reassessment of the 1907 sumatra tsunami earthquake based on macroseismic seismological and tsunami observations and modeling on 4 january 1907 an earthquake occurred off the west coast of sumatra indonesia with an instrumental surface wave magnitude ms in the range of 7 5 8 0 at periods of 40 s the tsunami it generated was destructive on the islands of nias and simeulue where it killed hundreds and gave rise to the legend of the s mong this tsunami was also observed in other parts of the indian ocean basin relative to its instrumented magnitude the size of the tsunami was anomalous qualifying the event as a tsunami earthquake however unusually for a tsunami earthquake the shaking on nias was severe 7 ems we revisit the 1907 earthquake with a multidisciplinary approach by extracting evidence describing shaking effects or the tsunami from written documents and by acquiring new seismograms combining these we discriminate two large earthquakes within an hour of each other with clear differences in seismological character the first we interpret to be a tsunami earthquake with characteristic low levels of shaking an estimated average seismic moment m0 of 2 5 1028 dyn cm mw 8 2 in the frequency band 6 8 mhz and an epicentral location close to the front of the sunda megathrust the seismograms we analyzed also document a regular growth of moment with period approaching mw 8 4 at the longest resolvable period 170 s for the second earthquake that caused damage on nias we estimate ms 7 based on seismograms and phase data we also identify two ms 6 aftershocks within 24 h of the mainshock additionally we present a dataset of 88 locations within the indian ocean basin where the tsunami was observed using a subset of these we forward modeled the tsunami to propose a seismic rupture model extending along the sunda megathrust for about 220 km 94 7 e to 97 e with a maximum modeled slip of 21 m our new rupture model provides an acceptable fit to our new dataset of tsunami runup and inundation values from 88 local and far field locations in the indian ocean basin we also urge caution against an over reliance on the s mong legend for tsunami evacuation as its premise that a tsunami will only follow an earthquake with very severe ground motions is rendered ineffective for tsunami earthquakes

long term seismic behavior of the focal and adjacent regions of great earthquakes during the time between two successive shocks we analyze the spatial temporal energy distribution of shallow depth h 70 km seismicity surface wave magnitude ms 7 occurring in the focal and adjacent regions of very great shallow earthquakes rupture lengths of the order of hundreds of kilometers in the circum pacific seismic belt for as many decades as possible before and after the occurrence of the main shock for this purpose we have revised the catalog of data for the world instrumental seismicity 1900 1995 by removing a series of heterogeneities in the earthquake reporting and magnitude determination this revised catalog is fairly complete for earthquakes with m 7 since early in the century our findings indicate that once a main shock aftershock sequence occurs the focal region enters a period of relative quiescence for large ms 7 earthquakes significant seismic activity ms 7 occurs during many decades prior to the next main shock this activity is fairly continuous or random in time and lasts until the onset of the main event but clusters in space around the ends of the forthcoming rupture and or in the vicinity of the principal epicenter except in the case of rare bilateral breaks the main epicenter is located at one of these ends thus major portions of the rupture zone experience no events with ms 7 during the seismic cycle larger aftershocks also cluster near the edges of the rupture and near the principal epicenter preshock activity minutes to weeks before the main shock if any occurs in general near the main epicenter we also find that the nucleation and ends of the rupture often coincide in space with recognizable geometrical and or geological inhomogeneities barriers existing in the lithosphere it appears that while strain energy accumulates high stress concentrations often occur at the ends of the future rupture zone which results in the long term foreshock activity and in the subsequent initiation of the main rupture from within those regions we suggest a simple mechanical model that explains the observed pattern of earthquake occurrence for both unilateral and bilateral ruptures in all cases of great earthquakes that have occurred this century for which a long and complete to a level of 2 to 3 orders of magnitude smaller than the moment of the main shock catalog of prior seismicity exists we can not recognize any statistically significant quiescent or doughnut patterns in the preceding seismicity at the ms 7 level

geometry of the subducted plate near kodiak island and lower cook inlet alaska determined from relocated earthquake hypocenters abstract using observations from 28 seismograph stations in southern alaska we have used the jhd method to relocate 341 well recorded events with focal depths beneath about 40 km which occurred between 56 4 n and 60 5 n and between 151 6 w and 156 5 w these hypocenters show that the wadati benioff zone has a dip of about 45 however its strike changes by about 15 beneath lower cook inlet at about 59 n near where the volcanic line also bends northward near this bend there is also a distinctly higher level of seismic activity than in the area to the southwest of 59 n a few events are situated about 20 km beneath the main wadati benioff zone in cook inlet and a focal mechanism we have determined for one of these differs from other mechanisms for events in this area focal mechanisms available from previous work show that at intermediate focal depths the area between 59 n and 60 5 n is controlled by horizontal north south compression and as such differs from the region to the southwest relying primarily on the observed change in strike and apparent thickness of the wadati benioff zone we interpret these data to suggest that the subducted lithophere separates into two distinct segments as it subducts beneath cook inlet because the direction of subduction is not perpendicular to the volcanic arc the events situated beneath the wadati benioff zone in cook inlet may be part of the southwestern plate segment although the geometry and available focal mechanisms for events beneath cook inlet are similar to what would be expected in a double wadati benioff zone we suggest instead that these observations result because we are at the boundary between two adjacent segments of the subducting plate

seismicity of the unalaska region alaska the wadati benioff zone beneath unalaska island in the eastern aleutian arc is shown to dip at approximately 48 between the depths of 50 and 150 km above this depth the seismic zone appears to dip at a more shallow angle 12 the depth of the wadati benioff zone beneath makushin volcano on unalaska island is about 100 km events located within the upper plate near the wadati benioff zone indicate that the maximum depth of seismic coupling between the subducting and overriding plates is about 30 km this suggests that the maximum width of seismic coupling between the downgoing and overriding plates is about 75 km earthquake locations based on the local network data and 20 yr of teleseismic data pde define similar seismically active and quiescent regions a major seismicity gap exists for events of magnitudes greater than at least 4 6 in the forearc region near unalaska island this seismicity gap correlates well with the eastern edge of the tsunami source area of the great mw 8 6 1957 earthquake and a large forearc basin 75 km south of unalaska island suggesting a similar process may be controlling the location of all three phenomena only one intermediate sized mb 6 1 earthquake has occurred within the seismicity gap during the past 20 yr this event is shown to be a high stress drop 690 bars intraplate event within the subducting slab at a depth of 35 km that may be related to lateral compressive stress induced by a change in slab curvature with depth a review of the historic record from about 1770 reveals that the unalaska region may have ruptured in a great earthquake in 1878 and a large earthquake in 1902 if this region is currently locked an earthquake of magnitude 8 2 could rupture this section of the alaska aleutian arc estimates of the recurrence interval for events of this size vary from between 40 and 70 yr

shumagin seismic gap alaska peninsula history of great earthquakes tectonic setting and evidence for high seismic potential the shumagin seismic gap a segment of the plate boundary along the eastern aleutian arc has not ruptured during a great earthquake since at least 1899 1903 because at least 77 years have elapsed since the shumagin gap last ruptured in a great earthquake and repeat times for the 1938 rupture zone and part of the shumagin gap are estimated to be 50 to 90 years a high probability exists for a great earthquake to occur within the shumagin gap during the next one to two decades reconsideration of the rupture zones of the aleutian earthquakes of 1938 1946 and 1948 suggests that those events did not break the interplate boundary beneath the shumagin islands thus the shumagin seismic gap extends from the western end of the 1938 rupture zone to the eastern end of that of 1946 these boundaries also coincide with transverse structural features at least the eastern half of the shumagin gap broke in great earthquakes in 1788 and 1847 and possibly in 1898 1903 the shumagin gap is probably not the result of aseismic slip rather plate motion is accommodated there seismically and episodically and can be expected to produce large earthquakes in the future although there is no definitive evidence of long term precursors of a possible future earthquake several observations suggest that the shumagin gap is in an advanced stage of the earthquake cycle both teleseismic and local network data indicate a near absence of seismic activity m 2 above a depth of 30 km along the main thrust zone within the gap this is in strong contrast to adjacent portions of the arc where seismic activity is scattered across most of the main thrust zone two earthquakes with high stress drops 600 900 bars which occurred at the base of the main thrust zone may indicate the accumulation of a considerable amount of strain energy within the gap a possible seismic gap at the eastern end of the aftershock zone of the aleutian earthquake of 1957 has been identified near unalaska island an earthquake that nucleates in the shumagin gap could also rupture the possible unalaska gap to the west the 1938 aftershock zone to the east or both with resultant magnitude up to mw 9 0 alternatively the shumagin gap alone or in one of the above combinations could rupture in a series of very large earthquakes instead of a single great shock past alaska aleutian earthquakes including those of 1788 1938 1946 1957 1964 and 1965 have generated very large tsunamis future large earthquakes in the shumagin islands region could generate wave heights of several tens of meters along shorelines near the rupture areas the shumagin gap is one of two major gaps along the united states portion of the alaska aleutian plate boundary and is one of the few areas in the united states where processes leading to a great earthquake are likely to be observed within a reasonable span of time

seismic rupture and arc segmentation within the shumagin islands seismic gap alaska the locations of teleseismically well recorded earthquakes suggest that up to 80 of the shumagin gap has ruptured seismically during the last 90 years an earthquake in 1917 ms 7 9 nucleated near the gap s eastern edge and appears to have ruptured as much as a 200 km long section of the gap and an event in 1948 ms 7 5 appears to have ruptured the deepest portion of the main thrust zone 30 km in the central section of the gap the rupture extents of these earthquakes suggest that the gap can be divided into two or three smaller arc segments these observations do not preclude the possibility of failure of the entire region in a single great earthquake mw 8 5 in the near future the two historically documented recurrence intervals for the eastern portion of the gap are 59 and 70 years if the average recurrence interval for large earthquakes near the shumagin islands is 65 years the conditional probability of a large earthquake rupturing this portion of the arc in the next 20 years is between 62 and 96

divergent evolution and the spatial structure of soil landscape variability abstract the spatial structure of soil variability at the landscape scale was examined on adjacent geomorphic surfaces dating from 80 to 200 ka in eastern north carolina the purpose was to determine whether there is evidence at broader scales distances of 102 104 m for the divergent evolution observed in the field at very detailed scales distances of 100 102 m the state probability function spf which measures spatial dependence for categorical environmental data along a transect was applied to soil series mapped at a 1 24 000 scale the older talbot terrace and younger pamlico terrace surfaces showed distinctly different patterns of spatial variability the range of spatial dependence was shorter on the older surface about 200 vs 300 m and the spf was higher at any given distance indicating more variability the spf for the pamlico surface also indicates a periodicity related to fluvial dissection of the landscape which is not readily detectable on the talbot transect despite its greater degree of dissection the results confirm earlier field studies which suggest that pedogenesis is marked by divergence whereby differences in initial conditions or local perturbations persist and increase to produce a more variable soil cover

teleseismic time functions for large shallow subduction zone earthquakes broadband vertical p wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum pacific in the last 45 yr most of the records studied come from a common instrument the pasadena california benioff 1 90 seismometer propagation and instrument effects are deconvolved from the p wave records using a damped least squares inversion to obtain the teleseismic source time function the inversion has the additional constraint that the time function be positive everywhere the period band over which the time functions are considered reliable is from 2 5 to 50 sec fourier displacement amplitude spectra computed for each of the 1 90 p wave trains indicate spectral slopes measured between 2 and 50 sec of 1 0 to 2 25 with an average value of 1 5 these values assume an average attenuation of t 1 0 the seismic moments derived from the p wave time functions compare well with other published values for earthquakes having moments smaller than 2 5 10 28 dyne cm m w 8 2 because the 1 90 seismometer has little response at very long periods this technique underestimates the moments of the very largest events the time functions are characterized using five parameters 1 spectral slope between 2 and 50 sec 2 roughness of the time function 3 multiplicity of sources 4 pulse widths of individual sources and 5 overall signal duration the 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere convergence rates and maximum size of earthquakes comparing the time function parameters with age rate and m w of the subduction zone does not yield obvious global trends however most of the subduction zones do behave characteristically and can be grouped accordingly

a seismological reassessment of the source of the 1946 aleutian tsunami earthquake summary we present a re evaluation of the seismological properties of the aleutian tsunami earthquake of 1946 april 1 characterized by a deceptively low conventional magnitude 7 4 in view of its catastrophic tsunami both in the near and far fields relocation of 40 aftershocks show that the fault zone extends a minimum of 181 km along the aleutian trench in a geometry requiring a bilateral rupture from the original nucleation at the epicentre their spatial and temporal distribution are typical of the aftershock patterns of a large earthquake and rule out the model of a landslide source exclusive of a dislocation the analysis of the spectra of mantle waves favours the model of a large seismic source with a static moment of 8 5 10 28 dyn cm making the event one of the ten largest earthquakes ever recorded hence the destructive tsunami in the far field and of a slow bilateral rupture at an average velocity of only 1 12 km s 1 hence the destructive interference in all azimuths for all but the longest mantle waves the exceptionally slow character of the earthquake is confirmed by a deficiency in radiated seismic energy expressed by the lowest value measured to date of the energy tomoment ratio the earthquake appears as an end member in the family of tsunami earthquakes resulting from the combination of anomalous but not unprecedented parameters such as low stress drop and rupture velocity

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

effects of human disturbance and cryoturbation on soil iron and organic matter distributions and on carbon storage at high elevations in the cairngorm mountains scotland soil profiles were sampled at 43 sites on granitic parent material at altitudes ranging from 970 to 1300 m in the cairngorm mountains scotland many soils under undisturbed vegetation showed evidence of iron and organic matter translocation with distinctive bh or bs horizons approximately 50 of the sites sampled had no or partial vegetation cover due either to human activity trampling or active geomorphic processes such as cryoturbation on patterned ground exposed cols and summit ridges were most heavily affected by trampling with extensive areas of path development and some erosion trampling was principally associated with loss of the upper soil horizons and cryoturbation processes with disturbance of horizon development median total organic matter at the vegetated sites ranged from 4 8 to 22 0 kg m y2 with a median of 9 5 kg m y2 there was significantly less total organic matter at the unvegetated sites with median of 4 6 kg m y2 and range from 1 5 to 11 9 kg m y2 there was little difference in total organic matter between sites where vegetation disturbance was due to human trampling or to cryoturbation q 2000 elsevier science b v all rights reserved

late quaternary sea level change in southern beringia postglacial emergence of the western alaska peninsula abstract postglacial sea level trends have varied dramatically across the bering platform because of differences in coastal and shelf geologic settings emergent shorelines and basal peats along the western alaska peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca 13 000 cal yr bp age elevation determinations on four shorelines 25 m 10 ka 16 m 9 6 6 ka 6 m 2 1 ka and 2 3 m 1 8 0 6 ka in the vicinity of cold and morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum lgm 22 17 ka isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle holocene but terrace cutting and a gap in the archaeological record about 2 1 ka suggest that sudden tectonic displacements also influence the record reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement periods of shoreline erosion during stillstands or transgressions and the episodic reorganization of intertidal environments that accompanies tectonic displacements have conditioned site preservation potential and long term adaptive strategies

evolution of the lower gangetic plain landforms and soils in west bengal india abstract three major landforms uplands old fluvial deltaic plains and young fluvial plains are identified from the lower gangetic plains of west bengal india on the basis of remote sensing and field studies morphologic quantitative and thermoluminescence studies of soils of the study area have been conducted two types of uplands are recognised upland in the west overlain by red soils autochthonous and allochthonous types and upland in the north barind tract characterised by three topographic levels aspects of the autochthonous upland red soils lower to middle pleistocene age show the ferrugination ferrisol phase of development soils of the old fluvial deltaic plains 6 3 ka and lower level of the barind tract have argillic horizons and exhibit the fersiallitisation phase of development development of ferrugination and fersiallitisation phases was favored due to the pre weathered nature of the parent material soils of the old fluvial deltaic plains barind tract lower level and young fluvial plains show effects of hydromorphism due to waterlogging in the form of segregations of fe mn oxides gleying and chloritisation probably due to ferrolysis in the upper horizons of some of these soils neotectonics seems to have affected development of landforms and soils significantly due to reactivation of some basement faults in the western region some tectonic blocks subsided causing transgression during the early pleistocene and at ca 7 ka subsequent uplift of these blocks caused regressions and development of soils on the exposed landscapes episodic uplift of the barind tract in the northern region may have given rise to three topographic levels some faults confine the courses of the damodar ganga and bhagirathi rivers

ground motions from subduction zone earthquakes a total of 258 horizontal components of accelerogram data recorded at soil sites during thrust normal and strike slip earthquakes occurring in seven subduction zones around the pacific ocean were analyzed the results of statistical analyses of 5 per cent damped pseudo velocities psv computed from these accelerograms at 10 periods t between 0 1 and 4 sec indicated no significant differences in the average psv levels of the thrust normal and strike slip data from the northern honshu zone each of these groups of northern honshu data which together comprised one half of the total data base were fit equally well by the same attenuation model the analyses also revealed that at intermediate periods 0 8 t 3 sec the psv observed at stiff soil sites within the northern honshu nankai kuril mexico and alaska zones were on the average significantly greater than the psv observed at similar sites in the peru northern chile and new britain bougainville zones this observation indicates that differences in the source and or travel path characteristics between the two groups accounted for the differences in psv independent evidence supporting source differences is the correlation noted between psv in this period band and the characteristic source complexities for these zones which hartzell and heaton inferred from the teleseismic data of the larger magnitude earthquakes certain anomalous tectonic characteristics of the new britain bougainville zone were noted that may have contributed in some systematic manner to the relatively unusual spectral characteristics of the ground motions recorded on stiff soil sites within this zone some of the differences in the psv among the zones at intermediate and long periods were probably the result of differences in local geologic characteristics geology greatly influenced the mexican psv data from soft soil sites to a lesser extent geology probably affected the alaskan data which were recorded mostly on deep stiff soils and the new britain bougainville data recorded at yonki which is underlain by softer soil deposits

modeling earthquake cycles in the shumagin subduction segment alaska with seismic and geodetic constraints deformation associated with the earthquake cycle in the shumagin islands segment of the alaska aleutian subduction zone is analyzed with the use of a two dimensional finite element model the model consists of an oceanic plate dipping under an upper plate both of which respond elastically to stress fluctuations in the earthquake cycle and these are underlain by asthenospheric mantle and mantle wedge regions which respond viscoelastically it is tailored to the geometry of the shumagin islands region by using seismicity to define the position of the interplate interface and partially coupled region along it the model is preconditioned by forcing this interface to undergo periodically repeated slips up to and including the time of the may 31 1917 event ms 7 4 in that region with each chosen to be consistent with the moment and estimated rupture area of that event we investigated the dependence of model results for geodetic signals on the strength of seismic coupling between the plates and viscoelastic relaxation of deviatoric stresses in the mantle including in the mantle wedge close to the plate junction and along the aseismic downdip continuation of the thrust interface in models with significant relaxation in the wedge or downdip thrust zone results show that as the intraseismic stage matures there is a region of diminished compressional strain rates and even of locally extensional rates on the earth s surface above the downdip end of the seismically coupled zone based on the seismic estimates of the location of the coupled zone this region is in the area of the shumagin islands we find that if approximately 20 of the convergence takes place seismically compatible with the previous seismic history and if an extensive region of relaxed deviatoric stress is assumed to be present in the wedge and or along the downdip interface then deformations predicted by the model can be made consistent with the measured strain data from the shumagin islands geodetic network lisowski et al 1988 larson and lisowski 1994 as well as uplift and tilt data savage and plafker 1991 beavan 1992 our model simulations here suggest that the shumagin segment is capable of large earthquakes the hypothesis of totally aseismic subduction is not similarly consistent with all geodetic constraints

effects of treethrow microtopography on the characteristics and genesis of spodosols michigan usa summary this study examined the pedogenic effects of pit and mound microtopography formed by tree uprooting in a spodosol haplorthods landscape most soils in treethrow pits were entic haplorthods or spodic upidsamments whereas mound soils usually classified as typic udipsamments suggesting that degree of profile development is undisturbed pit mound given that pit and mound soils are substantially younger than pedons on undisturbed sites rates of pedogenesis are thought to be pit undisturbed mound strong pedogenesis in pits was explained by 1 greater water contents in the upper sola which may facilitate weathering processes 2 thicker o horizons which may lead to increased production of organic acids and 3 greater insulation by thick litter and snow cover which reduces the incidence of soil freezing in winter mound soils may develop impermeable layers of concrete soil frost that impede infiltration of snowmelt waters whereas pit soils remain unfrozen or acquire only a porous granular frost layer thus saturated flow of snowmelt within pits is relatively unrestricted resulting in maximal leaching and profile differentiation

the rupture process and tectonic implications of the great 1964 prince william sound earthquake we have determined the rupture history of the march 28 1964 prince william sound earthquake m w 9 2 from long period wwssn p wave seismograms source time functions determined from the long period p waves indicate two major pulses of moment release the first and largest moment pulse has a duration of approximately 100 seconds with a relatively smooth onset which reaches a peak moment release rate at about 75 seconds into the rupture the second smaller pulse of moment release starts at approximately 160 seconds after the origin time and has a duration of roughly 40 seconds because of the large size of this event and thus a deficiency of on scale digitizable p wave seismograms it is impossible to uniquely invert for the location of moment release however if we assume a rupture direction based on the aftershock distribution and the results of surface wave directivity studies we are able to locate the spatial distribution of moment along the length of the fault the first moment pulse most likely initiated near the epicenter at the northeastern down dip edge of the aftershock area and then spread over the fault surface in a semi circular fashion until the full width of the fault was activated the rupture then extended toward the southwest approximately 300 km ruff and kanamori 1983 the second moment pulse was located in the vicinity of kodiak island starting at 500 km southwest of the epicenter and extending to about 600 km although the aftershock area extends southwest past the second moment pulse by at least 100 km the moment release remained low we interpret the 1964 prince william sound earthquake as a multiple asperity rupture with a very large dominant asperity in the epicentral region and a second major but smaller asperity in the kodiak island region

14 february 1983 earthquake sequence in the shumagin islands alaska abstract two moderate events m s 6 3 and 5 6 occurred just outside a local network in the shumagin islands alaska on 14 february 1983 these were the first events of magnitude greater than 5 5 in the region since 1979 they occurred within the subduction zone at a depth of 26 km of the more than 50 aftershocks that were recorded at one or more stations 12 events ranging from m b 2 5 to 4 0 were recorded digitally and located focal mechanisms were calculated for the two main events from first motion polarities and teleseismic body wave modeling the mechanisms for both events show similar nodal planes with p axes in the approximate direction of plate convergence and nearly vertical t axes the plane of motion is not constrained by the aftershocks but the shallowly dipping plane parallel to the subduction zone interface is the preferred solution dynamic stress drops of 80 and 70 bars are calculated from local strong motion records these events occurred in a mature seismic gap they nucleated in a shallow portion of the main thrust zone that apparently has a relatively low state of stress and thus were not capable of rupturing into the higher strength region at the base of the main thrust zone

rates of weathering and chemical depletion in soils across a chronosequence of lake michigan sand dunes abstract accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils i e o horizon and upper 15 cm of mineral soil across a 4150 year soil chronosequence of dune capped beach ridges bordering northern lake michigan within 400 years of beach ridge formation coniferous forest develops soil c and n accumulate to steady state levels of 40 and 1 3 mg ha 1 respectively and the ph of the upper mineral soil decreases from 8 5 to 4 3 as carbonate minerals dissolve after substantial proportions of ca and mg have been removed an incipient spodic horizon can be observed the upper surface of which progressively deepens with increasing soil age analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121 after several centuries of soil development after accounting for soil dilation quantities of ca mg p zn mn fe and v in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering resistant minerals mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as ca mg mn zn p v fe al k na ti this sequence is consistent with weathering of carbonates then ferromagnesian minerals then feldspars p levels are tightly coupled with ca losses in soils older than 200 years suggesting that ca rather than fe or al stabilizes p high concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants

source scaling of earthquakes in the shumagin region alaska time domain inversions of regional waveforms the scaling of pulse duration to seismic moment is estimated for earthquakes along an interplate thrust zone from digital waveforms recorded by short period and broad band instruments of the east aleutian shumagin seismic network we measure pulse duration using an empirical green s function technique based on damped time domain deconvolution from several thousand events 22 earthquakes with magnitudes 3 0 7 0 and depths 23 56 km are found to give reliable estimates of pulse duration durations are also determined directly from one parameter nonlinear inversions for a variety of simple functional forms of source time functions symmetric source pulses boxcar or triangle shapes fit waveforms better than an asymmetric model t exp 2t d for most 62 per cent of the waveform pairs while the asymmetric model fits best for only 8 per cent of the data pulse duration increases with the size of events from 0 1 to 10s over the seismic moment m0 range of 1014 to 3 1019 nm when normalized by the cube root of seismic moment pulse durations show 8 x variation comparable static stress drop estimates range from 0 2 to 135 mpa contrary to predictions of some laboratory and theoretical studies earthquakes at the deepest part of the thrust zone do not show significantly higher stress drops than do shallower events rupture properties however show a strong dependence on earthquake size the three largest events m0 5 1018nm have the three longest normalized durations on average 3 8 times longer than those for smaller events the durations require smaller events to have 10 100 x larger static stress drops or 4 x faster rupture velocities or some combination of the two possibly the largest events rupture both strong and weak patches while smaller events just rupture strong patches on the fault surface the characteristic dimension that separates large from small events 3 15 km is comparable to characteristic wavelengths of pacific basin bathymetry and may reflect the influence of the subducted sea floor upon fault zone heterogeneity

body wave and surface wave analysis of large and great earthquakes along the eastern aleutian arc 1923 1993 implications for future events the 500 km long alaska peninsula and shumagin islands segments of the aleutian arc have a moderate to high probability of rupturing in one or more large or great earthquakes in the next few decades to understand the likely modes of rupture in the next sequence of large and great events and to delineate the current geometry of the plate interface we determine focal mechanisms depths and source time functions from seismic records for the largest events since 1917 the great earthquake of november 10 1938 and seven events with surface wave magnitude ms of 6 9 to 7 5 teleseismic body waves and surface waves are used to estimate the seismic moment and gross rupture characteristics of the great earthquake of november 10 1938 along the alaska peninsula body wave inversion of five p and four sh waves gives a duration of about 110 s in which moment was released in two episodes each of about 50 s duration with the second being larger than the first the first source was located in the general vicinity of the epicenter of the mainshock and the second which occurred about 60 s later was centered about 180 km to the northeast the body wave derived seismic moment is 3 7 1021 n m mw 8 3 we corroborate the body wave results by calculating surface waves by normal mode summation and comparing them with data at periods greater than 50 s an adequate fit to observed seismograms is obtained for either a single point source or two point sources with one located about 180 km northeast of the mainshock epicenter rupture in 1938 appears to have been confined to the alaska peninsula segment uniform rupture into the shumagin region is not supported by the data the ms 6 9 earthquake of may 13 1993 ruptured a small portion of the shumagin gap the earthquake of may 14 1948 ms 7 5 occurred on a shallow dipping thrust fault with a depth of about 31 km not 60 km as originally suggested five ms 7 events in the 1938 rupture zone have locations depths and mechanisms that define a shallow dipping 16 19 plate interface which shallows to 8 under kodiak island subduction of seamounts of the gulf of alaska seamount province may explain the location moment focal mechanism and depth of the five ms 7 events the plate interface dips nearly uniformly between the alaska peninsula and shumagin segments indicating that segmentation if any is not controlled by the orientation of the plate interface a slight warp of the plate interface may form the boundary between rupture zones of great earthquakes along the kodiak and alaska peninsula segments of the arc and may explain why rupture zones of large to great earthquakes rarely cross this tectonic boundary

fine structure of the dipping seismic zone and subduction mechanics in the shumagin islands alaska microearthquake data from a permanent telemetered array have been used to elucidate the structure and tectonics of the subduction zone in the shumagin islands alaska the shallow microseismicity is characterized by active interplate thrusting in the 25 45 km depth range arcward of this interplate activity microearthquakes in the overlying plate have a strike slip mechanism the near horizontal p axis of this mechanism is oriented in the direction of plate convergence suggesting that the plate interface at shallow depths is currently efficiently coupled below 45 km depth the dipping seismic zone appears to be double planed the upper plane dips at 32 from 45 to 100 km depth where it exhibits a kneelike bend below the volcanic front the lower plane begins at about 65 km depth where it is separated from the upper plane by some 25 km and appears to converge with the upper plane at about 120 km depth the inferred geometry of the plate interface suggests that the double planed portion of the dipping seismic zone is a product of elastic unbending of the subducted plate a composite fault plane solution for events in the upper plane indicates however that downdip tension is currently present rather than the downdip compression that would be expected from unbending it is proposed that because of locking of the plate interface at shallower depths slab pull is currently overprinting the unbending stresses which predominate at times when the plates are unlocked this model is consistent with previous interpretations that there is a high probability of a great earthquake in the shumagin islands seismic gap within the next decade or two

the seismic coupling of subduction zones revisited 1 the nature of seismic coupling for many of the world s subduction zones has been reevaluated geodetic estimates of seismic coupling obtained from gps measurements of upper plate deformation during the interseismic period are summarized we compared those with new estimates of seismic coupling obtained from seismological data the results show that with a few notable exceptions the two methods agree to within about 10 the seismological estimates have been greatly improved over those made 20 30 years ago because of an abundance of paleoseismological data that greatly extend the temporal record of great subduction earthquakes and by the occurrence in the intervening years of an unusual number of great and giant earthquakes that have filled in some of the most critical holes in the seismic record the data also again with a few notable exceptions support the frictional instability theory of seismic coupling and in particular the test of that theory made by scholz and campos 1995 overall the results support their prediction that high coupling occurs for subduction zones subjected to high normal forces with a switch to low coupling occurring fairly abruptly as the normal force decreases below a critical value there is also considerable variation of coupling within individual subduction zones earthquake asperities correlate with areas of high coupling and hence have a semblance of permanence but the rupture zones and asperity distributions of great earthquakes may differ greatly between seismic cycles because of differences in the phase of seismic flux accumulation

modern warfare as a significant form of zoogeomorphic disturbance upon the landscape abstract the damage exerted by warfare on the physical landscape is one of many anthropogenic impacts upon the environment bombturbation is a term that describes the impacts of explosive munitions upon the landscape bombturbation like many other forms of zoogeomorphology is a disruptive force capable of moving large amounts of sediments and denuding landscapes to the point where changes in micro and mesotopography have long term implications the long term implication of bombturbative actions depends on the type and duration of explosive device that rendered the disturbance and the geographic context of the landscape disturbed i e cultural and physical factors recovery from bombturbative activity in the context of this research is measured by vegetative regrowth and soil development in cratered disturbances a comparison and contrast between the two battlefields of verdun france and khe sanh vietnam show that bombturbative actions have significantly altered the topography at each location thus influencing surface runoff and processes of soil development principals of the runge pedogenic model or the energy of water moving through the soil profile best explain how the varying climate and parent material at each location influence post disturbance soil development rates whereas the data collected at verdun suggest that explosive munitions have put that landscape on diverging path of development thus rendering it much different post disturbance landscape khe sanh displays much different recovery patterns preliminary research at khe sanh indicates that reforestation and soil development following disturbance are not so much influenced by bombturbative patterns as land use activities in the area of study

estimation of seismic moment and slip distribution of the april 1 1946 aleutian tsunami earthquake the 1946 aleutian earthquake produced a tsunami of tsunami magnitude mt 9 3 but the surface wave magnitude is only ms 7 4 making it a tsunami earthquake the discrepancy between the apparent size of the earthquake based on the seismic data and the size of the tsunami has been explained by several mechanisms including a landslide and a slow earthquake but there are few seismic data available to determine the correct mechanism we study the generating mechanism of the tsunami using tsunami waveforms recorded on tide gauges we have modeled the source of the 1946 aleutian tsunami as the result of an underthrusting earthquake we performed both forward and inverse modeling of the data using a finite difference calculation to compute synthetic tsunamis we include both vertical and horizontal deformation of the ocean bottom due to faulting in the computation the results of the inversion of the tsunami waveforms show that the slip on the fault is mainly concentrated in the shallow section of the fault near the epicenter there is little slip in the area of the aftershocks indicating that the aftershocks may represent an area of afterslip or triggered seismicity the moment estimate of the earthquake is 23 1020 n m or mw 8 2 the majority of the waveforms are well explained by this fault model and slip distribution including the honolulu waveform but the hawaiian data also suggest that other effects such as a landslide may be necessary for explaining the abnormal tsunami amplitudes in hawaii the 1946 earthquake is similar to other tsunami earthquakes such as the 1896 sanriku and 1992 nicaragua earthquakes indicating that slow shallow rupture may explain the disproportionally large tsunamis

the shumagin islands alaska earthquake of 31 may 1917 abstract although macroseismic reports indicate that great earthquakes have occurred in the vicinity of the shumagin gap of the eastern aleutian arc the largest well documented event within the gap has been an m s 7 5 event that occurred in 1948 this earthquake apparently ruptured only a 75 km long segment of the 200 km long gap and as such is not considered a gap filling event relocations of turn of the century seismicity by boyd and lerner lam 1988 suggest however that another more poorly documented event nucleated near the shumagin islands on 31 may 1917 an m s of 7 9 determined from a single station bulletin has been assigned to this event although consistent with its apparent aftershock distribution macroseismic reports appear to be too small for such a large event we use surface waves to estimate the moment and rupture bounds and body waves to constrain the focal mechanism and depth of the 1917 event the average m s at 13 azimuthally well distributed stations is 7 4 0 3 much smaller than the previous estimate of 7 9 the spatial variation in individual magnitude estimates is azimuthally dependent 7 9 to the west and 6 8 to the east implying source directivity assuming a thrust fault mechanism body wave inversion yields a source depth of 29 km and m w of 7 4 in addition assuming rupture velocity and rupture propagation along arc to the west consistent with the aftershock distribution a rupture length of 75 km and m w of 7 5 are required to match long period surface waves recorded at uppsala sweden and gottingen germany these results suggest that the average slip of the 1917 event was only about 75 to 150 cm and was restricted to the easternmost portion of the gap these results when combined with rupture zones and recurrence intervals of other eastern aleutian events imply a temporally heterogeneous rupture style where the rupture bounds and consequently the sizes of earthquakes vary from cycle to cycle estimating the magnitudes or rupture extents of the next series of events based on the previous series appears to be unjustified

strain accumulation in the shumagin and yakataga seismic gaps alaska strain accumulation during the 1980 85 interval has been measured by means of trilateration surveys in the shumagin and yakataga seismic gaps which are the two regions identified as the most likely sites for the next great thrust earthquakes along the alaska aleutian arc no significant strain accumulation was detected in the shumagin gap but experience at similar subduction zones and simple models of the subduction process suggest that a measurable amount of strain should have accumulated the most likely explanation of the observation is that subduction there is either aseismic or episodic the strain accumulation measured in the yakataga gap is consistent with that expected for the plate convergence rate although the direction of maximum compression may suggest a somewhat more oblique convergence than expected

variations in the mode of great earthquake rupture along the central peru subduction zone the historic record for the central peru subduction zone suggests significant variations in the earthquake size during the last 400 years during this century there have been four great underthrusting earthquakes along the central peru seismic zone from north to south these are the 17 october 1966 mw 8 1 24 may 1940 m 8 3 october 1974 mw 8 1 and 24 august 1942 m 8 2 earthquakes modified mercalli intensity data and tsunami observations for the earthquakes in this century are compared with the 29 october 1746 and 20 october 1687 earthquakes the 1746 earthquake had maximum intensity values between 9 and 13 s while the 1687 event had maximum values between 12 and 14 s suggesting that the two events failed different segments of the subduction zone we find that the 1746 event occurred along the segiment that includes both 1940 and 1966 earthquakes the size of the 1746 event is estimated to be mw 8 8 based on the ratio of near field tsunami heights for the 1746 and 1966 earthquakes the 1687 earthquake probably raptured the 1974 segment as well as the adjacent segment to the south where there is at present a gap between the 1942 and 1974 rupture zones the size of the 1687 event is estimated to be mw 8 7 based on both far field and near field tsunami height ratios of the 1687 and 1974 events both 1746 and 1687 earthquakes appear to be much larger than the events of this century in contrast to the simple single asperity nature of the 20th century earthquakes these older and larger events may represent multiple asperity ruptures along the peru subduction zone hence variations in the mode of earthquake rupture from cycle to cycle along the central peru seismic zone may explain the significant difference in earthquake size during die last 400 years

opposed shear senses inferred from neotectonic mesofracture systems in the north anatolian fault zone abstract the 1200 km long north anatolian fault zone is a right lateral intracontinental transform boundary which was initiated in the late neogene sediments of pliocene to holocene age in basins between cerkes and erbaa within the convex northwards arc of the fault zone are deformed by syn sedimentary and post depositional mesoscopic faults and joints the mesofractures which strike obliquely to the fault zone include reverse faults normal faults normal shear joints conjugate vertical joints and strike slip faults each type of structure occurs in two geometrical groups one comprises four systems of fractures the other is made up of five systems the directions of secondary compression and or extension inferred from the first group of mesofractures which are restricted to sediments of pliocene to early pleistocene age are interpreted as being related to left lateral shear along the north anatolian fault zone the directions of compression and or extension inferred from the second group of mesofractures which cut sediments of pliocene to late holocene age were generated during right lateral shear the presence of the second group of mesofractures is understandable because they are related to the shear sense which operates at the present day but those interpreted as being related to left lateral shear are more puzzling their development implies one or more reversals of the dominant sense of displacement several tentative models to explain such reversals are proposed including regional and local influences the latter related to mechanical constraints and or the effects of other fault systems

thermal stresses in subducting lithosphere can explain double seismic zones the discovery of double planed zones of intermediate depth seismicity associated with subducting oceanic lithosphere refs 1 7 and l s h and k h j in preparation has generated much interest in the origin and distribution of stresses in descending plates several mechanisms have been proposed to explain why double zones occur8 here we investigate the role of thermal stresses for the state of stress in a descending plate and test whether they can account for the observed characteristics of double seismic zones by modelling the descending slab as a thin elastic plate and using the temperatures in the slab estimated by toksoz et al 9 we find that the polarities of thermally generated stresses agree with those obtained from the focal mechanisms of earthquakes in the two zones thermal stresses also can explain the separation between the two zones of seismicity at shallow depths and their gradual merging at greater depth

gravity anomalies crustal structure and seismicity at subduction zones 2 interrelationships between fore arc structure and seismogenic behavior an ensemble averaging technique is used to remove the long wavelength topography and gravity field associated with subduction zones short wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates a paired positive negative fore arc anomaly is observed consisting of a long 1000 km linear trench parallel ridge landward of the deep sea terrace basin ridges have amplitudes of 1500 3000 m and 160 240 mgal wavelengths of 150 200 km and high gravity anomaly to topography ratios 50 75 mgal km 1 the ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in cascadia the updip limit of tremor epicenters the ridge crest may be interpreted as defining the boundary between the velocity weakening and seismogenic region of the subduction interface and the downdip frictional transition zone in tonga kermadec the kuril islands and chile landward ridges are associated with extinct volcanic arcs paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of a lower crustal underplating beneath the inner fore arc b the transformation of interseismic strain into permanent geologic strain via faulting folding or buckling of the inner fore arc and c the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit along strike transitions in fore arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates fore arcs have the added potential of recording the time integrated response of the upper plate to subduction processes and fore arc structure should be considered in tandem with seismological observations

emi as a non invasive survey technique to account for the interaction between ww i relicts and the soil environment at the western front abstract after the war the greater part of the disturbed areas within the western front zone of world war i ww i was taken back into culture even 100 years after date it can be assumed that the soil within these areas still contains the traces of the war to account for a thorough inventory of both the soil variability the ww i relicts and the anthropogenic disturbances and to identify their interactions a large scale non invasive approach employing a multi receiver frequency domain emi instrument was proposed with this instrument both lateral variations of the soil apparent electrical conductivity a and apparent magnetic susceptibility a from multiple overlapping soil volumes were obtained at a battlefield site within the western front zone inverting the multiple simultaneous a measurements allowed for a detailed representation of the depth to the interface between both contrasting loess and clay layers at the study site additionally anomalies caused by buried metal objects could be separated from more subtle anomalies caused by shell holes moreover inverting the a measurements improved the identification of different ww i trenches finally the integration of all ww i and soil features allowed for an enhanced understanding about the impact of the war activities on the soil environment and vice versa

alluvial soil chronosequence in the inner coastal plain central virginia abstract a chronological sequence of soils formed on a series of alluvial depositional surfaces ranging in age from late middle miocene to late pleistocene was characterized to clarify soil geomorphic relations and provide a basis for allostratigraphic subdivision of the inner coastal plain on quaternary river terraces ultic hapludalfs containing abundant weatherable mineral species and clast types are estimated to have formed in 60 000 120 000 yr whereas typic hapludults greatly depleted in weatherable minerals and showing strong weathering of clast types are estimated to be 700 000 1 600 000 yr old typic paleudults with incipient plinthite duripan and ferricrete development characterize interfluves that have been little eroded since early pliocene time 3 4 5 3 myr ago typic plinthic paleudults with intense weathering of siliceous clasts and moderate to strong duripan and ferricrete development are found on surfaces that formed near the beginning of late miocene time 10 8 13 0 myr ago chemical weathering in the chronosequence may be classified into three progressive stages 1 decomposition of unstable sand and silt sized minerals into a mixed stable unstable clay mineral suite stable fe al si bulk chemical composition 107 yr not all soil properties show unidirectional development nor is a steady state of pedon development observed even after approximately 107 yr of chemical weathering soil development in the chronosequence is episodic the transition from one phase to the next is marked by a change in rate and sometimes a reversal in the direction of development of one or more soil properties

link between plate fabric hydration and subduction zone seismicity in alaska subduction carries water into the earth where it can influence seismicity analysis of the structure of the alaskan subduction zone suggests fluid delivery is influenced by faults in the oceanic plate that formed at the mid ocean ridge

measurement of horizontal motions in alaska using very long baseline interferometry we have analyzed 6 years of very long baseline interferometry vlbi data beginning in 1984 from a network of sites in alaska the yukon and the conterminous united states the analysis of these 53 data sets includes constrained continuous piecewise linear estimation of the site atmospheres and clocks application of values and correlations from a self consistent earth orientation series derived from other vlbi data and simultaneous estimation of site positions and velocities from a solution that includes 21 007 observations with a fit of 40 ps in delay and 64 fs s in delay rate we have determined the horizontal velocities of seven sites with precisions of 0 5 2 mm yr 1 standard deviation the three vlbi sites within the alaska aleutian subduction boundary zone yakataga kodiak and sand point have higher instantaneous velocities relative to eastern north america than the interior sites of alaska fairbanks and sourdough the estimated velocity of yakataga relative to fairbanks is 37 8 1 3 mm yr at n27 w 2 modeling of the yakataga data suggests that the observed motion is the result of elastic straining of the overriding plate due to a locked main thrust zone with a component of oblique slip the estimated velocity of kodiak relative to fairbanks is 13 6 0 8 mm yr at n41 w 3 this result is lower than the rate predicted on the basis of simple elastic dislocation models the estimated velocity of sand point relative to fairbanks is 6 4 0 9 mm yr at n65 w 8 the component of this velocity in the plate direction 3 5 1 1 mm yr is not consistent with either an aseismic slip model i e no strain accumulation in the overriding plate or a model in which the site is undergoing compressional strain 10 9 mm yr at n28 w due to simple subduction at the predicted orientation of pacific plate convergence in a north america fixed reference frame the estimated velocities of fairbanks 1 5 0 5 mm yr at s12 e 20 and sourdough 3 9 1 0 mm yr at s13 w 13 are both southward these results may imply motion of this region relative to stable north america but more observations are required to reduce the uncertainties in the azimuths the time evolution of the estimated site positions from vlbi in alaska are in general consistent with constant velocity however in 1988 the yakataga site showed a significant departure from the position predicted from a constant velocity model obtained from the previously estimated position this departure may be static displacement associated with two major strike slip earthquakes that occurred in the gulf of alaska between the 1987 and 1988 measurement sessions

single station fault plane solutions abstract fault plane solutions are derived from systematic trial and error grid testing of three component body waveform data from a single station modeling p and sh waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between p and sh waveforms is sufficient to discriminate between fault type e g strike slip versus dip slip and often agrees with well constrained first motion studies events studied are the 9 april 1968 borrego mountain california 20 june 1978 thessaloniki greece 13 august 1978 santa barbara california 20 may 1979 alaska and 6 august 1979 coyote lake california earthquakes it is also shown using data from the 27 july 1980 sharpsburg kentucky earthquake that inclusion of pp p and sp p polarity and amplitude information to an otherwise unconstrained first motion study can significantly improve the quality of the fault plane solution although there are many potential problems source multiplicity directivity etc which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable the results of this study suggest that sparse high quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first motion studies at a minimum they should be performed together as a consistency check this procedure would be most useful in the common situation where only a few receivers are available for a particular event

transition from double to single wadati benioff seismic zone in the shumagin islands alaska a discontinuity exists in the moderate depth seismicity located by the shumagin seismic network in the eastern aleutian subduction zone the boundary is nearly perpendicular to the arc and has a double planed wadati benioff zone to the west and a single planed zone to the east the transition does not appear to be an artifact of mislocations as shown by three dimensional ray trace modeling and examination of phases of representative earthquakes current theory on the presence or absence of double seismic zones suggests a change in stress across the boundary if so the east and west regions may either have different aseismic to seismic slip ratios or be in different stages of the earthquake cycle

aftershocks of the 13 may 1993 shumagin alaska earthquake the 13 may 1993 ms 6 9 shumagin earthquake had an aftershock sequence of 247 earthquakes with magnitudes greater than or equal to 1 5 by 1 june 1993 of these aftershocks 79 were located by using s p travel times at the only two stations within 570 km of the mainshock epicenter the rupture area inferred from the aftershocks is about 600 km2 and we estimate for the mainshock a mean fault displacement of 1 0 m and a 28 bar stress drop the magnitude frequency plots give a b value for the aftershock sequence of about 0 4 which is low compared to the background value of approximately 0 8 the decay of the aftershock sequence followed the modified omori law with a p value of 0 79 which is also lower than the typical values of about 1 1 observed in alaska both of these facts can be interpreted as indicating relatively high ambient stress in the shumagin seismic gap and the possibility that the 13 may earthquake was a foreshock to a larger gap filling event to occur within the next few years

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

evaluation of tsunami amplitudes for the pacific coast of canada abstract maximum tsunami water levels and currents along the british columbia outer coast have been computed for waves originating from alaska chile the aleutian islands shumagin gap and kamchatka three computer models have been developed to generate and propagate a tsunami from each of these source regions in the pacific ocean to the continental shelf off canada s west coast and into 20 separate inlet systems the model predictions have been verified against water level measurements made at tide gauges after the march 28 1964 alaska earthquake simulated seabed motions giving rise to the alaskan and chilean tsunamis have been based on surveys of vertical displacements made after the great earthquakes of 1964 alaska and 1960 chile hypothetical bottom motions have been used for the shumagin gap and kamachatka simulations these simulations represent the largest tsunamigenic events to be expected from these areas maximum wave and current amplitudes have been tabulated for each simulated tsunami in 185 key locations along the british columbia coast on the north coast of british columbia the alaska tsunami generated the largest amplitudes in all other regions of the west coast the largest amplitudes were generated by the shumagin gap simulation wave amplitudes in excess of 9 m were predicted at several locations along the coast and current speeds of 3 to 4 m s were produced the most vulnerable regions are the outer coast of vancouver island the west coast of graham island and the central coast of the mainland some areas such as the north central coast are sheltered enough to limit expected maximum water levels to less than 3 m the computer models developed in this study are sufficiently general to be applicable to other tsunami affected regions on the globe

earthquakes plate subduction and stress reversals in the eastern aleutian arc plate subduction beneath the 1500 km long segment of the eastern aleutian arc between kodiak and atka islands 154 w and 176 w longitude is studied with observations from teleseismic data the primary data base consists of hypocenters of earthquakes for the period 1965 1975 carefully selected from the bulletins of the international seismological centre and of 44 new focal mechanism solutions the principal results of this study are that hypocenters of intermediate depth earthquakes in the eastern aleutians appear to define a weakly developed double seismic zone at depths between 70 and 170 km additional evidence for a double seismic zone comes from focal mechanisms which generally show downdip directed p axes for earthquakes in the upper zone and downdip directed t axes in the lower zone major features of the double zone can be explained by thermoelastic stresses in the downgoing plate the observed predominant downdip stress polarity at intermediate depths in the descending plate reverses along strike of the arc this stress reversal coincides in map view with a change from a continental to an oceanic arc the coincidence may result from spatial differences either in the coupling between the plates at shallow depths or in the rheology of the surrounding oceanic versus continental mantle alternatively the stress reversal may be related to the time since the last great earthquake if the observed stress polarity relates to the elapsed time since the last great earthquake it may be a significant observation for long to intermediate term prediction of great thrust earthquakes in subduction zones portions of the eastern aleutian arc where downdip tension predominates contain one or more seismic gaps that appear to have a high probability for great earthquakes in the next few decades a moderate sized bathymetric feature in the pacific plate the amlia fracture zone modifies subduction and produces a bend or offset in the downgoing plate as well as an offset in the line of active volcanoes in the upper plate subduction of the fracture zone appears also to cause formation of summit basins on the arc platform and some aseismic behavior of a 100 km long segment of the main thrust zone

seismicity trends and potential for large earthquakes in the alaska aleutian region the high likelihood of a gap filling thrust earthquake in the alaska subduction zone within this decade is indicated by two independent methods analysis of historic earthquake recurrence data and time to failure analysis applied to recent decades of instrumental data recent may 1993 earthquake activity in the shumagin islands gap is consistent with previous projections of increases in seismic release indicating that this segment along with the alaska peninsula segment is approaching failure based on this pattern of accelerating seismic release we project the occurrence of one or morem 7 3 earthquakes in the shumagin alaska peninsula region during 1994 1996 different segments of the alaska aleutian seismic zone behave differently in the decade or two preceding great earthquakes some showing acceleration of seismic release type a zones while others show deceleration type d zones the largest alaska aleutian earthquakes in 1957 1964 and 1965 originated in zones that exhibit type d behavior type a zones currently showing accelerating release are the shumagin alaska peninsula delarof and kommandorski segments time to failure analysis suggests that the large earthquakes could occur in these latter zones within the next few years

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

seismic potential of the queen charlotte alaska aleutian seismic zone the 5000 km long queen charlotte alaska aleutian seismic zone is subdivided into 17 unequally sized segments their boundaries are delineated based on the prior distribution of large and great earthquakes the 17 segments are chosen to represent areas likely to be ruptured by characteristic earthquakes this term usually implies repeated breakage of a plate boundary segment by either a large or great earthquake whose source dimensions remain consistent from cycle to cycle this definition does not exclude the possibility that occasionally adjacent characteristic earthquake segments may break together in a single giant event that is larger than the characteristic size outlined conversely a segment can also sometimes break in a series of smaller ruptures formal computations of the conditional probabilities for future large and great earthquakes in the 17 segments of the queen charlotte alaska aleutian seismic zone are based on the following data sets and findings 1 recurrence intervals from historic and geologic data 2 direct recurrence time estimates based on rates of relative plate motion and the size or displacement of the most recent characteristic event in each segment and 3 the application of a lognormal distribution of recurrence times for large and great earthquakes results of these computations indicate seven areas that have high i e 60 conditional probabilities for the recurrence of either large or great earthquakes within the next 20 years 1988 2008 these areas include cape st james yakataga the shumagin islands unimak island and the fox delarof and near islands segments of the aleutian arc when a shorter time interval is considered 1988 1998 those segments more likely to rupture in large ms 7 7 7 rather than great earthquakes have a high conditional probability these areas include the unimak fox and delarof islands segments the largest uncertainties in these forecasts stem from the short historic record providing a single recurrence time estimate for some segments or widely varying estimates for others from the unknown importance of aseismic slip and from a vague definition of characteristic earthquake size in fact characteristic earthquake size may not be a time invariant quantity

spatial distribution of turn of the century seismicity along the alaska aleutian arc abstract epicenters determined for instrumentally observed earthquakes occurring around the turn of the century have figured prominently in estimates of seismic hazard along the alaska aleutian arc unfortunately because of poor timing control and a sparse station distribution the locations quoted in the older catalogs can be very unreliable more reliable epicenter estimates and quantitative assessments of the errors associated with these estimates are needed to address issues related to seismic hazard seventeen earthquakes with surface wave magnitudes above 6 8 that were recorded between 1898 and 1917 are relocated using a modified least squares criterion epicentral estimates are determined using p s and s p arrival times with the a priori constraint that the final location must be near the geographically defined arc although epicenters determined using a standard least squares criterion can be located up to 800 km from the arc the arc proximity constraint provides tectonically more meaningful locations which to a high degree of confidence fit the travel time observations as well as the unconstrained locations epicentral shifts of up to 1 200 km are observed between the relocations and those reported in the earlier catalogs seventy five per cent confidence bounds on the along arc location of each event vary from 30 to 400 km several large events m s 6 9 occurred within or near the rupture zone of the 1965 rat islands earthquake and may indicate that this zone failed in a sequence of events around the turn of the century of the four events previously suggested as being possible candidates for rupturing either the shumagin or unalaska seismic gaps none relocate near these arc segments the relocation of a large m s 7 9 earthquake which occurred in 1917 within the shumagin islands region however provides the first strong evidence of largescale seismic moment release within this intensely studied seismic gap

absence of strain accumulation in the western shumagin segment of the alaska subduction zone gps measurements in the western shumagin segment of the alaska subduction zone show no significant strain the elastic dislocation model that best fits the data has the entire plate interface slipping freely the simplest explanation is that steady slip at the plate convergence rate is occurring on the entire plate interface although we cannot rule out the existence of a shallow locked patch close to the trench large enough to generate a m 7 earthquake the 99 confidence upper bound on the down dip width of the locked patch is 55 km assuming the trench is the the updip limit of the locked zone unless there is significant temporal variability in the locking of the plate interface or viscoelastic effects from a past earthquake the shumagin segment cannot by itself release enough moment to generate a great m 8 earthquake

crustal earthquakes in the cook inlet and susitna region of southern alaska abstract several large m 6 earthquakes have occurred in the vicinity of anchorage alaska within the past century the presence of the underlying subducting pacific plate makes it difficult to determine the origin of these older earthquakes as either crustal slab or the subduction plate interface we perform a seismological study of historical and modern earthquakes within the cook inlet and susitna region west of anchorage we first estimate hypocenters for historical large earthquakes in order to assess their likelihood of origin as crustal slab or plate interface we then examine modern crustal seismicity to better understand the style of faulting and the location of active structures including within and beneath the cook inlet and susitna basins we perform double couple moment tensor inversions using high frequency body waves 1 10 hz for small to moderate m 2 5 crustal earthquakes depth 30 km occurring from 2007 to 2017 our misfit function combines both waveforms differences as well as first motion polarities in order to obtain reliable moment tensor solutions the three focus regions beluga upper cook inlet and susitna exhibit predominantly thrust mechanisms for crustal earthquakes indicating an overall compressive regime within the crust that is approximately consistent with the direction of plate convergence mechanisms within upper cook inlet have strike directions aligned with active anticlines previously identified in cook inlet from active source seismic data our catalog of moment tensors is helpful for identifying and characterizing subsurface faults from seismic lineaments and from faults inferred from subsurface images from active source seismic data

a lithosequence of soils in extremely gravelly dolomitic parent materials bois blanc island lake huron abstract eight extremely gravelly pedons on bois blanc island were characterized and pathways and processes of genesis were examined the soils are developed in dolomitic gravels and cobbles and contain 1 50 mean 15 fine earth most pedons are in coarse loamy or skeletal particle size families in extremely gravelly parent materials with less than 5 fine earth b horizons have not formed accumulation of organic matter on the surface and between coarse fragments in the upper solum is the main pedogenic process in such soils borofolists in other soils distinct eluvial and illuvial zones are present with organic carbon silts fine sands and caco 3 being the primary constituents undergoing translocation quantity and mineralogical composition of the fine earth appear to alter the pathways of pedogenesis as the amount of fine earth and the percentage of non carbonate materials derived from crystalline rocks increase cambic horizons with spodic morphology may develop

relation of ongoing deformation rates to the subduction zone process in southern alaska the rate and orientation of ongoing strain associated with subduction of the pacific plate and the accretion of the yakutat terrane to southern alaska has been estimated at 13 sites from global positioning system measurements made in june 1993 and 1995 along the gulf of alaska coast near cape yakataga the average rate of deformation relative to fairbanks was 38 mm yr at n32 w further inland above the region where the dip of the downgoing pacific plate changes from about 10 to 30 the deformation rate was 12mm yr at n26 w in the sourdough paxson area the deformation rate drops to 2 5 mm yr and suggests a low short term deformation rate across the denali fault elastic straining of the overriding plate due to back slip on a main thrust zone with an average dip of about 10 can account for the overall rate and distribution of short term compressional strain across south central alaska above the transitional region between unstable and stable sliding we suggest that strain associated with 15 mm yr of right lateral strike slip occurs also if the strain accumulated since the two 1899 earthquakes both mw 8 1 from the offshore pamplona fault zone to south of the border ranges fault down dip width 100 km was seismically released on a single fault it would correspond to a m 8 1 earthquake

volcanic and tectonic deformation on unimak island in the aleutian arc alaska 3 3 10 6 m 3 yr 1 the gps data indicate that inflation may have slowed down slightly compared with interferometric synthetic aperture radar insar observations between 1993 and 1998 the accumulated subsurface volume increase during the gps and insar observation period 1993 2001 70 10 6 m 3 already accounts for at least 15 more than the erupted volume from the last eruption in 1991 1992 fisher caldera shows subsidence and contraction across the caldera center the data are fit best with a rectangular dislocation source at a shallow depth it is 14 km long and 0 5 km wide dips 80 to the nw and strikes n35 e with rather large uncertainties for most of these parameters its volume decrease is 2 0 10 6 m 3 yr 1 the main mechanisms to explain the subsidence and contraction are degassing and contractional cooling of a shallow magma body and depressurization of fisher s hydrothermal system possibly triggered by an earthquake in 1999 at the 95 confidence level no significant strain accumulation due to subduction is observed across the entire island the low coupling across the rupture zone of the 1946 earthquake is a strong argument for the idea that the earthquake and tsunami did not result from a purely double couple earthquake source index terms 1206 geodesy and gravity crustal movements interplate 8155 8135 tectonophysics evolution of the earth hydrothermal systems 8424 8145 tectonophysics evolution of the earth physics of magma and magma bodies 8150 tectonophysics evolution of the earth plate boundary general 3040 keywords volcanic deformation caldera deformation aleutian arc alaska unimak island citation mann d and j freymueller volcanic and tectonic deformation on unimak island in the aleutian arc alaska j geophys res 108 b2 2108 doi 10 1029 2002jb001925 2003

soil development on the wwi battlefield of verdun france abstract much research has been done on how the physical environment can influence the outcome of battle but few have studied the inverse the effects of warfare upon the environment the goal of this research is to characterize and help understand soil development within areas disturbed by explosive munitions on the wwi battlefield of verdun france 1916 encompassing an area of 29 000 km 2 the battlefield remains one of the most heavily shelled of all time twenty seven pedons were sampled and described at three sites on the battlefield some pedons were within artillery craters while others were on adjacent undisturbed soils site selection reflected the diversity of bedrock and drainage characteristics across the study area soil development was characterized within the crater bottoms and sides many craters penetrated the shallow limestone bedrock and blasted out fragments of limestone on nearby undisturbed pedons had already been incorporated into the profile despite the short period of time since the battle 88 years measurable amounts of weathering and pedogenesis has occurred in the soils within the craters a major pedogenic process operative here is the accumulation and decomposition of organic matter which is intimately associated with and aided by earthworm bioturbation based on elemental analysis of the fine earth fraction measurable amounts of leaching and weathering have occurred in the 88 years since the battle this study provides insight into the ability of a landscape to recover following a catastrophic anthropogenic disturbance

crustal deformation and the seismic cycle across the kodiak islands alaska 1 the kodiak islands are located 120 to 250 km from the alaska aleutian trench and are within the southern extent of the 1964 prince william sound mw 9 2 earthquake rupture and aftershock zone here we report new campaign gps results 1993 2001 from northeastern kodiak and reprocessed gps results 1993 1997 from southwestern kodiak the rate and orientation of the horizontal velocities relative to a fixed north america range from 29 7 1 7 mm yr at n30 3 w 3 3 located 120 km from the deepest point of the trench to 8 0 1 3 mm yr at n62 4 w 9 3 located 230 km from the trench we evaluated alternate models of coseismic and interseismic slip to test the importance of the mechanisms that account for surface deformation rates near the gulf of alaska coastal region of kodiak the horizontal velocity can be accounted for primarily by the viscoelastic response to plate motion and a locked main thrust zone mtz downdip creep and to a lesser extent slip in the 1964 earthquake farther inland the dominant mechanisms that account for post 1964 uplift rates are time dependent downdip creep and a locked mtz for the horizontal velocity component southwest translation of western kodiak may be important as well on the basis of the pre 1964 and post 1964 earthquake pattern of interseismic earthquakes we suggest that between the occurrences of great earthquakes like the 1964 event more moderate to large earthquakes occur in the southwestern kodiak region than near northeastern kodiak