activity of the offshore newport inglewood rose canyon fault zone coastal southern california from relocated microseismicity an offshore zone of faulting approximately 10 km from the southern california coast connects the seismically active strike slip newport inglewood fault zone in the los angeles metropolitan region with the active rose canyon fault zone in the san diego area relatively little seismicity has been recorded along the offshore newport inglewood rose canyon fault zone although it has long been suspected of being seismogenic active low angle thrust faults and quaternary folds have been imaged by seismic reflection profiling along the offshore fault zone raising the question of whether a through going active strike slip fault zone exists we applied a waveform cross correlation algorithm to identify clusters of microseismicity consisting of similar events analysis of two clusters along the offshore fault zone shows that they are associated with nearly vertical north northwest striking faults consistent with an offshore extension of the newport inglewood and rose canyon strike slip fault zones p wave polarities from a 1981 event cluster are consistent with a right lateral strike slip focal mechanism solution manuscript received 23 july 2003

empirical observations regarding reverse earthquakes blind thrust faults and quaternary deformation are blind thrust faults truly blind active thrust faults pose a significant seismic hazard worldwide many of these faults include blind thrusts where the propagating fault tip does not reach the earth s surface and buried faults where the geomorphic expression of the fault is obscured by subsequent sedimentation and or erosion this raises the issue of whether conventional geologic geomorphic and paleoseismic methods can be used to identify and characterize thrust faults for the assessment of seismic hazards or whether these faults sometimes are truly blind we compiled a data base of 148 worldwide moderate to large magnitude thrust reverse earthquakes to evaluate whether or not the event occurred on a fault that could have been identified prior to the earthquake on the basis of recognizable quaternary surface deformation i e a pre existing fault or fold analysis of the data shows that interplate reverse earthquakes almost always are associated with pre existing quaternary deformation that was or could have been recognized prior to the earthquake in particular most interplate reverse earthquakes are associated with an active reverse fault at the surface and or an active anticline in contrast intraplate reverse earthquakes seldom occur on faults associated with pre existing recognizable surface deformation we conclude that thrust faults can be detected in interplate regions with careful quaternary geologic and geomorphic mapping furthermore the absence of quaternary surface deformation can be used to infer the absence of an underlying active blind thrust fault in interplate tectonic settings however the data show that quaternary geologic mapping techniques alone likely are insufficient to characterize blind thrusts in intraplate regions in these areas inclusion of a floating or random earthquake may be necessary to assess earthquake hazards

u pb dating of zircon and 40ar 39ar dating of biotite at bingham utah uranium lead dating of zircon and 40ar 39ar dating of biotite provide a new estimate of the age of the bingham hydrothermal system the u pb age of zircon from the last chance monzonite establishes the age of crystallization of this intrusion at 38 55 0 19 ma 2 mswd 2 08 the oldest hydrothermal event in the monzonite is dated at 38 40 0 16 ma and is based on a 40ar 39ar determination plateau age of primary igneous biotite this age is indistinguishable from the u pb zircon age of emplacement of the monzonite petrographic and fluid inclusion data show that the biotite bearing sample was propylitically altered at 400 c which would reset the 40ar 39ar age within 115 ka thus the concordance of the biotite age with the intrusion age of the monzonite suggests that propylitic alteration was essentially contemporaneous with monzonite emplacement the 40ar 39ar ages from three hydrothermal biotites sampled within the 0 35 percent cu isopleth in the monzonite overlap within uncertainty and indicate that potassic alteration in monzonite occurred at 37 57 0 11 ma the youngest hydrothermal activity is identified from a biotite sample 37 07 0 21 ma correlation age in potassically altered quartz monzonite porphyry within the central mos2 zone hydrothermal biotite within the bingham deposit was produced over a time period of approximately 0 50 0 32 ma

hydrothermal evolution in the maher abad porphyry cu au deposit sw birjand eastern iran evidence from fluid inclusions abstract copper and gold mineralization in the maher abad deposit eastern iran is closely related to the multiple emplacement episodes of upper eocene granodiorite porphyries within andesitic volcaniclastic and coeval quartz monzonite stocks the magmatic hydrothermal fluids thereafter hydrofracturing provided appropriate conduits formed a stockwork of quartz and quartz sulfide veinlets within the porphyritic host rocks which were extensively altered into potassic propylitic phyllic and argillic assemblages four main vein veinlet groups have been identified a quartz k feldspar biotite anhydrite with pyrite chalcopyrite sporadic magnetite and pyrrhotite b quartz pyrite and minor chalcopyrite c chalcopyrite quartz and or minor bornite pyrite digenite and sporadic pyrrhotite and d quartz calcite and or clay minerals pyrite hematite galena the cu au mineralization is mainly associated with the early potassic biotite alteration zone in the deep central part of the madanha stock based on the phase contents at room temperature three types of fluid inclusions are recognized at maher abad 1 liquid rich two phase lv 2 vapor rich vl h and 3 halite bearing multiphase lvh homogenization experiments revealed a temperature range of 150 488 c for the studied inclusions ice melting of aqueous two phase inclusions and melting of halite in the aqueous multiphase inclusions provide salinity of 9 5 to 47 9 wt nacl equivalent fluid inclusion studies reveal that the single phase low salinity magmatic fluid exsolved from a granodioritic magma was separated into vapor and hypersaline brine 45 wt nacl eq phases the coexisting phases were trapped at temperature 460 c and lithostatic pressure of 350 bars corresponding to a depth of 1 3 km as vl h and lvh fluid inclusions respectively such magmatic derived fluids underwent phase separation episodically under lithostatic pressure conditions and formed the early copper sulfide bearing quartz veinlets intimately related to the potassic alteration zone copper iron sulfide precipitation and phase separation concomitant of boiling in this zone led to rapid depletion of the fluid in reduced sulfur as a result au hs 2 complexes are destabilized forcing most of the gold to precipitate above 400 c a positive trend of the homogenization temperature and salinity during the formation of the phyllic alteration zone is attributed to the cooling of a moderately saline fluid produced dominantly by magmatic vapor condensation and its subsequent boiling and mixing with meteoric waters at a hydrostatic pressure of 100 125 bars corresponding to a depth of 1 1 2 km the argillic alteration zone formed at temperature of 210 230 c from fluids with salinity of 16 18 nacl wt eq at a hydrostatic pressure of 80 bars and a depth of 800 m from paleo surface the fluid density is typically lower 3 than that of the potassic zone 1 g cm 3 indicating that the late trapped fluid was more dilute

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

crustal structure seismic stratigraphy and rift processes of the continental margin off eastern canada ocean bottom seismic refraction results off nova scotia two crustal seismic refraction profiles were obtained on the continental margin of eastern canada these lines were located on the upper continental rise and on the outer continental shelf off nova

late quaternary uplift and earthquake potential of the san joaquin hills southern los angeles basin california analysis of emergent marine terraces in the san joaquin hills california and 230 th dating of solitary corals from the lowest terraces reveal that the san joaquin hills have risen at a rate of 0 21 0 27 m k y during the past 122 k y movement on a blind thrust fault in the southern los angeles basin has uplifted the san joaquin hills and has the potential to generate an m w 7 3 earthquake within this densely populated area our structural modeling suggests that the fault dips to the southwest and slips at 0 42 0 79 m k y yielding an estimated minimum average recurrence interval of 1650 3100 yr for moderate sized earthquakes recognition of this blind thrust extends the known area of active blind thrusts and fault related folding southward from los angeles into coastal orange county

seismic hazard analysis for critical infrastructures in california abstract california is in a highly seismically active region and structures must be designed and constructed to withstand earthquakes seismic hazard analysis to estimate realistic earthquake ground motions and surface fault rupture offsets is done for various mitigation measures the best policy is to avoid constructing structures crossing seismogenic faults because earthquake timings are unpredictable within our current understanding the best method is time invariant deterministic seismic hazard analysis dhsa to assess effects from the largest single earthquake called maximum credible earthquake mces expected from seismogenic faults time dependent hazard estimates such as those arrived at through probabilistic seismic hazard analysis psha are inherently unreliable hazard analyses based on mces have been in continuous use for the design and construction of highways and bridges in california for over 30 years this paper presents an alternative to other methods of analysis e g abrahamson 2000 abrahamson n a 2000 state of the practice of seismic hazard evaluation melbourne proceedings of geoeng 2000

precious metals assemblages at the mikheevskoe porphyry copper deposit south urals russia as proxies of epithermal overprinting abstract mineral assemblages and formation conditions of precious metals au ag pge in ores of the mikheevskoe porphyry copper deposit south urals are the subject of our study three mineralization types can be distinguished 1 gold silver telluride mineralization overlapping porphyry style bornite chalcopyrite ores includes native gold fineness 863 873 electrum fineness 593 672 galena hessite coloradoite and more rarely petzite stutzite au ag ditellurides native tellurium tellurobismuthite tetradymite kawazulite altaite and extremely rare melonite nite2 merenskyite pdte2 and sopcheite ag4pd3te4 2 gold arsenopyrite base metal mineralization within quartz tetrahedrite sphalerite veinlets cutting porphyry style mineralization 3 gold telluride mineralization with argillic alteration and mineralogically similar to that of type 1 but distinct because of the presence of au ag ag and pb selenides textural relationships supported by fluid inclusions data and chlorite geothermometry provide evidence that occurrence of precious metals minerals at the mikheevskoe deposit is mostly linked to epithermal overprint of the porphyry mineralization and was deposited at ca 300 200 c from moderately saline fluids ca 5 10 wt eq nacl it is suggested that the observed variability in au and ag minerals results from small fluctuations of s2 and or te2 fugacity

prograde evolution and geothermal affinities of a major porphyry copper deposit the cerro colorado hypogene protore i region northern chile the middle eocene 51 8 0 6 ma hypogene protore underlying the supergene orebody of the cerro colorado porphyry cu mo deposit i region chile exhibits features not commonly documented in such hydrothermal systems early stage alteration of upper cretaceous plagioclase phyric andesite generated a sub horizontal blanket of pervasive extremely fine grained but texture preserving biotite 35 modal albite 40 magnetite 3 alteration 8 km 2 in area but lacking sulfide minerals at least seventy percent of the chalcopyrite pyrite stockwork mineralization was emplaced during the subsequent main stage alteration which comprises with decreasing depth quartz albite sericite chlorite clay smectite quartz sericite clay and andalusite diaspore pyrophyllite assemblages the deposit is apparently unique among documented central andean porphyry systems in the association of the highest grade copper mineralization with intermediate argillic alteration the subsequent transitional stage phyllic i e quartz sericite pyrite tourmaline alteration was associated with the emplacement of molybdenite rich breccia bodies the occurrence of undumortieri tized tourmaline veinlets cutting andalusite diaspore assemblages confirms that much of the advanced argillic alteration took place during the main stage early stage alteration was the product of nonboiling cool trapping temperature ca 380 c low salinity 8 wt nacl equiv fluids which added substantial k na mg fe 2 cl f and water to the host andesite the initial main stage fluids boiling at a paleodepth of ca 2 5 to 3 0 km were up to 160 c hotter 544 c and highly saline 52 wt nacl equiv as these fluids rose they cooled to 320 c were diluted to 37 wt nacl equiv deposited sulfides and leached k na ca mg fe 2 and cl from the host rocks yielding diverse broadly contemporaneous intermediate and advanced argillic alteration facies pressure estimates require that low density 0 3 g cm 3 and thus more acidic fluids were primarily responsible for the formation of the quartz sericite clay and shallow advanced argillic alteration subsequent phyllic alteration was similarly caused by boiling fluids which were hot 486 c and saline 47 wt at depth but cooler 334 c dilute 8 wt and vapor dominated at shallower levels even terminal stage pyrite veins formed at temperatures as high as 450 c albeit from low salinity 8 wt fluids following a major prograde thermal transition from the early to the main stage each sulfide depositing alteration episode at cerro colorado was generated by a pulse of high temperature fluid which cooled and diluted as it rose such changes in fluid characteristics temperature and alteration relationships are well documented in numerous geothermal fields where potassic alteration generally develops at ca 270 to 350 c and are likely to occur at an early stage in any hydrothermal system in which magmatic fluids exsolving at relatively high pressures ascend into the near surface environment the initial alteration at cerro colorado plausibly developed under conditions similar to those in nonexplosive geothermal systems in which hydrothermal fluids cool and disperse laterally at shallow depths extensive zones of biotite rich alteration generally barren and with a hornfelsic appearance occur in many andesite hosted porphyry copper deposits but few data are available elsewhere for mineralogical pressure temperature or metasomatic exchange relationships in such systems cerro colorado may however be representative of a subclass of porphyry copper deposits exhibiting unusually close analogies with geothermal systems

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

illite equilibria in solutions ii phase relationships in the system k2omgoal2o3sio2h2o the stability of the marblehead illite has been investigated in the five component system k2o mgo al2o3 sio2 h2o in the presence of kaolinite and microcline the mica like solubility controlling phases kx mgyal2 y alx ysi4 x y o10 oh 2 identified include i smectite x 0 29 0 04 y 0 26 0 02 ii illite x 0 50 0 05 y 0 22 0 14 iii illite x 0 69 0 08 y 0 16 0 03 iv illite x 0 85 0 05 y 0 12 0 04 and v muscovite possible stability regions have been defined for these solubility controlling phases using isothermal isobaric log amg12 2 2ah vs log ah diagrams when illite stability is referred to the quaternary system k2o al2o3 sio2 h2o the effect of r 2 vi substitution is neglected the error inherent in this simplification has been estimated inasmuch as a four fold increase in amg2 shifts the illite smectite kaolinite solution invariant point by less than 0 3 log units stability relationships in the quaternary system provide an adequate representation of illite solution equilibria to a first approximation however the error caused by neglecting mg 2 is close to or within experimental error thus a more precise determination of the effect of mg 2 on illite solution equilibria may not be possible using the solution equilibration method

evolution of hydrothermal fluid characteristics at the santa rita new mexico porphyry copper deposit mineralogic and fluid inclusion investigations conducted in the laboratory combined with in situ observations of temporal relationships among geologic features demonstrate that systematic changes in hydrothermal fluid characteristics occurred with time during evolution of mineralization and alteration of the granodiorite stock at the santa rita porphyry copper deposit the earliest fluids to circulate are recorded in potassically altered orthoclase and biotite stable veins as vapor rich h 2 o co 2 inclusions and hypersaline 30 70 equiv wt nacl or kcl inclusions which homogenize over a wide temperature range from 240 degrees to greater than 800 degrees c the high salinity fluid inclusions are complex chloride brines with significant concentrations of sodium potassium copper iron and sulfur but sulfide minerals are not associated with the early potassic assemblage produced by this fluid oxygen isotope ratios of quartz in the orthoclase and biotite stable veins are identical to phenocryst quartz in the intrusion 8 2ppm later solutions circulated through newly formed fractures and older reopened veins and are recorded in low salinity less than 15 equiv wt nacl fluid inclusions which homogenize primarily in the temperature range of 220 degrees to 360 degrees c these hydrothermal fluids formed two distinct alteration assemblages as they reacted with potassically altered rock chlorite is the dominant silicate gangue mineral of the earlier chalcopyrite bearing orthoclase and clay stable assemblages and sericite characterizes the later phyllic alteration assemblage with quartz and pyrite oxygen isotope ratios of quartz of the later assemblages 8 6 10 4ppm are heavier than quartz of the earlier potassic assemblages it is concluded that the earliest hydrothermal fluids to circulate within the stock localizing the orebody at santa rita could have been derived by phase separations of fluids exsolved from crystallizing magma into condensed hypersaline liquids and h 2 o co 2 vapors as these fluids moved through fractures potassic alteration of rock occurred without concomitant deposition of sulfides later solutions of dominantly meteoric origin progressively formed hypogene copper mineralization associated with chlorite stable alteration and then phyllic alteration

chlorite white mica and clay minerals as proximity indicators to ore in the shallow porphyry environment of quebrada de la mina deposit argentina abstract the mineralogy and chemical composition of mica like phyllosilicates 2 m and clay fraction 2 m and illite halo associated with phyllic and tourmaline rich phyllic assemblages the subhorizontal shallow level au rich 0 5 ppm au zone at the quebrada de la mina deposit coincides with the phyllic halo the distribution of au ag zn pb and as forms partially overlapping haloes toward shallower levels weak cu mo anomalies were found in potassic patches below the au rich zone high mn and fe contents in clinochlore from the peripheral propylitic halo suggest a distance of 1 km to a porphyry cu au mineralized core at deeper levels white micas 2 m in quebrada de la mina show a range of compositions between muscovite and illite in the propylitic halo and in the patches of potassic alteration white micas 2 m show the highest values of fe mg mn 0 40 0 55 apfu and the lowest of al 2 40 2 55 apfu in the phyllic alteration zone of quebrada de la mina white micas 2 m with al contents between 2 45 and 2 70 apfu and fe mg mn between 0 35 and 0 15 apfu match the areas with high gold content 0 5 ppm au the lowest values of fe mg mn 0 11 0 05 apfu and the highest al contents 2 80 2 85 apfu occur in white micas from the tourmaline rich phyllic zone values of the kubler index of illite of 0 19 0 1 2 in the clay fraction of deep samples are indicative of higher temperature and or higher fluid rock ratios during illite formation compared to values of the kubler index 0 2 2 recognized in shallow samples thus both the compositional variations in chlorite and white micas and the illite crystallinity could be used as a guide for exploration of copper gold mineralization in shallow levels of porphyry systems

late holocene rupture history of the rose canyon fault in old town san diego implications for cascading earthquakes on the newport inglewood rose canyon fault system

the bingham canyon porphyry cu mo au deposit i sequence of intrusions vein formation and sulfide deposition the bingham canyon porphyry copper gold molybdenum deposit is one of the largest and highest grade porphyry orebodies in the world this study focused on the northwest side of the deposit where quartz mon zonite porphyry qmp the first and largest porphyry intrusion hosts the bulk of the high grade copper gold ore 1 0 cu 1 0 ppm au the north northeast trending high grade zone had pre mining dimensions of 1 500 m strike 300 m vertical and 500 m width and contained more than 500 million tonnes mt of ore associated with potassic alteration and abundant quartz veins the lack of superimposed sericitic alteration yielded ideal exposures in which to study the early high temperature stages of ore formation a style of mineralization that in many porphyry deposits represents the major period of copper introduction we mapped multiple porphyry dikes in the sequence 1 qmp 2 latite porphyry lp 3 biotite porphyry bp 4 quartz latite porphyry breccia qlpbx and 5 quartz latite porphyry qlp porphyry dikes faults and quartz veins are steeply dipping and have two dominant orientations north northeast and northwest striking dikes have a north northeast strike but they thicken and develop northwest trending apophyses and host high grade copper gold zones at intersections with northwest faults indicating that magmatic hydrothermal fluids were focused by these structural intersections each porphyry intrusion was accompanied by a similar sequence of veins potassic alteration and sulfides biotite veinlets were followed by fractures with early dark micaceous edm halos of sericite k feldspar biotite andalusite and local corundum containing disseminated bornite chalcopyrite gold edm halos are cut by multiple generations of a quartz veins representing the main cu au ore forming event postdating all intrusions are quartz molybdenite veins followed by quartz sericite pyrite veins cathodoluminescence cl petrography identified distinct a quartz veinlets consisting of dark luminescing quartz filling fractures and dissolution vugs in earlier a quartz veins and adjacent porphyry wall rock these veinlets contain abundant bornite and chalcopyrite and minor k feldspar and are closely linked in time to the introduction of the bulk of the copper and gold although a similar sequence of veins was repeated on emplacement of all porphyry intrusions the vein density and intensity of potassic alteration declined with time the youngest porphyry qlp is mostly weakly mineralized and locally unaltered these observations indicate that magmatic hydrothermal fluids underwent a similar physiochemical evolution during and immediately following emplacement of each of several porphyry dikes the relationship between edm veins and a quartz veins requires that the flux of magmatic fluid from the magma chamber occurred in an episodic manner as opposed to a continuous discharge vein truncation relationships coupled with abrupt changes in copper gold grades sulfide ratios and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive hydrothermal cycles presumably due to depletion of metals and volatiles in the underlying magma chamber

origin of clay minerals in alluvial paleosols prince creek formation north slope alaska u s a influence of volcanic ash on pedogenesis in the late cretaceous arctic abstract paleosols formed from weathering of alluvial mudstones in the late cretaceous maastrichtian prince creek formation north slope alaska are dominated by detrital smectite discrete illite kaolinite chlorite quartz and pedogenic illite smectite i s mixed layer clays in the fine clay fraction 80 low bulk density phosphorus accumulation fe and al mass balance trends and the presence of fe al humus complexes in one paleosol profile is interpreted as evidence of andic soil properties and these paleosols are interpreted therefore as andept like alluvial soils these results demonstrate that clay mineralogical studies in conjunction with geochemical data of paleosols can be used to identify paleo andic soil properties which have not been widely recognized in the ancient rock record alternating wetting and drying conditions required to form pedogenic i s in these alluvial paleosols resulted from a highly seasonal moisture regime in the late cretaceous arctic

paleoseismic features as indicators of earthquake hazards in north coastal san diego county california usa abstract new road cut and mass grading excavations in the north coastal area of san diego county california expose heretofore generally unrecognized probable late holocene tsunami deposits and paleoseismically deformed sediments remnant tsunami deposits occur up to 100 m in elevation around the margins of modern coastal lagoons and estuaries and combined with local mima mounds of possible sand blow origin provide indirect but compelling evidence for the late quaternary activity of onshore and offshore faults in the immediate study area probable paleoliquefaction features are regionally widespread and range from fissures filled with sediments derived from overlying marine terrace sand and soil to the more traditional sand filled injection dikes and sills lateral spreads and filled craterlets the source of most liquefied sediment is underlying tertiary bedrock sand and local quaternary marine terrace deposits a paleoseismic liquefaction origin rather than soft sediment loading is deduced for these features based on morphology internal stratigraphy field setting and near proximity to known seismogenic sources some paleoseismic events impacted late holocene indian middens and burial sites the last seismic event probably occurred within the past 1 to 3 ka and possibly even records the historic earthquakes of either november 22 1800 or may 27 1862 the liquefaction features also affect marine terrace sediments tens of meters above modern regional water levels inferentially recording paleoseismic events in this mediterranean type climatic region during winter rains when high level perched water saturates the several meter thick source sediments based on their regional extent the paleoseismic features were likely caused by m 7 tectonic events inferentially generated by the nearby offshore newport inglewood rose canyon fault system or possibly by smaller recently exposed related and localized faults accordingly the seismic hazard of the north coastal area of san diego county may be substantially higher than previously assumed and hence of concern owing to the rapid ongoing and projected population increase

formation of a paleothermal anomaly and disseminated gold deposits associated with the bingham canyon porphyry cu au mo system utah a discussion sir the recent paper by cunningham et al 2004 presents reconnaissance apatite and zircon fission track conodont alteration index vitrinite and solid bitumen reflectance and stable isotope data documenting the extent of the paleothermal anomaly associated with the 37 ma bingham canyon porphyry cu au mo deposit based on these data the paleothermal anomaly encompasses the barneys canyon and melco sediment hosted gold deposits the authors conclude that the gold deposits are genetically related to the bingham porphyry system and that the maximum sustained temperature was 100 to 140 c at melco and near 100 c at barneys canyon cunningham et al 2004 contend that barneys canyon and melco are perhaps distal disseminated ag au deposits rather than carlin type deposits fluid inclusion data from ore grade samples at barneys canyon presnell 1992 presnell and parry 1996 and melco r d presnell 1991 constraints on a genetic model for the melco gold deposit based on mineralogy alteration and fluid inclusions unpub report for kennecott exploration 12 p yield homogenization temperatures in excess of 200 c we contend that the paleothermal data support our previous conclusion that the temperature at barneys canyon during formation of the bingham system was near ambient i e 70 c assuming 2 km of cover and a geothermal gradient of 35 c km and that the formation of barneys canyon was related to a hydrothermal system separate from bingham the data presented in presnell 1992 and presnell and parry 1996 are from drill core through the center and periphery of the orebodies at barneys canyon and the data from melco r d presnell 1991 unpub report for kennecott exploration are also from drill core through the orebody all of the samples from barneys canyon used in the study by cunningham et al 2004 were collected from the pit wall after the orebody was mined and only two samples from their

clay mineralogy of phyllic and intermediate argillic alteration at bingham utah the earliest alteration mineral zones in the porphyry cu mo au ore deposit at bingham utah include the outermost propylitic and inner potassic alteration of igneous rocks innermost phyllic and intermediate argillic alteration is superimposed on propylitic and potassic alteration petrographic x ray diffraction and electron microprobe analyses are used to characterize the clay mineralogy of phyllic and intermediate argillic alteration phyllic alteration affects monzonite near the contact with the quartz monzonite porphyry in the southwest and northeast portions of the deposit and consists primarily of veins and vein selvages of illite interstratified with an average of 7 percent smectite r 3 ordering the veins and selvages also contain small amounts of smectite and kaolinite the illite smectite interstratification is a mixture of 1m and 2m polytypes structural formulas for the illite show less k and al and more si than muscovite octahedral mg and both a tetrahhedral and an octahedral layer charge the kubler crystallinity index and smectite content increase systematically as particle size decreases consistent with an increase in smectite in the interstratification in the smaller size fractions intermediate argillic alteration consists of smectite illite and kaolinite that occur primarily as a replacement of plagioclase phenocrysts a few veins of intermediate argillic minerals are present in the quartz monzonite porphyry illite is interstratified with an average of 6 percent smectite r 3 ordering but a few samples contain a regular interstratification of illite with 40 to 50 percent smectite r1 ordering the smectite replacing plagioclase is montmorillonite and smectite that occurs in one vein is beidellite statistical trends in intermediate argillic alteration mineralogy within the quartz monzonite porphyry show that illite and kaolinite abundances increase generally upward and toward the northeast smectite abundance increases generally downward and toward the southwest in a cross section near the center of the deposit abundances of kaolinite and illite decrease as abundance of smectite increases with increasing depth the occurrence of interstratified illite smectite averaging 6 to 7 percent smectite together with discreet smectite suggest formation near 200 c a temperature difference between phyllic and intermediate argillic alteration could not be resolved from the mineralogy temperature estimates from fluid inclusions for phyllic alteration at other porphyry copper deposits generally range from 200 to 350 c the activity ratio of na k for the fluid calculated from na k in illite averages 5 0 for a phyllic vein that crosscuts propylitic alteration 1 4 for a phyllic vein that crosscuts potassic alteration and 2 8 for intermediate argillic alteration superimposed on potassic alteration log f h 2 o f hf of the hydrothermal fluid computed from the fluorine content of illite averages 6 1 for a phyllic vein that crosscuts propylitic alteration 5 8 for a phyllic vein that crosscuts potassic alteration and 5 7 for intermediate argillic alteration log f h 2 o f hf of fluids forming late stage biotite is about 5 0 intermediate argillic alteration could not be correlated with sulfides in the quartz monzonite porphyry an increase in illite upward and toward the northeast may correlate with massive sulfides in sediments recently discovered in that region

late quaternary uplift and earthquake potential of the san joaquin hills southern los angeles basin california comment and reply grant and et al 1999 1 rather unequivocally demonstrated that the san joaquin hills located in orange county california have risen at a rate of 0 021 0 027 mm yr over the past 122 k y based largely on geomorphic evidence they attribute this uplift as a fault bend fold above a southwest

a petrographic study of phyllic alteration superimposed on potassic alteration the sibert porphyry deposit rhone france zoned wallrock alteration surrounds each phyllic vein three zones distinguished 1 a nearest wallrock zone where the preexisting minerals except quartz are wholly transformed into muscovite 2 an intermediate wallrock zone where the alteration intensity decreases 30 of the rock is replaced by white micas and 3 a farthest wallrock zone where a small proportion of preexisting biotites and plagioclases recrystallizes less than 10 of the primary minerals recrystallize modified journal abstract

a geodesy and seismicity based local earthquake likelihood model for central los angeles we estimate time independent earthquake likelihoods in central los angeles using a model of interseismic strain accumulation and the 1932 2017 seismic catalog we assume that on the long term average earthquakes and aseismic deformation collectively release seismic moment at a rate balancing interseismic loading mainshocks obey the gutenberg richter law a log linear magnitude frequency distribution mfd up to a maximum magnitude and a poisson process and aftershock sequences obey the gutenberg richter and bath laws we model a comprehensive suite of these long term systems assess how likely each system would be to have produced the mfd of the instrumental catalog and use these likelihoods to probabilistically estimate the long term mfd we estimate m max 6 8 1 05 0 4 every 300 years or m max 7 05 0 95 0 4 assuming a truncated or tapered gutenberg richter mfd respectively our results imply that for example the median likelihood of one or more m w 6 5 mainshocks is 0 2 in 1 year 2 in 10 years and 18 21 in 100 years

coastal uplift of the san joaquin hills southern los angeles basin california by a large earthquake since a d 1635 late holocene marsh deposits and a shoreline along the coast of the san joaquin hills southern los angeles basin range from 1 to 3 6 m above the active shoreline radiocarbon dating of ancient marsh shows that emergence occurred after a d 1635 the age distribution and geomorphic expression of elevated marsh and shoreline are best explained by tectonic uplift due to a m 7 earthquake radio carbon dates and the historic record of seismicity suggest the earthquake occurred between a d 1635 and 1855 possibly in 1769 the historic record of earthquakes in the los angeles basin begins in a d 1769 and contains no other earthquakes greater than m 6 7 therefore the san joaquin hills earthquake may be the largest historic earthquake in the los angeles basin

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

source parameters of the 1933 long beach earthquake regional seismographic network and teleseismic data for the 1933 m l 6 3 long beach earthquake sequence have been analyzed both the teleseismic focal mechanism of the main shock and the distribution of the aftershocks are consistent with the event having occurred on the newport inglewood fault the focal mechanism had a strike of 315 dip of 80 to the northeast and rake of 170 relocation of the foreshock main shock aftershock sequence using modern events as fixed reference events shows that the rupture initiated near the huntington beach newport beach city boundary and extended unilaterally to the northwest to a distance of 13 to 16 km the centroidal depth was 10 2 km the total source duration was 5 sec and the seismic moment was 5 10 25 dyne cm which corresponds to an energy magnitude of m w 6 4 the source radius is estimated to have been 6 6 to 7 9 km which corresponds to a brune stress drop of 44 to 76 bars both the spatial distribution of aftershocks and inversion for the source time function suggest that the earthquake may have consisted of at least two subevents when the slip estimate from the seismic moment of 85 to 120 cm is compared with the long term geological slip rate of 0 1 to 1 0 mm yr along the newport inglewood fault the 1933 earthquake has a repeat time on the order of a few thousand years

precarious rock constraints on ground motion from historic and recent earthquakes in southern california new examples of precarious rocks are presented these rocks provide constraints on ground motion for historical and recent large earthquakes an approximate field calibration of the precarious rock methodology was provided by the m 7 1 hector mine earthquake of 16 october 1999 previously documented rocks at granite pass near kelso california brune 1996 were overturned by the earthquake and a nearby strong motion station indicated ground motions of about 0 2 g consistent with the toppling accelerations estimated in the published article the time of the last earthquake for the section of the fault nearest the precarious rocks has recently been determined to be more than 10 ka consistent with previously estimated ages for precarious rocks this first example of an actual earthquake field test lends strong support to the precarious rock methodology the other rocks discussed here give constraints on ground motions for historic earthquakes such as the 1812 and 1857 san andreas fault earthquakes the 1899 and 1912 san jacinto fault earthquakes the 1952 kern county earthquake and possibly recent but prehistoric earthquakes on the banning and garlock faults the ground motion constraints for these earthquakes are lower than predicted by some recent ground motion attenuation curves which are extrapolations to near fault distances from a data set dominated by data from larger distances but are generally consistent with peak ground accelerations observed from the recent large turkey and taiwan earthquakes and provide important additional information for seismic hazard analysis on the other hand there are areas where precarious rocks would be expected on the basis of previous studies but are apparently not found this suggests possible earthquakes on previously unrecognized or only recently recognized faults one such area is in northwestern san diego and southwestern orange county between the elsinore and newport inglewood faults the lack of precarious rocks in this area might be attributed to recent earthquakes on the blind thrust faults proposed in the area by grant et al 1999 2002 and rivero et al 2000

the mendocino triple junction active faults episodic coastal emergence and rapid uplift a complex zone of rapid holocene surface uplift and deformation occurs at the mendocino triple junction the juncture of three plate bounding faults the cascadia subduction zone san andreas fault and mendocino fault within this mountainous structural knot up to 1 4 m of coastal emergence occurred during the 1992 cape mendocino m s 7 1 earthquake surveying and radiometric dating of ancient marine strandlines 7 5 along the cascadia subduction zone megathrust however another plausible interpretation of the data is that multiple earthquakes resulting in smaller amounts of net surface uplift per event similar to the 1992 earthquake occurred closely spaced in time giving the appearance in the geologic record of less frequent and larger events regardless of the number and timing of paleoearthquakes the number of platforms is a minimum of the number of events that resulted in sudden rapid uplift because platform preservation is also a function of rising holocene sea level at present rates and patterns of net surface uplift are better constrained than the timing and magnitude of paleoearthquakes periods of rapid holocene emergence also are identified as far south of the area of 1992 uplift and the mendocino fault as 30 km along the unlocated san andreas fault these also might be associated with coseismic uplift based on new mapping of active faults in the region it is proposed here that this uplift is the result of multiple discontinuous thrust and strike slip fault segments which distribute plate boundary deformation along a restraining bend at the termination of the san andreas fault this interpretation is consistent with the fact that a single prominent strike slip fault has not been identified in the mendocino triple junction region while several small reverse faults crossing holocene deposits and geomorphic surfaces have been mapped and dated

late quaternary relative sea level in southern california and monterey bay abstract few records of late quaternary relative sea level rsl are available for the pacific coast of north america south of san francisco bay a region where rsl data would be particularly useful for constraining vertical rates of tectonic motion this paper provides the first regional uplift corrected late quaternary rsl history for southern california derived from a compilation of 132 previously published and unpublished radiocarbon ages from nearshore estuarine and freshwater deposits in sediment cores from coastal southern california we also provide a local uplift corrected rsl history for monterey bay central california generated from 48 radiocarbon ages from elkhorn slough and surrounding environments our resulting compilations show rapid sea level rise from 15 ka which begins to decelerate to present mean sea level pmsl between 6 and 8 ka late holocene

smectite to illite reactions in salton sea shales a transmission and analytical electron microscopy study tem aem study of a sequence of shales from the salton sea geothermal field revealed that the mechanism for the reaction of smectite to form illite is markedly different from that for gulf coast sediments illite in salton sea shales occurs principally as individual euhedral to subhedral pseudohexagonal crystals in open pore space smectite was not observed by tem in proximity to such illite and is shown by xrd data to decrease in amount with depth as the proportion of illite increases illite is thus implied to be derived by complete dissolution of smectite and other phases transport of components and crystallization of illite from solution however in shallow sediments detrital smectite is also observed to be in part directly replaced by illite in a manner duplicating gulf coast textures the mechanism by which smectite undergoes complete dissolution to allow precipitation of illite at a distant site is compatible with an open system such as the salton sea sediments characterized by high water rock ratio and relatively high permeability in contrast the mechanism involving a reaction front where the smectite is directly replaced by illite such as occurred in gulf coast shales is compatible with relatively impermeable shales

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

mineralogy of the aktogai giant porphyry cu deposit in kazakhstan insights into the fluid composition and oxygen fugacity evolution abstract it has been proposed that most giant porphyry cu deposits are closely associated with oxidized magmas most recently many methods including zircon trace elements mn content in apatite and magnetite ilmenite mineral pair were used to reveal the primary magmatic oxygen fugacity of the porphyry cu deposits hydrothermal alterations are products of water rock reactions and can form various hydrothermal minerals which can be used for exploration the aktogai group including aktogai aidarly and kyzilkia contains more than 12 5 mt cu 0 4 wt and 80 t au 0 007 g t 0 4 g t chlorites show significant variations in the aktogai deposit which are responsible for degrees of tschermak and di trioctahedral substitution chlorites are divided into type i and ii based on fe fe mg ratios of chlorites which are predominately controlled by hydrothermal fluid composition and oxygen fugacity the chlorite i have higher fe fe mg ratios than chlorite ii the formation temperatures of chlorite are 248 322 c based on empirical geothermometry t5 sericites belong to muscovite and phengitic muscovite and their compositions are controlled by tschermak and fe 3 vi al 3 vi substitution water rock reaction leaches out some elements into hydrothermal fluids therein si 4 and k precipitate as quartz and sericite at all alteration stages but fe 2 and ca 2 precipitate as specific minerals such as chalcopyrite and calcite at main mineralization or late stage the chlorite i form under a fe rich condition with high water rock ratio while chlorite ii form under a low water rock ratio and fe poor condition which may be responsible for the sulfides and epidote precipitation according to zircon trace elements mn content in apatite magnetite ilmenite mineral pair and fe fe mg and fe 3 tfe ratios of chlorites the oxygen fugacity changes from high at magmatic and early hydrothermal stages through low at main mineralization stage to slightly high at late or post mineralization stage our results combined with previous works suggest that fe contents and fe fe mg ratios of chlorites are good indicators for exploration

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

textures paragenesis and wall rock alteration of lode gold deposits in the charters towers district north queensland implications for the conditions of ore formation ore deposits of the charters towers goldfield ctgf are mainly hosted by fault fill veins extensional 8 of all veins and stockwork like 3 veins are less common and of little economic significance crosscutting relationships and published structural and geochronological data indicate a late silurian to early devonian timing of gold mineralization coincident with regional shortening d4 and i type magmatism paragenetic relationships which are uniform in veins everywhere within the ctgf suggest that vein formation commenced with the deposition of large volumes of buck quartz stage i followed by buck and comb quartz and significant pyrite and arsenopyrite precipitation stage ii gold was introduced during stage iii after earlier sphalerite and coincident with galena and chalcopyrite narrow discontinuous calcite veins of stage iv mark the waning of gold related hydrothermal activity or a later unrelated episode ore zones within the veins are everywhere composed of comb and or gray quartz calcite and or ankerite and bands or clusters of fractured pyrite that are spatially associated with galena sphalerite or chalcopyrite low grade or barren vein sections on the other hand are mainly composed of milky buck quartz with little evidence for modification overprinting or interaction with later fluids gold related hydrothermal wall rock alteration is symmetrically zoned displaying proximal sericite ankerite and distal epidote chlorite hematite assemblages that may be taken to imply wall rock interaction with near neutral fluids ph 5 6 isocon plots assuming immobile al p ti y and zr consistently indicate as k pb s and zn enrichment and na si and sr depletion in altered wall rock specimens relative to the least altered rocks alteration assemblages quartz textures fault rocks and published fluid inclusion and stable isotope data imply that the veins were formed under conditions of episodic fluid overpressuring 0 9 3 8 kbar at a depth of 7 km and a temperature of 310 c the published fluid inclusion data also imply that gold precipitation may have been brought about by fluid mixing however physi and chemisorption of gold complexes onto sulfide surfaces may have been important depositional processes and controls on gold enrichment at the millimeter to centimeter scale given that most gold particles are attached to the surfaces of pyrite crystals of stage ii or to etch pits and fracture surfaces within the earlier pyrite

geochemistry of hydrothermal sericite from roosevelt hot springs and the tintic and santa rita porphyry copper systems systematic variations in sericite composition are present in each of the areas studied in the roosevelt geothermal system si increases and tetrahedral al decreases with increasing depth in the system sericites from southwest tintic increase in si and decrease in interlayer cations from biotite through quartz sericite to chlorite epidote zones compositional variability is less at santa rita than the two other areas and interlayer site occupancy is greater than 0 9 but sericite with epidote and chlorite contains more si than sericite with biotite and or clay minor elements in sericite also show compositional trends sodium occupies from 0 to 0 1 of the interlayer sites and increases from the chlorite epidote to quartz sericite to biotite zones in porphyry copper systems sericite coexisting with biotite contains significantly more ti than sericite in other assemblages fluorine content of sericites ranges up to 0 14 ions per formula unit and correlates with mg modified journal abstract

porphyry to epithermal transition in the agua rica polymetallic deposit catamarca argentina an integrated petrologic analysis of ore and alteration parageneses abstract agua rica 27 26 s 66 16 o is a world class cu au mo deposit located in catamarca argentina in the e w 6969400 section examined the seca norte and the trampeadero porphyries that have intruded the metasedimentary rock are cut by interfingered igneous and hydrothermal heterolithic and monolithic breccias and sandy dikes relic biotite and k feldspar of the early potassic alteration 370 to 550 c with cu mo au mineralization are locally preserved and encapsulated in a widespread white mica quartz rutile or anatase halo phyllic alteration with pyrite covellite that suggests fluids with temperatures 360 c and high f s2 the trampeadero porphyry and the surrounding metasedimentary rock with phyllic alteration have molybdenite in stringers and b type quartz veinlets and the highest mo grades 1000 ppm multistage advanced argillic alteration overprinted the earlier stages early andalusite pyrite quartz is preserved in the roots of the argillic halo rimmed by an alumina silica material and white micas this alteration assemblage is considered to have been formed at temperatures 375 c from condensed magmatic vapor at higher levels pyrophyllite replaces muscovite and illite in clasts of hydrothermal breccias in the center and east sector of the study section suggesting temperatures of 280 to 360 c clasts of vuggy silica in the uppermost levels of the central breccia indicates that at lower temperatures hydrothermal brecciation was concurrent with fluid exsolution v which precipitated intermediate temperature advanced argillic alunite svanbergite woodhouseite diaspore zunyite as breccia cement along with abundant covellite pyrite enargite native sulfur kuramite at intermediate depths and in lateral transitional zones to unbrecciated rocks this mineral assemblage indicates temperatures near 300 c oxidized and silica undersaturated hydrothermal fluids with high sulfur fugacity to prevent gold precipitation multiple generations of pyrite emplectite colusite pb and bi bearing sulfosalts and native sulfur with au and ag accompanied by alunite introduction in the upper level breccias probably occurred at lower temperatures but still high sulfur and oxygen activity an independent zn and pb as galena mineralization stage locally coincides with au ag and sulfosalts and advanced at depth controlled by fractures and overprinting much of the previous mineralization a later paragenesis of veinlets of alunite woodhouseite svanvergite pyrite enargite that cut the phyllic halo suggests temperatures 250 c and without woodhouseite svanvergite temperatures 200 c kaolinite occurs in the phyllic halo as a late mineral in clots and in veinlets thus in this zone the fluid had cooled enough for its formation

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

the quaternary marine terraces of santa cruz california evidence for coseismic uplift on two faults the coast parallel elevation pattern of marine terraces along 50 km of coast centered about santa cruz california provides an opportunity to assess the relative roles of candidate uplift mechanisms we assemble 130 existing latitude longitude elevation inner edge locations from three of these marine terraces to constrain elastic dislocation models of coseismic uplift uplift resulting from repeated oblique slip seismic events similar to the loma prieta earthquake m s 6 9 of october 17 1989 appears to explain well the portion of the terrace uplift pattern south of santa cruz depending on whether the lowest terrace is assumed to correspond to isotope stage 5c or 5e the calculated mean repeat time for loma prieta events is either 490 or 820 yr corresponding to either 4 1 or 2 4mm yr slip rates on the loma prieta fault residual uplift not explained by such events increases monotonically to the north toward ano nuevo where the san gregorio fault zone intersects the coastline we assess whether this residual uplift may result from repeated events on the san gregorio fault given only the strike of the san gregorio fault we use an extensive parameter search to determine the geometry of and the style of motion on the implied rupture plane that best explains this residual uplift the fault parameters that minimize the misfit between data and model imply activity of a moderately steep 70 north east dipping san gregorio fault that ruptures in oblique thrust slip from 15 km to the surface the thrust slip component dominates the uplift pattern resulting in uplift of the coastline from santa cruz northward these parameters match available geological geodetic and seismic data on the dip and sense of motion on strictures within the san gregorio fault zone the san gregorio fault has therefore been an active late pleistocene participant in north american pacific plate boundary motion we conclude that the complex pattern of uplift along this 50 km reach of coastline can be explained by coseismic mechanisms tied to san andmas bend related fault structures onshore and to the san gregorio fault zone offshore as both of these mechanisms result locally in considerable shore normal uplift gradients caution is warranted in applying common correlation techniques based solely on uplift rates in the assignment of terrace ages in this and other such settings in addition while it is tempting to use terrace culmination offsets as a means of estimating san andreas fault dextral slip rates we provide a formalism to determine under what conditions such calculations are meaningful we conclude that the terrace offsets along the santa cruz coastline result not from dextral slip on the san andreas but from differential indentation of the loma prieta uplift pattern by the various sea level highstand coastlines

history of modern earthquake hazard mapping and assessment in california using a deterministic or scenario approach modern earthquake ground motion hazard mapping in california began following the 1971 san fernando earthquake in the los angeles metropolitan area of southern california earthquake hazard assessment followed a traditional approach later called deterministic seismic hazard analysis dsha in order to distinguish it from the newer probabilistic seismic hazard analysis psha in dsha seismic hazard in the event of the maximum credible earthquake mce magnitude from each of the known seismogenic faults within and near the state are assessed the likely occurrence of the mce has been assumed qualitatively by using late quaternary and younger faults that are presumed to be seismogenic but not when or within what time intervals mce may occur mce is the largest or upper bound potential earthquake in moment magnitude and it supersedes and automatically considers all other possible earthquakes on that fault that moment magnitude is used for estimating ground motions by applying it to empirical attenuation relationships and for calculating ground motions as in neo dsha zuccoloet al 2008 the first deterministic california earthquake hazard map was published in 1974 by the california division of mines and geology cdmg which has been called the california geological survey cgs since 2002 using the best available fault information and ground motion attenuation relationships at that time the california department of transportation caltrans later assumed responsibility for printing the refined and updated peak acceleration contour maps which were heavily utilized by geologists seismologists and engineers for many years some engineers involved in the siting process of large important projects for example dams and nuclear power plants continued to challenge the map s the second edition map was completed in 1985 incorporating more faults improving mce s estimation method and using new ground motion attenuation relationships from the latest published results at that time cdmg eventually published the second edition map in 1992 following the governor s board of inquiry on the 1989 loma prieta earthquake and at the demand of caltrans the third edition map was published by caltrans in 1996 utilizing gis technology to manage data that includes a simplified three dimension geometry of faults and to facilitate efficient corrections and revisions of data and the map the spatial relationship of fault hazards with highways bridges or any other attribute can be efficiently managed and analyzed now in gis at caltrans there has been great confidence in using dsha in bridge engineering and other applications in california and it can be confidently applied in any other earthquake prone region earthquake hazards defined by dsha are 1 transparent and stable with robust mce moment magnitudes 2 flexible in their application to design considerations 3 can easily incorporate advances in ground motion simulations and 4 economical dsha and neo dsha have the same approach and applicability the accuracy of dsha has proven to be quite reasonable for practical applications within engineering design and always done with professional judgment in the final analysis dsha is a reality check for public safety and psha results although psha has been acclaimed as a better approach for seismic hazard assessment it is dsha not psha that has actually been used in seismic hazard assessment for building and bridge engineering particularly in california

crustal structure of the nova scotian margin in the laurentian channel region a seismic refraction study on the outer scotian shelf of eastern canada carried out using large air gun sources and ocean bottom seismograph receivers has provided structural information on the entire crustal column a thick about 13 km sedimentary sequence is characterized by significant lateral variation in this area and a marked increase in seismic velocity around 8 km depth may delineate the synrift postrift transition beneath the sediments is highly attenuated continental crust about 11 km thick with some evidence for a lower crustal layer of velocity around 7 km s which may be partly due to under plating during rifting determination of the complete crustal structure including the tentative delineation of the rift drift transition in a region of large crustal extension provides a useful test for models of continental rifting and a simple uniform extension subsidence model is found to produce an adequate fit to the interpreted structure

paleoseismicity of the north branch of the newport inglewood fault zone in huntington beach california from cone penetrometer test data abstract application of cone penetrometer testing cpt is a promising method for studying subsurface fault zones in stratified unconsolidated sediment where trenching is not feasible analysis of data from 72 cpts spaced 7 5 to 30 0 m apart and 9 borings indicates that the north branch fault the active strand of the newport inglewood fault zone nifz in huntington beach has generated at least three and most likely five recognizable surface ruptures in the past 11 7 0 7 ka additional smaller earthquakes similar to the m w 6 4 1933 long beach earthquake may also have occurred but would not be recognizable with this method the minimum right lateral holocene slip rate of the nifz in the study area is estimated to be 0 34 to 0 55 mm yr the actual slip rate may be significantly higher

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900

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