newly found tunglo active fault system in the fold and thrust belt in northwestern taiwan deduced from deformed terraces and its tectonic significance we found active faults in the fold and thrust belt between tunglo town and the tachia river in northwestern taiwan the surface rupture occurred in 1999 and 1935 nearby the study area but no historical surface rupture is recorded in this area suggesting that the seismic energyhas been accumulated during the recent time deformed fluvial terraces aid in understanding late quaternary tectonics inthistectonicallyactivearea thisareacontainsnewlyidentifiedfaultsthatwegroupasthetunglofaultsystem whichformedafter the area s oldest fluvial terrace and appears at least 16km long in roughly n s orientation its progressive deformations are all recorded in associated terraces developed during the middle to late quaternary in the north the system consists of two subparallel activefaults thetunglofaultandtungloeastfault strikingn sandfacingeachotherfromoppositesidesofthenorthwardflowing hsihu river whose course may be controlled by interactions of above mentioned two active faults the northern part of the tunglo fault to the west of the river is a reverse fault with upthrown side on the west conversely the tunglo east fault to the east is also a reverse fault but with upthrown side on the east both faults are marked by a flexural scarp or eastward tilting of fluvial terraces considering a quaternary syncline lies subparallel to the east of this fault system the tunglo fault might be originated as a bending moment fault and the tunglo east fault as a flexural slip fault however they have developed as obvious reverse faults which have progressive deformation under e w compressive stress field of taiwan farther south a west facing high scarp the tunglo south fault strikes nne ssw oblique to the region s e w direction of compression probably due to the strain partitioning the tunglo southfaultgeneratesenechelon elongatedridgesandswalestoaccommodateright lateralstrike slipdisplacement otherstructures intheareaincludeeastward strikingportionofthesanyifault whichhasnoevidenceforlatequaternarysurfaceruptureonthisfault perhaps slip on this part of sanyi fault ceased when the tunglo fault system became active

an investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the united states in the 0 5 4 hz band summary studies of teleseismic p and s wave amplitudes and spectra in the 0 5 4 hz band show large variations in the attenuative properties of the upper mantle under the united states the data indicate that attenuation is greatest under the south western united states including but not confined to the basin and range province the lowest attenuation prevails under the north central shield regions the north eastern part of the country consisting of new england and possibly including a larger area along the eastern seaboard is characterized by moderate attenuation in the mantle the level of the high frequency energy in short period seismic waves and the differences between q values derived from short and long period data indicate that q is frequency dependent the form of frequency dependence of t compatible with the data in the 0 5 4 hz range does not allow a rapid decrease of t with increasing frequency rather it supports a gradual decrease covering the broader 0 1 4 hz range the curves of t versus frequency for shield to shield and mixed shield to western united states type paths are parallel with an average difference of 0 2 s in t in the short period band but may diverge towards the long period band for both curves t p is below 1 s for shield to shield paths t p must be below 0 5 s at 1 hz

precursory rise of p wave attenuation before the 2004 parkfield earthquake abstract on 28 september 2004 an m 6 0 earthquake occurred rupturing a 30 km stretch of the san andreas fault near parkfield california the fault segment which hosted a cluster of nearly identical microearthquakes a multiplet had been under close surveillance since the mid 1980s following a long term prediction by the united states geological survey that a characteristic earthquake of m 6 0 would occur near parkfield before 1993 the multiplet made possible a study of temporal changes in seismic propagation characteristics associated with the mainshock we show that a sharp rise in p wave attenuation operator t began to appear about 18 months before the belated seismic event accompanied by a rapid fall in p s ratio in both the frequency and time domains the p waves that interrogated the northern half of the impending rupture zone where the coseismic slip was to be the largest yielded the strongest t anomalies the anomalies peaked six weeks after the parkfield earthquake and then diminished rapidly in the months ensuing the preseismic rise of the t accompanied by a rapidly falling p s ratio pointed to a decline in pore fluid saturation due to microcracking that culminated in the catastrophic rock failure during the fault rupture

simultaneous determination of site responses and source parameters of small earthquakes along the atotsugawa fault zone central japan velocity seismograms recorded at nine local stations from 102 small earthquakes on the atotsugawa fault zone central japan with seismic moment from 3 10 17 to 3 10 21 dyne cm are analyzed to obtain the s wave spectra a genetic algorithm is applied to determine the earthquake source parameters and site responses simultaneously the stability of both site responses and source parameters are experimentally tested as well as the effects of different q models the resulting source parameters show that the stress drops appear to vary systematically with the location of earthquakes events located on the mozumi fault or the junction of the mozumi and the atotsugawa faults have higher stress drops than those on the creeping section and southernmost part of the atotsugawa fault the relationship between seismic moment and corner frequency constructed by combining our results and those of iio 1986 for other regions in japan shows that a single scaling relation does not apply in a moment range of 10 10 to 10 25 dyne cm a steplike change in scaling relationship occurs between 5 10 18 and 5 10 20 dyne cm corresponding to corner frequencies between 15 and 25 hz this observation suggests that earthquakes are most likely a multihierarchical system divided by characteristic sizes according to aki9s 1980 model a characteristic source dimension 100 200 meters may represent a critical size of the barriers distributed in the fault zone at which the barrier effects are balanced by the dynamic effect of the source process

geometrical spreading and q of pn waves an investigative study in eastern canada abstract station site effects uncertainties in seismic source spectrum and instrument response errors are among the well known frequency dependent contaminating factors that limit the reliability of short period q measurements of regional phases for the pn wave a regional phase of importance for both magnitude determination and nuclear test ban verification the problem is made worse by the added uncertainty of its geometric spreading function for realistic earth models the pn geometric spreading function is likely to depart drastically from that expected of canonical head waves the extent of this departure is sensitively dependent upon the regional crust mantle structure making geometric spreading assumption a conspicuous source of disagreement among the published pn attenuation q pn estimates we describe a technique referred to here as the extended reversed two station method rtsm for simultaneous determination of q pn and geometrical spreading function the formulation being designed to bring about direct cancellation of the contaminating source station and instrument effects is a reliable tool for mapping the pn propagation characteristics over continental paths long and short the extended rtsm has been tested using pn spectral amplitude data derived from seismic records of the eastern canada telemetered network ectn we find the spreading rate coefficient n in the power law representation of the geometric spreading d n d being epicentral distance to be frequency dependent increasing from 1 11 at 1 hz to 1 77 at 20 hz our q pn model in eastern canada takes the form of q pn 189 f 0 87 the results from eastern canada suggest that a there exists a significant positive velocity gradient in the uppermost mantle 0 0037 sec 1 b the regionally recorded pn waves are dominated by the superposition of a series of interfering diving waves bent by the velocity gradient and internally reflected at the underside of the moho discontinuity and c the very strong frequency dependence of q pn we found in this study region may not be unique among low attenuating shield and platform regions

a novel technique for measuring lg attenuation results from eastern canada between 1 to 10 hz spectral amplitudes of regionally recorded lg waves are studied in detail between 0 6 and 10 hz using vertical component velocity seismograms of the eastern canada telemetered network stations and a supplementary seismic research observatory type station at glen almond gac quebec we find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest furthermore they are found to be strongly frequency dependent consequently it is essential that they be taken into consideration in studies of lg wave attenuation and lg source spectra of regionally recorded seismic events we present a new method of measuring interstation surface wave attenuation which is closely related to the conventional two station method while retaining all the desirable features of the conventional two station method the new technique which we will call the reversed two station method allows simple direct one parameter determination of the lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error the reversed two station method is successfully tested over weakly attenuating short 53 to 210 km interstation paths in eastern canada a difficult experimental condition by normal standards the lg attenuation coefficient 0 6 to 10 hz in eastern canada is found to be frequency dependent and of the form f 0 0008 f 0 81 km 1 at higher frequencies the lg attenuation appears to be essentially frequency independent this latter finding is preliminarily interpreted as evidence that regionally recorded lg waves in the canadian shield are as in the case of lg waves propagating through the structurally complex appalachian province contaminated by the high frequency coda of sn waves the lg contamination over the shield paths becomes severe starting at 14 hz twice the frequency above which the lg signal propagating over the appalachian province becomes completely dominated by non lg arrivals

high frequency p wave attenuation determination using multiple window spectral analysis method yellowknife array northwest territories canada recordings of nuclear explosions detonated at french tuamotu south pacific and shagan river eastern kazakhstan ussr test sites are used to derive t values via the application of the spectral decay method an important factor that limits the reliability of this widely used method is the degree of accuracy with which one is able to determine the signal spectral shape for transient pulse like short period teleseismic phases the conventional single window spectral estimate methods may not be appropriate due to the trade off betgween the leakage resistance and variance a recently developed multiple window spectral analysis method is used in this study to effectively control spectral leakage a capability that is especially important when analyzing seismic data characterized by a rapid high frequency fall off rate such as the french tuamotu explosion data we compare the t estimates obtained using a conventional single window method with those obtained using the multiple window method and show that the latter are more reliable the f 0 5 to 4 5 hz found by the multiple window method for the tuamotu yellowknife path is 0 66 sec for the eastern kazakhstan yeliowknife path the multiple window t estimate is 0 42 sec in the 0 5 to 4 5 hz range a smaller value is obtained at higher frequencies 4 5 to 8 hz

spectral characteristics of p waves from nuclear explosions and yield estimation abstract spectra of teleseismic short period p waves from nuclear explosions show clear path related differences in their high frequency falloff rates p waves from kazakh explosions commonly show significant seismic energy above the frequency of 5 hz when recorded in shield regions peaceful nuclear explosions in the tectonically stable areas of the ussr have similar properties together with the amchitka explosions and salmon nuclear explosions in the western united states algeria and french polynesia show much less high frequency energy in their p wave spectra and signal energy above 5 hz is usually not seen we attribute these variations to lateral changes in the anelastic attenuation properties of the upper mantle for the events in the contiguous united states this interpretation is confirmed by the results of reciprocal measurements of q about 500 p wave spectra not including those utilized in the reciprocal measurements were used to estimate the contribution to t p of the upper mantle q structures under a number of nuclear test sites and observatories

reply to comment on teleseismic p wave attenuation and nuclear explosion source functions inferred from yellowknife array data by kin yip chun tianfei zhu and gordon f west

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

seismic energy for shallow earthquakes in southwest japan we estimated the radiated energy for 88 earthquakes with m w 4 0 that occurred in southwest japan by analyzing direct s waves recorded by the freesia broadband seismic network f net at local regional distances the attenuation factors for each source receiver group are estimated by the coda method using the recently established high sensitivity and high density seismic network hi net data the site amplification for each f net station is calculated by using the coda normalization method we find good agreement between the source spectra calculated by using these propagation effects and those determined by using an empirical green s function method for 4 m w 5 earthquakes the station variance of the energy estimates is a factor of 2 for earthquakes with m w 5 and it is a factor of 3 for the smaller ones the resultant energy estimations show that 1 the overall ratios between the radiated energy and seismic moment e s m 0 lie in a band of 5 10 7 to 5 10 5 for 88 earthquakes with m w 3 9 6 8 for the tottori 2000 earthquake and its 16 aftershocks with m 0 10 14 10 19 n m we found a very slight increase of e s m 0 with increasing seismic moment for the rest of earthquakes e s m 0 are almost constant for earthquakes occurring in the same source area the constants corresponding to each source area are slightly but systematically different indicating a location dependence of e s m 0 earthquakes that occur in volcanic areas show lower e s m 0 values relative to earthquakes occurring in nonvolcanic areas however the weak to non scaledependence is not certain because of the scantiness of large earthquakes in the data set 2 for earthquakes in the volcanic source areas there appears to be a trend of increasing e s m 0 with focal depth we believe this trend is a result of at least in part the decreasing attenuation with depth in volcanic areas for the nonvolcanic area earthquakes however e s m 0 tends to be a constant in a depth range of 12 50 km since the akinada earthquake 2001 m w 6 8 took place in the western part of subducting philippine sea slab and the two deeper earthquakes occurred in the upper mantle below the same subducting slab in its eastern part the constancy of e s m 0 may indicate that the apparent stress at the brittle patches in the ductile zone can be as high as in the brittle part of the crust 3 estimated e s m 0 are inversely related to the surface heat flow approximately such a relationship suggests that the geothermal structure may be the dominating tectonic factor that controls the level of apparent stress

body wave attenuation in the tonga subduction zone attenuation p and s waves of in the tonga subduction zone is estimated from locally recorded data using a spectral ratio method the data consist of three component digital seismograms of 77 earthquakes recorded at two stations in fiji and one in tonga the stations in the fiji islands lie above the deep earthquakes in the subduction zone while the tonga station is close to the top of the subducted slab variations in the high frequency spectral decay rate define four attenuation provinces paths from earthquakes deeper than 350 km to stations on viti levu fiji and the lau ridge traverse mantle with normal attenuation qp 570 qs 200 400 the subducting tonga slab has very low attenuation qp 2000 qs 1800 relative to the surrounding mantle the wedge of mantle above the slab at depths shallower than 350 km and east of the lau ridge is extremely attenuating for p waves qp 240 several paths from main thrust zone events to the station in tonga show intermediate attenuation qp 300 500 in the forearc region the observed spectra do not require q to be frequency dependent in the 1 0 hz to 7 6 hz band in this region

temporal changes in p wave attenuation in the loma prieta rupture zone 1 clusters of recurring nearly identical microearthquakes have been recorded near loma prieta california such events make possible direct measurement of temporal changes in the attenuation operator t along fixed paths under what are tantamount to laboratory conditions analysis of almost 10 years of p wave data following the 18 october 1989 loma prieta california main shock m 7 0 reveals a large amplitude t increase within the first 3 weeks of the main shock a gradual t recovery toward its level prior to the main shock is seen in the years ensuing the results point to changes in porosity and fluid saturation taking place in parts of the main shock source volume stemming from coseismic crack opening and postseismic relaxation processes such as postseismic fluid flow into the cracks crack healing and rock compaction

high resilience of harpacticoid copepods in the landward slope of the japan trench against disturbance of the 2011 tohoku earthquake

river terrace development in response to folding above active wedge thrusts in houli central taiwan abstract folding at the leading edge of the western taiwan thrust belt is well preserved by a flight of fluvial terraces at houli strain in this region is driven by slip on the north trending changhua and sanyi blind wedge thrusts and occurs at the boundary between the miaoli and taichung neotectonic domains located respectively to the north and south in the past century two large historical earthquakes occurred in these two domains and produced surface ruptures within or close to the study area indicating houli is not only tectonically active but also critical for understanding the interaction between the neighboring active systems although abundant river terraces and their deformation by active structures have long been well known in the area a kinematical model for this region has not yet been proposed we have therefore remapped the geomorphic features using the 40 m dem and aerial photos to identify often subtle structural features in order to separate the effects of folding interference produced by different active structural systems besides the tuntzuchiao fault ttcf which generated the 1935 earthquake two other active regional scale structural systems have been reported in houli area the tiechanshan tcs anticline and the changhua fault chf our results demonstrate a number of tectonic scarps and warped surfaces in association with the chf and its coupled back thrust indicating that the chf system is active in contrast the flight of fluvial terraces distributed in the middle of the study area cannot be related to the growth of the tcs anticline instead terraces here record growth of another smaller and previously unknown anticline yuehmei tentatively named in this study and shortened to ym in the text although it has developed parallel to the tcs anticline relevant seismic profiles show the ym anticline as a local drag fold attached to the southern limb of the tcs anticline and restricted in the houli area based on the above observation the tcs anticline can be interpreted as becoming less active where strain is instead transferred to the more rapidly uplifting ym anticline this structural switch may be the result of interference between the newly developed southern taichung system and the preexisting tcs anticline

teleseismic p wave attenuation and nuclear explosion source functions inferred from yellowknife array data we report here the results of a comprehensive seismic attenuation investigation along the paths connecting canada s yellowknife seismic array yka with seven active nuclear explosion testing areas the data consist of more than 600 explosion generated teleseismic p wave records a dual time frequency averaging technique is used to take advantage of the array recording characteristics without the drawback of the conventional beam forming excessive annihilation of high frequency signal energies the dual averaging technique deployed in conjunction with a multiwindow spectral analysis method yields smooth amplitude spectra whose falloff at high frequencies suffers little from spectral leakage due to the familiar presence of a prominent low frequency plateau measured in terms of t the highest attenuation 0 66 s is found along the path which originates from the tuamotu test area somewhat less attenuating are the two paths which depart from the pahute mesa 0 59 s and yucca flat 0 50 s nuclear test areas both located within the u s nevada test site we find t for these three paths to be substantially up to 0 21 s higher than recently published estimates e g der et al 1985 we attribute these disparities largely to differences in spectral leakage control capability between the conventional single window and the improved multiwindow spectral analysis methods the least attenuating paths all originate from the soviet test areas novaya zemlya nz west kazakhstan degelen mountain dm and shagan river sr the last two of these test areas dm and sr are both located in east kazakhstan the p wave signatures of the soviet explosions are rich in high frequency 4 5 hz energies and the yka data 0 5 8 0 hz support a frequency dependent t whose value at high frequencies 4 5 hz is as small as 0 17 s to gain a grasp of the ramifications of the t disparity between the multiple window and the single window results we have compared explosion source time functions obtained by the multichannel deconvolution technique of shumway and der 1985 in order to assess their sensitivity to the input t value in our example involving the deconvolved source functions of five french tuamotu explosions we find that a 0 1 s t difference is large enough to cause clearly discernible signature differences in terms of the signal frequency content as well as the extractability of a secondary arrival some 0 4 s behind the first p arrival this secondary arrival is believed to be the depth phase pp a seismic signature of importance in both yield estimation and earthquake explosion source discrimination the absorption band modeling minster 1978a b of the french tuamotu explosion data yields 1 08 0 05 and 0 079 0 008 s for t and tm respectively the corresponding parameter estimates derived from the u s explosion data are somewhat smaller the t and r m estimates are the smallest along the paths which depart from the four soviet test areas for the nz yka path the t and r m estimates are 0 56 0 08 and 0 061 0 013 s respectively plagued by a strong trade off between the two model parameters these estimates are not tightly constrained however

