tertiary extensional faulting and evolving ductile brittle transition zones in the northern snake range and vicinity new insights from seismic data new geologic mapping and high resolution seismic data from east central nevada shed light on the evolution of the northern snake range decollement nsrd and its relation to the present basins and ranges we suggest that the nsrd originated in oligocene time as a flat 20 km wide 7 km deep zone of decoupling between localized ductile stretching below and more widely distributed high angle normal faulting above younger east dipping normal faults cut the western part of the nsrd forming the tilted fault blocks and highly asymmetric grabens that constitute the duck creek range duck creek valley and schell creek range spring valley and folded the nsrd to its present antiformal geometry these youngest faults flatten into pervasive subhorizontal reflectors at a depth of 10 to 15 km that we interpret as the youngest ductile brittle transition

reverse slip structures at oceanic diverging plate boundaries and their kinematic origin data from tertiary crust of west and south iceland abstract normal faulting predominates within rift zones but reverse fault plane solutions are occasionally found for earthquakes along the mid atlantic ridge furthermore field observations of striae and in situ measurements in places show off rift compression and reverse faulting we analyse eight cases of reverse slip motion observed in the eroded tertiary crust of the borgarfjor ur and hreppar rift jump blocks respectively in west and south iceland these structures were the only ones observed where both striae and marker horizons could be used to deduce the sense of reverse slip motion the vertical displacements are less than 10 m and the motions are of local origin we believe these structures are formed independently from regional compression as they have variable kinematic origins some occur in association with dykes sills or cone sheet without evidence of horizontal shortening across intrusions others are due to local bends of regional steeply dipping normal faults or secondary fractures riedel or secondary fractures reverse slip striations are found at the irregularities of steeply dipping normal faults or at the tips of steeply dipping normal faults uplifted by an underlying propagating dyke striations even conspicuous ones do not necessarily reflect significant amounts of displacement if horizontal compression acts in iceland its magnitude is not sufficient to shorten the rocks and to close the fractures of various tectonic settings the observed examples are explained as local kinematic adjustments to companion structures without regional compressional stress field or shortening and can lead to misinterpretation if not put into the correct context

a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

object oriented classification of a high spatial resolution spot5 image for mapping geology and landforms of active volcanoes semeru case study indonesia the present work explores the object oriented classification ooc of high spatial resolution hsr satellite panchromatic imagery for mapping the geology of the persistently active semeru volcano and its ring plain east java indonesia a panchromatic spot5 image and a digital elevation model dem have been used to identify geologic units structures landforms and deposits the panchromatic image was georeferenced and enhanced using histogram equalization the enhanced image was segmented into polygons using the envifx exelis software the polygons were delineated and classified on the basis of spectral panchromatic hues and textures topographic slope elevation information and geologic geomorphic processes the validity of classification was evaluated by interpreting google earth images aerial photographs and limited field observations the classification consists of three hierarchical levels across the volcanic area of about 745 km2 the first operational spatial level includes seven large volcano domains based on the spectral content of the volcanic tectonic and lithological structures and principal catchments the second operational level based on contextual relationships topography drainage network vegetation cover type stratigraphy and slope dynamics encompasses 20 geological units that range between 30 and 80 km2 in area among the units the third operational level distinguishes as many as 47 geomorphological sub units 0 25 25 km2 according to slope gradient deposit type mass wasting process and weathering the resulting map provides a detailed pattern of geologic and geomorphic features unlike previous geologic maps that identified only 11 stratigraphic units we show that the high spatial resolution panchromatic spot5 scene can help to safely map the geology and landforms of persistently active volcanoes such as semeru we have applied the ooc technique on one hsr geoeye panchromatic image to map another active volcano merapi in central java after considerable geomorphic changes due to the large eruption in 2010

effect of lithospheric thickness on the formation of high and low angle normal faults it is accepted that extension of a homogeneous brittle layer should produce high angle normal faults the rotation of the upper parts of such a fault to a low dip requires fault offset that is greater than the local lithospheric thickness new model calculations indicate that a fault cutting lithosphere thicker than 10 20 km can build up only a few kilometres horizontal throw before a new fault replaces it such a small offset leaves the fault little rotated from its initial high dip angle for thinner lithosphere the fault offset may be much larger leading to rotation of the upper inactive parts of a high angle fault to a low dip angle in continents this can happen where thin upper crustal lithosphere is decoupled from mantle lithosphere by weak lower crust the calculations suggest that normal faults begin with high dip angles and only in areas of very thin lithosphere can they be offset enough to produce low angle fault structures this prediction is consistent with the occurrence of low angle faults in areas with higher than normal heat flow

the 1971 may 12 burdur earthquake sequence sw turkey a synthesis of seismological and geological observations summary it is now widely accepted that the rapid extension observed in western turkey is mainly accommodated by large active normal faults which control the geomorphology the ne sw trending burdur acigol and baklan basins bounded by large faults form a system of half graben whose orientation is evident in both the topography and the tilting of neogene sediments adjacent to them we used long period p and sh waveforms to determine the source parameters of the two largest earthquakes of the 1971 may 12 sequence that occurred in the burdur region the main shock was followed by many aftershocks which were distributed in a broad zone elongated ne sw parallel to the long axes of the basins in the region documented surface breaks of the 1971 event suggest that the northwest dipping faults along the southern margin of the burdur basin are those which moved well exposed fault planes are found dominantly to the south of burdur lake the surface dips of these faults are greater than that of the nw dipping nodal plane obtained for the main shock combined seismological and geological observations suggest that these faults have listric geometries

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

active submarine tectonism and formation of the gulf of saros northeast aegean sea inferred from multi channel seismic reflection data abstract active submarine tectonism and the formation of the gulf of saros northeast aegean sea were investigated by means of multi channel seismic reflection data this area is a key in understanding the development of major structures resulting from the interacting regimes of the western anatolia aegean sea and the north anatolian fault zone naf the major feature forming the gulf of saros is the ganos fault which is one of the main segments of the northern strand of the naf in this study a total of 159 km reflection seismic data were collected processed and interpreted in seven lines in order to map active submarine faults which were used to propose a tectonic model for opening of the gulf of saros interpretation of the seismic sections and their correlation with the geological morphological and earthquake data indicate that there are two main fault systems in the gulf i strike slip faults with normal components which bound the saros trough in the north and south and ii normal faults located within the trough we propose that the saros trough was first formed as a negative flower structure in response to the southward bending of the naf zone possibly in plio quaternary then it evolved as a dilated negative flower structure as the aegean extension intensified in late pliocene quaternary

geometry and mechanism of faulting of the 1980 el asnam algeria earthquake from inversion of teleseismic body waves and comparison with field observations the el asnam earthquake of october 10 1980 ms 7 3 provided a wealth of geological and seismological data and is an ideal event for comparing geologically and seismologically derived models the event produced extensive surface faulting in addition to the main tectonic deformation which is clearly a thrust widespread secondary normal faulting was observed at the surface in the southwest region the surface break of a thrust fault could be traced for 24 km in the northeast part of the fault zone normal faults with throws of several meters were observed although no clear thrust type surface breaks were observed in this region geodetic measurements and aftershocks indicate that thrusting was nonetheless the main tectonic mode of deformation in this paper the rupture process of the el asnam earthquake is investigated by inversion of teleseismic p and sh waves the effort is concentrated on the late part of the waveforms which carries information about the faulting in the least understood north eastern segment of the fault zone during the earthquake rupture initiated at the southern terminus of the southwestern fault segment and propagated northward as indicated by the epicentral location and the observable azimuthal directivity of the body wave shapes and amplitudes the seismogenic faulting in the southwestern segment has a thrust mechanism with the following average parameters seismic moment 3 9 1019 n m depth 6 km strike 220 dip 46 and rake 72 the duration of rupture on this fault segment was approximately 10 s which together with the observed fault length of 24 km indicates a rupture velocity of 2 4 km s unconstrained inversions suggest normal faulting in the northeast part of the source region that began immediately following the arrival of the rupture to the northeast region the normal faulting mechanism is in agreement with that observed for the large surface fault scarps in this region guided by the evidence from aftershocks and geodetic measurements a solution with a thrust type mechanism was also sought using a priori constraints based on the field observations the observed strike and slip angle we obtain the following thrust source mechanism for the northeast segment seismic moment 3 6 1019 n m depth 6 km strike 230 dip 20 and rake 91 this solution requires that the thrusting in the northeast be initiated 10 s after the arrival of the rupture from the southwest suggesting that some time is required to overcome the geometric barrier marked by the abrupt change in the dip and azimuth inversions are nonunique with respect to the seismic moment associated with normal faulting the ambiguity being caused by the limited bandwidth of the observed body waves the moment estimated from the surface waves at periods about 300 s however favors thrust faulting to be dominant in the northeast region

tertiary extension and contraction of lower plate rocks in the central mojave metamorphic core complex southern california several authors recently have proposed the rolling hinge model for the formation of extensional detachment faults in metamorphic core complexes in this model isostatic uplift of the denuded footwall of a major normal fault causes the near surface part of the fault to rotate from a higher to a lower dip for the rolling hinge model to be acceptable the footwalls of detachment faults must have undergone the strain pattern dictated by the rolling hinge in this paper the structural development of the footwall of the central mojave metamorphic core complex is used as a field test tertiary structures in the lower plate of the core complex record ne directed ductile extensional shear followed by cataclastic ne side up shear with a significant component of contraction along the previous extension direction this strain history agrees with the rolling hinge model and particularly with a version of the model in which footwall uplift occurs by a combination of elastic flexure and flexurally driven upper crustal failure similar late stage layer parallel contraction appears to be present in some other tectonically denuded terranes of the basin and range suggesting that the flexural failure rolling hinge model for extensional terranes may be widely applicable

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

the effects of pressure and porosity on the micromechanics of the brittle ductile transition in quartzite room temperature experiments on a quartzite with 7 porosity show that with increasing pressure there is a transition from brittle faulting to ductile cataclastic flow at about 600 mpa in contrast experiments on nonporous quartzite show only faulting up to 1000 mpa the transition to cataclastic flow in the porous quartzite is due to the changing influence of the pores microstructural observations and elastic theory suggest that the transition occurs at the pressure where the differential stress producing a compressive stress concentration sufficient to initiate pore collapse becomes less than that producing a tensile stress concentration sufficient to nucleate axial microcracks at the tops and bottoms of pores cataclastic flow of the porous quartzite is only transient deformation remains distributed and accompanied by work hardening only as long as pore collapse continues to 16 strain at higher strains microcracking produces a net dilatancy which causes strain weakening that leads to faulting at 26 strain at a confining pressure of 750 mpa the faults are stable whereas at 1000 mpa they are unstable the results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust but higher strains will cause deformation to localize

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

application of synthetic aperture radar sar imagery to volcano mapping in the humid tropics a case study in east java indonesia volcanoes in humid tropical environments are frequently cloud covered typically densely vegetated and rapidly eroded these factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes numerous previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions here cloud and vegetation penetrating lhh band 24 cm synthetic aperture radar sar data from the japanese earth resources satellite jers 1 are used to investigate persistently active volcanoes and prehistoric calderas in east java indonesia the lhh band jers 1 sar produces high spatial resolution 18 m imagery with relatively high incidence angle that highlights structures and topographic variations at or greater than the wavelength scale while minimising geometrical distortions such as layover and foreshortening these images along with internet browse data derived from the canadian radarsat mission provide new evidence relating regional tectonics to volcanism throughout east java volcanic events such as caldera collapse at the tengger caldera appear to have been partly controlled by northwest aligned faults related to intra arc sedimentary basins similar regional controls appear important at historically active lamongan volcano which is encircled by numerous flank maars and cinder cones a previously undocumented pyroclastic sheet and debris avalanche deposit from the jambangan caldera complex is also manifested in the synoptic radar images at the currently active semeru volcano these data permit identification of recent pyroclastic flow and lahar deposits radar data therefore offer a valuable tool for mapping and hazard assessment at late quaternary volcanoes the criteria developed in the analysis here could be applied to other regions in the humid tropics

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

on the development of zones of reverse shearing in mylonitic rocks abstract most shear zones contain a minor proportion of domains recognizable from thin section to outcrop scale which show an opposing shear sense relative to the overall kinematic framework in this paper we discuss how these universal features result from the evolving deformation strain partitioning that generally accompanies progressive general shear principally in low metamorphic grade shear zones because the rheologic properties and consequently the contributions of the different deformation mechanisms change continuously with progressive strain an individual domain with a predominant deformation mechanism much faster or slower than the average may depart from the general kinematics enhancing the viscosity contrast between adjacent layers and causing locally reverse shear in the domain boundaries care is needed therefore in interpreting opposing shear senses in the same shear zone as indicating superimposed deformation events

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

slickenside and fault surface kinematic indicators on active normal faults of the alpine betic cordilleras granada southern spain abstract twenty four mesoscopic slickenside kinematic indicators are described here for the pliocene quaternary active normal faults of the alpine betic cordilleras granada southern spain the indicators are classified into twelve groups depending on the down or up slope asymmetric orientation of features such as concavities damaged versus sharp grain borders or step edges v shaped markings fractures and trailed material seventeen of the indicators were not previously described in the literature the new kinematic indicators include two types of asymmetric grains a carrot shaped marking six substructures of congruous and incongruous steps trailed fault material a drop shaped figure a v shaped marking three types of synthetic hybrid fractures with congruous steps and two varieties of pluck holes we think that some of these kinematic indicators provide information on the amount of displacement aseismic versus seismic slip rates cataclastic flow frictional wear or surface polishing

slickenside kinematic indicators abstract a new classification of slickenside kinematic indicators is presented based on 61 criteria these slickensides have been subdivided into eleven major groups v or crescentic markings steps fractures trains of inclined planar structures trailed material asymmetric elevations deformed elements mineralogical crystallographic orientations asymmetric plan view features asymmetric cavities and asymmetric folds this classification constitutes a useful tool for geologists interested in the determination of the shear sense in fault surfaces bearing slickensides examples of application of this classification to natural fault surfaces at different scales are presented

shear zone model for the origin of metamorphic core complexes core complex tectonite results from simple shear rotational strain within regional ductile shear zones that have accommodated a tertiary crustal stretching the emplacement of younger and or upper level nontectonite rocks on older and or deeper level tectonites is the ordinary and predictable result of normal slip translation along shear zones that cut upward through the local geologic column progressive deformation produces a structural stratigraphy marked from bottom to top by normal country rock protolith mylonitic gneiss tectonite carapace microbrecciated tectonite microbreccia decollement and upper plate detachment rocks as young as mid miocene the reconstructions suggest that local regional crustal stretching locally exceeded 100

near n s paleo extension in the western deccan region india does it link strike slip tectonics with india seychelles rifting this is the first detailed report and analyses of deformation from the w part of the deccan large igneous province dlip maharashtra india this deformation related to the india seychelles rifting during late cretaceous early paleocene was studied and the paleostress tensors were deduced near n s trending shear zones lineaments and faults were already reported without significant detail an e w extension was envisaged by the previous workers to explain the india seychelles rift at 64 ma the direction of extension however does not match with their n s brittle shear zones and also those faults sub vertical ne sw nw se and few n s we report and emphasize in this work slickenside bearing fault planes brittle shear zones and extension fractures in meso scale enabled us to estimate the paleostress tensors directions and relative magnitudes the field study was complemented by remote sensing lineament analyses to map dykes and shear zones dykes emplaced along pre existing n s to ne sw nw se shears fractures this information was used to derive regional paleostress trends a nw se ne sw minimum compressive stress in the oldest kalsubai subgroup and a n s direction for the younger lonavala wai and salsette subgroups were deciphered thus a nw ne to n s extension is put forward that refutes the popular view of e w india seychelles extension paleostress analyses indicate that this is an oblique rifted margin field criteria suggest only ne sw and nw se with some n s strike slip faults brittle shear zones we refer this deformation zone as the western deccan strike slip zone wdsz the observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies these geophysical findings too indicate oblique rifting in this part of the w indian passive margin we argue that the seychelles microcontinent separated from india only after much of the dlip erupted further studies of magma rich passive margins with respect to timing and architecture of deformation and emplacement of volcanics are required

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

the aljibes half graben active extension at the boundary between the trans mexican volcanic belt and the basin and range province mexico the aljibes half graben is located 140 km west northwest of mexico city and is characterized by several parallel 10 km long south dipping and east striking normal faults late miocene basalt flows with 40 ar 39 ar ages of 7 7 0 1 ma and 7 1 0 5 ma are displaced along these faults with reference to this basalt the composite throw and heave of the half graben are 480 m and 270 m respectively and the relative extension is 5 whereas the vertical slip rate along the faults of the aljibes half graben after the deposition of the basalt is 0 07 mm yr the aljibes half graben is located at the northern margin of the trans mexican volcanic belt and perpendicularly intersects northstriking normal faults of the basin and range province the relative sequence of activity of the two stress fields and fault systems cannot be resolved in the study area and the two systems may have been active simultaneously we explain this structural configuration by horizontal migration of the boundary between the two stress provinces with time which requires intermittent permutations between the intermediate and least principal stresses 2 and 3 this is supported by the low stress ratio 2 3 1 3 obtained from modeling the stress tensor associated with the slip along the faults of the aljibes half graben the orientations of the fault planes and slip vectors of the aljibes half graben are practically identical to those of the nearby acambay graben and the venta de bravo fault which caused the acambay earthquake of november 19 1912 m s 6 9 and the maravatio earthquake of february 22 1979 m b 5 3 furthermore the aljibes half graben forms the extrapolated western continuation of the northern master fault of the mezquital graben which ruptured partly in the cardonal earthquake of march 26 1976 m b 5 3 this suggests the aljibes half graben may also be seismically active although no historical earthquake is known to have occurred along this structure further evidence for the likely seismic activity of the aljibes half graben are two east to eastnortheast trending epicenter alignments between the aljibes halfgraben and the mezquital graben and structural indication for stickslip behavior based on the structure of the aljibes half graben we believe the maximum credible earthquake that may occur along the faults of the aljibes half graben is on the order of 2 10 27 dyne cm m 0 6 10 25 dyne cm and 7 5 m w 6 5

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

geology tectonics and the 2002 2003 eruption of the semeru volcano indonesia interpreted from high spatial resolution satellite imagery abstract the paper illustrates the application of high spatial resolution satellite images in interpreting volcanic structures and eruption impacts in the tengger semeru massif in east java indonesia we use high spatial resolution images ikonos and spot 5 and aerial photos in order to analyze the structures of semeru volcano and map the deposits geological and tectonic mapping is based on two dems and on the interpretation of aerial photos and four spot and ikonos optical satellite images acquired between 1996 and 2002 we also compared two thermal surface kinetic temperature aster images before and after the 2002 2003 eruption in order to delineate and evaluate the impacts of the pyroclastic density currents semeru s principal structural features are probably due to the tectonic setting of the volcano a structural map of the tengger semeru massif shows four groups of faults orientated n40 n160 n75 and n105 to n140 conspicuous structures such as the se trending horseshoe shaped scar on semeru s summit cone coincide with the n160 trending faults the direction of minor scars on the east flank parallels the first and second groups of faults the semeru composite cone hosts the currently active jonggring seloko vent this is located on and buttressed against the mahameru edifice at the head of a large scar that may reflect a failure plane at shallow depth dipping 35 towards the se this failure plane may correspond to a weak basal layer of weathered volcaniclastic rocks of tertiary age we suggest that the deformation pattern of semeru and its large scar may be induced by flank spreading over the weak basal layer of the volcano it is therefore necessary to consider the potential for flank and summit collapse in the future the last major eruption took place in december 2002 january 2003 and involved emplacement of block and ash flows we have used the 2003 aster surface kinetic temperature image to map the 2002 2003 pyroclastic density current deposits we have also compared two 10 m pixel images acquired before and after the event to describe the extent and impact of an estimated volume of 5 45 106 m3 of block and ash flow deposits an ash rich pyroclastic surge escaped from one of the valley confined block and ash flows at 5 to 8 km distance from the crater and swept across the forest and tilled land on the sw side of the bang river valley downvalley the temperature of the pyroclastic surge decreased and a mud rich deposit coated the banks of the bang river valley thus hazard mitigation at semeru should combine 1 continuous monitoring of the eruptive activity through an early warning system and 2 continuous remote sensing of the morphological changes in the drainage system due to the impact of frequent pyroclastic density currents and lahars

factors controlling normal fault offset in an ideal brittle layer we study the physical processes controlling the development and evolution of normal faults by analyzing numerical experiments of extension of an ideal two dimensional elastic plastic brittle layer floating on an inviscid fluid the yield stress of the layer is the sum of the layer cohesion and its frictional stress faults are initiated by a small plastic flaw in the layer we get finite fault offset when we make fault cohesion decrease with strain even in this highly idealized system we vary six physical parameters the initial cohesion of the layer the thickness of the layer the rate of cohesion reduction with plastic strain the friction coefficient the flaw size and the fault width we obtain two main types of faulting behavior 1 multiple major faults with small offset and 2 single major fault that can develop very large offset we show that only two parameters control these different types of faulting patterns 1 the brittle layer thickness for a given cohesion and 2 the rate of cohesion reduction with strain for a large brittle layer thickness 22 km with 44 mpa of cohesion extension always leads to multiple faults distributed over the width of the layer for a smaller brittle layer thickness the fault pattern is dependent on the rate of fault weakening a very slow rate of weakening leads to a very large offset fault and a fast rate of weakening leads to an asymmetric graben and eventually to a very large offset fault when the offset is very large the model produces major features of the pattern of topography and faulting seen in some metamorphic core complexes

the threat of hazards in the semeru volcano region ineast java indonesia abstract semeru volcano 3676 m the highest volcano in java is one of the most active volcanoes in indonesia its activity has occurred almost continuously since 1967 the activity is manifested by mostly strombolian type eruptions with lava extrusions which extend into a lava tongue in kobokan breach southeast slope of the volcano the lava tongue is unstable after reaching a certain volume the tongue collapses and causes pyroclastic flows to the southeast direction traveling a maximum of about 11 km downslope the collapse is sometimes triggered by volcanic eruptions the main dangers are not due to eruption and collapse of the lava tongue but caused by the secondary dangers the secondary dangers are more destructive and distributed over a wider area tens of kilometres from the source the natural hazards in the semeru region are not only related to volcanic activity which is so called lahar but also non volcanic processes such as debris flow this phenomenon is related to the heavy rainfall which causes landslides in the altered volcanic deposit areas the flow of the mixture of water and landslide materials has devastated large areas the occurrences of the secondary flow is unpredictable and its viscosity is much lower than lahar this flow is distributed over a wide area and threatens cultivated land and densely populated and developing urban areas

the little skull mountain nevada earthquake of 29 june 1992 aftershock focal mechanisms and tectonic stress field implications the ml 5 6 29 june 1992 little skull mountain earthquake occurred in the southern nevada test site nye county nevada within 20 km of a potential national nuclear waste repository at yucca mountain nevada while microseismicity in the immediate epicentral vicinity occurred for years prior to the mainshock foreshock activity ml 2 were also sufficiently well recorded to provide local network p wave focal mechanism solutions the mainshock and the majority of the aftershocks through september 1992 display predominantly normal slip focal mechanisms but unambiguous strike slip and oblique slip focal mechanism solutions are also present in the aftershock series the mainshock and immediate foreshock depths were 10 1 km below sea level and depths of focus of aftershocks range from about 6 to 12 km a large subset of the aftershock hypocenters define a southeast dipping structure probably the mainshock fault plane no variation of mechanism style with depth is apparent two mainshock and 84 aftershock focal mechanism solutions were input into gephart s 1990 stressfield inversion program and principal compressional stress directions j j 1 2 3 were determined as well as the stress difference ratio r 1 2 1 3 the results indicate a uniform stress field in which 3 minimum stress is oriented 116 5 azi plunge and 1 maximum stress is oriented 219 69 with r 0 35 the inversion s selection of preferred nodal planes invokes bott s 1959 criterion which states that slip occurs in the direction of resolved shear traction on preexisting fault surfaces for the predominantly normal slip little skull mountain earthquake mechanisms having northeast striking planes the southeast moderately to steeply dipping dip 55 nodal planes are selected however for the dip slip earthquake mechanisms exhibiting more northerly trending strikes shallowly to moderately west dipping 25 dip 65 nodal planes are selected when a coulomb mohr analysis was applied to the focal mechanisms using the above principal stress directions and an assumed ratio 1 3 the ratio of resolved shear stress to normal stress n on the southeast dipping nodal plane of the mainshock exhibited a near maximum level suggesting a high fault strength in contrast a wide range of fault strengths or apparent coefficients of friction was suggested by the n ratios for little skull mountain aftershock preferred nodal planes seismicity on misoriented faults i e those on which shear stress was relatively low may have been the result of a temporarily elevated fluid pore pressure following the mainshock

dips of normal faults in british coal measures and other sedimentary sequences fault dip measurements n 3291 from 122 faults in british coalfields are presented two classes of normal fault are recognized a gently dipping 55 post coalification tectonic faults formed at depths of about 2 5 km which comprise 90 of the faults analysed dip data from the steeply dipping faults are variable standard deviation 9 both on single faults and between faults and 70 is a better approximation of fault dip than the commonly accepted value of 60 data on tectonic normal faults with comparable depths of formation using the modified griffith fracture criterion the dips of faults at varying depths up to 4 km are calculated for both unsaturated dry and saturated rocks the dips of normal faults are expected to vary from 90 at the surface to 60 at 3 4 km and this variation is consistent with the limited field data available the coalfield data are consistent with fault formation at standard hydrostatic pore fluid pressures at depths of about 2 5 km below depths of a few kilometres normal faults are expected to flatten out gradually to a dip of 45 but such flattening is not necessarily an indication of an underlying detachment

methods for quantitatively determining fault slip using fault separation abstract fault slip and fault separation are generally not equal to each other however they are geometrically related the fault slip s is a vector with a magnitude a direction and a sense of the movement in this paper a series of approaches are introduced to estimate quantitatively the magnitude and direction of the fault slip using fault separations for calculation the known factors are the pitch of slip lineations the pitch of a cutoff the dip separation smd or the strike separation smh for one marker the two main purposes of this work include 1 to analyze the relationship between fault slip and fault separation when slickenside lineations of a fault are known 2 to estimate the slip direction when the parameters smd or smh and for two non parallel markers at a place e g a point are known we tested the approaches using an example from a mainly strike slip fault in east quantoxhead united kingdom and another example from the jordan field ector county texas also we estimated the relative errors of apparent heave of the normal faults from the sierra de san miguelito central mexico

structural evolution of the dayman dome metamorphic core complex eastern papua new guinea a shallow dipping ductile mylonitic shear zone and concordant brittle detachment fault mai iu fault together make up the dominant geological structure that controls the orientation of dip slopes on the fl anks of mount dayman eastern papuan peninsula papua new guinea the dip slopes dip in all directions from the peak of mount dayman and form a domed landform that is much less dissected by streams compared to the adjacent mount suckling domed landform the orientation of megacorrugations on the domed surface of mount dayman footwall is consistent with nne directed transport of the hangingwall block which is composed of low grade undifferentiated volcanic and sedimentary rocks and minor ultramafi c rocks though previously documented as a thrust surface the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation s1 and mineral elongation lineation l1 the fi eld relationships are consistent with the domed landform comprising the core of a metamorphic core complex observations of dominantly nne trending regional lineaments in aerial photography and shuttle radar topography mission srtm data correlate with detailed fi eld analysis of mineral elongation lineations l1 in the main metamorphic core complex bounding shear zone field relationships show a crosscutting sequence of structures that includes 1 ductile s2 folia with ese plunging blue sodic calcic amphibole mineral elongation lineations 2 narrow steeply dipping ductile d2 shear zones and 3 semibrittle to brittle fault zones s c fabrics asymmetric strain shadows around porphyroclasts and fault drag indicate a top down to the nne sense of shear for most structures kinematic vorticity analysis of the highest grade ductile deformation indicates a kinematic vorticity number wk between 0 34 and 0 56 suggesting general shear for the early stage of deformation d1 the nne directed lineaments and l1 mineral elongation lineations are consistent with the australia woodlark eulerian pole for periods between the early pliocene 3 6 ma and pleistocene 0 52 ma this observation is consistent with ca 3 3 ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3 3 ma on mount suckling a se dipping sedimentary sequence gwoira conglomerate characterizes part of the hanging wall of the metamorphic core complex petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source the unit is in fault contact with the metabasite footwall across prehnite bearing d3 brittle fault zones

morphologically ductile criteria for the sense of movement on slickensides from an extensional detachment fault in southern spain abstract new criteria for the sense of movement on slickenside surfaces displaying evidence for mesoscopic ductility are described in the neogene jaloche extensional detachment fault in southern spain this detachment develops spectacular slickensides and fault gouges and four of the criteria for the sense of movement observed along the highly polished slip surfaces are new to the literature they are 1 synthetic secondary fractures with hangingwall drag effects in the form of roll over microsynclines 2 metre scale oval shaped asymmetric culmination and depression features 3 microthrusts verging towards the direction of motion of the opposite block and dragging overthrusting previous planar elements on the fault surface and 4 flakes of fault surface material trailed and plastered in the direction of the missing block the geometry and microstructure of these features reveal that they deformed in a morphologically ductile manner by the coupled processes of cataclastic flow and shear localization probably during aseismic sliding during transient seismic pulses deformation occurred along shiny polished slickenside fault planes occasionally bearing jigsaw implosion breccias fluids under high pressure present initially may have promoted distributed cracking whereas the process of dilatancy hardening may have served to facilitate cataclastic flow in the deformation history

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

the geometrical evolution of normal fault systems abstract the purpose of this paper is to examine the kinematic behaviour of normal fault systems and see what general conditions govern their geometrical evolution we pay particular attention to seismological and surface data from regions of present day active normal faulting as the instantaneous three dimensional geometry at the time of fault movement is better known in active regions than in areas where the faults are now static most normal faults are concave upward or listric this shape can be produced by geometric constraints either because the faults reactivate curved thrusts or because they must be curved to accommodate rotations another effect which will produce curved faults is the variation of rheology with depth brittle failure at shallow depths produces less fault rotation than does distributed creep in the lower part of the crust an important geometric feature of normal faulting is the uplift of the footwall the amount of such uplift is related not only to the elastic properties of the lithosphere but also to the throw and dip of the fault a striking feature of active normal faults is that they occur in groups in which all the faults dip in the same direction this behaviour arises because the faults cannot intersect if they do one must cease to be active the rotation which such fault systems produce reduces the dip of the faults until a new steeply dipping fault is formed once a new fault cuts pre existing faults the earlier faults become locked and a new set of faults must propagate rapidly across the whole region involved many of these geometric constraints also apply to thrust faulting

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

control of rupture by fault geometry during the 1980 el asnam algeria earthquake summary the el asnam earthquake of 1980 october 10 ms 7 3 occurred on a segmented reverse fault in the atlas mountains of algeria this report re examines the teleseismic data for the main shock and major aftershocks in the light of detailed studies of the surface breaks geodetic changes and aftershock distribution the observed thrust fault is split into southern central and northern segments by distinct offsets and changes in trend the southern and central segments are each about 12 km long but the northern segment showed only 3 4 km of surface thrust breaks however widespread tensional faulting on ridges in the north east area together with focal mechanisms of locally recorded aftershocks indicates that a series of imbricate listric thrusts exists to the north of the northern fault segment using isc arrival time lists a relative relocation scheme is applied to the main shock and major aftershocks to improve their locations with respect to the mapped faults the main shock epicentre was at the south west end of the fault system in a zone where the thrust has a zig zag surface trace by contrast most of the major aftershocks were located further north east and were associated with the northern thrust segment and the imbricate thrusts to the north the largest aftershock mb 6 1 which occurred about 3 hr after the main shock was located to the east of the main thrust fault beneath the chelif alluvial basin first motion fault plane solutions are presented for the main shock and largest aftershock the main shock solution indicates a fault plane dipping 54 nw with strike 040 the aftershock solution however has a more e w trend 080 in agreement with the trends of the basin edges near its location the rupture history of the main shock is investigated by forward modelling of the long period p waves four subevents are clearly distinguishable the first three subevents occurred in rapid succession and contributed to the first cycle of the p wave radiation these three subevents represent the successive rupturing of the southern central and northern fault segments in order to match the observed waveforms these three ruptures must have different mechanisms and moments the fault segments have successively shallower dipts from south to north 54 45 and 40 respectively and the central segment had the largest moment release in agreement with the geodetic data of ruegg et al the delay times between the three sources suggest a rupture velocity of about 3 5 km s 1 and their nucleation depths were 7 km the junctions between the fault segments acted as geometric barriers to the rupture propagation but were broken by its passage the fourth subevent of the main shock produced the second cycle of the p wave radiation it began about 18 s after the first i e several seconds after the end of the third rupture nabelek demonstrates that the fourth subevent occurred on a shallow angle 20 thrust plane examination of the locally recorded aftershocks suggests that this plane is a decollement surface underlying the imbricate thrusts of the north east area the total seismic moment found from the body wave modelling is 7 7 1026 dyne cm in good agreement with geodetic and surface wave studies

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

ductility in fault gouge from a normal fault system death valley california a mechanism for fault zone strengthening and relevance to paleoseismicity fault gouge along the badwater turtleback fault system displays abundant evidence for mesoscopic ductility as foliation isolated and or rotated inclusions and isoclinal folds fault gouge thicknesses also vary dramatically at the outcrop scale gouge thicknesses can range from 0 to 1 m and at the 100 m scale they can range from 0 to 5 m because these variations are closely associated with other ductility related features they probably also formed because of ductile flow ductile flow appears to locally strengthen the fault zone by severe attenuation of the gouge and by transport of inclusions where gouge pinches out to zero thickness hanging wall rock rests directly on footwall rock a condition that produces an overall stronger fault zone as well as stick slip behavior in laboratory tests transport of inclusions within the gouge zone may create local inclusion jams which may also have a strengthening effect the presence of these stronger portions of the fault zone may give indirect evidence for ancient seismicity on the fault

mantle core complexes and neogene extensional detachment tectonics in the western betic cordilleras spain an alternative model for the emplacement of the ronda peridotite abstract an alternative model for the emplacement of the ronda peridotite betic alpine orogenic belt southern spain is proposed involving mantle uprising during a major neogene extensional event the development of a detachment system and its further evolution by isostatic rebound and upward arching would have triggered the tectonic denudation of these ultramafic bodies forming what may be termed mantle core complexes mantle core complexes would represent a final step in the core complex forming processes once a complete separation of the upper and lower blocks has been achieved in a detachment system marking probably the transition from an intracontinental to a proto oceanic rift environment

volcanic hazards at mount semeru east java indonesia with emphasis on lahars mt semeru the highest mountain in java 3 676 m is one of the few persistently active composite volcanoes on earth with a plain supporting about 1 million people we present the geology of the edifice review its historical eruptive activity and assess hazards posed by the current activity highlighting the lahar threat the composite andesite cone of semeru results from the growth of two edifices the mahameru old semeru and the seloko young semeru on the se flank of the summit cone a n130 trending scar branched on the active jonggring seloko vent is the current pathway for rockslides and pyroclastic flows produced by dome growth the eruptive activity recorded since 1818 shows three styles 1 the persistent vulcanian and phreatomagmatic regime consists of short lived eruption columns several times a day 2 increase in activity every 5 to 7 years produces several kilometer high eruption columns ballistic bombs and thick tephra fall around the vent and ash fall 40 km downwind dome extrusion in the vent and subsequent collapses produce block and ash flows that travel toward the se as far as 11 km from the summit and 3 flank lava flows erupted on the lower se and e flanks in 1895 and in 1941 1942 pyroclastic flows recur every 5 years on average while large scale lahars exceeding 5 million m3 each have occurred at least five times since 1884 lumajang a city home to 85 000 people located 35 km e of the summit was devastated by lahars in 1909 in 2000 the catchment of the curah lengkong river on the ese flank shows an annual sediment yield of 2 7 105 m3 km 2 and a denudation rate of 4 105 t km 2 yr 1 comparable with values reported at other active composite cones in wet environment unlike catchments affected by high magnitude eruptions sediment yield at mt semeru however does not decline drastically within the first post eruption years this is due to the daily supply of pyroclastic debris shed over the summit cone which is remobilised by runoff during the rainy season three hazard prone areas are delineated at mt semeru 1 a triangle shaped area open toward the se has been frequently swept by dome collapse avalanches and pyroclastic flows 2 the s and se valleys convey tens of rain triggered lahars each year within a distance of 20 km toward the ring plain 3 valleys 25 km s se and the ring plain 35 km e toward lumajang can be affected by debris avalanches and debris flows if the steep sided summit cone fails

geologic structural and thermochronologic constraints on the tectonic evolution of the sierra mazatan core complex sonora mexico new insights into metamorphic core complex formation 1 the sierra mazatan in northwestern mexico is the southernmost metamorphic core complex in the north american cordillera large magnitude tertiary extension at sierra mazatan involved both ductile and brittle slip along a major normal fault that presently dips 10 15 west extension was polyphase and involved an early period of extension from 25 to 23 ma followed by major slip from 21 to 16 ma total slip was 20 km and occurred at rates of 3 4 mm a this extension predated the plate boundary change to transtension at 12 ma and was largely decoupled from relative pacific north american plate motion numerous lines of evidence suggest that the presently low angle normal fault initiated at a steep dip 50 60 and was rotated to lower angles during slip when corrected for this tilting fault corrugations at sierra mazatan had a similar geometry to the segmentation of many active normal faults which is compatible with their origin as primary fault features many aspects of the sierra mazatan are comparable to large active normal faults indicating that this core complex formed owing to prolonged extension on an otherwise typical high angle normal fault therefore core complexes need not represent a fundamentally unique mode of crustal extension

evaluation of simulation models of lateral spread sites treated with prefabricated vertical drains abstractfinite element analyses are performed of centrifuge tests consisting of untreated and drain treated lateral spread sites with the goal of evaluating the ability of numerical simulations to predict the response of sites improved with prefabricated vertical drains finite element models of varying complexity are analyzed a two dimensional model of the full centrifuge test a three dimensional unit cell model around a single drain and a two dimensional unit cell model all the finite element models predict pore pressures consistent with the centrifuge tests the deformation responses of the finite element models show that unit cell analyses produce significantly larger deformations than those observed in the centrifuge this result is caused by the fact that the centrifuge test geometry is not well represented by the infinite slope condition assumed in a unit cell the full two dimensional model predicts deformations that are more consistent with those of the centrifuge because it can capture the

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

soil liquefaction induced uplift of underground structures physical and numerical modeling abstractunderground structures located in liquefiable soil deposits are susceptible to floatation following a major earthquake event such failure phenomenon generally occurs when the soil liquefies and loses its shear resistance against the uplift force from the buoyancy of the underground structure numerical modeling accompanied with centrifuge experiments with shallow circular structures has been carried out to investigate the floatation failure at different buried depths of the structure the influence of the magnitude of input sinusoidal earthquake shaking was also studied both numerical and experimental results showed matching uplift response of the structures and acceleration and pore pressure measurements in the liquefied soil deposit a higher uplift displacement of the structure was observed for shallower buried depth thereby indicating the influence of overlying soil weight against floatation results also showed that the structures commenced floatation in the presence of high excess pore pr

the influence of inherited structures on dike emplacement during gondwana breakup in southwestern africa abstracta kinematic analysis of cretaceous and pre cretaceous structures was carried out along the west coast of southern africa extending from the cape town area into namibia with the aim of investigating whether inherited structural discontinuities controlled gondwana breakup and the associated opening of the south atlantic in the cretaceous this was augmented by map and satellite image analyses of mainly cretaceous mafic dikes exposed from sw angola to the southern tip of africa the combined results provide consistent evidence of e w to ne sw directed extension during the cretaceous e w extension dominated from southern angola to the namibian south african border and ne sw directed extension occurred in an area extending from west central namibia to the southwestern coast of south africa these two extension directions overlap from west central namibia to southernmost namibia the kinematic analysis of pan african structures provides evidence of ene wsw directed shortening in the western saldania

crustal thinning and subsidence in the north sea we present here the results of a detailed study of subsidence and crystal thinning across the central graben of the north sea basin two independent lines of evidence have been used to test how well the uniform extensional model1 2 can account for the evolution of the north sea basin a long range seismic profile was shot perpendicular to the central graben from edinburgh to southern norway and data were analysed from 11 exploration wells situated close to the seismic line fig 1 the estimates of the increase in surface area due to extension from the crustal structure determined using the seismic data and from the well subsidence patterns are both compatible with a simple uniform extensional mechanism for the post palaeozoic evolution of the north sea

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

experimental investigation of drainage during earthquake induced liquefaction earthquake induced liquefaction is typically viewed as an undrained phenomenon with undrained element tests forming the core of knowledge built around it however there is evidence to suggest that

stability of scour protection due to earthquake induced liquefaction centrifuge modelling abstract a key aspect of permanent offshore structures is protection against scour this is typically in the form of a blanket of coarse gravel or cobbles surrounding the structure these coarse particles are selected for their high resistance to being displaced by strong currents and thus protect the underlying finer sand particles from scour however in the event of an earthquake the foundation sand may be susceptible to some degree of liquefaction this research investigates the effects of seismic induced liquefaction over a scour blanket and if sinking is inhibited by some combination of the additional effective stress imposed by the gravel together with the interlocking resistance that develops when coarse particles are subjected to relative displacements in order to evaluate the stability of scour protection blankets a programme of physical modelling was carried out involving the assessment of different configurations of stone layers over a liquefiable material and a monopile type foundation models were subjected to scaled base shaking equivalent to earthquake loading a mass balance of particle sinkage showed that a filter layer was critical for maintaining the integrity of the armour stones based on displacement and pore water pressure measurements it was found that the presence of the scour protection blankets improved the response of the liquefiable sand under seismic loading and even inhibited the occurrence of liquefaction this implies that a well designed scour protection blanket can assist in protecting against earthquake effects also

the low temperature brittle ductile transition in a quartzite and the occurrence of cataclastic flow in nature the paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite oughtibridge ganister and compares its microstructural development with features of cataclastic deformation of rocks in nature

kinematic indicators on active normal faults in western turkey quaternary normal fault zones in western turkey comprise multiple slip planes and zone parallel layers of fault breccia they also contain several little known kinematic indicators that are probably typical of many formed at shallow levels in extending terrains the recent exhumation by contractors of about 2000 m2 of slip planes in a sse dipping fault zone separating quaternary colluvium from bedrock carbonates at yavansu 7 km se of kusadasi permits an unusually complete inventory of the indicators to be compiled the most spectacular indicators are metre scale 69 w pitching corrugations in slip planes and recemented breccia sheets underlying them corrugations characterized by sinusoidal profiles normal to their long axes and less commonly culminations and depression along their axes possibly developed as a result of upwards propagating slip planes seeking undemanding pathways through heterogeneous fault precursor breccias that formed in advance of tip lines parallel to corrugation long axes are those of gutters flat floored sleep sided channels a few centimetres wide probably related to the abrasion of subslip plane breccia sheets centimetre scale tool tracks scored in the uppermost subslip plane breccia sheet by resistant colluvial clasts are irregular at their proximal ends but distally they swing into alignment with corrugation axes frictional wear striae centimetres long but only a few millimetres wide and pitching 78 w are superimposed on the other slip parallel lineations comb fractures nearly perpendicular to slip planes define an intersection lineation which is normal to corrugation axes fault plane solutions of earthquakes on sse dipping active faults in the west anatolian extensional province indicate that mainly normal combined with minor dextral slip is the dominant mode a conclusion in accord with the sense of slip inferred from the indicators exposed on the yavansu slip planes

spatio temporal evolution of strain accumulation derived from multi scale observations of late jurassic rifting in the northern north sea a critical test of models for lithospheric extension abstract we integrate observations of lithospheric extension over a wide range of spatial and temporal scales within the northern north sea basin and critically review the extent to which existing theories of lithospheric deformation can account for these observations data obtained through a prolonged period of hydrocarbon exploration and production has yielded a dense and diverse data set over the entire viking graben and its flanking platform areas these data show how syn rift accommodation within the basin varied in space and time with sub kilometer scale spatial resolution and a temporal resolution of 2 3 myr regional interpretations of 2d seismic reflection refraction and gravity data for this area have also been published and provide an image of total basin wide stretching for the entire crust these image data are combined with published strain rate inversion results obtained from tectonic subsidence patterns to constrain the spatio temporal evolution of strain accumulation throughout the lithosphere during the 40 myr 170 130 ma period of late jurassic extension across this basin for the first 25 30 myr strain localisation dominated basin development with strain rates at the eventual rift axis increasing while strain rates over the flanking areas declined as strain rates across the whole basin were consistently very low 16 s l thermally induced strength loss cannot explain this phenomenon the strain localisation is manifest in the near surface by a systematic migration of fault activity the pattern and timing of this migration are inconsistent with flexural bending stresses exerting an underlying control especially when estimates of flexural rigidity for this area are considered the best explanation for what is observed in this time period is a coupling between near surface strain localisation driven by brittle or plastic failure and the evolving thermal structure of the lithosphere we demonstrate this process using a continuum mechanics model for normal fault growth that incorporates the strain rate dependence of frictional strength observed in laboratory studies during the final 10 myr of basin formation strain accumulation was focused within the axis and strain rates declined rapidly replacement of weak crust by stronger mantle material plus crustal buoyancy forces can adequately explain this decline

source parameters of the 28 october 1983 borah peak idaho earthquake from body wave analysis modeling of long period body waves of the m s 7 3 borah peak idaho earthquake suggests that the earthquake was a simple rupture that nucleated at a depth of about 16 km and propagated unilaterally northwestward toward the surface the seismic moment tensor obtained from the inversion of teleseismic body wave amplitude data agrees well with the fault plane solution obtained from short period first motion data strike 138 3 dip 45 3 rake 60 5 and the observed surface faulting the scalar double couple moment of 2 1 10 26 dyne cm obtained from the inversion is comparable to a moment of 1 4 10 26 dyne cm estimated from the observed surface faulting estimates of stress drop based on these values for the moment are 17 to 12 bars respectively

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

source processes of the 1981 gulf of corinth earthquake sequence from body wave analysis abstract teleseismic long period body waves from the 24 february 1981 gulf of corinth earthquake and its two principal aftershocks of 25 february 02h35m and 4 march 21h58m 1981 are studied to determine source characteristics focal mechanisms along with observed surface fault breaks suggest that the corinth earthquake sequence represents normal faulting due to the n s trending extension depths of the three shocks estimated by matching synthetic seismograms to observations are found to lie between 4 and 12 km the azimuthal variation of observed body wave duration indicates that the main shock is a multiple event and that the main rupture occurred about 3 to 4 sec after a relatively small foreshock and propagated toward the w nw seismic moments deduced from the body wave synthetics are 8 1 10 25 2 7 10 25 and 2 2 10 25 dyne cm for the main 25 february and 4 march shocks respectively average final displacements and stress drops are estimated to be 37 cm and 10 bars for the main shock for a circular fault of radius 15 km 22 cm and 8 bars for the 25 february shock and 18 cm and 7 bars for the 4 march shock for circular faults of radius 11 km the striking features of the earthquake sequence are the low stress drops of the main shock and its two principal aftershocks and the clear eastward migration of aftershock activities the unusually long source time function rise times 4 sec for the main shock 2 5 sec for both aftershocks and low stress drops suggest an overall slow energy release during the earthquake sequence

microstructures imply cataclasis and authigenic mineral formation control geomechanical properties of new zealand s alpine fault abstract the alpine fault is capable of generating large mw 8 earthquakes and is the main geohazard on south island nz and late in its 250 291 year seismic cycle to minimize its hazard potential it is indispensable to identify and understand the processes influencing the geomechanical behavior and strength evolution of the fault high resolution microstructural mineralogical and geochemical analyses of the alpine fault s core demonstrate wall rock fragmentation assisted by mineral dissolution and cementation resulting in the formation of a fine grained principal slip zone psz a complex network of anastomosing and mutually cross cutting calcite veins implies that faulting occurred during episodes of dilation slip and sealing fluid assisted dilatancy leads to a significant volume increase accommodated by vein formation in the fault core undeformed euhedral chlorite crystals and calcite veins that have cut footwall gravels demonstrate that these processes occurred very close to the earth s surface microstructural evidence indicates that cataclastic processes dominate the deformation and we suggest that powder lubrication and grain rolling particularly influenced by abundant nanoparticles play a key role in the fault core s velocity weakening behavior rather than frictional sliding this is further supported by the absence of smectite which is reasonable given recently measured geothermal gradients of more than 120 c km 1 and the impermeable nature of the psz which both limit the growth of this phase and restrict its stability to shallow depths our observations demonstrate that high temperature fluids can influence authigenic mineral formation and thus control the fault s geomechanical behavior and the cyclic evolution of its strength

estimated likelihood of observing a large earthquake on a continental low angle normal fault and implications for low angle normal fault activity the lack of observed continental earthquakes that clearly occurred on low angle normal faults lanfs may indicate that these structures are not seismically active or that these earthquakes are simply rare events to address this we compile all potentially active continental lanfs 24 in total and calculate the likelihood of observing a significant earthquake on them over periods of 1 100 years this probability depends on several factors including the frequency magnitude distribution for either a characteristic or gutenberg richter distribution we calculate a probability of about 0 5 that an earthquake greater than m6 5 large enough to avoid ambiguity in dip angle will be observed on any lanf in a period of 35 years which is the current length of the global centroid moment tensor catalog we then use bayes theorem to illustrate how the absence of observed significant lanf seismicity over the catalog period moderately decreases the likelihood that the structures generate large earthquakes

tension fractures and extensional tectonics a characteristic pattern of normal faults that we have studied in several regions illustrates successive geometries relating to increasing amounts of extension from 10 50 gulf of suez egypt to 50 100 western gulf of california mexico up to 200 southern basin and range usa tension fractures formed at an early stage of extension have an essential role the resulting structure is described as a multiple tilted packs of cards model in which rotational deformation within the major blocks is accommodated by normal faulting on previously formed tension fractures thus defining smaller blocks of second and third generation

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

active normal faulting along the seerteng shan north china geometry and kinematics abstract although rotation of fault blocks during seismic and long term periods has long been recognized in extensional tectonic regimes the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail in this study combining with the analysis of high resolution topography acquired by small unmanned aerial vehicle suav using the structure from motion sfm technique we present the results of our field observations on the structural characteristics of the seertengshan piedmont fault spf a major active normal fault bounding the northern margin of the hetao graben north china although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake average slip rate and repeat time of paleo earthquakes few of them have focused on geometric patterns of the outcropping fault zones which provide excellent outcrop scale examples to investigating geometry and kinematics of active normal faults besides the observed prominent fault scarps indicative of recent tectonic activity along the spf outcrop observations indicate that in some cases both planar and curved normal faults are developed forming complex fault zones sequential development of normal faults may have rotated the early formed fault blocks resulting in shallowly dipping faults and highly tilted strata collectively structural similarities probably exit among normal faults at multiple spatial scales we suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas

pedogenic slickensides indicators of strain and deformation processes in redbed sequences of the appalachian foreland pedogenic slickensides are convex concave slip surfaces that form during expansion contraction in expansive clay soils such as vertisols in the central appalachians they occur near the tops of fining upward cycles in paleozoic redbeds such as the bloomsburg catskill and mauch chunk formations pedogenic slickensides are found in association with other pedogenic or paleosol features such as clay skinned peds in situ calcareous nodules and root impressions repeated movements along these shear planes during pedogenesis produce strongly aligned clay particles adjacent to pedogenic slickensides as a result they are preserved as discrete fractures throughout diagenesis compaction and superimposed tectonic deformation during whole rock deformation pedogenic slickensides segregate penetratively deformed rocks into independent foliated packets and serve as discontinuities that are followed by later structural features because the original morphology of pedogenic slickensides is known they can be used as crude strain markers

a source study of the thessaloniki northern greece 1978 earthquake sequence summary the thessaloniki northern greece earthquake sequence appears to have occurred along faults forming a graben structure this graben situated in the border region between the serbomacedonian massif and the vardar zone is bounded to the south west by clearly exposed north west striking north east dipping normal faults relative hypocentre determinations fault plane solutions surface faulting and the aftershock distribution suggest that some of these faults have been reactivated during the 1978 earthquakes the source parameters of the mainshock mb 6 1 ms 6 4 were determined by computing body wave synthetic seismograms in the time domain and comparing them with the observed this modelling constrained the orientation of faulting determined by the p wave fault plane solution it also constrained the source depth to 6 mp 2 km similar depths were calculated by a relative relocation method for the other three large events of the sequence the dislocation time function required for the far field had a total duration of 9 mp 1 5 s the body wave moment was 5 2 mp 1 8 times 1025 dyne cm for a fault length of 35 km and a fault width of 17 km both estimated from the aftershock distribution the static stress drop was found to be 4 bar an accelerograph record of the mainshock shows two distinct events 3 4 s apart these two events were unresolved by the long period data in the far field but the unusually long duration of the mainshock time function suggests an overall slow energy release which probably occurred as a sequence of events close in space and time seismic energy released in this fashion can account for waveform complexities observed at some stations

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

erosion and aggradation on persistently active volcanoes a case study from semeru volcano indonesia erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on earth episodic sediment yields after large eruptions have been evaluated but not the long term and continuous patterns on persistently active volcanoes we have used high spatial resolution satellite imagery and dems dsms along with field based geologic mapping to assess accurately sediment budgets for the active semeru volcano in java indonesia patterns of aggradation and degradation on semeru differ from that of other active volcanoes because 1 both episodic pyroclastic density currents pdc and continuous supplies of tephra generate pulses of sediment 2 sediment is transferred via cycles of aggradation and degradation that continue for 15 years in river channels after each pdc producing eruption and 3 rain triggered lahars remove much greater material than fluvial transport during long intense rainfall events the geomorphic response of two of semeru s rivers to volcanic sediment migration indicates that 1 each river experiences alternating aggradation and degradation cycles following pdc producing eruptions and 2 spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches usually high degradation in the steep source reach is followed by a long bypassing middle reach aggradation predominates in the depositional reaches further down valley on the ring plain average sediment yields 103 105 t km2 year at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions but the continuous and steady sediment transfer in rivers removes more sediment on a mid term 10 years to long term 30 years basis in contrast to the trend observed on composite cones after large and infrequent eruptions decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from baf eruptions superimposed on the background remobilization of daily tephra have a greater cumulative effect

active aseismic creep on the alto tiberina low angle normal fault italy the existence of active low angle normal faults has been questioned because the standard theory of fault mechanics precludes normal faults from slipping at low

modelling the behaviour of large gravity wharf structure under the effects of earthquake induced liquefaction abstract gravity wharf structures are widely used worldwide to form shallow and deep water ports they are large structures with a height of 25 50 m depending on the water depth when these structures are to be sited on loose to medium dense sand earthquake induced liquefaction settlements present a significant risk this often requires expensive soil replacement or other ground improvement techniques in this paper the dynamic behaviour of these large structures that exert very high bearing pressures on the foundation soil was investigated for the first time the level of settlements they can suffer due to soil liquefaction was investigated using dynamic centrifuge testing it will be shown that the full liquefaction does not occur below the structure even when the free field soil fully liquefies during strong earthquakes however there will be some stiffness degradation owing to excess pore pressure generation and consequent structural settlements the level of these settlements are considered to be acceptable from a service limit state sls perspective in addition to this the hydro dynamic pressures that act on the gravity wharf structure were also investigated

pressure solution structures in a granite abstract syntectonic two mica granites in northwest spain have suffered regional late variscan shear deformation the deformed corcoesto granite shows a marked planar and linear fabric resulting from ductile behaviour and contains quartz veins at about 60 to the foliation offsets of these quartz veins along shear planes are commonly contrary to the general sense of shear and thus provide evidence for pressure solution processes

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes

a model for the development of the irish variscides a clear correlation exists in the southern irish variscides between extensional structures which controlled late palaeozoic sedimentation in the munster basin and contractional thrusts and folds of end carboniferous age this correlation is interpreted to indicate that the extensional structural framework of the basin including a basal low angle detachment and an array of superjacent normal faults was reused during transpressive inversion of the basin to produce the fold thrust belt the extensional framework which in turn was to some extent derived by reactivation of caledonian structures therefore exerted a fundamental control on the geometry and style of contractional deformation it is not evident that the detachment had a discrete link to the fold belt in south wales or the main variscan orogen in europe

permeability and stiffness of sands at very low effective stresses loose saturated sandy soils may undergo liquefaction under cyclic loading generating positive excess pore pressures due to their contractile nature and inability to dissipate pore pressures rapidly during earthquake loading these liquefied soils have a near zero effective stress state and hence have very low strength and stiffness causing severe damage to structures founded upon them the duration for which this near zero effective stress state persists is a function of the rate of reconsolidation of the liquefied soil which in turn is a function of the permeability and stiffness of the soil at this very low effective stress existing literature based on observation of physical model tests suggests that the consolidation coefficient cv associated with this reconsolidation of liquefied sand is significantly lower than that of the same soil at moderate stress levels in this paper the results of a series of novel fluidisation tests in which permeability k and coefficient of consolidation cv were indep