propagation characteristics of lg across the tibetan plateau abstract we present the results of a study on the propagation of lg within the tibetan plateau we analyze over 1200 seismograms for lg propagation from 185 local and regional earthquakes recorded at distances from 150 to 2000 km 52 of which are located within the tibetan plateau although the propagation of lg has been observed across most of asia lg has not been observed for paths crossing the tibetan plateau we analyze paths that cross the plateau boundaries and paths contained entirely within the tibetan plateau lg is generated within the tibetan plateau and can propagate to epicentral distances of at least 600 km for events located outside of the tibetan plateau lg is either absent or severely diminished for paths that cross both the himalayan and kunlun ranges confirming that the margins of the plateau weaken lg transmission based on the observations from our qualitative analysis we invert lg amplitudes for event station paths that are confined to the tibetan plateau to estimate the quality factor q the inversion yields a frequency dependent q function q f 366 37 f 0 45 0 06 0 5 f 16 h z similar observations in other areas indicate that frequency dependent apparent q within the tibetan plateau is well below that expected for a typical continental interior instead it has a frequency dependence that is characteristic of a tectonically active region

the 11 25 88 m 6 saguenay earthquake near chicoutimi quebec evidence for anisotropic wave propagation in northeastern north america on november 25 1988 a magnitude 6 earthquake occurred in the province of quebec canada this earthquake triggered nine digital strong motion instruments in new york and maine at epicentral distances of 200 to 820 km which were installed as part of an effort by the national center for earthquake engineering research nceer to study ground motions and wave propagation in eastern north america we calculate q f at discrete frequencies from 0 6 to 26 hz assuming that geometrical spreading causes a l r0 5 decay in spectral amplitudes of the nine stations four are in the adirondack mountains in new york and three are in eastern maine if we calculate q f for these two clusters of stations separately we obtain higher values for the adirondack stations the quebec adirondack path is along the strike of the predominant structural trends in northeastern north america in the grenville province crust while the quebec maine path is at high angle to the structural grain and crosses the boundary between the grenville and the appalachian provinces we thus have instrumental data in support of earlier observations based on contours of intensity from historic earthquakes seismic wave propagation in northeastern north america is more efficient along the predominantly ne sw striking geological trends we address possible biases due to site effects

reply to comment on revisiting the 1872 owens valley california earthquake by susan e hough and kate hutton by william h bakun bakun 2009 argues that the conclusions of hough and hutton 2008 are wrong because the study failed to take into account the sierra nevada attenuation model of bakun 2006 in particular bakun 2009 argues that propagation effects can explain the relatively high intensities generated by the 1872 owens valley earthquake using an intensity attenuation model that attempts to account for attenuation through the sierra nevada bakun 2006 infers the magnitude estimate m w 7 4 7 5 that is currently accepted by national earthquake information center neic

robust response of the east asian monsoon rainband to solar variability this study provides evidence of the robust response of the east asian monsoon rainband to the 11 yr solar cycle and first identify the exact time period within the summer half year 1958 2012 with the strongest correlation between the mean latitude of the rainband mlrb over china and the sunspot number ssn this period just corresponds to the climatological mean east asian mei yu season characterized by a largescale quasi zonal monsoon rainband i e 22 may 13 july both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei yu rainband to solar variability during the last five solar cycles during the high ssn years the mei yu mlrb lies 1 28 farther north and the amplitude of its interannual variations increases when compared with low ssn years the robust response of monsoon rainbandto solarforcing is relatedto an anomalous generalatmospheric patternwith an up downseesaw and a north south seesaw over east asia

near surface structural model for deformation associated with the february 7 1812 new madrid missouri earthquake the february 7 1812 new madrid missouri earthquake m moment magnitude 8 was the third and final large magnitude event to rock the northern mississippi embayment during the winter of 1811 1812 although ground shaking was so strong that it rang church bells stopped clocks buckled pavement and rocked buildings up and down the eastern seaboard little coseismic surface deformation exists today in the new madrid area the fault s that ruptured during this event have remained enigmatic we have integrated geomorphic data documenting differential surficial deformation supplemented by historical accounts of surficial deformation and earthquake induced mississippi river waterfalls and rapids with the interpretation of existing and recently acquired seismic reflection data to develop a tectonic model of the near surface structures in the new madrid missouri area this model consists of two primary components a north northwest trending thrust fault and a series of northeast trending strike slip tear faults we conclude that the reelfoot fault is a thrust fault that is at least 30 km long we also infer that tear faults in the near surface partitioned the hanging wall into subparallel blocks that have undergone differential displacement during episodes of faulting the northeast trending tear faults bound an area documented to have been uplifted at least 0 5 m during the february 7 1812 earthquake these faults also appear to bound changes in the surface density of epicenters that are within the modern seismicity which is occurring in the stepover zone of the left stepping right lateral strike slip fault system of the modern new madrid seismic zone

