simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

thrust top basin formation along a suture zone cantwell basin alaska range implications for development of the denali fault system the cantwell formation consists of a lower sedimentary sequence as much as 4000 m thick and an upper volcanic sequence with a maximum thickness of 3750 m that was deposited in the cantwell basin south central alaska previous to this study the cantwell basin was interpreted as a paleogene nonmarine mainly fluvial pull apart basin that formed in response to dextral strike slip displacement on the denali fault system this study proposes that the cantwell basin formed as part of the mesozoic accretionary phase of deformation prior to the development of the cenozoic postaccretionary denali fault system our reinterpretation is based on several new lines of data 1 age new data based on palynologic analyses of 135 fine grained samples indicate that the lower cantwell formation was deposited during the late campanian and early maastrichtian on the basis of previous regional tectonic studies and this new age constraint the formation of the cantwell basin was coeval with regional late cretaceous shortening associated with accretionary tectonics in southern alaska 2 depositional systems our analysis of the cantwell formation demonstrates that sedimentation occurred mainly in stream dominated alluvial fan axial braided stream and lacustrine settings these depositional systems were strongly influenced by a southward dipping asymmetric basin floor the presence of abundant terrestrially derived organic material together with palynological assemblages that include marine dinoflagellates and the associated presence of oncolites may be suggestive of a time of marginal marine influence during the deposition of the upper part of the lower cantwell formation the late campanian to early maastrichtian timing of this possible marine influence is within the range of the bearpaw transgressive event of the cordilleran foreland basin and allows for regional stratigraphic correlation of the cantwell basin with other sedimentary basins in northwestern north america 3 structural controls on basin formation mapping of intraformational angular unconformities and progressively tilted strata along the southern margin of the cantwell basin provides direct evidence that thrust fault deformation and lower cantwell formation sedimentation were synchronous distinctive cantwell formation conglomerate clasts derived from the uplifted hanging walls of nearby thrust sheets adjacent to the southern basin margin also support a syndepositional thrusting interpretation provenance data and the concentration of proximal alluvial fan deposits along the northwestern basin margin adjacent to the hines creek fault indicate that it too was active during deposition of the cantwell formation on the basis of the new data the cantwell basin is interpreted to have formed as a thrust top basin i e piggyback basin along the late cretaceous suture zone between the accreting wrangellia composite terrane and the north american continental margin in contrast to previous studies this reinterpretation of the formation of the cantwell basin implies that the lower cantwell formation is not a synorogenic deposit directly associated with strike slip displacement along the denali fault system therefore the cantwell basin cannot be used to constrain the timing for the early development of the denali fault system

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

structural evolution of the northern los angeles basin california based on growth strata subsurface structure contour maps and cross sections show that the northern los angeles basin is underlain by a south facing monocline complicated by secondary faults and folds the monocline and associated structures form a structural high the northern los angeles shelf which marks the northern margin of the los angeles central trough analysis of growth strata sediments deposited during structural growth shows that during the miocene the predominant structural style was extension growth strata show that at approximately the beginning of the pliocene 5 ma contraction reactivated the miocene normal faults as reverse faults and formed the monocline its secondary structures and the los angeles central trough lensing out of earliest pliocene delmontian stage growth sandstones onto the flanks of the monocline and secondary structures the south salt lake the east beverly hills and the las cienegas anticlines indicates that these contractional structures all began to form at this time all of the secondary structures became largely inactive prior to the deposition of upper pico member of early pleistocene age 1 2 ma however thick accumulations of growth strata of the upper pico member of the fernando formation within the los angeles central trough attest to continued monoclinal folding after the secondary structures became largely inactive the growth strata record both vertical and horizontal components of structural growth of the monocline so that the dip of the blind fault zone causing the monocline the los angeles fault can be calculated in the east beverly hills area the dip of the los angeles fault is 61 and at las cienegas the dip is 62 these are maximum values based on the assumption that the growth strata bed lengths record all shortening the pliocene pleistocene average fault slip rates for the los angeles fault are 1 1 1 3 mm yr in the east beverly hills and 1 3 1 5 mm yr at las cienegas the resulting pliocene pleistocene horizontal convergence rates are 0 5 0 6 mm yr and 0 6 0 7 mm yr respectively the pliocene pleistocene growth strata show increased dip with age indicating that the monocline grew by progressive limb rotation rather than by kink band migration therefore fault bend and fault propagation fold models based on kink band migration are inadmissible solutions to explain the growth of the monocline we suggest a basement involved shear zone to explain the geometry of the northern los angeles shelf

wilshire fault earthquakes in hollywood the wilshire fault is a potentially seismogenic blind thrust fault inferred to underlie and cause the wilshire arch a quaternary fold in the hollywood area just west of downtown los angeles california two inverse models based on the wilshire arch allow us to estimate the location and slip rate of the wilshire fault which may be illuminated by a zone of microearthquakes a fault bend fold model indicates a reverse slip rate of 1 5 1 9 mm yr whereas a three dimensional elastic dislocation model indicates a right reverse slip rate of 2 6 3 2 mm yr the wilshire fault is a previously unrecognized seismic hazard directly beneath hollywood and beverly hills distinct from the faults under the nearby santa monica mountains

a geo engineering classification for rocks and rock masses abstract in this article an attempt is made to assess the reliability of predicting the uniaxial compressive strength and the corresponding modulus of a rock mass by current approaches these two basic engineering properties when estimated from rock mass rating rmr q and geological strength index gsi indicate hardly any change in the modulus ratio with the change in the quality of the rock mass from very good to very poor however the modulus ratio obtained from the relations involving the joint factor j f indicate a definite decrease in the modulus ratio with a decrease in the quality of the rock mass the strength and modulus in the unconfined and confined states the modulus ratio and failure strain in the unconfined case were linked to j f in earlier publications based on a large experimental database some of these relations were adopted to verify the response of jointed test specimens the response of the rock mass during excavations for mining and civil underground chambers in establishing ground reaction curves including the extent of the broken zone and the bearing capacity of shallow foundations the joint factor is now linked to rmr q and gsi the prediction of compressive strength and modulus of the rock mass appears to be more suitable for classifying the rock based on these properties the deere and miller engineering classification applicable to intact rocks has been suitably modified and adopted the results of different modes of failure of jointed specimens establish definite trends of changes in the modulus ratio originating from the intact rock value on the modified deere and miller plot a geo engineering classification is evolved by considering strength modulus quantifiable weathering index and lithological aspects of the rock

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

orographically anchored el nino effect on summer rainfall in central china abstractyear to year variations in summer precipitation have great socioeconomic impacts on china historical rainfall variability over china is investigated using a newly released high resolution dataset the results reveal summer mean rainfall anomalies associated with enso that are anchored by mountains in central china east of the tibetan plateau these orographically anchored hot spots of enso influence are poorly represented in coarse resolution datasets so far in use in post el nino summers an anomalous anticyclone forms over the tropical northwest pacific and the anomalous southwesterlies on the northwest flank cause rainfall to increase in mountainous central china through orographic lift at upper levels the winds induce additional adiabatic updraft by increasing the eastward advection of warm air from tibet in post el nino summers large scale moisture convergence induces rainfall anomalies elsewhere over flat eastern china which move northward from june to august and amount to little in

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

unfolding an inverse approach to fold kinematics preservedfoldshapesusuallyreveallittleabouttheirkinematicevolution syntectonic strata preserved in growth synclines in contact with a fold however can permit unfolding a sequential reconstruction of fold growth backward through time from a geometry observed at present to an initial undeformed state such reconstructions can define the kinematics of fold growth growth strata associated with anticlinal forelimbs in the ebro basin exhibit depositional tapering of beds on fold flanks and progressive limb rotation unfoldingawell dateddetachmentfolddefinesitskinematicevolutionandcoevallyvarying rates of shortening forelimb uplift and forelimb rotation interplay of these rates with sedimentation rates controls onlap and offlap relations

a forward modeling strategy for balancing cross sections 1 a strategy to balance cross sections of complex structures is documented and illustrated by the interpretation of a compressional structure in the deep water gulf of mexico the strategy is applicable to structures formed in sedimentary rocks under low temperatures in both compressional and extensional environments and involves the comparison of the observed structure with simple balanced forward models forward models generated using fault related fold theory help in understanding the processes and kinematics involved in the deformation further forward models are completely constrained and easy to balance whereas it is difficult to balance data therefore forward models are useful in evaluating ideas without completely solving the structure models are constructed assuming parallel behavior preservation of layer thickness no net distortion where layers are horizontal and conservation of bed length unmetamorphosed sedimentary rocks are generally observed to deform obeying the assumptions of parallel behavior in field map well and seismic data

recognition of paleoearthquakes on the puente hills blind thrust fault california borehole data from young sediments folded above the puente hills blind thrust fault beneath los angeles reveal that the folding extends to the surface as a discrete zone 145 meters wide buried fold scarps within an upward narrowing zone of deformation which extends from the upward termination of the thrust ramp at 3 kilometers depth to the surface document the occurrence of at least four large moment magnitude 7 2 to 7 5 earthquakes on this fault during the past 11 000 years future events of this type pose a seismic hazard to metropolitan los angeles moreover the methods developed in this study can be used to refine seismic hazard assessments of blind thrusts in other metropolitan regions

active tectonics paleoseismology and seismic hazards of the hollywood fault northern los angeles basin california data from geotechnical boreholes and trenches in combination with geomorphologic mapping indicate that the hollywood fault is an oblique reverse left lateral fault that has undergone at least one surface rupturing earthquake during latest pleistocene to middle or late holocene time geomorphologic observations show that the fault extends for 14 km along the southern edge of the eastern santa monica mountains from the los angeles river westward through downtown hollywood to northwestern beverly hills where the locus of active deformation steps 1 2 km southward along the west beverly hills lineament to the santa monica fault rupture of the entire hollywood fault by itself could produce a m w 6 6 earthquake similar in size to the highly destructive 1994 northridge earthquake but even closer to more densely urbanized areas assuming a 0 35 mm yr minimum fault slip rate consistent with available geologic data we calculate an average maximum recurrence interval for such moderate events of 4000 yr although occurrence of such moderate events is consistent with the elapsed time since the poorly constrained age of the most recent surface rupture the data do not preclude a longer quiescent interval suggestive of larger earthquakes if earthquakes much larger than m w 6 6 occurred in the past we speculate that they may have been generated by the hollywood fault together with other faults in the transverse ranges southern boundary fault system

overlapping fault planes of the 1971 san fernando and 1994 northridge california earthquakes aftershocks of the 1971 san fernando and 1994 northridge earthquakes were relocated using a three dimensional velocity model that was derived from inverting p wave travel time data the hypocenters show clear orientations of the dipping fault planes the san fernando aftershocks form a plane extending from a depth of 15 km to the surface dipping toward the northeast at about 40 the northridge aftershocks delineate a fault extending from a depth of 18 km up to about 5 km dipping toward the southwest at about 40 in the region the aftershocks overlap in map view the san fernando plane cuts off the northridge plane at a depth of 5 to 8 km preventing it from reaching the surface the similar but oppositely dipping fault planes suggest a pair of conjugate planes reflecting a horizontal northeast southwest compression

