lower crustal deformation beneath the central transverse ranges southern california results from the los angeles region seismic experiment 1 we present a p wave velocity model derived from active source seismic data collected during the 1994 los angeles region seismic experiment our model extends previously published upper crustal velocity models to mantle depths our model was developed by both ray tracing through a layered model and calculating travel times through a gridded model it includes an 8 km thick crustal root centered beneath the surface trace of the san andreas fault north of the highest topography in the san gabriel mountains a simple mass balance calculation suggests that 36 km of north south shortening across the san andreas fault in the central transverse ranges could have formed this root if north south compression began when the big bend in the san andreas fault formed at 5 ma 36 km of shortening implies a north south contraction rate of 7 1 mm yr across the central transverse ranges if instead north south compression began when the transverse ranges formed at 3 4 3 9 ma 36 km of shortening implies a contraction rate of 9 2 10 6 mm yr north of the san andreas fault the mojave desert crust has a low velocity 6 3 km s mid and lower crust and a 28 km deep moho south of the san andreas fault beneath the los angeles and san gabriel valley basins there is a fast 6 6 6 8 km s thick 10 12 km lower crust with a 27 km deep moho farther south still the lower crust of the continental borderland is fast 6 6 6 8 km s and thin 5 km with a shallow 22 km deep moho

cenozoic tectonism in the central basin and range magnitude rate and distribution of upper crustal strain a wealth of pre cenozoic geologic markers across the central basin and range province defined mainly by thrust faults developed within a miogeoclinal wedge makes it one of the best areas on earth to reconstruct large scale continental extension we use this 100 000 km 2 region bounded by the southern sierra nevada on the west and the colorado plateau on the east to illustrate the concepts of correlation and misalignment for regional strain markers and of strain compatibility and kinematic viability in palinspastic reconstructions the results indicate 250 to 300 km of west northwest motion of the sierra away from the plateau accommodated by both crustal thinning and north south shortening tertiary intermontane basin deposits and mineral cooling ages of deeply exhumed rocks constrain the overall kinematics of motion most of the westward motion occurred between 16 and 5 ma at rates near 2 cm yr slowing to 1 to 1 5 cm yr in the last 5 ma we have quantified the partitioning of strain between vertical crustal thinning via normal faults and map view plane strain via conjugate strike slip faults by placing a grid of 10 x 10 km elements on a retrodeformed map of the region and measuring the increase in area of grid elements between the undeformed and present day grids this analysis yields a maximum finite elongation of the basin and range at 36 n to 37 n of 3 4 oriented n73 w map view area balance shows that 20 percent of this elongation is compensated by north south shortening and 80 percent by crustal thinning this yields an average thinning factor for the upper crust of 2 7 between the sierra and plateau inconsistent with the hypothesis that neogene deformation in the central basin and range is predominantly dextral shear plane strain these results in concert with the observation that the southern sierra nevada has similar crustal thickness to the central basin and range support the hypothesis of large scale eastward flow of sierran deep crust during extension

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

uplift of quaternary shorelines in eastern patagonia darwin revisited during his journey on the beagle darwin observed the uniformity in the elevation of coastal eastern patagonia along more than 2000 km more than one century later the sequences of quaternary shorelines of eastern patagonia have been described and their deposits dated but not yet interpreted in terms of geodynamics consequently we i mapped the repartition of the quaternary coastal sequences in argentinean patagonia ii secured accurate altitudes of shoreline angles associated with erosional morphologies i e marine terraces and notches iii took into account previous chrono stratigraphical interpretations in order to calculate mean uplift rates since 440 ka mis 11 and proposed age ranges for the higher and older features up to 180 m and iv focused on the last interglacial maximum terrace mis 5e as the best constrained marine terrace in terms of age and altitude in order to use it as a tectonic benchmark to quantify uplift rates along the entire passive margin of eastern south america our results show that the eastern patagonia uplift is constant through time and twice the uplift of the rest of the south american margin we suggest that the enhanced uplift along the eastern patagonian coast that interested darwin during his journey around south america on the beagle could originate from the subduction of the chile ridge and the associated dynamic uplift

integrated model of the crustal structure in the gulf of california extensional province abstract a method of constructing 3d earth models from a suite of 1d profiles is demonstrated using delaunay triangulation accurate crustal models are required to correct for crustal contamination in seismic tomography of the mantle and can be used as starting points for higher resolution tomography of the lithosphere and asthenosphere using a simple input data set 1d vertical profiles provides for rapid prototyping model building and modification any structural length scale in the final 3d model is possible using this method through precise placement of 1d profiles and triangulation collections of layers within the 1d profiles are grouped and identified by keys called superlayers allowing for 3d discontinuities and variations along these important interfaces the method was applied to the gulf extensional province and baja california regions to account for the laterally discontinuous crustal variations during a tomographic inversion for mantle structure use of the 3d model and appropriate regional crustal wave speeds minimizes wave speed variations in the tomographic model and assists interpretation of the final model

records and causes of holocene salinity shifts in laguna de bay philippines abstract a 7000 year record of salinity shifts from molluscan and diatom assemblages and verified geochemical salinity proxies c s s sr ca and sr ba is reconstructed from philippines largest freshwater lake laguna de bay the salinity shifts are interplays of millennial scale sea level change centennial scale tectonic activity from the west marikina valley fault wmvf and decadal scale climatic changes currently only 1 m above mean sea level the lake is connected to manila bay through the pasig napindan river which meanders across a densely populated paranaque strip partly occupied by metropolitan manila the controversial wmvf borders the lake on its western shore our 10 5 m sediment core from the western lobe reveal that the deposits are from a marine environment deposited 6600 cal bp to 4700 cal bp during a sea level still stand above present mean sea level apmsl in southeast asia and the philippines episodic decreases in salinity with 260 y cycles were traced to the activity of the wmvf that would have accounted for at least 6 m of uplift of the paranaque strip the vertical component of movement raised a sill and emergent landmass that started to isolate the paleo laguna de bay from manila bay subsequent episodic uplifts and sea level fall decreased depths to intertidal levels by 4700 cal bp salinity to brackish but highly influenced by marine waters by 4100 cal bp and to freshwater by 3100 cal bp the latest salinity increase since mid 1960 is attributed to renewed saltwater incursion due to abnormally dry years low lake levels and pasig river delta plain subsidence

lateral velocity variations in southern california i results for the upper crust from pg waves the plate boundary and major crustal blocks in southern california are imaged by a tomographic backprojection of the pg first arrivals recorded by the southern california array the method formulated specifically for local earthquake arrival times is a fast iterative alternative to direct least squares techniques with it we solve the combined problem of determining refractor velocity perturbations and source and station delays resolution and variance are found empirically by using synthetic examples a map showing lateral velocity variations at a depth of approximately 10 km is presented the results show a strong correlation with surface tectonic features clear velocity contrasts exist across the san andreas the san jacinto and the garlock faults the mojave region has the slowest velocities while the peninsula ranges have the highest the san jacinto block has velocities intermediate between mojave and peninsula range velocities and also has early station delays this may indicate that the san jacinto block has overridden mojave material on a shallow detachment surface no velocity variations are found associated with the transverse ranges which we interpret to mean that the surface batholithic rocks in this area do not extend to pg depths

crustal extension and magmatic processes cocorp profiles from death valley and the rio grande rift new crustal scale information on the interaction between normal faulting and magmatic activity is provided by recent cocorp deep seismic reflection profiles in death valley california and by reprocessing of the cocorp data from the socorro area of the rio grande rift new mexico the most striking feature on the seismic sections from these areas is a prominent subhorizontal series of reflectors at mid crustal depth previous studies have suggested that thin tabular magma bodies lie within the mid crustal reflective zones in addition because they are traced without apparent offset beneath faults both mapped at the surface and interpreted from the cocorp data these mid crustal horizons are here inferred to be detachments or zones of tectonic decoupling upper crustal cenozoic faults do not appear to penetrate deeper than 15 km in death valley and 13 km in the rio grande rift in death valley these faults are relatively planar with moderate dips 20 to 35 and appear to bound large basement rocks one such zone of normal faults can be traced from the magma body inferred at 15 km depth beneath central death valley to the surface location of a 690 000 yr old basaltic cinder cone listric and low to moderate angle normal faults are evident on the reprocessed new mexico data and constitute the structural component of upper crustal extension in particular a listric master fault traceable to depths as great as 13 km is inferred to underlie the albuquerque basin unlike the death valley data no faults are observed to merge with the socorro magma body per se rather subhorizontal to moderately west dipping packages of reflections are imaged between the base of the faulted upper crust 13 km depth and the mid crustal magma body about 20 km depth the middle crust marks a major rheological boundary between the faulted upper crust and a ductile lower crust extending by penetrative flow and intrusion events seen in the middle and lower crust are generally subhorizontal and prominent layering is observed a band of reflections attributed to the crust mantle boundary is evident on most seismic sections the upper mantle appears seismically transparent on some of the profiles the events attributed to the base of the crust are the deepest in a series of strong and continuous reflections at least one of which is a layer of magma this association supports the suggestion that magmatic intrusions are a probable cause for the high reflectivity observed in the deep crust of many extensional terranes

