paleomagnetic study of plio pleistocene sediments in the concentrated deformation zone along the eastern margin of the japan sea abstract paleomagnetic results are presented for a concentrated deformation zone cdz in a convergent plate boundary region along the eastern eurasian margin we sampled late pliocene early pleistocene tuffs and clastic sediments of the sasaoka formation 750 m thick in northeastern honshu japan to test whether the late pliocene quaternary crustal deformation within the cdz along the eastern margin of the japan sea was accompanied by rotation about a vertical axis rock magnetic experiments suggest that the principal magnetic carrier is magnetite in the fine tuffs and magnetic iron sulfide in the fine sandstones pre folding characteristic remanent magnetization was confirmed using a positive bootstrap fold test we obtained 21 acceptable site mean characteristic directions that include our preliminary published results and which cover an interval from ca 2 7 to 1 7 ma on the basis of magnetostratigraphic correlations an updated age depth model is given and this allowed us to make numerical age estimates for key interbedded tuff beds tephras a positive fold test also suggests that the gojome syncline began to develop after 1 7 ma which means the folding began long after the initiation of late pliocene crustal shortening in northeastern honshu after 100 unfolding the overall mean direction d 359 7 i 54 9 95 6 7 is indistinguishable from the geocentric axial dipole field direction indicating that the gojome syncline the most prominent structural element in the study area developed without vertical axis rotation a comparison of our results with plio pleistocene directions reported from other areas reveals no paleomagnetically detectable rotation in or adjacent to the cdz except for local rotation near strike slip faults in central honshu

a three dimensional surface velocity field for the mississippi delta implications for coastal restoration and flood potential accurate estimates of the current rate of subsidence in the mississippi delta southern united states provide a context for planning of wetland restoration and predictions of storm surge flooding we present a comprehensive three dimensional surface velocity field for the mississippi delta based on a network of 36 high precision continuous gps stations we show that while the majority of the delta is relatively stable the southern portion continues to experience high rates of subsidence 5 6 mm yr 1 our data are consistent with long term tide gauge records at grand isle louisiana and several stations in florida the current rate of relative sea level rise combined effect of land subsidence and sea level rise along parts of the coastal delta is 8 9 mm yr 1 most tide gauge stations have recorded sea level rise acceleration after a d 1970 these data have implications for land reclamation and wetland restoration in the region parts of the delta may not be viable in the long term

an attempt to reconcile subsidence rates determined from various techniques in southern louisiana abstract subsidence rates determined from geodetic releveling observations since 1920 in southern louisiana are consistently higher than subsidence rates determined from radiocarbon data in the same region over holocene timescales radiocarbon based subsidence rates are similar to numerically modeled shallow sedimentary compaction rates at similar timescales while recent geodetic observations are an order of magnitude higher possible explanations for the dramatic recent increase in regional subsidence rates suggested by the geodetic data that are considered here include 1 a recent increase in regional contributions from faulting 2 the recent contribution of a regional high impact process such as fluid withdrawal 3 accuracy in one or more of the datasets and 4 a strong dependence of subsidence rates upon the time frame over which different techniques are used faulting and regional groundwater withdrawals appear insufficient to explain the high regional geodetic rates the contribution of regional depressurization from deep fluid withdrawals remains unknown estimate errors are likely smaller than the magnitude of the discrepancies between rates from different datasets observations of subsidence rates may be biased by measurement duration

bookshelf tectonics rotated crustal blocks within the sovanco fracture zone the 15 kilometer wide sovanco fracture zone is a dextral slip transform fault linking the juan de fuca and explorer ridges in the n e pacific seabeam bathymetry shows that the sovanco comprises several rhomb shaped elevated blocks of oceanic crust bounded by northeast and northwest trending lineaments we hypothesize that the northeast trending lineaments are sinistral strike slip faults that are reactivated ridge parallel normal faults both the sinistral block bounding faults and the blocks themselves have rotated clockwise about 30 degrees in response to dextral shear within the sovanco zone

estimation of total lateral displacement including strike slip offset and broader drag deformation on an active fault tectonic geomorphic and paleomagnetic evidence on the tanna fault zone in central japan abstract when determining deformation along an active strike slip fault it is desirable to include the cumulative distributed deformation due to drag away from the fault trace in addition to offset on the fault we achieve this by integrating geomorphologic paleomagnetic and geologic data for the active left lateral strike slip tanna fault zone in central japan which previous studies suggest is slipping at about 2 mm yr we combine new detailed mapping of multiple quaternary strands of the fault zone with paleomagnetic measurements from volcanic rocks extruded across the faults from the taga volcano at about 0 6 ma from these data we determine differential counterclockwise rotations from which we infer cumulative strike slip drag deformation at distances of about 1 3 km from the faults these results suggest that the total strike slip displacement accompanying cumulative drag deformation along the fault zone from approximately 0 6 ma to the present is more than 2 3 2 7 km based on a kinematic model or about 6 0 km based on a power law rheology model after adding 1 km of offset along the fault trace thus depending on the model applied the total rate of strike slip deformation along the tanna fault zone is either more than 3 8 4 5 mm yr or about 10 mm yr respectively both of these rates are considerably higher than a previous estimate of about 2 mm yr based solely on strike slip offset without accommodating the drag deformation over the broader zone on either side of the fault break furthermore the deformation rate based on the power law rheology model is comparable to the rate detected by past gps observations

deformation processes adjacent to active faults examples from eastern california 1 major seismogenic faults are embedded within narrow zones of inelastic off fault deformation ofd where both distributed displacement and modification of rock properties occur active distributed displacement may affect slip rate estimates seismic energy radiation and geodynamic models this study addresses the role of ofd in the displacement history and mechanical behavior of seismogenic faults by multisite study of deformed geologic features adjacent to 30 60 km long active strike slip faults of 10 km of dextral displacement in the mojave desert eastern california we find that distributed displacement accommodates 0 to 25 of the total displacement over zones of one to two kilometers width displacement occurs mostly within 100 200 m of faults and decreases nonlinearly away from the main fault we show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the calico fault we also find evidence for shear via rotation and progressive fragmentation adjacent to the harper lake fault analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10 based on crosscutting relationships and the relationship of ofd to geophysically imaged compliant zones around active faults we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault

paleomagnetic evidence for 25 15 ma crust fragmentation of north indochina 23 26 n consequence of collision with greater india ne corner

intraplate rotational deformation induced by faults vertical axis rotations provide important constraints on the tectonic history of plate boundaries geodetic measurements can be used to calculate interseismic rotations whereas paleomagnetic remanence directions provide constraints on the long term rotations accumulated over geological timescales here we present a new mechanical modeling approach that links between intraplate deformational patterns of these timescales we construct mechanical models of active faults at their locked state to simulate the presumed to be elastic interseismic deformation rate observed by gps measurements we then apply a slip to the faults above the locking depth to simulate the long term deformation of the crust from which we derive the accumulated rotations we test this approach in northern israel along the dead sea fault and carmel gilboa fault system we use 12 years of interseismic gps measurements to constrain a slip model of the major faults found in this region next we compare the modeled rotations against long term rotations determined based on new primary magnetic remanence directions from 29 sites with known age the distributional pattern of site mean declinations is in general agreement with the vertical axis rotations predicted by the mechanical model both showing anomalously high rotations near fault tips and bending points overall the results from northern israel validate the effectiveness of our approach and indicate that rotations induced by motion along faults may act in parallel or alone to rigid block rotations finally the new suggested method unravels important insights on the evolution timing magnitude and style of deformation along major faults

quantifying holocene lithospheric subsidence rates underneath the mississippi delta abstract the pattern of holocene relative sea level rsl change on the us gulf coast has been a long standing subject of debate featuring opposing scenarios of continuous submergence versus one or more holocene rsl highstands the significance of this debate is that the relative role of eustasy glacial isostatic adjustment gia and lithospheric flexural subsidence associated with mississippi delta sediment loading remains unresolved here we present a new rsl record from the louisiana chenier plain 100 km west of the mississippi delta margin based on ams 14 c dated marsh basal peat this enables us to provide for the first time constraints on holocene lithospheric subsidence rates underneath one of the world s major deltas our new record conclusively shows that no middle holocene rsl highstands occurred on the central us gulf coast rather it exhibits a pattern of progressive rsl rise comparable to that from the mississippi delta suggesting that long wavelength gia is a dominant deformational process driving lithospheric subsidence in the entire region by means of forebulge collapse nevertheless a 0 15 0 07 mm yr differential rate of subsidence between the chenier plain and key portions of the mississippi delta including the new orleans metropolitan area exists this shows that while the sediment loading effect is real it is about an order of magnitude smaller than recent studies have postulated

quantitative evaluation of quaternary crustal deformation around the takayama basin central japan a paleomagnetic and numerical modeling approach abstract neotectonic crustal deformation in central japan is described quantitatively on the basis of paleomagnetic measurements and numerical modeling the welded part of the earliest quaternary nyukawa pyroclastic flow deposit npfd preserves stable remanent magnetization detailed paleo rock magnetic experiments reveal that remanence of the npfd near the takayama basin resides in unimodal titanomagnetite and comprises a component of thermoremanent magnetization trm and three components of thermoviscous remanent magnetization tvrm scatter in the untilted declinations of the syn depositional trm component represents differential rotation about vertical axes related to quaternary activity of three faults enako makigahora and harayama associated with the takayama basin the normal and reversed tvrm components probably acquired by warm water circulation near the active faults during the jaramillo subchron record a complicated rotational sequence since ca 1 ma dislocation modeling successfully simulates the spatial distribution of rotation and the uplift subsidence pattern around the takayama basin assuming strike slip motion on the enako and makigahora faults along the basin margin and vertical displacements on the harayama fault within the basin temporal changes in rotational motions recorded in the tvrms of near fault sites can be modeled by considering transition of active segments of the three faults which is geologically constrained

the block structure and quaternary strike slip block rotation of central japan central japan is situated on the inflection point of the bow shaped japanese islands numerous nw se trending active faults arranged in parallel at intervals of 20 to 80 km are found in this area these active faults are more than 30 km long with shattered zones from 30 to 300 m wide several active faults constitute a given block boundary which serves as the dividing line for one of the four blocks that make up central japan the block boundaries require careful study since numerous historical earth quakes have occurred along these lines offset measurements of basement rocks created during the quaternary period due to left lateral faulting amount to 1 to 7 km gravity lineaments which link points of sudden change and saddles of bouguer anomalies are clearly found along the block boundaries the nw se trending active faults appearing on the ground surface are associated with motions of the block boundaries block rotational movement caused by left lateral faulting plays an important role in the crustal deformation of central japan rotational angles of the blocks calculated from the amount of displacement of basement rocks initiated during the quaternary period are estimated to be 3 to 7 in a clockwise manner

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

orogen parallel transition from a decoupled fore arc sliver to andean type mountain chain paleomagnetic and geologic evidence from southern chile 37 39 s

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

paleomagnetic rotation pattern of the southern chile fore arc sliver 38 s 42 s a new tool to evaluate plate locking along subduction zones the chile fore arc at 37 s 47 s represents the coseismic deformation zone of the 1960 mw 9 5 valdivia earthquake here we report on the paleomagnetism of 43 oligocene pleistocene volcanic sites from the fore arc sliver between 38 s and 42 s sites were gathered west of the 1000 km long liquine ofqui dextral fault zone lofz that represents the eastern fore arc sliver boundary nineteen reliable sites reveal that the fore arc is characterized by counterclockwise ccw rotations of variable magnitude except at 40 s 41 s where ultrafast 50 myr clockwise cw rotations occur within a 30 km wide zone adjacent to the lofz ccw rotation variability even at close sites and rapidity 10 myr suggest that the observed block rotation pattern is related to nw se seismically active sinistral faults crosscutting the whole fore arc according to previously published data cw rotations up to 170 also occur east of the lofz and have been related to ongoing lofz shear we suggest that the occurrence and width of the eastern fore arc sliver undergoing cw rotations is a function of plate coupling along the subduction zone interface zones of high coupling enhance stress normal to the lofz induce high lofz strength and yield a wide deformation zone characterized by cw rotations conversely low coupling imply a weak lofz a lack of cw rotations and a fore arc entirely dominated by ccw rotations related to sinistral fault kinematics our locking inferences are in good agreement with those recently derived by gps analysis and indicate that seismotectonic segment coupling has remained virtually unchanged during the last 5 ma

paleomagnetism and crustal rotations along a shear zone las vegas range southern nevada in southern nevada paleozoic isopachs mesozoic structures and mountain ranges trend north south but as they approach the right lateral west northwest trending las vegas valley shear zone lvvsz they are bent clockwise up to 90 in oroflexes 30 km long in the las vegas range the declination of the characteristic magnetization of the cambrian bonanza king formation has likewise been rotated clockwise more than 50 for samples from eight sites 13 23 samples per site in the las vegas range and in its extension south of the lvvsz stepwise thermal demagnetization to 600 c removed recent and tertiary overprints revealing a nearly horizontal late paleozoic viscous partial thermoremanent magnetization vptrm which predates both the tertiary oroflexural bending and the sevier thrusting in the area the declination of the characteristic magnetization after correcting for the dip of bedding varies from 133 2 at a site 24 km north of the shear zone to 196 4 13 km north of it and 204 4 11 km south of the shear zone this parallels a similar change in the structural trend the paleomagnetic data indicate that the las vegas range is broken into rather small blocks 5 km which rotate in response to more continuous deformation at depth this deformation of the upper crust can be modelled using a thin non newtonian viscous plate model which when applied to the las vegas valley shear zone predicts rotations similar to those seen in the las vegas range

magnetic and plagioclase linear fabric discrepancy in dykes a new way to define the flow vector using magnetic foliation in basaltic dykes the magnetic lineation k1 maximum magnetic susceptibility axis is generally taken to indicate the flow direction during solidification of the magma this assumption was tested in tertiary basaltic dykes from greenland displaying independent evidence of subhorizontal flow the digital processing of microphotographs from thin sections cut in k1 k2 planes yields the preferred linear orientation of plagioclase which apparently marks the magma flow lineation in up to 60 of cases the angular separation between k1 and the assumed flow direction is greater than 45 this suggests that the uncorroborated use of magnetic lineations in dykes is risky a simple geometrical method is proposed to infer the flow vector from ams in dykes based solely on magnetic foliations

post glacial sediment load and subsidence in coastal louisiana 1 sea level rise in the gulf of mexico has occurred at a rate of 1 8 2 2 mm yr during the 20th century or nearly the same as observed globally due to combined steric and water mass changes tide gauges in coastal louisiana however record a substantially larger rate of rise and while a number of causal mechanisms may be responsible their specific contribution is poorly understood using a realistic viscoelastic earth model detailed geologic parameters for south louisiana and new gps data we demonstrate that holocene sedimentary loading in the gulf and mississippi river delta is capable of contributing to 1 8 mm yr of subsidence over areas of 30 0 75 103 km2

the role of deep processes in late 20th century subsidence of new orleans and coastal areas of southern louisiana and mississippi 1 geodetic leveling observations from biloxi ms to new orleans la and water level gauge measurements in the new orleans lake pontchartrain area were analyzed to infer late 20th century vertical motions these data were used to test the validity of previous subsidence rate measurements and the models that predict the location and causes of subsidence water gauges attached to bridge foundations and benchmarks affixed to deep rods that penetrate holocene strata subsided as much as 0 8 m locally between 1955 and 1995 the observed deep seated subsidence far exceeds model predictions and demonstrates that shallow processes such as compaction and consolidation of holocene sediments are inadequate by themselves to explain late 20th century subsidence deep seated subsidence occurring east and north of the normal faults marking the gulf of mexico basin margin can be explained by local groundwater withdrawal and regional tectonic loading of the lithosphere by the modern mississippi river delta mrd sharp changes in subsidence coincide with strands of the basin margin normal faults displacements are consistent with activity and show motions consonant with fault creep deep subsidence of the region to the south including new orleans can be explained by a combination of groundwater withdrawal from shallow upper pleistocene aquifers the aforementioned lithospheric loading and perhaps nongroundwater related faulting subsidence due to groundwater extraction from aquifers 160 to 200 m deep dominated urbanized areas and is likely responsible for helping to lower local flood protection structures and bridges by as much as 0 8 m

understanding subsidence in the mississippi delta region due to sediment ice and ocean loading insights from geophysical modeling the processes responsible for land surface subsidence in the mississippi delta md have been vigorously debated numerous studies have postulated a dominant role for isostatic subsidence associated with sediment loading previous computational modeling of present day vertical land motion has been carried out in order to understand geodetic data while the magnitudes of these measured rates have been reproduced the model parameter values required have often been extreme and in some cases unrealistic in contrast subsidence rates in the md on the 103 year timescale due to delta loading estimated from relative sea level reconstructions are an order of magnitude lower in an attempt to resolve this conflict a sensitivity analysis was carried out using a spherically symmetric viscoelastic solid earth deformation model with sediment ice and ocean load histories the model results were compared with geologic and geodetic observations that provide a record of vertical land motion over three distinctly different timescales past 80 kyr past 7 kyr and past 15 years it was found that glacial isostatic adjustment is likely to be the dominant contributor to vertical motion of the pleistocene and underlying basement present day basement subsidence rates solely due to sediment loading are found to be less than 0 5 mm yr 1 the analysis supports previous suggestions in the literature that earth rheology parameters are time dependent specifically the effective elastic thickness of the lithosphere may be 50 km on a 105 year timescale but closer to 100 km over 103 to 104 year timescales

quaternary strike slip crustal deformation around an active fault based on paleomagnetic analysis a case study of the enako fault in central japan abstract to evaluate cumulative strike slip deformation around an active fault we carried out tectonic geomorphic investigations of the active right lateral strike slip enako fault in central japan and paleomagnetic investigations of the kamitakara pyroclastic flow deposit kpfd 0 6 ma welded tuff distributed around the fault tectonic geomorphic study revealed that the strike slip displacement on the fault is ca 150 m during the past 600 ka we carried out measurements of paleomagnetic directions and anisotropy of magnetic susceptibility ams within the pyroclastic flow deposit stable primary magnetic directions at each sampling site are well clustered and the ams fabric is very oblate we then applied tilt correction of paleomagnetic directions at 15 sites using tilting data obtained by the ams property and orientations of eutaxitic structures within a distance of about 500 m from the fault trace differential clockwise rotations were detected the rotation angle is larger for zones closer to the fault because of this relation and absence of block boundary faults a continuous deformation model explains the crustal deformation in the study area the calculated minimum value of strike slip displacement associated with this deformation detected within the shear zone is 210 m the sum of this and offset on the enako fault is 360 m and the slip rate is estimated at 0 6 mm year

the use of paleomagnetic analysis to assess nonbrittle deformation within the san andreas fault zone a recently developed paleomagnetic extraction technique successfully permits sample collection from unconsolidated sediments traditional measurement and demagnetization procedures can subsequently be performed and several studies have already shown that soft sediment samples yield reliable magnetic polarity information to test the robustness of the extraction technique as well as the resolution limits of the resultant magnetic vector directions a total of 238 paleomagnetic samples were taken from unconsolidated strata exposed in an excavation across the san andreas fault zone in the carrizo plain california variable fault offset values for the most recent earthquakes at this locality favored the likelihood of rotational nonbrittle deformation such deformation could possibly be recorded in the drm detrital remanent magnetization of sediment deposited across the zone declination directions of sample groups taken from presumably unrotated strata show general agreement with the most recent secular variation curve constructed for southern california supporting the assumption that the stratigraphic units sampled do record an accurate drm however significant variations in declination directions are found between magnetically stable samples within sample groups i e taken as close as 1 cm apart within the same stratigraphic horizon probable causes of such declination variations include postdepositional physical disturbances associated with rupture events and errors generated by the sampling technique inadvertent sample rotation about the axis of the glass holders is one of the most evident sources of error found in this study although only samples which underwent large rotations 60 could be identified regardless of its origin the variability of the magnetic declination directions found for the 29 magnetically stable groups forces us to conclude that paleomagnetic results calculated in this study are not precise enough to discern reasonable 20 amounts of rotation these results question a similar soft sediment study upon which this study was modeled which claims to have successfully detected less than 20 in rotational deformation using an identical sampling method additional studies are needed preferably not within active fault zones to better define sources of error for this relatively new soft sediment sampling technique and to determine its resolution limits for discerning small changes in paleomagnetic vector directions

is there a 60 year oscillation in global mean sea level 1 we examine long tide gauge records in every ocean basin to examine whether a quasi 60 year oscillation observed in global mean sea level gmsl reconstructions reflects a true global oscillation or an artifact associated with a small number of gauges we find that there is a significant oscillation with a period around 60 years in the majority of the tide gauges examined during the 20th century and that it appears in every ocean basin averaging of tide gauges over regions shows that the phase and amplitude of the fluctuations are similar in the north atlantic western north pacific and indian oceans while the signal is shifted by 10 years in the western south pacific the only sampled region with no apparent 60 year fluctuation is the central eastern north pacific the phase of the 60 year oscillation found in the tide gauge records is such that sea level in the north atlantic western north pacific indian ocean and western south pacific has been increasing since 1985 1990 although the tide gauge data are still too limited both in time and space to determine conclusively that there is a 60 year oscillation in gmsl the possibility should be considered when attempting to interpret the acceleration in the rate of global and regional mean sea level rise

paleomagnetic measurement of nonbrittle coseismic deformation across the san andreas fault at pallett creek paleomagnetic data have been obtained to address a problem at the pallett creek paleoseismological site the 9 mm yr slip rate determined from three dimensional mapping of late holocene offsets across discrete faults is only a quarter of the expected value we suspected that nonbrittle deformation adjacent to the faults might account for the 26 mm yr discrepancy in our search for the missing slip we collected and analyzed 264 paleomagnetic samples from a 53 m wide transect across the fault zone half the samples came from a unit deposited immediately after a large earthquake of about a d 1480 these samples were affected by two large earthquakes that involved rupture at the site in 1812 and 1857 we collected the other half of the samples from a slightly older bed one that was deposited before the earthquake of about a d 1480 relative to control groups composed of 10 samples and collected 50 m from the fault samples closer to the fault display clockwise rotations of 30 or less if interpreted as block rotations the data from the older unit imply that it has sustained a total of 14 0 2 9 m of dextral warp during the past three major earthquakes and that the younger unit has experienced a total of 8 5 1 0 m of warp during the most recent two combining these values with the amounts of dextral slip across the mapped fault planes yields dextral offsets of 5 5 6 25 and 6 25 m for the events of a d 1480 1812 and 1857 and a slip rate of 35 6 6 7 mm yr this slip rate averaged over the past three complete seismic cycles is consistent with published rates from other sites offsets associated with the past three events are remarkably similar these amounts however appear independent of the length of interseismic cycles these observations suggest 1 that this part of the san andreas fault has a characteristic strength and 2 that conventional concepts of strain accumulation and relief for example time and slip predictable models of earthquake occurrence are unrealistic

understanding kinematics of intra arc transcurrent deformation paleomagnetic evidence from the liquine ofqui fault zone chile 38 41 s the liquine ofqui fault zone lofz is a major 1000 km long dextral shear zone of southern chile likely related to strain partitioning of nazca plate oblique convergence with south america to understand block rotation pattern along the lofz we paleomagnetically sampled 55 sites 553 samples between 38 s and 41 s we gathered oligocene to pleistocene volcanics and miocene granites at a maximum distance of 20 km from the lofz and at both sides of it rotations with respect to south america evaluated for 36 successful sites show that crust around the lofz is fragmented in small blocks 1 to 10 km in size while some blocks at both fault edges undergo very large 150 170 rotations others do not rotate even adjacent to fault walls we infer that rotations affected equidimensional blocks while elongated crust slivers were translated subparallel to the lofz without rotating rotation pattern across the lofz is markedly asymmetric east of the fault and adjacent to it rotations are up to 150 170 clockwise and fade out 10 km east of fault these data support a quasi continuous crust kinematics characterized by small rigid blocks drag by the underlying ductile crust flow and imply 120 km of total fault offset conversely crust west of the lofz is cut by seismically active nw se sinistral antithetic faults and yields counterclockwise rotations up to 170 at 8 10 km from lofz besides the unrotated blocks further data from the chile fore arc are needed to understand block rotation kinematics and plate dynamics west of the lofz

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

pop up tectonics of the shillong plateau in the great 1897 earthquake ms 8 7 insights from the gravity in conjunction with the recent seismological results 1 it was reported that a hidden 110 km long south dipping fault named oldham fault was responsible for the 1897 great earthquake ms 8 7 in the shillong plateau by reverse faulting due to pop up tectonics of the plateau in northeast india here we report the results of our geophysical investigations where we critically examine the crustal structure of the plateau on the basis of gravity modeling and attempt to shed light on the hitherto debated hidden oldham fault at the northern boundary of the shillong plateau our gravity model constrained by broadband seismological data suggests that the moho beneath the shillong plateau is at a shallower depth of about 35 km when compared to the bengal basin to the south and the assam valley to the north which is about 42 km thinning of the crust under the plateau may be a consequence of the pop up mechanism to examine the possible pop up of the plateau during the great 1897 earthquake we have estimated the energy released by this earthquake and compared it with the energy required for the pop up of the plateau using a simplistic rigid model it is found that the shillong plateau between the oldham fault and dauki dapsi thrust would require an energy of 4 5 1019 j which does match well with the energy released by the great earthquake of ms 8 7

quantifying near field and off fault deformation patterns of the 1992 mw 7 3 landers earthquake coseismic surface deformation in large earthquakes is typically measured using field mapping and with a range of geodetic methods e g insar lidar differencing and gps current methods however either fail to capture patterns of near field coseismic surface deformation or lack preevent data consequently the characteristics of off fault deformation and the parameters that control it remain poorly understood we develop a standardized method to fully measure the surface near field coseismic deformation patterns at high resolution using the cosi corr program by correlating pairs of aerial photographs taken before and after the 1992 m w 7 3 landers earthquake cosi corr offers the advantage of measuring displacement across the entire zone of surface deformation and over a wider aperture than that available to field geologists for the landers earthquake our measured displacements are systematically larger than the field measurements indicating the presence of off fault deformation we show that 46 of the total surface displacement occurred as off fault deformation over a mean deformation width of 154 m the magnitude and width of off fault deformation along the rupture is primarily controlled by the macroscopic structural complexity of the fault system with a weak correlation with the type of near surface materials through which the rupture propagated both the magnitude and width of distributed deformation are largest in stepovers bends and at the southern termination of the surface rupture we find that slip along the surface rupture exhibits a consistent degree of variability at all observable length scales and that the slip distribution is self affine fractal with dimension of 1 56

vertical axis rotations and deformation along the active strike slip el tigre fault precordillera of san juan argentina assessed through palaeomagnetism and anisotropy of magnetic susceptibility palaeomagnetic data from poorly consolidated to non consolidated late cenozoic sediments along the central segment of the active el tigre fault central western precordillera of the san juan province argentina demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical axis rotations of variable magnitude this deformation has affected in different amounts miocene to late pleistocene samples and indicates a complex kinematic pattern several inherited linear structures in the shear zone that are oblique to the el tigre fault may have acted as block boundary faults displacement along these faults may have resulted in a complex pattern of rotations the maximum magnitude of rotation is a function of the age of the sediments sampled with largest values corresponding to middle miocene lower pliocene deposits and minimum values obtained from late pleistocene deposits the kinematic study is complemented by low field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a n s stretching direction subparallel to the strike of the main fault

a nested fault system with block rotation caused by left lateral faulting the neodani and atera faults central japan abstract a detailed study of outcrops existing around the neodani and atera faults which are large scale left lateral faults oriented nw se in central japan revealed they were accompanied by two distinct fault systems of different scale and slip sense intermediate scale parallel right lateral faults and small scale parallel left lateral kink bands or faults a nested fault model with different geometric scales is proposed to explain the hierarchical occurrence of the fault systems in this model the secondary fault system is contained within the primary fault system as a mirror image of it left lateral movement of the atera or neodani fault induces right lateral movement of intermediate scale faults and results in counterclockwise rotation of the blocks between the faults this right lateral movement in turn induces left lateral movement of small scale faults or kink bands which causes clockwise rotation of the small blocks between them since the angle of the counterclockwise rotation of the primary fault systems is the same as that of the clockwise rotation of the secondary fault system these rotations cancel each other while the large scale fault movements cause block rotation the small blocks eventually show no rotation

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

active strike slip faulting and macroscopically nonrigid deformation of volcanic rocks in central japan inferred from a paleomagnetic study abstract detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault in central japan the early quaternary nyukawa pyroclastic flow deposit is cut by the active dextral enako fault activity level of the fault is evaluated on the basis of geological and geomorphological surveys then paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the enako fault stable thermoremanent magnetization trm of the pyroclastic deposit is isolated through progressive thermal and or alternating field demagnetization tests untilted site mean directions of the trms simultaneously acquired during initial cooling indicate significant clockwise vertical axis rotation the lineament was then activated with right lateral motions through the early quaternary together with the late quaternary activities along the adjoining enako fault evaluated by our study the present result exemplifies a migration of active segments within a fault system during the quaternary paleomagnetic directions on the strike slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

an evaluation of subsidence rates and sea level variability in the northern gulf of mexico 1 while subsidence is widely recognized as a driver of geomorphic change in the northern gulf of mexico gom there is considerable disagreement over the rates of subsidence and the interpreted variability in these rates which leads to controversies over the impacts of subsidence on surface land area change here we present a new method to calculate subsidence rates from the tide gauge record that is based on an understanding of the meteorological drivers of inter annual sea level change in grand isle la and galveston tx we explicitly show that temporal patterns of subsidence are closely linked to subsurface fluid withdrawal and coastal land loss and suggest changes in withdrawal rates can both increase and decrease rates of subsidence and wetland loss our results also imply that the volume of sediment needed to rebuild gom wetlands may currently fall within the low end of some restoration scenarios