late cenozoic tectonic evolution of the los angeles basin and inner california borderland a model for core complex like crustal extension we propose that the los angeles basin inner california borderland lab ib and the southern borderland off baja california formed by large magnitude crustal extension beginning in latest oligocene earliest miocene time and that these regions represent major late cenozoic rifts the southern borderland is analogous to the gulf of california rift but the onset of rifting in this region may have preceded the opening of the gulf by as much as 15 to 20 m y the lab ib rift is more complex than the southern borderland because it formed in the wake of the rotating western transverse ranges wtr a large crustal block that has undergone more than 90 of neogene clockwise rotation total extension in both rifted regions is estimated to be in excess of 200 km or comparable to the magnitude of late cenozoic crustal extension now estimated for the basin and range province also like the basin and range the crustal floors of the basins in these highly extended domains are characterized by metamorphic core complexes and detachment faults voluminous miocene volcanic rocks and hanging wall fragments of pre rift strata and basement rocks stranded atop detachments during extension in support of this model we synthesize a wide variety of existing geologic data and present interpretations of new geophysical data seismic reflection profiles these profiles image features that we infer are detachment faults and overlying remnants of fragmented and rifted hanging wall rocks we also suggest that a similar but slightly earlier onset of crustal extension affected the santa maria basin and adjacent regions in central california and that the southern margin of this santa maria basin rift was overridden during neogene clockwise rotation of the wtr

characteristics of near fault ground motions by dynamic thrust faulting two dimensional lattice particle approaches two dimensional lattice particle models have been used to simulate dynamic thrust faulting and its effects on near fault ground motions the lattice particle modeling approach has been demonstrated as an efficient way to model the dynamic rupture phenomena observed from a foam rubber experiment on dipping faults we constructed a 42 dipping fault model to simulate near fault ground motions under different site conditions in which different combinations of fault geometry blind fault underlying a sedimentary layer and outcropping thrust models and near surface sedimentary layers were investigated in particular dynamic behaviors between a blind fault with an overlying sedimentary layer and an outcropping fault without a sedimentary layer were compared in this simulation a dynamic slip pulse accompanied by fault separation was initiated at the deepest part of the fault and propagated updip along the fault under a subshear rupture velocity a strong asymmetrical ground motion pattern on the hanging wall and footwall caused by near source rupture effects was observed rupture directivity played an important role in determining the size and distribution of peak ground velocities and accelerations on the hanging wall and footwall in the case of an outcropping thrust without a sedimentary layer the hanging wall underwent a stronger ground motion caused by the near surface breakout phase as the rupture reached the free surface in the case of a blind thrust overlying a sedimentary layer the peak ground particle velocity and acceleration could be much larger on the footwall this is a result of the amplification effect of trapped long period seismic energy in the sedimentary layer the seismic energy emitted from the rupture stopping phase was incident to the sedimentary layer and radiated under the rupture directivity effect the radiated long period seismic energy was trapped in the sedimentary layer propagating away from the fault trace toward the footwall side the numerical results show that for an initial slip of 5 to 5 5 m the horizontal peak ground velocity and acceleration could reach about 1 5 m sec and 2 g respectively on the footwall for a blind thrust with a sedimentary layer with the same initial slip level the peak ground velocity and acceleration were about 1 1 m sec and 1 5 g respectively on the hanging wall for an outcropping thrust without a sedimentary layer these results can partially explain the field observations of precarious rock distributions and overturned transformers in the vicinity of the white wolf fault during the 1952 m s 7 6 kern county earthquake furthermore the current simulation can be used for near fault strong motion prediction for large thrust faults in the los angeles basin or similar tectonic settings around the world

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused

oceanside and thirtymile bank blind thrusts implications for earthquake hazards in coastal southern california we define an active blind thrust system in offshore southern california that extends from los angeles south to the united states mexico international border these blind thrusts formed by tectonic inversion of miocene extensional detachments we attribute the 1986 oceanside ml 5 3 earthquake local uplift of marine terraces seafloor fold scarps and observed geodetic convergence to motion on these faults single and multisegment fault rupture scenarios suggest the potential for large m 7 1 7 6 but infrequent earthquakes that would affect the los angeles and san diego metropolitan areas