attenuation of short period p pcp scp and pp waves in the earth s mantle the parameter t ratio of body wave travel time to the average quality factor q was estimated under various assumptions of the nature of the earthquake sources for short period p pcp and scp phases originating from earthquakes in the fiji tonga region and recorded at the warramunga seismic array at tennant creek northern territory australia spectral ratios were calculated for the amplitudes of pcp to p and of pp to p the data reveal a laterally varying q structure in the fiji tonga region the high q lithosphere descending beneath the tonga island arc is overlain above 350 km depth by a wedgelike zone of high attenuation with an average q between 120 and 200 at short periods the upper mantle farther to the west of the tonga island arc is less attenuating with q between 370 and 560 q is about 500 in the upper mantle on the oceanic side of the subduction zone the t estimates of this study are much smaller than estimates from the free oscillation model sl8 this can be partly explained by regional variations of q in the upper mantle if no lateral q variations occur in the lower mantle a frequency dependent q can make the pcp and sep observations consistent with model sl8 adopting the absorption band model to describe the frequency dependence of q the parameter 2 the cut off period at the high frequency end of the absorption band was determined for different source models with finite corner frequencies the average 2 for the mantle is between 0 01 and 0 10 s corresponding to frequencies between 16 and 1 6 hz as derived from the pcp data and between 0 06 and 0 12 s 2 7 and 1 3 hz as derived from the scp data

geomorphic evidence for prior earthquakes lessons from the 1999 chichi earthquake in central taiwan the september 21 1999 mw 7 6 chichi earthquake destroyed several thousand buildings and caused more than 2000 fatalities in central taiwan the earthquake occurred along the chelungpu fault a thrust fault on the western flank of the taiwan fold and thrust belt the surface rupture was more than 90 km long and vertical displacements ranged from 3 to 8 m although pre existing scarps were identified along the chelungpu fault the fault had previously been categorized as a less important active fault owing to the lack of geochronologic evidence and the failure to recognize fault related geomorphic features identifying geomorphic features at active faults in taiwan will permit the delineation of future sur face ruptures and the determination of past magnitudes of past earthquakes thus contributing to hazard assessment

neotectonic architecture of taiwan and its implications for future large earthquakes the disastrous effects of the 1999 chi chi earthquake in taiwan demonstrated an urgent need for better knowledge of the island s potential earthquake sources toward this end we have prepared a neotectonic map of taiwan the map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40 m resolution digital elevation model augmented by geodetic and seismologic data the active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin have created two neotectonic belts in taiwan in the southern part of the orogen both belts are in the final stage of consuming oceanic crust collision and suturing occur in the middle part of both belts and postcollisional collapse and extension dominate the island s northern and northeastern flanks both belts consist of several distinct neotectonic domains seven domains kaoping chiayi taichung miaoli hsinchu ilan and taipei constitute the western belt and four domains lutao lanyu taitung hualien and ryukyu make up the eastern belt each domain is defined by a distinct suite of active structures for example the chelungpu fault source of the 1999 earthquake and its western neighbor the changhua fault are the principal components of the taichung domain whereas both its neighboring domains the chiayi and miaoli domains are dominated by major blind faults in most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid 7 values