s wave attenuation in the coastal region of jalisco colima mexico abstract aftershock data from the october 9 1995 m 7 6 earthquake that occurred in the coastal subduction region of colima jalisco mexico are used to obtain estimates of the frequency independent quality factor q s and spectral decay parameter in the approximate frequency range 3 hz f 40 hz as functions of hypocentral distance r a regression analysis results in the relations for s waves q s 261 397 3 198r 15 536 0 009651 0 000462r 0 0012 the observed distance dependence of q s and is similar to that reported for the mexican regions of oaxaca and guerrero our q s values agree with those reported for oaxaca and northern baja ca for frequencies around 8 hz and are somewhat lower a factor of 0 8 to 0 5 for higher frequencies around 20 hz however they are significantly lower than all but the lowest values reported for the guerrero region attaining factors 0 25 and 0 13 for frequency ranges around 8 and 20 hz respectively it thus appears that the guerrero region has an anomalously low attenuation compared with the flanking coastal regions of oaxaca chiapas to the se and jalisco colima to the nw

ageostrophic geopotential fluxes in downstream and upstream development of baroclinic waves abstract with the use of a simple primitive equation model it is demonstrated that the convergence divergence of ageostrophic geopotential fluxes can be a major source sink of kinetic energy for both downstream and upstream development of baroclinic waves and can play a dominant role during the early stages of wave development it is also shown that both surface friction and effects lead to an asymmetry in the upstream versus downstream development with downstream development much stronger a total group velocity is defined based on ageostrophic fluxes and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed

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 transpressive left lateral sierra madre de chiapas and its buried front in the tabasco plain southern mexico the sierra madre de chiapas evolved in the vicinity of the triple junction between the cocos north america and caribbean plates the sierra madre de chiapas tectonics reflects positive topographic growth along its main core and a northwards directed collapse through a free border related to the gulf of mexico major exhumation and topographic growth occurred during the middle late miocene 16 10 ma evidence for this deformational event is provided by fault activity major stratigraphic unconformities along the sierra madre de chiapas and the tabasco coastal plain i e southern gulf of mexico major salt related motion northward progradation of the sedimentation and northward migration of the buried deformational front during the neogene strike slip deformation and its related exhumation migrated landwards from the western edge of the chiapas massif complex to the chiapas sierra horizontal displacement along the main strike slip faults in the chiapas sierra has been indirectly estimated to be between 30 and 43 km during the last 6 5 ma implying 0 5 0 8 cm a 1 of lateral accommodation these values suggest that a significant amount of the motion transferred by the caribbean and north american plates is currently being accommodated along the chiapas area supplementary material a geological map of the sierra madre de chiapas is available at www geolsoc org uk sup18507

the oaxaca mexico earthquake of 1931 lithospheric normal faulting in the subducted cocos plate a study of the great earthquake in oaxaca mexico on 15 january 1931 shows that it was a normal fault earthquake striking east west the lack of evidence of surface faulting near the source region1 and the focal depth of 40 km inferred from body wave modelling suggest that the earthquake occurred within the subducted slab the large size of the earthquake ms 8 0 strongly suggests that the rupture broke through the entire lithosphere of the subducted cocos plate other large normal fault earthquakes in the japanese2 aleutian3 peruvian4 and sumba5 arcs show lithospheric faulting seawards of the trench or very close to it the 1931 event however occurred farther down dip in the slab 150 km landward of the trench below the bottom of what appears to be the seismogenic plate interface we speculate here that large although infrequent normal fault earthquakes such as the 1931 oaxaca earthquake may have a role in decoupling at depth the subducted slab from the upper part of the slab and perhaps from the overriding mexican continental plate the epicentral location of the 1858 michoacan earthquake6 ms 7 5 suggests that it may represent another example of lithospheric normal faulting in the middle american arc such earthquakes for which the periods of recurrence are unknown constitute an extremely high seismic risk to population centres of mexico

a geodetic study of the 2003 january 22 tecoman colima mexico earthquake we use coseismic displacements and aftershock information from global positioning system gps measurements at 27 sites in western mexico and a 12 station local seismic network to determine the characteristics of the 2003 january 22 m w 7 2 subduction thrust earthquake near tecoman colima mexico estimates of the earthquake moment slip direction and best fitting slip distribution are derived by optimizing the fit to the gps displacements for a 3 d finite element mesh that simulates the study area the calculated moment release is 9 1 10 19 n m m w 7 2 with maximum slip of 2 m at a depth of 24 km and a maximum rupture depth of 35 40 km the inversion indicates that coseismic rupture extended downdip from depths of 9 to 40 km along a 80 km along strike region that is bounded by the edges of the manzanillo trough the optimal solution is robust with respect to plausible changes in the subduction interface geometry and differing subsets of the data a comparison of the cumulative post seismic slip that can be inferred separately from earthquake aftershocks and gps measurements within a year of the earthquake indicates that 95 per cent or more of the post seismic deformation was aseismic near term post seismic measurements indicate that slip propagated downdip to areas of the subduction interface beneath the coastline within days following the earthquake as also occurred after the nearby m w 8 0 colima jalisco subduction earthquake in 1995 the similar behaviours and locations of the 1995 2003 earthquake sequence to two earthquakes in june of 1932 suggests that thrust earthquakes along the subduction interface northwest of the manzanillo trough may trigger earthquakes in the vicinity of the manzanillo trough however our modelling of coulomb stress changes caused by the 1995 earthquake indicate that it induced only modest unclamping of the subduction interface in the vicinity of the tecoman rupture in addition gps measurements indicate that elastic shortening characterized areas onshore from the tecoman rupture from mid 1997 up until the time of the rupture consistent with progressively stronger clamping of the subduction interface during this period this precludes any obvious triggering relationship with the 1995 earthquake the apparent coincidence of the edge of both the 1932 and 1995 2003 rupture sequences with the edge of the manzanillo trough may indicate that the trough is a mechanical barrier to along strike rupture propagation this implies a limit to the area of potential slip and hence rupture magnitude during future large earthquakes in this region

statistical dynamics calculations of time dependent seismicity abstract as a general methodology for long term earthquake prediction an approach involving theoretical modelling of fault dynamics has been used the time dependent properties of the seismicity are obtained by allowing the system to evolve stochastically according to statistical dynamics i e by means of a chapman kolmogorov or pauli master equation the results of these calculations are consistent with what little data is available for the distribution of intervals between major events for example in the case of oaxaca the period over which a specific section of a fault may be considered to be most dangerous is the interval between 27 and 47 years after the last event in that particular region the method may be extended to the estimation of regional hazard given the occurrence of premonitory phenomena and this has been done in the case of foreshock events

images from galileo of the venus cloud deck images of venus taken at 418 violet and 986 near infrared nir nanometers show that the morphology and motions of large scale features change with depth in the cloud deck poleward meridional velocities seen in both spectral regions are much reduced in the nir in the south polar region the markings in the two wavelength bands are strongly anticorrelated the images follow the changing state of the upper cloud layer downwind of the subsolar point and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large scale planetary waves no optical lightning was detected

the galileo venus encounter the galileo spacecraft passed venus on its way to jupiter on 10 february 1990 less than 4 months after launch from earth aboard the shuttle atlantis because galileo s instruments were selected for broad based planetary exploration the spacecraft was able to obtain a wide range of measurements during the venus encounter together with ground based observations conducted during the encounter these observations have yielded more accurate information about the planet s plasma environment cloud patterns and the possible existence of lightning

statistics of small earthquakes and frequency of occurrence of large earthquakes along the mexican subduction zone abstract the validity of the gutenberg richter g r frequency magnitude relation over a wide range of magnitudes is usually accepted and the statistics of small earthquakes is often extrapolated to predict the frequency of occurrence of large earthquakes we take noaa and pde data from 1963 to 1981 related to the mexican subduction zone h 65 km and convert m b to m s in the range of 3 3 m b 5 7 for this conversion we use regression of m s on m b for mexican and central american events as well as an m s m b regression based on worldwide data wyss and habermann 1982 we also take into account the standard error in m s this may be important since the number of events decreases as m b increases the m s data of 18 5 yr is normalized to 75 5 yr and is compared to the statistics of observed large earthquakes m s 6 4 for the period 1906 to 1981 it is found that the g r relation in the range 4 5 m s 6 0 when extrapolated grossly underestimates the observed frequency of large earthquakes m s 6 5 for the oaxaca and jalisco regions there is strong evidence that the plate interface in the oaxaca region consists of a few 3 or 4 large fault zones each of which cyclically ruptures over its entire dimension without giving rise to smaller events in the manner implied by the g r relation the result is of profound importance in seismic risk analysis and in the understanding of fault mechanics this phenomenon has been reported for only a few regions e g turkey bath 1981 japan wesnousky et al 1983 it may have escaped detection in other regions due to a variety of causes the most important being the long recurrence periods of large earthquakes

estimation of ground motion in mexico city from a repeat of the m 7 0 acambay earthquake of 1912 abstract the acambay earthquake of 1912 m 7 0 which occurred in the central trans mexican volcanic belt ctmvb about 100 km west northwest of mexico city has been thought to be a critical scenario event in the estimation of seismic hazard of the city we use seismograms of two small earthquakes located near actopan 15 december 2003 18 may 2010 and recorded at station cuig a hill zone site in mexico city as empirical green s functions egfs for the acambay region because actopan like acambay is situated in the ctmvb and both are located at about the same distance from cuig the use of the recordings of the actopan earthquakes as egfs is partly justified we first analyze data of the two small earthquakes at a local station dhig to estimate their seismic moment and stress drop as there is considerable uncertainty in the estimated stress drops of the two events we choose a reasonable range of values for them and apply a technique of random summation of egfs to simulate ground motion at cuig from a postulated m w 7 earthquake the estimated geometric mean horizontal peak ground acceleration pga and peak ground velocity pgv at cuig range from 2 7 to 9 7 cm s 2 and from 1 1 to 3 0 cm s respectively ground motion maps for the entire city are presented using a simulated trace at cuig and the known transfer functions of many sites within the city the results are consistent with reported seismic intensities in mexico city and pga and peak ground displacement pgd at a 2 s period at the seismic station of tacubaya during the acambay earthquake estimated ground motions suggest that a repeat of the event does not present significant hazard to mexico city

relationship between subduction and seismicity in the mexican part of the middle america trench two catalogs of earthquakes in the mexican part of the middle america trench are analyzed to elucidate principal relations between structure of the subducting cocos plate and seismicity a catalog of historical events that have occurred during the last two centuries with large magnitudes ms 6 0 is used to obtain cumulative seismic moment mo and seismic moment release rate m 0 distributions along the mexican subduction zone the catalog of instrumentally observed earthquakes from 1963 to 1990 international seismological center and u s geological survey with 4 5 mb 6 0 is applied to investigate background seismicity for the region the strength of coupling between the cocos and north american plates would be expected to grow gradually from the southeast to the northwest according to the variation of convergence rate v and age a of the cocos plate this correlates in general with a steady reduction in background seismicity and a slight average increase of m 0 and seismic energy release rate w at the sites where the main fracture zones of the cocos plate tehuantepec o gorman orozco and rivera undergo the subduction the general correlation breaks down the background seismicity increases at fracture zones while m0 and m 0 decrease significantly this feature is interpreted as a drop of the coupling at the areas where transform faults are being subducted seismic slip rates along the trench obtained from m 0 are lower then the values of plate convergence rates but the average seismic slip is in agreement with the estimates from the v model interaction between lithospheric plates at convergent zones through the viscous layer of subducted sediments variability of m 0 and seismic slip rate in relation with tectonics should be taken into account when the seismic gap model is being used for the prediction of strong earthquakes an examination of space time plots for the historical catalogs supposes a probable tendency of northwest migration of strong events with a rate of 10 km yr

postlandfall tropical cyclone reintensification in a weakly baroclinic environment a case study of hurricane david september 1979 abstract an analysis is conducted from a potential vorticity pv perspective of the reintensification of tropical storm david over the northeastern united states in september 1979 david a major long lived hurricane originated near the cape verde islands in late august 1979 it made final landfall in georgia on 4 september 1979 and weakened rapidly thereafter the noteworthy aspect of david was its subsequent reintensification approximately 27 h after landfall as a warm core disturbance in a weakly baroclinic environment in this regard the redevelopment of david is unlike the classical extratropical transformation of a tropical storm in a strongly baroclinic environment that has been documented in the literature the authors analysis of the evolution of the dynamical tropopause subsequent to storm landfall revealed that david reintensified in response to tropopause lifting upward displacement of the dynamic tropopause ahead of a nondeepening and otherwise very weak upper tropospheric disturbance

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

attenuation of modified mercalli intensity with distance in mexico abstract two relations are proposed to predict the attenuation of modified mercalli intensity i with distance d for mexican earthquakes i e ln i b 0 b 1 ln d d 9 b 2 d d 9 b 3 ln m s ln i b 0 b 1 d d 9 b 2 ln d d 9 b 3 ln m s m s is the earthquake surface wave magnitude d is a distance related to the maximum i mapped for an earthquake i or to m s the coefficients b i i 0 1 2 3 were obtained by fitting in a least square sense the information contained in the intensity maps of 32 events to the relations those events were classified in three groups according to their epicentral location focal mechanism and depth i e events related to the subduction zone intermediate depth earthquakes in south central mexico and to shallow crustal events along the trans mexican volcanic belt the i predicted by the proposed relations compare well with the i observed for historical earthquakes not included in the fitting results obtained from a parametrical study showed that the attenuation of i with d is different for each of the three types of earthquakes for distances of less than about 200 km the earthquakes associated with the subduction zone have a larger attenuation than the ones originating in the south central region of mexico for greater distances d 200 km the opposite behavior is observed the events located in the trans mexican volcanic belt have a larger attenuation with distance than that of events in the other two regions from these results it seems advisable in mexico to use several attenuation relations to estimate the seismic hazard at a site depending on the particular tectonic setting and the path of the events under consideration

earthquake recurrence of a particular type the recurrence relation for turkish earthquakes expressed as the single frequency versus magnitude dependence exhibits significant maxima and minima reflecting true physical conditions various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity the results may be applicable to regions with high seismicity

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

patterns of local seismicity preceding the petatlan earthquake of 14 march 1979 local seismic activity m 2 3 during the 4 1 2 day period preceding the petatlan earthquake of 14 march 1979 ms 7 6 was monitored by a seismic network deployed by the hawaii institute of geophysics these data allow us to revise the location of that event and to study its pattern of foreshocks the foreshock hypocenters are concentrated above the ocean continent plate boundary and landward of the hypocenter of the main shock the spatial distribution of foreshocks suggests that the foreshocks occurred along existing zones of weakness within the continental plate during the 1 1 2 day period preceding the petatlan event foreshocks were concentrated within 100 km of the epicenter of that earthquake the pattern of precursory seismic activity we observed during that period is similar to that observed during the same time period prior to the oaxaca earthquake of 29 november 1978 however the 17 hr period of seismic quiescence for events with m 2 8 preceding the oaxaca earthquake is not found in our data where a magnitude 4 foreshock occurs within 28 min of and 2 km from the petatlan event this suggests that the spatially larger set of foreshocks may have greater diagnostic value than does the sequence of precursory events within 30 km of the main shock

the nature of the near infrared features on the venus night side near infrared images of the venus night side show bright contrast features that move from east to west in the direction of the cloud top atmospheric superrotation recently acquired images of the venus night side along with earlier spectroscopic observations allow identification of the mechanisms that produce these features their level of formation and the wind velocities at those levels the features are detectable only at wavelengths near 1 74 and 2 3 micrometers in narrow atmospheric windows between the co 2 and h 2o bands the brightest features have brightness temperatures near 480 kelvin whereas the darkest features are more than 50 kelvin cooler several factors suggest that this radiation is emitted by hot gases at altitudes below 35 kilometers in the venus atmosphere the feature contrasts are produced as this thermal radiation passes through a higher cooler atmospheric layer that has horizontal variations in transparency the 6 5 day east west rotation period of the features indicates that equatorial wind speeds are near 70 meters per second in this upper layer similar wind speeds have been measured by entry probes and balloons at altitudes between 50 and 55 kilometers in the middle cloud layer the bright features indicate that there are partial clearings in this cloud deck the presence of these clearings could decrease the efficiency of the atmospheric greenhouse that maintains the high surface temperatures on venus

a stochastic model for site ground motions from temporally dependent earthquakes a stochastic model is presented for estimating probabilities of exceeding site ground motions due to temporally dependent earthquake events the model reflects the hypothesized dependence of the size of large earthquake events on the time of occurrence of the last major earthquake an empirical attenuation relationship is used to describe the ground motion at a site originating from a well defined fault system the application of the model to the middle america trench is discussed the seismic hazard potential in mexico city is computed in terms of probabilities of exceeding peak ground acceleration levels the results indicate that consideration of the seismic gap is important for estimating the seismic hazard at a site it is also observed that site hazard estimates are greatly dependent on the specific attenuation relationship used the need for other approaches of ground motion estimation is recognized

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

geometry and state of stress of the wadati benioff zone in the gulf of tehuantepec mexico 1 data recorded in the gulf of tehuantepec and published moment tensor solutions were used to infer the geometry of the wadati benioff zone w b zone and the stress distribution of the subducted cocos plate from northwest to southeast the subducted slab gently increases its dip bends up at depths of the order of 100 km and about 240 km inland from the trench then unbends and increases its dip toward the southeast below chiapas contour lines of equal depth at 50 and 100 km show a significant contortion of the w b zone west of the isthmus of tehuantepec and coincide with significant changes in the topographic features of the crust we calculated a vp vs ratio of 1 75 for the whole area and a moho depth in the gulf of tehuantepec of 28 5 3 5 km near the trench along the coupling zone t axes of interplate and intraplate earthquakes are oblique to the interface and parallel to the dip direction of the subducted plate respectively at depths greater than 50 km the t axes are roughly horizontal best fit stresses using the gephart and forsyth 1984 code resulted in the following variation of the minimum stresses t axes from northwest to southeast as plunge azimuth 3 40 37 to 3 28 72 then to 3 11 54 and finally to 3 27 35 we also analyzed recordings from the 30 september 1999 oaxaca earthquake mw 7 5 and its aftershocks we inferred an approximate fault area of 80 by 30 km inside the subducted cocos plate

paleoseismology of the 1912 acambay earthquake and the acambay tixmadeje fault trans mexican volcanic belt the acambay graben is a major intra arc basin of the trans mexican volcanic belt trenching studies at four sites along the acambay tixmadeje fault reveal evidence for the 1912 acambay earthquake and at least four late pleistocene and holocene ground rupturing earthquakes with similar displacements to the 1912 event evidence for multiple events was recognized by a combination of upward terminating faults fissure fills erosionally truncated fissures colluvial wedge fills and downward increasing separation of stratigraphic units sites along the central part of the ese wnw trending rangefront fault indicates large dip slip separations across a multi event scarp in holocene colluvium with a penultimate event that occurred since 5230 calibrated years before present cal yr b p on the huapango plain near the eastern end of the 1912 rupture where slip was oblique the penultimate earthquake occurred after 4700 cal yr b p and there is evidence for at least four more earthquakes in the last 34 000 cal yr b p three dimensional excavation of lacustrine and channel deposits at las lomas yields a left normal slip vector of s40 5 e with 105 10 cm of slip for the last three events there this slip vector is consistent with nne oriented extension across the graben the amount and style of slip documented for prehistoric ruptures are also consistent with the 1912 rupture with a mean of 60 cm event of dip slip on the rangefront and a mean of 35 cm event of oblique slip on the n48 w trending huapango plain assuming these values represent a characteristic behavior yields an average recurrence interval of 3600 years for the last four large earthquakes since 11 570 cal yr b p and a slip rate of 0 17 mm yr across the rangefront empirical earthquake parameters calculated from our paleoseismic data support instrumental measures indicating that the 1912 acambay earthquake was of m 6 8 7 0 the 1912 event is representative of ground rupturing earthquakes on the acambay tixmadeje fault and demonstrates that large seismic events m 7 can be generated by faults in the trans mexican volcanic belt and in other intra arc settings

the theoretical seismicity of asperity models an application to the coast of oaxaca summary we solve the statistical dynamical equations of an asperity model to obtain both the time dependent seismicity and the stationary seismicity with its associated magnitude frequency relation the parameters of the model are chosen to reproduce the seismicity of the oaxaca region on the western coast of mexico the observed enhancement of the seismicity in the high magnitude range is well reproduced and the calculated b value of about 7 is also acceptable the predicted features of the time dependent seismicity are as follows there is an enhancement of the small scale seismicity immediately following a characteristic earthquake this enhancement approximately doubles the rate of occurrence of small events relative to the stationary values both intermediate and characteristic earthquakes present a gap with a subsequent enhancement of the seismicity superior to long term averages there are strong correlations between the characteristic and intermediate seismicities indicating that the latter have premonitory value

seismic gaps and recurrence periods of large earthquakes along the mexican subduction zone a reexamination abstract seismic gaps and recurrence periods of large shallow interplate earthquakes along the mexican subduction zone are reexamined after combining information from a catalog of nineteenth century9s earthquakes some relocated epicenters of the early part of this century source parameters of recent large earthquakes and redetermined magnitudes of great shallow earthquakes of this century tehuantepec and michoacan gaps have not experienced a large shock in this century and perhaps none in the past century they are either aseismic or have anomalously large repeat times guerrero jalisco and ometepec regions presently appear to have a high seismic potential observed average repeat times of large earthquakes m s 7 4 in six regions east central and west oaxaca san marcos petatlan and colima are between 32 to 56 yr data of this century indicate that the strain is released mostly in large events m s 7 4 a simple dislocation model with parameters obtained from the studies of recent earthquakes explains the observed recurrence periods quite well the b value for this zone is not meaningful an observation which is of significance for seismic risk estimation most of seismic moment or equivalently seismic energy release since 1800 appears to occur for 15 yr followed by relative quiescence in the next 15 yr

sedimentary and microfossil imprint from historical earthquakes and tsunamis jalisco coast mexican subduction abstract tsunamis are high energy events capable of leaving their imprint in the geological record the western mexican pacific coast located in the mexican subduction zone is prone to large earthquakes m 8 0 where tsunami hazard has been underrated the geologic archive obtained in a sheltered coastal lagoon was analyzed applying a multi proxy approach to reveal the occurrence of historical earthquakes in the jalisco coast foraminifera and ostracoda aid identifying earthquake and tsunami geologic evidence in this section of the mexican pacific coast where tropical conditions prevail we present the evidence of changes in stratigraphy grain size biostratigraphy supported by archaeomagnetic dating they were complemented with published 210pb dating magnetic properties and historical data we identified three events the tsunami deposit left by the june 3rd 1932 tsunami produced by the largest earthquake m 8 2 recorded in instrumental history in mexico and the coseismic deformation resulting from the 1932 event also a probable tsunami deposit likely produced by an historical earthquake in 1900 and the coseismic deformation associated to this event and the coseismic deformation resulting produced by the 1563 earthquake the site geomorphology with a marginal lagoon closed by a little barrier 7 m 1 m above sea level precludes tropical storms as responsible for marine incursions this work contributes to strengthening the earthquake and associated tsunamis chronology aiming to improve coastal hazard assessment for the area

conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone abstract time dependent conditional probabilities for the recurrence of large and great interplate earthquakes along the mexican subduction zone are presented for time intervals of 5 10 and 20 yr duration i e 1986 1991 1986 1996 and 1986 2006 at present the central oaxaca 97 3 to 97 7 w ometepec san marcos 98 2 to 99 5 w and central guerrero 100 to 101 w segments stand out as having the highest probability for the recurrence of large and great earthquakes in the near future segmentation of the margin is delineated by the rupture zones of the most recent earthquakes occurring in each area for segments of the mexican margin with one or more known recurrence intervals probability estimates are based on the observed average recurrence time for each segment and the lognormal probability distribution function use of a generic distribution function nishenko and buland 1987 allows a more stable estimate of average recurrence times than are available from a few observations a long term prediction time window is also defined based on the 90 per cent confidence interval for our estimates of the recurrence time use of a predetermined confidence interval conveys valuable additional information as to the precision and information content of the forecast for those segments of the margin with only one prior event and hence no historically observed recurrence times repeat times are estimated by extrapolating the observed recurrence time behavior in oaxaca subject to the assumptions that recurrence time scales only as a function of the ratio of seismic displacement and convergence rate and that all events are characterized as simple sources i e involve the rupture of a single asperity

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

theoretical calculations of the seismicity in oaxaca mexico the time dependent and time independent seismicity of the coast of oaxaca mexico is computed by solving the statistical dynamic equations of an asperity model the observed enhancement of the seismicity in the large magnitude range associated with characteristic earthquakes is well reproduced and the calculated b value of about 0 7 is also acceptable the predicted features of the time dependent seismicity are as follows there is an enhancement of the small scale seismicity immediately following a characteristic earthquake this enhancement approximately doubles the rate of occurrence of small events relative to the stationary values both intermediate and characteristic earthquakes present a gap with a subsequent enhancement of the seismicity superior to long term averages the predicted gap for large events is 17 yrs and the most likely interoccurrence time between characteristic earthquakes is 37 yrs with the most hazardous period being the interval 27 48 yrs after the previous event there is a maximum in the intermediate seismicity which precedes the maximum in characteristic seismicity indicating that these factors are of predictive value as foreshocks

the quetzalapa pumice a voluminous late pleistocene rhyolite deposit in the eastern trans mexican volcanic belt the study area is located in the east part of the trans mexican volcanic belt in the las cumbres volcanic complex lcvc which lies between two large stratovolcanoes pico de orizaba 5700 m a s l to the south and cofre de perote 4200 m a s l to the nne the most conspicuous structure of the lcvc is a 4 km diameter circular crater with a dacitic dome in the center which constitutes the remains of a destroyed stratovolcano the quetzalapa pumice qp was produced by a plinian eruption that was dated by the 14c method at 20 000 yr bp the eruptive sequence consists predominantly of pumice fall deposits and scarce intra plinian pyroclastic flow deposits which crop out on the west flank of the lcvc the absence of post plinian ignimbrite deposits is striking the deposits are well sorted clast supported with reverse grading at the base with a medium to high accessory lithics content the maximum average thickness of the deposit in the proximal areas is about 15 m and has been divided into three members the basal member bm 2 m thick with four submembers bmf1 bmf2 bmf3 and bmafl the intermediate member im 10 m thick with two submembers impf and imaf and the upper member um 3 m thick with four submembers umpl umsdf umwaf and umpls the predominant component of the fall deposits is a white highly vesiculated pumice with 71 sio2 content plagioclase is the most abundant mineral followed by 1 3 mm long biotite phenocrysts the accessory lithics are lavas mostly of andesitic composition their abundance increases toward the uppermost levels of the sequence we calculate a minimum volume of 8 4 km3 2 22 km3 dense rock equivalent for the entire qp deposit isopach and isopleth maps show that the im deposit has an elongated distribution with a nne ssw direction whereas the um deposit has a circular distribution we estimate a maximum eruptive column height for the im of 20 km field studies and isopach and isopleth maps indicate that the eruptive column was affected by a strong wind previous studies located the qp source in the las cumbres crater however based on the isopach and isopleth distribution and the lack of pumice fall deposits inside the las cumbres crater we consider that the qp emission center is located on the west flank of the lcvc and was buried by its own pumice fall deposits it coincides with an explosion crater called la capilla formed during the closing phase of the qp eruption a pumice fountain model is proposed to explain the observed sequence of deposits according to this model the material was emitted through a hose type conduit during a monogenetic eruption of rhyolitic composition this kind of volcanic activity is not extensively reported in the literature

space time clustering of large thrust earthquakes along the mexican subduction zone an evidence of source stress interaction the spatiotemporal plot of epicenters of large m s 6 9 subduction earthquakes in mexico 1900 to present day suggests that these earthquakes cluster in space and time in this work we test the hypothesis that the coseismic stress transfer may lead to this clustering for the analysis we estimate the spatial extent of the coseismic coulomb stress change for these large events and then perform a statistical analysis using the 2 goodness of fit test for the interevent time intervals we find that there are at least two groups of time intervals where the observed frequencies are much higher than that expected from a poisson model indicating a bimodal pattern for the first mode the observed frequencies for the 0 to 5 year interval becomes about 2 1 times the expectation with a probability of occurrence of about 30 these results show that large thrust mexican earthquakes between 1900 and 2003 are clustered in space and time probably due to stress interactions among them the second mode includes the time interval of 30 50 years in the interval of 30 40 years the observed frequencies become about 1 7 times the expectation and about 1 2 times the expectation for the 40 to 50 year interval this second mode could be associated with a reloading interval of tectonic stress due to the plate convergence and appears consistent with the long term recurrence periods of large thrust earthquakes in the mexican subduction zone

macroseismic study of shallow earthquakes in the central and eastern parts of the trans mexican volcanic belt mexico we present isoseismal maps for eight shallow earthquakes 1887 pinal de amoles 1912 acambay 1920 jalapa 1950 ixmiquilpan 1976 cardonal 1979 maravatio 1987 actopan and 1989 landa 4 1 mb 6 9 that occurred in the central and eastern parts of the trans mexican volcanic belt based on their intensity distributions we can relate several of these earthquakes to east west striking quaternary normal faults known from geological observations furthermore we derive for these events by empirical curve fitting linear relations between the magnitude calculated from the instrumental record the intensity distribution and the maximum intensity the comparison of these relations with equations from the literature suggests that the area shaken with a certain intensity by an earthquake in the trans mexican volcanic belt is approximately 10 times smaller than the area shaken by a shallow earthquake of the same magnitude in the intracratonic part of north america moreover we use the derived relationships between magnitude isoseismal area and maximum intensity to estimate the intensity magnitude mi of the 1887 pinal de amoles earthquake as 5 3 0 5

seismic strain release in the mexican subduction thrust abstract in this paper the seismic strain release in the mexican subduction zone is discussed the paper is based on a revised catalog of large earthquakes in mexico new in this catalog are estimates of the seismic moment for many of the larger pre 1962 earthquakes of this century based on instrumental recordings from uppsala sweden a regression between moment and magnitude is established and used to estimate moments for the remaining events of this and the previous century the envelopes of the cumulative seismic moment curves can thus be developed consistent with the nineteenth century seismicity these indicate that the guerrero region is currently the most likely within the mexican subduction zone to experience one great event or several large events with a moment deficit approaching 20 10 27 dyn cm this is comparable with the moment released between 1899 and 1912 in the region in guerrero and also perhaps in michoacan the seismic strain release is consistent with plate tectonic expectations for a seismogenic zone 50 km in width in oaxaca either the seismogenic zone is much narrower and there is considerable aseismic slip or events to rupture the downdip extremes of the subduction zone have not occurred so far this century this last alternative arises because in guerrero the 1907 and 1957 earthquakes have relatively strong 40 s surface waves recorded at uppsala compared with all the other events such events which we infer are deeper present new problems for seismic hazard estimation in mexico since they are not represented in the available strong motion records

multiple edifice collapse events in the eastern mexican volcanic belt the role of sloping substrate and implications for hazard assessment abstract the citlaltepetl cofre de perote volcanic chain forms an important physiographic barrier that separates the central altiplano 2500 masl from the gulf coastal plain gcp 1300 masl the abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the altiplano eastward sloping substrate caused by the irregular configuration of the basement rocks is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the gcp these collapses produced voluminous debris avalanches and lahars that inundated the well developed drainages and clastic aprons that characterize the coastal plain large catastrophic collapses from citlaltepetl las cumbres and cofre de perote volcanoes are well documented in the geologic record some of the avalanches and transformed flows have exceptionally long runouts and reach the gulf of mexico traveling more than 120 km from their source so far no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank collapses apparently instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration abrupt topographic change and intense fracturing in addition to the eastward slope of the substrate the reactivation of pre volcanic basement structures during the late tertiary and the e w to ene ssw oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows in addition to magmatic hydrothermal processes high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks it is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the eastern mexican volcanic belt however critical pore water pressure from extraordinary amounts of rainfall associated with hurricanes or other meteorological perturbation cannot be ruled out particularly for smaller volume collapses there are examples in the area of small seismogenic debris flows that have occurred in historical times showing that these processes are not uncommon assessing the stability conditions of major volcanic edifices that have experienced catastrophic sector collapses is crucial for forecasting future events this is particularly true for the eastern mexican volcanic belt where in many cases no magmatic activity was associated with the collapse therefore edifice failure could occur again without any precursory warning

p waveform of large shallow earthquakes along the mexican subduction zone abstract we combine qualitative analysis of wiechert seismograms with quantitative analysis of galizin wilip and press ewing seismograms from europe to draw conclusions regarding simplicity complexity of p waveforms of large shallow earthquakes since 1907 which occurred along the mexican subduction zone these seismograms are compared with lp wwssn seismograms of recent earthquakes it is found that the earthquakes in oaxaca are simple with two exceptions the earthquake of 15 january 1931 m s 8 0 was a complex intraplate event with normal or strike slip faulting some earthquakes are simple and others are complex in the subregions of guerrero and michoacan all three earthquakes in jalisco are complex the depths of the events are shallow 10 h 20 km with the majority being at 16 km the simplicity of events the evidence of a characteristic magnitude of m s 7 8 and the ratio of surface wave to p wave seismic moment of about 1 5 in oaxaca suggest rather homogeneous asperities of nearly equal dimension separated by barriers elsewhere the interface of the plates is characterized by smaller asperities of differing sizes separated by areas where aseismic deformation may occur the earthquakes of 22 february 1943 m s 7 7 and 14 march 1979 m s 7 6 which were supposed to have broken the same area show drastically different p waveforms it appears that the location of the 22 february 1943 earthquake is in error alternatively the same area may have been broken with entirely different rupture processes

playa azul michoacan mexico earthquake of 25 october 1981 ms 7 3 abstract the playa azul earthquake broke the central part of the michoacan gap along the mexican subduction zone the aftershock area estimated from field data for a 6 day period beginning 19 hr after the main shock is 40 km 20 km preliminary focal mechanism of the main shock is consistent with a shallow dipping thrust fault although there is some evidence of seismic quiescence for 5 1 2 yr followed by a foreshock about 3 months before the main shock and an above average microseismic activity in the western part of the epicentral region during the last 4 1 2 months or more the data is not sufficient quality to assert this conclusion the michoacan gap was previously assigned category 3 singh et al 1981 based on the classification of mccann et al 1979 the seismic potential of the unbroken segments of this gap 45 km to nw and 35 km to the se of the playa azul aftershock area remains uncertain corresponding to a rupture length of 40 km each segment could generate an earthquake of similar magnitude to the playa azul earthquake unfortunately the recurrence period of large earthquakes in the region is not known and great major earthquakes cannot be ruled out

regional variation in the number of aftershocks mb 5 of large subduction zone earthquakes mw 7 0 it is reasonable to expect that the number of aftershocks following a large earthquake should reflect the degree of heterogeneity on and near the fault plane to investigate this question we plot n the number of aftershocks with mb 5 0 occurring within the next 30 days after large subduction zone thrust faulting earthquakes mw 7 0 versus the magnitude mw of the main shock only earthquakes that occurred after the installation of the world wide standard seismographic network stations are considered because the detection threshold of aftershocks in many regions is greater than mb 5 0 n is obtained by fitting the data to gutenberg and richter s relation log n a b mb for the same mw n varies by a factor of about 40 in different regions n is less than expected in the eastern pacific including alaska and is greater than expected in the western pacific relative lack and excess of n correlates well with regions of supposedly strong and weak coupling respectively while small and large n also show some correlation with the expansion rate of aftershock area with time the variation in n is much larger than would be expected from the mere increase of aftershock areas in some cases it appears that the number of aftershocks n for earthquakes of similar mw may also reflect the complexity and enrichment of the p wave amplitude spectra from 1 to 10 sec for example the valparaiso chile earthquake of 1985 mw 8 0 generated n 46 earthquakes whereas for the michoacan mexico event of 1985 mw 8 1 n is only equal to 5 furthermore for the valparaiso earthquake p waveforms are much more complex and the spectra are more energetic at 1 to 10 sec as compared to the 1985 michoacan event

times of increased probability of large earthquakes ms 7 5 along the mexican subduction zone abstract using the method of pattern recognition of infrequent events we explore the possibility of identifying the times of increased probability tip of occurrence of large earthquakes ms 7 5 along the mexican subduction zone a tip refers to a 5 year period within which a strong earthquake has a high probability of occurrence we analyzed the seismicity for the regions of chiapas eastern oaxaca 91 97 w region 1 western oaxaca guerrero 97 102 w region 2 and michoacan colima jalisco 102 106 w region 3 for the time interval 1970 1991 with the national oceanic and atmospheric administration seismic catalog as the source data the premonitory intermediate term seismic activation to identify a tip was measured using the algorithm m8 three out of the five earthquakes of ms 7 5 that occurred during the studied period are diagnosed by algorithm m8 and for the region 3 segment a tip is identified that will end between 1994 and 1996 we consider the area between the western colima gap and the jalisco region 103 7 106 0 w as the zone where the forecast earthquake has a higher than usual probability of occurrence our results by no means constitute a definitive earthquake prediction but suggest the need for detailed seismic analysis and the study of other geophysical precursors along the colima jalisco segment

a catalog of shallow earthquakes of mexico from 1900 to 1981 a catalog of shallow earthquakes depth 65 km of mexico 15 to 20 n 94 5 to 105 5 w covering the period 1900 to 1981 is presented the catalog includes only those events whose magnitudes m ms or magnitude from pasadena are 5 9 it is most likely complete for shocks with ms 6 5 from july 1906 to december 1981 for many shocks ms has been determined from uppsala bulletins and or uppsala and gottingen wiechert seismograms the statistics of incremental frequency n ms shows a peak at ms 7 7 reinforcing a previous observation by singh et al 1981 in the range 6 4 ms 7 5 the observed n ms deviates significantly from an exponential distribution the catalog provides a basis for further statistical analysis of earthquakes in mexico

earthquake induced landslides in central america central america is a region of high seismic activity and the impact of destructive earthquakes is often aggravated by the triggering of landslides data are presented for earthquake triggered landslides in the region and their characteristics are compared with global relationships between the area of landsliding and earthquake magnitude we find that the areas affected by landslides are similar to other parts of the world but in certain parts of central america the numbers of slides are disproportionate for the size of the earthquakes we also find that there are important differences between the characteristics of landslides in different parts of the central american isthmus soil falls and slides in steep slopes in volcanic soils predominate in guatemala and el salvador whereas extensive translational slides in lateritic soils on large slopes are the principal hazard in costa rica and panama methods for assessing landslide hazards considering both rainfall and earthquakes as triggering mechanisms developed in costa rica appear not to be suitable for direct application in the northern countries of the isthmus for which modified approaches are required

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

the extratropical transition of tropical cyclone edisoana 1990 abstractdocumentation of southwest indian ocean swio tropical cyclones tcs and extratropical transition et events is sparse in the refereed literature the authors present a climatology of swio tc and et events for 1989 2013 the swio averages 9 tropical cyclones tcs per year in this modern era of these tcs 44 undergo extratropical transition et or four per year a case study of tc edisoana 1990 the most rapidly intensifying swio post et tc between 1989 and 2013 shows that extratropical interactions began when an approaching trough embedded in the subtropical jet stream stj induced et on 7 march as edisoana underwent et a subtropical ridge downstream amplified in response to poleward directed positive potential vorticity pv advection associated with diabatically convectively driven upper level outflow from tc edisoana this amplifying lower latitude ridge phased with a lower amplitude higher latitude ridge embedded in the polar front jet pfj resulting in the merger of the t