geology of panamint valley saline valley pull apart system california palinspastic evidence for low angle geometry of a neogene range bounding fault geological studies support the interpretation that northern panamint valley and saline valley southeast california form paired pull apart basins on opposite sides of the right slip hunter mountain fault zone eight to ten km of late cenozoic net slip can be established on the hunter mountain fault zone palinspastic reconstruction of northern panamint valley indicates that the valley was formed by movement on a shallow crustal low angle normal fault of 0 15 degree west dip during the last 3 0 ma this interpretation appears to contradict the notions that little extension is accomodated in the uppermost crust by low angle faulting and that the most recent extension in the basin and range province is accomodated exclusively by high angle faulting saline valley however is interpreted to have formed by extension on closely spaced rotated planar normal faults thus within one geometric system of paired pull apart basins extension appears to have been accommodated in the shallow crust in two different ways

fold related faults in the syrian arc belt of northern egypt abstract late cretaceous early tertiary syrian arc folds in northern egypt include both inversion and non inversion folds these folds are well exposed in northern sinai and the northern eastern desert but exist in the subsurface in the northern western desert in northern sinai the maghara yelleg and halal inversion folds are 45 50 km long similar size inversion folds with opposite vergence exist in the subsurface in the northern western desert and include the kattaniya mubarak alamein razzak and matruh basin folds smaller non inversion compressional folds include the falig and meneidret el etheili folds in northern sinai as well as the abu gharadig anticline in the subsurface in the northern western desert among others detailed surface and subsurface structural mapping made use of the excellent exposures and good 2d and 3d seismic data and led to the identification of the fault patterns of the inversion and non inversion syrian arc folds inversion folds have fault patterns that differ from the backlimb to the forelimb the backlimbs are pervasively dissected by long nw se oriented normal faults that were formed by the regional stress field on the contrary the forelimbs of inversion folds as well as the two limbs of non inversion folds are affected by the local stress in the folded areas and are dissected by three shorter fault sets a set of hinge transverse normal faults and two conjugate sets of hinge oblique faults that have oblique slip the hinge oblique faults dominate the steeper limbs of asymmetric non inversion folds

controls on the geometry of transfer zones in the suez rift and northwest red sea implications for the structural geometry of rift systems two main types of transfer zones are mapped in the suez rift and the northwestern red sea these are transfer zones between indi vidual faults fault to fault transfer zones f f tz and transfer zones between half grabens with different fault domains half graben to half graben transfer zones h h tz relay ramps and linking transfer faults are two main recognized types of f f tz different varieties of these f f tz have the form of en echelon fault belts with single or mixed polarity tilted fault blocks at rift offsets and zigzag fault arrays at major fault or rift jumps relay ramps transfer throw between overlapping normal faults of the same polarity linking transfer faults join normal faults that have the same polarity with no overlapping segments leading to a characteristic zigzag pattern if the linked faults are listric local anticlines and synclines develop at the corners of the zigzag fault array three h h tz in the suez rift and northwest red sea show the effect of prerift structures both faults and major folds on the location orientation and style of deformation of the transfer zones of continental rifts the widest one of these three h h tz 40 60 km has a broad antiformal structure lying between the overlapping ends of the listric faults bounding the two linked half grabens and is deformed by dip slip normal faults of opposite polarity the other two h h tz reactivate prerift faults by strike slip faulting due to the angular relationship between these faults and the direction of extension in the rift

evolution of miocene footwall derived coarse grained deltas gulf of suez egypt implications for exploration the miocene abu alaqa group exposed on the eastern side of the gulf of suez contains a series of coarse grained delta deposits located in the hanging wall of the northwest trending east margin fault zone seven major fan sequences have been identified the first three fan sequences are aggradational and cover an area of less than 2 sq km the sequences are dominated by pebble boulder conglomerates with predominantly sigmoidal high angle clinoforms between 15 and 25 degrees as much as 150 m high these fan sequences represent talus cones and fan deltas which were probably deposited during activity on the fault zone and are situated at transfer segments the other four fan sequences are predominantly progradational consisting of mixed carbonate siliciclastic braid d ltas with local reefs they are less than 30 m high have low angle clinoforms

late cenozoic extensional transfer in the walker lane strike slip belt nevada mid miocene to pliocene 11 to 6 ma displacement on the shallowly northwest dipping silver peak lone mountain detachment system transferred 30 to 40 km of right slip from the furnace creek transcurrent fault 85 km east northeast to the central walker lane strike slip faults top to the northwest slip on the detachment was accompanied by upper plate extension on steeply dipping faults and large scale exhumation of midcrustal rocks of the lower plate complex doubly plunging northwest trending folds turtleback structures control the outcrop distribution of the extensional complex and formed in response to simple shear of the footwall complex activity on the detachment ceased as miocene pliocene 6 4 8 ma volcanic rocks were erupted and deformed during the final stage of northwest trending folding late pliocene to holocene displacement transfer shifted north to a curved array of steeply dipping faults that may be underlain by a shallowly northwest dipping detachment

musings over sedimentary basin evolution field geologists and explorationists are of necessity immersed in numerous very detailed surface and subsurface observations they are often perplexed by the choice of relatively simple geophysical models that so elegantly explain the origin and evolution of sedimentary basins geophysicists on the other hand search for a simple theme to explain the origin of sedimentary basins and much like managers are often impatient with lengthy detailed geological discourse that often uses fancy jargon to hide the very real difficulty that geologists have in separating important evidence from mere encyclopaedic description the following musings address the quality and limitations of geologic and geophysical evidence that may be used to evaluate the relative roles of stress thermal effects and gravity loading which have been so lucidly summarized by m h p bott in the preceding summary the fine papers presented during this meeting of course have led to significant modifications of some of my earlier thoughts because these have been previously published elsewhere bally snelson 1980 bally 1980 they are summarized here only for the convenience of the reader

source dependent biomarker properties of five crude oils from the gulf of suez egypt abstract five crude oils from some producing wells in the southern part of the gulf of suez were characterized using a variety of organic geochemical parameters the results reveal significant differences within the oils from the gulf of suez basin that suggest two oil types and one mixed type type 1 oils from ras fanar and east zeit fields show a high relative abundance of gammacerane indicating a marine saline source depositional environment another related feature of these oils is the predominance of c 35 over c 34 17 h homohopanes type 2 oils from gama and amal 9 wells show oleanane indices over 20 indicating that they originated from an angiosperm rich tertiary source rock type 3 oil from amal 10 well has geochemical characteristics intermediate between those of types 1 and 2 this may reflect mixing of oils from the sources of both types 1 and 2 the geochemical characteristics of the oils vary sufficiently to suggest multiple sources the type 1 oils possess geochemical characteristics consistent with upper cretaceous brown limestone or lower eocene thebes formation carbonate source rocks type 2 oils are very similar in geochemical character to the lower miocene rudeis formation source rocks

fission track analysis of basement apatites at the western margin of the gulf of suez rift egypt evidence for synchroneity of uplift and subsidence fifty six apatite fission track ages and 52 horizontal confined track length measurements are reported from precambrian crystalline rocks along the western margin of the gulf of suez egypt ages fall in the range of ca 11 385 m y and older ages often occur within very close geographic proximity to younger ones indicating non uniform uplift the wide range in ages is accompanied by a systematic variation in the distribution of horizontal confined fission track lengths on the basis of apatite fission track ages and their length distributions data fall into three distinct groups group i ages ranging from 43 to 385 m y length distributions are all positively skewed and with decreasing age become progressively broader with shorter mean track length group ii ages ranging from 23 to 31 m y length distributions are negatively skewed with either a distinct tail or a small peak of short tracks group iii ages ranging from 11 to 20 5 m y length distributions are al unimodal narrow negatively skewed and have the longest mean lengths among samples studied apatite ages from groups i and ii are interpreted as mixed ages as a result of cooling during uplift from different levels within the apatite partial track annealing zone ages from group iii are interpreted as cooling ages due to uplift from the apatite total track annealing zone with minor partial annealing correcting the ages of the two oldest samples in this group for track length reduction yields ages of21 2 2and23 1 5m y it is proposed that the onset of rift flank uplift in the gulf of suez northern red sea area occurred between 21 and 23 m y ago fission track analysis in combination with subsidence data from the gulf of suez basin indicate that commencement of basement uplift postdate the start of rifting and is interpreted as evidence for passive rifting at the gulf of suez furthermore this uplift is contemporaneous with and is directly related to the process of extension and subsidence at the gulf of suez

sinai hinge belt a major crustal boundary in ne africa the sinai hinge belt is a major crustal boundary in northern sinai separating different tectonic terranes this boundary started as a number of ene wsw oriented faults of precambrian or palaeozoic age and played a major role in the mesozoic and cenozoic tectonic evolution of ne africa the sinai hinge belt was reactivated by normal faulting during early mesozoic opening of neotethys and was later reactivated by dextral transpression during late cretaceous early tertiary closure of neotethys and dextral transtension in the miocene this study highlights the structural characteristics of the hinge belt and the nature of deformation of its fault segments it also highlights the role of this basement structure as a crustal boundary between terranes of different tectonic settings as well as its relationship to the structural development of the nearby areas in ne africa supplementary material a google earth image and structural form line map of rishat saada fault google earth image and landsat tm image of rishat lehman fault and g ras ebeid geological map of el risha el hamra fault landsat tm image and structural form line map of the burqa riash fault and google earth image and geological map of el bruk fault are available at www geolsoc org uk sup18697

uplift and extension at the gulf of suez indications of induced mantle convection reconstruction of tectonic movements since the initiation of the gulf of suez rift indicates that there has been 25 27 km of extension the uplift bordering rift indicates that lithosphere heating greatly exceeds that producible by uniform lithosphere extension i propose that small scale convection induced by the rifting augments the heating introduced by extensional rifting and produces the broad uplifts flanking the rift

relay ramp forms and normal fault linkages canyonlands national park utah fieldwork within a series of mesoscale grabens in southeast utah has revealed a particularly well exposed system of interlinked extensional faults a series of down faulted grabens are developed within a 460 m thick brittle layer of upper paleozoic sandstone and shale which overlies a ductile layer with a high gypsum content all the major grabens consist of two or more overlapping elements which are composed of fault segments these segments may be hard linked fault surfaces are joined or soft linked fault surfaces are isolated but linked by ductile strain of the rock volume between them in map view relay structures are defined as zones connecting the footwalls and hanging walls of overlapping fault segments representing soft linkage of fault segments in the canyonlands grabens the transfer of displacement between soft linked fault segments is characterized by well de fined dipping relay ramps commonly rotated and extended to accommodate the ductile strain between the overlapping fault segments relay ramps develop as ephemeral structures eventually becoming breached by hard linkage of the fault segments breakdown of ramps by breaching is part of the process of fault growth by segment linkage within the canyonlands graben system four orders of segmentation are present this may be a consequence of different scales of mechanical heterogeneity but evidence from the canyonlands grabens and elsewhere points to a fundamental process of discontinuous fault growth by segment linkage

the 2019 mw 6 4 and mw 7 1 ridgecrest earthquake sequence in eastern california rupture on a conjugate fault structure revealed by gps and insar measurements

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

orogenically controlled sedimentation in the lechtaler kreideschiefer lechtal shale cretaceous and geodynamics of the inner western nca northern calcareous alps lechtal alps only recently have sedimentological studies been integrated with orogenic research the analysis of the lechtaler kreideschiefer lechtal shale lower cretaceous demonstrates that these sediments reflect orogeny subduction and compressive tectonics resulted in the formation of a nappe pile folding of the epicontinental shelf formed long syn and anticlines in contrast to the uplifting anticlines the synclines represent subsiding depocenters with continuous sedimentation sheet like olistostromes migrated in a broad front towards the axes of the inner calcalpine synclines the line source character of unchannelized clastic influx from anticlines is different from fault scarp breccias slope aprons and the point source of fan models some olistostromes document the initial tectonic elimination of various depocenters and can be recognized below following tectonic units the lechtal and the inntal nappe the braunarlspitz wedge the hasenfluh klippe the krabachjoch thrust outlier these tectonic bodies arose from apparent overturning ueberfaltung blumer 1905 untermuldung leiss 1988 1989 1990 and lie on synclines filled with synorogenic sediments the thrust distance is 5 10 km

extensional hard linkages eastern gulf of suez egypt the araba abu durba area on the eastern margin of the gulf of suez exhibits two superb outcrop examples of extensional hard linkages in a rift basin here three large domino style basement cored northeast dipping fault blocks are formed by a series of major northwest trending normal faults these are offset by two north northeast trending sinistral oblique slip transfer faults that terminate in horsetail normal fault splays the transfer faults do not extend across the entire rift basin detailed mapping and structural analysis show that they developed by breakage of initial low strain relay ramps along reactivated north northeast trending basement fabrics between overlapping northwest trending normal fault segments paleostrain analysis of fault slip indicators shows that both the normal and the sinistral oblique slip transfer faults were formed synchronously in response to northeast southwest extension perpendicular to the main northwest rift trend

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

strain accumulation across the central nevada seismic zone 1973 1994 five trilateration networks extending for 280 km along the central nevada seismic zone 1915 pleasant valley m 7 3 1954 dixie valley m 6 8 1954 stillwater m 6 8 1954 rainbow mountain m 6 6 1954 fairview peak m 7 1 and 1932 cedar mountain m 7 2 have been surveyed 6 times since 1973 to determine deformation along the zone within the precision of measurement the deformation appears uniform along the zone and is described by the principal strain rates 0 036 0 008 strain yr n60 w 3 and 0 031 0 008 strain yr n30 e 3 extension reckoned positive the observed strain rates are consistent with simple right lateral tensor shear at the rate of 0 033 strain yr across a shear zone striking n15 w this central nevada shear zone appears to be the northward continuation of the eastern california shear zone the orientation of the strike slip and normal slip ruptures within the central nevada seismic zone are consistent with principal stress axes parallel to the measured principal strain rate axes space based geodetic measurements very long baseline interferometry indicate that the relative motion accommodated across the basin and range province west of ely nevada is about 9 1 1 5 mm yr n16 w 8 dixon et al 1995 notice that the right lateral shear zone postulated to explain deformation in the central nevada seismic zone is properly oriented to accommodate that relative motion however a 135 km effective width of the shear zone would be required to accommodate all of the 9 1 mm yr relative motion at the strain rates observed in the nevada seismic zone only about 3 mm yr of that relative motion is accommodated within the span of the trilateration networks

initiation of deformation of the eastern california shear zone constraints from garlock fault geometry and gps observations 1 we suggest a 2 stage deformation model for the eastern california shear zone ecsz to explain the geometry of the garlock fault trace we assume the garlock fault was originally straight and then was gradually curved by right lateral shear deformation across the ecsz in our 2 stage deformation model the first stage involves uniform shear deformation across the eastern part of the shear zone and the second stage involves uniform shear deformation across the entire shear zone in addition to the current shape of the garlock fault our model incorporates constraints on contemporary deformation rates provided by gps observations we find that the best fitting age for initiation of shear in eastern part of the ecsz is about 5 0 0 4 ma and that deformation of the western part started about 1 6 myr later

late neogene motion of the pacific plate oceanic crust between 38 s and 65 s along the pacific antarctic ridge records a complete history of neogene pacific antarctic motion we have modeled magnetic stages corresponding to portions of isochrons 1 2 2a 3 3a 4 and 5 from 17 high quality marine magnetic traverses of the ridge to determine the neogene finite rotation poles for this plate pair we chose to model velocities over time intervals of about 0 5 m y because this greatly increased the number of estimates of pacific antarctic plate velocity our analysis shows that a change in pacific antarctic relative motion occurred between chron 2a 3 40 ma and the beginning of chron 3 time 3 86 ma we used 203 estimates of pacific antarctic spreading velocity to calculate a 0 3 4 ma and 3 86 10 3 ma euler pole combined with tracks of seamounts that record the passage of the pacific plate over mantle plumes our data show that this change in relative motion corresponds to a change in the absolute motion of the pacific plate with respect to the hotspot frame of reference using these euler poles to calculate pacific antarctic africa north america circuit euler poles show that this recent change in pacific plate absolute motion corresponds to a change from strike slip to transpressive motion along the coastal california pacific north america plate boundary interestingly this age of increased tectonism agrees in time with deformation in new zealand and northern japan

displacement transfer at thrust terminations in southern appalachians saltville thrust as example transition from faulting to noncylindrical folding involving rapid plunge change at the fold closure is the primary displacement transfer mechanism at the northern end of the south appalachian foreland fold and thrust belt regional thrust faults including the saltville narrows and st clair terminate in regional overturned asymmetric anticlines this mechanism of displacement transfer is distinct from thrust terminations where fold complexes of smaller noncylindrical folds converge toward the end of the fault trace the saltville thrust transition to the sinking creek anticline is representative of the southern appalachian structures deformation intensity patterns reflected by cleavage development mesoscopic folding and faulting suggest that the sinking cree anticline formed due to upwarping from shear thrusting at depth laboratory deformation analogs of folds formed above ramps support this contention experimentally produced folds are asymmetric overturned structures with high strains on overturned limbs and very low strains on upright limbs a deformation sequence involving shear thrusting with subsequent break thrusting may characterize fault propagation at thrust termini this will be important for layered sedimentary sequences where thick rigid members low in the sedimentary pile are overlain by thinner interbedded mechanically anisotropic strata

extensional tectonics in the death valley area california transport of the panamint range structural block 80 km northwestward in the hypothesis presented here the panamint range is a structural block that was detached during late cenozoic time from underlying rocks that now form the black mountains and was transported tectonically an estimated 80 km to the northwest transport occurred along a single low angle westward dipping detachment fault or perhaps along a system of such faults the estimate of 80 km of transport distance is based on the apparent right lateral offset of late precambrian and paleozoic facies and thickness trends along the furnace creek fault zone that bounds the detached block on the northeast the death valley turtleback surfaces are considered to be gigantic mullions related to the detachment surface

inception of the eastern california shear zone and evolution of the pacific north american plate boundary from kinematics to geodynamics 1 the san andreas fault saf is the transform boundary between the pacific and the north american plates yet up to 25 of the relative plate motion is now accommodated by the eastern california shear zone ecsz here we investigate the inception of the ecsz and its geodynamic interactions with the saf using a 3 d viscoelastoplastic finite element model for a given fault configuration of the plate boundary zone the model simulates long term slip on the faults and plastic strain outside the faults our results show that the formation of the big bend of the saf around 5 12 ma impeded fault slip and localized strain along the ecsz causing its inception development of the ecsz was further enhanced by the activation of the garlock fault gf and lithospheric weakening caused by the encroachment of the basin and range extension similarly the san jacinto fault sjf in southern california developed along a belt of localized strain which resulted from the formation of the restraining bend along the san bernardino mountains segment of the saf 2 myr ago once activated the sjf reduced slip on both the southern saf and the ecsz across the mojave desert these results indicate causative relationship between the saf and the ecsz the inception of the ecsz and other young faults is the consequence of the evolving saf plate boundary zone that continuously adjusts itself to accommodate the relative plate motion

rift segment interaction and its relation to hydrocarbon exploration in continental rift systems 1 in both the early stages of continental rifting and the onset of sea floor spreading in the more advanced rifting longitudinally continuous rifting is accomplished by the propagation and linkage of isolated pockets of extension in the early continental rift phase these isolated pockets of deformation are defined as rift segments rift segments initially are distributed in a loose association of in line and en echelon geometry their propagation interaction and linkage into a continuous rift system creates a variety of rift geometries including rift splays gaps offsets passes and large scale transfer zones an understanding of these geometries and their associated fault patterns is critical for effective hydrocarbon exploration in these zones

late cenozoic history and styles of deformation along the southern death valley fault zone california late cenozoic deposits in the southern death valley region have been offset 35 km by right lateral strike slip faulting on the southern death valley fault zone since miocene time virtually all slip took place prior to 1 m y ago along western traces of the fault zone during the past 1 m y the eastern traces of the fault zone have been active and characterized by oblique slip with a lateral component of only a few hundred metres movement along these eastern traces has formed normal faults and gentle to isoclinal folds that have uplifted fan gravel and lacustrine sediments as much as 200 m above the modern alluvial fan surface surveying of the longitudinal profile of the amargosa river which flows within the eastern traces of the fault zone suggests that vertical deformation continues today the 35 km of right lateral offset which is based on matching offset alluvial fan gravel with its source area refines earlier estimates of 8 to 80 km of movement for the southern death valley fault zone and it is consistent with the geometry of a pull apart basin model for central death valley causes for the observed differences in the style and timing of movement of the eastern and western subzones are not well understood the study area however is located a few kilometres north of the intersection of the southern death valley and garlock fault zones the garlock fault zone changes its sense of movement from left lateral strike slip to east vergent thrusting against the southern death valley fault zone the resulting compression may have caused the shift in activity and the change in style of deformation along branches of the southern death valley fault zone

tectonics of pliocene removal of lithosphere of the sierra nevada california pliocene ca 3 5 ma removal of dense eclogitic material under the sierra nevada has been proposed from variations in the petrology and geochemistry of neogene volcanic rocks and their entrained xenoliths from the southern sierra the replacement of eclogite by buoyant warm asthenosphere is consistent with present day seismologic and magnetotelluric observations made in the southern sierra a necessary consequence of replacing eclogite with peridotite is that mean surface elevations and gravitational potential energy both increase an increase in potential energy should increase extensional strain rates in the area if these forces are insuffi cient to signifi cantly alter pacifi c north american plate motion then increased extensional strain rates in the vicinity of the sierra must be accompanied by changes in the rate and style of deformation elsewhere changes in deformation in california and westernmost nevada agree well with these predictions existing geologic evidence indicates that a period of rapid uplift along the sierran crest of more than 1 km occurred between 8 and 3 ma most likely as a consequence of removal of lower lithosphere about this same time extensional deformation was initiated within 50 km of the eastern side of the sierra 5 3 ma and regional shortening began to produce the california coast ranges 5 3 ma we suggest that these events were induced by the 1 2 10 12 n m increase of gravitational potential energy generated by the sierran uplift evidence for pliocene uplift adjoining crustal extension and shortening in directly opposing parts of the coast ranges is found along nearly the entire length of the sierra nevada and implies that lithosphere was removed beneath all of the presentday mountain range the uplifted area lies between two large upper mantle high pwave velocity bodies under the south end of the san joaquin valley and the north end of the sacramento valley these high velocity bodies plausibly represent the present position of material removed from the base of the crust lithospheric removal may also be responsible for shifting of the distribution of transform slip from the san andreas fault system to the eastern california shear zone a prediction that awaits better defi ned slip histories on both faults overall the late cenozoic deformational history of the sierra nevada and vicinity illustrates that locally derived forces can infl uence deformation kinematics within plate boundary zones

structural architecture and tectonic evolution of the maghara inverted basin northern sinai egypt abstract large ne sw oriented asymmetric inversion anticlines bounded on their southeastern sides by reverse faults affect the exposed mesozoic and cenozoic sedimentary rocks of the maghara area northern sinai seismic data indicate an earlier jurassic rifting phase and surface structures indicate late cretaceous early tertiary inversion phase the geometry of the early extensional fault system clearly affected the sense of slip of the inverted faults and the geometry of the inversion anticlines rift parallel fault segments were reactivated by reverse slip whereas rift oblique fault segments were reactivated as oblique slip faults or lateral oblique ramps new syn inversion faults include two short conjugate strike slip sets dissecting the forelimbs of inversion anticlines and the inverted faults as well as a set of transverse normal faults dissecting the backlimbs small anticline syncline fold pairs ornamenting the steep flanks of the inversion anticlines are located at the transfer zones between en echelon segments of the inverted faults

transfer zones with en echelon faulting at the northern end of the suez rift detailed field mapping of the central part of the area between the northern end of the suez rift to the nile valley cairo suez area shows that the eocene to miocene rocks are affected by e w elongated belts of left stepped en echelon normal faults these belts act as transfer zones between nw oriented normal faults synchronous with faults of the same trend in the suez rift individual faults within the en echelon fault belts are oriented e w to wnw and dip in the same direction as the linked nw faults step faulting or horsts and grabens are two possible fault arrangements in the transfer zones depending on the geometry of the linked faults the linked faults and the transfer zones are joined together in zigzag fault belts that extend northwest ward from the northern part of the suez rift into the cairo suez area and possibly further northwestward a substantial amount of the throw of the nw faults of the suez rift is transferred northwestward by these zigzag fault belts the throw generally decreases northwestward away from the rift the en echelon fault belts were probably formed by right lateral divergent wrenching on e w oriented deep seated preexisting faults this right lateral divergent wrenching is kinematically related to the dip slip movement on the linked nw oriented normal faults

pattern of mantle thinning from subsidence and heat flow measurements in the gulf of suez evidence for the rotation of sinai and along strike flow from the red sea we have undertaken a combined analysis of tectonic subsidence heat flow and uplift data for the gulf of suez results show significant differences along the length of the rift the heat flow and subsidence in the northern gulf of suez can be fitted by close to uniform extension in the early miocene with minimal extension since the middle miocene in contrast the southern gulf of suez requires that the early miocene extension is followed by both continuous slow 1 mm yr extension and mantle thinning greatly in excess of the crustal thinning the continued extension of the southern gulf of suez is interpreted as indicating a counterclockwise rotation of the sinai peninsula that allows the southern gulf of suez to accommodate 10 15 of the motion of the dead sea transform our best estimate of the net crustal and mantle extension factors for southern suez are 1 4 1 5 and 2 2 2 6 respectively while these values are approximate they indicate a significant input of heat into the southern gulf of suez rift that is in excess of that directly advected by extension modeling indicates that while 1 2 of the extension occurred in the early miocene most of the lithospheric thinning and virtually all of the excess thinning of the mantle lithosphere developed since then in addition the gulf of suez is bordered by large and growing rift flank uplifts particularly on the sinai peninsula the geometry of the motions at the sinai triple junction region has created a large contrast in extension between the red sea and gulf of suez sinai since the middle miocene these lateral temperature gradients drove the flow of hot material that is responsible for the extra heating beneath southern suez and sinai the rift flank uplift along most of the gulf of suez is interpreted as resulting from a combination of secondary convection and flexure the much greater uplift in southern sinai is produced by the additional convective flow from the red sea

strain accumulation across the eastern california shear zone at latitude 36 30 n the motion of a linear array of monuments extending across the eastern california shear zone ecsz has been measured from 1994 to 1999 with the global positioning system the linear array is oriented n54 e perpendicular to the tangent to the local small circle drawn about the pacific north america pole of rotation and the observed motion across the ecsz is approximated by differential rotation about that pole the observations suggest uniform deformation within the ecsz strike n23 w 26 nstrain yr 1 extension normal to the zone and 39 nstrain yr 1 simple right lateral shear across it with no significant deformation in the two blocks the sierra nevada mountains and southern nevada on either side the deformation may be imposed by right lateral slip at depth on the individual major fault systems within the zone if the slip rates are death valley furnace creek fault 3 2 0 9 mm yr 1 hunter mountain panamint valley fault 3 3 1 6 mm yr 1 and owens valley fault 6 9 1 6 mm yr 1 however this estimate of the slip rate on the owens valley fault is 3 times greater than the geologic estimate

evolution of the central garlock fault zone california a major sinistral fault embedded in a dextral plate margin the garlock fault is an integral part of the plate boundary deformation system inboard of the san andreas fault california usa however the garlock is transversely oriented and has the opposite sense of shear the slip history of the garlock is critical for interpreting the deformation of the through going dextral shear of the walker lane belt eastern california shear zone the lava mountains summit range lmsr located along the central garlock fault is a miocene volcanic center that holds the key to unraveling the fault slip and development of the garlock the lmsr is also located at the intersection of the nnw striking dextral blackwater fault and contains several sinistral wsw striking structures that provide a framework for establishing the relationship between the sinistral garlock fault system and the dextral eastern california shear zone new field mapping and geochronology data 40 ar 39 ar and u pb show five distinct suites of volcanic sedimentary rock units in the lmsr overlain by pliocene exotic clast conglomerates this stratigraphy coupled with fifteen fault slip markers define a three stage history for the central garlock fault system of 11 7 ma 7 3 8 ma and 3 8 0 ma pliocene to recent slip occurs in a 12 km wide zone and accounts for 33 km or 51 of the total 64 km of left lateral offset on the garlock fault in the vicinity of the lmsr since 3 8 ma this history yields slip rates of 6 9 mm yr for the younger stage and slower rates for older stages the lmsr internally accommodates northwest directed dextral slip associated with the eastern california shear zone walker lane belt via multiple processes of lateral tectonic escape folding normal faulting and the creation of new faults the geologic slip rates for the garlock fault in the lmsr match with and explain along strike variations in neotectonic rates

evidence for post early miocene initiation of movement on the garlock fault from offset of the cudahy camp formation east central california the cudahy camp formation located in the el paso basin east central california consists of a 350 m thick volcanic and sedimentary sequence of early miocene age previous investigators determined from paleocurrent indicators that the source for these rocks was to the south and southeast but failed to suggest a specific location for that source restoration of 64 km of left slip on the garlock fault places cudahy camp rocks north and northwest of the early miocene eagle crags volcanic field the unique geochemical nature of basalts found in both locations coincident ages of volcanic rocks identical clast content of volcanic tuffs and identical stratigraphic sequence indicate that the source for the cudahy camp formation was the eagle crags volcanic field this is the first documented occurrence of miocene rocks offset by the garlock fault because the cudahy camp rocks and their sources appear to be offset by the full displacement on the garlock fault we conclude that movement on the garlock started after earliest middle miocene time further constraining initiation of movement on the garlock fault adds significantly to fully understanding the evolution of the western north american plate boundary in the middle to late cenozoic

long dormancy low slip rate and similar slip per event for the emerson fault eastern california shear zone excavations in a playa along the 1992 rupture of the emerson fault reveal evidence of two paleoseismic events with only one large prehistoric rupture in the past 15 millennia accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka trench wall exposures revealed clear evidence of at least one pre 9 ka rupture at the playa site the event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14 8 ka and 24 1 ka implying that the earthquake occurred about 20 000 years b p the actual bracketing ages for this rupture are likely a few thousand years older because of the mean residence time for the pedogenic carbonate and calibration of the 14c ages by 230th dating despite the large uncertainties a dormant period of at least 6 kyr to as much as 13 kyr separates the older event from the 9 ka event because the scarp formed by the penultimate event is similar in height to the scarp formed by the 1992 mw 7 3 landers earthquake the penultimate rupture was at least locally similar in size to the most recent rupture this similarity supports the concept of characteristic slip for the emerson fault preliminary results from paleoseismic studies at other sites on the 1992 rupture suggest that large ruptures occurred on other nearby faults within a few hundred years of this penultimate event on the emerson fault the interseismic period that preceded the 1992 earthquake on the emerson fault was about 40 times longer than the average interval between large events on the nearby san andreas fault therefore in comparison to events on the san andreas fault the 1992 landers earthquake was an exceedingly rare event

path and amount of dextral fault slip in the eastern california shear zone across the central mojave desert new total fault slip estimates for the central mojave desert portion of the eastern california shear zone support through going dextral shear of 18 km that is transferred northward to the garlock fault the eastern california shear zone accommodates 25 of the plate boundary shear with the transversely oriented garlock fault forming its northern boundary with the walker lane belt total fault slip estimates for the major faults in the central mojave desert were determined using detailed geologic mapping supplemented with aeromagnetic data offset data for the blackwater fault show a consistent 1 8 0 1 km of dextral slip along 55 km of strike length and they indicate that slip initiated at or after 3 8 ma the faults adjacent to the blackwater fault have dextral slip of 4 8 0 3 km harper lake fault 2 9 0 5 km mount general fault 1 0 0 7 km lockhart fault and 3 2 0 3 and 0 53 0 05 km paradise fault these slip data augment published data for the central mojave desert and allow evaluation of the strain path in the central mojave desert showing consistent along strike through going dextral slip contractional and extensional step overs in the central mojave desert accommodate a change from focused slip in the southern central mojave desert to a wider and more dispersed fault system northward with a shift in the locus of dextral shear westward we interpret these changes in the fault system to be a response to the garlock fault which inhibits through going faulting but allows through going dextral shear via clockwise deflection of its trace

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

control of extensional transfer zones on syntectonic and post tectonic sedimentation implications for hydrocarbon exploration the gulf of suez red sea rift system exhibits superb outcrop examples of extensional transfer zones and displays the control of these zones on syntectonic and post tectonic sedimentation hard and soft linkage transfer zones were identified at variable scales hard linkage transfer zones form inward and outward fault kinks whereas soft linkage transfer zones form relay ramps between overlapping rift parallel faults the two types of transfer zones invariably exerted fundamental control on the deposition of syn and post tectonic sediments flow direction of drainage systems and locations of sediment entry points as well as the intensity of erosion patterns of the structurally high sediment source areas this study highlights the close relationship between the transfer zones and hydrocarbon accumulations in clastic syntectonic reservoirs in rift basins

temporally constrained tectonic rotations derived from magnetostratigiraphic data implications for the initiation of the garlock fault california examination of declination anomalies within a well controlled chronologic framework can permit precise delineation of the progression of a tectonic rotation in the past declination anomalies from numerous spatially separated and individually dated localities have been synthesized in order to define regional progressive rotations rarely however have magneto stratigraphic data from a single locality been used successfully to chronicle a sequential rotation that resulted from movement along a nearby fault magnetostratigraphic studies from the el paso basin in southern california reveal progressively smaller amounts of counterclockwise rotation for strata dated between 11 and 7 ma two tests indicate that this is a temporally controlled rather than a spatially controlled rotation this rotation is interpreted to have resulted from sinistral shear along the garlock fault as such it appears to delimit the initiation of miocene movement along the western segment of this major strike slip fault

sedimentology and sequence stratigraphy of a transfer zone coarse grained delta miocene suez rift egypt this study focuses on miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the thal fault segment gulf of suez the succession generally shoals upwards from offshore mudstone containing pro delta turbidites into conglomeratic delta foresets and topsets with sandstone dominated shoreface facies coexisting laterally despite this upward shoaling key stratal surfaces marking abrupt changes in relative sea level allow the succession to be divided into four stratal units the stacking pattern of the stratal units suggests an initial relative sea level rise that generated a major marine flooding surface a relative sea level fall followed resulting in widespread exposure and incision during the ensuing relative sea level rise a lowstand coarse grained delta and coeval shoreface succession prograded several kilometres basinward the stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the baba sidri fault segment further south at the transfer zone low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea level in the fault centre location however higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas the results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins

is the san andreas big bend responsible for the landers earthquake and the eastern california shear zone the occurrence of a series of earthquakes including the 1992 landers event the geodetic strain measurements and geologic studies in california s mojave desert prior to the earthquake have precipitated the idea for the existence of a relatively young right lateral shear zone in eastern california the so called eastern california shear zone using a boundary element method together with a fault propagation criterion based on the maximum distortional strain energy density we explored the possibility that the big bend along the san andreas fault may have perturbed and amplified the stress field around the bend thereby inducing a zone of shearing in a north northwest orientation at the southern end of the bend the simulated fault propagation path agrees well with the data and sheds light on the origin and nature of the seismicity north and east of the big bend of the san andreas

late cenozoic history and slip rates of the fish lake valley emigrant peak and deep springs fault zones nevada and california several well dated stratigraphic markers permit detailed assessment of the temporal and spatial variation in slip rates along the interconnected faults of the fish lake valley emigrant peak and deep springs fault zones in west central nevada and east central california right lateral motion on the fish lake valley fault zone apparently began ca 10 ma 11 9 8 2 ma associated extensional faulting probably began ca 5 ma 6 9 4 ma and resulted in the opening of fish lake valley and deep springs valley the long term lateral slip rate for the fish lake valley fault zone since about 10 ma is 5 mm yr 3 12 mm yr our preferred lateral slip rate for the central most active part of the fish lake valley fault zone decreased from about 6 to 3 mm yr from the late miocene to the early pleistocene increased to about 11 mm yr during the middle pleistocene and decreased to about 4 mm yr during the late pleistocene extension may account for some of the change in lateral slip rate during the pliocene the large increase in lateral slip rate during the middle pleistocene is circumstantially linked to an increase in vertical slip rates on the fish lake valley and deep springs fault zones at about the time of the eruption of the bishop ash 0 76 ma vertical slip rates along the three fault zones are also related to fault strike vertical rates are highest on north striking faults and approach zero on northwest striking faults the long lived slip history of the fish lake valley fault zone fits a tectonic model in which the death valley furnace creek fish lake valley fault system is integrated with right lateral shear on faults of the central walker lane and the eastern california shear zone to accommodate part of the pacific north american relative plate motion our research demonstrates that the fish lake valley fault zone accounts for about half the rate of 10 12 mm yr of pacific north american plate boundary shear accommodated within the basin and range province between about lat 37 and 38 n