extratropical extended range precursors near the tropopause preceding persistent strong precipitation in south china a climatology the pre summer rainy season psrs april june is the period of most frequent strong precipitation in south china sc persistent strong precipitation events pspes can cause greater loss of life and property than short lived strong precipitation this paper investigates extended range signals near the tropopause preceding two persistent positive climatological intraseasonal oscillations ppcisos in precipitation corresponding to two climatological pspes in sc during the psrs using the ciso analysis of isentropic potential vorticity ipv it is found that precursor signals can be better seen in ipv cisos than in unfiltered ipv the first rainfall ppciso is caused by an eastward propagation of high ipv cisos along the dynamical tropopause originating from the arctic region and west of the tibetan plateau the second is the most persistent 13 days its high ipv cisos originate over the arctic region and the tropical monsoon region respectively 20 or more days prior to the rainfall ciso peak the west of the tibetan plateau and the northern region of the east asian westerly jet near the tropopause are two transit points where extratropical high ipv cisos strengthen and then change their propagation direction the southward high ipv cisos and the northward positive ipv ciso caused by the monsoon begin to interact about 10 days prior to rainfall peak since then the interaction leads a narrow meridional positive pv channel on the inclined 345 k isentropic surface a specific ciso pattern characterized by an elongated high ipv ciso isolated by three negative ipv cisos the south asian the okhotsk and the western pacific subtropical highs is responsible for the long duration of the second rainfall ppciso

slow deformation and lower seismic hazard at the new madrid seismic zone global positioning system gps measurements across the new madrid seismic zone nmsz in the central united states show little if any motion these data are consistent with platewide continuous gps data away from the nmsz which show no motion within uncertainties both these data and the frequency magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8 their recurrence interval should well exceed 2500 years longer than has been assumed alternatively the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed hence the hazard posed by great earthquakes in the nmsz appears to be overestimated

fluorian garnets from the host rocks of the skaergaard intrusion implications for metamorphic fluid composition zoned silica deficient calcic garnets containing up to 5 mol f substitution for 0 formed during contact metamorphism of basalts by the skaergaard intrusion in east greenland fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30 70 m from the intrusion paragenetically equivalent phases include fluorite wollastonite calcic clinopyroxene prehnite quartz and calcite electron microprobe analysis shows that the garnets are 93mol grossular andradite grandite solid solutions and that the f content does not fully compensate for the silica deficiency suggesting the presence of a hydrous component in the garnets the garnets display discontinuous zoning with respect to al and fe and increases in f calculated oh and the si deficiency with increasing al concentration are observed the garnets formed at temperatures between 200 and 420 c based on the coexisting mineral assemblage and stratigraphic reconstructions indicate pressures of 1 kbar assessment of isobaric isothermal phase relations in the system cao a1203 si02 h20hf allows estimation of fluid characteristics in equilibrium with fluorian grandite bearing assemblages the presence of fluorite wollastonite quartz and calcite with these garnets combined with fluid inclusion data require that the activity a of h20 was 1 and that ah af was 10 105 to 10 10 0in the coexisting hydrothermal solutions at 200 420 c and 1 kbar if ph was neutral at these pressure and temperature conditions 5 3 0 1 the value of af associated with fluorian garnet formation was 10 4 7to 10 52 the f content of garnet is extremely sensitive to minor changes in fluid composition the calculations show that a decrease in ph or an increase in log af of 0 3 at constant pressure and temperature will decrease the f concentration in garnet from 5 to 0 mol the results of this study show that fluorian hydrous grandites provide a mineralogical record of the activities off species in coexisting metamorphic and hydrothermal fluids

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

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

oceanic faulting and fault controlled subseafloor hydrothermal alteration in the sheeted dike complex of the josephine ophiolite based upon detailed mapping 1 10 and 1 100 of a large water polished outcrop of the sheeted dike gabbro transition zone in the josephine ophiolite of nw california and sw oregon the following history of alternating episodes of magmatic structural and hydrothermal events has been documented using crosscutting relationships petrography geochemistry and strontium and oxygen isotopic data 1 crystallization of gabbro and later subvertical mafic dike injection 2 amphibolite facies metamorphism 3 extensional faulting and tilting of dikes 4 continued faulting tilting and dike injection associated with retrograde metamorphism at greenschist facies conditions 5 continued extensional faulting and tilting synchronous with the development of a variety of hydrothermal veins at decreasing temperature and increasing fluid rock ratios and 6 subvertical injection of a highly fractionated dike which truncates all previous features features 1 5 trace element geochemistry indicates the highly fractionated dike feature 6 is genetically related to the other dikes and thus was intruded at or near the paleospreading axis hence all previous events features 1 5 can be constrained to have occurred at the rift axis including large scale tilting 50 of the sheeted dikes and extensional faulting the 87sr 86sr initial ratios from recrystallized whole rocks and from hornblende epidote and prehnite separates from veins display a systematic increase with relative age from 0 7033 for altered gabbro screens and mafic dikes to 0 7049 for prehnite in the youngest oceanic fault rock calculated oxygen isotope fluid compositions for the same suite of samples range from 18ofluid 5 to 1 with time indicating a change to a seawater dominated hydrothermal system with time consistent with observed increased permeability due to seafloor extensional faulting the crosscutting relationships alteration mineral assemblages and isotopic data suggest 1 an early stage of high temperature 450 c hydrothermal alteration with low permeability i e grain scale flow followed by 2 a decrease in temperature 350to 200 c and an increase in permeability due to faulting and accompanied by tectonic tilting at the rift axis the consistency of these crosscutting relationships at similar pseudo stratigraphic levels at different localities in the josephine ophiolite suggests that alternating magmatic and structural extension with synchronous retrograde alteration is common in crust formed at similar rates of spreading slow to intermediate spreading centers such as the modern mid atlantic ridge

