rheologic and structural controls on the deformation of okmok volcano alaska fems insar and ambient noise tomography 1 interferometric synthetic aperture radar insar data indicate that the caldera of okmok volcano alaska subsided more than a meter during its eruption in 1997 the large deformation suggests a relatively shallow magma reservoir beneath okmok seismic tomography using ambient ocean noise reveals two low velocity zones lvzs the shallow lvz corresponds to a region of weak fluid saturated materials within the caldera and extends from the caldera surface to a depth of 2 km the deep lvz clearly indicates the presence of the magma reservoir beneath okmok that is significantly deeper 4 km depth compared to previous geodetic based estimates 3 km depth the deep lvz associated with the magma reservoir suggests magma remains in a molten state between eruptions we construct finite element models fems to simulate deformation caused by mass extraction from a magma reservoir that is surrounded by a viscoelastic rind of country rock embedded in an elastic domain that is partitioned to account for the weak caldera materials observed with tomography this configuration allows us to reduce the estimated magma reservoir depressurization to within lithostatic constraints while simultaneously maintaining the magnitude of deformation required to predict the insar data more precisely the insar data are best predicted by an fem simulating a rind viscosity of 7 5 1016 pa s and a mass flux of 4 2 109 kg d from the magma reservoir the shallow weak layer within the caldera provides a coeruption stress regime and neutral buoyancy horizon that support lateral magma propagation from the central magma reservoir to extrusion near the rim of the caldera

physical properties of the lithosphere asthenosphere system in europe abstract all the geophysical fields considered evidence a clear structural difference between the adriatic sea ionian sea basin on one side and the tyrrhenian sea western mediterranean basin on the other the former displays continental type characteristics while the latter shows features definitely related to young ocean basins lateral variations in the thickness of the high velocity sub crustal layer the lid are clearly evidenced in the whole european area the lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic high velocity lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are present in the lithospheric part of the mantle

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

seasonal and interannual variability of the mid holocene east asian monsoon in coral δ18o records from the south china sea understanding the full range of past monsoon variability with reference to specific monsoon seasons is essential to test coupled climate models and improve their predictive capabilities we present a 54 year long high resolution skeletal oxygen isotope 6180 record extracted from a well preserved massive porites sp coral at hainan island south china sea to investigate east asian monsoon variability during summer and winter similar to 4400 calendar yr ago analysis of modem coral 6180 confirms that porites from hainan island are well positioned to record winter monsoon forcing of sea surface temperature sst as well as the influence of summer monsoon rainfall on sea surface salinity sss the coral record for similar to 4400 yr ago shows similar to 9 amplification of the annual cycle of 6 delta o 18 in good agreement with coupled ocean atmosphere models showing higher summer rainfall lower coral 618 0 and cooler winter ssts higher coral delta o 18 in response to greater northern hemisphere insolation seasonality during the middle holocene mean ssts in the south china sea during the mid holocene were within 0 5 degrees c of modem values yet the mean 6 180 for the fossil coral is similar to 0 6 parts per thousand higher than that for the modem coral suggesting that the 6 180 of surface seawater was higher by at least similar to 0 5 parts per thousand relative to modem values the o 18 enrichment is likely to be driven by greater advection of moisture towards the asian landmass enhanced monsoon wind induced evaporation and vertical mixing and or invigorated advection of saltier o 18 enriched pacific water into the relatively fresh south china sea the o 18 enrichment of the northern south china sea similar to 4400 yr ago contributes to mounting evidence for recent freshening of the tropical western pacific today winter sst and summer sss variability in the south china sea reflect the interannual influence of enso and the biennial variability inherent to monsoon precipitation spectral analysis of winter ssts similar to 4400 yr ago reveals a strong enso cycle at 6 7 y which is significantly longer than the average 3 6 y cycle observed since 1970 the results suggest that the influence of enso on winter ssts in the south china sea was well established by similar to 4400 yr ago however spectral analysis of summer sss similar to 4400 yr ago shows no significant enso cycle suggesting that teleconnections between enso and summer monsoon rainfall were restricted taken together the results indicate marked differences in enso monsoon interactions during the winter and summer monsoon seasons in the past the fossil coral delta o 18 record also shows that the amplitude of interannual sst and sss variability was stronger similar to 4400 yr ago despite enso variability being significantly weaker in the pacific region thus it appears that the strengthened mid holocene monsoon was sensitive to forces other than enso that acted as alternative drivers of interannual monsoon variability if this is the case greater interannual climate variability could accompany the strengthening of the asian monsoon predicted to occur during the 21st century as transient greenhouse warming preferentially warms eurasia even if enso perturbations remain relatively stable c 2005 elsevier b v all rights reserved

effect of an earthquake occurrence on the flow intensity of the subsequent events aftershocks or swarms indicate increase of the flow intensity in the vicinity of the initial earthquakes by normalizing their number according to the dynamic range of the standard frequency magnitude distribution the increase or positive aftereffect property of the initial earthquakes can be compared for different magnitude intervals periods of time or regions after applying accurate formal algorithm of aftershock identification it is possible to study negative aftereffect of the main events nonaftershocks in the catalog negative aftereffect means decrease of the probability of successive events in a time space vicinity of the main event when the aftershocks are over the negative effect is the most important part of the seismic cycle and seismic gaps approach global statistical test give high confidence level for the relative decrease in intensity of the flow of the events withm 7 in the first 20 25 years after the events withm 8 in their 1o vicinities in the total time period under study of approximately 60 years the decrease approximates 32 of the undisturbed intensity of the flow ofm 7 events in the vicinities self similar negative aftereffect was observed 3 7 years after 6 m 7 events it totals approximately 18 of the undisturbed intensity another type of self similarity of seismic regime with respect to the negative aftereffect is the decrease of probabilities of aftershocks with large magnitudes in aftershock sequences when we have adequate dynamic range in the catalog for the study of this property for example for main events withm 7 in the catalog with low cut off limitm 4 the statistical significance of the negative aftereffect is clear however the absolute value of the effect is also rather small about 10 which means that in 90 of the cases the aftershock sequences do not experience lack of energy due to the main shock energy release and follow a standard magnitude distribution for earthquakes in the entire catalog the small values of the negative aftereffect apparently indicate partial stress relase by earthquakes and may explain short recurrence time intervals after major earthquakes observed periodically in different places

decrease in seismic velocity observed prior to the 2018 eruption of kīlauea volcano with ambient seismic noise interferometry the 2018 k lauea eruption was a complex event that included deformation and eruption at the summit and along the east rift zone we use ambient seismic noise interferometry to measure time lapse changes in seismic velocity of the volcanic edifice prior to the lower east rift zone eruption our results show that seismic velocities increase in relation to gradual inflation of the edifice between 1 march and 20 april in the 10 days prior to the 3rd of may eruption onset a rapid seismic velocity decrease occurs even though the summit is still inflating we confirm that intereruptive velocity change is correlated with surface deformation while the velocity decrease prior to eruption is likely due to accumulating damage induced by the pressure exerted by the magma reservoir on the edifice the accumulating damage and subsequent decrease in bulk edifice strength may have facilitated increased transport of magma from the summit reservoir to the middle east rift zone

source mechanism and surface wave excitation for two earthquakes in northern baja california mexico summary two earthquakes of comparable local magnitude from different regions of northern baja california the 1975 july 17 pino solo earthquake ml 5 1 from the peninsular ranges region and the 1976 december 7 mesa de andrade earthquake ml 5 3 from the colorado river delta region are studied in detail to determine possible causes for the observed stronger excitation of surface waves by earthquakes from the delta region relative to earthquakes of comparable local magnitude in the peninsular ranges region data from distant stations are complemented with data from aftershock studies using local arrays and for the mesa de andrade earthquake with data from two strong motion stations the strong motion records for ihe mesa de andrade earthquake show that it consisted of two events 45 s apart which produced maximum recorded horizontal accelerations of 0 21 and 0 24g respectively at a distance of 18 km from the epicentre synthetic seismograms are used to help determine the depth of these events and their source time functions both events are relatively simple the second event is sharp and impulsive and could be thought of as an aftershock since it has a considerably smaller moment than the first event even though its recorded acceleration was higher comparison of measured parameters shows that while the local magnitude of the mesa de andrade earthquake is only 0 2 units larger than the pino solo earthquake and its source dimension is 2 2 times larger source areas 4 8 times larger its moment is larger by a factor of 6 2 8 5 this is approximately explained by the cy2 scaling law however the near source spectra and accelerations recorded on the strong motion accelerograph at riito at a distance of about 18 km are considerably larger than predicted by the scaling law this is probably a results of high stress drop asperities on the fault surface although near field focusing directivity may also have contributed

increased effective moisture in northern vietnam during the little ice age abstract we present a 650 yr record of hydroclimate inferred from 18o values of lacustrine carbonate from ao tien fairy pond in northern vietnam ao tien occupies a collapsed karst basin that formed during the worst drought of the last millennium i e the angkor i drought which marks a dry transitional period between the medieval climate anomaly and the little ice age a multi centennial trend of increasing effective moisture spans the little ice age ending with aridity in the late 18th century that accompanied great societal turmoil across southeast asia after 1850 ce the ao tien record exhibits a drying trend that continues to the present over the last 650 years the 18o inferred hydroclimate is significantly correlated with the reconstructed southern oscillation index of precipitation soipr suggesting that a prolonged la nina like state existed during the little ice age generating overall wetter conditions in vietnam decadal scale droughts and pluvials from the ao tien record agree with a robust tree ring hydroclimate reconstruction from southern vietnam that identified the angkor i and ii droughts of the late 13th early 14th centuries and significant droughts during the early and late 17th century and latter half of the 18th century the decrease in effective moisture during the last 30 years is also evident in the tree rings and is consistent with a documented weakening of the pacific walker circulation major pluvials are indicated for the period between the two angkor droughts and the wettest period of the record is during the early 18th century comparison of the ao tien data with records from indonesia to china indicates regionally coherent climate during the little ice age however the overall wet conditions in easterly sites are difficult to ascribe to shifts in the itcz rather the pattern suggests that pacific walker circulation may have been the overriding control on precipitation

