the 1906 earthquake fault rupture and paleoseismic investigation of the northern san andreas fault at the dogtown site marin county california our research describes historical observations of the 1906 earthquake rupture trace in marin county documents the style of subsurface deformation and summarizes our interpretation of the number and timing of pre 1906 ground rupturing earthquakes exposed in 18 trenches excavated across the northern san andreas fault nsaf at the dogtown site dogtown is located immediately southeast of what was known as the strain ranch in 1906 the trenches reveal two stratigraphic sections of late holocene age separated by a well constrained depositional hiatus the upper section deposited in the past 200 250 yr is separated from the lower section which was deposited between a d 250 and 650 by a hiatus during the interval a d 650 1700 we see evidence for two events in the upper section event i 1906 and event ii a likely penultimate earthquake plus a minimum of two events in the lower section event s a and b in the lower stratigraphic section the oldest exposed potential surface faulting evidence event b is constrained to the interval between a d 330 and 580 while there is sound evidence for ground rupturing earthquakes in the 1100 yr long interval between event b and event ii pedogenic processes have obscured their number and timing faulting evidence at the dogtown site suggests the penultimate earthquake occurred between a d 1695 and 1776 data from the dogtown site although equivocal suggest that the time interval 130 210 yr between the 1906 earthquake and the penultimate earthquake on the san andreas fault north of san francisco may be shorter than previously documented

a rupture model for the 28 june 1992 landers california earthquake we have modeled displacement time histories to infer the large scale rupture process of the 28 june 1992 m 7 4 landers california earthquake we have used integrated accelerograms from four terrascope stations at distances between 70 and 150 km the earthquake process consists of unilateral rupture propagation 3 km s on two distinct segments with different strikes n10 w and n40 w the two segments are 20 and 30 km long with constant slip of 3 5 m and 5 2 m respectively the excitation of surface waves resulting from a low velocity surficial layer plays a critical role in matching the synthetic waveforms to the observed displacements the displacements due to both body waves and surface waves are strongly affected by directivity matching the synthetics to the data requires a one second delay between the end of rupture on the first segment and the initiation of rupture on the second segment the seismic moment of the subevents are 2 8 1019 n m and 8 4 1019 n m leading to a total moment of 1 12 1020 n m m 7 4

an intermediate deep earthquake rupturing on a dip bending fault waveform analysis of the 2003 miyagi ken oki earthquake 1 using waveform analysis we propose a dip bending fault model for the 2003 miyagi ken oki earthquake dip angle of the upper fault plane is estimated as 87 on the basis of focal mechanism from p wave first motions s wave polarization analysis leads to a dip angle of 60 for the lower portion of the fault plane inversion results show that the rupture started on the southern fault plane in the beginning 5 seconds slip was mainly confined in the hypocenter area on the southern fault from 5 seconds on rupture propagated to the northern part where the largest slip 3 m occurred in the northern deep part the complex stress field in the slab and compositional difference in the upper and the other portion of the slab account for such a bending fault even at intermediate depth

preliminary slip rate estimates for the duzce segment of the north anatolian fault zone from offset geomorphic markers abstract new estimates on the quaternary slip rate of the active transform margin of north anatolia are provided we investigated the area struck by a mw 7 1 earthquake on the 12th of november 1999 that ruptured the duzce fault segment of the north anatolian fault in order to analyze the spectacular tectonically driven cumulative landforms and the drainage pattern settings we carried out a 1 25 000 scale geological and geomorphological mapping along the fault trace we reconstruct and describe as offset geomorphic markers right hand stream deflections and fluvial terraces inset into alluvial fan deposits radiocarbon dating indicates that 100 m stream deflections were built up by the last 7000 yrs of fault activity conversely two documented and correlated late pleistocene fluvial terraces are horizontally offset by 300 and 900 m respectively these were dated by means of optically stimulated luminescence osl to 21 ka bp and 60 ka bp assuming a constant rate of deformation for the duzce fault ages and related offsets translate to consistent slip rates that yield an average slip rate of 15 0 3 2 mm yr for the last 60 ka thus the duzce fault importantly contributes to the north anatolian margin deformation suggesting a present day partitioning of displacement rates with the mudurnu fault to the south and confirming its important role in the seismic hazard of the area