coseismic slip variation assessed from terrestrial lidar scans of the el mayor cucapah surface rupture abstract we analyze high resolution 103 points m2 terrestrial lidar surveys of the 4 april 2010 el mayor cucapah earthquake rupture baja california mexico collected at three sites 12 18 days after the event using point cloud based tools in an immersive visualization environment we quantify coseismic fault slip for hundreds of meters along strike and construct densely constrained along strike slip distributions from measurements of offset landforms uncertainty bounds for each offset determined empirically by repeatedly measuring offsets at each site sequentially illuminate measurement uncertainties that are difficult to quantify in the field these uncertainties are used to define length scales over which variability in slip distributions may be assumed to reflect either recognizable earthquake mechanisms or measurement noise at two sites characterized by 2 3 m of concentrated right oblique slip repeat measurements yield 2 uncertainties of 11 12 each site encompasses 200 m along strike and a smoothed linear slip gradient satisfies all measurement distributions implying along fault strains of 10 3 conversely the common practice of defining the slip curve by the local slip maxima distorts the curve overestimates along fault strain and may overestimate actual fault slip by favoring measurements with large positive uncertainties at a third site characterized by 1 2 5 m of diffuse normal slip repeat measurements of fault throw summed along fault perpendicular profiles yield 2 uncertainties of 17 here a low order polynomial fit through the measurement averages best approximates surface slip however independent measurements of off fault strain accommodated by hanging wall flexure suggest that over the 200 m length of this site a linear interpolation through the average values for the slip maxima at either end of this site most accurately represents subsurface displacement in aggregate these datasets show that given uncertainties of greater than 11 2 slip distributions over shorter scales are likely to be less uneven than those derived from a single set of field or lidar based measurements this suggests that the relatively smooth slip curves we obtain over 102 m distances reflect real physical phenomena whereas short wavelength variability over 100 101 m distances can be attributed to measurement uncertainty

the 2010 m w 7 2 el mayor cucapah earthquake sequence baja california mexico and southernmost california usa active seismotectonics along the mexican pacific margin the el mayor cucapah earthquake sequence started with a few foreshocks in march 2010 and a second sequence of 15 foreshocks of m 2 up to m4 4 that occurred during the 24 h preceding the mainshock the foreshocks occurred along a north south trend near the mainshock epicenter the mw 7 2 mainshock on april 4 exhibited complex faulting possibly starting with a m6 normal faulting event followed 15 s later by the main event which included simultaneous normal and right lateral strike slip faulting the aftershock zone extends for 120 km from the south end of the elsinore fault zone north of the us mexico border almost to the northern tip of the gulf of california the waveform relocated aftershocks form two abutting clusters each about 50 km long as well as a 10 km north south aftershock zone just north of the epicenter of the mainshock even though the baja california data are included the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border the spatial distribution of large aftershocks is asymmetric with five m5 aftershocks located to the south of the mainshock and only one m5 7 aftershock but numerous smaller aftershocks to the north further the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes thus the aftershocks also express a complex pattern of stress release along strike the overall rate of decay of the aftershocks is similar to the rate of decay of a generic california aftershock sequence in addition some triggered seismicity was recorded along the elsinore and san jacinto faults to the north but significant northward migration of aftershocks has not occurred the synthesis of the el mayor cucapah sequence reveals transtensional regional tectonics including the westward growth of the mexicali valley and the transfer of pacific north america plate motion from the gulf of california in the south into the southernmost san andreas fault system to the north we propose that the location of the 2010 el mayor cucapah as well as the 1992 landers and 1999 hector mine earthquakes may have been controlled by the bends in the plate boundary