two dilatancy based models to explain coda wave precursors and p s spectral ratio abstract some coda wave precursors can be predicted by the dilatancy model others need more complicated models the first of the models proposed here takes into account the compression of the medium around the swelling dilatancy zone and explains several observed precursor properties a simple theoretical model is employed to describe anisotropic s wave absorption in a microcracked medium under shear load the second model is used to explain the radiation bursts observed in coda in the preparation period and which overlap background scattered waves this model also explains the unusually high p s energy ratio of seismic waves from shocks in preparation zones the concept of seismic emission is employed to explain these phenomena two possible modes of emission are proposed 1 1 passive radiation generated by an abrupt dilatancy drop produced by stress drop in and around the earthquake source and 2 2 active radiation stimulated by seismic waves in a preparation zone or in any other volume of the lithosphere which is in a state of changing dilatancy

the influence of the interdecadal pacific oscillation on temperature and precipitation over the globe the interdecadal pacific oscillation ipo is a 40 60 year quasi oscillation seen mostly in the pacific basin but its impacts on surface temperature t and precipitation p have been found over australia the southwest u s and other regions here a global analysis of ipo s impacts on t and p and its modulation of enso s influence on t and p over the globe is performed using observational and reanalysis data and model simulations since 1920 there are two warm 1924 1944 and 1977 1998 and two cold 1945 1976 and 1999 present ipo phases whose change is associated with abrupt shifts in north pacific sea level pressure slp and contrasting anomaly patterns in t and p and atmospheric circulation over the eastern and western pacific the ipo explains more than half of the interdecadal variations in t and p over many regions such as northeastern australia western canada and northern india significant correlations between the ipo and local p are observed over eastern australia southern africa and the southwest u s the ipo also modulates enso s influence on local t and p over most of these regions t over northern india is positively correlated with nino3 4 enso index during cold ipo phases but the correlation turns negative or insignificant during ipo warm phases over northeastern australia the t versus enso and p versus enso correlations are stronger during the ipo cold phases than during the warm phases the p versus enso correlation over southern africa tends to be negative during ipo warm phases but becomes weaker or insignificant during ipo cold phases the ipo induced p anomalies can be explained by the associated anomaly circulation which is characterized by a high slp center and anti cyclonic flows over the north pacific and negative slp anomalies and increased wind convergence over the indonesia and western pacific region during ipo cold phases these observed influences of the ipo on regional t and p are generally reproduced by an atmospheric model forced by observed sea surface temperatures

lateral variations in the european lithosphere and seismic activity abstract in the mediterranean region an interesting correlation between the model of the lithospheric structure and the distribution of epicentres of shallow earthquakes with magnitudes larger or equal to 6 5 can be established in some areas these areas namely northern and southern italy the calabrian and hellenic arcs correspond to belts where high rigidity values in the lid are associated with very rapid changes in the lithospheric thickness

a mechanical model of precursory source processes for some large earthquakes a mechanical model is presented of precursory source processes for some large earthquakes along plate boundaries it is assumed that the pre seismic period consists of the upward progression of a zone of slip from lower portions of the lithosphere towards the earth s surface the slip front is blocked by local asperities of different size and strength these asperities may be zones of real alteration of inherent strength or instead may be zones which are currently stronger due to a local slowdown of a basically rate dependent frictional response such blocking by a single large asperity or array of asperities produces quiescence over a segment of plate boundary until gradual increase of the stress concentration forces the slip zone through the blocked region at one end of the gap thus nucleating a seismic rupture that propagates upwards and towards the other end this model is proposed to explain certain distinctive seismicity patterns that have been observed before large earthquakes notably quiescence over the gap zone followed by clustering at its ends prior to the main event a discussion of mechanical factors influencing the process is presented and some introductory modelling performed with the use of a generalized elsasser model for lithospheric plates and the line spring model for part through flaws slip zones at plate boundaries is outlined briefly

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

possible linkage between the monsoon trough variability and the tropical cyclone activity over the western north pacific abstractthe present study investigates the influence of the monsoon trough mt on the interannual variability of tropical cyclone tc activity over the western north pacific during july november for the period 1979 2007 it is shown that the tc activity is closely related to the mt location during the years when the mt extends eastward retreats westward more less tcs form within the southeastern quadrant of the western north pacific such a relationship can be explained by the changes in large scale environmental factors associated with the movement of the mt an eastward extension of the mt coincides with warmed ocean surface enhanced convection increased relative humidity in the lower and midtroposphere reduced vertical shear of zonal wind intensified upper level divergence and low level anomalous cyclonic vorticity over the southeast quadrant of the western north pacific these conditions associated with the eastern extension of the mt are favorable for tc genesis while those associated w

cluster analysis of typhoon tracks part ii large scale circulation and enso abstract a new probabilistic clustering method based on a regression mixture model is used to describe tropical cyclone tc propagation in the western north pacific wnp seven clusters were obtained and described in part i of this two part study in part ii the present paper the large scale patterns of atmospheric circulation and sea surface temperature associated with each of the clusters are investigated as well as associations with the phase of the el nino southern oscillation enso composite wind field maps over the wnp provide a physically consistent picture of each tc type and of its seasonality anomalous vorticity and outgoing longwave radiation indicate changes in the monsoon trough associated with different types of tc genesis and trajectory the steering winds at 500 hpa are more zonal in the straight moving clusters with larger meridional components in the recurving ones higher values of vertical wind shear in the midlatitudes also accompany the straight moving tracks compared to

stress transfer and nonlinear stress accumulation at subduction type plate boundaries application to the aleutians a study of stress accumulation in seismic gaps and of stress transfer along linear plate boundaries is presented time dependent reloading of plate boundaries following seismic ruptures is modeled by a modified elsasser model of a coupled lithosphere asthenosphere plate system this model is applied to study a series of large earthquakes in the aleutian islands and the alaska peninsula in 1938 1965 it is found that the rat island earthquake and the 1948 earthquake in the central aleutians are likely to have been triggered by adjacent ruptures in the sense that their occurrence would have come at a later time had their neighboring segments not been ruptured stresses in the unalaska gap and the shumagin gap are at a relatively high level and these segments of the plate boundary may be expected to rupture in the near future in general in the ten years about 16 of the earthquake cycle for the aleutians following an earthquake the stress recovery in the rupture zone is highly nonlinear resulting in a much more rapid stress accumulation than the linear case even at a later stage of an earthquake cycle adjacent ruptures can cause an acceleration of loading rate in addition to the coseismic stress jump a good example is the influence of the 1964 alaska earthquake on the 1938 rupture zone a general conclusion of this work is that long term earthquake prediction models must take into account the nonlinear stress accumulation behavior in seismic gaps also we have shown the interaction of adjacent plate boundary segments which suggests that some large earthquakes may have been triggered by nearby ruptures

magma flux at okmok volcano alaska from a joint inversion of continuous gps campaign gps and interferometric synthetic aperture radar 1 volcano deformation is usually measured using satellite geodetic techniques including interferometric synthetic aperture radar insar campaign gps and continuous gps differences in the spatial and temporal sampling of each system mean that most appropriate inversion scheme to determine the source parameters from each data set is different most studies either compare results from independent inversions or subsample the data sets to the lowest common factor it is unclear whether differences in the solution reflect differences in source behavior differences in measurement bias or differences in inversion technique here we develop a single inversion procedure that captures the benefits of each system especially the daily sampling of continuous gps and the high spatial resolution of insar okmok volcano alaska is an ideal target for such a test because a long series 15 years of insar and continuous gps measurement exists and the source is almost continuously active and in a stable location

shear wave polarizations near the north anatolian fault ii interpretation in terms of crack induced anisotropy summary the polarizations of shear waves recorded by networks of digital thxee component seismometers immediately above small earthquakes near the north anatolian fault in turkey display shear wave splitting on almost all shear wave seismograms recorded within the shear wave window this splitting is incompatible with source radiation patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths this paper interprets the phenomena in terms of widespread crack induced anisotropy distributions of stress induced cracks model many features of the observations and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns this evidence for widespread crack induced anisotropy lends strong support to the hypothesis of extensive dilatancy anisotropy eda suggested by laboratory experiments in subcritical crack growth the crucial evidence confirming some form of eda would be observations of temporal changes in shear wave splitting as the stress field alters the crack density and crack geometry there is some weak evidence for such temporal changes at one site but further analysis of suitable digital three component seismometer networks in seismic areas is required to confirm eda

climate variability in central china over the last 1270 years revealed by high resolution stalagmite records oxygen and carbon isotopic variations in the upper section of a stalagmite sf 1 from buddha cave 33 40 n 109 05 e dated by 230th 234u 210pb and lamination counting to a time resolution as fine as 1 3 years have recorded climate changes in central china for the last 1270 years the changes include those corresponding to the medieval warm period little ice age and 20th century warming lending support to the global extent of these events the isotopic records also show cycles of 33 22 11 9 6 and 7 2 years the 33 year cycle could well represent the 35 year periodicity of climate fluctuations previously recognized in china and europe cycles of 22 11 and 9 6 years have often been associated with the sunspot or lunar orbit variations the 7 2 year cycle was recently identified also in tree ring records from an area close to buddha cave these cycles suggest that external forcing e g solar irradiance may affect the summer monsoon over eastern china the general consistency between the climate characteristics inferred from the stable isotope records of sf 1 and those from other proxy records underscores the value of stalagmites as recorders of paleoclimate

monitoring crustal changes at volcanoes by seismic noise interferometry mt etna case of study abstract in this work we analysed the seismic noise recorded at mt etna by 18 stations during the interval 2007 2015 in the frequency band 0 1 0 3 hz chosen to avoid contamination from volcanic tremor variations in time of medium seismic velocity in the range 0 8 to 0 8 were found mostly affecting the stations located on the volcano summit and flanks based on the investigated frequency content the v v changes took place from the surface to a depth of 4 5 6 5 km to identify the source mechanism of the observed medium changes the variations were quantitatively compared by wavelet transform coherence with volcano tectonic and meteorological parameters a significant relationship with meteorological parameters with seasonal periodicity especially air temperature and snow loading was found probably caused by thermo elastic strain and increasing decreasing surface loading cycles moreover a sharp medium velocity decrease taking place in mid december 2009 and clearly time related to the largest volcano tectonic strain release phenomenon of the investigated period was also found such a velocity decrease was interpreted as resulting from ascent of fluids and gas exsolution taking place at the same time as the volcano tectonic swarm

speleothem evidence for temporal spatial variation in the east asian summer monsoon since the medieval warm period published annual to decadal resolution stalagmite d 18 o records since ad 900 from six caves dongge furong heshang buddha shihua and wanxiang in china were analyzed to detect temporal and spatial variability of the east asian summer monsoon strength which strongly affects wet dry conditions in eastern china the empirical mode decomposition method was used to obtain trends of the six cave records after the base trend was determined d 18 o anomalies of each record were computed by subtracting the base trend mean d 18 o anomaly values of the detrended time series for each cave record were calculated for four periods i medieval warm period mwp ad 900 1250 ii little ice age phase 1 lia 1 ad 1250 1550 iii little ice age phase 2 lia 2 ad 1550 1850 and iv modern period md ad 1850 2000 from these anomalies the temporal and spatial variability of wet dry conditions has been identified positive values of the mean d 18 o anomalies indicating drier conditions appeared in the lower yangtze river drainage area and southeast coast area during md 1 lia 1 and mwp whereas negative values existed in north south and yangtze areas of eastern china during lia 2 the results agree with the dryness wetness index reconstructed by chinese historic records in general these results illustrate that wet and dry conditions in different regions of eastern china could be opposite under monsoon influence so that no single speleothem d 18 o record could represent the monsoonal climate in this vast region climatic patterns in the monsoonal region can be either a combination of warm wet and cold dry or a combination of cold wet and warm dry on annual to centennial scales a 128 year periodic cycle exists in all six cave records whereas 64 year possibly a harmonic of 128 year periodicity and 42 year periodicities appear in shihua heshang and dongge records these cycles may reflect the influence of solar activity on the east asian summer monsoon copyright 2012 john wiley sons ltd

time variation of b and qc at mt etna 1981 1987 abstract time variations of seismic attenuation qc and of the coefficient b in the frequency magnitude formula are presented for mt etna during 1981 1987 significant variations of both parameters were found suggesting long period variations of the physical state of the volcano

monitoring of phreatic eruptions using interferometry on retrieved cross correlation function from ambient seismic noise results from mt ruapehu new zealand abstract since the last major eruption in 1995 96 mt ruapehu has erupted twice on 4 october 2006 and on 25 september 2007 these events occurred without any clear precursors and were mostly phreatic explosions the technique of interferometry on retrieved cross correlation function from ambient seismic noise irccasn is used to monitor subtle temporal changes of mt ruapehu s elastic properties the computation of cross correlation functions of seismic noise recorded at several stations around the volcano allowed us to observe variations during the 2006 eruption period the comparison between a reference cross correlation function and a current cross correlation function allows us to infer relative seismic velocity variations a 0 8 decrease of relative seismic velocity in the edifice starting two days before the 2006 eruption was observed this drop is due to a reversible and ephemeral effect which can be attributed to a pressurization of a magma pocket beneath the east flank of ruapehu due to new magma entering a small reservoir this pressure increase produced an inflation of the east flank of ruapehu and opened fractures in this area leading to a localised drop of seismic velocity we conducted the same analysis for the 2007 eruption but no significant seismic velocity variation was observed this difference is possibly due to the varying time scales of pressurization for the two events and also the irccasn time resolution an analysis of the seismicity before these two eruptions allows us to propose a conceptual model which explains the velocity drop for the 2006 eruption and the lack of velocity variations for the 2007 eruption since there was no surface deformation recorded by the geonet gps network we modelled the maximum radius and pressure change for a simple mogi point source at 5 km depth that produced no deformation we inferred the maximum fresh magma volume of 0 0017 km 3 entering the reservoir as a detectability threshold for gps ground deformation measurements

dynamics of the intertropical convergence zone over the western pacific during the little ice age precipitation patterns in the western pacific changed at the onset of the little ice age a synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone

spatio temporal changes in seismic velocity associated with the 2000 activity of miyakejima volcano as inferred from cross correlation analyses of ambient noise abstract miyakejima volcano japan showed strong and interesting volcanic activities in 2000 with the occurrence of dike intrusions caldera formation and a large amount of gas emission to understand temporal changes of the volcanic structure associated with this activity we apply ambient noise correlation analyses to the seismic records of five seismic stations at miyakejima volcano from july 1999 to december 2002 we calculate cross correlation functions ccfs for eight available station pairs at frequency bands of 0 4 0 8 hz and 0 8 1 6 hz and retrieve the rayleigh waves propagating with a group velocity of about 1 0 km s comparing ccfs obtained for each day with the reference ccfs that are calculated from a few months of data we estimate seismic velocity changes before and after the 2000 activity results at the two frequency bands show seismic velocity increase and decrease shallow structure at the volcanic edifice on the flanks experienced a seismic velocity increase up to 3 3 on the other hand the regions located close to the collapsed caldera show a seismic velocity decrease down to 2 3 to understand the mechanisms that may introduce these seismic velocity increase and decrease we examine several possible mechanisms of the velocity changes stress changes due to volcanic pressure sources and caldera formation and topographic changes by using the deflation sources previously determined from gps data we calculate the stresses at depths of 0 km and 1 km at the volcano the results suggest that the seismic velocity increases observed at seismic paths on the volcanic flank are explained by the compression caused by the deflation sources associated with magma activity in 2000 stress sensitivities of the seismic velocity changes are estimated to be 1 5 10 2 to 2 2 10 2 mpa 1 and 4 6 10 3 to 2 4 10 2 mpa 1 at frequency bands of 0 4 0 8 hz and 0 8 1 6 hz respectively which are in the range of the previously reported results our three dimensional numerical calculations on seismic wave propagation show that the seismic velocity decreases observed at seismic paths crossing the collapsed caldera can be explained by topographic changes introduced by a caldera we further suggest that the seismic velocity decreases detected around the regions close to the caldera may originate from the dilated regions cause by formation of the caldera

4 d noise based seismology at volcanoes ongoing efforts and perspectives monitoring magma pressure buildup at depth and transport to surface is a key point for improving volcanic eruption prediction seismic waves through their velocity dependence to stress perturbations can provide crucial information on the temporal evolution of the mechanical properties of volcanic edifices in this article we review past and ongoing efforts for extracting accurate information of temporal changes of seismic velocities at volcanoes continuously in time using records of ambient seismic noise we will first introduce the general methodology for retrieving accurate seismic velocity changes from seismic noise records and discuss the origin of seismic velocity temporal changes in rocks we will then discuss in a second part how noise based monitoring can improve our knowledge about magmatic activity at a long years to a short days time scale taking example from piton de la fournaise volcano la reunion we will also mention ongoing efforts for operational noise based seismic monitoring on volcanoes further we will discuss perspectives for improving the spatial localization of detected velocity changes at depth with a special focus on the use of dense seismic arrays in the last part we will finally explore the complex response of volcanic regions to seismic shaking with an example from japan and show how imaging seismic velocity susceptibility allows characterizing the state of pressurized fluids in volcanic regions

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

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

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

a 400 year record of hydroclimate variability and local enso history in northern southeast asia inferred from tree ring δ18o abstract we present here a chronology of tree ring cellulose 18 o for the period 1588 2002 based on individual measurements of seven fokienia hodginsii trees growing in northern laos response function analysis of meteorological data revealed that this oxygen isotope chronology has a significant negative correlation with monsoon season precipitation the water level of the mekong river and the palmer drought severity index pdsi our reconstructed monsoon season pdsi which accounts for 41 5 of pdsi variance showed that wetter phases occurred during the periods ad 1660 1695 and ad 1705 1790 that the main drier periods were ad 1630 1660 ad 1900 1940 and ad 1954 2002 and that there has been a trend of decreasing moisture during the monsoon season over the last 200 years a reduction in monsoon activity can also be seen in various tree ring oxygen isotope records from the himalaya tibet plateau and southeast asia rising sea surface temperatures over the tropical pacific and indian ocean could be responsible for this reduction in the asian summer monsoon by combining proxies sensitive to the el nino southern oscillation enso in northern laos and vietnam we were able to reconstruct the annual multivariate enso index mei and local enso event history and so improve our understanding of long term variations in enso and its influences on southeast asia

interdecadal pacific oscillation reconstructed from trans pacific tree rings 1350 2004 ce the interdecadal pacific oscillation ipo represents the decadal mode of the el nino southern oscillation phenomenon as such the ipo is one of the dominant modes of decadal climate variability on both sides of the pacific ocean basin for this paper we utilized a newly developed tree ring data network comprised of five multi centennial vietnamese cypress ring width chronologies that range from around 11 n 23 n latitude we combined these data with an average of tree ring derived drought indices from the north american drought atlas over the south central usa from a box that spans from 27 5 n 35 0 n 85 0 110 0 w and contains 55 gridpoints and more than 100 tree ring site chronologies these 2 locations exhibit rainfall variations that are strongly negatively correlated with each other and are representative of the influence of the ipo on terrestrial rainfall the final reconstruction model weighted most heavily on the three most southerly of the five vietnamese cypress records spans from 1350 to 2004 and explains nearly 57 of the variance in the original ipo data for the 5 month season of october february the reconstruction model passes all standard statistical tests using a split calibration verification scheme we reveal 15 positive and 15 negative phase shifts of the ipo prior to the period of instrumentation suggesting that the ipo has been active for at least the past seven centuries with varying degrees of intensity we compare our reconstruction with two related millennial records the macdonald and case geophys res lett 32 8 l08703 2005 tree ring derived reconstruction of the pacific decadal oscillation and an ice core derived reconstruction of the ipo from the law dome ice core in antarctica by vance et al geophys res lett 33 6 l06712 2015 while there is good general agreement with the latter record there are three key periods of the past where the two records are out of phase and we explore the reasons for this disparity direct comparison with the related tripole index tpi shows weaker correlation likely owing to the stronger relationship between our tree ring data and the equatorial pacific region relative to the north and south regions of the pacific that combine to comprise the tpi calculation

monitoring changes in seismic velocity related to an ongoing rapid inflation event at okmok volcano alaska okmok is one of the most active volcanoes in the aleutian arc in an effort to improve our ability to detect precursory activity leading to eruption at okmok we monitor a recent and possibly ongoing gps inferred rapid inflation event at the volcano using ambient noise interferometry ani applying this method we identify changes in seismic velocity outside of okmok s caldera which are related to the hydrologic cycle within the caldera we observe decreases in seismic velocity that are associated with the gps inferred rapid inflation event we also determine temporal changes in waveform decorrelation and show a continual increase in decorrelation rate over the time associated with the rapid inflation event the magnitude of relative velocity decreases and decorrelation rate increases are comparable to previous studies at piton de la fournaise that associate such changes with increased production of volatiles and or magmatic intrusion within the magma reservoir and associated opening of fractures and or fissures notably the largest decrease in relative velocity occurs along the intra station path passing nearest to the center of the caldera this observation along with equal amplitude relative velocity decreases revealed via analysis of intra caldera autocorrelations suggest that the inflation source may be located approximately within the center of the caldera and represent recharge of shallow magma storage in this location importantly there is a relative absence of seismicity associated with this and previous rapid inflation events at okmok thus these ani results are the first seismic evidence of such rapid inflation at the volcano

estimating lava volume by precision combination of multiple baseline spaceborne and airborne interferometric synthetic aperture radar the 1997 eruption of okmok volcano alaska interferometric synthetic aperture radar insar techniques are used to calculate the volume of extrusion at okmok volcano alaska by constructing precise digital elevation models dems that represent volcano topography before and after the 1997 eruption the posteruption dem is generated using airborne topographic synthetic aperture radar topsar data where a three dimensional affine transformation is used to account for the misalignments between different dem patches the preeruption dem is produced using repeat pass european remote sensing satellite data multiple interferograms are combined to reduce errors due to atmospheric variations and deformation rates are estimated independently and removed from the interferograms used for dem generation the extrusive flow volume associated with the 1997 eruption of okmok volcano is 0 154 spl plusmn 0 025 km sup 3 the thickest portion is approximately 50 m although field measurements of the flow margin s height do not exceed 20 m the in situ measurements at lava edges are not representative of the total thickness and precise dem data are absolutely essential to calculate eruption volume based on lava thickness estimations this study is an example that demonstrates how insar will play a significant role in studying volcanoes in remote areas

structure and variances of equatorial zonal circulation in a multimodel ensemble the structure and variance of the equatorial zonal circulation as characterized by the atmospheric mass flux in the equatorial zonal plane is examined and inter compared in simulations from 9 cmip3 coupled climate models with multiple ensemble members and the ncep ncar and era 40 reanalyses the climate model simu lations analyzed here include twentieth century 20c3m and twenty first century sres a1b simulations we evaluate the 20c3m modeled zonal circulations by com paring them with those in the reanalyses we then examine the variability of the circulation its changes with global warming and the associated thermodynamic maintenance the tropical zonal circulation involves three major com ponents situated over the pacific indian and atlantic oceans the three cells are supported by the corresponding diabatic heating extending deeply throughout the tropo sphere with heating centers apparent in the mid tropo sphere seasonal features appear in the zonal circulation including variations in its intensity and longitudinal migration most models and hence the multi model mean represent the annual and seasonal features of the circulation and the associated heating reasonably well the multi model mean reproduces the observed climatology better than any individual model as indicated by the spatial pattern correlation and mean square difference of the mass flux and the diabatic heating compared to the reanalysis based values projected changes in the zonal circulation under a1b forcing are dominated by mass flux changes over the pacific and indian oceans an eastward shift of the pacific walker circulation is clearly evident with global warming with anomalous rising motion apparent over the equatorial central pacific and anomalous sinking motions in the west and east which favors an overall strengthening of the walker circulation the zonal circulation weakens and shifts westwards over the indian ocean under external forcing whereas it strengthens and shifts slightly west wards over the atlantic ocean the forced circulation changes are associated with broad sst and atmospheric diabatic heating changes in the tropics linear trends of these forced circulation changes as characterized by regional spatial maximum amplitudes of mass fluxes and their longitudes over the three oceans are statistically significant at the 5 level for 2000 2099 for the multi model mean however wide differences of the trends are apparent across the models because of both deficiencies in the simulation of the circulations in different models and the high internal variability of the circulations

geochemistry of dissolved inorganic carbon and carbonate weathering in a small typical karstic catchment of southwest china isotopic and chemical constraints abstract the sources of dissolved inorganic carbon dic and rock weathering processes were studied in the houzhai catchment a typical karstic catchment in the changjiang river basin southwest china the carbon isotopic compositions 13 c dic of dic in the samples collected from the catchment vary from 13 5 to 6 9 with a mean value of 9 8 the dic in the catchment is thereby considered to be mainly derived from soil co 2 and weathering of carbonate rocks the dic concentrations and the 13 c dic values show pronounced seasonal variations with the lowest values being observed during the high flow season from may to october the logpco 2 values in the waters were positively correlated with the dic contents and negatively correlated to the saturation index of calcite sic and 13 c dic values these observations indicate that co 2 derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment based on a chemical mass balance the weathering rate of carbonate rocks in the houzhai catchment was estimated to be approximately 133 t km 2 year or 584 10 3 mol km 2 year in terms of co 2 consumption rate which is higher than the reported values for other rivers in southwest china