surface breakage of the 1992 landers earthquake and its effects on structures abstract the landers california earthquake m w 7 3 provides an exceptional opportunity to study surface rupture of an earthquake fault detailed maps of the lateral distribution of fracturing adjacent to main traces show that rupture patterns are much more complex than documented in past studies of surface ruptures the rupture occurs in tabular zones up to hundreds of meters wide a main trace within each rupture zone accommodates much of the shear deformation but considerable fracturing occurs throughout the tabular zone the en echelon pattern of fracturing in step over zones between main traces is typically even more complex than those along major fault zones inspection of several on grade concrete slabs indicates that unreinforced concrete foundations generally crack when subjected to distinct ground ruptures beneath them or when they are twisted because of differential ground movements across broad zones methods of mitigating the potential hazards associated with earthquake fault rupture are presented

the deformation of overburden soil induced by thrust faulting and its impact on underground tunnels overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake the deformed beds formed a triangular shear zone this coseismic faulting often causes damage to underground tunnels located in the shear zone the present research studies the deformation behavior of the overburden soil beds and the tunnel the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip based on sandbox experimental and numerical studies it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds location of the tunnel in this shear zone and deformations of the tunnel the potential major shear zone may be bent or bifurcated into two sub shear zones owing to existence of a tunnel inside the shear zone furthermore the occurrence of back thrust faulting will threaten the safety of nearby structures it was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones the stresses within the soil and the loads on tunnel linings based on the identified mechanisms the strategies for hazard prevention are accordingly suggested and discussed

initial investigation of the landers california earthquake of 28 june 1992 using terrascope the 1992 landers earthquake m s 7 5 m w 7 3 was recorded at six terrascope stations in southern california peak accelerations ranged from 0 16 g at svd 63 km to 0 0092 g at isa 245 km decreasing with distance away from the fault zone the peak velocity showed a different pattern reflecting the rupture directivity from south to north the largest peak velocity 19 cm sec was observed at gsc 125 km moment tensor inversion of long period surface waves yielded a mechanism with m 0 1 1 10 27 dyne cm m w 7 3 dip 74 rake 176 and strike 340 inversion of teleseismic p and s waves revealed two distinct sub events of 6 and 8 sec duration and about 10 sec apart the source parameters for the first and second events are m 0 1 9 10 26 dyne cm dip 83 rake 179 strike 359 and m 0 6 1 10 26 dyne cm dip 87 rake 178 strike 333 respectively the radiated wave energy e s was estimated as 4 3 10 23 ergs the ratio e s m 0 3 9 10 4 corresponds to a stress drop of 280 bars and suggests that the landers earthquake belongs to the group of high stress drop earthquakes and occurred on a fault with a long recurrence time the rupture directivity can be seen clearly in the records from pfo 68 km located to the south and gsc located to the north of the epicenter the maximum displacement at pfo is only 13 of that at gsc despite the shorter epicentral distance to pfo than to gsc the slip distribution determined with the empirical green s function method indicates that the landers earthquake consists of two distinct sub events about 30 km apart with the second sub event to the north being about twice as large as the first one this slip distribution is consistent with the teleseismic data and the surface offsets mapped in the field

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

coseismic ruptures and tectonic landforms along the duzce segment of the north anatolian fault zone ms 7 1 november 1999 1 this paper presents a comparison between the pattern of surface ruptures produced by a single earthquake and patterns of cumulative deformation we performed a detailed study of the 1999 earthquake coseismic ruptures and of the long term tectonic landforms in a key area of the duzce fault segment of the north anatolian fault we observed a scale independent en echelon arrangement of the coseismic surface ruptures as a whole the long term geomorphic expression of the duzce fault near the 1999 ruptures is evidence of the principal slip zone at depth that accommodates the bulk of the displacement during an individual rupture event this may stay localized through many rupture episodes with persistent geometry and kinematics the long term tectonic and geomorphic expression of the fault in a broader area around the 1999 ruptures defines a wider deformation zone in fact an old and complex fault arrangement has been mapped partially coinciding with the 1999 rupturing fault suggesting that the 1999 ruptures are an incomplete expression of the long term duzce fault system the relationships between the coseismic and the old fault systems suggest an evolution of the fault pattern trough time with a tendency to simplify a geometric complexity into a straighter mature trace the integrated investigation of long term tectonic morphologies and structural pattern offers a noteworthy frame to interpret the coseismic rupture kinematics and clarifies their complexities moreover to fully understand the principal slip zone at depth this work shows the importance of the study of strain distribution pattern and evolution of surface rupturing faults

quantitative description and analysis of earthquake induced deformation zones along strike slip and dip slip faults 1 deformation zones are belts of high strains that can occur at the ground surface centered or asymmetrical relative to the trace of an earthquake fault and can range in width from a meter or two up to hundreds of meters in order to minimize damage to engineering structures within deformation zones one needs to be able to determine the characteristics of the deformation zones we develop an elastic plastic model of fault slip propagation to explain formation of deformation zones and estimate certain parameters to characterize deformation zones our theory suggests the ratio of widths of deformation zones in hanging wall and footwall of dipping faults should be controlled by fault dip angle and the kind of fault the relations are different for strike slip and dip slip faults also the total width of the deformation zone normalized with fault slip during the earthquake should be determined by the dip angle the exponent of the yield condition and the kind of fault the theoretical parameters measured for deformation zones along the strike slip duzce bolu fault at kaynasli turkey and two deformation zones along the chi chi thrust fault taiwan agree well with parameters determined from geophysical and geological sources the theoretical model also indicates that the winnetka strain belts related to the 1994 northridge earthquake could have formed above a previously unknown blind fault at winnetka the analysis suggests that the winnetka fault is a normal dip slip fault dipping 54 s with a fault tip depth of 360 m

rupture segmentation and process of the 2001 mw 7 8 central kunlun china earthquake field investigations allow us to constrain the coseismic surface rupture zone of 400 km with a strike slip up to 16 3 m associated with the 2001 m w 7 8 central kunlun earthquake that occurred along one of the western segments of the kunlun fault northern tibet the rupture zone may be divided into four segments based on the geological structures tectonic landform features spatial displacement distributions obtained from field observations and analysis of teleseismic waveforms the deformational characteristics of the surface ruptures and focal mechanism solutions reveal that the earthquake had a nearly pure strike slip mechanism the inversion results from seismic data show that the rupture started from the west near the epicentral area bilaterally and rapidly extended to the east in an unilateral manner for 380 km and that the largest slip region was limited in the subsegment 150 280 km east of the epicenter consistent with field observations the average stress drop is estimated to be 7 mpa in the area where the largest displacements occurred a value typical of intraplate earthquakes the geologic evidence and the inversion results from seismic data clearly show that temporal and spatial displacement distributions and the rupture process are restricted by the pre existing geological structures of the kunlun fault

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

shear zones formed along long straight traces of fault zones during the 28 june 1992 landers california earthquake surface rupturing during the 28 june 1992 landers california earthquake east of los angeles accommodated right lateral offsets up to about 6 m along segments of distinct en echelon fault zones with a total length of 80 km the offsets were accommodated generally not by faults distinct slip sur faces but rather by shear zones tabular bands of localized shearing along simple stretches of fault zones at landers the rupture is characterized by telescoping of shear zones and intensification of shearing broad shear zones of mild sheafing containing narrow shear zones of more intense sheafing containing even nar rower shear zones of very intense sheafing which may contain a fault thus the ground ruptured across broad belts of shearing with clearly defined subparallel walls oriented nw each broad belt consists of a broad zone of mild sheafing extending across its entire width 50 to 200 m and much nan ower a few meters wide shear zones that accommodate most of the offset of the belt and are por trayed by en echelon tension cracks in response to right lateral shearing the slices of ground bounded by the tension cracks rotated in a clockwise sense producing left lateral sheafing and the slices were forced against the walls of the shear zone producing thrusting even narrower shear zones formed within the narrow shear zones although these probably are guides to right lateral fault segments below the surface rupturing during the earthquake is characterized not by faulting but by the formation of shear zones at various scales

variable fault tip propagation rates affected by near surface lithology and implications for fault displacement hazard assessment abstract the fabric of reverse fault zones close to the surface is usually partitioned in between a narrow discrete rupture zone and a more distributed one where folding is predominant this makes quite challenging the adoption of proper setbacks in surface rupture hazard studies for critical facilities or microzoning some of the parameters controlling fault zone fabric are related to mechanics of near surface geology lithology overburden thickness cohesion and water content whose interaction is complex and only partially understood nevertheless these can be seldom measured or derived kinematic models conversely express such an interaction of complex variables as simple synthetic parameters such as the amount of upward propagation of the fault tip for unit of slip usually referred to as the p s ratio propagation on slip here we discuss results on the trishear kinematic inverse modeling of a contractional fault propagation fold at monte netto hill capriano del colle n italy observing a two stage fault and fold growth evolution marked by a significant shift in the p s parameter at this site exceptional sequence of exposures due to ca 10 years of quarry excavations allowed to obtain a series of cross sections across the fault zone we use this detailed high resolution example as a natural analogue for more general large scale surface ruptures involving a thick alluvial cover a very common setting for the siting of critical facilities during the early stage of displacement the fault cut through clast supported fluvial gravels with a high propagation rate p s 7 and a discrete rupture width then during the latest movements of the thrust fault tip propagation slowed down to p s 2 9 as the fault started cutting through several stacked bodies of clays and silty clays pedogenized aeolian silts and overbank deposits causing a pronounced folding of the layers over a wider deformation zone these results strongly suggest that lithological changes in the underlying shallow stratigraphy common in an alluvial plain depositional setting would significantly affect the potential for surface faulting across the same tectonic structure with relevant implications in the fault displacement hazard assessment

surficial slip distribution on the central emerson fault during the june 28 1992 landers earthquake california we present the results of our mapping of a 5 6 km length of the central emerson fault that ruptured during the 1992 landers earthquake in the southwestern mojave desert california the right lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone in some locations a total of up to 110 cm of additional right lateral slip occurred on secondary faults up to 1 7 km away from the main rupture zone other secondary faults carried up to several tens of centimeters of left lateral or thrust displacement the maximum net vertical displacement was 175 cm east side up the sense of vertical slip across the main fault zone varied along strike but in most cases it was consistent with the sense of vertical slip in previous earthquakes as indicated by the locations of areas of older uplifted and abandoned alluvial fan surfaces although variations in surficial slip have been reported along previous strike slip ruptures our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously we document variations in slip as large as 1 m or more over distances ranging from 1 2 km to a few tens of meters suggesting that strains of the order of 10 1 may have occurred locally within the surficial sediments the long wavelength kilometer scale variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments the slip variations over shorter length scales tens of meters may be caused by variations in the proportion of the total shear that occurs on visible brittle fractures versus that which occurs as distributed shear warping or rotation the variability of slip along the ruptures associated with the landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

granite emplacement and its relation with regional deformation in the aravalli mountain belt india inferences from magnetic fabric abstract this contribution presents field microstructural and anisotropy of magnetic susceptibility ams data from the godhra granite a ca 1 ga pluton at the southern margin of the aravalli mountain belt western india that lies near the central indian tectonic zone citz the northern and southern margins of the granite are high strain zones with north dipping e w striking foliations and nw plunging stretching lineations the presence of preferentially oriented feldspars suggests that the granite was subjected to magmatic deformation during its emplacement high temperature solid state deformation fabrics are recorded from microstructural studies which imply that the granite is deformed ams data show magnetic foliations and magnetic lineations in the granite with orientations similar to the field data the magnetic foliation in the granite is parallel to the d 3 foliation in the gneissic host rock both the stretching lineations and the magnetic lineations at the granite margin high strain zones are parallel with the axes of d 3 reclined folds in the gneiss therefore the emplacement of the godhra granite is inferred to have taken place syntectonically while the gneiss was undergoing the d 3 phase of deformation the orientation and character of these lineations and the vergence of the d 3 folds imply oblique simple shear which is inferred to have controlled the emplacement of the granite the magnetic fabric data are compared with the regional structural trends of the metasedimentary rocks of the southern aravalli region and the available geochronological data from rocks of the southern aravalli region are summarised based on this information it is suggested that the emplacement of godhra granite deformation of the southern parts of aravalli mountain belt and tectonothermal events along the citz and rodinia supercontinent assembly were related events

formation of left lateral fractures within the summit ridge shear zone 1989 loma prieta california earthquake the 1989 loma prieta california earthquake is characterized by the lack of major throughgoing coseismic right lateral faulting along strands of the san andreas fault zone in the epicentral area instead throughout the summit ridge area there are zones of tension cracks and left lateral fracture zones oriented about n45 w that is roughly parallel to the san andreas fault in this area the left lateral fractures zones are enigmatic because their left lateral slip is opposite to the right lateral sense of the relative motion between the pacific and north american plates we suggest that the enigmatic fractures can be understood if we assume that coseismic deformation was by right lateral shear across a broad zone about 0 5 km wide and 4 km long beneath summit ridge the shear zone has an orientation of about n70 w and is oblique to the san andreas fault zone which has a trend of n45 to 50 w so that right lateral shearing along with some dilation can account for the orientation of the fracture zones using an analog kinematic model of the summit ridge shear zone and the observable geometric parameters a shear zone about 0 5 km wide an acute angle of 25 between the tension cracks and the shear zone walls left lateral slip of 5 cm and spacing of about 100 m in the tension cracks we estimate that the amount of right lateral shift across the summit ridge shear zone was on the order of 1 4 m this is comparable to the amount of slip for coseismic faulting at depth 1 9 to 2 4 m as computed by several investigators thus contrary to most previous reports on the loma prieta earthquake which assert that coseismic right lateral ground rupture was restricted to considerable greater than 4 km depths in the epicentral area we find that nearly all the right lateral offset is represented at the ground surface by the summit ridge shear zone

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults