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

nonvolcanic tremor observed in the mexican subduction zone nonvolcanic tremor nvt activity is revealed as episodes of higher spectral amplitude at 1 8 hz in daily spectrograms from the continuous seismological records in guerrero mexico the analyzed data cover a period of 2001 2007 when in 2001 2002 a large slow slip event sse had occurred in the guerrero oaxaca region and then a new large sse occurred in 2006 the tremor burst is dominated by s waves more than 100 strong nvt bursts were recorded in the narrow band of 40 150 km 2 to the south of iguala city and parallel to the coastline depths of nvt hypocenters are mostly scattered in the continental crust between 5 and 40 km depth tremor activity is higher during the 2001 2002 and 2006 sse compared with that for the quiet period of 2003 2005 while resistivity pattern in guerrero does not correlate directly with the nvt distribution gravity and magnetic anomaly modeling favors a hypothesis that the nvt is apparently related to the dehydration and serpentinization processes

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

low frequency earthquakes in the mexican sweet spot 1 we use data from the meso america subduction experiment to detect and locate low frequency earthquakes lfes in the mexican subduction zone we use visually identified templates to perform a network waveform correlation search that produced 17 000 robustly detected lfes that form 15 distinct families stacking an lfe family s corresponding detections results in seismograms with high signal to noise ratios and clear p and s wave arrivals we use these travel times to locate the sources the resulting locations superpose a previously identified region of permanent non volcanic tremor nvt activity husker et al 2012 called this region a sweet spot suggesting that the local conditions are adequate to continuously generate nvt the lfe hypocenters have been located at a depth of 40 45 km in an area that is surrounding the upper slab plate interface we characterize their focal mechanisms by comparing their stacked seismograms to synthetic seismograms this analysis reveals a common low dipping focal mechanism

non volcanic tremor associated with the march 2010 gisborne slow slip event at the hikurangi subduction margin new zealand 1 non volcanic tremor accompanies slow slip events at most circum pacific subduction zones previously the hikurangi subduction margin new zealand and the boso peninsula of japan have been noted as exceptions where slow slip which occurs at shallow depth compared to other subduction zones does not generate seismic tremor the lack of tremor observations raises questions whether tremor and slow slip are manifestations of the same process and whether different temperature and pressure conditions influence the physical mechanism of tremor production analysis of seismic data during the march 2010 gisborne slow slip event new zealand reveals that this slow slip event at the northern hikurangi margin is accompanied by tremor with distinctive characteristics compared to local microearthquakes both the gisborne area of new zealand and the boso peninsula of japan are underlain by thick accumulations of sedimentary rocks that likely inhibit the observation of low amplitude tremor due to high attenuation discovery of tremor in new zealand suggests that tremor may always accompany slow slip and that its apparent absence at the boso peninsula the hikurangi margin prior to this study and any future regions discovered to experience slow slip without concurrent tremor may be the effect of highly attenuating sediments

possible relationship between nonvolcanic tremor and the 1998 2001 slow slip event south central alaska 1 we document the occurrence of nonvolcanic tremor nvt in south central alaska for 3 months of each year between 1999 and 2001 to provide a first order attempt to understand the relationship between nvt and a large slow slip event that occurred over a 2 to 3 year period between 1998 and 2001 the majority of the nvt signals observed after the onset of the slow slip event are bursts lasting between 10 and 15 min with frequencies ranging from 1 to 6 hz by the summer of 2001 the quantity of nvt has decreased dramatically from the previous summers and episodes rarely last up to 10 min the decrease in nvt activity in the summer of 2001 is coincident with the end of the slow slip event there is a clear spatial correlation between the observed nvt and the slow slip event with most of the nvt events located on the downdip edge of the region of highest slip depth estimates range widely over the region with approximately half concentrated near the interpreted north america yakutat pacific plate interface and the remainder located above the plate interface however owing to inadequate station coverage and poor knowledge of the local structure determining accurate depths is difficult and thus the relationship between the nvt and the plate interface is problematic this is the first study giving evidence that the relationship between slow slip events and nvt seen in cascadia and southwest japan may also exist in alaska

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

triggered tectonic tremor in various types of fault systems of japan following the 2012 mw8 6 sumatra earthquake tectonic tremor an extremely stress sensitive seismic phenomenon occurring in the brittle ductile transition section of a fault is associated with the shearing mechanism of slow slip observations of triggered tremor can facilitate the evaluation of the existence of background ambient tremor and slow slip events this paper presents widespread triggered tremor sources in japan initiated by the surface waves of the 2012 mw8 6 sumatra earthquake on strike slip and thrust faults in the deep volcanic low frequency earthquake active area in the shallow tectonic tremor and very low frequency earthquake active regions and in the subduction zone in most regions the amplitudes of triggered tremor are generally logarithmically proportional to the dynamic stress caused by various triggering earthquakes our observations suggest that triggered tremor in the newly discovered sources is the result of a more rapid rate of background ambient tremor and evidence has suggested the existence of ambient tremor in some regions

detecting low frequency earthquakes within non volcanic tremor in southern taiwan triggered by the 2005 mw8 6 nias earthquake 1 we use a matched filter technique to detect 41 low frequency earthquakes lfes within 700 s of triggered tremor signals in the southern central range in taiwan during the surface waves of the 2005 mw8 6 nias earthquake off the coast of northern sumatra the depth distributions of lfes after double difference relocations concentrate at the depth range of 12 38 km below the background seismicity and above the moho depth inferred from receiver function studies the locations of lfes are close to the downward extension of the steep dipping chaochou lishan fault with only modestly high vp vs ratios 1 75 1 85 our observation indicates that at least portions of triggered tremor consists of many lfes similar to ambient tremor observed at other major plate boundary faults

statistical properties of low frequency earthquakes triggered by large earthquakes in southern taiwan abstract the recent discovery of triggered tremors tts and low frequency earthquakes lfes in various tectonic environments provides an opportunity for studying the fundamental properties and physical mechanisms of deep tectonic tremor here we quantify the relationship between tts and lfes beneath the central range in southern taiwan and their statistical properties during the teleseismic waves of six large distant earthquakes using waveforms of 11 lfes triggered by the 2005 m w 8 6 nias earthquake as templates we scan through 12 hours of waveform data around six mainshocks and identify a total of 783 lfes the lfes were mainly located in a compact region between 12 and 36 km in depth near the chaochou lishan fault most of lfes occurred within tt during the passage of large amplitude surface waves and the increase of the lfe rate during the surface waves is statistically significant the lfe rates do not follow an omori s type decay but rather abruptly return to the background rate immediately after the surface wave passage these findings suggest that lfes do not trigger any additional lfes at later times and are primarily driven by an external forcing our observations are consistent with the inference that tts consist of many reoccurring lfes

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

dense network intense seismicity and tectonics of taiwan abstract a temporary seismic network consisting of 295 land stations was deployed in 2009 in taiwan to monitor airgun sources during an onshore offshore experiment in taiwan we exploit the continuously recorded dataset to detect and map seismicity in the seismically very active taiwan by combining recent automatic detection and phase picking techniques we successfully generate an initial earthquake catalog of over 8400 events the hypodd algorithm is used to relocate and filter these events this network recorded smaller events than the permanent regional network because of the many stations around the high mountain ranges and the generally high station density along 6 lines the results based on the 2009 data generally reproduce the dominant seismicity features from many years of earthquake monitoring in taiwan in addition we map hitherto unknown dipping zones under the foothills and the central range that may correspond to seismogenic structures

from accretion to collision motion and evolution of the chaochou fault southern taiwan 1 the chaochou fault ccf is an important tectonic boundary of the taiwan orogenic belt between the metamorphosed slate belt to the east and the western foothills foreland fold and thrust belt to the west although the fault is known to be a high angle oblique sinistral thrust fault in places both its kinematic history and its current role in the development of the orogen are poorly understood field fabric data suggest that hanging wall structural orientations vary along strike particularly in the on land extension of the intersection of the eurasian continent ocean boundary and the luzon arc slip lineations also reveal a change in fault motion from dip parallel in the north to a more variable pattern in the south this correlates somewhat with recent gps results that indicate that the direction of current horizontal surface motion changes along strike from nearly perpendicular to the fault in the northern to oblique and nearly parallel to the fault in the south mountain front sinuosity and the valley floor width valley height ratio indicate higher activity and uplift in the north geodetic and geomorphic data together indicate that along the northern segment of the ccf the slate belt hanging wall is currently undergoing rapid uplift related to oblique arc continent collision between the eurasian continent and the luzon arc the southern segment of the fault is significantly less active perhaps because 1 the fault is blind or 2 this portion of the fault is south of the point where the eurasian continental platform intersects the orogenic front

lamellar nigerite in zn rich spinel from the falun deposit sweden lamellar nigerite is found in zn rich spinel from a sample that contains chiefly anthophyllite spinel cordierite lesser amounts of quartz and chlorite as well as sphalerite pyrite pyrrhotite and galena and rare cassiterite and rutile nigerite can be described as interlayering of spinel like r2 al2o4 and nolanite like sn ti al4o8 structures in nigerite the spinel like part is also compositionally related to spinel but in the nolanite like part only the structural analogy exists stoichiometric assumptions that relate the anhydrous cation sum to the amount of r4 cations present allow fe3 estimates from microprobe analyses and a representative analysis gives the following anhydrous formula mg1 30fe 0 65 2 zn3 03mn0 03al11 65fe 0 35 3 sn0 32ti0 18o24

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

temporal variation of tectonic tremor activity in southern taiwan around the 2010 ml6 4 jiashian earthquake deep tectonic tremor which is extremely sensitive to small stress variations could be used to monitor fault zone processes during large earthquake cycles and aseismic processes before large earthquakes in this study we develop an algorithm for the automatic detection and location of tectonic tremor beneath the southern central range of taiwan and examine the spatio temporal relationship between tremor and the 4 march 2010 ml6 4 jiashian earthquake located about 20 km from active tremor sources we find that tremor in this region has a relatively short duration short recurrence time and no consistent correlation with surface gps data we find a short term increase in the tremor rate 19 days before the jiashian mainshock and around the time when the tremor rate began to rise one gps station recorded a flip in its direction of motion we hypothesize that tremor is driven by a slow slip event that preceded the occurrence of the shallower jiashian mainshock even though the inferred slip is too small to be observed by all gps stations our study shows that tectonic tremor may reflect stress variation during the pre nucleation process of a nearby earthquake

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

thrust type focal mechanisms of tectonic tremors in taiwan evidence of subduction unlike tectonic tremors in subduction zones and along transform faults the hosting structure for tremors in taiwan remains debated tectonic tremors in taiwan have been discovered at 30 km depth beneath the southern central range which is a young and active collisional mountain belt here we provide the first evidence for the focal mechanism of tremor using moment tensor inversion in the very low frequency band employing broadband seismograms stacked relative to the hypocentral time of tremor the best solution corresponds to low angle thrust faulting suggesting the subduction of the eurasian plate this mechanism is consistent with strong tidal modulation of tremor activity but differs from the normal type faulting that dominates regional shallow earthquakes this result suggests vertical variations in the tectonic stress regime thrust faulting may be facilitated by a decrease in normal stress due to the buoyant roots of the mountain belt and local high fluid pressure

tectonic tremor and lfes on a reverse fault in taiwan we compare low frequency earthquakes lfes from triggered and ambient tremor under the southern central range taiwan we apply the pagerank algorithm used by aguiar and beroza 2014 that exploits the repetitive nature of the lfes to find repeating lfes in both ambient and triggered tremor we use these repeaters to create lfe templates and find that the templates created from both tremor types are very similar to test their similarity we use both interchangeably and find that most of both the ambient and triggered tremor match the lfe templates created from either data set suggesting that lfes for both events have a common origin we locate the lfes by using local earthquake p wave and s wave information and find that lfes from triggered and ambient tremor locate to between 20 and 35 km on what we interpret as the deep extension of the chaochou lishan fault

ambient tremors in a collisional orogenic belt deep seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt in this study we explore the general features of collisional tremors in taiwan and discuss the possible generation mechanism in the 4 year data we find 231 ambient tremor episodes with durations ranging from 5 to 30 min in addition to a coseismic slip induced stress change from nearby major earthquake increased tremor rate is also highly correlated with the active normal faulting earthquake swarms at the shallower depth both the tremor and earthquake swarm activities are confined in a small area where the high attenuation high thermal anomaly the boundary between high and low resistivity and localized veins on the surfaces distributed suggesting the involvement of fluids from metamorphic dehydration within the orogen

an autocorrelation method to detect low frequency earthquakes within tremor 1 recent studies have shown that deep tremor in the nankai trough under western shikoku consists of a swarm of low frequency earthquakes lfes that occur as slow shear slip on the down dip extension of the primary seismogenic zone of the plate interface the similarity of tremor in other locations suggests a similar mechanism but the absence of cataloged low frequency earthquakes prevents a similar analysis in this study we develop a method for identifying lfes within tremor the method employs a matched filter algorithm similar to the technique used to infer that tremor in parts of shikoku is comprised of lfes however in this case we do not assume the origin times or locations of any lfes a priori we search for lfes using the running autocorrelation of tremor waveforms for 6 hi net stations in the vicinity of the tremor source time lags showing strong similarity in the autocorrelation represent either repeats or near repeats of lfes within the tremor we test the method on an hour of hi net recordings of tremor and demonstrates that it extracts both known and previously unidentified lfes once identified we cross correlate waveforms to measure relative arrival times and locate the lfes the results are able to explain most of the tremor as a swarm of lfes and the locations of newly identified events appear to fill a gap in the spatial distribution of known lfes this method should allow us to extend the analysis of shelly et al 2007a to parts of the nankai trough in shikoku that have sparse lfe coverage and may also allow us to extend our analysis to other regions that experience deep tremor but where lfes have not yet been identified

subduction continent collision in southwestern taiwan and the 2010 jiashian earthquake sequence abstract we integrated a regional tomography model 20 year seismicity and earthquake focal mechanisms of the 4 march 2010 m l 6 4 jiashian earthquake source region to delineate the seismogenic structure and mechanics of a relatively rare damaging inland earthquake that occurred in the southwestern fold and thrust belt of taiwan the main shock of the jiashian earthquake occurred at a depth of 23 km beneath the slate belt of the southern central range with a sinistral thrust mechanism based on seismic tomography and seismicity the jiashian earthquake sequence occurred in the chishan transfer fault zone which we interpret to be located near the transition zone between the subducted eurasian plate to the south and the arc continent taiwan collision to the north the distribution of the jiashian aftershocks define a wnw ese striking fault plane that dips 30 40 nne which is consistent with the optimal fault plane of the gps derived coseismic slip model focal mechanisms and inverted stress results of the earthquake sequence indicate both thrust and strike slip motions with the maximum compressive stress at nearly 90 to the regional compressive stress and thus sub parallel to the strike of the taiwan orogen we propose that the 2010 jiashian earthquake resulted from rupturing of a buried oblique fault within the chishan transfer fault zone at the subduction collision transition zone in southern taiwan the orogen parallel p axis of the 2010 jiashian earthquake represents collision related lateral compression although a local stress deviation is also possible

a global search for triggered tremor following the 2011 mw 9 0 tohoku earthquake abstract the 2011 m w 9 0 tohoku japan earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide here we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified tremor was triggered in the following regions south central alaska the aleutian arc shikoku in southwest japan the north island of new zealand southern oregon the parkfield cholame section of the san andreas fault in central california the san jacinto fault in southern california taiwan and vancouver island we find no evidence of triggered tremor in the calaveras fault in northern california one of the most important factors in controlling the triggering potential is the amplitude of the surface waves data examined in this study suggest that the threshold amplitude for triggering tremor is 0 1 cm s which is equivalent to a dynamic stress threshold of 10 kilopascals the incidence angles of the teleseismic surface waves also affect the triggering potentials of love and rayleigh waves the results of this study confirm that both love and rayleigh waves contribute to triggering tremor in many regions in regions where both ambient and triggered tremor are known to occur tremor triggered by the tohoku event generally occurred at similar locations with previously identified ambient and or triggered tremor further supporting the notion that although the driving forces of triggered and ambient tremor differ they share similar mechanisms we find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor which is consistent with the prediction of the clock advance model online material table of measured parameters and other information related to triggering nontriggering information and figures of observed seismograms

petrology and geochemistry of rhyolites associated with tin mineralization in northern mexico 30 to 32 m y old rhyolite flows and domes host rhyolite capped by rhyolitic ignimbrites cap ignimbrites relatively low crystallization temperatures 700 degrees or 50 degrees c in the host rhyolites but higher 740 degrees or 40 degrees c in the cap ignimbrites the host rhyolites are high silica rhyolites 74 sio 2 that are metaluminous or slightly peraluminous they have high k 2 o na 2 o ratios are enriched in sn u th and rb and depleted in ca mg ti p co ni ba sr and eu relative to high k calc alkalic rocks rare earth element patterns exhibit marked negative eu anomalies and a slight enrichment of light rare earth elements relative to the heavy elements these characteristics suggest that the tin rhyolites formed as extreme differentiates in high level magma chambers closely related to caldera development initial sr isotope ratios of the tin rhyolites range from 0 7053 to 0 7078 differentiation was clearly the major factor in concentrating tin in the mexican tin rhyolites modified journal abstract

mineralogy and genesis of cordierite anthophyllite rocks from the sulfide deposit of falun sweden abstract cordierite anthophyllite rocks from the aureole of the falun sulfide deposit are characterized by the assemblages cordierite anthophyllite garnet gahnite quartz dierite staurolite quartz and cordierite andalusite quartz metamorphic conditions are estimated to be 550 50 c 2 5 1 kbar bulk rock chemistry trace element concentration and the variance of the system as defined by the parageneses hint at an origin from acid rocks altered metasomatically at rather low temperatures to chlorite quartz muscovite and subsequently metamorphosed under essentially isochemical conditions

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

is the lishan fault of taiwan active abstract the lishan fault has been characterized alternately as a major discontinuity in stratigraphy structures and metamorphism a ductile shear zone a tectonic suture or non existent in addition to being a geological boundary it also marks transitions in subsurface structures thus the seismicity to the west of the fault permeates through the upper and mid crust while beneath the central range it is noticeably less and largely concentrated in the upper 12 km a prominent west dipping conductive zone extends upward to meet the lishan fault also the eastward increase of crust thickness from 30 km in the taiwan strait quickens under the lishan fault to form a root of over 50 km under the central range in the past the small magnitude seismicity along the lishan fault has been noticed but is too diffuse for definitive association with the fault recent processing of aftershock records of the 1999 mw 7 6 chi chi earthquake using central weather bureau data and especially data from three post chi chi deployments of seismic stations across central taiwan yielded hypocenters that appear to link directly to the lishan structure the presence of a near 4 km long vertical seismic zone directly under the surface trace of the lishan fault indicates that it is an active structure from the surface down to about 35 km and the variety of focal mechanisms indicates that the fault motion can be complex and depth dependent

surface estimates of the atlantic overturning in density space in an eddy permitting ocean model 1 a method to estimate the variability of the atlantic meridional overturning circulation amoc from surface observations is investigated using an eddy permitting ocean only model orca 025 the approach is based on the estimate of dense water formation from surface density fluxes analysis using 78 years of two repeat forcing model runs reveals that the surface forcing based estimate accounts for over 60 of the interannual amoc variability in 0 coordinates between 37 n and 51 n the analysis provides correlations between surface forced and actual overturning that exceed those obtained in an earlier analysis of a coarser resolution coupled model our results indicate that in accordance with theoretical considerations behind the method it provides a better estimate of the overturning in density coordinates than in z coordinates in subpolar latitudes by considering shorter segments of the model run it is shown that correlations are particularly enhanced by the method s ability to capture large decadal scale amoc fluctuations the inclusion of the anomalous ekman transport increases the amount of variance explained by an average 16 throughout the north atlantic and provides the greatest potential for estimating the variability of the amoc in density space between 33 n and 54 n in that latitude range 70 84 of the variance is explained and the root mean square difference is less than 1 sv when the full run is considered

detecting deep tectonic tremor in taiwan with a dense array abstract we perform a systematic detection of deep tectonic tremor beneath the southern central range in taiwan using a dense small aperture seismic array deployed in february 2011 the array has been recording tectonic tremor nearly continuously for 134 days including tremor triggered by the 2011 m w 9 0 tohoku oki earthquake we use broadband frequency wavenumber beamforming and moving window grid search methods to compute array parameters for all continuous data and identify tremor as coherent nonimpulsive seismic signals with deep incidence angles the obtained array parameters closely match with those of relocated local earthquakes and triggered tremor bursts located by the waveform envelope correlation and clustering wecc method indicating the robustness of our array technique during the 134 day study period we detect tremor for 44 days with a total duration of 1481 min three to six times as long as the detection of tremor by the wecc method we find a relative quiescence in ambient tremor activity for about 20 days following the 2011 tohoku oki earthquake suggesting that dynamic stresses from the distant mainshock triggered most tremor close to failure resulting in a temporary lack of tremor activity in some cases we observe rapid tremor migration with a speed at the order of 40 50 km hr that is similar to the speed of fast tremor migration along dip on narrow streaks in japan and cascadia our results suggest that dense array techniques are capable of capturing detailed spatiotemporal evolutions of tremor behaviors in southern taiwan online material tables of station coordinates and tremor event parameters and figures of the moving window grid search test with local earthquakes tremor triggered by the 2011 tohoku oki earthquake and additional examples of detected ambient tremors

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

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

seismic tomography of taiwan improved constraints from a dense network of strong motion stations in this study a large collection of 41 141 s p times from the untapped records of the taiwan strong motion instrumentation program tsmip network is combined with the p and s wave arrival times from the taiwan central weather bureau seismic network cwbsn to image the v p and v p v s structures beneath taiwan the records from the 680 tsmip stations throughout taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously our result for the v p structure largely confirms previous studies but brings better constraint on the v p v s structure the colliding luzon volcanic arc is characterized by a belt of high v p and high v p v s with high seismicity that includes the offshore islands of lutao and lanyu and the coastal ranges in eastern taiwan at the depth between about 13 and 25 km this high v p v s belt can be traced to the subduction zone in the region between hualian and ilan in the deeper portion the shallow portions of the southwestern coastal plain and the pingtung region are also characterized by a belt of high v p v s with lower seismicity most of the events occurred at the base of the high v p v s zones we suggest that material strength in those regions may be too low to accumulate stress which may indicate water saturated young sediments finally the central range region is characterized by a low v p v s belt