the barrow in furness earthquake of 15 february 1865 liquefaction from a very small magnitude event high intensity and liquefaction phenomena are usually associated only with relatively large magnitude earthquakes an earthquake in 1865 in the northwest of england suggests that a sufficiently shallow small event can also produce liquefaction the effects are well documented in historical sources and include sand fountaining modern investigation is confined to documentary evidence owing to the tidal environment of the area where liquefaction occurred analysis shows that the felt area of the earthquake was probably only about 200 km2 however heavy damage occurred in the village of rampside and the maximum intensity is assessed at 8 liquefaction is not uncommon at this intensity but such a high intensity is not usually produced by such small erathquakes the magnitude was probably in the range 2 5 3 5 m l

solar influence on the indian ocean monsoon through dynamical processes 1 the result of paleoclimate studies on the relationship between the indian monsoon and solar activity inferred from the analysis of stalagmites in oman is confirmed by using a modern meteorological dataset from 1958 1999 the present result suggests that the solar influence on monsoon activity is not due to a change in radiative heating in the troposphere but rather originates from the stratosphere through modulation of the upwelling in the equatorial troposphere which produces a north south seesaw of convective activity over the indian ocean sector during summer higher precipitation over arabia and india thus occurs during high solar activity

location of aftershocks of the 4 april 2010 mw 7 2 el mayor cucapah earthquake of baja california mexico a magnitude m w 7 2 earthquake occurred on 4 april 2010 at approximately 50 km southwest of the city of mexicali baja california mexico the regional networks red sismica del noroeste de mexico resnom that the centro de investigacion cientifica y de educacion superior de ensenada cicese operates and the southern california seismic network scsn located the main event between the sierras el mayor and cucapah at the southeastern end of the pescadores fault twenty four hours after the origin time of the main event a temporal seismic network was installed around the faults that ruptured during this event we used body wave arrival times recorded by the first 14 stations installed to obtain precise hypocentral locations of this important sequence of earthquakes most of the aftershocks located on 6 and 7 april are distributed near the traces of the pescadores and cucapah faults particularly at the southern end of these faults the spatial distribution of the epicenters indicates that these faults and possibly others may extend southeast of sierra cucapah where the faults were buried by sediments and were activated during the seismic sequence in this area north of the sierra el mayor where no faults were previously mapped the epicenters align in the northwest southeast direction most hypocenters have depths less than 15 km suggesting that an important portion of the seismic slip was shallow based on the distribution of focal depths of the aftershocks we infer that the seismogenic zone must be between 5 and 10 km

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

late quaternary activity of the laguna salada fault in northern baja california mexico faulted alluvial fans and bajadas along the central laguna salada fault zone in northernbajacaliforniarecordarecurrent history of oblique slip holocene earthquakes alluvialsurfaces whichrangefrom late pleistocene to historic in age have been progressively displaced along the base of the crystalline rangefront as well as along more basinward fault splays in alluvium the recurrence interval determined from displacedalluvialdepositsthataredatedby soil profile development is in the range of 1 2 ka with a corresponding right lateral slip rate of 2 3 mm yr similar to that of thesouthernelsinorefaultinsoutherncalifornia the most recent event along the fault zone is probably the widely felt earthquake of february 23 1892 at least 22 km ofthefaultzonerupturedduringthisevent along both an oblique dextral section of the northwest strikinglagunasaladafaultand

on the modified mercalli intensities and magnitudes of the 1811 1812 new madrid earthquakes we reexamine original felt reports from the 1811 1812 new madrid earthquakes and determine revised isoseismal maps for the three principal mainshocks in many cases we interpret lower values than those assigned by earlier studies in some cases the revisions result from an interpretation of original felt reports with an appreciation for site response issues additionally earlier studies had assigned modified mercalli intensity mmi values of v vii to a substantial number of reports that we conclude do not describe damage commensurate with intensities this high we investigate several approaches to contouring the mmi values using both analytical and subjective methods for the first mainshock on 02 15 lt december 16 1811 our preferred contouring yields m 7 2 7 3 using the area moment regressions of johnston 1996 for the 08 00 lt on january 23 1812 and 03 45 lt on february 7 1812 mainshocks we obtain m 7 0 and m 7 4 7 5 respectively our magnitude for the february mainshock is consistent with the established geometry of the reelfoot fault which all evidence suggests to have been the causative structure for this event we note that the inference of lower magnitudes for the new madrid events implies that site response plays a significant role in controlling seismic hazard at alluvial sites in the central and eastern united states we also note that our results suggest that thrusting may have been the dominant mechanism of faulting associated with the 1811 1812 sequence

