lava trees and tree molds cannon stones of mt etna unique volcanic structures known in the literature as lava trees and tree molds have formed at several sites on mt etna volcano northeastern sicily italy they form when a fluid lava flow runs over a tree wraps around it and while the wood burns off solidifies forming a hollow cast of the tree the inhabitants of the etna area call these formations pietre cannone cannon stones because of their cylindrical shape the first documentation of lava trees is from hawaii but the first eye witnessed accounts of their formation are to our knowledge from etna s 1865 eruption although many of the literature examples of lava trees and tree molds formed in pahoehoe many of those reported in this work formed in a a the sites where we have found the lava tree molds are located within the territory of the etna regional park most occur next to walking trails and have a high potential for geotourism

near real time mapping of peak ground acceleration and peak ground velocity following a strong earthquake during a disastrous earthquake the early assessment and timely reporting of the peak ground acceleration pga and peak ground velocity pgv maps will be crucial in an effective emergency response operation in this study we first derive an empirical relationship between m l and m w the pga and pgv attenuation relationships are deduced with data from the taiwan strong motion instrumentation program tsmip and the taiwan rapid earthquake information release system treirs site corrections of the attenuation relationships for shallow and large earthquakes in taiwan region are also obtained peak values of earthquake strong ground motion can be well determined in taiwan as soon as the earthquake location is determined and magnitudes are calculated by the treirs this peak ground motion value information can be immediately turned into the calculated pga and pgv maps that can be issued within two minutes of the earthquake origin time during any disastrous earthquake these maps are found to be very useful for immediate seismic damage assessment and dispatching of emergency response missions manuscript received 1 december 2000

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

improving the amplitude source location asl method using multicomponent seismic data an assessment with active source seismic dataimproving the asl method using multicomponent seismic data an assessment with active source seismic data improving the amplitude source location asl method using multi component seismic data an assessment with active source seismic data

magnetic characterization of reduction in mount fuji basaltic tree mold a mount fuji basaltic tree mold presents the mineralogical record associated with a large oxygen fugacity gradient during the cooling of the basalt magnetic exchange anisotropy is postulated to be characteristic of cation excess in some spinel titanomagnetites the exchange anisotropy is characterized by loop shifting along the field and magnetization axes when cooled in a magnetic field large coercivity increase and magnetic viscosity which has discrete activation fields and logarithmic to linear decay characteristics the cryogenic loop characteristics attributable to exchange anisotropy are not found in the tree mold where iron and ilmenite are the main phases the coupling has been created in the laboratory with ordinary basalt artificially reduced in hydrogen gas the coupling is not found in spinel oxidation non stoichiometry these results imply that we are able to identify the presence of spinels that have equilibrated in the low oxygen fugacity range of the spinel stability field where cation excess is characteristic

a model for a seismic computerized alert network in large earthquakes damaging ground motions may occur at large epicentral distances because of the relatively slow speed of seismic waves it is possible to construct a system to provide short term warning as much as several tens of seconds of imminent strong ground motions from major earthquakes automated safety responses could be triggered by users after receiving estimates of the arrival time and strength of shaking expected at an individual site although warning times are likely to be short for areas greatly damaged by relatively numerous earthquakes of moderate size large areas that experience very strong shaking during great earthquakes would receive longer warning times

variations in lava composition during the march 1981 eruption of mount etna and the implications of a compositional comparison with earlier historic eruptions the march 1981 eruption of mount etna occurred on the northern slopes of the volcano in an area previously inactive for more than 400 a a radial fissure system extending 7 5 km and producing 20 2 106 m3 of basic hawaiite lava opened at 2600 m a s l on 17th march and migrated downslope to 1125 m a s l where activity ceased on 23rd march gravity evidence points to the draining of a radial storage dyke located between sea level and 1 km a s l whole rock chemistry and petrography suggests that the magma in the dyke was a hybrid supporting crystal and compositional gradients developed as a result of progressively greater mixing of residual 1979 basic hawaiite magma with fresh basic hawaiite magma during permissive filling of the dyke around september 1980 these mixing gradients caused the eruption to display a significant contrast in the concentrations of al2o3 sr cao mgo and fe2o3 total between early high altitude and later low altitude products the fresh magma which entered the high level system around september 1980 ascended rapidly from a deep storage region at 16 24 km depth

seismic velocity anisotropy of phyllosilicate rich rocks characteristics inferred from experimental and crack model studies of biotite rich schist summary seismic velocity anisotropy of biotite schist 30 per cent mode biotite was measured under confining pressures up to 150 mpa the rock shows weak orthotropy which was altered from transverse isotropy ti generated by biotite preferred orientation the orthotropy was caused by microfolding in the rock the velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes silicate sheet of the oriented biotite minerals the anisotropy of the rock is basically ti due to both the aligned biotite minerals and cracks which have a common symmetry axis we found that other sheet silicate rich rocks have a similar anisotropy with the biotite schist in which the ti type anisotropy is characterized by the slow p and s wave velocities along the symmetry axis this is caused by the preferred orientation of sheet silicate minerals and the extremely slow p and s wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet when rock contains a large percentage of highly oriented sheet silicates the fast and slow shear waves exchange their polarities at some off symmetry axis directions indicating that the qswave quasi s wave velocity exceeds the sh wave velocity the phase velocity distribution of qs wave shows an asymmetry with respect to the angle from the symmetry axis which is characterized by a bulge in this distribution located near the symmetric axis this is inherent to most sheet silicate minerals when crack density of aligned cracks increases the p wave velocity along the symmetry axis decreases considerably the qs wave phase velocity in the off axis directions also decreases in accordance with the decrease of the p velocity along the symmetry axis the asymmetry of the qs wave phase velocity distribution increases as the p wave velocity decreases along the symmetry axis this relationship can be well understood by means of berryman s extended thomsen approach

empirical green s function study of the january 17 1994 northridge california earthquake the january 17 1994 northridge main shock was analyzed using an empirical green s function approach to estimate the spatial and temporal distribution of fault slip far field source time functions obtained from seismograms recorded by the berkeley digital seismic network bdsn and terrascope stations reveal the distributed nature of the source and the presence of a second large subevent the location of the fault beneath the san fernando valley as well as the updip directivity of the rupture contributed to the locally heavy damage due to this earthquake

dehydration breakdown of antigorite and the formation of b type olivine cpo abstract peridotite formed by contact metamorphism and dehydration breakdown of an antigorite schist from the happo area central japan shows a strong olivine crystallographic preferred orientation ol cpo the lack of mesoscale deformation structures associated with the intrusion and the lack of microstructural evidence for plastic deformation of neoblastic grains suggest that olivine cpo in this area did not form as a result of solid state deformation instead the good correspondence between the original antigorite orientation and the orientation of the newly formed olivine implies the cpo formed by topotactic growth of the olivine after antigorite ol cpo is likely to develop by a similar process in subduction zone environments where foliated serpentinite is dragged down to depths where antigorite is no longer stable the happo ol cpo has a strong a axis concentration perpendicular to the lineation and within the foliation commonly referred to as b type ol cpo seismic fast directions parallel to the ocean trench are observed in many convergent margins and are consistent with the presence of b type ol cpo in the mantle wedge of these regions experimental work has shown that b type cpo can form by dislocation creep under hydrous conditions at relatively high stresses there are however several discrepancies between the characteristics of natural and laboratory samples with b type ol cpo 1 the formation conditions stress and temperature of some natural examples with b type cpo fall outside those predicted by experiments 2 in deformation experiments slip in the crystallographic c axis direction is important but has not been observed in natural examples of b type cpo 3 experimental work suggests the presence of h2o and either high shear stress or relatively low temperatures are essential for the formation of b type cpo these conditions are most likely to be achieved close to subduction boundaries but these regions are also associated with serpentinization which prevents strong olivine cpo patterns from forming we show b type ol cpo can form as a result of static topotactic growth of olivine after high temperature breakdown of foliated serpentinite these results resolve the discrepancies between experimental and natural examples of b type cpo and show the need to rethink the formation process of olivine cpo in convergent margins topotactic growth of olivine after antigorite can account for the inferred distribution of b type ol cpo in the mantle wedge more successfully than dislocation creep

