large scale velocity field and strain tensor in iran inferred from gps measurements new insight for the present day deformation pattern within ne iran a network of 26 gps sites was implemented in iran and northern oman to measure displacements in this part of the arabia eurasia collision zone we present the gps velocity field obtained from three surveys performed in 1999 september 2001 october and 2005 september and the deduced strain tensor this study refines previous studies inferred from only the two first surveys improvements are significant in ne iran the present day shortening rate across the mountain belts of ne iran is estimated to 5 1 mm yr 1 at about n11 2 1 mm yr 1 of ns shortening across the eastern kopet dag and 3 1 mm yr 1 of ns shortening across binalud and kuh e sorkh our gps measurements emphasize the varying character of the kopet dag deformation between its southeastern part with prevailing thrusting at low rates and its northwestern part with dominant strike slip activity at increasing rates the principal axes of the horizontal strain tensor appears very homogeneous from the zagros to the alborz and the kopet dag n20 and in eastern iran makran and lut block n30 only nw iran suffers a variable strain pattern which seems to wrap the caspian basin the strain tensor map underlines the existence of large homogeneous tectonic provinces in terms of style and amplitude of the deformation

constraints from gps measurements on the dynamics of the zone of convergence between arabia and eurasia we investigate the dynamics of deformation in the zone of convergence between the arabian and eurasian plates using a physical model that treats the lithosphere as a thin fluid sheet deforming in response to lateral variations in gravitational potential energy gpe this model has two free material parameters the power law exponent n of the vertically averaged rheology of the lithosphere and the argand number ar which expresses the relative importance of gpe and stresses required to deform the lithosphere with boundary conditions described by three free parameters the model fits the observed deformation as measured by 367 gps velocities with a root mean square residual of 2 4 mm yr we find negligible improvement when variations in material properties are introduced that represent increases or decreases in the lithospheric strength of the central iranian and turkish iranian plateaux and the zagros mountains effective viscosity of the lithosphere ranges from 5 1022 pa s at 10 nanostrain yr to 1022 pa s at 100 nanostrain yr as well as matching the decadal timescale predominantly interseismic strain rates determined from gps the computed distribution of strain rates is also consistent with the distribution and types of earthquake focal mechanism significant historical earthquake activity is seen in regions with strain rates lower than 20 nanostrain yr implying that it is prudent to base assessments of seismic hazard on regional strain rates

climatic versus tectonic control on river incision at the margin of ne tibet 10be exposure dating of river terraces at the mountain front of the qilian shan 1 we document late pleistocene holocene aggradation and incision processes at the mountain front of the qilian shan an active intracontinental fold and thrust belt accommodating a significant portion of the india asia convergence the shiyou river cuts through a nne vergent fault propagation fold with miocene red beds in the core and pliocene quaternary growth strata on the northern forelimb south of the anticline miocene strata dip 20 ssw suggesting a similar orientation for the basal decollement after aggradation of an 150 m thick late pleistocene valley fill the shiyou river formed three terraces the highest terrace located 170 m above the river constitutes the top of the fill the other terraces are fill cut terraces their treads are located 130 105 m and 37 m above the river respectively the 10be exposure dating of the terraces suggests that river incision accelerated from 0 8 0 2 mm yr 1 to 10 mm yr 1 at 10 15 kyr we interpret fast holocene river incision as largely unrelated to tectonic forcing the late pleistocene incision rate of 0 8 0 2 mm yr 1 places an upper limit of 2 2 0 5 mm yr 1 on the horizontal shortening rate assuming that incision is solely caused by rock uplift above a decollement dipping 20 however the actual shortening rate may lie between 2 2 mm yr 1 and zero because deformation of the terraces and the valley fill cannot be unequivocally demonstrated our estimate is consistent with the bulk shortening rate of 5 10 mm yr 1 across several faults in ne tibet derived from neotectonic and gps data although in case of the shiyou river holocene deformation is barely discernible owing to intense climate induced river incision