diagenesis and very low grade metamorphism of volcaniclastic sandstones from contrasting geodynamic environments north island new zealand the murihiku and waipapa terranes the mesozoic murihiku and waipapa terranes are two accretionary wedges of linked forearc and trench sediments respectively that were juxtaposed in the early cretaceous late triassic to late jurassic murihiku terrane volcaniclastic sediments are folded into a regional syncline and have been diagenetically altered there is a general relationship between zeolite occurrence clay mineralogy vitrinite reflectance and stratigraphic position youngest jurassic sediments contain heulandite analcime and stilbite whereas late triassic to mid jurassic sediments have laumontite and heulandite in detail the zeolite distribution is complicated tuffaceous horizons on the eastern limb of the syncline are calcitized rather than zeolitized post diagenetic fractures associated with uplift are laumontite filled the inferred geothermal gradient is c 15 c km 1 the waipapa terrane is an accretionary complex dominated by imbricated terrigenous sediments of triassic and jurassic age with enclosed permian to jurassic pelagic sediments and basalts late jurassic sediments are massive volaniclastic sandstones the sediments are non foliated and metamorphic minerals in the massive sandstones have crystallized in specific domains the observed metamorphic succession of prehnite pumpellyite and pumpellyite actinolite facies assemblages was overprinted in the imbricated rocks during a thermal event that was late in the deformation sequence and broadly coincident with hydraulic fracturing and veining the metamorphic successions in the two terranes and their relationships to structural features are in excellent accord with accretionary complex models

prehnite as an indicator mineral in the wadi nasb uralitized gabbro south sinai egypt abstract we report the first finding of prehnite in the southern sinai peninsula in a uralitized gabbro developed at the contact of the appinitic gabbro of the wadi nasb mafic intrusion wnmi with younger granitic intrusions subsolidus reactions with hydrothermal fluids caused the gabbro to gain al2o3 and cao while losing sio2 fe2o3 tio2 p2o5 ba nb zr and y uralitization proceeded through two stages of alteration and mineral replacement the early stage includes uralitization of pyroxene formation of new biotite as aggregates of small flakes transformation of primary amphiboles into actinolite and actinolitic hornblende and saussuritization of plagioclase the late stage of alteration is characterized by chloritization of mafic minerals apparent crystallization temperatures of the primary relics of pyroxene hornblende and biotite range from 800 1000 c 865 925 c and 700 c respectively suggesting partial resetting of the biotite exchange thermometer the early biotite forming alteration occurred at moderate temperature 300 450 c while the late chlorite forming alteration occurred at low temperature

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

tectonic deformation in the new madrid seismic zone inferences from map view and cross sectional boundary element models the lack of instrumental recordings and obvious fault scarps associated with the 1811 1812 new madrid earthquakes necessitates examination of more subtle indicators of the geometry and type of faulting associated with these events morphologic and geologic features and the distribution of modern seismicity are used to infer the slip distribution and type of faulting strike or dip slip number strike length and width of the major faults in the new madrid seismic zone nmsz this is accomplished through two dimensional boundary element modeling of the strain field arising from slip on hypothetical faults that is driven by either coseismic or uniform regional strains tectonic deformation is reflected in 1 the seismicity 2 the lake county uplift 3 reelfoot lake 4 the fractured rocks of the blytheville arch and 5 the st francis sunk lands many of these features can be qualitatively explained as resulting from tectonic deformation due to slip on two left stepping right lateral strike slip faults that are coincident with the northeast trending zones of seismicity and the blytheville arch the morphology appears to be at least in part a consequence of major earthquakes that rupture these faults the locations of the 1811 1812 and largest post 1812 earthquakes and the models are consistent with a process in which the 1811 1812 earthquakes relieved accumulated regional shear strain causing the greatest post 1812 shear strains to exist at the ends of the fault zone modeling results also suggest that the numerous small earthquakes in the nmsz are not aftershocks of the 1811 1812 earthquakes but instead represent continuous localized adjustments to a uniform regional strain field the bootheel lineament does not appear to be significant in shaping the morphology geologic structure and pattern of seismicity in the nmsz the absence of fault scarps and coherence of shallow reflectors overlying the blytheville arch suggests that the major nmsz faults may not have ruptured to the surface during the 1811 1812 earthquakes the inferred lengths of the 1811 1812 earthquake ruptures also suggest that their sizes may have been overestimated model predicted subsidence within the st francis sunk lands indicates that tectonic deformation also may have influenced alluvial processes in the nmsz

lg and rg waves on the california regional networks from the december 23 1985 nahanni earthquake we investigate lg and rg propagation in california using the central and southern california regional networks approximately 550 stations constitute these two short period networks providing a dense coverage of almost the entire state the waveforms recorded from the december 23 1985 nahanni canada earthquake are used to construct three profiles along the propagation path almost n s and three perpendicular to the propagation path almost e w to look at the nature of propagation of these two types of surface waves groups of records from stations in various geological and tectonic provinces in california are also examined in order to establish regional characteristics of the surface waves we find that the propagation characteristics of lg differ from those of rg across california lg waves are apparently more sensitive to crustal heterogeneities the most striking observations are the similarity of coda for both the lg and the rg waves within geologic provinces and the marked difference in coda between regions these differences are seen in the amplitudes coda duration shape of the energy envelope frequency content and sharpness of the phase initiation in general a decrease in the moho depth near the pacific coast is correlated with a decrease in the surface wave amplitude especially at higher frequencies 0 15 0 2 hz most interesting is the association of the san andreas fault with abrupt changes in the wave train amplitudes the surface waves are amplified in the vicinity of the fault zone and then decrease in amplitude after the zone is crossed in the coast ranges amplitudes are low and waveform coherence is poor the rg phase dominates the record in the sierra nevada and both surface waves are amplified by the thick sedimentary sequence of the great valley

the indian summer monsoon during peaks in the 11 year sunspot cycle 1 an analysis of sea level pressure anomalies at 14 sunspot peaks in the 11 year solar cycle in the indian region in summer shows that the mean sea level pressure anomalies consist of relatively high pressure over land surrounded by low pressure anomalies over the sea this signal is robust enough to appear when the data are divided into two segments the accompanying mean rainfall anomalies with anomalies as high as 20 above normal have maxima on the coasts and over water and are an enhancement of the mean indian monsoon rainfall in the sunspot peaks the findlater jet appears to shift east and strengthen somewhat consistent with the lower sea level pressure and stronger monsoon rainfall

quantifying the media bias in intensity surveys lessons from the 2001 bhuj india earthquake many seismologists have looked at the 26 january 2001 bhuj earthquake as a key modern calibration event that could be used to improve estimates of magnitudes of large historic mainshocks in stable continental regions since no instrumental data are available for important historic events such as the 1819 allah bund india and the 1811 1812 new madrid central u s mainshocks calibration hinges on comparisons of the macroseismic effects of these earthquakes with those of comparable modern earthquakes for which a reliable instrumentally determined moment magnitude is available however although such a comparison is conceptually straightforward in practice it is complicated by potentially significant inconsistencies in methods used to quantify macroseismic effects in different regions and or times for the bhuj earthquake extensive intensity data sets have been compiled and published from both media accounts and detailed direct surveys comparing the two provides a quantification of the previously suspected media bias whereby earthquake effects can be exaggerated in media accounts this bias is a strong function of intensity level with substantial bias at the highest shaking levels and significantly less bias at low intensities because only sparse documentary data are in general available for older historic earthquakes the results of this study suggest that their inferred intensity distributions might be similarly biased we further use the survey based intensity values to develop a new relationship between intensities and ground motions

epidote bearing veins in the state 2 14 drill hole implications for hydrothermal fluid composition epidote bearing veins in state 2 14 drill core from 900 to 2960 m depth were examined using backscattered electron microscopy and electron probe microanalysis to characterize the mineralogy parageneses texture and composition of vein minerals in order of decreasing abundance minerals in epidote bearing veins are pyrite calcite k feldspar quartz anhydrite hematite chlorite fe cu zn sulfides actinolite titanite and allanite the downhole distribution of minerals in epidote bearing veins pyrite and quartz varies as a function of depth and includes 1 calcite above 2000 m 2 k feldspar between 1700 and 2745 m 3 anhydrite between 2195 and 2745 m 4 hematite sulfides above 2773 m and 5 actinolite below 2890 m where present k feldspar was the first mineral to precipitate in veins followed by epidote in all other veins epidote was the earliest vein mineral to form calcite quartz anhydrite hematite and sulfides were paragenetically later compositional zoning common in most vein epidotes is typically symmetric with al rich cores and fe3 rich rims the minimum mole fraction of ca2fe3si3o12 oh xps in vein epidotes decreases systematically with increasing depth from 0 33 at 906 m to 0 21 at 2900 m and the maximum xps at any given depth is greater than 0 33 thermodynamic analyses of phase relations among vein filling minerals and aqueous solutions at depths near 1867 m and 300 c indicate that the modern reservoir fluid in the salton sea geothermal system is in equilibrium with calcite hematite quartz epidote xps 0 33 anhydrite the predicted fugacity of co2 14 bars for the modern salton sea brine is in close agreement with the calculated value of fco2 for the 1867 m production fluid theoretical phase diagrams in the system cao k2o fe2o3 al2o3 sio2 h2o o2 s2 co2 demonstrate that the mineralogies and mineral parageneses recorded hi epidote bearing veins and the observed variations in al fe3 content of vein epidotes may result from only minor changes in the fugacity of co2 o2 and s2 of the geothermal fluid

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

reassessment of the 1892 laguna salada earthquake fault kinematics and rupture patterns we present the results of intensive field investigations of the scarp associated with the 23 february 1892 earthquake in northern baja california newly recognized additional offsets suggest the rupture was about 58 km in length twice as long as previous estimates slip produced in the 1892 event varied from purely dextral slip near the international border to roughly 1 1 oblique normal slip farther south along the 2 4 km deep portion of the laguna salada basin the portion of the 1892 rupture with oblique normal slip comprises a number of short poorly organized and discontinuous fault scarps with heights that vary in concert with their strike slip was linked farther south to a short purely normal fault that forms a large releasing bend at the southern termination of the fault zone given the distribution of slip along the earthquake and a likely range of locking depths we conclude the 1892 earthquake was between m w 7 1 7 3 in magnitude consistent with previous estimates from macroseismic observations the length of the laguna salada fault that ruptured in 1892 also accommodated minor normal sense displacement along much of its length in the recent 2010 m w 7 2 el mayor cucapah earthquake which guided the remapping effort online material table of displacement measurements with uncertainty location waypoint number soil unit designation and the strike dip and type of feature measured

revisiting the 23 february 1892 laguna salada earthquake according to some compilations the laguna salada baja california earthquake of 23 february 1892 ranks among the largest earthquakes in california and baja california in historic times although surface rupture was not documented at the time of the earthquake recent geologic investigations have identified and mapped a rupture on the laguna salada fault that can be associated with high probability with the 1892 event mueller and rockwell 1995 the only intensity based magnitude estimate for the earthquake m 7 8 was made by strand 1980 based on an interpretation of macroseismic effects and a comparison of isoseismal areas with those from instrumentally recorded earthquakes in this study we reinterpret original accounts of the laguna salada earthquake we assign modified mercalli intensity mmi values in keeping with current practice focusing on objective descriptions of damage rather than subjective human response and not assigning mmi values to effects that are now known to be poor indicators of shaking level such as liquefaction and rockfalls the reinterpreted isoseismal contours and the estimated magnitude are both significantly smaller than those obtained earlier using the method of bakun and wentworth 1997 we obtain a magnitude estimate of m 7 2 and an optimal epicenter less than 15 km from the center of the mapped laguna salada rupture the isoseismal contours are elongated toward the northwest which is qualitatively consistent with a directivity effect assuming that the fault ruptured from southeast to northwest we suggest that the elongation may also thus reflect wave propagation effects with more efficient propagation of crustal surface lg waves in the direction of the overall regional tectonic fabric

investigation of teleseismic lg blockage and scattering using regional arrays abstract incoherent beamforming and continuous frequency wavenumber polar scan analysis have been applied to study the characteristics of p coda and lg waves recorded at the regional arrays noress and arcess from presumed explosions on the northwestern russian platform and at test sites of novaya zemlya and eastern kazakh also recordings at the graefenburg array near the new geress regional array of novaya zemlya events and an eastern european platform white sea event have been compared with the norwegian array recordings of the same events the white sea explosion at distances of 14 and 22 from noress and graefenburg respectively exhibits lg rms amplitudes on incoherent beams that exceed those of sn however for explosions at novaya zemlya at 20 from noress and eastern kazakh at 30 from arcess the lg waves have much smaller amplitudes than sn in the case of novaya zemlya the lg wave is almost completely blocked at both noress and arcess but is well recorded at graefenburg this reduction of the lg amplitudes relative to those from events at longer distances cannot be accounted for by anelastic attenuation and spreading comparison of propagation paths suggests that the reduction in amplitudes may be due to blockage and scattering of lg in the barents sea analysis of sn coda waves on incoherent beams and continuous frequency wavenumber analysis polar scans suggests that they can result from lg to sn scattering from the coastline between the barents sea and scandinavia recent geologic studies have revealed significant variations in crustal structure in the barents sea basin which may cause the blockage of lg waves from novaya zemlya in the case of eastern kazakh explosions arcess incoherent beams show much reduced lg amplitudes relative to the p coda waves compared with noress even though the distance to arcess 31 is less than that to noress 38 this reduction in lg amplitude at both noress and arcess is accompanied by enhancement of p and sn coda the timing of the coda waves and the propagation paths suggest that lg waves may be partially blocked and scattered by the ural mountains and that the p and sn coda waves may result from lg to pn pn to sn sn to lg and lg to sn conversions from lateral heterogeneities in the crust beneath the urals the blockage is greater for the eastern kazakh to arcess path because it crosses the middle part of the urals whereas the eastern kazakh to noress path crosses the southern part of the urals chain these blockage effects seem to result from sudden lateral variations in shallow crustal structure such as variations in sediment thicknesses in the sedimentary basins of the russian platform and adjacent to the urals these blockage effects can be predicted from geologic studies and need to be accounted for when using lg amplitudes to estimate absolute yields of explosions and for event identification

