the mechanisms of shallow earthquakes and the monitoring of a comprehensive test ban summary the ability of seismological criteria to identify earthquakes from underground explosions depends partly on the orientation of the earthquake source well determined double couple moment tensor solutions for a large number of earthquakes have been published in the harvard centroid moment tensor cmt and united states geological survey usgs catalogues statistical analyses of these catalogues indicate that the distribution of the orientation of earthquake mechanisms is not random the distribution of the t axes shows significant clustering around the downward vertical indicating that a larger number of earthquake mechanisms radiate compressional p wave energy to teleseismic distances from near the maximum of the radiation pattern than is predicted if earthquake sources are randomly oriented double couples the clustered t axes correspond to compressional dip slip mechanisms and it is this type of mechanism which is believed to cause both the mb kfs the ratio of body wave to surface wave magnitude and first motion criteria to misidentify an earthquake as an explosion

the october 30 1994 seismic disturbance in south africa earthquake or large rock burst the relative amplitude method is applied to body waves recorded at teleseismic distances from the october 30 1994 mb 5 6 seismic disturbance in south africa to determine the source depth and moment tensor the results indicate that the source is shallow and that moment tensors with a positive volume change component are inconsistent with the observations observations of rg in the frequency range 0 5 2 0 hz at two regional distance stations also indicate that the source is shallow less than about 3 km deep three component broadband and long period seismograms recorded at regional distances show strong love wave excitation and a lobed rayleigh radiation pattern observations that are inconsistent with collapse mechanisms recently proposed for some large rock bursts mine tremors modeling of teleseismic broadband p and regional distance surface waves shows that the source depth is shallow 2 3 km and that the observed source radiation is consistent with that expected from a 45 normal dip slip fault the results of the modeling are confirmed by reports from the mining region that the disturbance was a mine tremor caused by slip on the stuirmanspan fault in the president brand mine at a depth of between 2 and 3 km the close match between observed and synthetic p and rayleigh wave amplitudes suggests that the explosion like mb ms of the mine tremor mb 5 6 ms 4 7 is attributable to the effect of the mechanism and the shallow depth of the source the above results are at odds with those of fan and wallace 1995 who interpreted this disturbance as an earthquake at a depth of 12 km based on a broadband inversion of three component waveforms from two regional distance stations this study confirms the need to interpret both broadband waveforms to match amplitude and polarity and short period waveforms to confirm relative onset times in the model structure if inversion of regional broadband waveforms is to provide a reliable estimate of the moment tensor and source depth

a transportable mb lg scale for central europe and implications for low magnitude ms mb discrimination summary we have extended the mb lg method of nuttli using root mean square rms amplitudes corrected for noise and a 1 dependence for geometrical spreading lg waves recorded on the german regional seismic network grsn for earthquakes in south central europe were used to develop an mb lg formula requiring a new calibration constant crms to keep rms mb lg on the same baseline as nuttli s traditional formula based on 3rd peak amplitudes grsn stations had to be calibrated for site terms and for lg attenuation lateral variations in lgq appear to be significant across the study area and a regional q model consisting of constant q partitions north south and in the central alps was developed using measurements based on interstation and two event single station methods when plotted against surface wave estimates of mw rms mb lg measurements in central europe are found to be consistent with mw mb lg relationships for north america and southern asia thus supporting the transportability of our mb lg formula frequency wavenumber processing of grafenberg array data enabled us to extract rayleigh waves for small events and regional ms were measured using the marshall and basham formula our ms mb lg relationship extends to ms 2 5 and agrees well with observations in other regions including the western united states the discrimination potential of ms mb lg observations was examined under realistic monitoring conditions where path corrections were inferred from earthquake data and applied uniformly to natural sources and explosions under these conditions mb pn p are greater than mb lg for large nts explosions however ms mb scaling slopes are steeper for p waves than they are for lg and ms mb observations for nts explosions converge near mb 4 thus allowing for measurement errors and additional uncertainty in mb pn due to regional bias there is little difference in the discrimination potential for pn and lg waves at small magnitudes as such a regional ms mb discriminant based on lg might be preferred owing to the better detectability of lg waves for small earthquakes these results need to be confirmed for explosions at other test sites compared to teleseismic experience regional ms mb observations extend the discrimination capability to lower magnitudes by at least one ms unit

a 550 000 year record of east asian monsoon rainfall from 10be in loess cosmogenic 10 be flux from the atmosphere is a proxy for rainfall using this proxy we derived a 550 000 year long record of east asian summer monsoon easm rainfall from chinese loess this record is forced at orbital precession frequencies with higher rainfall observed during northern hemisphere summer insolation maxima although this response is damped during cold interstadials the 10 be monsoon rainfall proxy is also highly correlated with global ice volume variations which differs from chinese cave 18 o which is only weakly correlated we argue that both easm intensity and chinese cave 18 o are not governed by high northern latitude insolation as suggested by others but rather by low latitude interhemispheric insolation gradients which may also strongly influence global ice volume via monsoon dynamics

on the seasonality of the hadley cell abstract the annual march of the climatological mean meridional circulations mmcs in the ncep ncar reanalyses is dominated by two components of roughly comparable mean squared amplitude 1 a seasonally invariant pair of hadley cells with rising motion centered near and just to the north of the equator and subsidence in the subtropics and 2 a seasonally reversing sinusoidally varying solsticial cell with ascent in the outer tropics of the summer hemisphere and subsidence in the outer tropics of the winter hemisphere the meridional structure and seasonal evolution of the solsticial cell are suggestive of a close association with the monsoons these results are consistent with previous analyses of the mean meridional circulation based on radiosonde data

abrupt seasonal variation of the itcz and the hadley circulation 1 using global precipitation climatology project gpcp daily data we show that the seasonal migration of the global zonal mean intertropical convergence zone itcz is not smooth but jumps from the winter hemisphere to the summer hemisphere the abrupt migration is within 10 days detailed analyses reveal that the phenomenon of the abrupt seasonal migration of the itcz mainly exists over particular tropical domains such as indian ocean western and central pacific and south america which gives the rise of the jump of the global zonal mean itcz because the itcz constitutes the ascending branch of the hadley circulation we also examine whether there exists such an abrupt seasonal change in the hadley circulation it is found that the intensity of the hadley cells evolves smoothly with time however the horizontal scales of the hadley cells demonstrate abrupt seasonal changes corresponding to the abrupt seasonal migration of the global itcz the winter cell extends rapidly across the equator while the summer cell rapidly narrows this suggests that the solsticial cell is the dominant component of the hadley circulation and that the equinoctial symmetric pattern is ephemeral

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

climatology of the itcz derived from era interim reanalyses 1 the intertropical convergence zone itcz is usually analyzed in terms of the precipitation field this study presents a new climatology of the itcz based on winds from era interim reanalyses for the period 1990 2009 the central latitude of the itcz is defined as the zero crossing of the meridional wind averaged over 10 model levels below 900 hpa results of the zonal averaging of the meridional wind and wind convergence are compared with the zonally averaged precipitation from the era interim and trmm data sets collocation properties of precipitation maxima and the central latitude of the itcz are discussed for different land and ocean regions it is found that the location of the itcz in wind and precipitation fields coincides over the atlantic and east pacific over other regions and especially over the tropical continents the fields on average do not coincide

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

detecting the itcz in instantaneous satellite data using spatiotemporal statistical modeling itcz climatology in the east pacific abstract a markov random field mrf statistical model is introduced developed and validated for detecting the east pacific intertropical convergence zone in instantaneous satellite data from may through october the mrf statistical model uses satellite data at a given location as well as information from its neighboring points in time and space to decide whether the given point is classified as itcz or non itcz two different labels of itcz occurrence are produced ir only labels result from running the model with 3 hourly infrared data available for a 30 yr period 1980 2009 all data labels result from running the model with additional satellite data visible and total precipitable water available from 1995 to 2008 ir only labels detect less area of itcz than all data labels especially where the itcz is shallower yet qualitatively the results for the two sets of labels are similar the seasonal distribution of the itcz through the summer half year is presented showing typical location and e

global maps of rayleigh wave attenuation for periods between 40 and 150 seconds studies of seismic attenuation must account for the large amplitude deviations caused by elastic focusing of energy in a new approach we jointly invert phase and amplitude measurements of 19 000 minor arc rayleigh waves between periods of 40 and 150 seconds the simultaneous inversion ensures that attenuation and phase velocity are mutually consistent because the phase and focusing term of amplitude are modelled using a common elastic model at the shortest periods the maps show a good correlation between attenuation and phase velocity suggesting a common cause in the uppermost mantle most probably thermal in origin this correlation is lost at longer periods the main signal beyond periods of 100 seconds is a strongly attenuating circum pacific zone and a pronounced ring of high attenuation around africa this feature seems reliable in our attenuation maps but not correlated to an equivalent structure in phase velocity we thus favour scattering of wave energy on large size structures as a possible cause

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

seasonal and interannual variability of atmospheric convergence zones in the tropical pacific observed with ers 1 scatterometer monthly images of atmospheric convergence zones in the tropical pacific were produced with 1992 1994 ers 1 scatterometer wind vectors from the images the position width and intensity of the convergence zones can be determined latitude time sections of ocean surface wind divergence show that the summer position of the itcz in the eastern pacific during the observed period exceeded the normal position northward by 3 6 latitude and the annual cycle in the western pacific for 1994 was quite weak implying a persistently unusual case

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

evidence of bias in estimations of earthquake size magnitudes of earthquakes determined using traditional methods show systematic deviations dependent on tectonic setting from accurate estimates of earthquake size magnitudes are overestimated for most of the continental earthquakes underestimated for mid oceanic ridges and differences of varying sign are obtained for subduction zones this is important in evaluating the seismic risk or consideration of effects such as the seismic versus aseismic strain release as seismic moments determined from magnitudes can be wrong by as much as a factor of four

vertical and latitudinal variation of the intertropical convergence zone derived using gps radio occultation measurements abstract using gps radio occultation refractivity data collected over the period of 2002 2013 we present a new method for identification of the intertropical convergence zone itcz the itcz is identified by estimating the maximum in the monthly meridional refractivity and specific humidity field by applying a gaussian fit at each longitude the interannual variability and climatology of the itcz is presented from 12 years of refractivity data this new method captures all the general features of itcz extent and its variability we also examine the effects of the itcz vertically during different seasons the itcz is observed mostly at eastern pacific in may month and it is zonally distributed in the september and october months of each year the zonal variability is large between lower and higher levels particularly over the indian monsoon and western pacific the latitudinal difference in the vertical extent between 850 hpa and higher levels is larger during the northern hemisphere nh summer than nh winter

empirical path and station corrections for surface wave magnitude ms using a global network summary one of the most commonly used methods of estimating the size of shallow earthquakes is the surface wave magnitude scale ms it has been known since the inception of the scale that the ms of a seismic disturbance recorded at different stations can vary due to path propagation and station terms but it has been difficult to quantify these variations on a global basis because until recently there has been no attempt to record ms in a uniform way on a worldwide network here we use ms measurements within the reviewed event bulletin reb of the international data centre idc which is produced to help monitor compliance with the comprehensive nuclear test ban treaty ctbt the idc collects waveforms from the as yet incomplete seismological network of the international monitoring system ims and ms is then measured using an automatic algorithm providing a unique set of surface wave observations in this paper we show that the ms values reported in the reb show distinct geographic variations we present preliminary attempts to model these observations in terms of a set of station corrections and a 2 d model which can be used to predict path corrections for ms the model shows a striking correlation with the known tectonic regions of the earth suggesting that this type of data set may provide a valuable tool for investigating shallow earth structure after modelling the residuals show some systematic patterns which cannot be explained using the model basis we have used these residuals are presumably due either to source radiation patterns or to complicated propagation effects not allowed for in the model such as refraction at ocean continent boundaries from the ctbt monitoring viewpoint ms station and path corrections are valuable because they should improve the effectiveness of event screening using mb ms however we recommend that implementation of such corrections should wait until the full seismological network of the ims is in place and until a fuller understanding of path effects on ms is available in particular it is vital that path propagation effects do not distort station corrections and that earthquake radiation patterns should not influence corrections which may be applied to surface waves from suspected explosions

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

intertropical convergence zones during the active season in daily data synoptic scale variability of vorticity structures in the lower troposphere of the tropics is analyzed in 23 yr of daily averaged high resolution reanalysis data the vorticity structures can be divided into zonally elongated vorticity strips classified as intertropical convergence zones itczs and more localized maxima termed westward propagating disturbances a composite of such variability is presented for the east to central pacific and for the east atlantic africa region both in summer the composite in the east pacific is zonally elongated and itcz like propagating westward over a number of days before dissipating the spatial structure of the vorticity strip shows the characteristic cyclonic tilt into the latitudinal direction with time that is also seen in modeling experiments the composite over the atlantic africa region shows two active regions that are correlated on synoptic time scales the disturbances in the southern region are better developed and longer lasting even though the time and space scales are smaller than over the east pacific overall variability over the atlantic is consistent with variability due to african easterly waves the double itcz in spring in the east pacific is different from the few earlier studies available it is stronger south of the equator and located at 10 s which is farther poleward than earlier studies have indicated the northern branch that is weak in comparison is located at 5 n the two branches of the double itcz tend to appear in tandem on the 2 week time scale

improved resolution in bayesian lithology fluid inversion from prestack seismic data and well observations part 1 methodology the focus of our study is lithology fluid inversion with spatial coupling from prestack seismic amplitude variation with offset avo data and well observations the inversion is defined in a bayesian setting where the complete solution is the posterior model the prior model for the lithology fluid lf characteristics is defined as a profile markov random field model with lateral continuity each vertical profile is further given as an inhomogeneous markov chain model upward through the reservoir the likelihood model is defined by profile and it relates the lf characteristics to the seismic data via a set of elastic material parameters and a convolution model the likelihood model is approximated the resulting approximate posterior model is explored using an efficient block gibbs simulation algorithm the inversion approach is evaluated on a synthetic realistic 2d reservoir seismic avo data and well observations are integrated in a consistent manner to obtain predictions of the lf characteristics wi