the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

the rupture history of the mw 8 0 jalisco mexico earthquake of 1995 october 9 summary finite fault broad band teleseismic p waveform inversion was applied to the large mw 8 0 jalisco mexico earthquake of 1995 october 9 the earthquake hypocentre was located at shallow depths just near the boundary zone between two lithospheric plates rivera and cocos and was felt with a maximum intensity of 9 mm on the pacific coast it was the first earthquake of magnitude greater than 6 to occur in this region since the two great jalisco earthquakes ms 8 0 and 7 6 of 1932 for inversion we used vertical records from 14 digital stations situated 30d to 90d from the epicentre we used the fixed rake of the thrust type focal mechanism given by the preliminary harvard cmt the low angle dipping fault plane was taken as a 180 90 km2 rectangle divided into 162 subfaults of 10 10 km2 each subfault had five intermediate point sources along strike and five intermediate point sources downdip the size of the fault plane was changed from an initial size of 110 60 km2 estimated by resco as an aftershock area to the final size of 180 90 km2 which included all significant displacements along the fault the hypocentre was embedded 40 km from the left edge of the 180 km long fault 40 km down dip from the top of the fault which was situated practically along the trench axis a boxcar source time function of width 2 0 s was used for each discrete rupture interval of each subfault the rupture velocity was taken to be 2 8 km s 1 which is approximately 80 per cent of the shear wave speed in the layer containing the hypocentre the following results on the rupture history were obtained 1 the rupture duration was about 55 s and slip occurred within an area of about 180 90 km2 along the middle american trench in the depth interval from 9 to 33 km 2 there were two main stages in the rupture history during the first 18 s two main asperities at a distance of about 30 km from the earthquake hypocentre were ruptured with maximum slip up to 610 cm at a depth of 12 15 km then during the next 37 s rupturing was observed to the north along the trench the slip distribution obtained shows that the faulting originating near the boundary between the rivera and cocos plates went mainly along the rivera north american plate boundary and is consistent with the subduction of the rivera plate beneath north america

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

the macroseismic field generated by the mw 8 0 jalisco mexico earthquake of 9 october 1995 abstract the mw 8 0 earthquake of 9 october 1995 occurred within the jalisco block that represents the northern part of the mexican subduction zone where the rivera plate subducts beneath the north america plate along the middle american trench the source rupture of the 1995 low angle thrust type event was complicated the studies of rupture history had shown that the slip occurred within an area of about 180 90 km 2 along the middle american trench at the depth interval from 9 to 33 km the rupture duration was estimated in interval from 55 to 62 sec at least three main asperities ruptured along the fault plane the earthquake was felt along the 600 km coast of the mexican states of colima jalisco and michoacan and in the continental part of mexico the macroseismic study presented in this article was carried out in march through july 1997 more than one year after the earthquake we had about 300 interviews with people who felt the earthquake in their houses located in 56 cities and towns of the states of colima jalisco and michoacan all our estimates of the earthquake intensity were referred to the intermediate type of masonry situated on the intermediate type of soils for this purpose corrections were introduced for type of soil and masonry the study of macroseismic effects related to the 1995 jalisco earthquake allows description of some properties of the macroseismic field generated by the earthquake 1 three zones of intensity 4 5 and 6 to 7 grades of mm modified mercalli scale were distinguished 2 the zone of maximum intensity of 6 to 7 mm was heterogeneous this heterogeneity was in accordance with the rupture asperities distribution 3 the study of intensity attenuation along the coast had demonstrated the asymmetry in intensity distribution according to the epicenter the maximum intensities were observed for the sites that were situated to the northwest of the epicenter 4 a good correlation was observed between the observed intensities and the values of gps displacements

the relationship between quaternary volcanism in central mexico and the seismicity and structure of subducted ocean lithosphere late quaternary volcanism in central mexico is related to the subduction of young ocean lithosphere at the middle america trench along arc variations in seismicity volcano structure and composition of volcanic products bear a remarkable correlation with the age and structural framework of the downgoing slab morphological and petrographic characteristics of major volcanoes within the trans mexican volcanic belt tmvb serve to distinguish two calc alkaline subprovinces 1 a western arc averaging 60 km in width associated with aseismic subduction of the rivera plate the main cones of this region are dominated by two pyroxene andesites comprise volumes 70 km 3 and stand less than 3 000 m above sea level 2 a broad central and eastern arc related to subduction of a gently inclined segment of the cocos plate bounded by the rivera transform and the tehuantepec ridge major volcanic edifices possess summit elevations in the range 4 000 to 6 000 m have appropriately larger volumes typically 200 km 3 and are constructed with a high proportion of amphibole bearing lavas the boundary between these subprovinces is marked by a north south oriented structural depression the colima graben and it coincides with a 100 km offset in the volcanic front extensional tectonism in the colima graben accompanied by mixed calc alkaline and alkaline volcanism of potassic affinity is likely related to a hinge type transform fault which marks the cocos rivera plate juncture in the downgoing slab a third segment of ocean floor is presently interacting with continental lithosphere south of the gulf of tehuantepec where quaternary volcanism is weakly developed within a tectonically complex region that marks the diffuse cocos noam caribbean triple junction the northern limit of this triple junction is defined by the seismically active isthmus fault which may be related to alkaline volcanic activity at san andres tuxtla a tectonic reconstruction based on the evolution of oceanic crust reveals that the distribution of intermediate depth earthquakes along the arc is directly dependent upon the age of the subducted slab ocean lithosphere younger than approximately 20 m y is subducted aseismically at convergence rates approaching 9 cm yr the length of the inclined seismic zone indicates that the time constant for thermal relaxation in the slab is approximately 4 m y the tmvb overlies the aseismic extension of this young ocean lithosphere several aspects of this study have a bearing on the segmented nature of converging margins in general 1 the tectonic evolution of the ocean floor may determine the nature of segmentation at the site of subduction 2 the complete record of volcanism in the tmvb over the past million years can be related to the present plate configuration 3 alkaline and calc alkaline volcanism have developed contemporaneously at a converging plate margin 4 lineaments in volcanic arcs may reflect the structural complexity of the crust rather than segment boundaries in the subducted slab

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

earthquake clustering in shallow subduction zones kamchatka and mexico this paper studies regularities in earthquake clustering at shallow depths 0 60 km in two pacific subduction zones the mexican and the kamchatkan these zones were formed by subduction under the north american plate of old and fast pacific plate kamchatkan region and young and slow rivera and cocos plates mexican region we use events of magnitude 5 5 and greater 95 events for 1964 1993 from the kamchatkan region and 52 events for 1974 1993 from the mexican region we have two active kamchatkan and cocos and one passive rivera subduction zones for the passive rivera zone where subduction may be considered aseismic after the great jalisco event of 1932 magnitude ms 8 2 and its aftershock activity during 1932 1934 we can study only seismic events along the western border of the plate related to oceanic rises and the rivera fracture zone here we have a well developed clustering of earthquakes 47 of all 17 studied events occurred in clusters mainly of swarm type for the two active subduction zones the kamchatkan and the cocos we can formulate the following results 1 most of the studied events of the cocos subduction zone 74 occurred in clusters and within the kamchatkan subduction zone 45 of the events recorded were in clusters 2 the clustering events occurred mainly at a depth interval from 0 to 40 km 98 of all clustering events in kamchatka and 61 for the cocos subduction zone at the same time the single events were distributed mainly in a depth interval from 30 to 60 km 73 of all single events in kamchatka and 100 for the cocos subduction zone 3 comparison of the spatial distribution for the different types of clustering in kamchatka and the cocos zone shows the absence of a band of swarms along the slope of the middle american trench whereas such a band is obvious in the kamchatkan region 4 the study of temporal distribution for single events and mainshock aftershock sequences within the region of large earthquakes shows that there was a change from a long term sequence of single events to events with aftershocks 1 4 years before a large earthquake this regularity was observed before both large magnitude greater than seven earthquakes in kamchatka and before the magnitude 8 1 michoacan earthquake in mexico

microbial methane and ethane from gas hydrate nodules of the makassar strait indonesia abstract intact white nodules of gas hydrate were recovered in piston cores 0 6 4 m sediment depth from the deep water region of the makassar strait between the islands of borneo and sulawesi offshore indonesia consistent with structure i gas hydrate the dominant hydrocarbon is methane 99 96 the hydrate bound methane is relatively depleted in 13 c mean 13 c 70 6 mean d 189 9 microbial ethane also present in the hydrate is more highly depleted in 13 c mean 52 6 than nearly all previously discovered gas hydrates and is accompanied by trace volumes of microbial ethylene and propylene detrital higher plant material is the likely sedimentary carbon source the source of microbial methane and ethane appears to be in situ reduction of co 2 by extremophile bacteria adapted to high pressure the hydrate occurs several hundred meters above the base of the gas hydrate stability zone nodular hydrate is associated with seafloor authigenic carbonate rock and chemosynthetic clams characteristic of deep cold vent sites

spectral analysis of quikscat surface winds and two dimensional turbulence a spectral decomposition of quikscat surface wind vectors reveals different levels of variance and different values of the spectral slope in various regions of the world ocean for the 12 months investigated the traditional considerations on the factors affecting the shape of the spectra are reviewed and compared to the results in particular the influence of large scale synoptic systems is shown by comparing the steeper and more energetic spectra of the midlatitudes to the shallower spectra of the tropics similarly the signature of convection is investigated by comparing spectra in the tropical convectively active and dry zones of the pacific ocean spectra of vorticity and divergence are calculated along with spectral vorticity to divergence ratios their spatial and temporal variations are discussed it is hypothesized that when convection is enhanced in the tropics the spectral analysis captures the mesoscale synoptic structures in which convection is embedded and that the spectra exhibit some of the characteristics of their midlatitude counterparts i e steeper and more energetic

mesoscale spectral analysis of in situ horizontal and vertical wind measurements at 6 km as part of the aloha anlc 93 campaign to investigate atmospheric dynamics in situ wind measurements collected at 6 km with the gust probe sensor attached to the national center for atmospheric research electra aircraft were analyzed for 16 flight segments between 61 n and 14 s and between 92 w and 170 w over land and water horizontal wavenumber spectra for the vertical wind and both zonal and meridional horizontal wind components were calculated the zonal and meridional wavenumber spectra exhibited a decrease in the spectral slope from 1 98 0 02 for wavelengths between 2 km and 100 km to 3 18 0 06 for the longer wavelengths between 100 km and 330 km the wavenumber spectrum for the vertical wind component showed a 2 power law dependence for wavelengths in excess of 5 km and a generally flat shape at shorter wavelengths an increase in power at the wavelength of 10 km was detected for the meridional wavenumber spectrum these results were compared with predictions from two spectral models and with spectral results from other observations

stochastic analysis of southern and pacific ocean sea surface winds abstract this paper shows that the synoptic variability of zonal and meridional midlatitude pacific and southern ocean sea surface winds can be well described by a univariate stochastic dynamical system directly derived from data the method used to analyze blended quick scatterometer quikscat ncep winds is a general method to estimate drift and diffusion coefficients of a continuous stationary markovian system almost trivially the deterministic part consists of a simple nearly linear damping term more importantly the stochastic part appears to be a state dependent white noise term that is multiplicative noise the need for a multiplicative noise term to describe the variability of midlatitude winds can be interpreted by the fact that the variability of midlatitude winds increases with increasing wind speed the results indicate that a complete stochastic description of midlatitude winds requires a state dependent white noise term that is multiplicative noise a simple ornstein uhlenbeck proces

far field simulation of tsunami propagation in the pacific ocean impact on the marquesas islands french polynesia the islands in the marquesas archipelago are most exposed to far field tsunamis in french polynesia four recent earthquakes located at the pacific rim kurile 1994 chile 1995 mexico 1995 and peru 1996 earthquakes generated trans pacific tsunamis and caused contrasting inundations in several inhabited marquesian bays the aim of this study is to better understand the amplification phenomena observed in the marquesas islands and to improve the risk assessment we present here numerical simulations of these four tsunamis by means of a finite difference model solving the equations of tsunami propagation at different scales the water heights computed in the bays are in excellent agreement with the available observations and thus validate our numerical method these numerical results allow us to determine 1 which propagation azimuths are dangerous for the whole marquesas archipelago and 2 the behavior of each studied bay amplitude frequency in response to tsunami waves we observe that the seismogenic subduction zone along south america is likely to define one of the most dangerous tsunami generation areas for the marquesas archipelago owing to the source geometries and to the trapping of the tsunami energy by bathymetric features in the southern pacific ocean fracture zones seamount chains

inversion for slip distribution using teleseismic p waveforms north palm springs borah peak and michoacan earthquakes we have inverted the teleseismic p waveforms recorded by stations of the global digital seismograph network for the 8 july 1986 north palm springs california the 28 october 1983 borah peak idaho and the 19 september 1985 michoacan mexico earthquakes to recover the distribution of slip on each of the faults using a point by point inversion method with smoothing and positivity constraints in the inversion procedure a fault plane with fixed strike and dip is placed in the region of the earthquake hypocenter and divided into a large number of subfaults rupture is assumed to propagate at a constant velocity away from the hypocenter and synthetic ground motions for pure strike slip and dip slip dislocations are calculated at the teleseismic stations for each subfault the observed seismograms are then inverted to obtain the distribution of strike slip and dip slip displacement for the earthquake results of the inversion indicate that the global digital seismograph network data are useful for deriving fault dislocation models for moderate to large events however a wide range of frequencies which includes periods shorter than those within the passband of the long period global digital seismograph network instruments is necessary to infer the distribution of slip on the earthquake fault although the long period waveforms define the size dimensions and seismic moment of the earthquake data at shorter periods provide additional constraints on the variation of slip on the fault dislocation models obtained for all three earthquakes are consistent with a heterogeneous rupture process where failure is controlled largely by the size and location of high strength asperity regions

rupture histories of eastern north american earthquakes abstract digital worldwide records of p and sh waves are used to invert for rupture histories of the recent larger eastern north american earthquakes the data include a broad bandwidth to facilitate recovery of both source details and total moment the following events are studied 9 january 1982 new brunswick 5 october and 23 december 1985 nahanni 25 november 1988 saguenay and 25 december 1989 ungava earthquakes we employ a finite fault waveform inversion scheme that discretizes the slip history as a function of position on the fault this formulation allows estimation of rise time and slip velocity in addition to the spatial distribution of slip static stress drops averaged over the entire rupture surface range from a few tens of bars to just over 100 bars and are similar to values estimated for western united states earthquakes estimates of stress drop for spatially limited asperities are in the range of a few hundred bars with the value for the saguenay earthquake asperity being the largest approaching 1 kbar the variation in stress drop is considerable but no evidence is seen for a scaling relation in which stress drop increases with moment maximum slip velocities on the fault also have a wide range from 50 cm sec to perhaps greater then 200 cm sec with the saguenay and 5 october nahanni earthquakes lying at the upper end of this range of the events studied the saguenay earthquake is unique in terms of its greater depth spatially concentrated source and large asperity stress drop

the global characteristics of the wavenumber spectrum of ocean surface wind the wavenumber spectra of wind kinetic energy over the ocean from quick scatterometer quikscat observations have revealed complex spatial variability in the wavelength range of 1000 3000 km with spectral slopes varying from 21 6 to 22 9 here the authors performed a spectral analysis of quikscat winds over the global ocean and found that i the spectral slopes become steeper toward the poles in the pacificandin the south atlantic and theslopes exhibitminimallongitudinaldependencein the southpacific ii thesteepestslopesare inthe tropical indianocean andthe shallowest slopesarein thetropicalpacificand atlantic and iii the spectra are steeper in winter than summer in most regions of the midlatitude northern hemisphere thenewfindingsreportedinthepaperprovideatestbedfortheoreticalstudiesandatmospheric general circulation models

massive vein filling gas hydrate relation to ongoing gas migration from the deep subsurface in the gulf of mexico abstract a gas hydrate mound that contains massive vein filling structure ii gas hydrate occurs on the upper continental slope 540 m water depth of the gulf of mexico southwest of the mississippi delta the mound is located in the green canyon gc block 185 adjacent to jolliet field in gc 184 jolliet field contains oil and gas that filled fault traps caused by salt deformation during late pleistocene holocene time in contrast to reservoir oil in jolliet field which shows bacterial oxidation effects the c 1 c 5 reservoir gas is unaltered by bacterial oxidation disassociated gas is assumed to have recently entered from the subsurface hydrocarbon system vertical migration of gas along faults is ongoing manifested on the sea floor by gas vents gas hydrate complex chemosynthetic communities and by a large gas plume that extends from the vents to the sea surface the isotopic properties of c 1 c 5 hydrocarbons from reservoirs gas vents and gas hydrate correlate closely although outcropping gas hydrate is transiently stable because of variations in seawater temperature the bulk of buried gas hydrate at gc 185 is stable and perhaps increasing in volume because of the copious gas flux the massive accumulation of gas hydrate at the gc 185 site is attributed to the gas that has recently entered the vents largely from jolliet field and to the synchronous activation of fault conduits allowing gas migration to the sea floor synchronous late gas charge and faulting could also explain the wide distribution of gas hydrate across the upper gulf slope

the impact of resolution on the representation of southeast greenland barrier winds and katabatic flows southern greenland is characterized by a number of low level high wind speed weather systems that are the result of topographic flow distortion these systems include barrier winds and katabatic flow that occur along its southeast coast global atmospheric reanalyses have proven to be important tools in furthering our understanding of these orographic winds and their role in the climate system however there is evidence that the mesoscale characteristics of these systems may be missed in these global products here we show that the arctic system reanalysis a higher resolution regional reanalysis is able to capture mesoscale features of barrier winds and katabatic flow that are missed or underrepresented in era i a leading modern global reanalysis this suggests that our understanding of the impact of these wind systems on the coupled climate system can be enhanced through the use of higher resolution regional reanalyses or model data

the great jalisco mexico earthquakes of 1932 subduction of the rivera plate we have analyzed seismograms of the 3 june 1932 ms 8 2 and the 18 june 1932 ms 7 8 jalisco earthquakes and their aftershocks at manzanillo mnz guadalajara gum and tacubaya tac the aftershocks locations the first motions at mnz and the isoseismic maps of the two main shocks strongly suggest that a the 3 june 1932 earthquake initiated nw of but close to mnz and propagated nw for an estimated length of rupture of 220 km b the 18 june 1932 earthquake nucleated sw of mnz offshore and perhaps ruptured a length of about 60 km and c the width of rupture was approximately 80 km there is no evidence of events occurring se of mnz even up to 1 1 2 yr after the first main shock a gap of about 60 km remains between the aftershock areas of the 1932 jalisco and the 1973 colima earthquakes whose seismic potential is unknown although the boundary between the rivera and cocos plates is uncertain there is little doubt that the 1932 earthquakes broke the shallow part of the rivera subduction zone our results may help in quantifying seismic potential of tectonically similar areas such as the juan de fuca subduction zone in the nw united states

carbon isotope fractionation during natural gas generation from kerogen abstract in petroleum exploration it is important to be able to determine the origin of any gas which is found this paper describes a new method of estimating the source type and maturity of a gas based on a rayleigh fractionation model kerogen is divided conceptually into a labile dominantly oil generating fraction and a refractory gas prone component 13 c of methane from either kerogen type and ethane propane and butane for gases from labile kerogen can be defined as a function of 13 c of the gas precursor groups in kerogen a kinetic isotope fractionation factor k and the extent of gas generation the isotopic ratio of the methane precursors relative to bulk kerogen determined from laboratory pyrolysis are 17 5 for labile kerogen and 1 4 for refractory kerogen values for ethane propane and butane from labile kerogen based on field correlations are 4 9 2 2 and 1 6 respectively the corresponding fractionation factors are 0 9892 0 9919 0 9947 and 0 9975 for methane ethane propane and butane respectively from labile kerogen and 0 9984 for methane from refractory kerogen using these parameters summary diagrams are constructed which allow differentiation of these sources from each other and from biogenic gases and cracked oil and recognition of gases of mixed origin if an independent estimate of 13 c for the source kerogen is possible then 13 c of the gas components can be used to estimate maturity in terms of the gas generation index the fraction of gas potential which has been realized

scatterometer and ecmwf derived wind vorticity over the mediterranean basin this article investigates the spatial and temporal structures of the monthly mean vorticity fields and over the mediterranean basin derived respectively from satellite scatterometers and ecmwf global atmospheric model t799 wind fields from february 2006 to january 2010 statistics show a mean difference between and over the whole mediterranean sea relative bias of 0 108 10 5 s 1 furthermore both the cyclonic and the anticyclonic components of are stronger than those of the analysis of the spatial features of and shows that the greatest discrepancies occur along coasts and in the adriatic sea due to the ability of to describe vorticity features smaller than about 6 9 103 km2 roughly corresponding to square areas of side 83 km or circular areas of radius 46 km that are not present in given the effective spatial resolution of the model the temporal features of and have shown a substantially similar trend in anticyclonic and a deep difference in cyclonic circulations again related to the limited ability of to describe small scale vorticity patches as the main source of the differences local characterization of and along six transects across areas where the wind vorticity features are well known has confirmed the results of substantial similarity of and at spatial scales larger than 100 km or so and remarkable differences in those regions such as the adriatic and crete seas affected by vorticity variability at smaller scales copyright 2012 royal meteorological society

seismicity and tectonics of the rivera plate and implications for the 1932 jalisco mexico earthquake seismicity on and near the boundaries of the rivera plate is examined in order to determine the subduction regime of the rivera plate and its influence on the earthquake behavior of the northernmost section of the mid america trench in particular we address the question of a rivera cocos boundary there have been several large historic earthquakes in the coastal areas of the mexican states colima and jalisco but the last large event was in june 1932 the 1932 jalisco earthquake ms 8 1 the present quiescence has lasted longer than the average recurrence interval for the mexican subduction zone and the jalisco area is now categorized as a seismic gap however if subduction in this area is dominated by the motion of the rivera plate which is subducting at half the rate of the cocos plate the deficiency of earthquake activity may not be unusual in an attempt to better delineate the rivera cocos boundary intermediate sized earthquakes along and near the rivera fracture zone and the mid america trench were relocated with the joint epicenter determination method we found that in general the catalog locations are fairly accurate with the average change in epicenter upon relocation being 12 km seismicity along the rivera fracture zone follows the physiographic trend of the fracture zone but east of its intersection with the east pacific rise seismicity is more diffuse two intermediate sized earthquakes in this diffuse area have focal mechanisms suggesting that they represent rivera cocos boundary motion reexamination of arrival time data for the 1932 jalisco earthquake yields an epicenter at 19 57 n 104 42 w close to the boundary zone inferred from these two earthquakes we conclude that the possibility that the 1932 jalisco earthquake broke the northernmost section of the cocos north american plate interface as opposed to the rivera north american plate interface cannot be ruled out

gas hydrate systems at hydrate ridge offshore oregon inferred from molecular and isotopic properties of hydrate bound and void gases abstract we report and discuss molecular and isotopic properties of hydrate bound gases from 55 samples and void gases from 494 samples collected during ocean drilling program odp leg 204 at hydrate ridge offshore oregon gas hydrates appear to crystallize in sediments from two end member gas sources deep allochthonous and in situ as mixtures of different proportions in an area of high gas flux at the southern summit of the ridge sites 1248 1250 shallow 0 40 m below the seafloor mbsf gas hydrates are composed of mainly allochthonous mixed microbial and thermogenic methane and a small portion of thermogenic c2 gases which migrated vertically and laterally from as deep as 2 to 2 5 km depths in contrast deep 50 105 mbsf gas hydrates at the southern summit sites 1248 and 1250 and on the flanks of the ridge sites 1244 1247 crystallize mainly from microbial methane and ethane generated dominantly in situ a small contribution of allochthonous gas may also be present at sites where geologic and tectonic settings favor focused vertical gas migration from greater depth e g sites 1244 and 1245 non hydrocarbon gases such as co2 and h2s are not abundant in sampled hydrates the new gas geochemical data are inconsistent with earlier models suggesting that seafloor gas hydrates at hydrate ridge formed from gas derived from decomposition of deeper and older gas hydrates gas hydrate formation at the southern summit is explained by a model in which gas migrated from deep sediments and perhaps was trapped by a gas hydrate seal at the base of the gas hydrate stability zone ghsz free gas migrated into the ghsz when the overpressure in gas column exceeded sealing capacity of overlaying sediments and precipitated as gas hydrate mainly within shallow sediments the mushroom like 3d shape of gas hydrate accumulation at the summit is possibly defined by the gas diffusion aureole surrounding the main migration conduit the decrease of gas solubility in shallow sediment and refocusing of gas by carbonate and gas hydrate seals near the seafloor to the crest of the local anticline structure

mesoscale structure of cape farewell tip jets abstractcape farewell greenland s southernmost point is characterized by a number of low level jets that are the result of topographic flow distortion associated with passing extratropical cyclones the heavy seas associated with these wind events are a hazard to maritime traffic in the region in addition the air sea heat flux associated with these weather systems plays an important role in the climate system by contributing to the forcing of the lower limb of the atlantic meridional overturning circulation in this paper the north american regional reanalysis will be used to generate a higher resolution climatology of these mesoscale jets as compared to previous studies through the use of a diagnostic that partitions the occurrence frequency of high speed wind events by wind direction the author shows that there are four different types of cape farewell tips jets that are characterized as having either northwesterly southwesterly northeasterly or southeasterly wind direction all four types hav

cross spectral analysis of the sst 10 m wind speed coupling resolved by satellite products and climate model simulations this study aims to determine the spatial temporal scales where the sst forcing of the near surface winds takes places and its relationship with the action of coherent ocean eddies here cross spectral statistics are used to examine the relationship between satellite based sst and 10 m wind speed w fields at scales between 10 2 10 4 km and 10 1 10 3 days it is shown that the transition from negative sst w correlations at large scales to positive at oceanic mesoscales occurs at wavelengths coinciding with the atmospheric first baroclinic rossby radius of deformation and that the dispersion of positively correlated signals resembles tropical instability waves near the equator and rossby waves in the extratropics transfer functions are used to estimate the sst driven w response in physical space w c a signal that explains 5 40 of the mesoscale w variance in the equatorial cold tongues and 2 15 at extratropical sst fronts the signature of ocean eddies is clearly visible in w c accounting for 20 60 of its variability in eddy rich regions to provide further insight on the role of ocean eddies in the sst driven coupling the analysis is repeated for two climate model ccsm simulations using ocean grid resolutions of 1 circ eddy parameterized lr and 0 1 circ eddy resolving hr the lack of resolved eddies in lr leads to a significantly underestimated mesoscale w variance relative to hr conversely the w c variability in hr can exceed the satellite estimates by a factor of two at extratropical sst fronts and underestimate it by a factor of almost six near the equator reflecting shortcomings of the ccsm to be addressed in its future developments

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

the geodetic signature of the m8 0 oct 9 1995 jalisco subduction earthquake the october 1995 mw 8 0 jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process an 11 station regional gps network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest directed extension with measured displacements reaching 1 meter unusually shallow and non uniform faulting is required to explain the displacements we determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km and that slip was likely distributed in two main patches the paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting

the impact of polar mesoscale storms on northeast atlantic ocean circulation every year thousands of mesoscale storms termed polar lows cross the climatically sensitive subpolar north atlantic ocean high resolution numerical simulations of the ocean circulation taking into account the effect of these storms on deep water formation suggest that polar lows significantly affect the global ocean circulation

multibeam bathymetry and sidescan imaging of the rivera transform moctezuma spreading segment junction northern east pacific rise new constraints on rivera pacific relative plate motion to better understand the recent motion of the pacific plate relative to the rivera plate and to better define the limitations of the existing rivera pacific plate motion models for accurately predicting this motion total field magnetic data multibeam bathymetric data and sidescan sonar images were collected during the bart and famex campaigns of the n o l atalante conducted in april and may 2002 in the area surrounding the moctezuma spreading segment of the east pacific rise located offshore of manzanillo mexico at 106 16 w between 17 8 n and 18 5 n among the main results are 1 the principle transform displacement zone of the rivera transform is narrow and well defined east of 107o15 w and these azimuths should be used preferentially when deriving new plate motion models and 2 spreading rates along the moctezuma spreading segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the moctezuma spreading segment or this spreading center is not a rivera pacific plate boundary as has been previously assumed comparison of observed transform azimuths with those predicted by the best fit poles of six previous models of rivera pacific relative motion indicate that in the study area a significant systematic bias is present in the predictions of rivera pacific motion although the exact source of this bias remains unclear this bias indicates the need to derive a new rivera pacific relative plate motion model

shape of the subducted rivera and cocos plates in southern mexico seismic and tectonic implications the geometry of the subducted rivera and cocos plates beneath the north american plate in southern mexico was determined based on the accurately located hypocenters of local and teleseismic earthquakes the hypocenters of the teleseisms were relocated and the focal depths of 21 events were constrained using a body wave inversion scheme the suduction in southern mexico may be approximated as a subhorizontal slab bounded at the edges by the steep subduction geometry of the cocos plate beneath the caribbean plate to the east and of the rivera plate beneath north america to the west the dip of the interplate contact geometry is constant to a depth of 30 km and lateral changes in the dip of the subducted plate are only observed once it is decoupled from the overriding plate on the basis of the seismicity the focal mechanisms and the geometry of the downgoing slab southern mexico may be segmented into four regions 1 the jalisco region to the west where the rivera plate subducts at a steep angle that resembles the geometry of the cocos plate beneath the caribbean plate in central america 2 the michoacan region where the dip angle of the cocos plate decreases gradually toward the southeast 3 the guerrero oaxaca region bounded approximately by the onshore projection of the orozco and o gorman fracture zones where the subducted slab is almost subhorizontal and underplates the upper continental plate for about 250 km and 4 the southern oaxaca and chiapas region in southeastern mexico where the dip of the subduction gradually increases to a steeper subduction in central america these drastic changes in dip do not appear to take place on tear faults suggesting that smooth contortions accommodate these changes in geometry the inferred 80 and 100 km depth contours of the subducted slab lie beneath the southern front of the trans mexican volcanic belt suggesting it is directly related to the subduction thus the observed nonparallelism with the middle american trench is apparently due to the changing geometry of the rivera and cocos plates beneath the north american plate in southern mexico and not to zones of weakness in the crust of the north american plate as some authors have suggested

molecular and stable isotope compositions of natural gas hydrates a revised global dataset and basic interpretations in the context of geological settings abstract a global dataset of molecular and stable isotope compositions of gases released from 209 different specimens of natural gas hydrate is presented and discussed the 26 hydrate bearing areas from 21 geographic regions are grouped into high gas flux hgf settings low gas flux lgf settings and hydrated gas accumulations hga methane ch4 is the most abundant hydrate bound gas while co2 and c2 hydrocarbon gases are frequently present in small amounts non hydrocarbon gases such as h2s are uncommon the stable isotope composition of hydrate bound gases varies significantly e g 13c of ch4 from 74 7 to 39 6 suggesting that gases of both microbial and thermogenic origin form gas hydrates hydrate bound gases are derived from autochthonous located predominantly within the gas hydrate stability zone ghsz and allochthonous located in deep sediments sources the occurrence and concentration of gas hydrates in sediments are controlled not by the origin of gases but rather by their sources which in turn strongly depend on geological setting allochthonous gases microbial and or thermogenic dominate in hgf and hga settings where they are focused in the shallow ghsz along faults within mud volcanoes in permeable carrier beds and other geological features from underlying petroleum systems relatively high concentrations of gas hydrate average 5 15 of pores and locally up to 100 of volume occurring over small areas are typical of hgf and hga settings in contrast autochthonous and diffuse allochthonous gases mostly microbial occur in stratigraphically and structurally simple lgf settings and result in relatively low concentrations of gas hydrate average 2 of pores in the ghsz spread over large areas the major implication of this finding is that successful prediction of resource and geohazard potential of gas hydrates is possible only if regional petroleum systems extending well below the ghsz are properly evaluated in addition to the diagnosis of origins and sources of hydrate bound gases molecular and isotopic data help to better identify hydrate bearing intervals and provide valuable insights into the dynamics of hydrate bearing sites

the slip history of the 1994 northridge california earthquake determined from strong motion teleseismic gps and leveling data we present a rupture model of the northridge earthquake determined from the joint inversion of near source strong ground motion recordings p and sh teleseismic body waves global positioning system gps displacement vectors and permanent uplift measured along leveling lines the fault is defined to strike 122 and dip 40 to the south southwest the average rake vector is determined to be 101 and average slip is 1 3 m the peak slip reaches about 3 m our estimate of the seismic moment is 1 3 0 2 10 26 dyne cm potency of 0 4 km3 the rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike nearly 20 km in the dip direction and there is no indication of slip shallower than about 5 to 6 km the up dip strong motion velocity waveforms are dominated by large s wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals a few seconds apart stations at southern azimuths indicate two main s wave arrivals separated longer in time about 4 to 5 sec these observations are best modeled with a complex distribution of subevents the initial s wave arrival comes from an asperity that begins at the hypocenter and extends up dip and to the north where a second larger subevent is centered about 12 km away the secondary s arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km 8 km west of the hypocenter the resolving power of the individual data sets is examined by predicting the geodetic gps and leveling displacements with the dislocation model determined from the waveform data and vice versa and also by analyzing how well the teleseismic solution predicts the recorded strong motions the general features of the geodetic displacements are not well predicted from the model determined independently from the strong motion data likewise the slip model determined from geodetic data does not adequately reproduce the strong motion characteristics whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data the strong motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong motion velocity recordings it does a poor job of predicting the geodetic data consequently a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets

gas venting and subsurface charge in the green canyon area gulf of mexico continental slope evidence of a deep bacterial methane source abstract questions as to the role of modern carbon in methanogenesis and the maximum depth of methane sources in the gulf of mexico continental slope remain unanswered a research submersible was used to sample mixed bacterial and thermal gas 13 c of methane 62 8 d 176 venting to the water column from the gulf slope in green canyon gc 286 the 14 c value of the methane 998 is consistent with fossil carbon another gas vent on gc 185 is 100 methane 13 c 62 9 d 155 and may be from a bacterial source the 14 c 997 of this bacterial methane is also consistent with fossil carbon fossil bacterial methane and thermal hydrocarbons are present in pliocene to pleistocene reservoirs 3509 4184 m of genesis field gc 205 161 160 oil in these reservoirs is biodegraded but gas is not suggesting that gas charge to reservoirs continues presently at 3 4 km depth mixed thermal and bacterial methane may charge the deep reservoirs and fossil methane from depth may ultimately vent on the sea floor at gc 286 and gc 185 results of this study of green canyon suggest that bacterial methane in gas vents and in reservoirs is from deep fossil sources

deep biogenic methane and drilling associated gas artifacts influence on gas based characterization of petroleum fluids classical interpretation of drilling mud gas molecular and isotopic data in petroleum systems can be impacted by both natural and engineering processes which can introduce allochthonous and or isotopically unrepresentative gas species this study investigates 1 widespread primary biogenic methane c1 and its impact on mud gas based petroleum system interpretation and on the properties of the petroleum fluids in the subsurface 2 differentiation of migration mixing versus diffusion leakage in petroleum systems and 3 bias introduced by gases generated at the drill bit including alkenes and isotopically changed gaseous alkanes our goal was to provide solutions to flag impacted intervals by the above processes minimize resulting interpretative bias and extract additional information about the fluid using advanced mud gas logging amgl tools and workflows an amgl interpretative methodology was developed using a combination of logs of c1 to pentane c5 concentrations and 13c c1 this approach allows identification of subsurface intervals containing nearly pure background primary biogenic c1 and can quantify its concentration per rock volume consequently thermogenic end member fluid types can be differentiated from mixtures with the biogenic c1 and assess its impact on the gas oil ratio of the mixture additionally two different processes can be responsible for mixing trends apparent on classical interpretation charts e g modified schoell diagram the presented analysis of amgl allows the deciphering of migration mixing versus diffusion leakage mixing trends using studied wells as examples another bias of mud gas based interpretation originates from artificial gases generated by drill bit metamorphism dbm evidence that dbm produced artificial alkanes in addition to alkenes via cracking of oil based drilling mud included strong correlation of concentrations among alkenes furthermore the concentration of alkenes strongly correlated with the magnitude of shift in 13c of c1 and ethane c2 between mud gas and solution gas from bottomhole fluids sampled at equivalent depths the artificial alkanes contributed by the drilling process can strongly bias and interfere with petroleum systems early interpretation based on mud gas molecular and isotopic ratios the bias depends on relative contributions of petroleum reservoir liberated mud gases and dbm gases which in this study reached half of the total c1 and c2 in the analyzed mud gas conversely alkene concentrations can be used as mud gas quality check parameters and early indicators of excess heat generated at the drill bit

stable isotope geochemistry of coal bed and shale gas and related production waters a review coal bed and shale gas can be of thermogenic microbial or of mixed origin with the distinction made primarily on the basis of the molecular and stable isotope compositions of the gases and production waters methane ethane carbon dioxide and nitrogen are the main constituents of coal bed and shale gases with a general lack of c2 hydrocarbon species in gases produced from shallow levels and more mature coals and shales evidence for the presence of microbial gas include 13c ch4 values less than 50 covariation of the isotope compositions of gases and production water carbon and hydrogen isotope fractionations consistent with microbial processes and positive 13c values of dissolved inorganic carbon in production waters the co2 reduction pathway is distinguished from acetate methyl type fermentation by somewhat lower 13c ch4 and higher d ch4 but can also have overlapping values depending on the openness of the microbial system and the extent of substrate depletion crossplots of 13c ch4 versus 13c co2 and d ch4 versus 13c h2o may provide a better indication of the origin of the gases and the dominant metabolic pathway than the absolute carbon and hydrogen isotope compositions of methane in the majority of cases microbial coal bed and shale gases have carbon and hydrogen isotope fractionations close to those expected for co2 reduction primary thermogenic gases have 13c ch4 values greater than 50 and 13c values that systematically increase from c1 to c4 and define a relatively straight line when plotted against reciprocal carbon number although coals and disseminated organic matter in shales represent a continuum as hydrocarbon source rocks current data suggest a divergence between these two rock types at the high maturity end in deep basin shale gas reversals or rollovers in molecular and isotopic compositions are increasingly reported in what is effectively a closed shale system as opposed to the relative openness in coal measure environments detailed geochemical studies of coal bed and shale gas and related production waters are essential to determine not only gas origins but also the dominant methanogenic pathway in the case of microbial gases

wavenumber spectra of pacific winds measured by the seasat scatterometer abstract vector winds measured by the seasat a satellite scatterometer sass are analyzed to determine the spatial structure of oceanic surface winds over wavelengths from 200 to 2200 km the analysis is performed in four latitudinal bands in the pacific ocean sampling characteristics of sass preclude the possibility of determining full two dimensional spectra the analysis is therefore limited to one dimensional along the satellite ground track spectra of vector wind components and kinetic energy the salient features of the results are summarized as follows i for each of the four geographic regions the spectra of meridional and zonal wind components and of kinetic energy are consistent with a power law dependence on wavenumber for midlatitude regions in both the northern and southern hemispheres the wave number dependence of kinetic energy is k 2 2 while for tropical regions in both hemisphere it is k 1 9 ii for each individual region the spectral dependence on wavenumber is nearly the same

dynamical structure and turbulence in cirrus clouds aircraft observations during fire abstract aircraft data collected during the first international satellite cloud climatology project regional experiment fire i are used to examine dynamical processes operating in cirrus cloud systems observed on 19 and 28 october 1986 measurements from lagrangian spiral soundings and constant altitude flight legs are analyzed comparisons are made with observations in clear air each cirrus case contained a statically stable layer a conditionally unstable or neutrally stratified layer ice pseudoadiabatic in which convection was prevalent and a neutral layer in which convection was intermittent the analysis indicates that a mixture of phenomena occurred including small scale convective cells gravity waves 2 9 km quasi two dimensional waves 10 20 km and larger two dimensional mesoscale waves 100 km the intermediate scale waves observed both in clear air and in the cloud systems likely played an important role in the development of the cloud systems given the magnitude of the associ

slip distribution of the 19 september 1985 michoacan mexico earthquake near source and teleseismic constraints we simultaneously invert the strong motion velocity records and the long and intermediate period teleseismic p waveforms of the 19 september 1985 michoacan mexico earthquake to recover the distribution of slip on the fault using a point by point constrained and stabilized least squares inversion method a fault plane with strike fixed at 300 and dip fixed at 14 is placed in the region of the earthquake hypocenter and divided into 120 subfaults rupture is assumed to propagate at a velocity of 2 6 km sec away from the hypocenter synthetic near source ground motions and teleseismic p waveforms for pure strike slip and dipslip dislocations are calculated for each subfault the observed data are then inverted to obtain the amount of strike slip and dip slip displacement required of each subfault we also invert the data sets using a time window procedure where the subfaults are allowed to slip up to three times this approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity inversion of the strong motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms this result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong motion recordings our simultaneous inversion of both data sets suggests that rupture during the michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150 km segment of the cocos north america plate boundary the solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6 5 meters two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter one of these sources with a peak slip of 5 meters covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km the third source region is somewhat smaller 30 km by 60 km area 3 1 meters peak slip and extends further downdip at depths between 27 km and 39 km aftershock activity following the earthquake was associated mainly with the two shallow sources these two sources are separated by the aftershock zone of the 1981 playa azul earthquake

space time interpolation of satellite winds in the tropics 1 a space time interpolator for creating average geophysical fields from satellite measurements is presented and tested it is designed for optimal spatiotemporal averaging of heterogeneous data while it is illustrated with satellite surface wind measurements in the tropics the methodology can be useful for interpolating analyzing and merging a wide variety of heterogeneous and satellite data in the atmosphere and ocean over the entire globe the spatial and temporal ranges of the interpolator are determined by averaging satellite and in situ measurements over increasingly larger space and time windows and matching the corresponding variability at each scale this matching provides a relationship between temporal and spatial ranges but does not provide a unique pair of ranges as a solution to all averaging problems the pair of ranges most appropriate for a given application can be determined by performing a spectral analysis of the interpolated fields and choosing the smallest values that remove any or most of the aliasing due to the uneven sampling by the satellite the methodology is illustrated with the computation of average divergence fields over the equatorial pacific ocean from seawinds on quikscat surface wind measurements for which 72 h and 510 km are suggested as optimal interpolation windows it is found that the wind variability is reduced over the cold tongue and enhanced over the pacific warm pool consistent with the notion that the unstably stratified boundary layer has generally more variable winds and more gustiness than the stably stratified boundary layer it is suggested that the spectral analysis optimization can be used for any process where time space correspondence can be assumed

satellite based midlatitude cyclone statistics over the southern ocean 1 scatterometer derived pressure fields and storm tracking 1 a wavelet based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the european centre for medium range weather forecasts ecmwf the resulting modified pressure fields are used to identify low pressure centers over the southern ocean and to build statistics of midlatitude cyclones during 7 years of the seawinds on quikscat operational period july 1999 to june 2006 the impact of the scatterometer derived pressure swaths is assessed with a statistical analysis of cyclone characteristics central pressure radius depth performed in parallel on the ecmwf and on the modified pressure fields more low pressure centers 5 10 depending on the season are identified with the modified pressure fields in particular incipient lows captured earlier than ecmwf and more short lived mesoscale cyclones with a life span less than 4 days the cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average a parallel spectral analysis reveals 1 additional energy at scales less than 2000 km in the modified pressure fields

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

comparison of l1 and l2 norms in a teleseismic waveform inversion for the slip history of the loma prieta california earthquake abstract broadband digital teleseismic body waves p and sh are inverted to obtain the history of slip for the 17 october 1989 loma prieta earthquake comparison of finite fault waveform inversion results using an l 1 norm and an l 2 norm reveal some basic uncertainties in the rupture history that are not usually appreciated in earthquake source studies however the more robust features of the source can be identified that are less dependent on the choice of minimization norm from a consideration of first motion data and forward modeling of body waves the strike and dip of our model fault plane are set at 126 and 67 respectively the waveform inversion results indicate that the majority of the moment release occurs over a fault length of 35 to 40 km and a depth range of 2 to 18 km the hypocenter 18 km depth experienced a relatively small amount of slip the rupture propagated upward and bilaterally with a peak slip of about 3 m occurring at a depth of 10 km the average velocity of the rupture propagation is 2 5 km sec the details of the slip distribution depend on the minimization norm but two main sources can be identified with the larger source above and to the southeast of the hypocenter the rake vector varies considerably over the fault the southern source is mostly strike slip while the northern source is approximately equally partitioned between dip slip and strike slip there is also a trend for more strike slip motion at shallower depths the majority of the moment release occurs in the first 7 5 sec with an integrated moment of 2 6 10 26 dyne cm including smaller peripheral sources that are less well resolved raises the moment estimate to 3 0 10 26 dyne cm

source time functions of large mexican subduction earthquakes morphology of the benioff zone age of the plate and their tectonic implications we study source parameters of large shallow mexican subduction zone earthquakes 95 w to 106 w which occurred between 1928 and 1986 by modeling the p waves recorded on galitzin wilip seismograph in debilt dbn holland for post 1962 events the source parameters retrieved from dbn seismograms alone agree well with those obtained from long period world wide standardized seismograph network records giving us confidence in our results for pre 1962 events all earthquakes are shallow h 10 to 20 km with few exceptions the sources in oaxaca 95 w to 99 w are very simple to the northwest of 99 w they are simple as well as complex the ratio of surface wave to body wave seismic moment mos mop which is a measure of long to short period radiation is smaller in oaxaca 1 5 0 5 than in the regions northwest of 99 w 3 1 1 3 these results suggest a change in the plate interface characteristics near 99 w the sharp change in the rupture mode and the intersection of the o gorman fracture zone ofz with the trench occur near 99 w two strike slip events offshore close to ofz suggest a segmentation of the subducting plate near 99 w the age of the plate near the trench in oaxaca is not well known it is possible that it does not increase continuously from northwest to southeast in the region but jumps across 99 w if so then the older age of the subducted plate southeast of 99 w may be the cause of the distinct rupture mode of the oaxaca earthquakes the length of the benioff zone which is greatest below oaxaca 400 km and decreases toward the northwest can be explained by the correlation between the length of the subducted slab and the product of the lithosphere age and convergence rate the relative complexity of sources the weaker background seismicity and the lesser number of aftershocks northwest of oaxaca may be explained by a stronger interface coupling resulting from subduction of younger oceanic slabs 5 to 13 m y old in this region this however explains neither larger mos mop values northwest of oaxaca nor the low stress drop estimates obtained from the analysis of near field strong motion data for the michoacan earthquake of 1985 both of which indicate weaker coupling of the interface thus the issue of whether subduction of very young plates 10 m y old results in strong or weak coupling remains unsolved from the presently available mexican data