a continuum of stress strength and slip in the cascadia subduction zone movement of the down going oceanic plate in subduction zones is accommodated by earthquakes slow slip and free slip with increasing depth analysis of accompanying tremor reveals a continuum of slow slip events in the cascadia subduction zone which suggests that deep free slip of the subducted plate may cause stress to be gradually transferred up the plate interface towards the seismogenic zone

dynamic triggering stress modeling and a case study 1 changes in the static stress can trigger nearby earthquakes that occur within a few fault lengths from the causative event transient stresses caused by passage of surface waves commonly trigger events at remote distances yet little is documented or understood about the processes and stresses necessary for remote triggering to understand the causative stresses and environments behind remote or dynamic triggering we must decipher the stresses caused by the passage of the surface waves in relation to the local stress field and fault conditions where the triggered events occur in this study we model the change in the stress field that the passing of rayleigh and love waves causes on a fault plane of arbitrary orientation relative to the direction of propagation of the waves and we apply a coulomb failure criterion to calculate the potential of these stress changes to trigger reverse normal or strike slip failure we compare these model results with data from dynamically triggered earthquakes in the australian bowen basin an area with low seismicity and mapped regional stress and that is at the margin of a stable continental craton our data analysis shows that for this region surface waves arriving at 45 from the average strike direction are the most likely to trigger local seismicity this agrees with our observations

delayed dynamic triggered seismicity in northern baja california mexico caused by large and remote earthquakes we analyze the seismicity in northern baja california mexico that occurred one month before and one month after the 11 march 2011 m w 9 1 tohoku oki japan earthquake and for two other large and remote earthquakes the 27 february 2010 central chile m w 8 8 earthquake and the 11 april 2012 northern sumatra earthquake m w 8 6 the northern region of baja california exhibits high microseismic activity and moderate size earthquakes the seismicity in this region is monitored by the seismic network red sismica del noroeste de mexico resnom operated by the centro de investigacion cientifica y de educacion superior de ensenada cicese we use the resnom seismic catalog to search for changes in local seismic rates that occurred after the passing of surface waves generated by the three large earthquakes studied when we compare one month of seismicity before and after the m w 9 1 japan earthquake in the biggest of the three events analyzed we observe the absence of triggered seismicity in the northern peninsular ranges and an increase of seismicity south of the mexicali valley where the imperial fault jumps southwest and the cerro prieto fault continues south we also observe an increase of seismicity rate in the cucapah fault and in the san pedro martir fault regions the cucapah fault region the most active of the three regions during the studied period shows an increase of seismicity several days after the 2010 chile m w 8 8 and the 2011 japan m w 9 1 earthquakes this observation can be interpreted as evidence of delayed seismicity and confirms the observation of rubinstein et al 2009 that earthquakes tend to be triggered in regions with high ambient seismicity rates we observed delayed triggering of earthquakes generated by two of the three remote earthquakes analyzed these observations can be explained by dynamic triggering of prolonged fault creep as proposed by shelly et al 2011 online material maps of seismicity and m c

marked differences between van genuchten soil water retention parameters for temperate and tropical soils a new water retention pedo transfer functions developed for tropical soils all of the physical chemical and soil water retention data suitable for the derivation of a pedo transfer functions ptf for water retention for tropical soils 771 suitable horizons were extracted from the igbp dis soil database the parameters s r and n of the van genuchten vg soil sci soc am j 44 1980 892 equation were derived and compared with parameter values from two published data sets of temperate region soils thirty five percent of the soils in the tropical igbp t database were classified as clays compared with only 4 and 7 in the temperate databases the igbp t soil bulk densities were significantly lower p 0 001 for nine textural classes for the more clayey textural classes the value of was higher for the igbp t soils implying more large pores and more structure for kaolinitic soils in the igbp t database was typically around 0 4 kpa 1 compared with 0 04 kpa 1 for montmorillonitic soils mineralogy is clearly important and should be included in ptfs if available the value of n for clay soils in the igbp t data set was significantly higher than for temperate soils and s was significantly higher for nine textural classes p 0 001 reflecting their lower bulk density r was also significantly higher for all textural classes except sand for clay the mean value of r was 0 27 m3 m 3 compared to only 0 11 m3 m 3 for temperate soils for 17 of the igbp t data r exceeded 0 3 m3 m 3 a value often used as a fitting constraint a tropical soil ptf was developed using multiple regression techniques this predicted water retention curves more reliably than either class ptfs or soil class ptfs but was not reliable for low density soils such as andosols the igbp t data set includes some groups of soils e g andosols and ferralsols whose properties are extremely different from those of most temperate soils these differences emphasise the need to develop separate ptfs for tropical soils or perhaps for specific groups of soils there were few water retention data from below 1 5 m depth and a complete lack of hydraulic conductivity data in the igbp t database this is a major impediment to the modelling of water movement and uptake in deep rooted ecosystems for example tropical forest and savannah

variety and spatial heterogeneity of tectonic tremor worldwide 1 deep tectonic tremor occurs at various sites worldwide and the source characteristics are heterogeneous even at small scales in this study tremor sources were determined using data sets of seismic waveforms from various locations some of which are not well recognized as being a site of tremor activity the regions of interest are subduction zones at nankai and kyushu japan cascadia in western north america mexico southern chile and new zealand tremor locations are consistent with the geometry of subducting plates and tremor depth tends to be shallower where younger plate is subducting tremor duration shows a negative correlation with tidal sensitivity as reported previously in western shikoku in the nankai subduction zone the duration is also related to the width of the tremor zone in the dip direction of the subducting plate linear structures resembling striations are observed in hypocenter distributions in western shikoku and in the probability of short term migration direction these spatial heterogeneities in tremor activity may be controlled by the heterogeneous frictional properties of the downgoing slab due to long term plate subduction thereby providing information on the maturity of the plate interface

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

a tremor and slip event on the cocos caribbean subduction zone as measured by a global positioning system gps and seismic network on the nicoya peninsula costa rica in may 2007 a network of global positioning systems gps and seismic stations on the nicoya peninsula of northern costa rica recorded a slow slip event accompanied by seismic tremor the close proximity of the nicoya peninsula to the seismogenic part of the cocos caribbean subduction plate boundary makes it a good location to study such events several centimeters of southwest motion were recorded by the gps stations over a period of several days to several weeks and the seismic stations recorded three distinct episodes of tremor during the same time span inversion of the surface displacement data for the depth and pattern of slip on the plate interface shows peak slip at a depth of 25 30 km downdip of the main seismogenic zone estimated temperatures here are 250 300 c lower than in other subduction zones where events of this nature have been previously identified there may also be a shallower patch of slip at 6 km depth these results are significant in that they are the first to suggest that slow slip can occur at the updip transition from stick slip to stable sliding and that a critical temperature threshold is not required for slow slip tremor and low frequency earthquake locations are more difficult to determine our results suggest they occur on or near the plate interface at the same depth range as the deep slow slip but not spatially colocated

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

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

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

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

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

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

depth dependent activity of non volcanic tremor in southwest japan 1 with a new location method we obtained a high resolution map of non volcanic tremor along the subducting philippine sea plate in southwest japan and clarified the depth dependent behavior of the tremor activity a bimodal distribution of tremor along dip is apparent in regions where short term slow slip events sses and very low frequency earthquakes are frequently detected the separation of bimodal peaks is 5 to 10 km in depth the updip tremor activity occurs episodically coincident with major bursts that often accompany geodetically detectable sses the downdip tremor activity is however rather stable with frequent minor bursts this depth dependent tremor activity likely reflects variation of interplate slip properties specifically weakening with increasing depth and temperature in westernmost shikoku anomalous tremor activity was detected in only the updip section in late 2003 this is interpreted as being triggered by a long term sse in the shallower edge of the tremor zone

tectonic tremor and deep slow slip on the alpine fault 1 tectonic tremor is characterized by persistent low frequency seismic energy seen at major plate boundaries although predominantly associated with subduction zones tremor also occurs along the deep extension of the strike slip san andreas fault here we present the first observations of tectonic tremor along new zealand s alpine fault a major transform boundary that is late in its earthquake cycle we report tectonic tremor that occurred on the central section of the alpine fault on 12 days between march 2009 and october 2011 tremor hypocenters concentrate in the lower crust at the downdip projection of the alpine fault coincide with a zone of high p wave attenuation low qp and bright seismic reflections occur in the 25 45 km depth range below the seismogenic zone and may define the deep plate boundary structure extending through the lower crust and into the upper mantle we infer this tremor to represent slow slip on the deep extent of the alpine fault in a fluid rich region marked by high attenuation and reflectivity these observations provide the first indication of present day displacement on the lower crustal portion of the australia pacific transform plate boundary

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

triggering of tremor and inferred slow slip by small earthquakes at the nankai subduction zone in southwest japan the correlation of earthquakes with tremor and slow slip has not been clearly quantified we investigate 12 year earthquake and tremor catalogs for southwest japan and find that nearby small intraslab earthquakes are weakly correlated with tremor in particular the intraslab earthquakes with magnitudes 2 7 tend to be followed by tremor more often than expected at random by a factor of 2 to 6 the excess number of tremor before earthquakes is not as significant although marginally more than expected the underlying physical mechanism of the observed triggering of tremor and inferred slow slip by earthquakes is most likely to be the dynamic stress changes several to several tens of kilopascals rather than the much smaller static stress changes the rate of triggering of tremor by earthquakes is similar to although somewhat lower than rates observed for similar amplitude stress changes due to the lower frequency teleseismic surface waves and tidal stressing

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

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

tectonic tremor along the northern hikurangi margin new zealand between 2010 and 2015 we present the first comprehensive tectonic tremor catalog for the northern hikurangi margin obtained from the systematic analysis of data from the new zealand seismic network between 2010 and 2015 the recent densification of this array along the northern hikurangi margin has allowed for the detection and location of tectonic tremor associated with 20 out of 26 identified transients in the continuous gps record along the east coast of the raukumara peninsula eighteen of these transients have never been reported in the literature and are likely to be slow slip events with magnitudes smaller than those previously studied we also investigate the spatiotemporal relationships between shallow offshore slow slip tectonic tremor and earthquakes for the duration of the study period

rare dynamic triggering of remote m 5 5 earthquakes from global catalog analysis probing the effects of a transient stress on the timing of an earthquake occurrence is necessary for understanding the remote interaction of large magnitude events global catalog data containing 35 years of m 5 5 earthquakes allow us to explore for periods of enhanced or suppressed seismic activity we consider 113 m 7 5 main shocks between 1977 and 2012 and focus on seismic activity on time scales from seconds to days following these main shocks we search for evidence of dynamic triggering of large magnitude events similar to the previously observed global increase during the first few days following the 2012 m8 6 indian ocean main shock we restrict the analysis to regions of elevated strain during the passage of surface waves using a threshold of 0 1 microstrain 3 kpa and a temporal window of 1 year we stack daily seismicity rate curves using the exclusion zone declustered m 5 5 catalog events in order to resolve deviations from the background rate our results do not indicate a significant change in activity for at least 10 days when considering the collective set of 113 main shocks and subsets at m8 0 and m8 5 thresholds the results also do not indicate immediate triggering of m 5 5 events we do find two instances of increased seismicity in the elevated strain region within 10 days these increases are subsequent to two main shocks the 1977 m8 3 and 2012 m8 6 both located in the indian ocean we conclude that a global change in m 5 5 earthquake rates following a transient stress from distant earthquakes is a rare occurrence

limited dynamic earthquake triggering in the socorro magma body region rio grande rift new mexico abstract dynamic earthquake triggering the process through which stresses transmitted through the passage of seismic waves can trigger remote faults to fail has been shown to be fairly common throughout the globe and especially in seismically active areas of high heat flow and geothermal activity we explore the possibility of dynamic earthquake triggering around the socorro magma body a feature within the rio grande rift in new mexico that exhibits high heat flow and heightened seismicity because the area fits the environment type in which triggering preferentially occurs we examine 319 global mainshocks with m w 6 0 for the possibility of increased seismicity rates following the passage of the mainshock waves we examine local event locations and origin times relative to mainshock phase arrivals for patterns distinguishing triggering mainshocks from nontriggering mainshocks we find a small triggering response during the time period analyzed unlike following the 2002 denali fault earthquake dfe this small response corresponds to smaller peak dynamic stresses than are found in other triggering studies m w 7 0 at a regional to small teleseismic distance

soil physicochemical properties and moisture dynamics of a large soil profile in a tropical monsoon forest abstract evergreen forests in tropical monsoon asia experience a severe dry season lasting several months deep soil moisture is responsible for evergreen forest transpiration during this season this study provides preliminary information on soil physicochemical properties in a large soil profile 800 cm deep and evaluated the influences of deep soil moisture dynamics on the transpiration of evergreen forests in cambodia using a water flow model in general changes in soil physicochemical properties with depth were small excluding topsoil the soil texture in the large soil profile was characterized by very little gravel and a large sand fraction the soil carbon stock was 71 7 and 130 1 mg c ha 1 at depths of 0 150 and 0 800 cm respectively the coarse pore volume 100 k s clearly decreased with depth from 100 to 600 cm and were extremely low at 600 700 cm in the water flow simulation a rooting depth deeper than 400 cm was necessary for the evergreen forest to maintain transpiration during the dry season on the other hand when the k s of deep soil 550 750 cm depth was assumed to be higher than that estimated by the cylinder sample a rooting depth of 800 cm was necessary since most of the soil water that was replenished during the rainy season was rapidly lost during the dry season also it was necessary for evergreen forests to effectively use soil water within the deep root zone 400 800 cm depth the compacted deep soil horizons played an important role in maintaining the moist conditions in the root zone of an evergreen tropical monsoon forest in asia that experienced a severe dry season

persistent tremor within the northern costa rica seismogenic zone 1 we identify tremor using a spectral detection method and characterize its occurrence over a period of four years 2006 2009 in the vicinity of the nicoya peninsula costa rica although a few major tremor events accompanied by geodetic slow slip occur much of the tremor record consists of minor episodes with short duration and no detectable geodetic slip its persistent occurrence suggests that some portion of the interface is experiencing slow slip nearly continuously driving small patches to fail in accelerated slip locations indicate that much of the tremor occurs at shallow depth in freely slipping regions of the seismogenic zone this result is significant in that locations of slow slip and tremor at other subduction zones are largely limited to the downdip frictional transition tremor locations may help to refine the heterogeneous distribution of locked and freely slipping patches within the costa rica seismogenic zone

the 2006 slow slip event and nonvolcanic tremor in the mexican subduction zone the last decade featured an explosive sequence of discoveries of slow slip events sse and nonvolcanic tremor nvt in different subduction zones and continental faults many observations show that sse is usually associated with an increased nvt activity but it is not clear yet if those events are the result of the same process or are independent expressions of a common underlying seismotectonic source a large sse in central mexico occurred in 2006 during the meso american subduction experiment mase which provided continuous observations of the nvt for the years 2005 2007 gps and abundant seismic data show that although the nvt energy increased notably during the 2006 sse the two phenomena were separated spatially and not completely synchronized in time significant nvt episodes occur during the period between sses suggesting again that large slow slip events and nvt observed in the mexican subduction zone are of different origins the results presented here contribute to uncovering the nature of these two separate phenomena that have been indistinguishable in some other regions

soil pore characteristics of evergreen and deciduous forests of the tropical monsoon region in cambodia both evergreen and deciduous forests efs and dfs are widely distributed under similar climatic conditions in tropical monsoon regions to clarify the hydraulic properties of the soil matrix in different forest types and their effects on soil water storage capacity the soil pore characteristics spc were investigated in ef and df stands in three provinces in cambodia soils in the ef group were characterized in common by large amounts of coarse pores with moderate pore size distribution and the absence of an extremely low ks at shallow depths compared to df group soils the mean available water capacity of the soil matrix awcsm for all horizons of the ef and df group soils was 0 107 and 0 146 m3 m 3 respectively the mean coarse pore volume of the soil matrix cpvsm in the ef and df groups was 0 231 and 0 115 m3 m 3 respectively a water flow simulation using a lognormal distribution model for rain events in the early dry season indicated that variation in spc resulted in a larger increase in available soil water in ef soils than in df soils further study on deeper soil layers in ef and each soil type in df is necessary for the deeper understanding of the environmental conditions and the hydrological modelling of each forest ecosystem copyright 2010 john wiley sons ltd

striations duration migration and tidal response in deep tremor deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components it occurs at a depth of about 30 kilometres and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes tremor has been suggested to repeat at a regular interval migrate at various velocities and be modulated by tidal stress here i show that some time invariant interface property controls tremor behaviour using precise location of tremor sources with event duration in western shikoku in the nankai subduction zone japan in areas where tremor duration is short tremor is more strongly affected by tidal stress and migration is inhibited where tremor lasts longer diffusive migration occurs with a constant diffusivity of 10 4 m 2 s 1 the control property may be the ratio of brittle to ductile areas perhaps determined by the influence of mantle wedge serpentinization on the plate interface the spatial variation of the controlling property seems to be characterized by striations in tremor source distribution which follows either the current or previous plate subduction directions this suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure such as seamounts for periods as long as ten million years

remotely triggered microearthquakes and tremor in central california following the 2010 mw 8 8 chile earthquake 1 we examine remotely triggered microearthquakes and tectonic tremor in central california following the 2010 mw 8 8 chile earthquake several microearthquakes near the coso geothermal field were apparently triggered with the largest earthquake ml 3 5 occurring during the large amplitude love surface waves the chile mainshock also triggered numerous tremor bursts near the parkfield cholame section of the san andreas fault saf the locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from coso but can be identified by applying high pass or matched filters both triggered tremor along the saf and the ml 3 5 earthquake in coso are consistent with frictional failure at different depths on critically stressed faults under the coulomb failure criteria the triggered tremor however appears to be more phase correlated with the surface waves than the triggered earthquakes likely reflecting differences in constitutive properties between the brittle seismogenic crust and the underlying lower crust

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

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

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

triggered tremor sweet spots in alaska 1 to better understand what controls fault slip along plate boundaries we have exploited the abundance of seismic and geodetic data available from the richly varied tectonic environments composing alaska a search for tremor triggered by 11 large earthquakes throughout all of seismically monitored alaska reveals two tremor sweet spots regions where large amplitude seismic waves repeatedly triggered tremor between 2006 and 2012 the two sweet spots locate in very different tectonic environments one just trenchward and between the aleutian islands of unalaska and akutan and the other in central mainland alaska the unalaska akutan spot corroborates previous evidence that the region is ripe for tremor perhaps because it is located where plate interface frictional properties transition between stick slip and stably sliding in both the dip direction and laterally the mainland sweet spot coincides with a region of complex and uncertain plate interactions and where no slow slip events or major crustal faults have been noted previously analyses showed that larger triggering wave amplitudes and perhaps lower frequencies 0 03 hz may enhance the probability of triggering tremor however neither the maximum amplitude in the time domain or in a particular frequency band nor the geometric relationship of the wavefield to the tremor source faults alone ensures a high probability of triggering triggered tremor at the two sweet spots also does not occur during slow slip events visually detectable in gps data although slow slip below the detection threshold may have facilitated tremor triggering

estimating seismic moment magnitude mw of tremor bursts in northern cascadia implications for the seismic efficiency of episodic tremor and slip 1 we develop a method to estimate the seismic moments of deep non volcanic tremor bursts observed in northern cascadia for each tremor burst the maximum amplitudes at individual stations within a time window 5 s around the predicted arrivals of the s phase are measured and compared to the maximum s amplitudes measured from synthetic seismograms the proposed method is thoroughly calibrated using 464 local earthquakes and the results show excellent consistency between the reported ml and the estimated mw we apply the method to northern cascadia tremors and infer that most bursts have mw 1 0 1 7 the corresponding b value appears to be 1 consistent with that of ordinary earthquakes but over a narrower mw range comparison of cumulative tremor mw and the mw estimated from the accompanying slow slip suggests that the seismic efficiency of the episodic tremor and slip ets is of the order of 0 1 or less

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

deep low frequency earthquakes in tectonic tremor along the alaska aleutian subduction zone 1 we characterize and locate tremor not associated with volcanoes along the alaska aleutian subduction zone using continuous seismic data recorded by the alaska volcano observatory and the alaska earthquake information center from 2005 to present visual inspection of waveform spectra and time series reveal dozens of 10 to 20 min bursts of tremor along the length of the alaska aleutian subduction zone we use autocorrelation to demonstrate that these tremor signals are composed of hundreds of repeating low frequency earthquakes lfes the tremor activity we characterize is localized in four segments from east to west kodiak island shumagin gap unalaska and andreanof islands although the geometry age thermal structure frictional and other relevant properties of the alaska aleutian subduction zone are poorly known these characteristics are likely to differ systematically from east to west locations near kodiak island are the most reliable because station coverage is more complete lfe hypocenters in this region are located on the plate interface near the down dip limit of the 1964 mw 9 2 alaska earthquake rupture area lfe hypocenters in the remaining areas along the arc are also located down dip of the most recent mw 8 megathrust earthquakes although these locations are less well constrained our results support the hypothesis that tremor activity marks the down dip rupture limit for great megathrust earthquakes in this subduction zone lastly there is no correlation between the presence of tremor and particular aspects of over riding or subducting plate geology or coupling it appears that lfes are a fundamental characteristic of the alaska aleutian subduction zone

slow slip phenomena in cascadia from 2007 and beyond a review recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults the traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on locked plate boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow slip phenomena mostly in the deeper reaches of subduction zones the cascadia subduction zone located in the pacific northwest of the conterminous united states and adjacent canada is an archetype of exploration and learning about slow slip phenomena these phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals although secondary failure processes may be involved in generating the seismic signals the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip probably facilitated by fluids on a plate interface that is critically stressed or weakened in cascadia this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes and it occurs between the 30 and 40 km depth contours of the plate interface where information was previously elusive although there is some underlying organization that relaxes nearly all the accrued plate motion stresses along the entirety of cascadia we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts our new understanding provides key constraints not only on the region where the slow slip originates but also on the probable characteristics of future megathrust earthquakes in cascadia herein we review the most significant scientific issues and progress related to understanding slow slip phenomena in cascadia and highlight some of their societal implications we provide a comprehensive review from the big picture as inferred from studies of regional scale monitoring data to the details revealed by innovative focused experiments and new instrumentation we focus on what has been learned largely since 2007 when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data

high frequency identification of non volcanic tremor triggered by regional earthquakes 1 subsequent to the discovery of ambient non volcanic tremor activity along the parkfield cholame section of the san andreas fault in central california triggered tremors associated with the surface waves of large teleseismic earthquakes have been recognized however no evidence of triggered tremors from regional earthquakes has previously been found either here or in other tremor regions by systematically filtering seismograms to higher frequencies i e above 20 hz associated with 99 regional m5 earthquakes since 2001 we identify four regional earthquakes that have triggered tremors in central california significant high frequency energy is also observed in previously identified teleseismically triggered and ambient tremors suggesting a common mechanism we find that long period and large amplitude surface waves from both regional and teleseismic events have a greater potential of triggering tremor in the same region and that the inferred minimum triggering dynamic stress is 1 kpa

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

dynamic stresses coulomb failure and remote triggering dynamic stresses associated with crustal surface waves with 15 30 sec periods and peak amplitudes 5 km the latter is consistent with the observation that extensional or transtensional tectonic regimes are more susceptible to remote triggering by rayleigh wave dynamic stresses than compressional or transpressional regimes locally elevated pore pressures may have a role in the observed prevalence of dynamic triggering in extensional regimes and geothermal volcanic systems

nonvolcanic tremor in the aleutian arc nonvolcanic tremors nvt have been observed across the aleutian arc the tremorlike events are observed over a large region spanning seismic networks on several volcanoes and are therefore unlikely to be related to any one volcanic complex although locating the events is not possible at the present time we provide general locations based on move out times and amplitudes across multiple networks the majority of nvt events are recorded in regions where the subducting pacific plate is inferred to be locked or transitioning from creeping to locked one nvt event was recorded during a time of increased seismic and volcanic activity in the area near the rat and andreanof islands similar simultaneous increases have been observed in the aleutians in the past and are hypothesized to be caused by large regional stress changes possibly caused by slow slip events a prominent recent nvt event was recorded on the korovin and great sitkin seismic networks approximately one hour after the onset of the 12 july 2008 eruption of okmok volcano nvt does not appear sporadically across the aleutian arc but seems to concentrate in a few regions with 2500 km of subduction zone we have an opportunity to examine these regions and compare them to regions not producing nvt in an attempt to identify factors that may play a role in its creation

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

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

microseismicity but no tremor accompanying slow slip in the hikurangi subduction zone new zealand abstract geodetically detected episodes of slow slip appear in several subduction zones to be accompanied by bursts of low frequency coherent noise known as seismic tremor but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved detailed analysis of broadband seismic data spanning a slow slip episode in the hikurangi subduction zone new zealand reveals that slow slip was accompanied by distinct reverse faulting microearthquakes rather than tremor the timing location and faulting style of these earthquakes are consistent with stress triggering down dip of the slow slip patch either on the subduction interface or just below it these results indicate that tremor is not ubiquitous during subduction zone slow slip and that slow slip in subduction zone environments is capable of triggering high frequency earthquakes near the base of the locked subduction thrust in this and other locations hawaii boso peninsula where slow slip is accompanied by triggered microseismicity the estimated upper extent of the slow slip is shallower less than 20 km than in those locations from which tremor has been reported this suggests that ambient temperature or pressure dependent factors govern the character of the seismic response to slow slip on subduction thrusts and other large faults with rheological or lithological conditions at shallow depths triggering high frequency microearthquakes and those at greater depths triggering seismic tremor

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

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

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

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

propagation of an earthquake triggering front from the 2011 tohoku oki earthquake 1 increases in seismicity have been widely observed at varying distances from the source area following large earthquakes the increased number of earthquakes are usually called aftershocks if the area is within a rupture length of the mainshock and called remotely triggered events if they are well beyond that distance these earthquakes can be explained as being induced by static and or dynamic stress changes due to the mainshock however clear observations of dynamic triggering have been inadequate to differentiate between the two mechanisms this study shows that early post seismic events triggered by the 2011 mw 9 0 tohoku oki earthquake systematically propagated over japan in a southwestern direction associated with the strong seismic waves from the source the propagation front was consistent with the arrivals of large amplitude surface waves traveling at 3 1 to 3 3 km s and extending to a distance of 1 350 km there were no observations of triggered earthquakes in the northern direction dynamic stress changes toward the north were comparable to or smaller than those necessary for triggering in the southwestern direction static stress changes were one to two orders smaller than dynamic stress changes at remote distance indicating that static stress was not the main mechanism of the triggering furthermore the dynamic stress strain changes play an important role for remote triggering if the value is more than 500 kpa in stress or 10 6 in strain

spatial and temporal distributions of b values related to long term slow slip and low frequency earthquakes in the bungo channel and hyuga nada regions japan abstract long term slow slip events sses and low frequency earthquakes lfes repeatedly occur in the area encompassing the bungo channel and hyuga nada region in japan sses are slow earthquake events with a duration of months to years characterized by a type of slip that is considered transitional between the fast rupture of regular earthquakes and stable sliding along a plate interface and have characteristics sensitive to stress states near the plate interface in addition since lfes are also thought to occur at the plate interface it would be useful to infer the stress state in this region this study focuses on the stress dependent characteristics of the b values of regular earthquakes sses and lfes as well as the spatio temporal relationships between b values and these events in this area using the japan unified high resolution relocated catalog for earthquakes juice the b value which represents the relative proportion of large to small earthquakes is inversely related to differential stress or effective stress the b values are moderate to low b 0 6 1 1 in regions with a high incidence of long term sses this spatial b value anomaly is attributed to the partial release of accumulated stress in regions with a relatively high differential stress due to sse activity furthermore the b value distributions estimated in this study provide constraints on the mechanisms that generate lfes on the other hand the b values increase and decrease before and during periods of enhanced lfe activity in the bungo channel respectively the increase and following decrease in b values are thought to reflect episodes of low and high shear strength along the plate interface which were caused by the presence of abundant slab derived fluids under undrained conditions above the plate interface and decreased pore pressure related to fluid depletion via lfe generation respectively

nonvolcanic tremor evolution and the san simeon and parkfield california earthquakes nonvolcanic tremors occur adjacent to locked faults and may be closely related to the generation of earthquakes monitoring of the san andreas fault in the parkfield california region revealed that after two strong earthquakes tremor activity increased in a nearly dormant tremor zone increased and became periodic in a previously active zone and has remained elevated and periodic for over 4 years static shear and coulomb stress increases of 6 to 14 kilopascals from these two earthquakes are coincident with sudden increases in tremor rates the persistent changes in tremor suggest that stress is now accumulating more rapidly beneath this part of the san andreas fault which ruptured in the moment magnitude 7 8 ft tejon earthquake of 1857

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

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

triggered seismic events along the eastern denali fault in northwest canada following the 2012 mw 7 8 haida gwaii 2013 mw 7 5 craig and two mw 8 5 teleseismic earthquakes we conduct a systematic search for remotely triggered seismic activity along the eastern denali fault edf in northwest canada an intraplate strike slip region we examine 19 distant earthquakes recorded by nine broadband stations in the canadian national seismograph network and find that the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig alaska earthquakes triggered long duration 10 s emergent tremor like signals near the southeastern portion of the edf in both cases tremor coincides with the peak transverse velocities consistent with love wave triggering on right lateral strike slip faults the 2011 m w 9 0 tohoku oki and 2012 m w 8 6 indian ocean earthquakes possibly triggered tremor signals although we were unable to locate those sources in addition we also identify many short duration 5 s bursts that were repeatedly triggered by the rayleigh waves of the 2012 m w 7 8 haida gwaii earthquake although we were unable to precisely locate the short duration 5 s events they appear to be radiating from the direction of the klutlan glacier and from a belt of shallow historical seismicity at the eastern flank of the wrangell st elias mountain range the fact that these events were triggered solely by the rayleigh waves suggests a different source mechanism as compared with triggered tremor observed along the edf and other plate boundary regions online material description of rayleigh wave polarization detection figures of spectograms s wave amplitudes polarization analysis and static stress changes tables of earthquake catalogs and velocity model and animations of tremors and bursts

tremors along the queen charlotte margin triggered by large teleseismic earthquakes 1 we conduct a systematic search of tectonic tremors along the queen charlotte margin qcm in western canada triggered by distant earthquakes we identify triggered tremor as non impulsive high frequency signals coherent among several stations and coincident with passing surface waves so far the 2002 mw7 9 denali fault the 2004 mw9 2 sumatra and the 2011 mw9 1 tohoku oki earthquakes have triggered clear tremor in this region the 2010 mw8 8 maule chile and the 2012 mw8 6 sumatra earthquakes may have triggered but tremors in these two cases did not meet all of our criteria the triggered tremors are mostly located east of the queen charlotte fault in the southern portion of haida gwaii near the epicenter of the 28 october 2012 mw7 7 earthquake similar to the observations in other regions the triggered tremors were initiated by the love waves and continued during the subsequent rayleigh waves tremor bursts correlate with both the particle velocity and displacement of the love waves indicating they are triggered at either low angle thrust or vertical strike slip faults in addition we find that the triggering potential for the qcm is controlled by a combination of amplitude period and incident angles

late quaternary spring fed deposits of the grand canyon and their implication for deep lava dammed lakes one of the most intriguing episodes in the quaternary evolution of the grand canyon of the colorado river arizona was the development of vast lakes that are thought to have backed up behind lava erupted into the gorge stratigraphic evidence for these deep lava dammed lakes is expectedly sparse possible lacustrine deposits at six areas in the eastern canyon yielded no compelling evidence for sediment deposited in a deep lake at two of the sites the sediment was associated with late quaternary spring fed pools and marshes water lain silt and sand at lower havasu creek was deposited 3000 cal yr ago the deposit contains an ostracode assemblage similar to that living in the modern travertine dammed pools adjacent to the outcrop the second deposit at lees ferry formed in a spring fed marsh 43 000 cal yr ago as determined by 14 c and amino acid geochronology it contains abundant ostracode and mollusk fossils the richest assemblages reported from the grand canyon to date our interpretation of these sediments as spring fed deposits and their relative youth provides an alternative to the conventional view that deposits like these were formed in deep lava dammed lakes that filled the grand canyon c 2002 university of washington

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

deep tremor in new zealand triggered by the 2010 mw8 8 chile earthquake 1 deep non volcanic tremor nvt is usually associated with episodic slow slip events new zealand is one notable exception where numerous slow slip events have been identified yet nvt has remained undetected here we present the first known case of triggered nvt at new zealand s hikurangi subduction margin following the mw8 8 chilean earthquake of february 27 2010 we identify coherent high frequency tremor signals that are in phase with and modulated by the passing rayleigh waves this is consistent with the surface wave triggering potential for strike normal incidence on a low angle thrust fault after constraining the tremor depth on the plate interface we locate the tremor source within 20 km of the source area of episodic slow slip the tremor location is also near the edge of a region with high seismic attenuation that marks the boundary between dehydrated subducted slab and inferred hydrated underplated sediment we speculate that reduced interface friction and high fluid pressures provided by fluid rich underplated sediment facilitates the tremor generation

slow slip and frictional transition at low temperature at the hikurangi subduction zone temperature changes with depth do not appear to be a primary control for either slow slip or fault locking processes at the hikurangi margin north island new zealand both slow slip events and the geodetically observed transition from fault locking to free slip at depth occur at temperatures as low as 100 c shallow portions of faults exhibit brittle stick slip behaviour that gives way to more stable sliding with increasing depth limiting the depths to which earthquake inducing slip can occur the increase of temperature with depth is often assumed to transform friction in the fault from velocity weakening unstable to velocity strengthening stable and to change conditions from brittle to ductile1 2 3 4 5 a temperature of 350 c has been suggested to mark the base of the frictionally unstable portion of the fault which becomes free slipping at depth where temperatures rise above 450 c refs 2 4 6 here we show that both slow slip events and the geodetically observed transition from fault locking to free slip at the hikurangi subduction zone east of the north island new zealand occur at temperatures as low as 100 c suggesting that temperature is not a primary control on either slow slip or fault locking processes at the hikurangi margin although globally shallow slow slip events are rare five out of seven events observed so far at the hikurangi margin are less than 15 km deep

automated detection and location of cascadia tremor 1 a new autonomous seismic location and detection methodology enables real time opportunities for high resolution spatio temporal monitoring of non volcanic tremor combining a unique cross correlation technique with epicenter clustering analysis in northern cascadia automatically yields thousands of tremor epicenters from the may 2008 episodic tremor and slip ets event while routinely detecting and locating inconspicuous inter ets tremor bursts although ets events in this area produce about two weeks of continuous tremor we find a nearly equal amount of tremor during the last 15 month inter ets period the resulting ets and inter ets epicenters occur in the slow slip region where the plate interface is 30 45 km deep and have a sharp well resolved updip boundary about 75 km east of the downdip edge of the seismogenic megathrust zone this ability to track tremor with high spatio temporal resolution facilitates automatic tremor monitoring and the mapping of the transition zone and regions of locked zone stress accumulation

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

tectonic tremor beneath cuba triggered by the mw 8 8 maule and mw 9 0 tohoku oki earthquakes we provide additional evidence of tectonic tremor in cuba triggered by the 2010 m w 8 8 maule chile and the 2011 m w 9 0 tohoku oki japan earthquakes the high frequency tremor signals are modulated by long period surface waves similar to triggered tremors observed in other tectonically active regions we are able to locate two tremor sources triggered by the tohoku oki earthquake near the east west trending oriente fault around guantanamo bay the tremor around guantanamo bay was triggered primarily by a love wave of the maule mainshock and by both love and rayleigh waves of the tohoku oki mainshock this is consistent with frictional failures at a vertical strike slip fault under a coulomb failure criterion online material figure of envelope functions of tremor records and movies of spectogram and tremor correlation

propagation of distinct love wave pulses from regional to teleseismic distances in continental and oceanic environments this study was conducted with support from grants in aid from the japan society for the promotion of sciences nos 17k01322 19h00807

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

surface wave potential for triggering tectonic nonvolcanic tremor 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 is 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 0 2 however documented instances of tremor triggered by surface waves with strike parallel incidence along the nankai megathrust beneath shikoku japan is 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

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