antigorite crystallographic preferred orientations in serpentinites from japan abstract foliated antigorite serpentinites are contributing to seismic anisotropy in subduction zones however uncertainty remains regarding the development of antigorite crystal preferred orientations cpo this study analyzes the cpos of antigorite and olivine in variably serpentinized samples of antigorite serpentinite from three localities in southwest japan using u stage ebsd and synchrotron x rays in all samples 010 poles show a maximum parallel to the lineation and 001 poles concentrate normal to the foliation with a partial girdle about the lineation 100 poles are less distinct and scatter widely the three measurement methods give similar results though orientation distributions from x ray analysis which averages over larger sample volumes are more regular and weaker than u stage and ebsd which focuses on local well crystallized grains in olivine bearing serpentinite the olivine cpo does not appear to control the antigorite cpo though there are some topotactic relationships the antigorite cpo formed contemporaneously with serpentinization and shear deformation based on our analyses in a subduction zone mantle wedge the 010 pole of antigorite is parallel to the direction of the subduction and 001 lattice planes are parallel to the interface of the subducting oceanic plate by averaging single crystal elastic properties over orientation distributions wave velocities have been calculated fast p velocities are parallel to the subduction direction and slow velocities are perpendicular to the subducting plate with an anisotropy of 10 15

seismic amplitude ratio analysis of the 2014 2015 bar arbunga holuhraun dike propagation and eruption magma is transported in brittle rock through dikes and sills this movement may be accompanied by the release of seismic energy that can be tracked from the earth s surface locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions the seismic amplitude ratio analysis sara method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases this study validates this methodology by comparing sara locations filtered between 2 and 16hz with the earthquake locations same frequency band recorded during the 2014 2015 bar arbunga holuhraun dike intrusion and eruption in iceland integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption during the intrusion sara locations correspond remarkably well to the locations of earthquakes several exceptions are however observed 1 a low frequency signal was possibly associated with a subglacial eruption on 23 august 2 a systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source this behavior may be controlled by the dike s shape and or by dike inflation 3 during the eruption sara locations consistently focused at the eruptive site 4 tremor rich signal close to ice cauldrons occurred on 3 september this study demonstrates the power of the sara methodology provided robust site amplification quality factors and seismic velocities are available plain language summary locating earthquakes usually implies picking phase arrivals p and s waves another technique called seismic amplitude ratio analysis sara was recently introduced to locate them only by using the amplitude recorded at different pairs of seismic stations however this technique was never proven to be true this study shows that the earthquake locations derived by sara compares remarkably well with the locations of 30 000 seismic events triggered when magma migrated in the icelandic crust prior to the 2014 2015 holuhraun eruption but the results also provide new insight into the magma dynamics that led to the largest eruption of the last two centuries in europe we show that ground vibration was continuously triggered during the 2week period preceding the eruption when magma forced its way toward the eruption site but also during the eruption itself several intriguing features were observed including low frequency vibrations possibly associated with eruption below the ice or large patches of seismic activity when the magma stopped propagating toward the eruption site this methodology performs very well provided some parameters are available and allows to gain insights into the complex dynamics associated with magma movements

serpentine in active subduction zones abstract serpentinization is a key phenomenon for understanding the geodynamics of subduction zones in the 10 200 km depth range serpentines are a major water carrier and their rheological properties have a strong influence on deformation partitioning and seismicity at depths i review experimental investigations that have been conducted on serpentines with emphasis on the large body of data acquired over the past decade determinations of physical properties at the pressure and temperature conditions of subductions allow interpreting geophysical data in active subduction in terms of mineralogy and petrology and to link the presence of serpentinites with deformation and fluid circulation the fluid budget can be partially constrained from geophysical data elasticity data provide a quantitative basis for mapping serpentinization in the mantle wedge and slab from seismic tomography anisotropy suggests the existence of thin serpentinite channels above the plate interface that account for mechanical decoupling inferred from down dip limit of the seismogenic zone and heat flow strain rate dependent rheology of antigorite serpentine is consistent with stable deformation of this thin layer or channel over timescales ranging from those of the seismic cycle to those of thermal equilibration and exhumation of high pressure rocks and with the geological record of subduction related deformation circulation of serpentinizing fluids depends on the permeability structure and is imaged by electrical conductivity tomography it could be controlled by fracturing in the undeformed cold nose of the mantle wedge and by plastic deformation along the plate interface fluid migration mechanisms are similar to those inferred from petrological and geochemical data on exhumed serpentinites estimation of the fluid budget associated with serpentine formation will rely on numerical simulations for which coupling of kinetics of hydration and dehydration at scales ranging from grain size up to faulting pattern needs to be established especially for water cycling to the transition zone in the core of the slab

rapid source mechanism determination of large mw 5 earthquakes in the western united states inversion of complete long period ground motions is used for rapid determination of source mechanisms of mw 5 earthquakes in the western united states the first few minutes of ground motions on local and regional distance waveforms are inverted for point source centroid moment tensors waveforms recorded at regional distances 300 1500 km can be adequately modeled at periods longer than 50 s using the laterally homogeneous prem model dziewonski and anderson 1981 at closer distances 300 km waves with periods as short as 35 s can be analyzed using prem best double couple focal mechanisms for 18 recent large western u s earthquakes compare very well with those obtained by other methods our procedure interfaced with automated data retrieval and source location methods is a viable tool for reliable determination of seismic moment and fault mechanism within 30 minutes after an earthquake

tomographic evidence for hydrated oceanic crust of the pacific slab beneath northeastern japan implications for water transportation in subduction zones 1 we estimate detailed seismic velocity structure around the pacific slab beneath northeastern japan by double difference tomography a remarkable low velocity zone with a thickness of 10 km which corresponds to much hydrated oceanic crust is imaged coherently along the arc at the uppermost part of the slab the zone gradually disappears at depths of 70 90 km suggesting the occurrence of intensive dehydration reactions there the concentration of intraslab earthquakes at these depths supports dehydration embrittlement hypothesis as a mechanism for generating intraslab earthquakes a low velocity zone imaged immediately above the slab at depths 70 km probably reflects a hydrous layer that absorbs water expelled from the slab and carries it to deeper depths along the slab our observations suggest that an along arc variation in arc volcanism might be related to that in the development of the hydrous layer above the slab

an automatic processing system for broadcasting earthquake alarms in japan most of the damage caused by large earthquakes is concentrated within areas less than about 100 km from the focal regions we have developed an earthquake alarm system that determines earthquake parameters within a few seconds of the p wave s arrival at the closest station and then transmits the earthquake information before the s wave arrival in areas of possible serious earthquake damage since an earthquake alarm system requires the determination of reliable earthquake parameters as quickly as possible it is unreasonable to wait until waveform data from numerous stations have been collected for analysis for this reason we have developed a novel method of determining the hypocentral location by using the arrival times for only a few stations as well as the lack of p wave arrivals at other stations at a given time the use of not yet arrived data makes it possible not only to determine reliable hypocenter parameters within a few seconds but also to detect erroneous arrival time readings and remove them automatically since the available waveform data increases with time the system was designed to redetermine earthquake parameters every second our method was deployed in a real time system starting in july 2002 the real time system locates 10 20 events per day which includes a few felt earthquakes occurring in and around japan it was shown from the waveform data for about 100 felt earthquakes that almost all the events except those far from the network could be located within a few seconds when most of seismic energy has not even arrived at some stations close by we recently started widespread broadcasting of earthquake information in real time by using a satellite transmission system

routine estimation of earthquake source complexity the 18 october 1992 colombian earthquake we describe two methods suitable for routine application to tele seismic recordings that characterize the time history of seismic events stacking short period signals from large regional arrays provides stable estimates of high frequency radiation from the source and an empirical green s function decon volution procedure extracts reliable broadband time functions suitable for anal ysis of faulting complexity and the spatio temporal extent of rupture combined these procedures characterize the source radiation of large events ms 7 be tween 200 and 0 5 sec periods

shifting styles of basaltic explosive activity during the 2002 03 eruption of mt etna italy abstract the 2002 03 flank eruption of etna was characterized by two months of explosive activity that produced copious ash fallout constituting a major source of hazard and damage over all eastern sicily most of the tephra were erupted from vents at 2750 and 2800 m elevation on the s flank of the volcano where different eruptive styles alternated the dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes which we refer to as ash rich jets and plumes similarly ash rich explosive activity was also briefly observed during the 2001 flank eruption of etna but is otherwise fairly uncommon in the recent history of etna here we describe the features of the 2002 03 explosive activity and compare it with the 2001 eruption in order to characterize ash rich jets and plumes and their transition with other eruptive styles including strombolian and ash explosions mainly through chemical componentry and morphology investigations of erupted ash past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid our findings suggest that the abundant presence of a solid phase microlites may also control vent degassing and consequent magma fragmentation and eruptive style in fact in contrast with the strombolian or hawaiian microlite poor fluidal sideromelane clasts ash rich jets and plumes produce crystal rich tachylite clasts with evidence of brittle fragmentation suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency

empirical green s function analysis of loma prieta aftershocks abstract following the 18 october 1989 loma prieta earthquake an array of 22 three component iris passcal instruments was deployed in the santa cruz mountains we use an empirical green9s function method to study source properties of aftershocks as well as attenuation in the epicentral area using pairs of closely spaced events we show that the largest aftershocks are well modelled by an 2 source spectrum and we obtain estimates of the p wave corner frequency for a total of 15 events brune stress drops are observed to have no systematic variation over the range of moments spanned by the data set down to 10 19 dyne cm there is a suggestion that aftershocks that occurred outside the mainshock rupture have higher stress drops than those that occurred within the mainshock rupture a m l 3 4 foreshock in the subsequence associated with the 18 april 1990 m l 5 4 watsonville earthquake yields a stress drop estimate of 820 bars this value is well outside the stress drops obtained for all other events 6 to 266 bars site specific attenuation parameters suggest large lateral and vertical heterogeneity in p wave q structure station holy in a valley near the surface trace of the san andreas fault is characterized by low q values while stations to the north of the aftershock zone are characterized by the highest q values

rapid estimation of rupture directivity application to the 1992 landers ms 7 4 and cape mendocino ms 7 2 california earthquakes using empirical green functions with regional and teleseismic surface waves it is possible to resolve fault finiteness effects in many cases uniquely defining the fault plane for relatively large earthquakes the technique requires very little data processing and can be applied in near real time with the current distribution of seismic stations the landers strike slip earthquake was dominated by two sub events with predominantly north northwestward rupture the second sub event was 1 5 times larger and rotated in strike by 12 counterclockwise relative to the first the cape mendocino thrust event had a relatively smooth rupture that propagated to the southwest on a shallow dipping fault

fault plane solutions of microearthquakes and small events in the hellenic arc abstract the hellenic arc is the most active seismic region of the transition zone between the african and eurasian plates in this rapidly deforming region the physical state of the crust and upper mantle may vary laterally and vertically however a detailed 3d model of the region is lacking the reliable determination of fault plane solutions is crucial if such a model is to be produced on this basis fault plane solutions have been determined from recent microearthquakes and small events to assess their reliability for use in tectonic interpretation a search algorithm on first motion data and amplitude ratios and also a waveform matching scheme were employed on data from our temporal network operated on the western part of the island of crete there a network of 47 three component digital stations with an aperture of 60 km and an average station spacing of 5 km was operated in 1997 the majority of the shallow microearthquakes under crete for which fault plane solutions were determined have a near horizontal t axis oriented essentially e w differences between well determined fault plane solutions from the search algorithm and the waveform matching technique were significant strike up to 45 dip up to 10 and slip up to 50 second data of small events within the hellenic subduction zone were obtained from recently installed broadband stations at local and regional distances and inverted for a deviatoric seismic moment tensor available solutions from other sources such as the harvard group emsc or sed show drastic differences in part owing to still limited azimuthal station coverage the resulting fault plane solutions of small events have generally not been well constrained the observed large variation of fault plane solutions for micoearthquakes and small events poses a caveat to tectonic interpretation in case of using data from a few stations only

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

calibration of the regional crustal waveguide and the retrieval of source parameters using waveform modeling regional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller m 4 8 seismic events this path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration or master events this information can be difficult to obtain especially for smaller events generally explosion or quarry blast generated travel time data with known locations and origin times are useful for developing the path calibration parameters but in many regions such data sets are scanty or do not exist we present a method which is useful for regional path calibration independent of such data i e with earthquakes which is applicable for events down to m w 4 and which has successfully been applied in india central asia western mediterranean north africa tibet and the former soviet union these studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events we find that the error in source depth does not necessarily trade off only with the origin time for events with poor azimuthal coverage but with the horizontal location as well thus resulting in poor epicentral locations for example hypocenters for some events in central asia were found to move from their fixed depth locations by about 20 km such errors in location and depth will propagate into path calibration parameters particularly with respect to travel times the modeling of teleseismic depth phases pp sp yields accurate depths for earthquakes down to magnitude m w 4 7 this m w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth with the relative amplitude of the p nl waves to the surface waves and the interaction of regional spmp and ppmp phases being good indicators of event depths we also found that for deep events a seismic phase which follows an s wave path to the surface and becomes critical developing a head wave by s to p conversion is also indicative of depth the detailed characteristic of this phase is controlled by the crustal waveguide the key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms the regionalization scheme can also incorporate mixed path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures we also demonstrate that once depths are established we need only two stations travel time data to obtain reliable epicentral locations using a new adaptive grid search technique which yields locations similar to those determined using travel time data from local seismic networks with better azimuthal coverage

the 1992 cape mendocino earthquake broadband determination of source parameters the april 25 1992 cape mendocino earthquake ms 7 1 has renewed speculation about the nature of subduction along the cascadia subduction zone and the associated seismic hazard this event may represent the first large m 6 thrust event along the entire cascadia subduction zone in historic times last 200 years we analyze long period surface waves and broadband body waves in order to estimate the mainshock source parameters we also examine broadband body waves from the nearby 1991 honeydew earthquake m 6 in order to assess the contributions of both rupture complexity and unmodeled source and receiver structure in the cape mendocino waveforms from both body and surface wave inversions as well as forward modeling of body waves we estimate a best double couple mechanism for the cape mendocino earthquake strike 330 10 dip 12 2 rake 75 15 seismic moment 1 93 1019 n m and mw 6 8 this mechanism contains a significant component of slip in the estimated direction of gorda north america plate convergence although this earthquake had suitable geometry for relieving strain accumulated by gorda north america plate convergence we cannot resolve whether it occurred on the interplate megathrust or on a fault within the overriding accretionary prism we find evidence for southwest offshore rupture toward an azimuth of 240 in addition we find evidence for early aftershocks in both the teleseismically recorded body waves and in locally recorded strong motions we model one aftershock delayed 13 s from the mainshock with a mechanism that is different from the mainshock mechanism but is consistent with the north south trending horizontal compression found offshore within the gorda plate we postulate that this aftershock and two additional large strike slip aftershocks that ruptured the gorda plate within 24 hours of the mainshock were caused by the transfer of stress accumulated across the cascadia subduction zone and accretionary prism far offshore to the gorda plate where it reduced the normal stress across nw se oriented faults triggering failure the complexity of fault interactions near the mendocino triple junction needs to be understood before potential seismic hazards of the southern cascadia subduction zone can be quantified

elasticity of antigorite seismic detection of serpentinites and anisotropy in subduction zones abstract serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites which thus far has not been possible in the absence of single crystal elastic properties of antigorite the elastic constants of antigorite the dominant serpentine at high pressure in subduction zones were measured using brillouin spectroscopy under ambient conditions in addition antigorite lattice preferred orientations lpo were determined using an electron back scattering diffraction ebsd technique isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography the isotropic v p v s ratio is 1 76 in the voigt reuss hill average not very different from that of 1 73 in peridotite but may vary between 1 70 and 1 86 between the voigt and reuss bonds antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions v p varies between 8 9 km s 1 and 5 6 km s 1 46 anisotropy and 8 3 km s 1 and 5 8 km s 1 37 and v s between 5 1 km s 1 and 2 5 km s 1 66 and 4 7 km s 1 and 2 9 km s 1 50 for the single crystal and aggregate respectively the v p v s ratio and shear wave splitting also vary with orientation between 1 2 and 3 4 and 1 3 and 2 8 for the single crystal and aggregate respectively thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation these properties can be used to detect serpentinite quantify the amount of serpentinization and to discuss relationships between seismic anisotropy and deformation in the mantle wedge regions of high v p v s ratios and extremely low velocities in the mantle wedge of subduction zones down to about 6 and 3 km s 1 for v p and v s respectively are difficult to explain without strong preferred orientation of serpentine local variations of anisotropy may result from kilometer scale folding of serpentinites shear wave splittings up to 1 1 5 s can be explained with moderately thick 10 20 km serpentinite bodies

source parameters and rupture velocity of small m 2 1 reservoir induced earthquakes summary we calculate stress drop and rupture speed for ml 2 1 shallow reservoir induced earthquakes and find them to be similar to those of large natural earthquakes previous studies have suggested that hydrofractures mining and reservoir induced earthquakes have lower average stress drop than natural tectonic earthquakes this difference might result from the different tectonic setting or the shallower hypocentral depths of induced earthquakes alternatively difficulties in correcting for attenuation and site effects in earlier studies may lead to underestimation of stress drop in addition most studies assume the rupture velocity of small reservoir induced earthquakes to be the same as for the large earthquakes we analyse a set of 101 ml 2 1 earthquakes induced by changing water level in the acu reservoir ne brazil the earthquakes are shallow depth 5 km and the region has negligible natural seismicity we use three different approaches to calculate the source parameters of the six largest 1 9 ml 2 1 earthquakes we model the individual spectra to find corner frequency frequency independent q and long period amplitude we use collocated small earthquakes as empirical green s functions to calculate the spectral ratios and determine the relative source time functions estimates of the source duration and corner frequency imply stress drops in the range of 26 179 mpa these are similar to or higher than tectonic earthquakes suggesting that the shallow hypocentral depth and the presence of water do not affect stress drop we observe clear directivity for one of the earthquakes and use the azimuthal variation in pulse width to estimate a rupture velocity of 0 6

sequential deformation from serpentinite mylonite to metasomatic rocks along the sashu fault sw japan the deformation of serpentinites along the sashu fault saganoseki peninsula sw japan involved both mylonitization and brecciation the brecciation was accompanied by metasomatism and the metasomatized rocks record additional ductile deformation serpentinite mylonite is composed mainly of antigorite with minor magnetite and cr spinel foliation and lineation in this rock type are defined by the shape preferred orientation of antigorite and the alignment of fine grained magnetite and carbonate minerals the antigorite also shows a lattice preferred orientation lpo as measured with a universal stage with c axes oriented near perpendicular to the foliation and b axes oriented parallel to the lineation brecciation is concentrated in the reaction zone along the boundary between serpentinites and surrounding country rocks talc and chlorite schists developed in this zone as a result of associated metasomatism and deformation consequently they contain composite planar fabrics and drag folds the breccias themselves are composed of serpentinite fragments cut by veins of calcite and talc analyses of fluid inclusions in calcite from the breccia indicate that brecciation occurred at 200 300 c at depths of 3 8 11 8 km metasomatic reactions particularly the formation of talc contributed to weakening of this serpentinite bearing fault zone

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

the importance of serpentinite mylonites for subduction and exhumation of oceanic crust abstract in the ultramafic erro tobbio unit voltri massif western alps a set of overprinting structures in serpentinite mylonites is related to alpine subduction to about 80 km depth and to subsequent exhumation antigorite mylonites are cut by en echelon olivine veins which in turn are dissected by multiple sets of shear bands containing olivine and titanian clinohumite the transition from olivine free to olivine bearing structures indicates recrystallization during prograde metamorphism all structures display the same top to the nw kinematics providing evidence for a continuous non coaxial deformation the serpentinite mylonites surround km scale bodies of pre alpine peridotite which show only minor alpine overprint this indicates that during subduction related deformation recrystallization and fluid flow were strongly localized within serpentinite mylonites olivine bearing discontinuous shear planes with top to the se sense of movement crosscut the prograde structures the inversion of shear sense suggests a change in position of the serpentinites relative to the downgoing slab i e from the subducted slab to the upper plate during accretion thus the shear sense inversion marks the change from burial to exhumation of the serpentinites the low density of antigorite serpentinites 2 75 g cm3 causes strong buoyancy thus providing a mechanism for the exhumation of deeply subducted rocks it is suggested that serpentinites may act as carriers for the uprise of eclogite bodies which have higher densities than the peridotitic upper mantle

the march 9 1994 m w 7 6 deep tonga earthquake rupture outside the seismically active slab we investigate the rupture process of the march 9 1994 m w 7 6 deep tonga earthquake and its relationship to the background seismicity of the subducted tonga slab variations in observed p and s wave pulse duration indicate that the rupture propagated to the nne and extended well beyond the background seismicity we inverted 47 p and sh waveforms including regional broadband waveforms from the southwest pacific seismic experiment using a method that solves for the focal mechanism change during the rupture and the distribution of moment release along the fault plane the results indicate that significant moment release occurred in previously aseismic regions outside the active seismic zone and that the rupture terminated 10 20 km beyond the bounds of the previous seismic activity a significant change in focal mechanism occurred when the rupture propagated into the previously aseismic region rupture along the near vertical nne striking nodal plane provides a somewhat better fit to the body waveforms than rupture along the near horizontal nodal plane this result combined with the planar alignment of aftershocks and the general nne directivity of the waveforms provides strong evidence that the rupture occurred on the near vertical plane thermal modeling of the tonga slab indicates that the rupture terminated in material about 200 c warmer than the temperature that normally limits the occurrence of smaller earthquakes additionally aftershocks seem to be suppressed in the outer regions of the rupture which contain about half of the moment release but only 1 of the 15 well located aftershocks we suggest that slabs may be composed of an inner cold core where seismic rupture initiates and small earthquakes occur and a thermal halo of warmer material which can sustain rupture and only a few aftershocks the mechanism by which rupture propagates through the warmer material need not be similar to the process governing rupture nucleation in the cold slab core nucleation may occur through a process limited to the cold core such as transformational faulting and propagation through the warmer material may occur through ductile faulting or plastic instabilities isolated deep earthquakes in other subduction zones such as the 1994 bolivia event may occur almost completely within the warmer zone accounting for the lack of background seismicity and the dearth of aftershocks

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

determination of local magnitude using bdsn broadband records the berkeley seismographic station operated standard wood anderson torsion seismographs from 8 april 1928 through 16 january 1994 these seismographs are historically significant in that their seismograms have been used to determine local richter magnitude of earthquakes that occurred in northern and central california and adjacent regions routinely since 1948 and ad hoc back to 1928 broadband digitally recording seismographs were co sited at four stations with wood anderson instruments to compare the records the wood anderson seismographs became redundant for the purpose of determining the maximum horizontal trace amplitudes once procedures were developed to synthesize their seismograms accurately from the broadband digital recordings operation of the wood anderson seismographs was subsequently discontinued this article demonstrates the ability to determine an unbiased measure of local magnitude from synthesized wood anderson seismograms thereby maintaining a seamless catalog of local magnitude at berkeley

single station location of seismic events a review and a plea for more research abstract traveltime based location methods are ineffective for locating regional seismic events which are recorded by few stations however the comprehensive test ban treaty ctbt makes it imperative that we monitor sparsely observed events this paper reviews the current status of single station location ssl methods the location of seismic events using records from one three component broadband digital station we argue here that ssl methods may ultimately provide the most effective and economical means for monitoring small magnitude m 3 seismic events over most of the earth potentially station event distance and focal depth may be determined accurately by utilizing broadband three component data and matching observed and synthetic waveforms station event azimuth is determinable from the polarization of the p wave arrival and p coda however more research is required before ssl methods become a practical alternative to traveltime based methods currently the most significant problem is that regional seismograms are strongly dependent on regional crustal structure thus future research efforts should focus both on determining appropriate crustal models in specific regions and also on improved methods for dealing with regional variations in crustal structure a second important problem concerns location errors with ssl they may involve 180 errors in station event azimuth or other highly non gaussian blunders

seismic velocity anisotropy in mica rich rocks an inclusion model summary we calculated seismic wave velocity anisotropy caused by the preferred orientation of mica minerals by using the differential effective medium method dem spheroidal biotite crystals with their c axes coinciding with the symmetry axis of the spheroid are embedded in an isotropic matrix up to a volume ratio of 30 per cent all crystals are aligned with their c axes parallel to the symmetry axis of the effective homogeneous medium which shows transverse isotropy the effect of crystal shape on anisotropy was studied by changing the aspect ratio the ratio between the minor axis and the major axis of the spheroid from 0 01 flat spheroid to 1 sphere the s velocity anisotropy becomes large as the crystal shape becomes flat whereas the p velocity anisotropy shows only small changes with changes of the crystal shape in particular biotite generates large s wave anisotropy and the anisotropy becomes stronger as the aspect ratio of the biotite crystal becomes smaller when the volume ratio of the mica mineral is large the p wave phase velocity surface shows considerable deviation from the ellipse and the sv wave phase velocity surface forms a large bulge and crosses the sh wave phase velocity surface singularity in the plane including the symmetry axis these results show an interesting contrast when compared with the effect of crack or pore shape on seismic velocity anisotropy crack or pore shape affects the p velocity more than the s velocity we also calculated thomsen s anisotropic parameters e and as functions of the crystal aspect ratio and the mica volume ratio

plastic deformation and development of antigorite crystal preferred orientation in high pressure serpentinites we have inferred the deformation mechanisms of antigorite by high resolution ebsd mapping of samples from cerro del almirez ultramafic massif betic cordillera se spain textural relations and phase diagram calculations constrain the foliation development conditions to the subduction prograde path at up to 600 630 c and 1 6 1 9 gpa deformation was followed by static annealing of antigorite at ca 680 c the crystal preferred orientation cpo of antigorite is characterised by a strong alignment of 001 poles normal to the foliation plane and a weaker but clear parallelism between 100 axes and the macroscopic lineation defined by the elongation of magnetite aggregates analysis of misorientations across subgrains shows predominance of 010 rotation axis consistent with activation of the 100 001 slip system however tilt subgrain boundaries subparallel to 100 probably formed by edge dislocations of this system are subsidiary most subgrain boundaries are subparallel to 001 planes they are interpreted as 001 twins wherein continuing viscoplastic deformation resulted in a slight increase of the misorientation between the twins modelling of the evolution of the antigorite cpo using a lower bound approach and considering different deformation regimes and sets of basal and non basal slip systems has shown that intensities of 100 and 010 maxima reflect the relative strength of the antigorite 100 001 and 010 001 systems activation of other basal or non basal slip systems does not change significantly the cpo patterns but results in less concentrated cpo 3d transpression models better reproduce the cpo of natural antigorite serpentinites we propose that the widespread occurrence of strong cpo in high pressure antigorite serpentinite is consistent with deformation by dislocation creep with dominant glide on hk0 001 together with the activation of twinning implying that a power law rheology would better account for the mechanical behaviour of antigorite serpentinite deep in the subduction channel and mantle wedge

real time seismology at uc berkeley the rapid earthquake data integration project the rapid earthquake data integration project is a system for the fast determination of earthquake parameters in northern and central california based on data from the berkeley digital seismic network and the usgs northern california seismic network program development started in 1993 and a prototype system began providing automatic information on earthquake location and magnitude in november of 1993 via commercial pagers and the internet recent enhancements include the exchange of phase data with neighboring networks and the inauguration of processing for the determination of strong motion parameters and seismic moment tensors

frictional sliding in serpentine at very high pressure abstract using a new four channel system for detecting acoustic emissions in a multianvil apparatus we have assessed the pressure temperature range for such emissions as well as the role of dehydration by deforming samples of extensively serpentinized peridotite we show that in the absence of dehydration and for samples initially faulted at low pressure acoustic emissions occurred well outside the expected pressure temperature field of unassisted brittle failure emissions were also detected during and after dehydration of serpentine microstructures of post run specimens revealed fault slip with offsets up to 500 m regardless of whether or not dehydration took place dehydration appears to effectively stop slip on pre existing faults and create new ones analysis of p wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip these observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration

rupture process of the 1995 antofagasta subduction earthquake mw 8 1 a finite source rupture model of the july 30 1995 m w 8 1 antofagasta northern chile subduction earthquake is developed using body and surface waves that span periods from 20 to 290 s a long period 150 290 s surface wave spectral inversion technique is applied to estimate the average finite fault source properties deconvolutions of broadband body waves using theoretical green s functions and deconvolutions of broadband fundamental mode surface waves using empirical green s functions provided by a large aftershock yield effective source time functions containing periods from 20 to 200 s for many directivity parameters the source time functions are used in an inverse radon transform to image a one dimensional spatial model of the moment rate history the event produced a predominantly unilateral southward rupture yielding strong directivity effects on all seismic waves with periods less than a few hundred seconds the aftershock information spectral analysis and moment rate distribution indicate a rupture length of 180 200 km with the largest slip concentrated in the first 120 km a rupture azimuth of 205 10 along the chilean coastline and a rupture duration of 60 68 s with a corresponding average rupture velocity of 3 0 3 2 km s the overall rupture character is quite smooth accentuating the directivity effects and reducing the shaking intensity however there are three regions with enhanced moment rate distributed along the rupture zone near the epicenter 50 to 80 km south of the epicenter and 110 to 140 km south of the epicenter

the exceptional activity and growth of the southeast crater mount etna italy between 1996 and 2001 between 1971 and 2001 the southeast crater was the most productive of the four summit craters of mount etna with activity that can be compared on a global scale to the opening phases of the pu u k paianaha eruption of k lauea volcano hawai i the period of highest eruptive rate was between 1996 and 2001 when near continuous activity occurred in five phases these were characterized by a wide range of eruptive styles and intensities from quiet non explosive lava emission to brief violent lava fountaining episodes much of the cone growth occurred during these fountaining episodes totaling 105 events many showed complex dynamics such as different eruptive styles at multiple vents and resulted in the growth of minor edifices on the flanks of the southeast crater cone small pyroclastic flows were produced during some of the eruptive episodes when oblique tephra jets showered the steep flanks of the cone with hot bombs and scoriae fluctuations in the eruptive style and eruption rates were controlled by a complex interplay between changes in the conduit geometry including the growth of a shallow magma reservoir under the southeast crater magma supply rates and flank instability during this period volume calculations were made with the aid of gis and image analysis of video footage obtained by a monitoring telecamera between 1996 and 2001 the bulk volume of the cone increased by 36 106 m3 giving a total 1971 2001 volume of 72 106 m3 at the same time the cone gained 105 m in height reaching an elevation of about 3 300 m the total dre volume of the 1996 2001 products was 90 106m3 this mostly comprised lava flows 72 106 m3 erupted at the summit and onto the flanks of the cone these values indicate that the productivity of the southeast crater increased fourfold during 1996 2001 with respect to the previous 25 years coinciding with a general increase in the eruptive output rates and eruption intensity at etna this phase of intense summit activity has been followed since the summer of 2001 by a period of increased structural instability of the volcano marked by a series of important flank eruptions

high pressure creep of serpentine interseismic deformation and initiation of subduction the supposed low viscosity of serpentine may strongly influence subduction zone dynamics at all time scales but until now its role could not be quantified because measurements relevant to intermediate depth settings were lacking deformation experiments on the serpentine antigorite at high pressures and temperatures 1 to 4 gigapascals 200 to 500 c showed that the viscosity of serpentine is much lower than that of the major mantle forming minerals regardless of the temperature low viscosity serpentinized mantle at the slab surface can localize deformation impede stress buildup and limit the downdip propagation of large earthquakes at subduction zones antigorite enables viscous relaxation with characteristic times comparable to those of long term postseismic deformations after large earthquakes and slow earthquakes antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation

deformation of antigorite serpentinite at high temperature and pressure abstract deformation experiments were conducted in a griggs type apparatus to constrain the rheology of antigorite serpentinite at high temperatures and pressures samples deformed at temperatures of 400 625 c and pressures of 0 85 1 5 gpa experienced semi brittle deformation resulting in localization on faults at 5 to 25 strain samples deformed at 300 c exhibited transitional behavior the stresses measured for our samples are in good agreement with recent experiments conducted in the deformation dia apparatus however our results indicate that steady state ductile flow is not achieved in contrast with interpretations based on the deformation dia experiments extrapolation of our data to geologic conditions suggests that serpentinites may be weak enough during localized frictional sliding to account for slab wedge decoupling inferred from geologic observations experiments conducted above the thermal stability of antigorite at 700 c and 1 5 gpa show evidence for distributed deformation this observation does not support the hypothesis that intermediate depth earthquakes result directly from dehydration embrittlement in addition samples exhibit velocity strengthening from 300 to 700 c a frictional behavior that inhibits earthquake nucleation

a new method for calculating seismic velocities in rocks containing strongly dimensionally anisotropic mineral grains and its application to antigorite bearing serpentinite mylonites abstract seismic velocity is one of the most important sources of information about the earth s interior for its proper interpretation we must have a thorough understanding of the dependence of seismic velocity on microstructural elements including the modal composition the crystal preferred orientation cpo the grain shape the spatial distribution of mineral phases etc the conventional voigt reuss and hill averaging schemes take into account only the modal composition and the cpo the information about the earth s interior is thus poorly constrained for a better interpretation it is critical to have a calculation method which accounts for the grain shape and the spatial distribution of mineral phases etc we propose a calculation method which accounts for the grain shape of strongly dimensionally anisotropic minerals like micas and serpentines our method can be applied to a distributed geometrical orientation of mineral grains comparison was made between calculated and measured velocities in three antigorite serpentinite mylonites judging from the root mean square relative error our method provides velocities closer to measured values than the voigt reuss and hill averaging schemes the input of the grain shape considerably improves the prediction of seismic properties however large discrepancies 0 1 km s between measured and calculated velocities can be seen in some directions the discrepancies might come from microstructural elements which were not considered in the calculation layer structures and cracks

metamorphic history of serpentinite mylonites from the happo ultramafic complex central japan serpentinite mylonites from the happo ultramafic complex show evidence of two stages of mylonitization at different temperature conditions peridotite mylonites exhibit two types of olivine porphyroclasts and neoblasts produced at the earlier stage the olivine neoblasts have a stretching lineation with a fabric suggesting plastic deformation along 0 1 0 0 0 1 in addition to the olivine fabric the stable association of olivine orthopyroxene and tremolite in the peridotites that survived later serpentinization and the si and na contents of tremolite suggest that the earlier mylonitization took place at temperatures between 700 and 800 c later mylonitization was associated with high temperature serpentinization to form serpentinite mylonites in contrast to a common type of serpentinite in orogenic belts the serpentinite mylonites are cohesively foliated rich in olivine and diopside and poor in antigorite the diopside has low al cr and na contents typical of a retrograde origin and the olivine has a homogeneous composition except in areas subjected to contact metamorphism at a later stage modal composition and mineral chemistry suggest that the serpentinite mylonites were formed by a hydration reaction of tremolite and olivine to produce diopside and antigorite under stable conditions of olivine at temperatures between 400 and 600 c later stage mylonitization has preferentially been superimposed on the earlier stage mylonite zone with a common direction of foliation the difference in temperature between the two mylonitization stages suggests that the shear zone was episodically active during the emplacement of the happo complex conditions of relatively high temperature for serpentinization at a convergent plate boundary and high permeability caused by the early mylonitization favoured the formation of the serpentinite mylonites

calibrating the amplitude source location asl method by using active seismic sources an example from te maari volcano tongariro national park new zealand a frequently applied amplitude source location asl method is here calibrated and optimized by using active seismic sources located at the surface of a dry stream channel the asl produced location discrepancies larger than 1 0 km laterally and 500 m in depth by using independently determined velocity model attenuation and site amplification factors afs sensitivity tests for asl input parameters show that attenuation and velocity have moderate influence on the location but are easy to independently constrain afs are shown to strongly influence the location and their application may introduce substantial location uncertainties model uncertainties are accommodated with either lateral or depth changes depending on the input parameters station corrections and the source station geometry

locating earthquakes with surface waves and centroid moment tensor estimation traditionally p wave arrival times have been used to locate regional earthquakes in contrast the travel times of surface waves dependent on source excitation and the source parameters and depth must be determined independently thus surface wave path delays need to be known before such data can be used for location these delays can be estimated from previous earthquakes using the cut and paste technique ambient seismic noise tomography and from 3d models taking the chino hills event as an example we show consistency of path corrections for 10 s love and rayleigh waves to within about 1 s obtained from these methods we then use these empirically derived delay maps to determine centroid locations of 138 southern california moderate sized 3 5 m w 5 7 earthquakes using surface waves alone it appears that these methods are capable of locating the main zone of rupture within a few 3 km accuracy relative to southern california seismic network locations with 5 stations that are well distributed in azimuth we also address the timing accuracy required to resolve non double couple source parameters which trades off with location with less than a km error required for a 10 compensated linear vector dipole resolution

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

moment magnitude determination for local and regional earthquakes based on source spectra we investigated the use of an automated routine to determine moment magnitudes from the displacement spectra of local and regional earthquakes two algorithms a genetic algorithm and a converging grid search were developed and tested with earthquake data from mexico norway and deception island antarctica it was found that compared with manual analysis the algorithms give reliable automatic moment magnitude m w estimates in the range 1 m 8 the converging grid search appeared to be more cost effective than the genetic algorithm m w at local and regional distances seems superior to amplitude based magnitudes that saturate for large earthquakes the application of the automated algorithm in near real time may help to obtain a nonsaturated magnitude estimate in the case of a large earthquake immediately after the earthquake has occurred also the method can be useful for processing large amounts of data manuscript received 27 july 2001

real time determination of seismic moment tensor for the italian region this work has been funded by the 2005 2007 dpc s4 and 2008 2010 dpc s3 italian civil protection contracts

high pressure elasticity of serpentine and seismic properties of the hydrated mantle wedge 1 a subset of the single crystal elastic moduli of natural antigorite has been measured using brillouin scattering at high pressure up to 9 gpa aggregate properties and axial compressibilities are in good agreement with equation of state results from x ray diffraction stiffness along the c axis increases becoming close to those within the silicate layer near 7 gpa a slight discontinuity in the evolution of the elastic moduli near 7 gpa is associated with a phase transition raman spectroscopy shows that the transition does not occur in subducting slabs except in the core of the coldest slabs where serpentine may be subducted to depths of about 200 km varying temperature and pressure has limited effects on the interpretation of seismic velocities principally because of the limited depth range of serpentine stability mostly above 100 km depth and also due to the compensating effects of pressure and temperature that maintain velocity variations well within the uncertainties and statistical variability of seismological studies serpentinites are excellent candidates for explaining low velocities in the hydrated mantle wedge inversion of the moho and thin anisotropic low velocity layers at the plate interface serpentinite layers provide an alternative explanation to fluid saturated oceanic crust for explaining these phenomena and account for a transition to an aseismic decoupled plate interface

variation of downdip limit of the seismogenic zone near the japanese islands implications for the serpentinization mechanism of the forearc mantle wedge abstract it has been proposed that the downdip limit of interplate thrust type earthquakes in subduction zones dlt is determined either by the brittle ductile transition around 350 450 c of the crustal material at the plate interface or the moho of the forearc of the upper plate the latter is due to possible serpentinization of the forearc mantle wedge above the subducting plate which makes the thrust zone slide in a stable manner i examine this criterion in subduction zones near japan where the pacific and philippine sea plates are subducting i show that in most of n honshu where the old pacific plate is subducting and in kanto and s kyushu where the izu bonin and kyushu palau ridges of the philippine sea plate are subducting the dlt is located at a depth of 60 70 km which is deeper than the moho of the upper plate this shows that the criterion does not hold and the mantle wedge is not likely to be serpentinized in these regions in contrast in the region off iwate in n honshu and in bonin where the old pacific plate is subducting the dlt is located at a depth of 20 30 km around the moho of the upper plate suggesting that the mantle wedge is serpentinized in these regions in sw japan where the young shikoku basin is subducting the dlt is around 30 km in depth which coincides with the moho but also with the 350 c temperature at the plate interface although seismic tomography indicates that the mantle wedge is serpentinized the dlt here does not help to examine the criterion assuming that hydration of the mantle wedge is conducted through hydro fracturing by water released from the dehydrating subducted crust i propose that the stress state of the wedge would determine the extent of serpentinization of the mantle wedge in the reverse fault type stress regime of n honshu kanto and s kyushu hydro fracturing is not favored and fractures in the thrust zone associated with repeated interplate earthquakes provide conduits for water to flow in the updip direction resulting in no serpentinization of the mantle wedge no serpentinization of the mantle wedge in turn causes interplate earthquakes in contrast in the normal fault type stress regime of the region off iwate and bonin and the strike slip fault type stress regime of sw japan hydro fracturing is favored resulting in serpentinization of the mantle wedge the frictional property at the thrust zone is governed by stable sliding resulting in no interplate earthquakes deeper than the moho thus the stress regime of the mantle wedge would determine bifurcation whether it is serpentinized or not and then the depth of dlt

serpentine mineral replacements of natural olivine and their seismic implications oceanic lizardite versus subduction related antigorite we report on microstructural data obtained by optical microscopy and transmission electron microscopy concerning the crystallographic relationships of serpentine minerals with their host olivine in two contrasting situations in the first case mesh textured lizardite liz is developed in a standard 60 serpentinized oceanic harzburgite from the oman ophiolite where olivine converts to columnar lizardite the joined columns are perpendicular to the basal plane 001 liz corresponding to the pseudofibres observed optically the plane 001 liz is locally parallel to the narrow boundary ol liz thus column orientations register the interface of serpentinization the ol liz relationships are not strictly topotactic but reflect preferred cracking orientations in olivine parallel to 010 ol in the second case antigorite atg develops in a rare sample of antigorite schist in a kimberlite from moses rock colorado plateau representative of a suprasubduction zone mantle wedge high resolution transmission electron microscopy hrtem images along 010 atg show domains of very regular modulation with a 43 center dot 5 a wavelength m 17 where m is the number of silicate tetrahedra along the wave with few defects indicative of hp ht antigorite and also heavily kinked regions as fingerprints of strong tectonic shear tem imaging and electron diffraction patterns reveal two topotactic relationships between antigorite and olivine 100 atg 010 ol and atg ol the planes in contact are 001 atg 100 ol and 001 atg 010 ol respectively the 010 atg 001 ol and antigorite lamellae are parallel to the forsterite b axis in both cases the topography of olivine serpentine interfaces is controlled by open fluid pathways along microcracks oriented according to the anisotropy of the olivine aggregate in the cases studied the serpentine aggregate exhibits a preferred orientation inherited from that of the peridotite these results have some relevance to the seismic anisotropy of serpentinized mantle anisotropy of propagation of seismic waves as a result of the olivine fabric is maintained and reinforced with the development of lizardite conversely the development of antigorite produces a trench parallel fast s wave polarization and an anisotropy that is lowered at low degrees of serpentinization and then increased with increasing serpentinization

locating earthquakes with amplitude application to real time seismology earthquakes are traditionally located using travel times however since the ground motion amplitude generally decays with the distance from the source it should also be possible to locate earthquakes using amplitude data amplitudes are affected by many factors other than the distance so that we do not expect to be able to locate the epicenter the location of the initial rupture very accurately with amplitude data however locating earthquakes with amplitudes has its own merits 1 for postearthquake emergency services it is often more important to know the spatial distribution of strong motion parameters such as peak acceleration and peak velocity than the rupture initiation point itself national research council 1991 this is especially true for thrust earthquakes e g 1971 san fernando earthquake 1987 whittier narrows earthquake or events with large rupture zones 2 the amplitudes are usually much easier to determine than the arrival times especially for events with complex rupture patterns or with immediate foreshocks in which event association can be difficult for application to real time earthquake information systems such as cube caltech usgs broadcast of earthquakes kanamori et al 1991 the amplitude method could provide a quick and robust way to send useful information for emergency operations here we report a few examples and propose a method for future implementation in a cube type system

early warning system for aftershocks a prototype early warning system to provide san francisco and oakland california a few tens of seconds warning of incoming strong ground shaking from already occurred m 3 7 aftershocks of the magnitude 7 1 17 october 1989 loma prieta earthquake was operational on 28 october 1989 the prototype system consisted of four components ground motion sensors in the epicentral area a central receiver a radio repeater and radio receivers one of the radio receivers was deployed at the california department of transportation caltrans headquarters at the damaged cypress street section of the i 880 freeway in oakland california on 28 october 1989 and provided about 20 sec of warning before shaking from the m 4 5 loma prieta aftershock that occurred on 2 november 1989 at 0550 utc in its first 6 months of operation the system generated triggers for all 12 m 3 7 aftershocks for which trigger documentation is preserved did not trigger on any m 3 6 aftershocks and produced one false trigger as a result of a now corrected single point of failure design flaw because the prototype system demonstrated that potentially useful warnings of strong shaking from aftershocks are feasible the usgs has completed a portable early warning system for aftershocks that can be deployed anywhere

monitoring of strain release in central and northern california using broadband data systematic cataloguing of seismic moment depth and mechanism of regional earthquakes down to magnitude m 4 can now be achieved in close to real time using data from sparse networks of digital broadband stations the procedure we have developed relies on 3 independent methods for the determination of moment tensor providing confidence limits on the results we show the results of application to the seismicity in central and northern california for a one year period starting in march 1992 and illustrate how patterns of stress and strain release can now be monitored systematically and reliably in a timely fashion

the 1968 tokachi oki and the 1969 kurile islands earthquakes variability in the rupture process the may 16 1968 tokachi oki mw 8 2 and the august 11 1969 kurile islands mw 8 2 shallow thrust earthquakes occurred along the japan kurile arc about 500 km apart and possess similar static fault parameters their dynamic source processes were investigated using the observable directivity in the source time functions deconvolved from long period p waves the rupture processes of both earthquakes can be understood in terms of a combination of the end member asperity and barrier models of earthquake rupture the 1969 kurile islands earthquake ruptured in the sense of the asperity model one region of the fault plane radiated most of the seismic moment i e the asperity and is surrounded by the rupture zones of large precursor events the rupture process of the 1968 tokachi oki earthquake contains elements of both end member rupture models a dominant asperity is bounded to the south by a region of the fault plane ruptured by a large precursor event and is bounded to the north by a geometric barrier where the plate margin changes direction this geometric feature is responsible for the abrupt termination of the rupture front it appears that the tectonic setting plays a vital role in determining the rupture mode earthquakes that occur along linear trenches where no geometric or topographic complications exist seem to rupture in the sense of the asperity model whereas earthquakes that occur in the vicinity of such complications are more likely to possess rupture processes intermediate between the two end member models

minimizing and quantifying mis indexing in electron backscatter diffraction ebsd determinations of antigorite crystal directions antigorite is common in hydrated mantle domains and commonly shows strong alignment either due to deformation or growth in a preferred orientation the alignment of antigorite imparts a strong anisotropy to the host rock affecting physical properties a quantitative analysis of how antigorite affects these properties requires a reliable measurement of the crystallographic preferred orientation of antigorite and ebsd analysis is the most widely used technique potential problems include i mis indexing which can add significant uncertainties to the results and ii sample preparation which may affect the measured cpo in particular for automated mapping combining results derived from x ray goniometry ebsd and u stage techniques with fib tem analysis leads to the following conclusions concerning these two issues i there is a significant issue with mis indexing a and b axes due to rotational similarities about the c axis similar problems may also affect the c axes measurements but this is less significant than the a and b axes when data are filtered using lower mad values filtering using mad values of 0 7 can significantly change the resulting cpo ii sample preparation can also affect the measured cpo sections prepared parallel to the foliation show only minor differences with mad values of 2 0 mis indexing problems can be minimized by using an mad value of 0 7 and analysing thin sections cut parallel to the foliation

trench parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source using high pressure deformation experiments ikuo katayama and colleagues show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine the strong trench parallel anisotropy observed in several subduction systems is difficult to explain in terms of olivine anisotropy using high pressure deformation experiments it is now shown that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in such subduction systems seismic anisotropy is a powerful tool for detecting the geometry and style of deformation in the earth s interior as it primarily reflects the deformation induced preferred orientation of anisotropic crystals1 2 although seismic anisotropy in the upper mantle is generally attributed to the crystal preferred orientation of olivine3 the strong trench parallel anisotropy delay time of one to two seconds observed in several subduction systems4 5 is difficult to explain in terms of olivine anisotropy even if the entire mantle wedge were to act as an anisotropic source here we show that the crystal preferred orientation of serpentine the main hydrous mineral in the upper mantle can produce the strong trench parallel seismic anisotropy observed in subduction systems high pressure deformation experiments reveal that the serpentine c axis tends to rotate to an orientation normal to the shear plane during deformation consequently seismic velocity propagating normal to the shear plane plate interface is much slower than that in other directions the seismic anisotropy estimated for deformed serpentine aggregates is an order of magnitude greater than that for olivine6 and therefore the alignment of serpentine in the hydrated mantle wedge results in a strong trench parallel seismic anisotropy in the case of a steeply subducting slab this hypothesis is also consistent with the presence of a hydrous phase in the mantle wedge as inferred from anomalously low seismic wave velocities7

relationship between anisotropy of p and s wave velocities and anisotropy of attenuation in serpentinite and amphibolite velocities and q values of p and s waves as functions of pressure and temperature at 100 and 600 mpa are presented for a serpentinite and an amphibolite both rocks exhibit a strong lattice preferred orientation lpo of the major mineral phases antigorite and hornblende respectively velocities and q values increase with pressure the rate of increase is different in the three orthogonal directions normal and parallel to foliation and lineation and closely related to progressive closure of microcracks increasing temperature decreases velocities and q values only slightly as long as thermal cracking is prevented by the applied confining pressure substantial anisotropy of velocities and q in p and s waves is observed in both rocks but is found to be different in origin anisotropy of p and s wave velocities is highest at low pressure and basically caused by constructive interference of effects related to oriented microcracks and to the lpo of major minerals increasing confining pressure decreases velocity anisotropy at a smaller and smaller rate the residual anisotropy of p and s wave velocities shear wave splitting at high confining pressure is mainly a result of preferred mineral orientation by contrast anisotropy of q is very low at low confining pressure and markedly enhanced as pressure is increased at high confining pressure substantial anisotropy of q in p waves is apparent but reversed from that of p wave velocities qp is highest in the direction normal to the foliation plane whereas vp and vs is lowest in this direction the generation of a pronounced anisotropy of qp by increasing pressure is due to a directionally dependent increase of contact areas on the oriented grain boundaries of the platy minerals defining the foliation the increase of q with pressure in the direction normal to foliation is mainly caused by the decrease of energy loss due to compressive strain relative to shear strain the reverse is true for the x and y directions serpentinite and x direction amphibolite parallel to the foliation plane

investigating physical and thermal interactions between lava and trees the case of kīlauea s july 1974 flow to examine whether there was any physical or thermal interaction between trees and lava when a lava flow inundates a forest we studied the k lauea s july 1974 lava flow we mapped the location of 600 lava trees and the lava type p hoehoe versus a and sampled an additional ten lava trees for chemical and textural analysis to infer flow viscosity and dynamics the emplacement event lasted 3 5 h and markers on the outer surface of the lava trees allowed us to define initial high effusion rate and velocity 400 m3 s and 5 10 m s that then declined to 9 m3 s and 4 m s during a waning phase we find that lava passing through the forest underwent an initial cooling rate of 4 c km which increased to 10 c km late in the eruption this is no different to cooling rates recorded at k lauea for tree free cases there thus appears to be no effect on cooling for this case the lava trees did though form a network of vertical cylinder obstacles and evidence for local diversion of flow lines are noticed however this varies with lava type as almost no lava trees form in a we find a relation between the percentage of a and the number of lava trees per hectare the p hoehoe a transition for this flow occurs at a viscosity of 103 pa s and this appears to be a threshold below which lava trees can form so as to behave as a network of obstacles and above which they cannot

fabric development in a fragment of tethyan oceanic lithosphere from the piemonte ophiolite nappe of the western alps valtournanche italy abstract south of the matterhorn the valtournanche cuts through alpine serpentinites metagabbros meta pillowbasalts and metasediments dismembered remnants of the jurassic tethyan oceanic crust reassembled in the piemonte ophiolite nappe this study deals with a serpentinized ultramafic to mafic layered complex stemming from a spreading ridge environment cumulus fabrics of various kinds can be read through antigorite pseudomorphs still allowing the detailed reconstruction of deep oceanic crust relics of igneous and metamorphic olivine prove crustal conditions during deformation fracturing of cumulus olivine was succeeded by plastic flow that activated low temperature slip systems concomitant recrystallization produced metaperidotite only along shear zones which are ascribed to subduction of the oceanic crust at the turning point from subduction to obduction a static metamorphic event resulted in recovery and grain growth of recrystallized olivine afterwards serpentinization of the complex took place still under static conditions deformation of the serpentinite led to a sequence of four phases involving non penetrative cleavage formation stretching and folding this deformation is structurally related to obduction of the complex although partly accompanied by subduction zone metamorphism final movements of the ophiolites were due to cataclastic thrusting forming subnappe boundaries