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

sea level rise and coral reef development of northwestern luzon since 9 9ka abstract coral reef growth and relative sea level record for the early mid holocene are established from three boreholes drilled on a raised holocene reef at currimao northwestern luzon philippines age control is provided by 230th dates of 13 corals mostly in living position the cores cover a depth interval from 3 8 m above to 26 7 m below present mean sea level msl and consist of four lithofacies including 1 reef facies 2 bioclastic facies 3 clayey facies and 4 tuffaceous facies the ages of dated corals vary from 6588 27 ya at 1 4 m below msl to 9855 42 ya at 22 m below msl results of this study indicate that the reef started growing about 9 9 ka when the minimum sea level relative to the western luzon coast was about 27 m below msl after tectonic correction during 9 2 8 2 ka reef accretion rate was as high as 10 13 m ky coral reef developed to near paleo sea level at about 6862 28 ya and emerged due to tectonic uplift the sea level curve of currimao is generally similar to that of the western australia coast but at least 8 11 m higher than that of tahiti from 10 to 8 5 ka

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

estimating crustal thickness in southern california by stacking pmp arrivals we use observations of the moho reflected phase pmp to constrain crustal thicknesses and upper mantle velocities in southern california we stack normalized absolute values of seismograms from local events in time and range bins after aligning on the initial p arrival and applying a range correction to adjust the various source depths to the surface although most individual seismograms do not allow accurate determination of a pmp arrival time imaging the whole data set in this way shows clear pmp arrivals at ranges from about 90 km to over 250 km pmp pg and pmp pn differential times can be measured from the image and used to estimate the moho depth and upper mantle velocity for southern california we obtain an average crustal thickness of 28 km and an upper mantle velocity of 7 8 km s next we map lateral variations by repeating this procedure for stacks of subsets of the data in which the traces are grouped in caps by moho reflection point estimates of moho depth range from 18 km in the salton trough to 33 km beneath the eastern transverse ranges and 36 km beneath the southernmost sierra nevada the upper mantle velocities generally increase from southwest to northeast across the region we also map postcritical pmp pg amplitudes which vary by a factor of 4 with the highest amplitudes in the northwest mojave desert preliminary experiments with stacking sms arrivals indicate strongly correlated sms and pmp amplitude variations these results provide a guide to source receiver paths that may produce anomalously strong moho reflected phases during future earthquakes

crustal structure of eastern nevada from cocorp deep seismic reflection data the western nevada segments of the cocorp 40 n deep seismic reflection survey of the north american cordillera reveal the geometry of structures of cenozoic and possibly earlier ages to travel times of 10 s corresponding to depths of 30 km the most striking feature of the data is a band of prominent reflections typically at traveltimes of 9 5 to 10 5 s that are present discontinuously across the entire data set few reflections are observed from beneath the base of this reflective zone which is interpreted as the crust mantle transition this reflection mono is inferred to be continuous across the survey area varying gradually in depth but without resolvable offsets it appears to have taken its present form or position during basin range crustal extension the middle to lower crust in much of the survey area is characterized by discontinuous reflections that are typically subhorizontal and locally dip gently west these reflections may represent intrusions or shear zones related to basin range or pre basin range extension but some are likely to be inherited from earlier compressional deformation reflections from the upper crust are interpreted as images of basin fill strata basin range normal faults and mesozoic and paleozoic thrusts related to back arc thrusting and accretion of oceanic and arc related rocks

seismic reflection constraints on the structure of the crust beneath the san bernardino mountains transverse ranges southern california a 30 km long n s seismic reflection line was shot by california consortium for crust studies calcrust across the southern mojave desert and onto the northern flank of the san bernardino mountains in southern california on the northern end of the seismic section the reflectivity increases markedly in the midcrust at a depth corresponding to a two way travel time of 4 to 5 s 12 15 km suggesting a transition between nonreflecting brittle upper crust and reflecting ductile lower crust the high reflectivity disappears at about 8 s 24 km and may be correlated with a change in seismic velocity in the lower crust from 6 3 km s to 6 8 km s a band of reflectivity between 9 5 and 10 s 27 30 km is believed to represent the moho the midcrustal relectivity transition and moho both deflect downward toward the san bernardino mountains uplift over the entire length of the profile the deflection of the midcrustal transition 12 appears greater than that of the moho 6 resulting in a thinning of the lower crust to the south beneath the uplift in addition the midcrustal transition coincides with the base of the seismogenic zone brittle ductile transition which is also dipping southward beneath the san bernardino mountains while the moho deflection is consistent with elastic flexure resulting from edge loading by the san bernardino mountains which have been thrust over the mojave block it is suggested that the thinning of the lower crust beneath the san bernardino mountains is a result of north directed ductile flow in response to loading by the over thickened upper crust since a portion of the load is transmitted through the lower crust to the moho the time constant for flow equilibrium must be of the order of or greater than that for the time of uplift 2 m y

evidence of large prehistoric offshore earthquakes deduced from uplifted holocene marine terraces in pangasinan province luzon island philippines abstract uplifted holocene marine terraces in pangasinan province westernmost luzon island philippines are reported here for the first time as geomorphic evidence of large prehistoric offshore earthquakes we recognized up to three holocene terrace steps elevations of shoreline angles are ti 1 to 5 m tii 2 to 7 m and tiii 4 to 11 m above mean sea level amsl the lateral variation in the elevation of terrace steps indicates differential uplift along the coast the staircase topography characterized by horizontal abrasion platforms meter scale terrace risers and wave cut notches suggests that these geomorphic features were formed by large coseismic uplift events terrace morphology and radiocarbon ages further suggest that at least three coseismic coastal uplift events have occurred since the culmination of the post glacial sea level rise 6000 years ago we interpret tiii to be the holocene transgressive surface 6000 ybp and estimated a maximum uplift rate of 1 7 mm yr which is almost the same as the late pleistocene uplift rate of 1 3 mm yr we infer that proximity to offshore seismic sources has contributed to the deformation pattern of holocene terraces and variation in the number of terrace steps uplift patterns of marine terraces also suggest that the magnitude and location of prehistoric earthquakes may have varied between individual coseismic uplift events we conducted simple elastic dislocation modeling to evaluate the source parameters of the causative faults our preliminary models show that a landward dipping offshore reverse fault located at the base of a steep slope separating the fore arc basin and continental shelf could be responsible for coastal uplift along the western pangasinan peninsula

regional crustal thickness variations of the peninsular ranges southern california we used the teleseismic receiver function technique to obtain a profile of the crustal thickness of the northern peninsular ranges california depth to the moho varies from 37 km beneath the western peninsular ranges batholith to 27 km at the western edge of the salton trough an average apparent dip of 10 to the west over a lateral distance of 60 km we previously obtained a similar result for a profile 100 km to the south a moho dip of 20 over 30 km lateral distance in both cases the moho depth variations do not correlate with topography of the eastern batholith but rather appear to parallel the trend of a boundary that separates compositionally distinct eastern and western terranes these observations suggest that a steeply dipping moho is a regional feature beneath the eastern peninsular ranges and that compensation is through lateral variations in crustal or upper mantle density rather than through an airy root

a notch structure on the moho beneath the eastern san gabriel mountains synthetic waveform modeling of the anomalous receiver functions for two stations in the eastern san gabriel mountains california suggests that a flat topped notch structure exists on the moho north of the san andreas fault saf the moho depth is 36 38 km and is 33 35 km south of the san gabriel fault sgf but in between under the mt baldy block it is only 29 km the inferred notch structure is also supported by the pms arrival times along the scsn and the larse i profiles the shallow moho block correlates well with the surficial exposure of the lower plate pelona schist or where it resides at very shallow depth the large moho offsets across the two major faults can be either related to differential uplifting reflected by the difference in the denudation rate and the exposure of the lower plate pelona schist or it can be the result of the juxtaposition of the distinctive terranes with initially different moho depth due to the strike slip movements along the two major faults

the age and origin of the straits of singapore abstract consideration of the quaternary stratigraphy sea level history and detailed bathymetry of the straits of singapore suggests that a marine connection between the indian ocean and south china sea through the straits may not have existed until the last interglacial period oxygen isotope stage ois 5e after this time a tenuous connection may have also existed during stages 5a and 5c as well as possibly 5b the geomorphologic evidence is consistent with flow from west to east during these periods the opposite direction to modern net flow along a narrow palaeochannel that can be traced across the floor of the modern straits strong currents flowing through the straits at these times are likely to have been responsible for scouring the 204 m over deepened basin known as the singapore deeps and a similar 102 m deep basin south of the southern outfall of the riau straits the evidence suggests that the region has been undergoing down warping at a rate of 0 06 to 0 19 mm year since the beginning of the last interglacial period and the most likely value is at the lowest end of this range while a more precise estimate of this rate will require further study it is likely that the singapore straits has not been acted as a significant barrier to migration from mainland asia to emergent areas of the sunda shelf for most of the quaternary

the climatic signature of incised river meanders climate controls landscape evolution but quantitative signatures of climatic drivers have yet to be found in topography on a broad scale here we describe how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the western north pacific spatially averaged river sinuosity generated from digital elevation data peaks in the typhoon dominated subtropics where extreme rainfall and flood events are common and decreases toward the equatorial tropics and mid latitudes where such extremes are rare once climatic trends are removed the primary control on sinuosity is rock weakness our results indicate that the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers

paleomagnetic results from luzon and the central philippines samples were collected from 86 paleomagnetic sites from the islands of luzon marinduque mindoro panay negros cebu and mindanao in the philippine arc the sampling sites range in age from pleistocene to jurassic characteristic directions of magnetization of the samples were determined by the use of vector plots curie temperature determinations thin section studies and hysteresis studies showed that remanence of these samples is carried by fine grained pseudo single domain magnetite positive fold tests from miocene data from panay jurassic data from mindoro and cretaceous data from cebu suggest that the magnetization of these regions was acquired prior to folding rotations reported below are measured with respect to the axial goecentric dipole field the plio pleistocene data set shows no resolvable rotation for the 22 sites this data set suggests that the various terranes that make up the philippine arc have behaved as a single unit during the past 5 m y or that deformation has been below the limits of resolution the inclination data from the plio pleistocene sites have anomalously shallow inclination and are consistent with other plio pleistocene data from vietnam taiwan and the marianas these data support earlier suggestions for a late neogene offset dipole effect the late miocene sites fall into two separate groups ten sites from western luzon show evidence for around 20 of clockwise rotation in contrast to this late miocene samples from the bicol region negros marinduque and mindanao are not rotated the cause of the postlate miocene clockwise rotation of luzon is unknown but a pliocene collision of the north luzon arc with taiwan is suggested early neogene results also separate into two different populations the population from marinduque shows evidence for a large counterclockwise rotation the second early neogene population comes from panay cebu and mindanao and clearly shows evidence for a clockwise rotation the validity of this rotation is further supported by a fold test and a reversal test these early neogene data sets are consistent with a middle to late miocene collision of the palawan continental terrane and the central philippine arc data from six dikes of possible oligocene age from the zambales ophiolite are highly discordant from the present field being rotated approximately 60 clockwise the directions from these dikes are similar to a direction reported earlier from late oligocene sediments also from the zambales region these two data sets support the interpretation that the eocene direction from zambales is recording a large clockwise rotation of the region data from the mesozoic sites are from two regions data from the cretaceous pandan formation of cebu are discordant with data from the upper jurassic from mindoro the presence of a fold test from each region and a reversal test from mindoro supports the interpretation that each of these data sets is reliable the vgp of mindoro is displaced southward from the late jurassic vgp of south china suggesting a post jurassic southward migration of mindoro

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

the influence of light attenuation on the biogeomorphology of a marine karst cave a case study of puerto princesa underground river palawan the philippines karst caves are unique biogeomorphological systems cave walls offer habitat for microorganisms which in turn have a geomorphological role via their involvement in rock weathering erosion and mineralisation the attenuation of light with distance into caves is known to affect ecology but the implications of this for biogeomorphological processes and forms have seldom been examined here we describe a semi quantitative microscopy study comparing the extent structure and thickness of biocover and depth of endolithic penetration for samples of rock from the puerto princesa underground river system in palawan the philippines which is a natural unesco world heritage site organic growth at the entrance of the cave was abundant 100 occurrence and complex dominated by phototrophic organisms green microalgae diatoms cyanobacteria mosses and lichens thickness of this layer was 0 28 0 18 mm with active endolith penetration into the limestone mean depth 0 13 0 03 mm in contrast phototrophs were rare 50 m into the cave and biofilm cover was significantly thinner 0 01 0 01 mm p 0 000 and spatially patchy 33 occurrence endolithic penetration here was also shallower 0 01 mm p 0 000 and non uniform biofilm was found 250 m into the cave but with a complete absence of phototrophs and no evidence of endolithic bioerosion we attribute these findings to light induced stress gradients showing that the influence of light on phototroph abundance has knock on consequences for the development of limestone morphological features in marine caves this includes notches which were most well developed at the sheltered cave entrance of our study site and for which variability in formation rates between locations is currently poorly understood

crustal thickness variations in southern california from los angeles region seismic experiment passive phase teleseismic travel times the goal of the 1993 los angeles region seismic experiment larse93 passive phase was to collect waveform data from local and distant earthquakes to study lower crust and upper mantle structural features in southern california particularly under the san gabriel mountains and san andreas fault during larse93 approximately 88 stations were deployed in a 175 km long linear array across the los angeles basin san gabriel mountains and mojave desert northeast of los angeles during the four weeks of continuous recording teleseismic events recorded at each site provided a wide range of ray path backazimuths the teleseismic events included a number of intermediate magnitude earthquakes with epicenters in the aleutian island kamchatka kuril island mid atlantic ridge solomon island japan fiji island and chile regions this experiment was followed by larse94 which involved land refraction and deep crustal seismic reflection profiles from offshore and onshore explosion sources we have used the joint data sets in this study to distinguish upper crustal features from adjacent lower crustal and upper mantle structures p wave travel times were determined from 17 teleseisms and upper crustal residual signatures were removed by incorporating larse94 upper crustal velocity model results within each backazimuth range the resulting relative traveltime residuals increase from negative values 0 5 sec average recorded in the northern san gabriel valley southern san gabriel mountain foothills to positive values 0 2 sec average in the central and northern san gabriel mountains the residual patterns display variations for different backazimuths and incidence angles but show almost no lateral spatial shift of maximum or minimum residual along the array indicating that the dominant source of the residual pattern is shallow 50 km the patterns of residuals require a sharp lateral gradient in shallow velocities between the northern san gabriel valley located in the northernmost los angeles basin and the san gabriel mountains over a distance of less than 50 km most of the residual pattern can be explained by laterally varying crustal thickness and a high velocity anomaly in the upper mantle in our model of moho depth variations the northern san gabriel valley to the southwest of the array is underlain by thinned continental crust crustal thickness increases laterally by 12 km over a distance of less than 50 km into the san gabriel mountains this conclusion is supported by widespread surface evidence for rift style volcanism and crustal extension in southern california crustal rocks

u series dates of pleistocene corals and their implications to the paleo sea levels and the vertical displacement in the central philippines abstract results of high precision alpha spectrometric 230th 234u dating of hermatypic corals in palawan in western philippines and cebu bohol and panglao islands in the central philippines confirm the presence of mis 5e reef terraces at 2 to 13 m above the present mean sea level similar to stable regions this suggests the relative vertical stability of the islands since the last interglacial period in panglao island the elevation of the 5e terrace increases to the northeast indicating tilting of the island to the southwest the continued sense of uplift since at least the last interglacial is indicated by the similarity in the spatial variation of middle holocene tidal notch a 5c terrace though less developed is also recognized in panglao island along the san isidro coast the inner margins of 5c and 5e terraces are at elevations of 5 and 7 1 8 m respectively and the difference in altitude between the terraces is only ca 2 3 m assuming that the sea level during mis 5e was 3 6 m above the present sea level sea level at mis 5c is estimated to be equal to or slightly higher than the present mean sea level

an igneous origin for features of a candidate crater lake system in western memnonia mars the association of channels inner terraces and delta like features with martian impact craters has previously been interpreted as evidence in favor of the past existence of crater lakes on mars however examination of a candidate crater lake system in western memnonia suggests instead that its features may have formed through igneous processes involving the flow and ponding of lava accumulations of material in craters and other topographic lows throughout much of the study region have characteristics consistent with those of volcanic deposits and terraces found along the inner flanks of some of these craters are interpreted as having formed through drainage or subsidence of volcanic materials channels previously identified as inlets and outlets of the crater lake system are interpreted instead as volcanic rilles these results challenge previous interpretations of terrace and channel features in the study region and suggest that candidate crater lakes located elsewhere should be reexamined

the philippine wrench fault system in the ilocos foothills northwestern luzon philippines abstract luzon is part of the taiwan luzon mindoro mobile belt which marks the plate boundary between the eurasian and philippine sea plates on luzon the philippine fault runs parallel to the philippine archipelago for more than 1300 km and is an active left lateral strike slip fault which forms a braided system detailed field mapping together with structural and biostratigraphic analysis have been conducted in the ilocos foothills on the western flank of the central cordillera cenozoic magmatic arc this area on the northwestern tip of luzon appears to consist of three large tectonic units which are continuous for more than 200 km and bounded by major left lateral strike slip faults related to the philippine fault from west to east these units are as follows 1 1 the vigan laoag coastal strip vlcs consists of an ultramafic basement which is strongly tectonized and unconformably overlain by a relatively undeformed middle miocene to pliocene sedimentary cover 2 2 the vintar median strip vms is bounded to the west by the vigan aggao wrench fault which upthrusts westwards and to the east by the abra river strike slip fault this unit is composed of a thick 6 10 km late eocene to pliocene volcaniclastic sequence deposited in a basin which was fed mainly by the central cordillera but also until the early miocene by an ultramafic high composed of the vlcs basement this sequence is strongly folded 3 3 the eastern strip es is a late eocene to miocene volcaniclastic sequence intruded by oligocene and miocene rocks this structural pattern results from two major tectonic episodes 1 1 the late middle to late miocene episode comprises the abra river strike slip faulting this is characterized by the folding of a 20 km wide band and by the creation of a ridge transverse to the tectonic strips related to the abra river fault restraining bend this ridge seems to have absorbed the compressive deformation whereas the strike slip component was accommodated by the nearly pure strike slip faulting along the abra river fault 2 2 the pliocene to quaternary episode involved strike slip activity propagating westward from the abra river fault relatively inactive during this phase to the vigan aggao wrench fault the vigan aggao fault is located at the boundary between an ultramafic palaeo high highly deformed mesozoic ophiolite and a palaeobasin filled with a thick late eocene to miocene sedimentary sequence this particular location seems to attest to the recent use of an older major tectonic feature

a tomographic image of mantle structure beneath southern california we determined the variations in seismic structure beneath southern california by using a tomographic method of inversion on teleseismic p delays recorded with the southern california array the algorithm employed was a modified form of an algebraic reconstruction technique art used in medical x ray imaging deconvolution with an empirically estimated point spread function was also used to help in focusing the image the inversion reveals two prominent features beneath the region the first is a thin vertical wedge directly beneath the transverse ranges that is 2 3 faster than the surrounding region this feature deepens to the east attaining a maximum depth of about 250 km beneath the san bernardino mountains the second feature is a major zone of low velocity material that is 2 4 slow under the salton trough rift valley extending to a depth of about 125 km two possible explanations for the spatial association of the transverse ranges with the velocity anomaly below are lithospheric subduction or small scale sublithospheric convection in the region of the big bend of the san andreas fault the low velocity anomaly beneath the salton trough is consistent with convective upwelling there

lithospheric instability beneath the transverse ranges of california recent high resolution seismic experiments reveal that the crust beneath the san gabriel mountains portion of the transverse ranges thickens by 10 15 km contrary to earlier studies associated with the transverse ranges there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle this high velocity anomaly has previously been interpreted as a lithospheric downwelling both lithospheric downwelling and crustal thickening are associated with the oblique convergence of pacific and north america plates across the san andreas fault though it seems likely that the lithospheric downwelling is driven at least partly by gravitational instability of the cold lithospheric mantle we show by means of numerical experiment that the balance between buoyancy forces that drive deformation and viscous stresses that resist deformation determines the geometry of crustal thickening and mantle downwelling we use a simple two layered lithospheric model in which dense lithospheric mantle overlies relatively inviscid and less dense asthenosphere and is overlain by buoyant crust external plate motion drives convergence which is constrained by boundary conditions to occur within a central convergent zone of specified width a fundamental transition in the geometry of downwelling is revealed by our experiments for slow convergence or low crustal viscosity downwelling occurs as multiple sheets on the margins of the convergent zone for fast convergence or crust that is stronger than mantle lithosphere a single downwelling occurs beneath the center of the convergent zone this complexity in the evolution of the system is attributed to the interaction of crustal buoyancy with the evolving gravitational instability in order for a narrow downwelling slab to have formed beneath the transverse ranges within the last 5 myr the effective lithospheric viscosity of the convergent region is at most about 10 20 pa s

crustal thickness of the peninsular ranges and gulf extensional province in the californias we estimate crustal thickness along an east west transect of the baja california peninsula and gulf of california mexico and investigate its relationship to surface elevation and crustal extension we derive moho depth estimates from p to s converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at 318n latitude depth to the moho is 33 63 km near the pacific coast of baja california and increases gradually toward the east reaching a maximum depth of 40 64 km beneath the western part of the peninsular ranges batholith the crust then thins rapidly under the topographically high eastern peninsular ranges and across the main gulf escarpment crustal thickness is 15 18 62 km within and on the margins of the gulf of california the moho shallowing beneath the eastern peninsular ranges represents an average apparent westward dip of 258 this range of moho depths within the peninsula ranges as well as the sharp east west gradient in depth in the eastern part of the range is in agreement with earlier observations from north of the international border the moho depth variations do not correlate with topography of the eastern batholith these findings suggest that a steeply dipping moho is a regional feature beneath the eastern peninsular ranges and that a local airy crustal root does not support the highest elevations we suggest that moho shallowing under the eastern peninsular ranges reflects extensional deformation of the lower crust in response to adjacent rifting of the gulf extensional province that commenced in the late cenozoic support of the eastern peninsular ranges topography may be achieved through a combination of flexural support and lateral density variations in the crust and or upper mantle

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

lower crustal flow in an extensional setting constraints from the halloran hills region eastern mojave desert california postextensional uplift and tilting of quaternary lake sediments in the halloran hills eastern mojave desert california suggest that regional scale flow within the lower crust is occurring in response to tectonic loads created during upper crustal extension in late miocene time the concept that significant flow within the lower crust may occur for millions of years after the cessation of extension indicates that topographic gradients can be modified by regional scale flow within the lower crust and that direct constraints on lower crustal flow can be obtained by quantitative analysis of rates of postextensional surface tilting an analytic solution developed in this paper combines viscous flow in the lower crust flexural bending within the midcrust and isostasy into an invertible linear differential equation that describes the topographic response to upper crustal extension assuming that there was no topographic relief across the halloran hills region prior to extension inversion of modern topographic data indicates that crustal thinning above the halloran hills detachment increases westward with a listric geometry and that little crustal thinning has occurred east of the western flank of clark mountain in good agreement with the known geometry of the fault and the location of its breakaway zone incorporation of quaternary tilting data indicates that the modern viscosity beneath the halloran hills assuming a 10 km lower crustal channel is a maximum of 1019 pa s and that the viscosity of the lower crust has decreased by at least 1 to 2 orders of magnitude since 8 ma this corresponds to a temperature increase of at least 75 to 100 c at the moho in our opinion the most likely source of this temperature increase is a regional scale thermal event within the underlying mantle and diffusion of heat upward into the lower crust if correct these results have important implications for the way in which crustal extension is linked to mantle heating within the basin and range province

crustal thickness variations beneath the peninsular ranges southern california we investigate the crustal thickness under the peninsular ranges using p to s converted phases of teleseismic body waves recorded on a temporary broadband seismometer array and isolated by the receiver function method ps minus p times at sites west of a compositional boundary that separates the peninsular ranges batholith into east and west zones indicate a relatively flat deep moho ps minus p times at sites east of the compositional boundary decrease eastward moho depth estimates made from the ps delays and crustal velocities from seismic tomography indicate a relatively constant 36 to 41 km thick crust in the western zone in the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the salton trough a lateral distance of 30 km the lack of correlation between topography and moho depths suggests compensation via lateral density variations in the lower crust or upper mantle we propose that the compositional boundary decouples the eastern and western portions of the batholith and that the eastern portion has thinned in response to regional miocene extension or salton trough rifting or both

lithospheric deformation beneath the san gabriel mountains in the southern california transverse ranges high resolution tomographic images from los angeles region seismic experiment larse array and southern california seismic network scsn teleseismic data suggest that the entire lithosphere below the san gabriel mountains and san andreas fault in the transverse ranges has thickened in a narrow vertical sheet p wave travel time inversions of the combined data support the presence of the well documented upper mantle high velocity anomaly that extends 200 km into the mantle under the northernmost los angeles basin and transverse ranges and is associated with mantle downwelling due to oblique convergence we find that the high velocity high density upper mantle anomaly comprises a 60 80 km wide sheet of mantle material that lies directly below a substantial crustal root in the san gabriel mountains the velocity perturbations are as large as 3 in the anomaly corresponding to a 2 density increase the tomographic images suggest that deformation in the ductile lower crust and mantle lithosphere may be partially coupled mechanically and thermally if the thickening is occurring together in response to convergence and that it may be a local compressional feature

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

three dimensional vp and vp vs velocity models of the los angeles basin and central transverse ranges california we use p and s arrival times from 5225 earthquakes and 53 explosions recorded by the southern california seismographic network to invert for the three dimensional p velocity v p and the p and s velocity ratio v p v s in the central transverse ranges and the los angeles basin to model long wavelength features of the velocity structure we invert for the models by interpolating models determined successively from a sparse medium to a dense grid with 40 20 and 10 km spacing of horizontal grid nodes layers of grid nodes are placed at depths of 1 4 6 8 12 16 and 20 km the data variance decreased about 80 in the gradational inversion ample data from the 1994 northridge and other earthquake sequences the rich background seismicity and the dense station distribution along with controlled sources made the model well resolved except along the edges to the southwest in the offshore region and at depths greater than 20 km the v p model images the shape of the los angeles and east ventura basins down to depths of 8 and 12 km three low velocity areas at 1 km depth in the los angeles basin that coincide with recent sediment depositional areas are also imaged the north edge of the peninsular ranges the santa monica and the san gabriel mountains form discontinuous high velocity ridges extending to depths of 20 km the high v p v s ratios in the near surface are consistent with high pore fluid pressures in the basin sediments at depth beneath the east ventura basin the high v p v s and high v p suggest the presence of ophiolitic assemblages or mid miocene volcanics in contrast a body with normal v p and low v p v s that is identified in the upper crust beneath santa monica bay may be a fragment of quartz rich continental crust the v p model of both the ventura and the los angeles basins shows features that suggest deformation of the hanging wall or basin closure at seismogenic depths of 16 km the hypocenters of moderate sized and large earthquakes are located within or adjacent to high v p velocity bodies in most cases these high velocity bodies form the upper block consistent with shortening of the lower crust as described in thick skinned tectonic interpretations

history of sedimentary infilling and faulting in subic bay philippines revealed in high resolution seismic reflection profiles abstract subic bay sediments and faults identified in seismic reflection profiles were dated using sea level curves the oldest sedimentary packages are marine sediments subaerially exposed and eroded 20 ka fluvio marine to wholly marine sediments were deposited during the ensuing transgression and prograding units were deposited during stillstands or minor sea level falls faults within the bay have three age ranges the oldest set cuts through the pre 18o stage 2 rock units 18 ka a second disrupts 10 2 11 3 ka sediments and the youngest which cut the uppermost sedimentary package show that movements occurred about every 2 ky most recently about 3 ka northwest southeast faults that parallel onshore structures associated with paleogene emplacement of the zambales ophiolite complex to the west and north likely represent rejuvenated tectonism the northern coastline and north south trending axial bay islands appear related to a lineament that dissects mt pinatubo farther northeast a breach in the caldera of mt natib is the most likely source of a presumed pyroclastic deposit in the eastern bay that is associated with sediments about 11 3 18 ka indicating that a natib eruption occurred much more recently than previously documented for this volcano

surf beat induced overwash during typhoon haiyan deposited two distinct sediment assemblages on the carbonate coast of hernani samar central philippines abstract wave set up steepened and accentuated the storm surge during typhoon haiyan in november 2013 resulting in bore like flooding with surge heights of 7 m and flow velocities reaching 5 m s 1 on the open sea coastal plain near hernani this study investigates two distinct sediment assemblages left behind by the coastal flooding associated with this surge the first assemblage consists of numerous coastal boulders that now occupy the reef flat and the second pertains to a laterally extensive sand sheet that blanketed the coastal plain up to 300 m inland the majority of the boulders has b axes between 1 and 2 m weigh no 10 t and were originally submerged on the reef edge the boulders found more landwards of the reef edge were potentially lying loosely on the reef flat prior to haiyan in contrast the coarse carbonate sand sheet starts at 10 m inland of the current shoreline and has a maximum thickness of 10 cm and gradually thins to 3 mm at 300 m inland the haiyan sand contains moderate concentrations of foraminifera amphistegina spp baculogypsina sphaerulata and peneroplis spp that were both abraded and unaltered pointing to a reef flat and beach source for the sand sediment transport inverse modeling complements previous flow velocity estimates using numerical modeling which altogether indicate sustained high velocity overland flow despite the presence of coral reefs and mangroves as natural defenses to extreme waves

systematic receiver function analysis of the moho geometry in the southern california plate boundary region we investigate the geometry of the moho interface in the southern california region including the san andreas fault saf san jacinto fault zone sjfz elsinore fault ef and eastern california shear zone with systematic analysis of receiver functions the data set consists of 145 teleseismic events recorded at 188 broadband stations throughout the region the analysis utilizes a 3d velocity model associated with detailed double difference tomographic results for the seismogenic depth section around the saf sjfz and ef combined with a larger scale community model a 3d ray tracing algorithm is used to produce effective 1d velocity models along each source receiver teleseismic ray common conversion point ccp stacks are calculated using the set of velocity models extracted for each ray the ccp stacks are analyzed with volumetric plots maps of maximum ccp stack values and projections along profiles that cross major faults and other features of interest the results indicate that the moho geometry in the study area is very complex and characterized by large prominent undulations along the ne sw direction a zone of relatively deep moho 35 40 km with overall n s direction crosses the saf sjfz and ef a section of very shallow moho 10 km below and to the se of the salton trough likely associated with a young oceanic crust produces large moho offsets at its margins locations with significant changes of moho depth appear to be correlated with fault complexity in the brittle crust the observations also show vertical moho offsets of 8 km across the saf and sjfz close to cajon pass and sections with no clear moho phase underneath cajon pass and adjacent to the sjfz near anza likely produced by complex local velocity structures in the brittle upper crust these features are robust with respect to various parameters of the analysis procedure

geothermal evidence from canada for a cold period before recent climatic warming three deep boreholes in a small area in quebec each having two high accuracy temperature logs separated by 22 years allow reliable determination of the ground surface temperature history during the past few centuries the temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area the presence of such a cold period is also suggested by borehole temperature data from other areas in canada

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

interpretation of crustal seismic velocities in the san gabriel mojave region southern california the increased concern over seismic hazards in the los angeles region has created interest in the crustal structure and mechanical properties associated with faults like the sierra madre and san andreas this study presents the seismic properties of major lithologies found in the vicinity of the san andreas fault zone in order to correlate with the los angeles region seismic experiment lars e results scientists from the larse group have recently acquired high quality seismic data along three transects thirty nine rock samples were collected along the larse line i which trends ne sw across the central mojave desert and the san gabriel mountains these rock samples represent the following lithologies precambrian gneisses san gabriel anorthosite mesozoic granitic intrusives pelona schist mendenhall granulite gneisses and san andreas fault zone cataclasites the seismic properties were determined by measuring compressional and shear wave velocities as a function of confining pressure average compressional and shear wave velocities at 150 mpa show a wide range of values the mendenhall gneiss and the san gabriel anorthosite complex have high velocities 6 5 km s and 6 4 km s respectively the pelona schist the mojave granitic intrusives and the san andreas cataclasitic rocks have average velocities of 5 8 km s 5 2 km s and 5 1 km s respectively average densities range from 2320 kg m3 for fault zone cataclasites to 3100 kg m3 for a mendenhall granulite gneiss gneisses and schists show significant seismic anisotropy 5 20 due to preferred mineral orientation while most other rocks are nearly isotropic poisson s ratios range from a high of 0 29 in the san gabriel anorthosite to a low of 0 22 in the san gabriel gneiss comparison of the measured seismic properties with the larse velocity model allows interpretation of crustal structure in terms of rock compositions the upper crust southwest of the san andreas fault contains granitic intrusives gneisses and schists while under the mojave desert the upper crust is dominated by gneisses high velocities under the san gabriel mountains represent either lower crustal granulites or anorthosite the velocity decrease beneath the san andreas fault zone originates from minor amounts of cataclasite or the presence of low velocity lithologies such as pelona schist 1998 elsevier science b v all rights reserved

cenozoic and mesozoic structure of the eastern basin and range province utah from cocorp seismic reflection data cocorp seismic reflection data collected from the eastern basin and range in west central utah provide information on cenozoic extensional tectonics mesozoic thrusting and their interrelationships those data show a series of remarkably continuous low angle reflectors that extend more than 120 km perpendicular to strike and can be traced as deep as 15 20 km over that distance none of these events are significantly cut by any high angle normal faults a major detachment beneath the sevier desert can be traced from a surface zone of normal faulting to a depth of 12 15 km with a regional apparent westward dip of 12 tentative correlation of upper and lower plate events suggests 30 60 km of extensional displacement on this detachment whether this structure is a reactivated mesozoic thrust is uncertain west steepening splays off the end of the detachment reach depths of 20 km and may represent a major mesozoic ramp or zones of distributed ductile shearing during extension some events are interpreted to be mesozoic thrusts of which at least one beneath the house range has been reactivated during the cenozoic the snake range decollement dips gently east and has a sense of cenozoic displacement opposite to that of other cenozoic detachments farther east deep events are most numerous beneath the east side of the sevier desert where they occur to depths of 30 km at the top of or perhaps partly within the anomalously low velocity upper mantle

paleoenvironmental investigations chemical analysis and characterization of underwater strata of marigondon cave abstract the submarine marigondon cave mc is not only one of the most spectacular diving caves but also an unstudied submerged rock shelter with potential for intact stratigraphy the marigondon cave yielded two rock samples one coral limestone fossil with a travertine mantle and a sclerosponge specimen that provided evidence to understand the external and environmental conditions to which the cave might have been exposed the study s aimed to determine the links between the cave s underwater conditions and the samples studied analytical methodologies such as ir spectroscopy x ray diffraction optical microscopy sem edx and u series isotope analyses were carried out to determine the chemical composition of two rock samples and their crystal structures and formation ages results concluded that the two samples were composed mainly of the two calcium carbonate polymorphs calcite and aragonite however the sclerosponges contained a low percentage of mg calcite illustrating a period of submergence at other periods marigondon cave would have been above water and favorable for pleistocene fauna as well as possibly human settlement as demonstrated by the travertine deposit on the coral limestone this suggests that mc provides prospects for discovery of fossil assemblages that may be preserved in terrestrial deposits in the caves during periods of emergence these periodic submersions conform to eustatic sea level changes during the past 130 000 years during the late pleistocene and demonstrate that in that period a marine coral reef platform was the substrate within which the marigondon cave formed as a flank margin cave during nearly 80 000 years of emergence when sea level was lower than the present elevation of the cave

uplifted marine terraces in davao oriental province mindanao island philippines and their implications for large prehistoric offshore earthquakes along the philippine trench abstract we conducted systematic mapping of holocene marine terraces in eastern mindanao island philippines for the first time raised marine platforms along the 80 km long coastline of eastern davao oriental province are geomorphic evidence of tectonic deformation resulting from the westward subduction of the philippine sea plate along the philippine trench holocene coral platforms consist of up to four terrace steps t1 1 5 m t2 3 6 m t3 6 10 m and t4 8 12 m amsl from the lowest to highest respectively terraces are subhorizontal exposing cemented coral shingle and eroded coral heads while terrace risers are 1 3 m high radiocarbon ages 8080 4140 cal yr bp reveal that erosional surfaces were carved onto the holocene transgressive reef complex which grew upward until 8000 years ago the maximum uplift rate is 1 5 mm yr based on the highest holocene terrace at

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

crustal structure and tectonics from the los angeles basin to the mojave desert southern california a seismic refraction and low fold reflection survey known as the los angeles region seismic experiment larse was conducted along a transect line 1 extending from seal beach california to the mojave desert crossing the los angeles and san gabriel valley basins and san gabriel mountains the chief result of this survey is an interpreted cross section that addresses a number of questions regarding the crustal structure and tectonics of southern california that have been debated for decades and have important implications for earthquake hazard assessment the results or constraints are as follows 1 the maximum depth of the los angeles basin along line 1 is 8 9 km 2 the deep structure of the sierra madre fault zone in the northern san gabriel valley is as follows the duarte branch of the sierra madre fault zone forms a buried 2 5 km high moderately north dipping buttress between the sedimentary and volcanic rocks of the san gabriel valley and the igneous and metamorphic rocks of the san gabriel mountains for deeper structure see following 3 there are active crustal decollements in southern california at middle crustal depths the sierra madre fault zone appears to sole into a master decollement that terminates northward at the san andreas fault and projects southward beneath the san gabriel valley to the puente hills blind thrust fault 4 the dip and depth extent of the san andreas fault along line 1 dips steeply 83 northward and extends to at least the moho 5 the subsurface lateral extent of the pelona schist in southern california is as follows along line 1 the pelona schist underlies much if not all of the san gabriel mountains south of the san andreas fault to middle crustal depths north of the san andreas fault it is apparently not present along the transect

holocene antarctic melting and lithospheric uplift history of the southern okinawa trough inferred from mid to late holocene sea level in iriomote island ryukyu japan abstract relative sea level deduced from fossil oysters and mangroves are reported for iriomote island ryukyus southwestern japan radiocarbon dated fossil oysters as well as previously analyzed mangrove muds are compared to geophysical and glacio hydro isostatic adjustment gia models that describe earth deformation due to changing surface loading the holocene high stand hhs inferred from oyster fossils saccostrea echinata and saccostrea malaboensis is 2 7 m at ca 3500 years ago after which sea level gradually fell to present level the hhs magnitude attributed to gia for the last ca 4000 is between 1 and 1 5 m above present day sea level and the residual indicates the long term lithospheric uplift rate of the island the timing of peak hhs also indicates that late holocene melting mainly from antarctica ceased by approximately 4000 years ago

holocene sea level highstand and its implications for the vertical stability of panglao island southwest bohol philippines abstract emerged tidal notches in panglao island southwest bohol central philippines were used to investigate relative sea level changes during the holocene the elevation and profile of a laterally continuous notch were surveyed at 22 sites around panglao island the tidal notch documents higher than present mean sea level pmsl consistent with regional field observations and predictions for mid holocene time the reconstructed paleo shoreline elevations range from 0 to 1 6 m above pmsl exhibiting a general increase to the northeast the more protected part of the coast this lateral variation in the holocene paleo mean sea level msl along with changes in notch depth and profile suggests tilting of the island best explained by differential land movement last interglacial msl estimates by previous workers also show tilting to the southwest moreover the holocene notch data suggest segmentation of the island into several blocks that tilt consistently to the southwest suggesting the presence of faults lineations in aerial photographs trending northeast southwest confirm the presence of these faults these data indicate differential land movements during the holocene and late pleistocene calculated rates of uplift are 0 3 and 0 06 mm yr for the holocene and for the late pleistocene respectively these values relative to the high uplift rates from tectonically active regions imply that panglao is relatively vertically stable after accounting for tectonic tilting mid holocene sea level is estimated at approximately 0 3 0 6 m

overview of the cocorp 40 n transect western united states the fabric of an orogenic belt the cocorp 40 n transect of the cordillera of the western united states crosses tectonic features ranging in age from proterozoic to recent and provides an acoustic cross section of a complex orogen affected by extension compression magmatism and terrane accretion the key features of the transect centered on the basin and range province include 1 asymmetric seismic fabrics in the basin and range including west dipping reflections in the eastern part of the province and predominantly subhorizontal ones in the west 2 a pronounced reflection moho at 30 2 km and locally as deep as 34 km in the basin and range with no clear sub mono reflections and 3 complex dipping reflections and diffractions locally as deep as 48 km in the colorado plateau and sierra nevada the eastern part of the transect shot above known and inferred precambrian crystalline basement probably records features related to the entire history of the orogen locally perhaps as old as 1800 ma in this region major paleotectonic features probably controlled subsequent structural development in title western half of the transect however most reflectors are probably no older than mesozoic within the basin and range province there appears to be a strong cenozoic overprint that is characterized by asymmetric half grabens low angle normal faults and a pervasive subhorizontal system of reflections in the lower crust no one model of intracontinental extension is universally applicable processes that produce or are accompanied by thermal anomalies magmatism enhanced ductility and extension appear to be essential in developing a highly layered lower crust

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

a comparative study of the 2013 typhoon haiyan overwash sediments from a coastal cave and beach system at salcedo eastern samar central philippines abstract typhoon haiyan crossed the central philippines on 8 november 2013 and generated storm surge up to 7 m with runup reaching 12 m which deposited overwash sediments inland in many different locations and environments collectively these overwash sediments serve as key modern analogs to compare with geological records of storm events in the region to date comparatively few studies have been conducted on sandy storm deposits in carbonate coasts with none to date on storm sediments in coastal caves here we report the grain size and microfossil assemblages of the typhoon haiyan overwash sediments from a coastal cave and carbonate beach system in eastern samar central philippines and infer the source of the haiyan overwash sediments we show that overwash sediments inside and immediately outside the cave beach system are similar but they can be discriminated from the underlying pre haiyan soil through field evidence grain size organic matter and microfossil content to investigate the source of both the cave and non cave overwash sediments and in the absence of pre storm beach sediment samples we collected post haiyan beach sediments in february 2018 when the beach has indicated recovery to its pre storm condition we assume that these post haiyan beach sediments are representative of pre storm sediments the underlying pre haiyan soil comprises poorly sorted coarse to very coarse sands with higher organic matter content and a lower microfossil concentration also the pre haiyan soil contains foraminifera species similar to those identified in the haiyan overwash sediments but rarely containing subtidal foraminifera species in comparison the haiyan overwash sediments share similar attributes with the post haiyan coastal sediments consisting of moderately sorted gravelly sands predominantly carbonate grains with low organic matter content the typhoon haiyan overwash sediments contain foraminifera species dominated by amphistegina radiata baculogypsina sphaerulata calcarina gaudichaudii calcarina splengeri suggesting an intertidal environment although lower abundances of benthic species peneroplis planatus and quinqueloculina parkeri imply contributions from the subtidal environment notably the haiyan overwash sediments dominantly contain intertidal foraminifera species with abraded tests similar to foraminifera found in the post haiyan beach sediments the similarity of foraminiferal assemblage and taphonomic condition strongly indicates that the overwash sediments found on the coastal cave were most likely sourced from the beach and reef flat our results show overwash sediments in coastal caves are indistinct from those in the nearby beach system indicating the potential of coastal caves to harbor well preserved archives of paleo storm deposits

the san gabriel mountains bright reflective zone possible evidence of young mid crustal thrust faulting in southern california abstract during the los angeles region seismic experiment larse a reflection refraction survey was conducted along a line extending northeastward from seal beach california to the mojave desert crossing the los angeles basin and san gabriel mountains shots and receivers were spaced most densely through the san gabriel mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area a stack of common midpoint cmp data reveals a bright reflective zone 1 s thick that dominates the stack and extends throughout most of the mid crust of the san gabriel mountains the top of this zone ranges in depth from 6 s 18 km depth in the southern san gabriel mountains to 7 5 s 23 km depth in the northern san gabriel mountains the zone bends downward beneath the surface traces of the san gabriel and san andreas faults it is brightest between these two faults where it is given the name san gabriel mountains bright spot sgmbs and becomes more poorly defined south of the san gabriel fault and north of the san andreas fault the polarity of the seismic signal at the top of this zone is clearly negative and our analysis suggests it represents a negative velocity step the magnitude of the velocity step is approximately 1 7 km s in at least one location an event with positive polarity can be observed 0 2 s beneath the top of this zone indicating a thickness of the order of 500 m for the low velocity zone at this location several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone possibly a master decollement 1 it represents a significant velocity reduction if the rocks in this zone contain fluids such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the sgmbs near lithostatic fluid pressure is required in the sgmbs such differential changes are believed to occur in the neighborhood of active fault zones where fault value action has been postulated less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke 2 it occurs at or near the brittle ductile transition at least in the southern san gabriel mountains a possible zone of concentrated shear 3 a thin reflection rising from its top in the southern san gabriel mountains projects to the hypocenter of the 1987 m 5 9 whittier narrows earthquake a blind thrust fault earthquake with one focal plane subparallel to the reflection alternatively one could argue that the bends or disruptions in the reflective zone seen at the san gabriel and san andreas faults are actually offsets and that the reflective zone is therefore an older feature possibly an older fault zone

death valley bright spot a midcrustal magma body in the southern great basin california a previously unrecognized midcrustal magma body may have been detected by cocorp deep seismic reflection profiles in the death valley region of the southern great basin high amplitude relatively broad band reflections at 6 s 15 km are attributed to partially molten material within a subhorizontal intrusion this bright spot extends laterally at least 15 km beneath central death valley a moderately dipping normal fault can be traced from the inferred magma chamber upward to a 690 000 yr old basaltic cinder cone the fault zone is inferred to have been a magma conduit during the formation of the cinder cone vertical variations in crustal reflection character suggest that the death valley magma body may have been emplaced along a zone of decoupling that separates a faulted brittle upper crust from a more ductile and or intruded lower crust the death valley bright spot is similar to reflections recorded by cocorp in 1977 in the rio grande rift where both geophysical and geodetic evidence support the inference of a tabular magma chamber at 20 km depth

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

mantle compensation of active metamorphic core complexes at woodlark rift in papua new guinea in many highly extended rifts on the earth tectonic removal of the upper crust exhumes mid crustal rocks producing metamorphic core complexes these structures allow the upper continental crust to accommodate tens of kilometres of extension but it is not clear how the lower crust and underlying mantle respond also despite removal of the upper crust such core complexes remain both topographically high and in isostatic equilibrium because many core complexes in the western united states are underlain by a flat moho discontinuity it has been widely assumed that their elevation is supported by flow in the lower crust or by magmatic underplating these processes should decouple upper crust extension from that in the mantle in contrast here we present seismic observations of metamorphic core complexes of the western woodlark rift that show the overall crust to be thinned beneath regions of greatest surface extension these core complexes are actively being exhumed at a rate of 5 10 km myr 1 and the thinning of the underlying crust appears to be compensated by mantle rocks of anomalously low density as indicated by low seismic velocities we conclude that at least in this case the development of metamorphic core complexes and the accommodation of high extension is not purely a crustal phenomenon but must involve mantle extension

philippine fault a key for philippine kinematics on the basis of new geologic data and a kinematic analysis we establish a simple kinematic model in which the motion between the philippine sea plate and eurasia is distributed on two boundaries the philippine trench and the philippine fault this model predicts a velocity of 2 to 2 5 cm yr along the fault geologic data from the visayas provide an age of 2 to 4 ma for the fault an age in good agreement with the date of the beginning of subduction in the philippine trench the origin of the philippine fault would thus be the flip of subduction from west to east after the locking of convergence to the west by the collision of the philippine mobile belt with the eurasian margin

post laramide removal of the farallon slab western united states i propose that post laramide removal of the subhorizontally subducting farallon slab occurred by buckling downward along an approximately east northeast trending axis this process was accomplished by a tearing or necking separation of the subducted slab near the northern and southern boundaries of the united states and propagation of the separated edges toward the central axis of downwelling accompanied by aesthenosphic upwelling behind the trailing edges initial buckling probably began near 50 ma and slab removal was complete by 20 ma this model is based primarily on the space time evolution of the ignimbrite flare up a major mid tertiary igneous event of mantle origin which involved two propagating fronts of initiation of volcanism that followed the proposed motions of the separated slab edges as they converged on central nevada from the north and southeast post laramide uplift extension establishment of the cascadia subduction zone and active magmatism may be consequences of lithosphere scale modifications caused by the laramide removal of the slab and the resulting asthenospheric upwelling

tectono stratigraphic terranes and detachment faulting of the south china sea and sulu sea abstract geoscientific data acquired from the south china sea and sulu sea areas by bgr since 1977 are compiled and interpreted as comprehensive data sets together with available information of commercial wells and drillsites of the ocean drilling program odp generalized stratigraphy and lithology are discussed and correlated with the interpreted seismic profiles on the basis of the stratigraphic and structural analysis 5 main tectono stratigraphic terranes are defined for the south china sea and 4 main terranes for the sulu sea respectively the dangerous grounds reed bank palawan nw borneo trough and palawan island represent terranes of continental origin which developed on the proto china margin by uniform sense low angle simple shearing within the crust in late cretaceous to early paleocene this rift was abandoned and a new westward propagating rift system developed north of the dangerous grounds reed bank area from the middle eocene to the oligocene early miocene together with seafloor spreading in the south china sea basin the leading edge of the southward drifting continental terranes collided with the late cretaceous to early eocene subduction complex of the northernmost terrane of the proto sulu sea continuous convergence of these terranes back arc spreading creating the se sulu sea terrane and the assumed anti clockwise rotation of borneo are responsible for the complex collision compression structures of the sulu sea terranes including the formation of splinters of oceanic crust major right lateral wrench systems are nnw sse running up to 500 km long and cut across most of the identified terranes wrenching presumably ceased 12 to 16 myr ago

collapse of southwestern north america and the evolution of early miocene detachment faults metamorphic core complexes the sierra nevada orocline and the san andreas fault system plate reconstructions indicate that early miocene pacific north american relative motion was not parallel to the transform but was instead oblique and transtensional we propose that the western edge of the north american plate east of the transform gravitationally collapsed to the southwest in response to this divergence the northern and eastern edges of the collapsed region underwent extension between 24 and 20 ma whereas extension in southeastern california and southern arizona during this interval was coaxial with the overall s50 60 w collapse direction the extension direction along the northern oundary mojave extensional belt was north south and the result of the combined effects of the southwestward collapse and the independent northwestward translation of the region to the north collapse continued between 20 and 16 ma and extension persisted in southeastern california and southern arizona extension along the northern boundary waned owing to the apparent cessation of motion of the region to the north thus the kinematics of the northern boundary changed to dextral shear and extension along what is here named the trans mojave sierran shear zone this east west zone of mainly right shear oroclinally folded the southern tail of the sierra nevada and the central mojave desert rocks within this 83 110 km wide zone were rotated approx 40 60 clockwise about vertical axes finally as collapse moved the north american plate progressively west across the locus of transform shear its western edge became increasingly subject to the motion of the pacific plate over time the edge of north america was truncated by faults of the san andreas system and transferred to the pacific plate

higher than present holocene mean sea levels in ilocos palawan and samar philippines abstract holocene paleo mean sea levels along the coasts of ilocos palawan and samar in the philippines are established using estimates from emerged tidal notches and coral reef terraces age control is provided by 17 14 c and 22 230 th 234 u dates the notches and terraces with the oldest dating back to approximately 8 2 ky have elevations from 0 1 to 6 7 m above the present mean sea level in each of the study sites adjacent coastal areas show different paleosea level histories in both the level and number of relative stillstands due to local faulting in ilocos paleosea levels show greater elevation and number of recorded stillstands due to a significant thrust component along this segment of the philippine fault in samar a general increase in the elevation of paleosea level to the east indicates tilting of the island towards the philippine fault abrupt changes in the elevations of correlative paleosea level indicators and an overall northeast and southwest tilting respectively of northern and southern palawan suggest the presence of active faults in central palawan discrete double notches suggest two emergent stillstands occurring between 7 3 and 2 4 ky the lower and higher notches respectively correspond to earlier and later stillstand events possible across site variation in the duration and timing of initiation and termination of these stillstands can be due to differences in regional tectonics and crustal response to hydro isostasy or an artifact of sampling

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

estimation of the magnitudes and epicenters of philippine historical earthquakes abstract the magnitudes and epicenters of philippine earthquakes from 1589 to 1895 are estimated based on the review evaluation and interpretation of historical accounts and descriptions the first step involves the determination of magnitude felt area relations for the philippines for use in the magnitude estimation data used were the earthquake reports of 86 recent shallow events with well described effects and known magnitude values intensities are assigned according to the modified mercalli intensity scale of i to xii the areas enclosed by intensities iii to ix a iii to a ix are measured and related to magnitude values the most robust relations are found for magnitudes relating to a vi a vii a viii and a ix historical earthquake data are obtained from primary sources in libraries in the philippines and spain most of these accounts were made by spanish priests and officials stationed in the philippines during the 15th to 19th centuries more than 3000 events are catalogued interpreted and their intensities determined by considering the possible effects of local site conditions type of construction and the number and locations of existing towns to assess completeness of reporting of these events 485 earthquakes with the largest number of accounts or with at least a minimum report of damage are selected the historical epicenters are estimated based on the resulting generalized isoseismal maps augmented by information on recent seismicity and location of known tectonic structures their magnitudes are estimated by using the previously determined magnitude felt area equations for recent events although historical epicenters are mostly found to lie on known tectonic structures a few however are found to lie along structures that show not much activity during the instrumented period a comparison of the magnitude distributions of historical and recent events showed that only the period 1850 to 1900 may be considered well reported in terms of magnitude distribution each earthquake is evaluated for its quality of determination based on the number of intensity reports earlier than 1850 the data collected are few and most earthquakes had fewer than ten reports good quality reports began to be collected from 1850 partly correlative to an increase in the number of towns and partly to the start of a systematized collection of earthquake accounts by the manila observatory parameters of these well reported earthquakes may be used for conducting various seismological studies examples of how the parameters of poorly reported events were arrived at are also discussed

tectonic uplift sea level changes and plio pleistocene evolution of a coastal karst system the mount saint paul palawan philippines the st paul karst palawan philippines is a tropical coastal karst consisting of towers cones huge depressions and large caves this area hosts the puerto princesa subterranean river ppsr 24 km long whose main entrance is a large spring along the coast and which is one of the largest cave complexes in eastern asia a geomorphological study performed by several field surveys and a morphometric analysis of the digital terrain model dtm and 3d cave models allowed formulation of a first evolutionary framework of the karst system the dtm was extracted from maps and aerial photographs in order to find different generations of relict landforms through the morphometric analysis of topographic surface and karst landforms several features suggest a long and multi stage evolution of the karst whose age ranges from pliocene to present the southern and northern sectors of the area differ in their altimetric distribution of caves in the southern sector some large caves lie between 300 and 400 m asl and were part of an ancient system that developed at the base level of a past river network in the northern sector some mainly vadose caves occur with a phreatic level at 120 130 m asl an important phase of base level cave development is well documented in the inactive passages of ppsr at 50 80 m asl morphological features such as horizontal solution passages and terraced deposits suggest a phase of stillstand of the base level which is recorded in the topography as low relief surfaces at 40 50 m asl the age of this phase is probably early pleistocene on the basis of assumed uplift rates the more recent caves are still active being located at the current sea level but they show more than one cycle of flooding and dewatering with calcite deposition in the ppsr several morphologic features such as two main water level notches at 12 4 and 7 7 m asl and terraced alluvial deposits suggest that the lower and active level passed through more than two high stands of sea level and so it could have formed throughout most of the middle late pleistocene copyright 2010 john wiley sons ltd

a kinematic model for the late cenozoic development of southern california crust and upper mantle a model is presented for the young and ongoing kinematic deformation of southern california crust and upper mantle that accounts for both the known late cenozoic geologic record and upper mantle structure in this model the high velocity upper mantle transverse ranges anomaly is created through the convergence and sinking of the entire thickness of subcrustal lithosphere using typical scaling relations we estimate this anomaly to be 500 c colder and 1 more dense than average southern california mantle of the same depth we infer that subcrustal lithosphere from both sides of the convergence zone participates nearly equally in the construction of the anomaly the low velocity upper mantle anomaly beneath the salton trough region is attributed to high temperatures and 1 4 partial melt related to adiabatic decompression during mantle upwelling our model has crustal motions in the central transverse ranges region differing from mantle motions while the subcrustal lithosphere south of the transverse ranges moves toward and sinks beneath the transverse ranges the corresponding crust largely avoids convergence by adopting a more westerly direction of motion the differing velocity fields necessitates of a decoupling zone immediately south of the transverse ranges near the moho we interpret the upper mantle anomalies as results of small scale convection beneath southern california to which we attribute much of the recent tectonic activity in the region

structural variety and tectonic evolution of strike slip basins related to the philippine fault system northern luzon philippines the northern part of the philippine fault zone in luzon corresponds to a complex braided system of left lateral strike slip faults the nw oriented main active branch which emerges from the philippine sea splits into an array of north striking splays responsible for the tectonic evolution of the central cordillera this complex fault pattern has favored local stress field variations strike slip basins have evolved in this framework along or in the vicinity of the main splays of the philippine fault apart from the classical pull apart tectonics on a releasing fault termination overlap or bend we describe other mechanisms such as the strike slip tilting or the warping of a strip limited by two strike slip faults the strike slip basins are good recorders of the evolution of the philippine fault system those located along the north striking cordilleran faults individualized in late early pliocene to pleistocene time when the present day philippine fault initiated but their main control is the fault shape acquired in upper middle miocene time the recent tectonic evolution of the fault system is best recorded in central luzon where the active basins trace an asymmetrical v shape with the longest branch trending ne parallel to the east luzon trough and the shortest one trending nw related to the philippine fault both the fault pattern and the basin distribution demonstrate the influence of the benham rise in the tectonic evolution of luzon the structural setting is interpreted as the result of an early miocene collision event between the benham rise and the eastern margin of luzon and subsequent inception of the nw striking strand of the philippine fault the present locations of the basins result from the interaction between the structural heritage and the present day regional plate motion

structure of the subduction transition region from seismic array data in southern peru data from three seismic arrays installed in southern peru were analysed using receiver functions from p pp and pkp wave phases in order to image the subducted nazca slab the arrays cover the transition region from flat slab subduction in central peru to normal subduction with an angle of about 30 further south a previous study used data from the first array in the normal subduction region to image the moho depth and slab and showed the existence of a mid crustal structure at 40 km depth that is suggested to be a possible underthrusting of the brazilian shield here we discuss new observations from the other two arrays that span the transition between the two subduction regimes and the flat subduction region the results provide an image of the flattened slab from the coast to approximately 300 km inland and also across the transition region from flat to 30 subduction which appears to be a bend rather than a tear in the slab in the flat slab region the slab is well defined near the coast and flattens out at 100 km depth beneath the altiplano the slab appears to start flattening some 400 km in advance of the subduction of the nazca ridge and the flattening is maintained for 1300 km after its passage the moho begins at a depth of around 30 km near the coast and has a maximum depth of 75 km beneath the altiplano consistent with the results of the other arrays both arrays also show a positive impedance mid crustal structure at 40 km depth which if explainable by underthrusting of the brazilian shield would add further support to the observations from the normal subduction region and show the northward and westward extent of the signal the underthrusting hypothesis would explain the missing crust from the shortening budget needed to support the altiplano the vp vs ratios for both arrays exhibit average values between 1 73 and 1 75 indicating a lesser likelihood that there is a high degree of partial melting or magma bodies at depth in this region the receiver function results provide new imaging of the flat slab and transition from normal to flat slab subduction which allows for comparison of different subduction regimes