short paper terrane rotations in the irish caledonides palaeozoic palaeomagnetic data from scotland and ireland have been compared on a terrane model and early caledonide clockwise rotation of a terrane through 65o 30 connemara massif and later anticlockwise rotation of up to 50 in the vicinity of clew bay have been deduced these are the firfirst estimates of terrane rotations in the european part of the caledonian appalachian orogen terrane analysis of orogenic belts is currently a major field of study to a large extent this has been stimulated by studies in the north american cordillera where large rotations and translations have been determined palaeomagnetically see beck et al 1986 and references therein terrane analysis may be applied to older orogenic belts such as the caledonides which have been particularly intensively studied previously published palaeomagnetic data from connemara morris tanner 1977 and nw galway morris et al 1973 had indicated local block rotations but furnished few constraints on either their age and magnitude or on the identities of the blocks this paper relates the currently available palaeomagnetic dataseto a terrane model of w ireland hutton dewey 1986 see fig 1 new data new palaeomagnetic data from the irish caledonides comprise the following connemara gabbro robertson 1988 the dalradian rocks of the connemara massif are unique in the british caledonides in lying to the south of a caledonian ophiolite and also south of a thick sequence of ordovician shales and volcanics of low metamorphic grade in clew bay and the south mayo trough respectively the structural

geodetic constraints on postseismic deformation following the 1990 ms 7 8 luzon earthquake and implications for luzon tectonics and philippine sea plate motion 1 we have obtained three epochs of high quality dual frequency gps data at 15 stations in the luzon philippines region since the july 16 1990 ms 7 8 earthquake from which we generate horizontal velocity fields at the earth s surface for the 1993 1996 and 1996 1998 periods we use these velocities plus 1996 1998 gps velocity results reported elsewhere from 13 additional stations to show that present day deformation in luzon is dominated by strike slip motion along the philippine fault system the measured strike slip rate across central luzon is faster than the expected long term slip rate on the fault which we attribute to postseismic deformation following the 1990 earthquake the 1993 1996 and 1996 1998 deformation patterns cannot be statistically distinguished within the 10 uncertainties of the data if the observed deformation is interpreted using an elastic half space model with uniform slip below a subsurface locking depth we find a fault slip rate of 40 mm yr and a locking depth of 15 km this is too fast to be a steady interseismic rate as it disagrees with what is known from paleoseismic and other evidence about earthquake recurrence and long term slip rate on the philippine fault system in central and northern luzon also a 15 km locking depth for steady interseismic slip is probably too shallow compared to the depth of rupture in the 1990 earthquake if the deformation is instead interpreted with two types of viscoelastic model we find that the observed velocities can be fit well for a range of values of lower lithosphere viscosity and long term slip rate using a two dimensional 2 d viscoelastic coupling model the minimum allowable lower lithosphere viscosity is 0 5 1019 pa s with an associated long term slip rate of 15 22 mm yr faster long term slip rates also fit well with correspondingly higher values of viscosity with a possibly more realistic model that includes 3 d viscoelastic effects we find preferred long term velocities in the range 20 35 mm yr and viscosities in the range 2 6 1019 pa s our preferred viscosities correspond to maxwell times on the order of 7 20 of the typical earthquake recurrence interval and are several times higher than values found for a number of californian strike slip earthquakes other implications of our 1993 1998 surface velocities are that the philippine sea eurasia ph eu euler vector of seno et al 1993 is a better description of the ph eu convergence rate than a euler vector recently estimated from gps velocities in the northern ph and that the great majority of the normal component of ph eu plate convergence is taking place west of luzon presumably largely at the manila trench we also find that luzon is rotating counterclockwise relative to ph at 1 2 myr only 25 of the rate recently suggested by other workers on the basis of limited gps data

present day stress orientations adjacent to active strike slip faults california and sumatra present day stress directions interpreted from well bore breakouts adjacent to two crastal scale active strike slip faults the san andreas fault in california and the great sumatran fault in sumatra indicate that the maximum horizontal stress direction sh is oriented at a high angle 70 90 to both faults the regionally defined stress fields spanning these faults show that adjacent young or actively growing folds have formed orthogonal to sh and are therefore in the thrust fault orientation these observations indicate a decoupling of the strike slip and compressional components of the deformation within these broadly transpressive zones borehole breakouts in 118 wells in western california indicate a regionally consistent stress pattern with sh generally oriented ne sw nearly perpendicular 80 90 to the strike of the san andreas fault the orientation of sh nearly perpendicular to the san andreas fault implies low shear stress on the fault and is consistent with geological interpretations of the coast and transverse ranges indicating active compressional deformation fault plane solutions for recent dip slip style earthquakes principal stress directions determined from inversion of earthquake focal mechanisms and induced hydraulic fracture orientations a stress trajectory map for western california is computed using an iterative statistical algorithm in which observed directional data such as breakout directions are used to obtain a model regional stress field analysis of well bore breakouts in 25 wells within the central and southern oil districts of sumatra indicates that the regionally defined sh adjacent to the active great sumatran strike slip fault is oriented at a high angle 70 80 to the fault this orientation of sh is consistent regionally with geologic stress indicators and focal mechanisms of dip slip earthquakes preliminary analysis of the stress field in the vicinity of the philippine and alpine faults suggests sh is also oriented at a high angle to these active strike slip faults similarly the minimum horizontal stress sh is oriented at a high angle to the the kane and dead sea transforms the observation of sh and sh in the vicinity of active strike slip faults being oriented nearly perpendicular and parallel to the faults suggests that large crustal scale strike slip faults may in general be inherently weak surfaces

source mechanism of the luzon philippines earthquake of july 16 1990 the luzon philippines earthquake of july 16 1990 with ms 7 8 was generated by left lateral faulting in the central luzon island ground breakage was observed along a linear trace extending 110 km the maximum horizontal offset as measured on the fault was as much as 6 m a fault area of 120 20 km2 was inferred from a field study and aftershock data this event is one of the largest strike slip earthquakes ever recorded in the world for long period surface waveform analysis we used very broadband records from 14 stations of the gdsn geoscope iris and erios networks the centroid moment tensor cmt solution from surface waves represents almost pure left lateral strike slip faulting on a steep fault with strike 155 dip 88 and rake 7 the seismic moment is 3 9 1020 nm 1027 dyn cm which gives mw 7 7 the average dislocation on the fault is 5 4 m and the stress drop is 5 2 mpa 52 bars teleseismic p and sh waves from 14 stations are used to model the spatiotemporal distribution of subevents five subevents are detected in an interval of 44 sec their sequence indicates a bilateral rupture the mean velocity of rupture toward the north is 2 7 km sec the total seismic moment of the subevents is 3 6 1020 nm the largest aftershock ms 6 6 occurred on july 17 near the recognized northern end of the main fault the cmt solution for the aftershock represents a reverse faulting with moment of 6 4 1019 nm mw 6 5 this aftershock was probably caused by compression produced by block motion of the eastern block of the main fault

paleomagnetism of the dewey lake formation late permian northwest texas end of the kiaman superchron in north america the remanent magnetization of red beds of the late permian dewey lake formation from northwest texas was investigated using thermal chemical and alternating field demagnetization after removal of a small present day viscous overprint the dewey lake shows univectorial decay of the remanence revealing a dual polarity characteristic direction of d 152 4 i 11 1 k 39 5 95 5 9 n 16 sites three polarity transitions were observed defining at least four polarity zones the observed polarity zones are roughly layer parallel and may correlate with the illawarra magnetozone at the end of the kiaman if this is so k ar age determinations of an interbedded ash layer kolker and fracasso 1985 suggest that the kiaman superchron ended before 251 4 ma the paleopole located at 51 4 n 126 2 e confirms the reliability of previously reported late permian poles from southwest united states which fall significantly off the late permian segment of the paleomagnetic euler pole pep track of gordon et al 1984 this implies that a more segmented set of small circles is required to model the north american apparent polar wander path diminishing the usefulness of the pep method

paleomagnetic study of the ordovician table head group port au port peninsula newfoundland a paleomagnetic study of the ordovician table head group in the port au port peninsula of western newfoundland reveals a simple two component magnetization history comprising a reversely magnetized stable southeasterly remanence with a shallow to moderate inclination and an unstable present day overprint pole positions for the stable component both with and without tectonic tilt correction correspond with the early to middle ordovician pole positions for north america suggesting this remanence is early although the nature of the geomagnetic field in the ordovician is not well known the polarity observed is consistent with that reported from other mid ordovician studies and appears to reflect a predominance of reverse polarity for this time interval evidence of significant rotation of any of the sites studied is absent indicating that the continental margin in this region acted in an integral rather than a fragmented fashion during deformation previously published and new but preliminary resul

earthquake induced crustal gravitational potential energy change in the philippine area abstract the crustal gravitational potential energy change gpe caused by earthquakes in the philippine area from january 1976 to november 2011 was estimated in this study the active convergence between the philippine sea plate and the sundaland eurasian margin is reflected by the greatest gains in gpe along the philippine negros and cotabato trenches whereas the manila trench is covered by a gpe loss pattern although the philippine mobile belt pmb itself is actually affected by the ongoing collision and subduction processes almost the entire philippine fault zone is dominated by gpe loss revealing a slightly extensional environment along the fault the time evolution of the cumulated gpe for different segments along the philippine archipelago shows distinct patterns due to the numerous large underthrusting events that have occurred along the philippine trench the cumulated gpe is regularly increasing in its most southern segment however in the middle segments where the palawan block enters into collision with the pmb the increase in cumulated gpe is relatively small in the most northern segment where the north luzon is located a decrease of cumulated gpe demonstrates that the seismic characteristic of the manila trench is dissimilar from other subduction systems in the world we suggest that the collision of both the palawan block and the benham rise with the pmb promotes the rotation of the pmb and facilitates the northward escape of the northeastern luzon resulting in a decrease of cumulated gpe in the northern philippines

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

fore arc deformation at the transition between collision and subduction insights from 3 d thermomechanical laboratory experiments 1 three dimensional thermomechanical laboratory experiments of arc continent collision investigate the deformation of the fore arc at the transition between collision and subduction the deformation of the plates in the collision area propagates into the subduction collision transition zone via along strike coupling of the neighboring segments of the plate boundary in our experiments the largest along strike gradient of trench perpendicular compression does not produce sufficiently localized shear strain in the transition zone to form a strike slip system because of the fast propagation of arc lithosphere failure deformation is continuous along strike but the deformation mechanism is three dimensional progressive along strike structural variations arise because coupling between neighboring segments induces either advanced or delayed failure of the arc lithosphere and passive margin the modeling results suggest that orogenic belts should experience deeper subduction of continental crust and hence higher pressure metamorphism where the two plates first collided than elsewhere along the plate boundary where collision subsequently propagated furthermore during the initial stage of collision the accretionary wedge is partially subducted which leads to lubrication of the interplate zone and a reduction of shear traction therefore a large convergence obliquity angle does not produce a migrating fore arc sliver rather the pressure force generated by subduction of the buoyant continental crust causes fore arc motion it follows that convergence obliquity during collision does not yield trench parallel deformation of the fore arc and its influence on the collision process is limited however convergence obliquity may control the geometry of the active margin during the oceanic subduction stage prior to collision and inherited structures may influence the propagation mechanism

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

the ordovician evolution of the south mayo trough western ireland the south mayo trough a broad synclinorium containing a 10 km sequence of early ordovician turbidites passing up into shallow water sandstones is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north facing arc the arc collided with the laurentian margin in early llanvirn times to deform the dalradian supergroup rifted margin clastic sequence prior to the late llandovery sinistral transcurrent faulting transposed the connemara dalradian terrane to its present position on the outboard ocean ward side of the south mayo trough the south mayo trough was fed principally by arc and ophiolite derived elastics during the arenig with an increasing metamorphic component during the llanvirn the late ordovician transpressional docking of connemara provided the southerly source for high grade metamorphic clasts in the deny veeny formation

palaeomagnetism of the early carboniferous deer lake group western newfoundland no evidence for mid carboniferous displacement of acadia early carboniferous visean to possibly earliest namurian sedimentary rocks of the deer lake group of western newfoundland rest unconformably on grenvillian basement rocks of the canadian shield which form the western border of the early palaeozoic appalachian orogen in addition to magnetically soft magnetizations directed along the present field three families of magnetization directions are found two of them referred to as n north and s south are antiparallel and prefolding and were probably acquired during the depositional process n and s are roughly of equal frequency they have a mean direction irrespective of sign of 0 7 35 2 k 40 95 8 9 and a palaeopole 21 5 n 121 8 e 10 3 6 0 corresponding to a palaeolatitude of 20 6 s this agrees with the palaeolatitude 17 5 s determined from the somewhat older early carboniferous tournaisian terenceville formation of the avalon platform on the eastern side of the appalachian orogen in newfoundland the third magnetization referred to as h roughly horizontal has a mean direction 156 8 13 3 k 37 95 10 1 and a palaeopole 45 4 n 140 3 e 10 3 5 3 corresponding to a palaeolatitude of 7 4 n we interpret this to be an early kiaman latest carboniferous to early permian overprint probably acquired chemically the palaeolatitude determined from the h overprint agrees with that determined from early carboniferous rocks of cratonic north america west of the appalachians therefore we argue early carboniferous palaeofield determinations for cratonic north america have been strongly biased by unremoved kiaman overprints because of this and because of the good agreement between early carboniferous palaeolatitudes obtained from opposite margins of the appalachian orogen we suggest that there is at present no palaeomagnetic evidence for the previously proposed 1500 km displacement from the south of an eastern portion of the appalachians acadia relative to cratonic north america during the carboniferous

interseismic deformation and moment deficit along the manila subduction zone and the philippine fault system we examine interseismic coupling of the manila subduction zone and fault activity in the luzon area using a block model constrained by gps data collected from 1998 to 2015 estimated long term slip rates along the manila subduction zone show a gradual southward decrease from 90 100 mm yr at the northwest tip of luzon to 65 80 mm yr at the southern portion of the manila trench we provide two block models models a and b to illustrate possible realizations of coupling along the manila trench which may be used to infer future earthquake rupture scenarios model a shows a low coupling ratio of 0 34 offshore western luzon and continuous creeping on the plate interface at latitudes 18 19 n model b includes the north luzon trough fault and shows prevalent coupling on the plate interface with a coupling ratio of 0 48 both models fit gps velocities well though they have significantly different tectonic implications the accumulated strain along the manila subduction zone at latitudes 15 19 n could be balanced by earthquakes with composite magnitudes of mw 8 8 9 2 assuming recurrence intervals of 500 1000 years gps observations are consistent with full locking of the majority of active faults in luzon to a depth of 20 km inferred moments of large inland earthquakes in luzon fall in the range of mw 6 9 7 6 assuming a recurrence interval of 100 years

plate convergence measured by gps across the sundaland philippine sea plate deformed boundary the philippines and eastern indonesia summary the western boundary of the philippine sea ph plate in the philippines and eastern indonesia corresponds to a wide deformation zone that includes the stretched continental margin of sundaland the philippine mobile belt pmb extending from luzon to the molucca sea and a mosaic of continental blocks around the ph australia sunda triple junction the gps geodyssea data are used to decipher the present kinematics of this complex area in the philippines the overall scheme is quite simple two opposing rotations on either side of the left lateral philippine fault clockwise to the southwest and counterclockwise to the northeast transfer 55 per cent of the ph sundaland convergence from the manila trench to the northwest to the philippine trench to the southeast further south 80 per cent of the ph sunda convergence is absorbed in the double subduction system of the molucca sea and less than 20 per cent along both continental margins of northern borneo finally within the triple junction area between the sundaland ph and australia plates from sulawesi to irian jaya preferential subduction of the celebes sea induces clockwise rotation of the sulu block which is escaping toward the diminishing celebes sea oceanic space from the eastwardadvancing ph plate to the south we identify an undeformed banda block that rotates counterclockwise with respect to australia and clockwise with respect to sundaland the kinematics of this block can be defined and enable us to compute the rates of southward subduction of the banda block within the flores trench and of eastward convergence of the makassar straits with the banda block the analysis made in this paper confirms that this deformation is compatible with the eastward motion of sundaland with respect to eurasia determined by the geodyssea programme but is not compatible with the assumption that sundaland belongs to eurasia as was often assumed prior to this study

a geological and tectonic cross section of the caledonides of western ireland geological and geophysical criteria allow division of the caledonides of western ireland into four principal zones zone 1 in the north contains grenvillian basement with late proterozoic supra crustals zone 2 contains the westport complex the deer park complex and the south mayo trough connemara and the delany dome formation occupy zone 3 zone 4 contains the south connemara group and mid to late ordovician and silurian sediments and volcanic rocks the various tectonic models proposed for these zones are discussed and a minimum tectonic model is presented which involves early ordovician collision of the northern part of zone 2 with the laurentian margin zone 1 followed by subduction flip northern part of zone 4 the site of early collision between zones 1 and 2 subsequently underwent orogenic collapse and strike slip dismemberment leading to the sinistral transpressive emplacement of zone 3 assemblages in zone 4 were accreted to the now south facing arc northwards stress transfer consequent on suturing deformed the thinned crust and overlying silurian sequences in zones 2 and 3

the cooling history of connemara western ireland from k ar and rb sr age studies k ar age determinations are reported on 26 hornblendes 17 coexisting muscovites and biotites nine muscovites and nine biotites from the dalradian connemara schists metagabbros and gneisses these are supplemented by 19 rb sr whole rock mica ages and four 40 ar 39 ar incremental heating ages on micas a long at least 75 ma and complex cooling history without a simple pattern of ages has been obtained the ages are not correlated with the grain sizes or the chemical compositions of the analysed minerals or the topographic elevation from which the samples came but there is an irregular increase of hornblende k ar ages to 480 10 ma with increase of metamorphic grade southwards towards the metagabbros and gneiss the preservation of the complex cooling pattern is ascribed to the action of syn and post metamorphic slides or faults which moved slices of the massif upwards by varying amounts closely spaced samples give results which rule out simple tilting of the massif rapid cooling c 30 ma 1 at 480 10 ma arenig llanvirn during the f3 fold phase was followed by slower cooling until 455 10 ma caradoc when renewed rapid uplift occurred possibly correlated with the southward thrusting of connemara and with synchronous renewed uplift in the scottish dalradian rocks widespread biotite k ar and rb sr ages of 440 5 ma end ordovician throughout connemara and the dalradian rocks of scotland are ascribed to the major taconic tectonic event which docked the dalradian rocks against the flanking folded ordovician successions of the midland valley and the south mayo trough biotites giving k ar ages of about 415 ma may have been reset during the late silurian folding of the cover rocks the importance of very close sampling integrated with structural studies is emphasized

present day crustal deformation along the philippine fault in luzon philippines abstract the philippine fault results from the oblique convergence between the philippine sea plate and the sunda block eurasian plate the fault exhibits left lateral slip and transects the philippine archipelago from the northwest corner of luzon to the southeast end of mindanao for about 1200 km to better understand fault slip behavior along the philippine fault eight gps surveys were conducted from 1996 to 2008 in the luzon region we combine the 12 yr survey mode gps data in the luzon region and continuous gps data in taiwan along with additional 15 international gnss service sites in the asia pacific region and use the gamit globk software to calculate site coordinates we then estimate the site velocity from position time series by linear regression our results show that the horizontal velocities with respect to the sunda block gradually decrease from north to south along the western luzon at rates of 85 49 mm yr in the west northwest direction this feature also implies a southward decrease of convergence rate along the manila trench significant internal deformation is observed near the philippine fault using a two dimensional elastic dislocation model and gps velocities we invert for fault geometries and back slip rates of the philippine fault the results indicate that the back slip rates on the philippine fault increase from north to south with the rates of 22 37 and 40 mm yr respectively on the northern central and southern segments the inferred long term fault slip rates of 24 40 mm yr are very close to back slip rates on locked fault segments suggesting the philippine fault is fully locked the stress tensor inversions from earthquake focal mechanisms indicate a transpressional regime in the luzon area directions of 1 axes and maximum horizontal compressive axes are between 90 and 110 consistent with major tectonic features in the philippines the high angle between 1 axes and the philippine fault in central luzon suggests a weak fault zone possibly associated with fluid pressure

spatial variations of the crustal stress field in the philippine region from inversion of earthquake focal mechanisms and their tectonic implications abstract this paper presents the spatial variations in the crustal stress field for the philippine region based on the stress configuration we divided the stress regime in the area of the philippines into four parts 1 trench perpendicular compressive stress axes 1 with an intermediate plunge were observed along the eastern subduction systems of the philippine mobile belt pmb which suggests that the subduction of the philippine sea plate psp is the primary factor controlling the stress distribution 2 characterized by systematically rotated 1 with very shallow plunge the central western portion of the philippines appears to be largely affected by the collision between the palawan block and the pmb 3 the 1 distribution in the northern part of luzon island north of 14 n is compatible with the plate motion of the psp whereas the extensional axes 3 has a fan shaped stress signature with n s direction at the south and a more spreading direction to the north which implies its north escapement 4 bounded by the scarborough seamount the northern and southern portions of the manila trench reveal a very distinct stress pattern with a trench parallel 3 to the north and a trench perpendicular 3 to the south this observation may infer a potential effect caused by the presence of the oceanic bathymetric highs on the behavior of the subduction process in addition to the identification of the four provinces with different stress regimes we suggest that the philippine fault zone may play an important role to alter the stress state in the region of the philippines

siluro devonian palaeomagnetism terrane emplacement and rotation in the caledonides of western ireland summary the palaeomagnetism of a silurian succession lough mask formation lavas and sediments and intrusive rocks kilbride dolerites and andesites and microgranodiorites killary harbour area in the connemara mayo segment of the irish caledonides is described magnetizations are related to the regional tectonic history with the aid of fold conglomerate and contact tests they describe sequences of shallow to intermediate inclinations in both the eastern and western sectors of this caledonian inlier the shallow components appear to pre date siluro devonian folding while the intermediate ones post date this episode the change in palaeofield inclination is identical to the transition described by contemporaneous deep level silurian to shallow and surface level lower devonian bodies in the british and scandinavian caledonides but declinations are rotated consistently to the west the lower middle silurian vector is rotated clockwise by c 100 this difference is progressively reduced to c 50 by the time of the siluro devonian d2 folding showing that this fold generation now oriented e w developed in parallelism with contemporaneous folds on the ne strike continuation of the caledonides post folding remanences continue to deviate in a clockwise sense from the remainder of the caledonides showing that rotation continued into middle upper devonian times and finally ceased during carboniferous times the integrated effect of this rotation is recognized in ordovician magnetizations from the dalradian metamorphic terrane of south connemara it can be explained by block rotations within a zone of distributed deformation according to the mckenzie jackson model and illustrated by many neovolcanic zones palaeomagnetism defines a tectonic regime commencing with rotations of c 3 myr and lasting from mid silurian to carboniferous times western ireland is sited within a closure gap along the iapetus suture extending from ireland to newfoundland and these terranes were apparently emplaced by progressive elimination of this gap during sinistral transpression across the caledonian orogen

detection of creep along the philippine fault first results of geodetic measurements on leyte island central philippine geodetic trilateration gps measurements were acquired from experiments conducted in 1991 and 1993 in the central part of the philippine fault on leyte island displacement vectors deduced from two least squares adjustments indicate a mean slip rate of 26 10 mm yr at an azimuth of about n130 e these values are consistent with the tectonic and kinematic data our results indicate that the displacements are 1 almost parallel to the philippine fault and 2 related to creep along the fault because no moderate seismic events occurred between the two observation epochs

a synthesis and review of historical eruptions at taal volcano southern luzon philippines abstract the philippines is an area of persistent volcanism being located in one of the most tectonically active regions in the world taal volcano in southern luzon is the second most frequently erupting volcano of the 24 active volcanoes in the philippines a comprehensive and critical review of published and unpublished references describing the 33 known historical eruptions of taal may provide answers to knowledge gaps on past eruptive behavior processes and products that could be utilized for hazard and risk assessment of future eruptions data on the prehistoric eruptions and evolution of taal caldera and subsequent deposits are limited only four caldera forming events were identified based on four mapped ignimbrite deposits from oldest to youngest these are the silicic alitagtag ali and caloocan cal pumice flow deposits the dacitic sambong ignimbrite sam and the basaltic andesitic taal scoria flow renamed scoria pyroclastic flow sfl except for sfl with 14c dating yielding 5380 70 to 6830 80 ky there are no age constraints or estimates of extent for the three older deposits a comprehensive review of the historical eruptions of taal volcano is the central element of this paper and includes all eruptions from ad1572 the first known historic event to ad1977 eruption styles and the interplay between processes and products for each eruption are reinterpreted based on the narrative descriptions from all available accounts a change of classification of eruption styles and eruptive products is undertaken for some events at least nine reported eruptions were deemed uncertain including the ad1605 ad1611 event more likely seismic swarms the ad1634 ad1635 and ad1645 may simply be solfataric or hydrothermal activity events and the ad1790 ad1825 ad1842 ad1873 and ad1903 events that were listed in recent published and unpublished documents but do not provide any details to describe and confirm the eruptions except for listing a default vei of 2 pyroclastic density currents brought devastating impacts to the communities around taal during the ad1749 ad1754 ad1911 and ad1965 eruptions and remain the biggest threat in the case of renewed volcanic activity significant implications for aviation are implied by the narrative of tephra fall dispersal towards manila the central gateway of international aviation operation in the philippines during the ad1754 eruptions the dispersal of tephra in the event of an explosive eruption at taal towards metro manila would have catastrophic effects to transport utilities and business activity potentially generating enormous economic losses hazards from earthquake events associated with future volcanic activity may also have localized impacts occurrences of liquefaction phenomena as a consequence of severe ground shaking are interpreted during the ad1749 ad1754 and ad1911 eruptions more work needs to be done to develop a comprehensive understanding of the hazards and risks associated with an explosive eruption at taal volcano especially related to the older quaternary caldera forming eruptions that produced large volume pyroclastic deposits that are extensively distributed and exposed we acknowledge that there may be additional prehistoric eruptions where the eruptive products have not been preserved recognized or reported events that cannot be verified or do not have sufficient details to confirm the eruption have been downgraded to uncertain eruptions that are confirmed with identified dispersal and emplacement of tephra fall and other eruptive deposits as interpreted from narrated records could provide crucial information that may be utilized in hazard assessment

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

arc and backarc geochemical signatures of the proto philippine sea plate insights from the petrography and geochemistry of the samar ophiolite volcanic section abstract remnants of a cretaceous lithosphere are found at the peripheries of the west philippine basin these mesozoic fragments preserve arc affinity and include the amami plateau the east halmahera ophiolite and the ophiolites along the eastern margin of the philippine archipelago the eastern margin of the philippines is composed of early to late cretaceous ophiolites and ophiolitic complexes that exhibit strong subduction imprints the early late cretaceous samar ophiolite in the central philippines forms part of this eastern belt recent surveys in southern samar revealed the presence of peridotites gabbros and massive and pillowed flows of the samar ophiolite major trace and rare earth element signatures of the volcanic rock samples indicate moderate to strong subduction related influences and formation in an island arc setting in contrast to other similarly aged ophiolites along the eastern margin of the archipelago those to the north of samar island exhibit weak to almost mid oceanic ridge characteristics these differences in the geochemical signatures of the ophiolites and ophiolitic complexes along eastern philippines require a re evaluation of a previous model suggesting that these ophiolites originated from a single oceanic lithosphere possibly the proto philippine sea plate

paleomagnetism of lower cambrian volcanics and a cross cutting cambro ordovician diabase dyke from buckingham quebec the buckingham area quebec is characterized by cambrian volcanic flows 573 32 ma cut by a cambro ordovician diabase dyke which is dated at 497 14 ma by k ar method the volcanics yield multicomponent magnetizations a hard characteristic magnetization and a relatively soft one these components could be separated easily and the intensity decay curves of the different components could also be obtained separately using zijderveld s method three different groups of site mean characteristic magnetizations can be distinguished each representing a different stratigraphic level the paleopoles derived from these magnetizations are from oldest to youngest 186 e 10 s 173 e 01 n and 154 e 06 n this is interpreted as a rapid motion of the paleopole for the north american craton during the early cambrian the paleopole derived from the hard characteristic dyke direction is 123 e 03 s this magnetization direction was also found at one of the sites in the volcanics this means that the contact test

role of strike slip faulting in the evolution of allochthonous terranes in the philippines concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate collide with the upper plate and are emplaced there movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip in the northern philippines allochthonous terranes originate primarily within the arc system have been translated along it by strike slip faults and were emplaced by cessation of that slip the authors suggest that in the philippines some originally vertical strike slip boundaries may have evolved into shallow dipping sutures marked by fold and thrust systems this mode of terrane evolution may be more common than generally appreciated particularly in orogenic belts developed in response to oblique convergence

oroclinal bending in the caledonides of western ireland new palaeomagnetic data from the caledonides of western ireland indicate that the silurian rocks of south mayo underwent oroclinal bending following folding in siluro devonian time bending was accommodated on faults cutting the silurian sequence and was driven by strike slip motion across the antrim galway line a recently recognized major curvilinear lineament we propose that the silurian rocks in the east of the region suffered up to 30 clockwise rotation increasing towards the west to approximately 70 this newly inferred differential rotation of the silurian rocks about a sub vertical axis implies that the underlying dalradian rocks of the connemara massif to the south must also have undergone clockwise rotation in late silurian early devonian time this is consistent with published palaeomagnetic data from the connemara gabbro and accounts for the swing in strike of the caledonian orogen in this part of western ireland from this we deduce that the swing in strike of the caledonian rocks elsewhere on the west coast of ireland might have a similar explanation

a middle late silurian paleomagnetic pole from limestone reefs of the wabash formation indiana u s a a middle late silurian paleomagnetic pole has been obtained from reefal limestones in north central indiana eleven of 25 collected sites yielded well clustered characteristic directions after stepwise alternating field demagnetization one additional site gave the same characteristic direction after great circle analysis these 12 site level directions were used to calculate the mean paleomagnetic pole reef flank beds dip steeply about 38 away from reef centers field and petrographic studies demonstrate that part of this dip is a primary depositional dip and that part is due to a tilt caused by early postdepositional differential compaction of underlying mudstone beds present attitudes of geopetal surfaces indicate that the postdepositional component of the observed bedding dip is about 12 a 12 tilt correction to paleomagnetic directions from oppositely dipping flank beds brings the mean directions into significantly better agreement indicating that the magnetization was acquired early the presence of both normal and reversed polarities also suggests early acquisition of the characteristic remanence the mean of the site paleomagnetic poles with sites from steeply inclined flank beds corrected for 12 of tilt is 16 8 n 124 9 e k 74 a95 5 1 in good agreement with the middle silurian rose hill pole for north america

paleomagnetism of the cambrian royer dolomite and pennsylvanian collings ranch conglomerate southern oklahoma an early paleozoic magnetization and nonpervasive remagnetization by weathering the cambrian royer dolomite in the arbuckle mountains oklahoma contains an early paleozoic magnetization and a nonpervasive late paleozoic remagnetization caused by meteoric fluids the royer was uplifted and underwent karst conditions and eroded clasts were deposited in the collings ranch conglomerate during the pennsylvanian an early paleozoic depositional or chemical remanent magnetization dec 109 inc 10 tilt corrected residing in magnetite is found in gray brown ferroan dolomite a pennsylvanian permian chemical remanent magnetization crm residing in hematite dec 147 inc 4 in situ is associated with dedolomitized rocks in an alteration zone around and below the karst features clasts of the royer in the pennsylvanian collings ranch conglomerate correlated with the parent rock by petrographic isotopic and rock magnetic methods also contain two magnetizations the clast centers contain a predepositionai magnetization whereas the clast margins contain a postdepositional crm dec 152 inc 4 in situ conglomerate tests using these magnetization components constrain the timing of remanence acquisition in the royer dolomite field relations and the results of oxygen and carbon stable isotope analyses indicate that the dedolomitization events were caused by near surface meteoric fluids that altered the royer around the margin of the karst dissolution caves and the outer rims of royer dolomite clasts remagnetization was not pervasive and an early paleozoic magnetization is preserved in the dolomite below the zone affected by weathering

palaeomagnetism of the foyers and strontian granites scotland abstract palaeomagnetic data from the newer granites of foyers and strontian show similar directions of magnetization with southerly declinations and horizontal to intermediate mostly downward dipping inclinations these palaeomagnetic directions which accord with previous data from the helmsdale granite are thought to be of siluro devonian age the present results are not sufficiently precise to justify discussion of possible lateral displacements along the great glen fault of the order of a few hundred kilometres but it is clear that the recent idea of a c 15 20 latitudinal offset along the fault in the carboniferous has to be disregarded

end silurian modifications of ordovician terranes in western ireland the ordovician elements in the caledonides of western ireland may be divided into the clew bay south mayo north connemara and south connemara sub zones evidence suggests the presence of a number of proximal suspect terranes and the remnants of one or possibly two arc complexes palaeontological and sedimentary evidence suggests an allochthonous relationship between the silurian rocks of croagh patrick and north galway these successions may therefore not represent a single sedimentary overlap to the ordovician suspect terranes end silurian deformation was the result of transpression which was responsible in part for the present configuration of the area s geology deep seated shear zones with fuchsite and gold mineralization were foci for lateral translation concomitant with southward directed thrusting northward directed back thrusts and variable degrees of metamorphism being of higher grade in the north the end silurian event is intermediate between the high grade metamorphism in parts of the appalachians and the non metamorphic silurian sequences of scotland

a basin model for the silurian of the midland valley of scotland and ireland identification of terranes is frequently based on the apparent disparity of source area for sediment supply palaeontological evidence and the presence of faults whose sense and amount of displacement is sometimes conjectural as an example of such superficially unrelated stratigraphies the silurian successions of the midland valley of scotland and the northern part of ireland are compared a diachronous late llandovery early middle telychian transgressive episode which is earlier in the midland valley inliers is common to many of the successions the transgression resulted in the development of comparable sedimentary facies and fossil assemblages the clast compositions of llandovery and wenlock conglomerates suggest erosion of a common provenance of volcanic rocks founded on a metaquartzite basement areas of active volcanism appear to have migrated in a north westerly direction with time a similar sequence is evident in canada it is suggested that the common features of the scottish irish successions may be accommodated in a unified basin model for silurian sedimentation and volcanism such a basin may have formed in an intra arc environment and been controlled by oblique slip fault mechanisms although evidence for the presence of a silurian arc is equivocal

gps observation of crustal deformation in the taiwan luzon region fifteen gps stations in the batan luzon area were surveyed three times during 1996 to 1998 in order to study crustal deformation in the taiwan luzon region the data from these annual surveys are processed together with data from 20 permanent stations in the taiwan area and igs stations in the asia pacific region we found that the chinese continental margin is moving in directions of 102 112 with rates of 11 12 mm yr relative to stable eurasia there is a significant southward increase in crustal motion with respect to eurasia along the n s trend of the luzon arc in the coastal range of taiwan the velocity is 53 mm yr in the direction 313 further south at two volcanic islands lanhsu and batan the velocities increase to 68 mm yr in the direction 306 and 81 mm yr in the direction 299 respectively in northern luzon the velocity reaches 86 mm yr in the direction 301 remarkable fault slips of 17 31 mm yr across the philippine fault system are detected

plate coupling along the manila subduction zone between taiwan and northern luzon abstract we use gps data trench parallel gravity anomaly tpga and bathymetry to infer plate coupling patterns along the manila subduction zone using a block model and a fault geometry constrained by seismicity we simultaneously solve for the location of euler pole and angular velocity between the sunda and luzon blocks as well as the slip deficit rate on plate interface our estimates show that the euler pole between the sunda and luzon blocks is situated at southern palawan near 8 3 n and 119 4 e with the angular velocity of 4 6 myr 1 the estimated convergence rate along the manila trench continuously decreases southward from 91 mm yr at the northern tip of luzon to 55 mm yr north of mindoro the inversion of gps data reveals partially locked fault patches extending from the west luzon trough to the east of scarborough seamount chain the slip deficit rate in this region is in the range of 20 30 mm yr corresponding to a coupling ratio of 0 4 however the fault slip behavior is not well resolved near the north luzon trough based on a good correlation between locations of large subduction zone earthquakes and areas possessing gravity low we investigate a variety of tpga based plate coupling models assuming different scaling between tpga values and plate coupling ratios the tpga based plate coupling models offer plausible rupture scenarios which are not constrained by current gps data the partially locked fault zone near 15 16 5 n may be associated with the subducted scarborough seamount wherein oceanic floor is highly fractured the great subduction zone earthquake propagates beneath the scarborough seamount seems to be unlikely the densification of gps network in central luzon and seafloor geodetic observations close to trench axis are crucial to distinguish the detailed fault coupling patterns and the role of subducted seamounts

role of fluids in faulting inferred from stress field signatures the stress orientation signature of weak faults containing high pressure fluids has been observed for segments of the san andreas fault system in southern california the inferred lithostatic fluid pressures extend into the surrounding relatively intact rock in a zone scaling with the width of the interseismic strain accumulation repeated strain related fracturing and crack sealing may have created low permeability barriers that seal fluids into the network of currently active fractures

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

palaeomagnetic and geochemical evaluation of a terrane linking ignimbrite evidence for the relative position of the grampian and midland valley terranes in late silurian time the proposed correlation of lower old red sandstone dacitic ignimbrites between the northern midland valley and grampian terranes of central scotland has been investigated in a combined palaeomagnetic and geochemical study statistically indistinguishable late silurian palaeolatitudes grampian terrane 27 0 s 3 5 northern midland valley terrane 22 9 s 1 8 comparable remagnetization histories a shared normal polarity for the primary magnetization and equivalent gyroremanence acquisition favour correlation across the highland boundary fault similar chemistry for biotite phenocrysts further corroborates correlation which was initially made on the basis of a similar field appearance and petrography this correlation together with evidence from provenance studies suggests that the separation of the northern midland valley and grampian terranes inferred for the ordovician period was largely removed by late silurian times with scope for relative displacements of the order of only tens of kilometres after lower old red sandstone deposition

implications of early devonian poles from the canadian arctic archipelago for the north american apparent polar wander path lower devonian red beds from the upper member of the peel sound formation at prince of wales island canadian arctic yield two different paleopoles at 25n 099e and at 01n 091e the first one being

seismotectonics of mindoro philippines article i nfo mindoro island is located where the palawan continental block indented into the philippine mobile belt during the early miocene and where the manila trench terminates having ceased convergence due to collision the seismotectonics of mindoro are crucial to understanding the processes of arc continent collision and slab dynamic responses of convergence cessation this study was conducted using data from both the ehb and global centroid moment tensor catalogues it is shown that following the southeasterly reduction of convergence rates from the manila trench offshore nw mindoro to onshore sw mindoro the slab dipping angles steepen were initiated at depth 200 km and propagate upwards the horizontal distances of the trench and slab as measured from the wadati benioff zone at 200 km depth also reduce in a southeasterly direction observations of intermediate depth earthquakes that exhibit predominantly down dip extensional stress patterns attest that the steepening of slab dipping angles is due to the negative buoyancy of the slab in contrast a broad region covered by central and south mindoro the romblon group and nw panay is characterized by a sporadic distribution of shallow earthquakes of mostly strike slip type among these the significantly sized events mw n 5 5 tend to dis tribute around the borders suggesting that the region roughly acts as a unit block moving or rotating coherently events in the vicinity of the wawa mamburao valley exhibiting normal faulting of nw se horizontal extension suggest rifting of the macolod corridor extending southwestward to nw mindoro

palaeozoic terrane accretion in the western irish caledonides the southern boundary of the early caledonides in the british isles the dalradian supergroup is represented by the major highland boundary fair head clew bay line in the west of ireland accretion along this laurasian margin occurred by sinistral strike slip during two phases the earliest was responsible for the docking of the connemara terrane a displaced part of the dalradian outboard of the south mayo trough in the llanvirnian llandeilian this event is recorded independently by radiometrically dated sinistral strike slip deformation in the ox mountains of western ireland following deposition of a silurian overlap sequence sinistral movements were renewed between the upper llandoverian and the siegennian this event is part of a major phase of sinistral strike slip throughout the british isles involving accretion of the cadomian terrane and the devonian accretion of the avalon terrane in the northern appalachians

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

paleomagnetism of the maringouin and shepody formations new brunswick a namurian magnetic stratigraphy two hundred thirty five oriented cores were taken in a stratigraphic sequence of 575 m of red sediments from the namurian maringouin and shepody formations these samples were taken from the south

the utility of gnss for earthquake early warning in regions with sparse seismic networks abstract real time global navigation satellite systems gnss data are on their way to being well integrated into earthquake early warning eew systems the strength of gnss data lies in the resolution of large dynamic and static displacements because of the limits in precision gnss data alone cannot resolve small ground displacements due to for instance p waves therefore their use is currently limited to refining early warnings with more precise earthquake characteristics such as magnitudes or ground motion predictions here we analyze 1 hz global positioning system gps data from the 24 january 2016 m w 7 1 iniskin earthquake which ruptured 125 km under cook inlet in alaska to motivate the inclusion of gnss derived s wave measurements into the trigger algorithms of eew systems in regions lacking dense early warning instrumentation networks we derive a relationship between earthquake depth and distance to help determine whether gnss s wave observations could expedite warnings to specific locations because the iniskin earthquake was deep by the time the s wave reached the surface the p wave had already been observed over a wide region limiting the potential for unique contributions from gnss data to this event for the same earthquake occurring near the surface however s waves derived from gnss data have the potential to increase the warning time regardless of the depth the iniskin earthquake is an excellent example of the utility of gnss in rapidly assessing the magnitude improving predictions of ground shaking and estimating the area of impact for the earthquake

crustal motion and block behaviour in se asia from gps measurements results acquired using global positioning system gps data taken over a large part of se asia indicate that sundaland i e indochina along with the western and central part of indonesia constitutes a stable tectonic block moving approximately east with respect to eurasia at a velocity of 12 3 mm yr 31 with respect to india and australia this block moves due south significant motion has not been detected along the northern boundary to south china i e along the red river fault whereas nearly 50 mm yr 31 of right lateral motion has to be accommodated between india and sundaland in the andaman burma region fl 2001 elsevier science b v all rights reserved

a lower ordovician paleomagnetic pole from the oneota dolomite upper mississippi river valley of 149 oriented specimens of the lower ordovician oneota dolomite subjected to stepwise thermal or alternating field demagnetization 50 contained a characteristic shallow east southeasterly or west northwesterly component of magnetization identifiable on orthogonal vector projections for 48 other specimens the demagnetization trajectories defined greats circle paths which intersect close to the characteristic direction the site mean directions for the characteristic component were determined by using both the characteristic directions and great circle data and these yield a formation mean direction obtained from 10 sites with a declination of 105 an inclination of 2 and a precision parameter k of 17 6 95 11 9 the mean of the site virtual poles falls at 10 4 n 166 4 e k 48 0 a95 7 0 which is close to previously published late cambrian paleopoles both polarity groups have predominantly positive inclinations suggesting the presence of an uncleaned downward component whose unblocking temperature and coercivity spectra overlap very strongly with those of the characteristic magnetization we interpret this downward component as a drilling induced remanent magnetization and we hope to have removed its contribution by averaging the dual polarity results multicomponent magnetizations were also present in samples collected from blocks of oneota dolomite incorporated into the overlying new richmond sandstone lower ordovician but only six out of eight samples yielded well defined greats circle paths the best fit intersection of these defines a northerly and steep recent component while the directions of the higher stability components are different for each block due to the small number of samples and imperfect resolution of magnetic directions the conglomerate test is not conclusive nevertheless it suggests that the stable remanence in the oneota dolomite was acquired prior to the deposition of the new richmond sandstone

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

palaeomagnetism of silurian sediments in w ireland evidence for block rotation in the caledonides summary a palaeomagnetic study of mid silurian wenlock sediments of the salrock formation in nw galway yields a reliable silurian palaeomagnetic pole position for w ireland at latitude 1 6 s longitude 287 7 e dp 2 5 dm 4 6 n 27 sites a further 12 sampling sites were located in silurian redbeds on clare island s mayo where a palaeomagnetic remanence of silurian age was also identified both remanences pre date local late caledonian folding however the clare island result has an anomalous azimuth when compared with the salrock result and with published silurian results for britain the two irish results can be reconciled by anticlockwise block rotation of the clare island region through 40 50 the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment strike slip displacement across the clew bay fault zone producing a sinistral shear couple might have enabled such a rotation the timing and geographic extent of the proposed block rotation is as yet poorly defined however a younger age limit for rotation is provided by a late devonian or carboniferous partial magnetic overprint observed throughout both study areas and from geological evidence it seems likely that rotation is confined to the clew bay fault zone the dalradian rocks of the connemara massif located to the south of the salrock district have an e w structural grain some workers have proposed clockwise rotation of the connemara massif of ca 30 at between 500 and 390 ma which would bring the structural trends in w ireland into parallelism with caledonian trends in scotland because the silurian salrock succession which rests unconformably on the dalradian basement of connemara shows no such anomaly it provides a younger age limit for the possible rotation of connemara

deformation and stress states along the central segmentof the philippine fault implications to wrench fault tectonics abstract this paper discusses the space time evolution of deformation and states of stress along the central segment of the left lateral philippine fault from bondoc peninsula to leyte island this segment is characterized by deformations and stress states which do not always conform to predictions of classical wrench tectonics directions of the maximum principal stress axis 1 are in some cases oriented perpendicular to the fault trace contradicting the classical fault strike 1 angle of 30 45 in other cases it is the minimum axis 3 that orients perpendicular to the fault or in other cases parallel to it rotations of 1 directions as functions of time and space are observed all along the fault more complex stress regimes are observed in areas where the philippine fault intersects with two other major left lateral strike slip faults namely the legaspi lineament in the ragay gulf area and the sibuyan sea fault in masbate these observations strongly underline the urgence of prudence and precaution in applying wrench fault tectonic principles in natural examples

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

the relationship between seismic and aseismic slip on the philippine fault on leyte island bayesian modeling of fault slip and geothermal subsidence delineating seismic and aseismic slip on faults allows the exploration of the complex relationship between these different modes of slip further quantifying them helps in the assessment of seismogenic potential we present a distributed slip model of the rate of aseismic slip along the leyte island section of the philippine fault and make comparisons with the extent of seismic slip from the latest significant earthquakes in july 2017 we derived both coseismic and aseismic slip distributions from kinematic inversions of synthetic aperture radar interferometric insar observations using a probabilistic bayesian framework velocity maps from stacking and time series analysis of alos interferograms spanning 4 years 2007 2011 show a step change in ground deformation right on the fault inverting for slip at depth reveals along strike variations of aseismic slip rate over 100 km aseismic slip on the surface reaches rates of more than 3 cm yr equivalent to the long term slip rate 3 3 0 2 cm yr over the same period a 20 km segment in tongonan appears to be locked this segment ruptured in mw 6 5 and mw 5 8 earthquakes on 6 and 10 july 2017 respectively as constrained by sentinel 1 and alos 2 insar data seismic slip appears to be restricted within the tongonan segment with up to 152 21 cm of left lateral displacement the slip budget and complementarity between the extents of interseismic and coseismic slip suggest that a seismogenic asperity exists in tongonan the presence of active hydrothermal systems and rate strengthening materials provide physical conditions that can promote aseismic slip

tsunami hazard from the subduction megathrust of the south china sea part i source characterization and the resulting tsunami abstract the subduction megathrust under the manila trench has been accumulating strain over a period of 440 years or more and could be the source for a giant earthquake of m w 9 we present a plausible earthquake rupture model constructed from seismic and geodetic data together with hydrodynamic simulations of the potential tsunami with comcot cornell multi grid coupled tsunami model results indicate that this megathrust poses a risk of devastating tsunami for the philippines southern china vietnam and other population centers bordering the south china sea

magnetism of igneous rocks from the tourmakeady and glensaul inliers w ireland mode of emplacement and aspects of the ordovician field pattern summary results of palaeomagnetic and rock magnetic studies are reported mainly for quartz porphyry collected at 18 sites from an ordovician igneous sedimentary succession at tourmakeady and glensaul in co mayo eire both magnetite and haematite are shown to be prominent magnetic constituents the magnetite is usually in the form of large multidomain grains these are held responsible for a soft remanence component called the b magnetization with d i 000 75 95 3 7 i e practically identical to the direction of the present axial geocentric dipole field in the area hence it is inferred that the b magnetization which is dominant at most sites is of recent origin haematite which has a more patchy occurrence apparently formed through high temperature oxidation of magnetite haematite is the main carrier of the palaeomagnetically significant component the a magnetization which gave well grouped in situ directions 29 samples from 10 sites with a mean value of d i 182 6 corresponding to a north pole at 31 n 169 e dp dm 2 1 4 2 correction for folding along the glensaul tourmakeady are shows that the a magnetization is of post folding age an earlier suggestion that the rocks represent a lower ordovician extrusive suite is discussed and discounted it is inferred that the quartz porphyries constitute syntectonic intrusions having formed during the taconic orogeny these rocks as well as their characteristic magnetization are therefore regarded as late ordovician in age it is concluded that a c 50 relative clockwise shift between the mid ordovician and late ordovician silurian geomagnetic field axes previously demonstrated for scotland has now been recognized also in ireland

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

analysis of crustal deformation in luzon philippines using geodetic observations and earthquake focal mechanisms we utilize regional gps velocities from luzon philippines with focal mechanism data from the harvard centroid moment tensor cmt catalog to constrain tectonic deformation in the complex plate boundary zone between the philippine sea plate and eurasia the sundaland block processed satellite imagery and digital elevation models are used with existing gravity anomaly seismicity and geologic maps to define a suite of six elastic blocks geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault locking parameters for each of the tectonic blocks and faults comprising luzon major tectonic structures that were found to absorb the plate convergence include the manila trench 20 100 mm yr 1 and east luzon trough 9 15 mm yr 1 philippine trench 29 34 mm yr 1 which accommodate eastward and westward subduction beneath luzon respectively the left lateral strike slip philippine fault 20 40 mm yr 1 and its northward extensions the northern cordillera fault 17 37 mm yr 1 transtension and the digdig fault 17 27 mm yr 1 transpression the macolod corridor a zone of active volcanism crustal thinning extension and extensive normal and strike slip faulting in southwestern luzon is associated with left lateral transtensional slip of 5 10 mm yr 1 the marikina fault which separates the central luzon block from the southwestern luzon block reveals 10 12 mm yr 1 of left lateral transpression our analysis suggests that much of the philippine fault and associated splays are locked to partly coupled while the manila and philippine trenches appear to be poorly coupled luzon is best characterized as a tectonically active plate boundary zone comprising six mobile elastic tectonic blocks between two active subduction zones the philippine fault and associated intra arc faults accommodate much of the trenchparallel component of relative plate motion 2006 elsevier b v all rights reserved

seismotectonics of the 6 february 2012 mw 6 7 negros earthquake central philippines abstract at 03 49 utc on the 6th of february 2012 negros island in the visayan region of central philippines was struck by a magnitude mw 6 7 earthquake causing deaths of over 50 people and tremendous infrastructure damage leaving hundreds of families homeless the epicenter was located in the vicinity of the eastern coastal towns of la libertad and tayasan of the province of negros oriental earthquake induced surface deformation was mostly in the form of landslides liquefaction ground settlement subsidence and lateral spread there were no clear indications of a fault surface rupture the earthquake was triggered by a fault that has not been previously recognized earthquake data including epicentral and hypocentral distributions of main shock and aftershocks and focal mechanism solutions of the main shock and major aftershocks indicate a northeast striking northwest dipping nodal plane with a reverse fault mechanism offshore seismic profiles in the tanon strait between the islands of negros and cebu show a northwest dipping reverse fault consistent in location geometry and mechanism with the nodal plane calculated from earthquake data the earthquake generator is here proposed to be named the negros oriental thrust not geologic transects established from structural traverses across the earthquake region reveal an east verging fold thrust system in the latitude of guihulngan this fold thrust system is represented by the razor back anticline negros oriental thrust pair and by the pamplona anticline yupisan thrust pair in the latitude of dumaguete to the south together these active fold thrust systems are causing active deformation of the western section of the visayan sea basin under a compressional tectonic regime this finding contradicts previous tectonic models that interpret the tanon strait as a graben bounded on both sides by normal faults supposedly operating under an extensional regime the negros earthquake and the active fold thrust systems that were discovered in the course of the structural analysis provide strong arguments for basin inversion processes now affecting the visayan sea basin albeit under very slow strain rates derived from previous gps campaigns the occurrence of the earthquake in an area where no active faults have been previously recognized and characterized by slow present day strain rates underscores the necessity of paying more attention to and exerting more effort in the evaluation of earthquake hazards of regions that are seemingly seismically quiet especially when they underlie highly urbanized areas

paleomagnetic results from the peterhead granite scotland implication for regional late caledonian magnetic overprinting abstract palaeomagnetic results from the peterhead granite silurian ne grampian highlands define a characteristic magnetization with overall parameters of dec 180 4 inc 22 3 and a 95 5 2 these results agree with other newer granite data from north scotland an east west trending dyke cutting the peterhead granite shows an extremely well defined paleomagnetic direction with dec 192 5 inc 19 1 and a 95 1 3 suggesting a permo carboniferous age the peterhead granite results are seen in conjunction with other palaeozoic palaeomagnetic data from scotland it is concluded that the observed directional spread of characteristic remanence directions previously reported from the aberdeenshire gabbros are not related to slow post orogenic cooling watts and briden but is rather seen as the result of late caledonian magnetic overprinting

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

the western central luzon volcanic arc the philippines two arcs divided by rifting abstract the western central luzon arc is apparently a complex zone of volcanism and tectonism the volcanoes of the northern segment of the arc the bataan arc ba fall along two semi parallel lineaments the western bataan lineament wbl and the eastern bataan lineament ebl this northern segment is cut off from the southern extension of the arc by a ne sw cross arc zone of volcanism the macolod corridor mc the volcanoes of the southern segment of the arc mindoro arc ma fall along two parallel lineaments the western mindoro lineament wml and the eastern mindoro lineament eml samples collected from the mc ebl and ma are alkali and lil enriched compared with the wbl the enrichment of the ebl is believed to be the result of the release of smaller amounts of hydrous rich fluids within the mantle below the ebl than below the wbl this process generated smaller degrees of partial melting below the ebl as compared to the wbl which resulted in the higher concentrations of lil elements in the ebl magmas as compared to the wbl magmas the alkali and lil enriched nature of the mc is believed to be the result of small degrees of partial melting during rifting the enriched nature of the ma is thought to be due to slivers of crustal material from the palawan mindoro block being incorporated into the mantle during subduction this region has the highest radiogenic sr values found in the philippines the mc may represent a pull apart rift zone between the philippine and west luzon shear zones and the transform between the manila and philippine trenches

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

on the temporal variability of the surface gulf stream and near bottom flows long 3 4 years time series of the surface gulf stream position and near bottom flow south of nova scotia support earlier findings of a barotropic semimonthly periodicity in the region a bimodal gulf stream path downstream of the new england seamount chain and a seasonal shift in the gulf stream position new results are 1 a marked reduction of the meridional shifts of the surface gulf stream when it is in its north position mode 2 the semimonthly periodicity seeming to be related at times to the mf tide the most energetic long period tide and 3 an energetic highly coherent but out of phase motion with a near 40 day period in the surface gulf stream position and near bottom flow

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

magnetic properties of the lower old red sandstone lavas in the midland valley scotland palaeomagnetic and tectonic considerations abstract thermal demagnetization studies of lavas in the strathmore area of the midland valley scotland support overall palaeomagnetic data found in previous studies of these rocks reduced directional scatter as compared to some earlier studies is attributed to more effective demagnetization resolving some of the directional complexity of previous studies combined magnetic fabric and directional analysis suggest that at least some deviating directions may be explained by local tectonism the existence of almost antiparallel directional groups and field tests give supporting evidence for a primary deuteric origin of the main magnetization of these rocks additionally a second remanence component having shallow reverse directions of magnetization is attributed to later remagnetization in old red sandstone time the midland valley results are seen in conjunction with other palaeozoic palaeomagnetic results and possible geodynamic implications are discussed