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

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

revisiting the 1872 owens valley california earthquake the 26 march 1872 owens valley earthquake is among the largest historical earthquakes in california the felt area and maximum fault displacements have long been regarded as comparable to if not greater than those of the great san andreas fault earthquakes of 1857 and 1906 but mapped surface ruptures of the latter two events were 2 3 times longer than that inferred for the 1872 rupture the preferred magnitude estimate of the owens valley earthquake has thus been 7 4 based largely on the geological evidence reinterpreting macroseismic accounts of the owens valley earthquake we infer generally lower intensity values than those estimated in earlier studies nonetheless as recognized in the early twentieth century the effects of this earthquake were still generally more dramatic at regional distances than the macroseismic effects from the 1906 earthquake with light damage to masonry buildings at nearest fault distances as large as 400 km macroseismic observations thus suggest a magnitude greater than that of the 1906 san francisco earthquake which appears to be at odds with geological observations however while the mapped rupture length of the owens valley earthquake is relatively low the average slip was high the surface rupture was also complex and extended over multiple fault segments it was first mapped in detail over a century after the earthquake occurred and recent evidence suggests it might have been longer than earlier studies indicated our preferred magnitude estimate is mw 7 8 7 9 values that we show are consistent with the geological observations the results of our study suggest that either the owens valley earthquake was larger than the 1906 san francisco earthquake or that by virtue of source properties and or propagation effects it produced systematically higher ground motions at regional distances the latter possibility implies that some large earthquakes in california will generate significantly larger ground motions than san andreas fault events of comparable magnitude

compositional order disorder and stable isotope characteristics of al fe epidote state 2 14 drill hole salton sea geothermal system epidote ca2fe3si3o12 oh ca2al3si3o12 oh is a common hydrothermal mineral in metasediments and veins at depths 900 m in the state 2 14 drill hole of the salton sea geothermal system the mole fraction of ca2fe3si3o12 oh in epidotes xps from this drill hole ranges from 0 11 to 0 42 and complex compositional zoning of octahedral fe3 and al is typical within single grains with increasing depth there is an overall but irregular decrease in the fe3 content of epidotes in metasandstones in most samples vein epidotes are more fe3 rich and exhibit a wider compositional range than metasandstone epidotes from the same depth octahedral fe3 in the m 1 sites in four epidotes evaluated by 57fe mossbauer spectroscopy ranges from 7 5 1 7 to 11 4 1 5 of the total iron the most ordered epidote formed in veins at 2618 m in the biotite zone this epidote has an ordering parameter 1 2xfe3 m 1 of 0 85 0 03 which corresponds to a calculated state of equilibrium order disorder at 390 60 c in close agreement with the probable downhole temperature of 340 c two epidote samples from the chlorite calcite zone 1420 m 265 c 1867 m 300 c are more disordered corresponding to calculated states of equilibrium order disorder of 450 c these data suggest that the analyzed epidotes from the chlorite calcite zone are in a metastable state of substitutional order disorder the measured value of depidote from 1420 m is 96 which is 5 6 lighter than epidotes from 1867 m depidote 90 2227 m depidote 91 and 2618 m depidote 90 when compared to the reservoir fluid from the december 1985 flow test the derived fractionation of hydrogen isotopes between epidote and the geothermal brine is 19 at 1867 m and 340 c this value is in accord with published experimental hydrogen isotope fractionations between iron rich epidote and aqueous electrolyte solutions therefore considering the complexity of the salton sea brine the isotopic temperature is similar to the inferred downhole temperature

multiple late holocene earthquakes along the reelfoot fault central new madrid seismic zone the reelfoot fault is an east vergent reverse fault underlying the lake county uplift a low amplitude late holocene anticline bordered on the east by the 32 km long reelfoot scarp fluvial deposits across the scarp define an 8 m high east facing monocline most near surface deformation along the scarp is accommodated via folding rather than faulting we interpret the scarp as a fault propagation fold developed over a wcst dipping reverse fault interpreted from shallow seismic reflection data trench exposurcs provide evidence for three episodes of deformation along the reelfoot fault within thc past approximately 2400 years between a d 780 and 1000 between a d 1260 and 1650 and during a d 1812 our best estimate of the average recurrence interval for deformation along the scarp is 400 500 years each episode of deformation had a slightly different style the third most recent event produced a small graben a few tens of centimeters deep in the hanging wall of the reverse fault the second most recent earthquake produced about 1 3 m of throw in the graben as well as folding along the updip projection of the reverse fault and development of the scarp thesc relations suggest that graben development increased through time concomitant with growth of the monocline or that the events are of different magnitude the 1811 1812 episode of deformation produced abundant liquefaction prominent folding of fluvial strata along the scarp and minor faulting in the graben

new evidence for a large earthquake in the new madrid seismic zone between a d 1400 and 1670 in an integrated geological archaeological and geophysical study in the new madrid seismic zone of the southeastern united states we documented a prehistoric sand blow and related feeder dikes at an archaeological site near steele missouri archaeological analysis combined with radiocarbon dating suggest that the earthquake induced features formed between a d 1400 and 1670 this paleoseismic study provides the best evidence to date for a large earthquake occurring in the zone within 400 yr prior to the 1811 1812 new madrid earthquake sequence to determine an optimal location for excavating at the study site we mapped surficial artifact density and conducted geophysical surveys in doing so we were able to reveal critical relationships for constraining the age of the prehistoric earthquake with minimal impact to the archaeological site

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure