an intensity survey of households affected by the northridge california earthquake of 17 january 1994 following the northridge california earthquake of 17 january 1994 the humboldt earthquake education center heec conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake s effects on individual households we tabulate human responses to the earthquake and observations of the earthquake s effects on inanimate objects from the heec survey as a function of independently assigned u s geological survey modified mercalli usgs mm intensity for the same communities human responses and subjective judgments about the severity of shaking when averaged over a large number of samples are useful discriminants of the levels of strong ground motion up to those associated with usgs mm intensity vii notwithstanding that individual human responses and subjective judgments are notoriously unreliable a threshold of strong ground motion corresponds to usgs mm intensity of about vii above which over 40 of respondents described the earthquake as violent and most people reported difficulty standing furniture displaced and some damage to their homes even at intensities viii and ix however relatively few people about 15 described their reaction as panic and only about 12 reported major damage to their homes the heec phone survey data show that in communities of low to moderate shaking usgs mm intensities estimated from a single postal questionnaire are quite robust at usgs mm intensity of v and below 88 of usgs mm intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous heec telephone survey data for the same community we introduce the concept of a community decimal intensity scale cdi based on telephone survey data and calibrated to agree on average with the usgs mm intensities the cdis are more regularly distributed than the usgs mm intensities and show much less scatter when plotted as a function of epicentral distance cdis show promise as a tool for comparing regional attenuation for delineating variations in shaking strength within areas mapped as a single mm zone and for rapid preliminary intensity estimates utilizing electronic media

seismic images of continental lithosphere seismic reflection profiles in usa and west germany over thirty years ago showed strong reflections from the lower crust but technical advances through the 1970s were needed for the method to image the continental lithosphere the british institutions reflection profiling syndicate birps found advantage in working offshore and has obtained over 12 000 km of profiles around britain during the past decade giving the densest regional coverage anywhere reflections are observed from strata in sedimentary basins from low angle faults that can be followed from surface to mid crust from a laterally variable reflective zone in the lower crust from the moho and from fault like features in the upper mantle there is evidence around britain that faults bounding sedimentary basins are older structures which have been reactivated it is argued that lower crustal reflectivity around britain is mainly due to anastomosing ductile shears which accommodate extension in the lower crust commensurate with extension in the upper crust by faulting and block rotation there is also evidence of reflections preserved from older orogenic features so that reflections interpreted as extensional ductile shears in the lower crust may also derive from older features that have been reactivated most reflections in the lower crust arise from rocks that have been highly strained evidence of lateral variability in the reflective character of the moho suggests that the moho has been actively involved in the structural evolution of the lithosphere upper mantle reflections are interpreted as shear zones which transfer crustal deformation through the lithosphere

slip rates on the chelungpu and chushiang thrust faults inferred from a deformed strath terrace along the dungpuna river west central taiwan the chelungpu fault produced the september 1999 m w 7 6 chi chi earthquake central taiwan the shortening rate accommodated by this structure integrated over several seismic cycles and its contribution to crustal shortening across the taiwanese range have remained unresolved to address the issues we focus our study on the chelungpu and chushiang thrust faults within the southernmost portion of the chi chi rupture area structural measurements and available seismic profiles are used to infer the subsurface geometry of structures the chushiang and chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the chelungpu surface trace we survey a deformed strath terrace along the dungpuna river buried under a 11 540 309 years old fill deposit given this age the dip angles of the faults and the vertical throw determined from the offset of the strath terrace across the surface fault traces we estimate slip rates of 12 9 4 8 and 2 9 1 6 mm yr on the chelungpu and chushiang faults respectively these yield a total shortening rate of 15 8 5 1 mm yr to be absorbed on their common decollement at depth this total value is an upper bound for the slip rate on the chelungpu fault further north where the chushiang fault disappears and transfers shortening to adjacent faults combining these results with the recently constrained shortening rate on the changhua blind thrust reveals that all these frontal faults presently absorb most of the long term horizontal shortening across the taiwanese range they thus stand as the major sources of seismic hazards in this heavily populated area the return period of earthquakes similar to the chi chi event over a 80 km long stretch of the western foothills is estimated to be 64 years this value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening

5 9 mw 18th june 2010 earthquake and fault segment linkage at andaman a study based on macroseismic survey gps geodesy and coulomb stress changes abstract 18th june 2010 5 9 mw earthquake at north andaman triggered along nw se pre existing fault with reverse fault mechanism macroseismic survey and gps geodesy reveal maximum damages following ne sw trend due to normal fault mechanism coulomb stress modeling for post and inter seismic earthquakes after the 2004 mega earthquake show different stages of fault segment linkage at north andaman the present earthquake has been explained as co shock due to asiesmic soft linkage of fault propagation

first order splay faults dip slip examples first order splay faults are secondary faults that form at acute angles to the primary fault when the latter becomes critically misaligned with the direction of maximum principal stress they are first order in the sense that their slip rate is of the same order as their primary fault first order splay faults have been previously described for strike slip faults and examples are hereshownoffirst order dip slipsplayfaults fordip slipfaultsinsedimentarysequences fric tion is often anisotropic being lower parallel to rather than oblique to bedding and the position of the primary fault is often controlled by a decollement guided by a layer of particularly low friction or a structural feature in this latter situation the primary fault may become frictionally misaligned with the direction of maximum principal stress and first order splay faults may then form examples shown are megasplays in subduction zones ramp faults in fold and thrust belts and syn thetic and antithetic splays of low angle normal faults anderson 1951 proposed that faults form accord ing to the coulomb fracture criterion and with the additional provision that the free surface is a princi pal plane explained the optimum orientation of faults with respect to the principal stress directions and the earth s surface implicit in his thesis which employed a mohr circle analysis is that the orientations of the principal stresses are regionally uniform this assumption has been validated by the world stress map project the main finding of which was stress orientations are remarkably uniform over broad regions length scales up to thousands of kilometers despite large changes in crustal geology tectonic history and crustal thick ness zoback zoback 2007 p 254

indication of transpressional tectonics in the gullfaks oil field northern north sea abstract new seismic data have provided important insights into the tectonic evolution of the gullfaks area and the northern north sea extensional tectonics which predominate in the north sea basin were accompanied by subordinate compressional deformation in the gullfaks field involving the formation of thrust and reverse faults and compressional folds the local compression is interpreted as a product of dextral strike slip movement along the ne sw trend of the tampen spur in late jurassic to early cretaceous times in a regional context the strike slip movement may be related to dextral strike slip movements along the more trondelag fault zone further to the northeast

optimizing earthquake early warning alert distance strategies using the july 2019 mw 6 4 and mw 7 1 ridgecrest california earthquakes

impacts of the october 2012 magnitude 7 8 earthquake near haida gwaii canada on 27 october 2012 a magnitude m w 7 8 earthquake occurred in the sparsely populated region of haida gwaii british columbia canada formerly called the queen charlotte islands this was the second largest recorded earthquake in canadian history it was felt throughout british columbia and as far away as the yukon alberta and montana roughly 1600 km from the epicenter in some locations notably on haida gwaii the perceivable shaking lasted 1 5 2 min with very strong shaking for about 30 s strong ground motions recorded at three locations in the region reached a maximum horizontal acceleration of 0 2 g fortunately this earthquake resulted in very limited damage partly because of the relatively large distance more than 60 km between population centers and the fault rupture and partly because of seismic resistance of the generally low wood frame construction found on the islands we examine the various physical effects from the shaking e g tsunami landslides building damage loss of hot springs cataloged by field crews and reported by the inhabitants of haida gwaii and the surrounding regions these will serve as a guide toward the potential impact from future large earthquakes on the various haida gwaii communities through a community decimal intensity evaluation of people s accounts it was revealed that although intensities were close to expected near the source zone regional intensities were lower than predicted by the conventional western north america theoretical relation finally the october 2012 earthquake may be used as a scenario event for moderate subduction earthquakes in other more populated areas of british columbia canada and the world online material abridged did you feel it reports

seismic images of an extensional basin generated at the hangingwall of a low angle normal fault the case of the sansepolcro basin central italy abstract the study of syntectonic basins generated at the hangingwall of regional low angle detachments can help to gain a better knowledge of these important and mechanically controversial extensional structures constraining their kinematics and timing of activity seismic reflection images constrain the geometry and internal structure of the sansepolcro basin the northernmost portion of the high tiber valley this basin was generated at the hangingwall of the altotiberina fault atf an e dipping low angle normal fault active at least since late pliocene affecting the upper crust of this portion of the northern apennines the dataset analysed consists of 5 seismic reflection lines acquired in the 80s by eni agip for oil exploration and a portion of the nvr deep crop03 profile the interpretation of the seismic profiles provides a 3 d reconstruction of the basin s shape and of the sedimentary succession infilling the basin this consisting of up to 1200 m of fluvial and lacustrine sediments this succession is much thicker and possibly older than previously hypothesised the seismic data also image the geometry at depth of the faults driving the basin onset and evolution the western flank is bordered by a set of e dipping normal faults producing the uplifting and tilting of early to middle pleistocene succession along the anghiari ridge along the eastern flank the sediments are markedly dragged along the sw dipping sansepolcro fault both ne and sw dipping faults splay out from the ne dipping low angle altotiberina fault both atf and its high angle splays are still active as suggested by combined geological and geomorphological evidences the historical seismicity of the area can be reasonably associated to these faults however the available data do not constrain an unambiguous association between the single structural elements and the major earthquakes

the 19 january 2011 mw 7 2 dalbandin earthquake balochistan abstract the 19 january 2011 m w 7 2 dalbandin earthquake at 01 23 a m local time 18 january 2011 20 23 utc occurred south of the makran balochistan volcanic arc at a depth of 70 km and was followed by two globally recorded aftershocks it appears to have occurred on a normal fault within the subducting arabian ormara plate where it descends beneath a southern promontory of the eurasian plate an unusual feature of this earthquake was that it was felt from tehran to delhi and from the northern persian gulf states to central asia a radial felt extent of up to 1400 km however it caused few fatalities and relatively modest damage from the european macroseismic scale ems 98 intensities at 242 locations that are based on media reports and a field visit to the epicenter we compare the attenuation of intensity with distance from the dalbandin earthquake with observations from other intermediate focus earthquakes in the indian subcontinent we also briefly discuss other similar historical earthquakes in western balochistan as well as the potential for site response in the city of karachi in lieu of the varied intensities experienced during earthquakes since the mid twentieth century online material tabulated summaries of macroseismic accounts from 242 locations in the indian subcontinent central asia and the middle east where the 19 january 2011 dalbandin earthquake was felt

the cape mendocino california earthquakes of april 1992 subduction at the triple junction the 25 april 1992 magnitude 7 1 cape mendocino thrust earthquake demonstrated that the north america gorda plate boundary is seismogenic and illustrated hazards that could result from much larger earthquakes forecast for the cascadia region the shock occurred just north of the mendocino triple junction and caused strong ground motion and moderate damage in the immediate area rupture initiated onshore at a depth of 10 5 kilometers and propagated up dip and seaward slip on steep faults in the gorda plate generated two magnitude 6 6 aftershocks on 26 april the main shock did not produce surface rupture on land but caused coastal uplift and a tsunami the emerging picture of seismicity and faulting at the triple junction suggests that the region is likely to continue experiencing significant seismicity

evidence for extensional shear zones in the mantle offshore britain and their implications for the extension of the continental lithosphere deep seismic profiles recorded in the seas around the british isles have revealed bands of seismic reflections in the uppermost mantle on the basis of their appearance geophysical characteristics and association with major crustal faults these features are best interpreted as mantle shear zones furthermore in the north sea the mantle reflectors appear to follow an extensional trend and when interpreted as extensional shear zones help explain the regional stratigraphy of the overlying basin the crosscutting relationships between mantle reflections to the west of scotland and a major strike slip fault the great glen fault ggf suggest that the mantle structure postdates the ggf and hence is probably related to subsequent extension furthermore kinematic analysis of lithospheric deformation to the north of scotland is consistent with the structure observed on the seismic data if the flannan mantle reflection is an extensional shear zone reconstruction of the lithosphere prior to permian extension restores the flannan to the edge of the rockall trough a rift probably initiated in the carboniferous thus the flannan fault may have developed during carboniferous rifting it is concluded that most of the mantle reflections are some form of extensional shear zone in the mantle and the role of such structures during lithospheric extension is considered

lithospheric stretching and north sea jurassic clastic sourcelands uniform lithospheric stretching cannot explain three important aspects of north sea basin evolution namely 1 the rapid growth of middle jurassic uplands from which were liberated major fluvial deltaic clastic wedges now forming the main hydrocarbon reservoirs 2 the occurrence of basin centre upwarp and basaltic volcanism and 3 widespread and significant 1 km subsidence outside the area of demonstrable crustal thinning i present here the suggestion that a combination of nonuniform stretching and lithospheric flexuring accounts for these fine tuning effects of the uniform stretching model with magnitudes close to those demanded by independent geological evidence

geometry and slip distribution in normal fault systems implications for mechanics and fault related hazards normal faults are important sources of large destructive earthquakes in continental rift provinces we investigate the mechanical characteristics of multiple linked master and subsidiary faults using two dimensional boundary element models the master fault system is a coulomb frictional fault that dips 50 from the surface to a depth of 15 km where it is linked to a subjacent shear zone that creeps under low resolved shear stress we consider two basic configurations one in which the shear zone and master fault are coplanar and the other in which the shear zone dips 20 forming a bent or crudely listric fault system antithetic and splay faults are added to the master fault system in each case to model failure of multiple fault systems that are typical of half grabens we focus on the mechanical interactions between the various faults in order to identify points of initial failure spatial variations in the amount of fault slip and the patterns of surface deformation that may precede catastrophic failure of the master fault system in all cases failure on the master frictional fault initiates at the base where it joins the creeping shear zone and at the earth s surface during the same stress increment the listric fault system fails at lower regional differential stress than the planar fault system failure of a large antithetic fault that dips at 70 from the surface to the base of the frictional master fault initiates at lower regional differential stress for the listric than for the planar case several repeated failure episodes may be required to cause surface offset on the antithetic fault if the master fault system is planar but antithetic surface faulting may occur during each master fault failure episode in the listric case modeled splay faults dip from the surface at either greater 70 or lower 50 angles than the frictional master fault to a depth of 5 km where they intersect the master fault in both cases surface slip is greater on the master fault and lesser on the splay fault surface deformation prior to catastrophic failure of the frictional master fault is generated by creep on the deep seated shear zone and during the initial stages of master fault rupture footwall uplift is predicted above a steeply dipping locked coulomb fault and creeping shear zone but the footwall uplift is absent in the listric fault shear zone case a localized zone of increased extensional strain is centered on the surface trace of the master fault as the result of near surface extensional and shear fracturing during the initial stages of fault slip these geodetic anomalies are of interest because they are a near surface phenomenon which may also alter fluid flow and gas flux and be detectable by hydrologic and geochemical instrumentation as well as geodetic measurements

high density macroseismic survey in urban areas part 2 results for the city of rome italy high density macroseismic surveys were carried out in rome following both the 14 october 1997 m w 5 6 i 0 viii mcs and the 26 march 1998 m w 5 3 i 0 vi vii mcs umbria marche central italy earthquakes the aim of the work was to investigate the relationship between intensity and local geology for the modern urban area of rome an issue yet to be examined in contemporary times intensity data for both earthquakes were correlated with near surface geology the results show a statistically significant amplification in holocene alluvial deposits in particular we found one degree of difference in mcs intensity between hard rock and recent alluvium formations furthermore the distribution of the earthquake effects in alluvium filled valleys was studied as a function of the shape ratio h l of the alluvial basins in the tiber river valley higher effects were found to be concentrated within a 150 m wide band along the bedrock alluvium surface contact suggesting the occurrence of an edge effect surprising results were observed in the minor alluvial valleys which displayed the strongest effects in terms of shaking the narrowest valleys width

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

the 17 august 1991 honeydew earthquake north coast california a case for revising the modified mercalli scale in sparsely populated areas we present an isoseismal map of the 17 august 1991 ms 6 2 honeydew earthquake and proposed modifications of the 1931 modified mercalli scale of wood and neumann to accurately estimate peak intensities for this earthquake and others in similar rural settings modifications introduced de emphasize reliance on damage to masonry construction in assigning intensities and attempt to bring physical phenomena such as rockfall landsliding tree and limb fall and water changes in line with the damage indicators

lithosphere rheology and sedimentary basins introduction the dynamics of sedimentary basins is re flected in the wide range of observational scales inside sedimentary basins the advent of high qu ality data sets have significantly improved the resolution of the record of near surface tectonic processes crustal thinning mechanical and thermal sub sidence sediment filling are involved in exten sional basin evolution and controlled by complex interactions between ductile and brittle modes of deformation of the whole lithosphere the rate of loading extension and sediment filling and the thermal evolution are among the most important controlling parameters these nonlinear interac tions do possess a memory of the evolution his tory and loading quantitative understanding of basin subsidence and the offlap onlap strati graphic patterns of a specific basin obviously benefits from progress in understanding the geo dynamical context horvlth 1993 this issue in compressional settings foreland basins re sult from the flexural lithospheric response to loading most of the models proposed so far have considered the lithosphere as a rheological unit and have been based on classical elastic and viscoelastic plate theory the wavelength and am plitude of the flexural response is not an intrinsic property of the lithosphere but result from the history of the competitive interactions between rate of loading and rate of viscous dissipation thermally activated a clear physical description of this flexural mode has not yet been proposed even though some recent results on the mecha nisms of uplift shoulder formation during rifting evolution may be considered bassi 1991 chery et al 1992 the geodynamical context of those basins is complex and the relationship between the transition of extensional and compressional domains is a topic of vigorous research current models for extensional and compressional basins are strongly based on a bulk rheological descrip tion of the whole lithosphere and on a kinematic description of the deformation mechanisms sawyer 1985 houseman and england 1986 quinlan et al 1993 this issue the basin record does reveal to some extend the memory of the deformation history starting from the construction of the internal structure of the basins i e from the processes leading to the formation of rocks sedimentation diagenesis compaction including possible buildup of fluid overpressures and the pattern of the large de formations by faulting or folding to enhance the understanding of the formation and evolution of sedimentary basins it is important to fully address the physical mechanisms operating at different scale in the continental lithosphere for example faulting forms a most important expression at least at the surface of large scale deformation in the basins how those basins are related to the faulting process and the fault interactions is an unsolved question pull apart basins are certainly

potentially induced earthquakes during the early twentieth century in the los angeles basin recent studies have presented evidence that early to mid twentieth century earthquakes in oklahoma and texas were likely induced by fossil fuel production and or injection of wastewater hough and page 2015 frohlich et al 2016 considering seismicity from 1935 onward hauksson et al 2015 concluded that there is no evidence for significant induced activity in the greater los angeles region between 1935 and the present to explore a possible association between earthquakes prior to 1935 and oil and gas production we first revisit the historical catalog and then review contemporary oil industry activities although early industry activities did not induce large numbers of earthquakes we present evidence for an association between the initial oil boom in the greater los angeles area and earthquakes between 1915 and 1932 including the damaging 22 june 1920 inglewood and 8 july 1929 whittier earthquakes we further consider whether the 1933 m w 6 4 long beach earthquake might have been induced and show some evidence that points to a causative relationship between the earthquake and activities in the huntington beach oil field the hypothesis that the long beach earthquake was either induced or triggered by an foreshock cannot be ruled out our results suggest that significant earthquakes in southern california during the early twentieth century might have been associated with industry practices that are no longer employed i e production without water reinjection and do not necessarily imply a high likelihood of induced earthquakes at the present time online material summary of background information about the wilmington oil field information about revisited earthquakes between 1900 and 1935 tables of felt events and accounts of three earthquakes

origin of a crustal splay fault and its relation to the seismogenic zone and underplating at the erosional north ecuador south colombia oceanic margin 1 splay faults within accretionary complexes are commonly associated with the updip limit of the seismogenic zone prestack depth migration of a multichannel seismic line across the north ecuador south colombia oceanic margin images a crustal splay fault that correlates with the seaward limit of the rupture zone of the 1958 mw 7 7 tsunamogenic subduction earthquake the splay fault separates 5 6 6 km s velocity inner wedge basement rocks which belong to the accreted gorgona oceanic terrane from 4 to 5 km s velocity outer wedge rocks the outer wedge is dominated by basal tectonic erosion despite a 3 km thick trench fill subduction of 2 km high seamount prevented tectonic accretion and promotes basal tectonic erosion the low velocity and poorly reflective subduction channel that underlies the outer wedge is associated with the aseismic decollement thrust subduction channel fluids are expected to migrate upward along splay faults and alter outer wedge rocks conversely duplexes are interpreted to form from and above subducting sediment at 14 to 15 km depths between the overlapping seismogenic part of the splay fault and the underlying aseismic decollement coeval basal erosion of the outer wedge and underplating beneath the apex of inner wedge control the margin mass budget which comes out negative intraoceanic basement fossil listric normal faults and a rift zone inverted in a flower structure reflect the evolution of the gorgona terrane from cretaceous extension to likely eocene oblique compression the splay faults could have resulted from tectonic inversion of listric normal faults thus showing how inherited structures may promote fluid flow across margin basement and control seismogenesis

creep and locking of a low angle normal fault insights from the altotiberina fault in the northern apennines italy while low angle normal faults have been recognized worldwide from geological studies whether these structures are active or capable of generating big earthquakes is still debated we provide new constraints on the role and modes of the altotiberina fault atf in accommodating extension in the northern apennines we model gps velocities to study block kinematics faults slip rates and interseismic coupling of the atf which is active and accounts with its antithetic fault for a large part of the observed chain normal 3 mm yr tectonic extension a wide portion of the atf creeps at the long term slip rate 1 7 0 3 mm yr but the shallow locked portions are compatible with m 6 5 earthquakes we suggest that positive stress accumulation due to atf creep is most likely released by more favorable oriented splay faults whose rupture may propagate downdip along low angle normal fault surface and reduce the probability of occurrence of a seismic rupture of the shallower locked portion

origin and evolution of a splay fault in the nankai accretionary wedge subduction zones are often characterized by wedge shaped sedimentary complexes called accretionary prisms that form when sediments are scraped off the subducting plate and added to the overriding plate large landward dipping thrust faults can cut through such a prism these faults known as megasplay faults 1 2 originate near the top of the subducting plate and terminate at the shallow landward edge of the prism1 3 4 5 6 megasplay faults have been the subject of numerous geological and geophysical studies4 5 6 7 8 9 10 11 12 13 14 15 but their initiation and evolution through time remains poorly constrained here we combine seismic reflection data from the nankai accretionary wedge with geological data collected by the integrated ocean drilling program iodp and find that the splay fault cutting this wedge initiated approx1 95 million years myr ago in the lower part of the prism as an out of sequence thrust oost after an initial phase of high activity the movement along the fault slowed down but uplift and reactivation of the fault resumed about 1 55 myr ago the alternating periods of high and low activity along the splay fault that we document hint at episodic changes in the mechanical stability of accretionary prisms

crustal stretching in the scandinavian caledonides as revealed by deep seismic data the normalization of overthickened orogenic crust after a continent continent collision typically involves several different processes including erosion plate divergence gravity driven collapse of the orogenic wedge and viscous flow of the lower crust as a contribution to this discussion we here utilize reprocessed deep seismic data to image the scandinavian part of the major caledonian continent continent collision zone where we identify a double set of extensional shear zones one in the upper to middle crust hardangerfjord shear zone and a major oppositely dipping moho offsetting shear zone in the lower crust and upper mantle the latter shear zone may have a true displacement close to 50 km and appears to offset the moho vertically by 10 km extending downward beyond the 50 km depth limit of the seismic data while the upper structure offsets the basal caledonian thrust the moho shear zone is more difficult to date however they are kinematically consistent and located at the transition zone between thick and thin skinned post collisional tectonics and we suggest that they may represent a crustal pinch or zipper like structure that separated viscously flowing caledonian lower crust from cooler rigid basement representative for the rest of the baltic shield later extension created the north sea rift but the general rift axis and the associated riftrelated thinning developed in a narrower zone that runs oblique to the devonian trend hence the two generations of extension and thinning can be distinguished at the crustal scale

the 1868 hayward fault california earthquake implications for earthquake scaling relations on partially creeping faults the 21 october 1868 hayward california earthquake is among the best characterized historical earthquakes in california in contrast to many other moderate to large historical events the causative fault is clearly established published magnitude estimates have been fairly consistent ranging from 6 8 to 7 2 with 95 confidence limits including values as low as 6 5 the magnitude is of particular importance for assessment of seismic hazard associated with the hayward fault and more generally to develop appropriate magnitude rupture length scaling relations for partially creeping faults the recent reevaluation of archival accounts by boatwright and bundock 2008 together with the growing volume of well calibrated intensity data from the u s geological survey did you feel it dyfi system provide an opportunity to revisit and refine the magnitude estimate in this study we estimate the magnitude using two different methods that use dyfi data as calibration both approaches yield preferred magnitude estimates of 6 3 6 6 assuming an average stress drop a consideration of data limitations associated with settlement patterns increases the range to 6 3 6 7 with a preferred estimate of 6 5 although magnitude estimates for historical earthquakes are inevitably uncertain we conclude that at a minimum a lower magnitude estimate represents a credible alternative interpretation of available data we further discuss implications of our results for probabilistic seismic hazard assessment from partially creeping faults online material table of locations with intensity assignments

crustal thinning and nature of extension in the northern north sea from deep seismic reflection profiling a regional network of deep seismic reflection profiles recorded in the northern north sea has been used to map mesozoic and cenozoic basin thickness and crustal thickness in the viking graben and adjacent platform areas depth to the reflection moho varies from about 20 km in parts of the viking graben to about 32 km beneath the shetlands and the norwegian margin the shallowing of the reflection moho beneath the viking graben implies crustal stretching factors for mesozoic extension greater than 2 in the center of the north sea basin the axis of crustal thinning is located directly beneath the viking graben the axis of the sedimentary basin steeply dipping basin bounding faults are imaged in the upper crust and several dipping reflectors are observed in the upper mantle but no continuous reflective feature extending from the sedimentary basin to beneath the moho is observed on any of the deep profiles thus these data do not support the existence of lithosphere penetrating low angle detachments zones of simple shear as the cause of extension in the northern north sea some of the mantle reflectors dip to the west and some to the east suggesting that simple shear if it occurs in the upper mantle is not of uniform sense rather these data suggest a complex depth dependent pattern of brittle extensional deformation in the upper crust pervasive ductile extension bulk pure shear in the lower crust which is decoupled from deformation in the mantle and extension accommodated by discrete dipping shear zones in the lithospheric mantle

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

a proposed rupture scenario for the 1925 mw 6 5 santa barbara california earthquake abstract the 29 june 1925 santa barbara earthquake is among the largest 20th century earthquakes in southern california the earthquake also predated the installation of strong motion and local monitoring instruments in southern california some instrumental data are however available from long period instruments at regional and teleseismic distances the current catalog moment magnitude is mw 6 8 initial intensity magnitudes mi estimated from original coast and geodetic survey intensity assignments were lower mi 6 3 in this study we assign modified mercalli intensity values at 239 locations including 144 specific locations within the city of santa barbara for which detailed damage information is available comparing the reinterpreted intensities with did you feel it intensities for recent events in california we estimate mw 6 5 with a plausible range of 6 3 6 6 we further consider reported instrumental amplitudes to estimate an instrumental moment magnitude of mw 6 6 0 5 our preferred final estimate is mw 6 5 based on available constraints including aftershock locations inferred from data recorded on portable instruments we propose that the earthquake nucleated east of the city of santa barbara closer to the coast than previously estimated and ruptured unilaterally 30 km to the west possibly along the south dipping mesa rincon creek and the more ranch fault systems contrary to suggestions made in earlier studies e g willis 1925a relatively high intensities 50 km west of santa barbara can then be explained by directivity rather than involvement of the santa ynez fault finally we discuss the possibility that the earthquake was triggered by the larger mw 6 6 clarkston montana earthquake the previous day or induced by oil production in the summerland oil field

the magnitude 6 7 northridge california earthquake of january 17 1994 the most costly american earthquake since 1906 struck los angeles on 17 january 1994 the magnitude 6 7 northridge earthquake resulted from more than 3 meters of reverse slip on a 1 5 kilometer long south dipping thrust fault that raised the santa susana mountains by as much as 70 centimeters the fault appears to be truncated by the fault that broke in the 1971 san fernando earthquake at a depth of 8 kilometers of these two events the northridge earthquake caused many times more damage primarily because its causative fault is directly under the city many types of structures were damaged but the fracture of welds in steel frame buildings was the greatest surprise the northridge earthquake emphasizes the hazard posed to los angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes

common features of the excitation and propagation of strong ground motion for north american earthquakes the central matter of this investigation is the commonly held belief that eastern north america ena earthquakes are felt to much greater distances at all levels of intensity than their western u s wus counterparts of the same source strength by comparing the areas enclosed by modified mercalli intensities i to iii felt iv v vi and vii for ena and wus earthquakes at the same source strength we find that this proposition is mostly false at damaging levels of ground motion intensities vi to vii and greater for m 7 neither should such differences exist if strong ground motion is confined to r 150 km and arrives principally as body waves and if ena and wus earthquakes share the same average stress drop in fact observable differences in the areas enclosed by intensity vi a vi for ena and wus earthquakes at the same m point to slight but significant differences in stress drop the ena earthquakes having stress drops a factor of about 2 higher only for the largest earthquakes m 7 as the 1811 to 1812 new madrid and 1886 charleston earthquakes seem to be can strong ground motion propagate to much greater distances as low loss higher mode surface waves in ena relative to wus the strong dependence of high frequency strong ground motion on stress drop and its weak dependence on m admit the possibility that the 1811 to 1812 events and the 1886 charleston earthquakes are no larger than m 6 to 7 provided that their stress drops are higher than average by a factor of 2 or so

correlation between earthquake damage and seismic site effects the study case of lentini and carlentini italy abstract on december 13th 1990 a magnitude 5 6 seismic event felt throughout sicily and having maximum seismic intensity vii viii occurred although it is classified as moderate magnitude it caused causalities and the collapse of a few buildings two of the most struck cities were carlentini and lentini located in south eastern sicily at about 20 km from the instrumental epicenter in order to evaluate the influence of ground features on the damage distribution both vulnerability and damage maps were drawn using information collected in about 6000 forms coming from official ascertainments significant damage observed in some portions of the investigated areas appears related to the modest quality of the buildings that were classified as medium to high vulnerability to evaluate the role played by the geologic setting two sites were instrumented to measure shear wave velocity of the main lithotypes sixty three ambient vibrations measurements were also performed both in free field and inside some buildings moreover using information coming from geological and geophysical surveys 1d numerical modelling were done to achieve information about the main ground motion parameters the results highlight the occurrence of significant site effects and the potential presence of resonance phenomena between site and structure during the occurrence of a seismic event seismic site amplifications together with the buildings vulnerability observed through damage surveys contributed to enhance the inherent seismic risk of the investigated area

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

heterogeneous stretching simple shear and basin development abstract the models of basin development which involve either homogeneous stretching of the whole lithosphere or displacement on a lithospheric scale shear zone are but two end members of a range of possible extensional models the homogeneous extension model thins the lower lithosphere beneath the thinned upper crust and superimposes a thermal subsidence basin on the earlier fault bounded basin the shear zone model offsets the zone of lower lithospheric stretching and thermal subsidence it is more likely that the zones of upper and lower lithospheric stretching will be heterogeneous and patchy but will often overlap in plan view this will produce localised uplift and subsequent thermal subsidence within the faulted basin and may explain many of the anomalies between the various stretching estimates made using different structural stratigraphic and geophysical techniques the model which combines heterogeneous lithospheric stretching and associated simple shear may explain 1 variations in dip of the major detachment zones in the large basins 2 variations in types of strain on or beneath the detachment zones 3 regional uplift of part of a basin to erode the earlier fault blocks and 4 the development of volcanism in basins with only low values of upper crustal extension the zone of stretched lower crust and lithospheric mantle may lie beneath the centre of the zone of upper crustal stretching or to one side it may be linked to the upper crustal zone by faults which dip consistently in one direction or by extensional systems which change their dominant dip direction with depth pulling out the mid crust as one or more wedges possible examples are discussed from the basin and range province and northwest european continental shelf

how preexisting weaknesses control the style of continental breakup continental breakup is a highly variable process differences occur in the relative timing and extent of volcanism uplift and graben formation as well as in the mode and amount of continental extension before breakup we propose a model which reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends continental lithosphere is viewed as a composite material composed of two strong layers one in the upper mantle and one in the middle crust finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust this leads to early melt segregation and volcanism margin uplift during the late stages of the extension process and relatively narrow symmetrical extended margins in contrast failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle this produces initial graben formation cooling in the lower crust and upper mantle and broad asymmetrical extended margins volcanism only occurs late in the process failure at laterally offset weaknesses within both strong layers leads to a deformation pattern dominated simple shear thus differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup

palaeomagnetic dating of fault rocks evidence for permian and mesozoic movements and brittle deformation along the extensional dalsfjord fault western norway summary palaeomagnetic and structural studies of the dalsfjord nappe western norway show that the basal ow angle detachment dalsfjord fault is a long lived fault zone and that the most important phase of faulting was of devonian extension probably nucleated on an earlier silurian scandian thrust fault rocks produced during subsequent movements indicate that the dalsfjord fault underwent periods of brittle low angle extensional reactivation during the permian 250 260 ma and upper jurassic lower cretaceous c 150 ma corresponding with stages of major extensional movements on the continental shelf palaeomagnetic studies may be of great importance for dating faults and major movement stages in long lived fault systems the particular importance of the results is that they show that low angle normal faults can operate in a brittle upper crustal regime

the structural evolution of the northern viking graben and its bearing upon extensional modes of basin formation recent advances in the understanding of rift basin formation coupled with the increasing public availability of seismic and well data across the northern viking graben 60 61 n have enabled a detailed analysis of its development two rifting episodes can be recognized late permian early triassic and bathonian ryazanian major regional unconformities thought to be primarily tectonic rather than eustatic in origin separate and subdivide the rifting episodes the earlier episode involved extension about a n s axis ensuing triassic mid jurassic thermal subsidence was accommodated on steep faults during the later episode a new ne sw fault trend was superimposed on pre existing patterns major block rotation marking active rifting ceased at the end of the ryazanian during the second post rift episode there was a progressive migration of active faulting towards the basin margins and as a result a widening with time of the area undergoing subsidence asymmetric subsidence of the central part of the basin was hinged at the western margin of the horda platform and accommodated to the nw on major faults within the tampen spur factors for the second rifting episode were calculated both by relating subsidence to extension and by measuring observed extension values calculated by both methods increase consistently towards the basin axis for both rifting and thermal subsidence phases but are greater for the latter phase subsidence patterns are similar for both rifting and thermal subsidence episodes so that there is vertical stacking of relatively thick sequences in the axis of the northern viking graben these factors preclude the application of models involving uniform and non uniform stretching and also preclude oblique extension depth dependent stretching is preferred

numerical simulation of rifting in the northern viking graben the mutual effect of modelling parameters numerous basin modelling studies have been performed on the viking graben in the northern north sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations in such modelling it is important to include lithospheric flexure the values derived for the lithospheric strength by these studies vary considerably i e up to a factor of 30 in this study which is based on new interpretation of a regional transect we show that both the estimated value of the effective elastic thickness and the derived b profile are dependent on the assumed value of the depth of necking the use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength and an overestimation of the thinning factors in the northern viking graben a necking depth at intermediate crustal levels gives results comparable to the observations extension by faulting is modelled to be a significant factor in conclusion rifting in the northern viking graben can be explained with various models of effective elastic thicknesses eet varying from 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking it is also shown that the development of the basin during the post rift phase cannot be explained by pure shear simple shear extension two mechanisms are proposed here to explain the post rift subsidence pattern namely intra plate stress and phase boundary migration the two extreme models for eet mentioned above 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking give very different responses to compressional stress the latter gives basically no response for realistic intra plate stress d 2004 elsevier b v all rights reserved

comparing intensity variation of the 2001 nisqually earthquake with geology in victoria british columbia this article compares the variation in observed intensity of the 2001 m w 6 8 nisqually washington earthquake in victoria british columbia 150 km from the epicenter with amplification hazard predictions based on the average shear wave velocity of geologic units modified mercalli intensities were assigned from 750 felt reports collected by online web submission augmented by door to door canvassing in regions of particular interest an intensity map was created based on high resolution sub city block georeferencing with the canadian postal code system site specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear wave velocity substrates bedrock and glacial till versus soft clay and peat overall the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear wave velocities across greater victoria

ramp initiation and spacing in a homogeneous thrust wedge 1 fold and thrust belts grow largely through sequential initiation of thrust faults and subsequent motion on them from hinterland to foreland i e away from the plate boundary while perturbations in basal geometry stratigraphy excess fluid pressure folding and surface slope have all been suggested as mechanisms for thrust ramp nucleation we show that preexisting inhomogeneities are not necessary we present a mechanically homogeneous finite element wedge model to assess the effects of variations in yield stress dilation angle and basal friction angle on foreland fold and thrust belt evolution computer experiments produce a broad foreland dipping plastic strain band that marks the topographic inflection produced by the previous ramp this band migrates toward the rigid base where the plastic strain is preferentially concentrated in a thrust ramp subsequent ramps develop toward the foreland in a self similar fashion the ramp formation process is systematic ramps form at the same location with respect to the wedge origin regardless of significant variations in yield stress dilation angle or basal friction however the backstop displacement required to initiate a new ramp is dependent on these variables we conclude that the wedge geometry is the primary factor in determining both thrust ramp location and spacing syntectonic erosion and deposition or any other process that changes wedge geometry may in some cases control the location of thrust ramps

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

lithospheric stress and deformation the study of the mechanisms magnitudes and modes of lithospheric stress and deformation occupies a central position in the discipline of tectonophysics it is therefore difficult in assembling a comprehensive review to place limits on what should be included for example one cannot discuss stress and deformation apart from considerations of the rheological models of the lithosphere which link the two and ultimately control the behavior of plates at their margins and in their interiors once admitting to the importance of rheological considerations in discussing stress and deformation one is then compelled to include information relating to the thermal state of the lithosphere since temperature is one of the foremost environmental variables controlling rheology furthermore lithospheric processes cannot be considered in isolation from those affecting the asthenosphere since surely there exists some coupling between the motion of the lithosphere and convection in the earth s interior in fact an understanding of lithospheric stress and deformation can be considered a prerequisite to solving problems in geodynamics because it is through the lithospheric filter that one detects the consequences of thermal and compositional anomalies at greater depth the topic of this report cannot even be cleanly separated from reviews in other disciplines such as seismology and geodesy the magnitude and orientation of lithospheric stress is often indicated by earthquakes while lithospheric strain can be observed geodetically the philosophy i have adopted here is that some overlap with other review papers in this series is unavoidable and probably desirable from the standpoint of emphasizing how recent work n other areas of geophysics has contributed to the advancement in our understanding of the lithosphere s state of stress and mechanisms of deformation i have however resisted the temptation to include extraterrestrial studies presumably covered in the planetary section despite the similar causes for deviatoric stress and deformational mechanisms operating on other terrestrial planets certainly ideas of how silicate materials behave and how lithosphere responds to internal forces benefit from the perspective of omparative planetology finally in defining the scope of this portion of the u s national report to the iugg i did not consciously exclude papers by non u s citizens work done at non u s institutions projects not funded by the u s government or however else foreign might be defined topics in geophysical research cannot be divided along political boundaries however i did not attempt to seek out articles written in languages other than english or published in journals not readily available in the united states and i apologise for this obvious shortcoming

the 1952 kern county california earthquake a case study of issues in the analysis of historical intensity data for estimation of source parameters abstract seismic intensity data based on first hand accounts of shaking give valuable insight into historical and early instrumental earthquakes comparing an observed intensity distribution to intensity prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available however the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties in this paper we illustrate these challenges and possible solutions using the 1952 kern county california earthquake as a case study published estimates of its magnitude vary from mw 7 2 7 5 making it possibly the second largest in california during the 20th century we considered over 1100 first hand reports of shaking supplemented with other data and inferred the magnitude in several ways using intensity prediction equations yielding a preferred intensity magnitude mi 7 2 0 2 where the uncertainty reflects our judgement the revised intensity distribution reveals stronger shaking on the hanging wall south of the surface expression of the white wolf fault than on the footwall characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region such reinterpreted intensities for historic earthquakes combined with u s geological survey usgs did you feel it data for more recent events can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed

a high resolution intensity study for the 1906 san francisco earthquake in the vicinity of san jose california abstract variation of shaking intensity for the 18 april 1906 earthquake in and around the city of san jose california is established based on 607 damage locations using a methodology suitable for high resolution mapping of intensity this detailed methodology uses a refined modified mercalli intensity mmi scale and is based on the premise that an intensity estimate can be calculated from the damage to a single building provided extent of damage and style of building construction are sufficiently well known to reflect the rich detail in the damage descriptions the refined scale recognizes partial steps in the range mmi 6 9 for the 138 km 2 area of study earthquake damage is compiled from published descriptions mostly made by building industry professionals within 10 days after the 1906 earthquake and never before evaluated for an intensity study sanborn perris map company fire insurance maps provide precise location and nature of construction for 483 damaged structures within and 124 outside the 1906 san jose city limits the distribution of assigned intensities approximates a normal distribution with median intensity 7 5 mean intensity 7 36 and standard deviation 0 687 maximum intensity 8 5 9 0 is identical to contoured mmi from previous intensity studies with lower density of data for analysis damage data points are grouped at two scales at the first 227 modern census blocks contain as many as 31 buildings each with mean of block median intensities 7 46 and standard deviation 0 660 in 71 of 101 blocks with two or more data points intensity range is one point or less this low variability indicates consistent building response in these blocks to ground shaking moderate to larger variations in intensity within some blocks may be attributed to differences in construction prior damage to structures or anthropogenic factors at the second scale geographically distinct associations of neighboring blocks are grouped into six microzones from 1 5 to 7 0 km across with mean microzone intensity 6 6 to 8 2 and standard deviation 0 160 to 0 637 these intensity differences which match variations observed in modern ground motion studies are inferred to reflect real variation in damage causing ground motion in 1906 methods presented here can be used to constrain ground motion models identify seismic hot spots and improve site specific assumptions for probabilistic seismic hazard analysis psha

quantitative analysis of triassic extension in the northern viking graben it has been recognized for over a decade that large displacement pre jurassic faults are present in the northern viking graben part of the north sea rift these faults define a series of major fault blocks below the more obvious jurassic rift basin we attempt here to quantify the amount of extension associated with this older rift event which is probably of early triassic age quantitative modelling of the triassic rift and the succeeding period of thermal subsidence has been undertaken using a combination of flexural backstripping and flexural cantilever forward modelling these techniques suggest that triassic extension across the horda platform norwegian sector reached c 40 s 1 4 the consequences of this extension were deposition of a thick 3 km triassic upper jurassic syn rift and post rift sequence prior to renewed but minor extension in the late jurassic earliest cretaceous the thickness of the viking group reservoirs in the troll area appears to have been almost entirely controlled by sediment loading during post triassic thermal subsidence jurassic extension on the horda platform was in the uk sector of the viking graben triassic structures are less obvious than those below the horda platform because of jurassic overprinting they are however still present average triassic extension across the east shetland basin was c 15 comparable with the magnitude of jurassic extension in the same area we believe that the tern eider and cormorant fault blocks with proven shallow basement comprised a large eroded horst during the early triassic uplifted in the footwalls of major faults flanking the magnus and statfjord half graben during the triassic the magnus half graben was contiguous with the unst basin now situated in the western footwall of the younger jurassic basin the presence of the unst basin suggests that triassic extension occurred across the area that is now the northern shetland platform continuing into the west shetland area although the more obvious structures in the viking graben are jurassic in age the earlier triassic event was equally as important in controlling the structural and stratigraphic history of the basin

investigation of surface geology and intensity variability in the palermo italy urban area after the 6 september 2002 earthquake this work was funded by the miur legge 488 92 delibera cipe 08 08 96 r catalano 60 2000 2001

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

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

stress strain and fault behavior at a thrust ramp insights from the naukluft thrust namibia we report observations from a kilometer scale thrust ramp on the naukluft thrust namibia the naukluft thrust is a low angle thrust that was active at subgreenschist facies conditions and accommodated several tens of kilometers of displacement at the base of the naukluft nappe complex in the pan african damara orogeny the fault zone is generally planar and a few meters thick comprising predominantly a dolomite rich cataclasite at the ramp the fault rock assemblage increases in thickness and the hanging wall which elsewhere is relatively intact contains a high density network of inclined quartz veins subvertical dolomite and calcite veins breccia zones as well as injectites of cataclastic fault rock emanating from the fault surface the geometry of the hanging wall structures indicates local subhorizontal extension local tensile stress can be explained by bending in the hanging wall as it deformed to slide above the ramp structure high fluid pressures created dynamically during fast slip by decarbonation of carbonate fault rock and by dewatering of the footwall under an impermeable fault during interseismic periods led to additional reduction in local effective compressive stresses in this location the ramp is more optimally oriented for slip in the inferred regional stress field and therefore likely to fail before the contiguous thrust flats that are subparallel to the maximum principal stress as such the ramp represents the likely location for nucleation of fault slip which could both trigger dynamic failure of the adjacent thrust faults and produce hanging wall extensional structures

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults