh arrival as recorded on the nearby broadband seismic station pkd a more pronounced burst coincides with the love arrival followed by a series of impulsive tremor bursts apparently modulated by the 20 to 30 s period rayleigh wave the triggered tremor was located at depths between 20 and 30 km beneath the surface trace of the fault with the burst coincident with the s wave centered beneath the fault 30 km northwest of parkfield most of the subsequent activity including the tremor coincident with the shsh arrival was concentrated beneath a stretch of the fault extending from 10 to 40 km southeast of parkfield the seismic waves from the tohoku epicenter form a horizontal incidence angle of 14 with respect to the local strike of the saf computed peak dynamic coulomb stresses on the fault at tremor depths are in the 0 7 10 kpa range the apparent modulation of tremor bursts by the small strike parallel rayleigh wave stresses 0 7 kpa is likely enabled by pore pressure variations driven by the rayleigh wave dilatational stress these results are consistent with the strike parallel dynamic stresses s associated with the s shsh and surface wave phases triggering small increments of dextral slip on the fault with a low friction 0 2 the vertical dynamic stresses d do not trigger tremor with vertical or oblique slip under this simple coulomb failure model

nonvolcanic tremors deep beneath the san andreas fault we have discovered nonvolcanic tremor activity i e long duration seismic signals with no clear p or s waves within a transform plate boundary zone along the san andreas fault near cholame california the inferred epicentral region of the 1857 fort tejon earthquake moment magnitude 7 8 the tremors occur between 20 to 40 kilometers depth below the seismogenic zone the upper 15 kilometers of earth s crust where earthquakes occur and their activity rates may correlate with variations in local earthquake activity

non volcanic tremor beneath the central range in taiwan triggered by the 2001 mw 7 8 kunlun earthquake summary non volcanic tremor nvt is an extended duration and non impulsive seismic signal observed away from volcanic regions although nvt has been found along the circum pacific subduction zones and the transform plate boundary in california it is not clear whether nvt occurs in other tectonic environments nvt is often associated with slow slip events and can be triggered instantaneously during the surface waves of teleseismic events however the underlying mechanisms of tremor generation remain mysterious here we show clear evidence of nvt beneath the central range cr in taiwan triggered by the 2001 m w 7 8 kunlun earthquake in northern tibet tremor occurs when the love wave displacement is to the southwest the lateral motion direction for the cr suggesting a simple frictional response to the driving force we hypothesize that tremor occurred on the weak basal detachment fault beneath the cr our observations indicate that tremor may exist at a wide range of active tectonic environments

the accuracy of seismic estimates of dynamic strains an evaluation using strainmeter and seismometer data from pinon flat observatory california abstract the dynamic strains associated with seismic waves may play a significant role in earthquake triggering hydrological and magmatic changes earthquake damage and ground failure we determine how accurately dynamic strains may be estimated from seismometer data and elastic wave theory by comparing such estimated strains with strains measured on a three component long base strainmeter system at pinon flat california we quantify the uncertainties and errors through cross spectral analysis of data from three regional earthquakes the m 0 4 10 17 n m st george utah m 0 4 10 17 n m little skull mountain nevada and m 0 1 10 19 n m northridge california events at distances of 470 345 and 206 km respectively our analysis indicates that in most cases the phase of the estimated strain matches that of the observed strain quite well to within the uncertainties which are about 0 1 to 0 2 cycles however the amplitudes are often systematically off at levels exceeding the uncertainties about 20 in one case the predicted strain amplitudes are nearly twice those observed we also observe significant strains tangential direction which should be zero theoretically in the worst case the rms strain exceeds the other nonzero components these nonzero strains cannot be caused by deviations of the surface wave propagation paths from the expected azimuth or by departures from the plane wave approximation we believe that distortion of the strain field by topography or material heterogeneities give rise to these complexities

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

a seismotectonic analysis of the anza seismic gap san jacinto fault zone southern california small earthquake epicenters near the anza seismic gap define a 20 km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity recent moderate earthquakes on and near the san jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism the locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting from the convergent geometries of the local active discontinuous faults and the oblique orientation of the regional maximum compressive stress strain is not being relieved by aseismic fault creep a swarm of small earthquakes in the crustal block 13 km southwest of the anza gap beneath the cahuilla valley recently released stress in an area which was previously highly active before the 1918 m 6 8 and 1937 m l 6 0 earthquakes the occurrence of these periods of increased seismicity near cahuilla in the years immediately before the nearby closer than 35 km large earthquakes and the recent swarm suggest that the ground beneath cahuilla may be acting as a stress meter signaling the presence of high stresses before large local earthquakes the length of the quiescent fault segment suggests potential for about an m 6 5 earthquake if the entire segment ruptures at once

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

remote triggered seismicity caused by the 2011 m9 0 tohoku oki japan earthquake 1 seismic waves from large earthquakes have been shown to trigger seismicity large distances from a mainshock and this is termed remotely or dynamically triggered seismicity we performed a global search for seismicity potentially triggered by the seismic waves from the 2011 m9 0 tohoku oki japan earthquake using seismograms from global seismic networks and an event catalog we search for earthquakes and tremors instantaneously triggered during the passing of the seismic waves as well as for statistically significant changes in local and global seismic rates after the passing of the waves for earthquakes we find potential cases of instantaneous triggering in the united states russia china ecuador and mexico while for tremors we find evidence for triggering in taiwan armenia cuba and the united states in addition we observed a potential case of delayed triggering of larger magnitude earthquakes including a m5 2 in baja california mexico

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

delayed and sustained remote triggering of small earthquakes in the san jacinto fault region by the 2014 mw 7 2 papanoa mexico earthquake we apply a move max matched filter method to detect heightened seismicity triggered in the san jacinto fault sjf zone by the 2014 mw 7 2 papanoa mexico earthquake the move max matched filter detects 5 4 and 1 7 times the number of earthquakes in the southern california seismic network catalog and those detected by the matched filter method respectively the seismicity rate increases significantly 3 5 hr after the passage of the teleseismic waves and persists above the background level for about 1 week this observation of delayed triggering may imply that dynamic stresses had initiated a time dependent advance to failure or a secondary process a highly active triggered patch is located 10 km west of the sjf near anza on a previously unmapped fault focal mechanisms and a best fit plane suggest a normal fault perpendicular to the sjf the unmapped fault may indicate higher seismic hazard in the surrounding areas if a large earthquake nucleated around the anza seismic gap

strong tremor near parkfield ca excited by the 2002 denali fault earthquake 1 we show clear evidence of non volcanic tremor triggered by 2002 mw7 8 denali fault earthquake near parkfield triggered tremor is identified as bursts of high frequency 2 8 hz non impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves the tremor originates from at least three hypocenters near the san andreas fault with differing frictional regimes two in the creeping section and the other where the san andreas is transitional between creeping and locked all the sources originate below the seismogenic zone suggesting that transitional frictional properties are necessary conditions for tremor generation tremor is excited by the love waves when the san andreas is sheared in a right lateral sense encouraging slip and is absent when the san andreas is sheared in a left lateral sense consistent with a simple frictional response to the driving stress

p wave seismic velocity structure derived from sonic logs and industry reflection data in the los angeles basin california 1 we present a new three dimensional seismic p wave velocity model of the los angeles basin that is based on more than 150 sonic logs and 7000 stacking velocities from industry reflection profiles the model was developed using kriging techniques implemented in gocad a commercial application specializing in the construction of surfaces the analysis of spatially distributed data and the modeling or simulation of properties and is characterized by a heterogeneous spatial varying velocity gradient with maximum velocities of 5000 m s in the sedimentary section variability of the observed p wave velocities increases with depth reflecting complex structural and sedimentological controls the model contains a new representation of the basin shape as defined by the sediment basement interface which was mapped using well control and seismic reflection profiles our model differs substantially in approach and outcome from previous representations of crustal velocity structure in southern california

seismology dynamic triggering of earthquakes the landers earthquake of 1992 triggered a series of earthquakes in other parts of california focusing attention on the mechanism of remote triggering laboratory experiments on granular material under pressure suggest that triggering is a result of seismic waves impinging on a fault and inducing elastic nonlinear behaviour of the fault core accompanied by instantaneous weakening and failure the resulting softening to weakening model fits in well with field observations of real earthquakes after an earthquake numerous smaller shocks are triggered over distances comparable to the dimensions of the mainshock fault rupture although they are rare at larger distances here we analyse the scaling of dynamic deformations the stresses and strains associated with seismic waves with distance from and magnitude of their triggering earthquake and show that they can cause further earthquakes at any distance if their amplitude exceeds several microstrain regardless of their frequency content these triggering requirements are remarkably similar to those measured in the laboratory for inducing dynamic elastic nonlinear behaviour which suggests that the underlying physics is similar1 2

magma emplacement during arc perpendicular shortening an example from the cascades crystalline core washington it is increasingly inferred by others that active arcs at all crustal levels are undergoing arc perpendicular extension and that magma utilizes this extension or extension along arc parallel strike slip faults during emplacement however a review of stress fields in modern arcs and deformation which occurred during magmatism in ancient arcs and our own emplacement studies of individual plutons indicate that magma emplacement typically occurred during arc perpendicular shortening without the aid of strike slip faulting this conclusion raises the question of how host rock is displaced during magma emplacement in shortening and thickening orogens evaluation of host rock material transfer processes that operated during emplacement of the 93 ma 10 to 14 km deep mount stuart batholith washington provides one example and includes the following 1 ductile downward flow in a narrow 0 2 body radii structural aureole 2 stoping and of lesser importance 3 regional folding thrusting and subhorizontal arc parallel extension we see no evidence that arc perpendicular extension or local extension along strike slip faults made space for this pluton nor for most other plutons in contractional arcs instead we argue that both localized and rapid around plutons and regional and slower downward flow during growth of crustal roots is a common process in such arcs

lack of additional triggered tectonic tremor around the simi valley and the san gabriel mountain in southern california abstract we conduct a systematic search of tectonic tremor triggered by distant large earthquakes around the simi valley sv and the san gabriel mountain sgm in southern california out of 59 large earthquakes between 2000 and 2013 only the 2002 m w 7 9 denali fault earthquake triggered clear tremor in the region the observed travel times of the triggered tremors are consistent with theoretical predictions from tremor sources that are spatially clustered in the sv close to the rupture zone of the 1994 m w 6 7 northridge earthquake we also estimate the triggering stress threshold as 12 kpa from measuring the peak ground velocities near the tremor source the lack of clear tremor beneath the sgm provides a negative example for a region where tremor is expected to occur because of clear evidence of fluid rich zones at the middle crust the results imply that the necessary conditions for tremor to occur are more than fluid induced low effective normal stress online material figures of additional tremor inspection tables of earthquake catalogs and tremor locations

dynamic stresses coulomb failure and remote triggering corrected abstract dynamic stresses associated with crustal surface waves with 15 30 s periods and peak amplitudes

martian fluvial conglomerates at gale crater observations by the mars science laboratory mast camera mastcam in gale crater reveal isolated outcrops of cemented pebbles 2 to 40 millimeters in diameter and sand grains with textures typical of fluvial sedimentary conglomerates rounded pebbles in the conglomerates indicate substantial fluvial abrasion chemcam emission spectra at one outcrop show a predominantly feldspathic composition consistent with minimal aqueous alteration of sediments sediment was mobilized in ancient water flows that likely exceeded the threshold conditions depth 0 03 to 0 9 meter average velocity 0 20 to 0 75 meter per second required to transport the pebbles climate conditions at the time sediment was transported must have differed substantially from the cold hyper arid modern environment to permit aqueous flows across several kilometers

hydrology of early mars valley network incision 1 widespread occurrences of valley networks on mars provide geomorphic evidence for an active hydrologic cycle to constrain the climatic conditions capable of forming the valley networks a hydrological model was used to analyze the valley incision depth and volume of eroded valleys because the absolute magnitudes of precipitation runoff and evaporation are uncertain we have used the ratio of these quantities the x ratio to express climatic conditions the spatial distribution and strength of the correlations between 1 the estimated depth and volume of eroded material and 2 estimated flood magnitude and valley gradients were investigated as a function of the assumed x ratio we also conducted an analysis of conditions required to have appreciable discharge in selected valley networks which provided the most definitive constraint on martian paleoclimate the other methods show a relatively weak dependency of incision depths and volumes upon the assumed x ratio the multiple regression analyses indicate that incision depth is strongly influenced by gradient and weakly related to modeled flood discharge the factors determining relative depth of incision depend partly on the type of channel bed however postflow modification of the valley networks by mass wasting cratering aeolian infilling and ice related processes precludes direct determination of bed morphology our hydrological analyses suggest that climatic conditions on early mars were at least as moist as those that occurred in the great basin region of the u s when large lakes were present during the pleistocene in terms of the balance of runoff and lake evaporation

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

palaeoflow reconstruction from fan delta morphology on mars abstract alluvial fans and deltas on mars record past hydrological conditions until now these conditions have been inferred from the morphology of the feeder channels and the deposits from images and digital terrain models dtms and from calculations of the bulk fluxes of water and sediment based on the dimensions of upstream channels neither method can distinguish between dilute river like flows and dense sediment laden flows however while the formation time scales for these two sediment transport modes differ by orders of magnitude the objective of this paper is to compare dtm data quantitatively with a morphological model to infer sediment transport mode and formative duration we present a quantitative morphological model for fan and delta formation that assumes as little as possible the model calculates the growth of a sedimentary body in a crater lake represented by a low gradient subaerial cone on top of a high gradient subaqueous cone the volume of the cone is constrained by the influx of sediment while the elevation of the break in slope that is the shoreline is constrained by the influx of water the water and sediment fluxes were calculated with physics based predictors based on the feeder channel small scale morphology such as crater wall irregularities concavity of the fan surface and channel avulsion is ignored the model produces alluvial fans stair stepped fan deltas and gilbert fan deltas as well as hitherto unidentified crater wall drapes the parameters that determine which morphology emerges are the supply of sediment and water to the basin the size of the basin and the duration of the flow a direct comparison between the cone model and hrsc dtm data for five deltas and an alluvial fan demonstrates that single event dilute flows of short duration days to years have created all of the deposits two gilbert fan deltas were formed in overspilling crater lakes from long low gradient upstream channels one alluvial fan was formed in a similar manner except that the damaged crater did not lead to ponding three stair stepped deltas were formed from short high gradient upstream channels that only partially filled the crater lakes

a new method to identify earthquake swarms applied to seismicity near the san jacinto fault california understanding earthquake clustering in space and time is important but also challenging because of complexities in earthquake patterns and the large and diverse nature of earthquake catalogues swarms are of particular interest because they likely result from physical changes in the crust such as slow slip or fluid flow both swarms and clusters resulting from aftershock sequences can span a wide range of spatial and temporal scales here we test and implement a new method to identify seismicity clusters of varying sizes and discriminate them from randomly occurring background seismicity our method searches for the closest neighbouring earthquakes in space and time and compares the number of neighbours to the background events in larger space time windows applying our method to california s san jacinto fault zone sjfz we find a total of 89 swarm like groups these groups range in size from 0 14 to 7 23 km and last from 15 min to 22 d the most striking spatial pattern is the larger fraction of swarms at the northern and southern ends of the sjfz than its central segment which may be related to more normal faulting events at the two ends in order to explore possible driving mechanisms we study the spatial migration of events in swarms containing at least 20 events by fitting with both linear and diffusion migration models our results suggest that sjfz swarms are better explained by fluid flow because their estimated linear migration velocities are far smaller than those of typical creep events while large values of best fitting hydraulic diffusivity are found

quantifying focal mechanism heterogeneity for fault zones in central and southern california summary we present a statistical analysis of focal mechanism orientations for nine california fault zones with the goal of quantifying variations of fault zone heterogeneity at seismogenic depths the focal mechanism data are generated from first motion polarities for earthquakes in the time period 1983 2004 magnitude range 0 5 and depth range 0 15 km only mechanisms with good quality solutions are used we define fault zones using 20 km wide rectangles and use summations of normalized potency tensors to describe the distribution of double couple orientations for each fault zone focal mechanism heterogeneity is quantified using two measures computed from the tensors that relate to the scatter in orientations and rotational asymmetry or skewness of the distribution we illustrate the use of these quantities by showing relative differences in the focal mechanism heterogeneity characteristics for different fault zones these differences are shown to relate to properties of the fault zone surface traces such that increased scatter correlates with fault trace complexity and rotational asymmetry correlates with the dominant fault trace azimuth these correlations indicate a link between the long term evolution of a fault zone over many earthquake cycles and its seismic behaviour over a 20 yr time period analysis of the partitioning of san jacinto fault zone focal mechanisms into different faulting styles further indicates that heterogeneity is dominantly controlled by structural properties of the fault zone rather than time or magnitude related properties of the seismicity

detection of triggered deep low frequency events from the 2003 tokachi oki earthquake 1 we show the level of increased decreased seismicity mapped across japan immediately following the 2003 tokachi oki earthquake mw 8 1 of september 25 2003 ut by use of the statistic significant dynamic triggering of events is found near the nankai subduction zone 900 1400 km from the earthquake the events are inferred to be dynamically triggered deep low frequency earthquakes of a type that often occur in this region the triggering appears to be caused by the long period oscillations of the surface waves which may be effective in triggering fluid related events the region that showed the highest level of triggered events was an area of elevated activity in the bungo strait where a slow slip event was in progress

widespread triggering of nonvolcanic tremor in california we identified seven locations on or near the transform plate boundary in california where nonvolcanic tremor was triggered by the 2002 denali earthquake this result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments models explaining tremor typically require conditions endemic to subduction zones that is high temperatures and fluid pressures because previously tremor was nearly exclusively documented in subduction zones the absence of tremor in geothermal areas is inconsistent with such models additionally we found no correlation between creeping or locked faults and tremor contrary to predictions of frictional models of tremor

controls on emplacement of the caledonian ross of mull granite nw scotland anisotropy of magnetic susceptibility and magmatic and regional structures abstract anisotropy of magnetic susceptibility ams was measured from 139 sites across the exposed portion of the caledonian ross of mull granite argyllshire nw scotland to investigate the internal architecture of the pluton field and petrographic observations support the results of the ams study and a complementary suite of rock magnetic experiments was used to quantify the magnetic mineralogy of the granite ams data reveal a fabric that records a partial tectonic overprint of an emplacement related magma inflow fabric the partially preserved inflow pattern indicates a south to north emplacement of subhorizontal sheets that coalesced to form a tabular pluton the ams data are remarkably consistent across the intrusion with clear north south strikes and trends dominating the magnetic foliation and lineation patterns respectively these ams fabrics are discordant to internal zonation in the granite in the southernmost part of the granite ams data are parallel to bedding cleavage orientations preserved in many large 100 m proterozoic moine blocks the scarcity of moine blocks in the northern part of the intrusion and the prevalence of randomly oriented stoped blocks suggest that this part of the intrusion is nearer to the ceiling of the pluton the partial tectonic overprint consistent with east west compression occurred during the latter stages of emplacement and mainly affected the younger granite facies rm2 while the oldest granite facies rm1 and certain magmatic structures diorite enclaves preserve the original emplacement fabric an alternative explanation interprets the magnetic lineations as an intersection fabric between a shallowly dipping emplacement fabric and a steep tectonic fabric we argue that emplacement was not associated with eastward orogenic collapse of the scandian moine nappes as proposed by previous workers but occurred either before orogenic collapse or during a period of compressional reactivation

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses

surface creep and slip behavior segmentation along the northwestern xianshuihe fault zone of southwestern china determined from decades of fault crossing short baseline and short level surveys abstract this study examines the 200 km long northwestern xianshuihe fault zone nwxfz southwestern china using more than three decades of geodetic observations from fault crossing short baseline and short leveling surveys at seven sites these data enable estimates of creep rates and depths and examination of the long term slip behavior the surface motion of the nwxfz is dominated by sinistral creep although sinistral transverse and vertical slip components show spatio temporal variations combining these slip variations with data of earthquake rupture coseismic slip seismicity fault geometry and far fault movement velocity and using the velocity and state friction theory our analysis indicates that the surface slip behavior of the nwxfz is segmented along strike the 1973 rupture section of this fault zone exhibits spatio temporally variable slip behavior showing time decaying post 1973 afterslip on the northwestern and southeastern parts of the rupture at depths above 5 8 7 0 km with average sinistral creep rates of 1 3 and 3 5 mm yr respectively but being relocked in the central part of the rupture the 1923 1981 rupture section is generally in locking state with postseismic and interseismic sinistral creep at 1 1 mm yr on its central part at depths above 2 0 2 8 km the 1893 rupture section has been tightly locked without creep since at least the early 1980s the thickness of the shallow velocity strengthening or creep layer and the restraining bend geometry of the nwxfz are the key factors that control spatio temporal variations in surface creep rates two surface observed locked fault portions are located within two different restraining bends in the nwxfz both of which act as compressive asperities and hence have enabled the long term locking of these portions creep along the nwxfz has also been affected to varying degrees by m6 5 mw9 2 earthquakes at distances of 50 3800 km from the fault zone most of these effects have been removed from our estimates of the long term average creep rates