eddy resolving observation of the north pacific subtropical mode water abstracthydrographic data obtained by high resolution shipboard observations and argo profiling floats have been analyzed to study the mesoscale structure and circulation of the north pacific subtropical mode water stmw the float data show that in the late winter of 2008 stmw having a temperature of approximately 18 8 17 7 and 16 6 c formed west of 140 e at 140 150 e and east of 150 e respectively in the recirculation gyre south of the kuroshio extension after spring the newly formed stmw gradually shift southward decreasing in thickness simultaneously the stmws of 16 6 and 17 7 c are gradually stirred and then mixed in terms of properties in late fall they seem to be integrated to form a single group of stmws having a temperature centered at 17 2 c such stmw circulation in 2008 is much more turbulent than that in 2006 which was investigated in a previous study the difference between the two years is attributed to the more variable state of the kuroshio extension in 2008 associate

surface wave dispersion analysis in mexico city abstract in this article we present an observational investigation of ground motion at mexico city focused on surface waves our purpose is 2 fold first to understand incident ground motion during the great michoacan earthquake of 19 september 1985 and second to characterize surface waves propagating in the lake bed zone to this end we analyze the strong motion records obtained at mexico city for the large m s 8 1 earthquake of 19 september 1985 it is shown that in the low frequency range we observe the rayleigh fundamental mode in both the vertical and the radial components and the love fundamental mode in the transverse component at all the strong motion stations the vertical component also shows the first higher mode of rayleigh waves we use a very broadband record obtained at station cu for the smaller m s 6 7 earthquake of 14 may 1993 to verify that the dispersion computed from the model of campillo et al 1989 represents well the average surface wave propagation between the coast and mexico city in the 7 to 10 sec period range we use this result to assign absolute times to the strong motion records of the michoacan event this allowed us to identify additional wave trains that propagate laterally in directions other than great circle in the 3 to 5 sec period range these wave trains are identified as love waves in a second analysis we study a set of refraction data obtained during a small scale 250 m experiment on the virgin clay of the lake bed zone phase velocity dispersion curves for several modes of rayleigh waves are identified in the refraction data and inverted to obtain an s wave velocity profile this profile is used as the uppermost layering in a 2d model of mexico city valley the results of numerical simulation show that surface waves generated by lateral finiteness of the clay layer suffer large dispersion and attenuation we conclude that surface waves generated by the lateral heterogeneity of the upper most stratigraphy very significantly affect ground motion near the edge of the valley but their importance is negligible for distances larger than 1 5 km from the edge thus locally generated surface waves propagating through the clay layer cannot explain late arrivals observed for the 1985 event we suggest that the long duration of strong motion is due to the interaction between lateral propagation of waves guided by deep layers 1 to 4 km and the surficial clay layer this interaction is possible by the coincidence of the dominant frequency of the uppermost layers and the frequency of the deeply guided waves

barrier effect on mjo propagation by the maritime continent in the mjo task force gewex atmospheric system study models abstractthe simulated madden julian oscillation mjo events in 27 general circulation models gcms are identified using an mjo tracking method the results suggest that the occurrence frequencies

analysis of wave induced pore pressure changes recorded during the 1980 mammoth lakes california earthquake sequence abstract acceleration and wave induced pore pressure were recorded in a saturated sand during the 1980 mammoth lakes california earthquake sequence for the largest event recorded the pore pressure was observed to be proportional to vertical surface acceleration during the p wave arrivals and proportional to horizontal surface velocity during the s wave arrivals the results can be quantitatively explained with a linear elastic model of a porous saturated medium such that pore pressure depends on dilatation and is independent of shear strain a slight frequency dependence in the ratio of pore pressure to dilatation indicates local fluid flow on the scale of individual pores the good agreement between observations and theory indicates that the deformation was primarily linear even though maximum shear strains were close to the typical thresholds for liquefaction

possible resonance effect in the distribution of earthquake damage in mexico city the destruction caused by the earthquake of 19 september 1985 in mexico city shows three remarkable features1 first a concentration of damage in the former lake bed second a peculiar distribution of high and low damage areas alternating within a few city blocks and third a selectivity for buildings between five and fifteen storeys high while the last point is understood by civil engineers2 and the first confirms the relevance of the soft ground the second feature is the most puzzling to a physicist such a pattern evokes the idea of a standing wave with low and high damage areas corresponding to nodes and antinodes this suggests a resonance phenomenon of the waterlogged ground moving collectively from the navier equations of classical elasticity it is known3 that a transfer of the incoming seismic wave energy to longitudinal waves takes place if a sharp change from hard to soft ground exists solving then the two dimensional poisson equation for the longitudinal waves within the ancient lake boundaries we show that for the observed seismic wave period of 2 s a standing wave solution exists which explains qualitatively the damage distribution pattern

erratum to observation and prediction of dynamic ground strains tilts and torsions caused by the mw 6 0 2004 parkfield california earthquake and aftershocks derived from upsar array observations online material corrected figures and strain rotation and displacement gradient time series

formation and spreading of subtropical mode water in the north pacific a time averaged description of the formation and spreading of north pacific subtropical mode water npstmw is presented the formation of npstmw is studied using transpac expendable bathythermograph data the data are transformed into a stream coordinate system and averaged the coordinate system uses the position of the kuroshio front as its origin maps are presented of the temperature structure and mixed layer distribution in winter relative to the kuroshio front the formation of npstmw occurs in two separate stages cooling and thickening as water flows at the surface in the kuroshio in winter the water is cooled by the intense ocean atmosphere heat flux taking place in the area when water leaves the kuroshio to the south the thermocline underneath becomes deeper convection is able to penetrate deep into the water column and the heat flux acts more to thicken the surface mixed layer rather than reduce the temperature the area south of the kuroshio where relatively homogeneous waters are found is the source region for npstmw at the end of the winter the thick mixed layers are assumed to be covered over by a seasonal thermocline and become npstmw the levitus 1982 data are used to study the way in which npstmw is spread away from its source region by the subtropical circulation the distribution of potential vorticity pv on four npstmw isopycnals is studied with low pv used as a tracer for npstmw the pv reveals a pattern of differential spreading whereby npstmw formed in the western part of the source region is advected to the west after its formation npstmw formed farther east is advected more to the south or east after formation differential spreading allows npstmw to be found in a large part of the northwestern subtropical gyre well away from its source region the distribution of npstmw described by masuzawa 1969 with npstmw getting colder from west to east is explained as a combination of the distribution of npstmw at its source and the way it is spread after it is formed

impact of aleutian low activity on the stmw formation in the kuroshio recirculation gyre region 1 to understand the formation of north pacific subtropical mode water stmw in the kuroshio recirculation gyre region the cause of stmw thickness variation is investigated using temperature profiles in a historically archived data set the thickness variation is predominantly controlled by the main thermocline depth mtd when the main thermocline deepens shoals the wintertime mixed layer depth can develop not develop and consequently thicker thinner stmw is observed in summer the large scale atmospheric forcing controlling the mtd is explored using a wind driven hindcast ocean model the mtd variation stems primarily from a baroclinic response in the ocean to the aleutian low al activity especially the meridional movement of the al exerts a remarkable influence

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

marked freshening of north pacific subtropical mode water in 2009 and 2010 influence of freshwater supply in the 2008 warm season 1 changes in salinity of the north pacific subtropical mode water stmw were investigated using profiles for 2003 2011 in 2009 and 2010 the stmw freshened markedly s 34 7 psu with salinity 0 1 psu lower than other years freshening in 2009 was caused by excess rainfall in the 2008 warm season which was related to an increase in the number of low pressures passing over the stmw formation region associated with a southeastward shrinkage of the summertime north pacific subtropical high the freshening signal persisted under the seasonal pycnocline during the 2009 warm season this resulted in the freshening of stmw in 2010

role of the boundary layer moisture asymmetry in causing the eastward propagation of the madden julian oscillation the moisture budget associated with the eastward propagating madden julian oscillation mjo was diagnosed using 1979 2001 40 yr ecmwf re analysis era 40 data a marked zonal asymmetry of the moisture relative to the mjo convection appears in the planetary boundary layer pbl below 700 hpa creatingapotentiallymoreunstablestratificationtotheeastofthemjoconvectionandfavoringtheeastward propagation of mjo the pbl integrated moisture budget diagnosis indicates that the vertical advection of moisture dominates the low level moistening ahead of the convection a further diagnosis indicates that the leading term in the vertical moisture advection is the advection of the background moisture by the mjo ascending flow associated with pbl convergence the cause of the zonally asymmetric pbl convergence is further examined it is found that heating induced free atmospheric wave dynamics account for 75 90 of the total pbl convergence while the warm sst anomaly induced by air sea interaction contributes 10 25 of the total pbl convergence the horizontal moisture advection also plays a role in contributing to the pbl moistening ahead of the mjo convection the leadingterm in the moistureadvectionis the advectionacross the backgroundmoisture gradient by the mjo flow in the western indian ocean maritime continent and western pacific the meridional moisture advection by the mjo northerly flow dominates while in the eastern indian ocean the zonal moisture advection is greater the contribution of the moisture advection by synoptic eddies is in generalsmall ithas a negativeeffect overthetropicalindianoceanand westernpacificandbecomespositive in the maritime continent region

triggering of the ms 5 4 little skull mountain nevada earthquake with dynamic strains abstract we have developed an approach to test the viability of dynamic strains as a triggering mechanism by quantifying the dynamic strain tensor at seismogenic depths we focus on the dynamic strains at the hypocenter of the m s 5 4 little skull mountain lsm nevada earthquake this event is noteworthy because it is the largest earthquake demonstrably triggered at remote distances 280 km by the m s 7 4 landers california earthquake and because of its ambiguous association with magmatic activity our analysis shows that if dynamic strains initiate remote triggering the orientation and modes of faulting most favorable for being triggered by a given strain transient change with depth the geometry of the most probable lsm fault plane was favorably oriented with respect to the geometry of the dynamic strain tensor we estimate that the magnitude of the peak dynamic strains at the hypocentral depth of the lsm earthquake were 4 strain 2 mpa which are 50 smaller than those estimated from velocity seismograms recorded at the surface we suggest that these strains are too small to cause mohr coulomb style failure unless the fault was prestrained to near failure levels the fault was exceptionally weak and or the dynamic strains trigger other processes that lead to failure

coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales abstract coherent fluctuations between extratropical circulation and tropical conviction in the intraseasonal time scale are studied possible relationships between 500 mb height field and outgoing longwave radiation olr are examined using correlation complex eof and composite techniques results show that in the 20 70 day bands data there is a systematic evolution of extratropical wavetrains from eurasia across the pacific to north america and the north atlantic in the time scale of 5 to 10 days over the tropics the dominant mode of intraseasonal variation in convection is an east west dipole like feature which propagates from the western indian ocean eastward to the dateline with a quasi period of 40 50 days the space time evolution of these extratropical wavetrains is found to he coherent with the tropical dipolar convection and with the strongest convection over indonesia central pacific in approximate quadrature with the peak phase of the eurasia and pacific north america wavetrains while the

climatology and decadal variations in multicore structure of the north pacific subtropical mode water the pycnostad of the north pacific subtropical mode water stmw often displays multiple vertical minima in the potential vorticity profile argo profile data from 2004 to 2015 are used to investigate inter annual to decadal variations of the multicore structure climatologically about 24 pycostads of stmw have multicore structure and most of them distribute in the region west of 150 e stmw cores are classified into three sub modes the cold middle and warm ones with potential temperatures of 16 0 17 c 17 18 c and 18 19 5 c respectively the kuroshio extension ke varies between stable and unstable states the unstable ke with large meanders increases the subsurface stratification and shoals the winter mixed layer east of 150 e with warmer temperatures there the dominant stmw type varies from the cold single type in stable ke years making up 72 of the profiles with stmw to the middle single one 53 in unstable years the variation of the dominant stmw type in the region east of 150 e subsequently affects the multicore structure of stmw west of 150 e in a broad region between 130 e and 180 e profiles with stmw are fewer in unstable years but the proportion of multicore profiles increases among stmw profiles this might be due to the split recirculation gyre with a chaotic ke

soil basin and soil building soil interaction effects on motions of mexico city during seven earthquakes starting with the destructive 1985 michoacan mw 8 0 earthquake the lake zone of mexico city has been experiencing ground motions bearing the effects of strong soil amplification at specific site d

mexico 1985 the case for gravity waves summary the argument for the existence of gravity waves in sedimentary layers during strong earthquakes such as the 1985 mexico earthquake is based on a theory which predicts a discontinuity in surface wave propagation at a finite strain value b effects of stress strain non linearity in sediments and c observations suggesting the presence of ultra short wavelengths in soils during the 1985 mexico earthquake

the energy partitioning and the diffusive character of the seismic coda following recent theoretical developments of the radiative transfer the ory of elastic waves we propose to use the ratio r of energies of curl and divergence part of the ground displacement to distinguish between the different possible domi nant scattering regimes in the lithosphere a consequence of the diffusion regime is the partitioning of the energy between different vibrational modes which is inde pendent of time it results in the stabilization of r this behavior is not expected if low order diffraction such as single scattering is dominant we apply our technique to seismograms recorded by a small aperture seismic array operated during june august 1997 in guerrero mexico we estimate the energy ratio r in the coda of 13 earthquakes recorded by the array we find it to be very stable in the coda window while the energy level itself changes by several orders of magnitude the value of r is 7 1 independent of the earthquake location and the magnitude the observed stabilization of r is a strong indication of the diffusive regime of the seismic coda

role of maritime continent land convection on the mean state and mjo propagation abstractthe maritime continent mc region is known as a barrier in the life cycle of the madden julian oscillation mjo during boreal winter the mjo detours the equatorial mc land region sout

dynamic deformations of shallow sediments in the valley of mexico part ii single station estimates abstract we develop simple relations to estimate dynamic displacement gradients and hence the strains and rotations during earthquakes in the lake bed zone of the valley of mexico where the presence of low velocity high water content clays in the uppermost layers cause dramatic amplification of seismic waves and large strains the study uses results from a companion article bodin et al 1997 in which the data from an array at roma a lake bed site were analyzed to obtain displacement gradients in this article we find that the deformations at other lake bed sites may differ from those at roma by a factor of 2 to 3 more accurate estimates of the dominant components of the deformation at an individual instrumented lake bed site may be obtained from the maximum horizontal velocity and displacement max and u max at the surface the maximum surface strain max is related to max by max max c with c 0 6 km sec from the analysis of data from sites equipped with surface and borehole sensors we find that the vertical gradient of peak horizontal displacement u max z computed from sensors at 0 and 30 m equals u max z 0 z z 30 m within a factor of 1 5 this is the largest gradient component and the latter simple relation permits its estimation from surface records alone the observed profiles of u max versus depth suggest a larger gradient in some depth range of 10 to 20 m in agreement with synthetic calculations presented in bodin et al 1997 from the free field recordings of the 19 september 1985 michoacan earthquake we estimate a maximum surface strain max between 0 05 and 0 11 and a lower bound for the peak vertical gradient u max z between 0 3 and 1 3 this implies that 1 the extensive failure of water pipe joints during the michoacan earthquake in the valley occurred at axial strains of about 0 1 not 0 38 as previously reported and 2 the clays of the valley behave almost linearly even at shear strain of about 1 in agreement with laboratory tests the available data in the valley can be used to predict deformations during future earthquakes using self similar earthquake scaling

propagating and nonpropagating mjo events over maritime continent abstractthe observed outgoing longwave radiation olr and era interim data during 1979 2008 from november to april were analyzed to reveal fundamental differences between eastward propagating ep and nonpropagating np mjo events across the maritime continent mc it was found that when the maximum mjo convection arrives near 120 e a positive moisture tendency lies in a longitudinal zone 10 s 10 n 130 170 e for the ep cases whereas a negative tendency appears in the same region for the np cases in the latter cases there are clearly detectable westward propagating rossby wave type dry signals over the equatorial central western pacific the dry rossby wave signal may hinder the development of new convection to the east of the mjo convective center preventing the eastward propagation of the mjo a moisture budget analysis shows that the positive tendency of specific humidity in the ep composite is mainly attributed to the advection of the mean moisture by an intraseasonal ascending motion ano

variations of current path velocity and volume transport of the kuroshio in relation with the large meander abstract the variations of the kuroshio current path and their relations with current velocity volume transport and upstream position of the kuroshio are examined using sea level data after the long time non large meander nlm path during 1963 75 the kuroshio takes a large meander lm path during most of 1975 91 1975 80 1981 84 1986 88 and 1989 91 the study of these meanders confirms the description of the path of the kuroshio based on the three typical paths and the transitions between them with an exception being the 1981 84 lm path the formation and decay of the large meander are associated with velocity and position of the kuroshio in the tokara strait south of kyushu a small meander precursor of the large meander seems to be formed southeast of kyushu in relation with a temporary increase of kuroshio velocity and a northward shift of the kuroshio in the tokara strait an eastward propagation of the small meander leading to the lm formation is associated with remaining in the northe

potential vorticity distribution in the north pacific abstract vertical sections and maps of potential vorticity 1f z for the north pacific are presented on shallow isopycnals high potential vorticity is found in the tropics subpolar gyre and along the eastern boundary of the subtropical gyre all associated with ekman upwelling low potential vorticity is found in the western subtropical gyre subtropical mode water in a separate patch near the sea surface in the eastern subtropical gyre and extending around the gyre and near sea surface outcrops in the subpolar gyre the last is analogous to the subpolar mode water of the north atlantic and southern ocean meridional gradients of potential vorticity are high between the subtropical and subpolar gyres at densities which outcrop only in the subpolar gyre lateral gradients of potential vorticity are low in large regions of the subtropical gyre on these isopycnals on slightly denser isopycnals which do not outcrop in the north pacific there are large regions of low potential vorticity gradients

is there truly a hard rock site in the valley of mexico to understand the cause of observed amplification of seismic waves even at hill zone sites in the valley of mexico digital accelerographs have been installed at three especially chosen sites two of these sites madi and texc located on hard pleistocene lava a few meters in thickness overlying oligocene andesites were expected to be free of site effects analysis of the data recorded by these and other accelerographs during three moderate shallow subduction zone events however shows significant amplification at madi and texc between 0 2 and 0 6 hz with respect to established attenuation relations the cause of the amplification at hill zone sites in the valley of mexico including madi and texc may be pervasive low s wave velocity in and complex structure of the upper layers of the volcanic rocks if so then there may not be a truly hard rock site in the valley

dynamics oriented diagnostics for the madden julian oscillation abstractrealistic simulations of the madden julian oscillation mjo by global climate models gcms remain a great challenge to evaluate gcm simulations of the mjo the u s clivar mjo working group developed a standardized set of diagnostics providing a comprehensive assessment of statistical properties of the mjo here a suite of complementary diagnostics has been developed that provides discrimination and assessment of mjo simulations based on the perception that the mjo propagation has characteristic dynamic and thermodynamic structures the new dynamics oriented diagnostics help to evaluate whether a model produces eastward propagating mjos for the right reasons the diagnostics include 1 the horizontal structure of boundary layer moisture convergence blmc that moistens the lower troposphere to the east of a convection center 2 the preluding eastward propagation of blmc that leads the propagation of mjo precipitation by about 5 days 3 the horizontal structure of 850 hpa zonal wind and its

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

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

spatial gradient analysis for linear seismic arrays i incorporate the spatial gradient of the wave field recorded from one dimensional arrays into a processing method that yields the horizontal wave slowness and the change of geometrical spreading with distance in general the model for seismic wave propagation is enough to be appropriate for body and surface waves propagating from nearby seismic sources but can be simplified into a plane wave model although computation of the spatial gradient requires that array elements be closer than 10 of the horizontal wavelength seismic array apertures in the usual sense may extend over many horizontal wavelengths and illuminate changes within the wave field array images of horizontal slowness and the relative geometrical spreading changes of seismic waves are derived using filter theory and used to interpret observed array wave fields errors in computing finite difference spatial gradients from array nodes are explicitly considered to avoid spatial aliasing in the estimates i apply the method to interpret waves in strong ground motion and small scale refraction data sets use of the wave spatial gradient accentuates spatial differences in the wave field that can be theoretically exploited in fine scale tomographic studies of structure and is complementary to frequency wavenumber or beam forming array processing techniques

comment on evidence of the dominance of higher mode surface waves in the lake bed zone of the valley of mexico by shapiro et al 2001 summary the purpose of this note is to contribute to the understanding of seismic ground motion in mexico city to this end we 1 compute theoretical transfer functions for various models for the deep structure and the shallow clay layers 2 study the seismic responses of various sites within the city using spectral ratios of horizontal motion relative to the motion of nearby rock sites and relative to the vertical motion at the same site and 3 discuss some characteristics of surface waves for models of the deep structure and the shallow clay layers in the valley of mexico

north pacific subtropical mode water volume decrease in 2006 09 estimated from argo observations influence of surface formation and basin scale oceanic variability abstractanalysis of argo temperature and salinity profiles gridded at 0 5 0 5 resolution for 2005 12 shows a strong north pacific subtropical mode water npstmw volume and density decrease during 2006 09 in this time period upper ocean temperature stratification and potential vorticity pv all increased within the region in and around the npstmw low pv pool contributing to the npstmw volume decrease in two ways i the volume of water satisfying the low pv constraint that is part of the mode water definition decreased and ii some water that was initially in the npstmw density range 25 0 25 5 kg m 3 was transformed into lighter water both changes in density and in pv in the npstmw region were a manifestation of basinwide changes a positive pv anomaly started to propagate westward from the central pacific in 2005 followed by a negative density anomaly in 2007 which caused a dramatic npstmw volume and density decrease a walin estimate of surface formation in the npstmw density ran

circulation factors determining the propagation speed of the madden julian oscillation abstractthe eastward propagating madden julian oscillation mjo events exhibit various speeds ranging from 1 to 9 m s 1 but what controls the propagation speed remains elusive this study attempt

propagating versus nonpropagating madden julian oscillation events abstractbasinwide convective anomalies over the indian ocean io associated with the madden julian oscillation mjo sometimes propagate eastward and reach the west pacific wp but sometimes do not long term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating mjo events io convection onset events associated with the mjo are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern maritime continent and wp the io convection anomaly preferentially makes eastward propagation and reaches the wp when the dry anomaly is stronger analysis of the column integrated moist static energy mse budget shows that horizontal advection moistens the atmosphere to the east of the positive mse anomaly associated with the active convection over the io and is of sufficient magnitude to explain the eastward propagation of the positive mse anomaly interpretation is complicated however by lack of closure in

the strain in the array is mainly in the plane waves below 1 hz abstract we compare geodetic and single station methods of measuring dynamic deformations and characterize their causes in the frequency bands 0 5 1 0 hz and 4 0 8 0 hz the geodetic approach utilizes data from small aperture seismic arrays applying techniques from geodesy it requires relatively few assumptions and a priori information the single station method uses ground velocities recorded at isolated or single stations and assumes all the deformation is due to plane wave propagation it also requires knowledge of the azimuth and horizontal velocity of waves arriving at the recording station data employed come from a small aperture dense seismic array deployed in geyokcha turkmenistan and include seismograms recorded by broadband sts2 and short period l28 sensors poor agreement between geodetic and single station estimates in the 4 0 8 0 hz passband indicates that the displacement field may vary nonlinearly with distance over distances of 50 m sts2 geodetic estimates provide a robust standard in the 0 5 1 0 hz passband because they appear to be computationally stable and require fewer assumptions than single station estimates the agreement between sts2 geodetic estimates and single station l28 estimates is surprisingly good for the s wave and early surface waves suggesting that the single station analysis should be useful with commonly available data these results indicate that in the 0 5 to 1 0 hz passband the primary source of dynamic deformation is plane wave propagation along great circle source receiver paths for later arriving energy the effects of scattering become important the local structure beneath the array exerts a strong control on the geometry of the dynamic deformation implying that it may be difficult to infer source characteristics of modern or paleoearthquakes from indicators of dynamic deformations however strong site control also suggests that the dynamic deformations may be predictable which would be useful for engineering seismically resistant structures

wave gradiometry in two dimensions the spatial displacement gradient of a seismic wave is related to dis placement and velocity through two spatial coefficients for any one dimension one coefficient gives the relative change of wave geometrical spreading with distance and the other gives the horizontal slowness and its change with distance the essential feature of spatial gradient analysis is a time domain relation between three seismo grams that yields information on the amplitude and phase behavior of a seismic wave filter theory is used to find these coefficients for data from 2d areal arrays of seismometers termed gradiometers a finite difference star is used to compute the displacement gradient for irregularly shaped gradiometers and a relation for the frequency dependent error in the displacement gradient is obtained and applied to ensure accurate estimates this kind of array analysis is useful for gradiometers at any distance from a source and yields a variety of time domain and frequency domain views of wave amplitude changes and horizontal phase velocity estimates across the gradiometer for example time dependent horizontal slowness and wave azimuth plots are natural results of the analysis these time domain maps may be used in conjunction with time distance and horizontal slowness distance models to locate seismic sources or may be used directly to study earth structure these methods are demonstrated by using data from a small aperture 40 m seismic gradiometer

response of storm tracks to bimodal kuroshio path states south of japan abstracta large meridional shift of the sea surface temperature front occurs off the south coast of japan associated with transitions between the large meander and straight paths of the kuroshio most extratropical cyclones generated in winter near the kuroshio in the east china sea pass through the region where the kuroshio takes either the meander or the straight path to examine whether such cyclones change their tracks and intensities according to the two states of the path a new dataset of winter cyclone tracks derived from surface weather charts from the period 1969 70 2008 09 was produced the composite analysis of cyclone tracks with respect to the meander and straight path states reveals the following the cyclone track axis for the meander path state is located away from the south coast of japan with a dispersive tendency while that for the straight path state is attached to the south coast with a long extending feature a difference in track between these two states also occurs to the east of

influence of kuroshio path variation south of japan on formation of subtropical mode water abstractdistributions of subtropical mode water stmw in the northwestern part of the north pacific subtropical gyre were investigated using temperature salinity profiles from 2005 to 2011 with particular reference to the kuroshio meander and non meander path states south of japan in spring of meander years warm stmw with a potential temperature of 19 20 c potential density anomaly of 24 6 24 9 kg m 3 was found in the shikoku basin whereas cold stmw below 19 c was distributed throughout the southern region of japan in non meander years the warm stmw was formed in a spatially isolated and warm winter mixed layer ml in the shikoku basin where a local recirculation developed in association with the kuroshio meander path both the absence of horizontal mixing with a cold ml south of the kuroshio extension because of the spatially isolated ml and an increase in horizontal heat advection due to the westward flow associated with this local recirculation caused the ml warming in the shikoku basin a

mjo propagation shaped by zonal asymmetric structures results from 24 gcm simulations abstracteastward propagation is an essential characteristic of the madden julian oscillation mjo yet simulation of mjo propagation in general circulation models gcms remains a major challenge and understanding the causes of propagation remains controversial the present study explores why the gcms have diverse performances in mjo simulation by diagnosis of 24 gcm simulations an intrinsic linkage is found between mjo propagation and the zonal structural asymmetry with respect to the mjo convective center the observed and realistically simulated mjo eastward propagations are characterized by stronger kelvin easterly waves than rossby westerly waves in the lower troposphere which is opposite to the gill pattern where rossby westerly waves are 2 times stronger than kelvin easterly waves the gcms simulating stronger rossby westerly waves tend to show a stationary mjo mjo propagation performances are robustly correlated with the quality of simulated zonal asymmetries in the 850 hpa equatorial zonal w

transient stresses at parkfield california produced by the m 7 4 landers earthquake of june 28 1992 observations from the upsar dense seismograph array the m 7 4 landers earthquake triggered widespread seismicity in the western united states because the transient dynamic stresses induced at regional distances by the landers surface waves are much larger than the expected static stresses the magnitude and the characteristics of the dynamic stresses may bear upon the earthquake triggering mechanism the landers earthquake was recorded on the upsar u s geological survey parkfield small aperture array array a group of 14 triaxial accelerometers located within a 1 square km region 10 km southwest of the town of parkfield california 412 km northwest of the landers epicenter no triggered earthquakes were observed at parkfield multiple filter analysis shows that the displacements obtained by double integration are dominated by the fundamental mode love and rayleigh modes with some higher mode contributions for periods shorter than 10 s most of the surface waves propagated along the great circle path from landers but a late arriving surface wave appears to have been scattered from the sierra nevada mountains we used a standard geodetic inversion procedure to determine the surface strain and stress tensors as functions of time from the observed displacements peak dynamic strains and stresses at earth s surface are about 7 strain and 0 035 mpa respectively and they have a flat amplitude spectrum between 2 s and 15 s period these stresses agree well with stresses predicted from a simple equation using the ground velocity spectrum observed at a single station peak stresses ranged from about 0 035 mpa at the surface to about 0 12 mpa between 2 and 14 km depth with the sharp increase of stress away from the surface resulting from the rapid increase of rigidity with depth and from the influence of mode shapes because of the free surface boundary conditions the horizontal components of the stress tensor tend to dominate in the top 5 6 km of the crust which might cause triggered seismicity to have strike slip or normal mechanisms comparison of dynamic stresses induced by the landers loma prieta and petrolia earthquakes at a variety of sites indicates that the landers stresses were not spectacularly larger than those induced by the other sources landers dynamic stresses were comparable to coalinga static stresses at parkfield the effective strain caused by landers at parkfield where no earthquakes were triggered are the same amplitude as those at some sites in nevada where earthquakes were triggered comparing various authors observations of dynamic stresses there is no obvious characteristic of these stresses that correlates with the triggered seismicity

evidence for anomalous body wave radiation between 0 3 and 0 7 hz from the 1985 september 19 michoacan mexico earthquake summary in order to better understand the causes of unprecedented damage to mexico city during the 1985 september 19 michoacan earthquake mw 8 0 spectral ratios of teleseismic p waves of this earthquake are studied with respect to those from five recent large mexican subduction zone earthquakes 7 0 mw 7 7 the data are from vertical component digital seismographs it is found that the spectral ratios at stations in the ne quadrant are anomalously more energetic than those predicted by the 2 source model in the critical frequency range for mexico city 0 3 0 7 hz the evidence is especially convincing for the spectral ratios with respect to the earthquakes of 1985 september 21 mw 7 6 and 1986 mw 7 0 since the data are available from several stations in the ne quadrant the teleseismic p wave spectral ratio in this quadrant with respect to the 1985 september 21 earthquake in the critical frequency range is close to the acceleration spectral ratio found in and near mexico city also in the ne quadrant velocity traces in the epicentral region of the michoacan earthquake obtained by integrating the accelerograms also show oscillations with a frequency of about 0 4 hz furthermore a regression study of fourier acceleration spectra at a hill zone site in mexico city demonstrates that the michoacan earthquake was anomalously energetic in the city at the critical frequencies for an event of that magnitude and at that distance if the data from 7 0 mw 7 7 events can be extrapolated to estimate the ground motions from mw 8 0 earthquakes then the evidence supports an anomalously large body wave radiation towards mexico city between 0 3 and 0 7 hz during the michoacan earthquake this anomalous radiation and the dramatic local amplification of seismic waves in the lake bed zone of the city 10 50 times at frequencies between 0 3 and 0 7 hz appear to be the principal natural causes of the disaster the anomalous teleseismic p wave spectral ratios with respect to the earthquakes of 1985 september 21 and 1986 found in the ne quadrant are not observed in the data available from a small number of stations in the other quadrants if this observation is true then it suggests a directional property to the anomalous radiation

the effects of seismic rotations on inertial sensors summary with the important increase in the number of instruments especially in the near field of quite significant earthquakes unsaturated traces have led seismologists to question what they are really measuring we have performed a review of previous studies related to the effects of rotations on both horizontal and vertical components of various sensors illustrations of near field records show that the recovering static displacement requires an accurate rotation estimation that present day seismometers cannot achieve estimations of coseismic tilts rotation around an horizontal axis using seismometers cannot be achieved independently of translational motion therefore for specific configurations such as near field or long period far field reconstruction of the ground motion requires specific rotation measurements effects of the chi chi earthquake 1999 on accelerograms make the static displacement estimation unreliable for long period background noise far field horizontal seismic signals present unexpected n45 polarization which is explained by the similar influence of the rotation around the vertical axis on the two horizontal components for the geoscope network this feature has been seen for stations with a streckeisen sts 1 sensor while those with a streckeisen sts 2 sensor do not show this polarization feature this study suggests that sensor installation should follow a protocol that will better guarantee the verticality of the sensors moreover rotational recordings with ad hoc sensors are necessary and by adequately correcting the traces they will enable us to reconstruct the translational motion from recorded seismic signals

3d analysis of s wave propagation in soft deposits during the 1985 michoacan earthquake surface wave magnitude 8 1 large amplitude seismograms of extremely long duration were recorded in the lake bed zone of mexico city large amplification in soft surficial deposits has not been well understood ground subsidence of the soft clay deposits might heavily influence s wave propagation in the present study we attempt to explain both s wave amplification and propagation time between surface and borehole recordings under the action of gravity on the basis of a 3d nonlinear finite element fe technique where a bilinear model with a mohr coulomb criterion is used we identify body wave s wave time sections in the recordings with a cross correlation analysis the fe simulation successfully predicts the s wave amplification and propagation time which cannot be explained by a purely 1d linear model although subsidence changes s wave linear amplification s wave propagation time decreases little

the subtropical mode water circulation in the north pacific abstract historical hydrographic data are analyzed to investigate the seasonal variation of the subsurace pycnostad in the northwestern part of the north pacific and to relate it to the circulation of subtropical mode water stmw a gyre scale scheme of stmw circulation is deduced based on its observed climatological formation area and climatological geostrophic flow fields the deduced circulation is supported by climatological features of the subsurface hydrography presented separately for the non large meander period and the large meander period of the kuroshio zonal and meridional sections and isopycnal maps of potential vorticity and apparent oxygen utilization the kuroshio countercurrent composing the kuroshio recirculation system advects stmw formed in the wintertime thick mixed layer immediately off the kuroshio and the kuroshio extension during the non large meander period the recirculation system has a single anticyclonic gyre centered near 30 n 137 e and advects stmw formed off the kurosh

a role of eddies in formation and transport of north pacific subtropical mode water 1 hydrographic data acquired during 2001 by argo profiling floats deployed in the kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of north pacific subtropical mode water npstmw that is the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies in the succeeding seasons mesoscale eddies retain npstmw during their southwestward movement from the npstmw formation region so that anticylonic eddies contribute substantially to the npstmw transportation the spatial distributions of the mixed layer depth in winter and the npstmw thickness in the succeeding seasons based on the float data suggest that they are affected by mesoscale eddies the float data also provide the statistical relations of these quantities against the thermocline depth which are consistent with our inference

fundamental causes of propagating and nonpropagating mjos in mjotf gass models abstractthis study investigates the fundamental causes of differences in the madden julian oscillation mjo eastward propagation among models that participated in a recent model intercomparison project these models are categorized into good and poor groups characterized by prominent eastward propagation and nonpropagation respectively column integrated moist static energy mse budgets are diagnosed for the good and the poor models it is found that a zonal asymmetry in the mse tendency characteristic of eastward mjo propagation occurs in the good group whereas such an asymmetry does not exist in the poor group the difference arises mainly from anomalous vertical and horizontal mse advection the former is attributed to the zonal asymmetry of upper midtropospheric vertical velocity anomalies acting on background mse vertical gradient the latter is mainly attributed to the asymmetric zonal distribution of low tropospheric meridional wind anomalies advecting background mse and moisture fields base

topographic effects on the eastward propagation and initiation of the madden julian oscillation abstract this study investigates the relationship between deep convection and heating anomaly in the madden julian oscillation mjo and the tropical topography the eastward propagation of the deep heating anomalies is confined to two regions the indian ocean and the western pacific warm pool superimposed on the eastward propagation is a series of quasi stationary deep heating anomalies that occur sequentially and discretely downstream in a leapfrog manner in the central indian ocean the maritime continent tropical south america and tropical africa the deep heating anomaly usually preceded by near surface moisture convergence and shallow heating anomalies tends to occur on the windward side of the tropical topography in these regions except the central indian ocean under the prevailing surface easterly anomaly of the mjo it is suggested that the lifting and frictional effects of the tropical topography and landmass induce the near surface moisture convergence anomaly which in turn triggers

effects of enhanced front walker cell on the eastward propagation of the mjo abstractwell organized eastward propagation of the madden julian oscillation mjo is found to be accompanied by the leading suppressed convection lsc over the maritime continent mc and the wes

barrier effect of the indo pacific maritime continent on the mjo perspectives from tracking mjo precipitation abstractexplanations for the barrier effect of the indo pacific maritime continent mc on the mjo should satisfy two criteria first they should include specific features of the mc namely its intricate land sea distributions and elevated terrains second they should include mechanisms for both the barrier effect and its overcoming by some mjo events guided by these two criteria a precipitation tracking method is applied to identify mjo events that propagate across the mc mjo c and those that are blocked by the mc mjo b about a half of mjo events that form over the indian ocean propagate through the mc most of them 75 become weakened over the mc the barrier effect cannot be explained in terms of the strength horizontal scale or spatial distribution of mjo convection when it approaches the mc from the west a distinction between mjo b and mjo c is their precipitation over the sea versus land in the mc region mjo c events rain much more over the sea than over land whereas rainfall over

observations of the subtropical mode water evolution from the kuroshio extension system study abstract properties and seasonal evolution of north pacific ocean subtropical mode water stmw within and south of the kuroshio extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard adcp measurements taken during 2004 the presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of stmw within the recirculation gyre stmw formed from late winter convection that reached depths greater than 450 m near the center of the gyre the lower boundary of stmw corresponding to 25 5 kg m 3 was set by the maximum depth of the late winter mixed layer properties within the deep portions of the stmw layer remained largely unchanged as the season progressed in contrast the upper boundary of the stmw layer eroded steadily as the seasonal thermocline deepened from late april to august vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

introduction to the special issue on rotational seismology and engineering applications rotational seismology is an emerging field for studying all aspects of ro tational ground motions induced by earthquakes explosions and ambient vibrations it is of interest to a wide range of geophysical disciplines including strong motion seismology broadband seismology earthquake engineering earthquake physics seis mic instrumentation seismic hazards seismotectonics and geodesy as well as to physicists using earth based observatories for detecting gravitational waves generated by astronomical sources predicted by einstein in 1916 in this introduction to the bssa special issue on rotational seismology and engineering applications we will include 1 some background information 2 a summary of the recent events that led to this special issue and 3 an overview of its 51 papers 27 articles 11 short notes 4 reviews 6 tutorials and 3 supplementary articles our comments on these 51 papers are very brief and give just a hint of what the papers are about papers in this special issue demonstrate that earthquake monitoring cannot be limited to measuring only the three components of translational motion we also need to simultaneously measure the three components of rotational motion and the many components of strains a golden opportunity to improve our understanding of earth quakes lies in the near field of large earthquakes within about 25 km of the earthquake ruptures where nonlinear rock and soil response influences ground motions in a com plicated way

a mass flux scheme view of a high resolution simulation of a transition from shallow to deep cumulus convection in this paper an idealized high resolution simulation of a gradually forced transition from shallow nonprecipitating to deep precipitating cumulus convection is described how the cloud and transport statistics evolve as the convection deepens is explored and the collected statistics are used to evaluate assumptions in current cumulus schemes the statistical analysis methodologies that are used do not require tracing the history of individual clouds or air parcels instead they rely on probing the ensemble characteristics of cumulus convection in the large model dataset they appear to be an attractive way for analyzing outputs from cloud resolving numerical experiments throughout the simulation it is found that 1 the initial thermodynamic properties of the updrafts at the cloud base have rather tight distributions 2 contrary to the assumption made in many cumulus schemes nearly undiluted air parcels are too infrequent to be relevant to any stage of the simulated convection and 3 a simple model with a spectrum of entraining plumes appears to reproduce most features of the cloudy updrafts but significantly overpredicts the mass flux as the updrafts approach their levels of zero buoyancy a buoyancy sorting model was suggested as a potential remedy the organized circulations of cold pools seem to create clouds with larger sized bases and may correspondingly contribute to their smaller lateral entrainment rates our results do not support a mass flux closure based solely on convective available potential energy cape and are in general agreement with a convective inhibition cin based closure the general similarity in the ensemble characteristics of shallow and deep convection and the continuous evolution of the thermodynamic structure during the transition provide justification for developing a single unified cumulus parameterization that encompasses both shallow and deep convection

dynamic deformations of shallow sediments in the valley of mexico part i three dimensional strains and rotations recorded on a seismic array abstract we study the spatial variation in earthquake ground motions or equivalently the dynamic displacement gradient field using a novel analysis procedure borrowed from geodesy seismic data recorded in the valley of mexico by a microarray of three three component surface accelerographs and two three component accelerographs at depths of 30 m and 102 m constrain our estimates of the dynamic displacement gradient field from which strains and rotations derive for four moderate earthquakes at distances of 250 to 300 km our study focuses on the effects of low velocity surface materials on the deformation at the surface the gradients corresponding to deformation across vertical planes dominate and vertical axis rotations are of similar magnitudes as strains the greatest peak surface gradient we observed was 206 strain for the 14 september 1995 m w 7 5 earthquake at a distance of 300 km however much larger gradients occur across horizontal planes u z where u is a horizontal displacement and z is depth at some depth between 0 and 30 m these values are about a factor 10 greater than the corresponding gradient components at the surface u z for the 14 september earthquake equaled or exceeded 665 strain at depth the dynamic deformations experienced in mexico city undoubtedly have occurred before and will occur again in other densely populated areas however in many other regions the sediment response will not remain linear and elastic resulting instead in liquefaction and ground failure

borehole volumetric strainmeter calibration from a nearby seismic broadband array at etna volcano strainmeter and broadband seismic signals have been analyzed jointly with the aim of calibrating a borehole strainmeter at etna volcano by using a seismo geodetic technique our results reveal a good coherence between the dynamic strains estimated from seismometer data and strains recorded by a dilatometer in a low frequency range 0 03 0 06 hz at the arrival of teleseismic waves this significant coherence enabled estimating the calibration coefficient and making a comparison with calibration results derived from other methods in particular we verified that the proposed approach provides a calibration coefficient that matches the results obtained from the comparison of the recorded strain both with theoretical strain tides and with normal mode synthetic straingrams the approach presented here has the advantage of exploiting recorded seismic data avoiding the use of computed strain from theoretical models

decadal variation in winter mixed layer depth south of the kuroshio extension and its influence on winter mixed layer temperature abstractthe long term behavior of the wintertime mixed layer depth mld and mixed layer temperature mlt are investigated in a region south of the kuroshio extension ke 30 37 n 141 155 e an area of the north pacific subtropical gyre where the deepest mld occurs using historical temperature profiles of 1968 2014 both the mld and mlt in march have low frequency variations which show significant decadal 10 yr variations after the late 1980s observational data and simulation outputs from a one dimensional turbulent closure model reveal that surface cooling is the main control on winter mld in the late 1970s and 1980s whereas there is a change in the strength of subsurface stratification is the main control after 1990 in the latter period a weak strong subsurface stratification is caused by a straight path convoluted path of the ke and by a deepening shallowing of the main thermocline depth due to oceanic rossby waves formed as a result of positive negative anomalies of wind stress

some aspects of source characteristics of the 19 september 1985 michoacan earthquake and ground motion amplification in and near mexico city from strong motion data abstract the fourier amplitude ratio of the 19 september m s 8 1 to the 21 september 1985 m s 7 6 michoacan earthquakes obtained from data in and near mexico city increases from about 3 5 at 0 5 hz to about 10 at 0 2 hz this increase is neither seen in the coastal data nor in the teleseismic broadband gdsn p wave spectra it is also not predicted by 2 or gusev9s scaling laws we tentatively attribute the increase at frequencies of less than 0 5 hz to a special path and or a depth of energy release effect for the 19 september earthquake the damage to mexico city is mostly related to 0 5 hz energy since at f 0 5 hz the fourier amplitude ratios in and near mexico city along the coast and at teleseismic distances are nearly equal we attribute this energy to the source characteristics of the 19 september earthquake the evidence suggests that the 19 september was about twice more energetic at f 0 5 hz than expected from scaling laws and from spectral regression of coastal earthquakes recorded in mexico city the analysis of strong motion data recorded in mexico city shows that the ground motions in the lake bed zone are amplified by 8 to 50 times with respect to a hill zone site in ciudad universitaria the frequency at which the maximum relative amplification occurs varies from site to site and lies between 0 2 and 0 7 hz the data suggest that f o 4 h where f o frequency at which maximum relative amplitude occurs and and h are the shear wave velocity and the thickness of the clay layer respectively relatively small if any nonlinear behavior of the clay is found at strains of about 0 2 per cent during the great 19 september earthquake for a given lake bed site maximum relative amplitude and f o are roughly constant independent of magnitude depth and azimuth of sources located more than about 200 km ground motion at lake bed sites in mexico city with f o 0 5 hz appear to be amplified 75 times with respect to hard rock coastal sites at equal distances from the source this is also confirmed by m l calculation of the 19 and 21 september earthquakes for the 19 and 21 september earthquakes the average values of m l at hard rock coastal sites 100 distance 250 km are 7 4 and 6 7 whereas they are 8 7 and 8 4 in the lake bed zone distance 300 km respectively

ground motion in mexico city during the april 25 1989 guerrero earthquake abstract instrumental observations of ground motion in mexico city during the april 25 1989 guerrero earthquake were analyzed our aim was to understand various aspects of the seismic response of the valley that had not been completely resolved such understanding of the basic mechanisms that control the seismic behavior of the valley sediments is crucial in any modeling attempt the study of vertical motion for this event which was shown to be practically unaffected by site conditions lead to the identification of a prominent long period rayleigh wave this together with the availability of absolute time for some stations allowed the establishment of a common time reference for all recordings horizontal motion in contrast was significantly amplified with large increases in duration at lake bed sites in order to interpret the observed complexity of ground motion we studied two simplified models of soft alluvial valleys one of these is two dimensional and it is excited by plane s waves with variable polarization and incidence angles this model allows three dimensional response the other is a three dimensional axi symmetric flat valley with a rigid base computations were performed in the frequency domain by means of a boundary integral method for the two dimensional model and using a collocation least squares technique for the three dimensional one seismograms were obtained through fourier synthesis it was found that the irregular soft layer response produces polarization patterns which are similar to the observations suggesting that the latter are a consequence of three dimensional effects

barrier effect of the indo pacific maritime continent on mjo propagation in observations and cmip5 models abstractthis study explores possible mechanisms for the barrier effect of the indo pacific maritime continent mc on mjo propagation in particular this study examines whether similar mechanisms

primary and successive events in the madden julian oscillation conventional analyses of the mjo tend to produce a repeating cycle such that any particular feature cannot be unambiguously attributed to the current or previous event we take advantage of the sporadic nature of the mjo and classify each observed madden julian mj event as either primary with no immediately preceding mj event or successive which does immediately follow a preceding event 40 of mj events are primary events precursor features of the primary events can be unambiguously attributed to that event a suppressed convective anomaly grows and decays in situ over the indian ocean prior to the start of most primary mj events an associated mid tropospheric temperature anomaly destabilises the atmosphere leading to the generation of the active mj event hence primary mj events appear to be thermodynamically triggered by a previous dry period although stochastic forcing may also be important other theories predict that boundary layer convergence humidity propagation of dynamical structures around the equator sea surface temperatures and lateral forcing by extratropical transients may all be important in triggering an event although precursor signals from these mechanisms are diagnosed from reanalysis and satellite observational data in the successive mj events they are all absent in the primary mj events hence it appears that these apparent precursor signals are part of the mjo once it is established but do not play a role in the spontaneous generation of the mjo the most frequent starting location of the primary events is the indian ocean but over half of them start elsewhere from the maritime continent to the western pacific copyright 2008 royal meteorological society

explosion source strong ground motions in the mississippi embayment two strong motion arrays were deployed for the october 2002 embay ment seismic excitation experiment to study the spatial variation of strong ground motions in the deep unconsolidated sediments of the mississippi embayment because there are no comparable strong motion data from natural earthquakes in the area each linear array consisted of eight three component k2 accelerographs spaced 15 m apart situated 1 2 and 2 5 km from 2268 kg and 1134 kg borehole explosion sources respectively the array data show distinct body wave and surface wave arrivals that propagate within the thick unconsolidated sedimentary column the high velocity basement rocks and small scale structure near the surface time domain coherence of body wave and surface wave arrivals is computed for acceleration velocity and displacement time windows coherence is high for relatively low frequency vertical component rayleigh waves and high frequency p waves propagating across the ar ray prominent high frequency ps conversions seen on radial components a proxy for the direct s wave from earthquake sources lose coherence quickly over the 105 m length of the array transverse component signals are least coherent for any ground motion and appear to be highly scattered horizontal phase velocity is com puted by using the ratio of particle velocity to estimates of the strain based on a plane wave propagation model the resulting time dependent phase velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three component waveforms displacement gradient analysis is a complementary technique for processing general spatial array data to obtain hori zontal slowness information

evidence of the dominance of higher mode surface waves in the lake bed zone of the valley of mexico summary we compare ground motions recorded at the surface and in boreholes at five different locations of the lake bed zone of the valley of mexico with theoretical dispersion curves and eigenfunctions calculated for the first two modes of rayleigh and love waves we find that 1 the maximum in the horizontal to vertical displacement ratio which occurs at the dominant frequency of the site 0 4 hz corresponds to the higher mode rather than to the fundamental mode of the rayleigh waves 2 borehole records at depths from 0 to 100 m show that the normalized vertical displacement does not decrease rapidly below the superficial clay layer as should be the case for the fundamental mode but remains 0 8 and 3 the measured phase velocity at a period of about 2 5 s 2 0t0 5 km s x1 is too fast for the fundamental mode predicted for the known crustal velocity structure these observations lead us to conclude that the wavefield in the lakebed zone in mexico city is dominated by higher mode surface waves this provides a plausible explanation for the long duration of the coda in the lake bed zone although shear wave q is very small 10 20 in the clay layer the higher modes of surface waves do not propagate in the superficial clay layer but in the underlying structure where q values are likely to be relatively high thus while the clay layer plays the passive role of amplifying the ground motion its contribution in damping out the motion is insignificant the results have two important practical implications 1 the strain estimate from recorded ground velocity differs significantly for the fundamental mode as compared to the higher mode surface waves 2 if the ground motion is dominated by the fundamental mode then knowledge of the superficial layer and the velocity contrast with the underlying structure is sufficient for understanding and modelling of the ground motion if however the higher mode surface waves dominate then a detailed knowledge of the deeper structure is required