slip rate estimate and past earthquakes on the doruneh fault eastern iran summary the doruneh fault with a length of 600 km is one of the longest and most prominent faults in iran it performs an important role in the regional tectonics but has no record of large earthquakes the geomorphology of the doruneh fault contains numerous indications of cumulative left lateral slip over various scales we describe three sites where late quaternary landforms are displaced by the fault a an incised alluvial fan near the village of uch palang is displaced by 800 850 m b the kuh e teagh ahmad fold is composed of folded quaternary gravels and is displaced by 200 400 m c a sequence of three terraces of the shesh taraz river are displaced left laterally by a maximum of 25 m infrared stimulated luminescence irsl dating of the uppermost shesh taraz river terrace gives a deposition age of 10 ka which correlates with changes in global climate 10 12 ka ago and provides a provisional slip rate estimate of 2 4 0 3 mm yr 1 no major recent or historical earthquakes are recorded on the doruneh fault relatively fresh scarps and partially infilled fractures appear to be the preserved surface ruptures from an earthquake event of unknown age a series of small streams showing left lateral displacements of 3 to 5 5 m with an average slip of 4 7 m record the possible magnitude of slip during this earthquake which from scaling relationships would have had an m w of 7 5 and ruptured the fault over a length of 100 km at the estimated slip rate of 2 5 mm yr 1 the average recurrence time between large magnitude earthquakes on the doruneh fault is 2000 yr

holocene right slip rate determined by cosmogenic and osl dating on the anar fault central iran summary be cosmic ray exposure cre and optically stimulated luminescence osl dating of cumulative offset of alluvial fan surfaces have been performed to derive the long term sliprate of the anar fault at two sites the comparison between osl ages obtained within the latest sediments emplaced during the aggradation of the fan and cosmogenic exposure ages of the pebbles abandoned on the surface before its incision and subsequent dextral offset indicates a significant and variable cre inheritance combining offset risers with cre and osl dating implies the southern anar fault slips at a minimum rate of 0 8 mm yr 1 a little faster than formerly estimated by assuming the incision which created the risers was coeval with the onset of the holocene 12 2 ka the latest regional incision in the anar area appears rather coeval with the onset of the early middle holocene pluvial episode 6 10 5 ka evidenced in the neighbouring region of northern oman

estimation of slip rates in the southern tien shan using cosmic ray exposure dates of abandoned alluvial fans cosmic ray exposure dates based on in situ produced 10 be in combination with measured heights of fault scarps that cut three abandoned fans imply a slip rate of less than 2 mm yr on the bounding thrust fault along a segment of the southern flank of the tien shan of central asia this rate somewhat lower than those for the segment farther west and for the northern margin of the belt implies that the distribution of shortening across the tien shan must change markedly along the belt the date of abandonment of the smallest of the three fans is consistent with fan formation since the last glacial maximum but the other two fans appear to have been formed and abandoned prior to that time these and other results suggest that advances and retreats of alpine glaciers may not be synchronized with continental ice sheets and that not all prominent geomorphological features in arid asian regions have formed since the last glacial maximum in this study we have assessed the relationship between cosmogenic nuclide content of individual clasts and the time since their deposition on a surface cosmogenic nuclide accumulation represents the integrated total surface exposure of rocks in source regions during transport and since deposition postdepositional processes erosion burial bioturbation and cryoturbation all of which decrease the quantity of cosmogenic nuclides produced in a rock in a given time and hence the apparent exposure age also cause significant scatter among apparent ages of samples from the surfaces very low 10 be concentrations in material from active streambeds and at depth below one of the fan surfaces indicate that exposure prior to deposition onto fan surfaces was minimal

slip rates along active faults estimated with cosmic ray exposure dates application to the bogd fault gobi altai mongolia dating morphological features displaced along active faults presents a major difficulty in evaluation of slip rates we used in situ produced 10 be to calculate minimum ages for alluvial surfaces misaligned by movement along a major active fault in the gobi altai western mongolia the maximum slip rate of 1 2 mm yr suggested by this method contrasts strongly with rates of 20 mm yr that we estimated by correlation of alluvial deposition with warm humid periods associated with the last glacial termination estimated to have occurred about 12 ka in western tibet the 10 be based slip rate indicates that strong earthquakes can occur along faults with low slip rates and demonstrates the contribution of cosmic ray exposure dating in quaternary tectonic analyses

speleothem evidence from oman for continental pluvial events during interglacial periods growth periods and stable isotope analyses of speleothems from hoti cave in northern oman provide a record of continental pluvial periods extending back over the past four of earth s glacial interglacial cycles rapid speleothem growth occurred during the early to middle holocene 6 10 5 ka b p 78 82 ka b p 120 135 ka b p 180 200 ka b p and 300 325 ka b p the speleothem calcite deposited during each of these episodes is highly depleted in 18 o compared to modern speleothems the d 18 o values for calcite deposited within pluvial periods generally fall in the range of 24 to 28 relative to the vienna peedee belemnite standard whereas modern speleothems range from 21 to 23 the growth and isotopic records indicate that during peak interglacial periods the limit of the monsoon rainfall was shifted far north of its present location and each pluvial period was coincident with an interglacial stage of the marine oxygen isotope record the association of continental pluvial periods with peak interglacial conditions suggests that glacial boundary conditions and not changes in solar radiation are the primary control on continental wetness on glacial interglacial time scales

strike slip kinematics in central and eastern iran estimating fault slip rates averaged over the holocene 1 according to gps measurements the right lateral shear between central iran and afghan blocks amounts to 16 mm yr a model based on very long term estimates of fault rates suggests the current shear originated about 5 ma ago and has been accommodated by strike slip faulting limited to the western 2 mm yr gowk nayband fault and eastern 14 mm yr sistan system fault edges of the lut block we have used high resolution spot5 pixel size 2 5 m images to measure recent cumulative offsets and estimate slip rates over shorter time periods that average several seismic cycles only recent offsets a few tens of meters have been found along the anar fault inside the central iran plateau and along the sistan faults east of the lut the offset morphologies postdate the last incision of the network and are most probably of holocene age 12 2 ka the corresponding slip rates range between 0 5 0 75 mm yr 1 75 2 5 mm yr 1 5 mm yr 1 2 5 mm yr for the anar east neh west neh and asagie fault respectively these estimates suggest the gps shear rate across the lut may not extrapolate over the holocene they also indicate strike slip faulting is not confined to the lut edges but also occurs in central iran suggesting the ongoing strike slip tectonics might have originated between 8 and 22 ma ago earlier than considered previously and consistent with observations in ne iran

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

the post eocene evolution of the doruneh fault region central iran the intraplate response to the reorganization of the arabia eurasia collision zone

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

holocene slip rate on the sabzevar thrust fault ne iran determined using optically stimulated luminescence osl abstract fault slip rates and the recurrence interval between earthquakes can be determined from reliable dating of deformed sediments we report optically stimulated luminescence osl ages of alluvial gravels fine grained sediments and colluvial deposits associated with the sabzevar thrust fault in northeastern iran six samples of the late quaternary deposits were dated by osl using the single aliquot regenerative dose sar protocol the osl ages indicate deposition of alluvial gravels in the study region between 30 and 9 13 ka followed by a period of fluvial incision which is ongoing at the present day the alluvial deposits have been uplifted by 9 5 m relative to the river level indicating a holocene slip rate of 1 mm yr and a rate of convergence across the fault of 0 4 0 6 mm yr assuming a maximum fault dip of 60 the average interval between large earthquakes on the sabzevar fault will be 3000 years if the fault dips 60 and less if the fault dip is less the last earthquake to destroy sabzevar was in 1052 a d

10be dating of alluvial deposits from southeastern iran the hormoz strait area abstract a key area for the understanding of the southeastern iran geodynamics the hormoz strait area was investigated tectonically active it provides useful sequences of quaternary deposits whose deposition may have ended either when the climate dried or when the tectonic activity uplifted the riverbed in situ produced cosmogenic 10be provides surface abandonment ages at 5 6 0 6 8 4 1 0 12 8 1 0 20 1 1 5 and 44 0 3 4 10be kyr located at the transition between the mediterranean winter rain and the indian monsoon domains and south of the northernmost position of the itcz intertropical convergence zone the studied area is very sensitive to climate changes some of the calculated 10be abandonment ages are within the entire investigated area coincidental with large scale climate shifts the offset of the mid holocene humid period 5 6 0 6 10be kyr the onset of the dry younger dryas cold and dry episode 12 8 1 010be kyr and the end of the last glacial maximum lgm 21 2 kyr at 20 1 1 5 10be kyr these events correspond to large scale changes in atmospheric circulation linked to global climate changes and or to sea level fluctuations in the persian gulf which was totally dry during the lgm locally observed abandonment ages at 8 4 1 0 and 44 0 3 4 10be kyr may likely be related to enhanced tectonic activity without regional impact

late pleistocene slip rate of the chaman fault based on 10be exposure dating of offset geomorphic surfaces near kabul afghanistan abstract we report the first late pleistocene left lateral slip rate of the northern chaman fault in afghanistan based on 10be dating of offset alluvial fan surfaces field mapping complemented with the analysis of corona and alos prism satellite images and shaded relief and topographic data allows us to identify piercing points across the fault zone at two displaced alluvial fans ghat bandakul and azadkhail at wardak province south of kabul we constrain the ages of offset alluvial fans based on 10be terrestrial cosmogenic nuclides tcn dating of well embedded quartzite sandstone boulders and cobbles the ghat bandakul alluvial fans are offset at 165 15 m and 235 24 m for which 10be tcn model ages average 46 9 3 5 kyr and 66 6 4 9 kyr respectively yielding a slip rate of 3 5 0 4 mm yr at the azadkhail site we identified two offset terraces based on 500 50 m offset of a geomorphic surface with 111 2 10 5 kyr age we obtain a slip rate of 4 5 0 6 mm yr combining the 800 70 m left lateral offset matching with an average age of 176 8 17 1 kyr for the fan yields the same geomorphic slip rate of 4 5 0 6 mm yr these slip rates are considerably lower than geologically geomorphologically and geodetically defined slip rates previously obtained along the southern chaman fault these results show a clear trend of decreasing fault slip rate with increasing distance to the northeast the observations suggest that the southern portion of the fault accommodates most of the fault parallel component of relative motion between the indian and eurasian plates the lower slip rate of the chaman fault in afghanistan may be explained by the transfer of the left lateral shear onto the gardez and mokur faults that splay northward from the chaman fault

cosmogenic ages for earthquake recurrence intervals and debris flow fan deposition owens valley california model exposure ages beryllium 10 aluminum 26 of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 10be 26al years for a strand of the owens valley fault in california which last ruptured in an earthquake of moment magnitude 7 5 in 1872 cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern sierra nevada are consistent with stratigraphic relations and suggest that these surfaces were abandoned after 1000 8000 and 21 000 10be 26al years ago the wide scatter and nonconcordance of 10be 26al ages on an older fan surface suggest that boulder erosion and lowering of the fan surface there have influenced apparent exposure ages

evidence of quaternary activity along the deshir fault implication for the tertiary tectonics of central iran summary geological and geomorphologic offsets are used to constrain the total displacement and estimate the slip rate of the right lateral deshir fault cumulative morphologic offsets have been found along the southern portion of the fault on the iranian plateau high resolution spot5 images pixel size 2 5 m combined with srtm dem document right lateral offsets of rills terrace risers and successive alluvial fan systems cumulative offsets range from 25 to 900 m and increase with relative elevation hence relative age of offset markers the smallest cumulative offsets are most probably of holocene age 12 2 ka and suggest that the fault slips at an average slip rate close to 2 mm yr 1 coeval normal faulting is associated to strike slip motion at several places along the southern portion of the fault normal and probably active faults are encountered within the high zagros 70 km ahead the tip of the deshir fault and may suggest the fault is propagating southwards the total displacement of the deshir fault estimated from right lateral offset of the nain baft suture is 65 15 km the total displacement would have accumulated over the last 25 40 ma at an averaged holocene slip rate of 2 mm yr 1 placing these observations within the framework of the tectonics of iran allows a discussion of the timing of the transition between collision and subduction in eastern iran

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

elevated shear zone loading rate during an earthquake cluster in eastern california we compare geodetic velocity to geologic fault slip rates to show that tectonic loading was doubled across the eastern california shear zone ecsz during a cluster of major earthquake activity new slip rates are presented for six dextral faults that compose the ecsz in the central mojave desert these rates were determined from displaced alluvial fans dated with cosmogenic 10 be and from a displaced lava flow dated with 40 ar 39 ar we find that the sum geologic mojave ecsz slip rate 6 2 1 9 mm yr is only half the present day geodetically measured velocity of 12 2 mm yr these rates account for cumulative fault slip and geodetic observations that span the 60 km wide shear zone therefore this difference cannot be attributed to postseismic relaxation redistribution of tectonic loading over the earthquake cycle at a regional scale suggests that earthquake clustering may be enhanced via feedback with weakening of ductile shear zones

cosmogenic dating ranging from 20 to 700 ka of a series of alluvial fan surfaces affected by the el tigre fault argentina it is crucial to date continental landforms to quantify processes involved in terrestrial surface evolution especially in regions affected by active tectonics andean quaternary alluvial fan surfaces affected by the el tigre strike slip fault have been studied using combined geomorphic and 10 be exposure age approaches field observations and spot french acronym for satellite for observation of the earth image analysis enable the identification of six alluvial fan units measurements of in situ produced cosmogenic 10 be concentrations in quartzite boulders exposed on the top of fan surfaces show that the depositional periods ended during successive major interglacial stages the calculated minimum exposure ages date the abandonments of the alluvial fan surface from 41 000 8500 yr for the youngest to 670 000 140 000 yr for the oldest unit when linked to the measured maximum cumulative right lateral displacement of stream channels the exposure ages yield a horizontal slip rate of about 1 mm yr on the el tigre fault this study shows that for arid regions where fan surface erosion is minimal in situ produced 10 be can be used to constrain the age of stratigraphically separate alluvial fan surfaces these fan surface exposure ages can be further used to calculate slip rates on active faults and infer depositional periods correlative with climatic events

holocene left slip rate determined by cosmogenic surface dating on the xidatan segment of the kunlun fault qinghai china cosmogenic dating using in situ sup 26 al and sup 10 be in quartz pebbles from alluvial terrace surfaces constrains the late holocene slip rate on the xidatan segment of the kunlun fault in northeastern tibet two terrace risers offset by 24 3 and 33 4 m having respective ages of 1799 388 and 2914 471 yr imply a slip rate of 12 1 2 6 mm yr the full range of ages obtained le 22 8 k y most of them between 6 7 and 1 4 k y confirm that terrace deposition and incision hence landform evolution are modulated by post glacial climate change coupled with minimum offsets of 9 12 m this slip rate implies that great earthquakes m approximately 8 with a recurrence time of 800 1000 yr rupture the kunlun fault near 94 e

in situ produced 10be measurements at great depths implications for production rates by fast muons in situ cosmogenic 10be values have been used to investigate a brazilian quartz vein from the surface to a depth of 15 m at depths greater than 1000 g cm2 deep enough for neutron induced reactions to be insignificant there is only a slight decrease in 10be concentration with increasing depth our results are consistent with deep production of 10be by a mechanism presumably induced by fast muons with an attenuation length of 5300 950 g cm2 and a contribution of 0 65 0 25 to the total surface production results are compared with values from the literature and implications of this re evaluation are discussed

the 1998 march 14 fandoqa earthquake mw 6 6 in kerman province southeast iran re rupture of the 1981 sirch earthquake fault triggering of slip on adjacent thrusts and the active tectonics of the gowk fault zone summary the 1998 march 14 fandoqa earthquake ms 6 6 was the penultimate in a series of five substantial earthquakes on the gowk fault system of southeast iran since 1981 all of which were associated with co seismic surface ruptures we use observations of surface faulting analysis of p and sh body waves sar interferometry and geomorphology to investigate the ruptures in these earthquakes and how they are related both to each other and to the regional active tectonics the 1998 fandoqa earthquake produced 23 km of surface faulting with up to 3 m right lateral strike slip and 1 m vertical offsets sar interferometry and seismic waveforms show that the main rupture plane dipped west at 50 and had a normal component although the surface ruptures were more complicated being downthrown to both the east and the west on steep faults in near surface sediments in addition sar interferometry shows that a nearby thrust with a similar strike but dipping at 6 w moved about 8 cm in a time interval and in a position that makes it likely that its slip was triggered by the fandoqa earthquake the 1998 surface ruptures in the gowk valley followed part of a much longer 80 km set of co seismic ruptures with smaller offsets that were observed after larger earthquakes in 1981 mw 6 6 and 7 1 the main ruptures in these 1981 earthquakes probably occurred on different deeper parts of the same fault system producing only minor reactivation of the shallower faults at the surface although the 1981 1998 earthquake sequence apparently ruptured parts of the same fault system repeatedly these earthquakes had very different rupture characteristics an important lesson for the interpretation of both palaeoseismological trenching investigations and historical accounts of earthquakes the regional kinematics which involve oblique right lateral and convergent motion are evidently achieved by a complex configuration of faults with normal reverse and strike slip components some of the complexity at the surface may be related to a ramp and flat fault geometry at depth but could also be related to the large topographic contrast of 2000 m across the fault system which separates the high kerman plateau from the low dasht e lut desert details of the fault geometry at depth remain speculative but it must be unstable and evolve with time it may be this requirement that causes the principal features of geological flower structures to develop such as series of subparallel faults which accommodate dip slip components of motion

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

shocked quartz grains in the polymict breccia of the granby structure sweden verification of an impact the middle ordovician granby structure in sweden is generally considered the result of an asteroidal or cometary collision with earth although no hard evidence i e shock metamorphic features or traces of the impactor have been presented to date in this study drill core samples of a sedimentary breccia from the granby structure have been investigated for microscopic shock metamorphic evidence in an attempt to verify the impact genesis of the structure the finding of multiple sets of decorated planar deformation features pdfs in quartz grains in these samples provides unambiguous evidence that the structure is impact derived furthermore the orientation of the pdfs e g 1013 1012 and r z 1011 is characteristic for impact deformation the fact that a majority of the pdfs are decorated implies a water bearing target the shocked quartz grains can be divided into two groups rounded grains found in the breccia matrix likely originated from mature sandstone and angular grains in fragments from crystalline target rocks the absence of melt particles provides an estimated maximum shock pressure for the sedimentary derived quartz of 15 20 gpa and the frequency distribution of pdf orientations in the bedrock quartz implies pressures of the order of 10 gpa

dating inset terraces and offset fans along the dehshir fault iran combining cosmogenic and osl methods summary be and 36 cl cosmic ray exposure cre and optically stimulated luminescence osl dating of offset terraces have been performed to constrain the long term slip rate of the dehshir fault analysis of cosmogenic 10 be and 36 cl in 73 surface cobbles and 27 near surface amalgamscollectedfrominsetterracesdemonstratestheoccurrenceofalowdenudationrateof 1mm a 1 and of a significant and variable inheritance from exposure prior to the aggradation of these alluvial terraces the significant concentrations of cosmogenic nuclides measured in the cobbles collected within the riverbeds correspond to 72 20 ka of inheritance the mean creageofthesurfacesamplescollectedontheolderterracet3is469 88kabuttheanalysis of the distribution of 10 be concentration in the near surface samples discard ages older than 412 ka the mean cre age of the surface samples collected on terrace t2 is 175 62 ka but the 10 be depth profile discard ages older than 107 ka for each terrace there is a statistical outlier with a younger age of 49 9 3 3 and 235 5 35 4 ka on t2 and t3 respectively the late sediments aggraded before the abandonment of t2 and inset levels t1 b and t1a yielded osl ages of respectively 26 9 1 3 21 9 1 5 and 10 0 0 6 ka for a given terrace the osl ages where available provide ages that are systematically younger than the cre ages these discrepancies between the cre and osl ages exemplify the variability of the inheritance and indicate the youngest cobble on a terrace that minimizes the inheritance is the most appropriate cre age for approaching that of terrace abandonment however the upper bound on the age of abandonment of a terrace that is young with respect to the amount of inheritance is best estimated by the osl dating of the terrace material for such terraces the cre measurements are complementary of osl dating and can be used to unravel the complex historyofweatheringandtransportinthecatchmentofdesertalluvialfans thiscomprehensive set of dating is combined with morphological offsets ranging from 12 2t o 380 20 m to demonstrate the dehshir fault slips at a rate in the range 0 9 mm yr 1 1 5 mm yr 1 t he variable inheritance exemplified here may have significant implications for cre dating in arid endorheic plateaus such as tibet and altiplano

in situ10be 26al exposure ages at meteor crater arizona a new method of dating the surface exposure of rocks from in situ production of 10be and 26al has been applied to determine the age of meteor crater arizona a lower bound on the crater age of 49 200 1 700 years has been obtained by this method