a high resolved record of the asian summer monsoon from dongge cave china for the past 1200 years abstract two annually laminated and 230th dated stalagmite oxygen isotope 18o records from dongge cave china provided a high resolution asian summer monsoon asm history for the past 1200 years a close similarity between annual band thickness and stable isotope analyses 13c and 18o suggests the calcite 18o is most likely a proxy associated with asm precipitation the two duplicated stalagmite 18o records show that the asm varies at a periodicity of 220 years concordant with a dominant cycle of solar activity a period of strong asm activity occurred during the sporer minimum 1450 1550 a d followed by a striking drop circa 1580 a d potentially consistent with the social unrest in the final decades of china s ming dynasty 1368 1644 a d centennial scale changes in asm precipitation over the last millennium match well with changes in tropical atlantic sea surface temperatures ssts and south american summer monsoon precipitation our findings suggest that variations in low latitude monsoon precipitation are probably driven by shifts in the mean position of the intertropical convergence zone itcz which is further mediated by solar activity and tropical ssts

post glacial evolution of the indo pacific warm pool and el nino southern oscillation recent research has revealed new insights into the temperature size and variability of the indo pacific warm pool ipwp and the nature of the el nino southern oscillation enso since the last glacial maximum lgm sea surface temperature sst reconstructions from foraminiferal mg ca alkenone and revised coral sr ca palaeothermometry agree that ssts in the ipwp during the lgm were similar to 3degreesc cooler than at present in the central portion of the ipwf the rapid post glacial rise in sst led the deglaciation by similar to 3000 years to produce near modern ssts by the early holocene in contrast further west and north post glacial shifts in ssts in the south china and sulu seas are synchronous with abrupt climate changes in the north atlantic new evidence for the nature of the little ice age in the tropics has been obtained from a 420 year record of coral sr ca and 6180 from the great barrier reef australia this indicates that ssts and salinity were higher in the 18th century than in the 20th century the results suggest that the tropical pacific played a role as a source region of water vapour during the global expansion of little ice age glaciers the onset of modern enso periodicities is identified by palaeo enso records throughout the tropical pacific region similar to 5000 years ago with an abrupt increase in enso magnitude similar to 3000 years ago individual enso events recorded by corals reveal that the precipitation response to el nino temperature anomalies was subdued in the mid holocene the apparent non linear onset of enso in the late holocene appears to reflect abruptly enhanced interaction between the southern oscillation and the pacific intertropical convergence zone comparisons of precipitation variability recorded by great barrier reef corals with enso indices for the last 350 years confirms that non stationarity of enso teleconnections is a natural characteristic of modern climate c 2003 elsevier ltd and inqua all rights reserved

tracking magma volume recovery at okmok volcano using gps and an unscented kalman filter 1 changes beneath a volcano can be observed through position changes in a gps network but distinguishing the source of site motion is not always straightforward the records of continuous gps sites provide a favorable data set for tracking magma migration dense campaign observations usually provide a better spatial picture of the overall deformation field at the expense of an episodic temporal record combining these observations provides the best of both worlds a kalman filter provides a means for integrating discrete and continuous measurements and for interpreting subtle signals the unscented kalman filter ukf is a nonlinear method for time dependent observations we demonstrate the application of this technique to deformation data by applying it to gps data collected at okmok volcano seven years of gps observations at okmok are analyzed using a mogi source model and the ukf the deformation source at okmok is relatively stable at 2 5 km depth below sea level located beneath the center of the caldera which means the surface deformation is caused by changes in the strength of the source during the 7 years of gps observations more than 0 5 m of uplift has occurred a majority of that during the time period january 2003 to july 2004 the total volume recovery at okmok since the last eruption in 1997 is 60 80 the ukf allows us to solve simultaneously for the time dependence of the source strength and for the location without a priori information about the source

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

coda waves a review the analysis and interpretation of coda waves have received increasing attention since the early seventies in the past few years interest in this subject has spread worldwide and the study of high frequency seismic coda waves has become a very important seismological topic as a conclusion of the studies accomplished in this time coda waves are considered the result of scattering processes caused by heterogeneities acting on seismic waves p ands waves play a particularly important role in this interaction the process introduces an attenuation which added to the intrinsic absorption gives the observed apparent attenuation therefore coda waves constitute a thumbprint left by the heterogeneities on the seismograms coda waves offer decisive information about the mechanism of how scattering and attenuation take place this review describes coda waves in detail and summarizes the work done in this subject to 1986 the relation between coda waves and attenuation in the context of research on seismic scattering problems is stressed particular attention has been given to the application of coda waves to estimate source and medium parameters the state of the art of the temporal variations of coda wave shape and the possible use of these variations as an earthquake precursor also are presented care has been taken to introduce the statistical models used to deal with the heterogeneities responsible for scattering

monsoon tropical ocean interaction in a network of coral records spanning the 20th century abstract the 20th century evolution of basin wide gradients in surface ocean properties provides one essential test for recent models of the interaction between the asian monsoon and the tropical ocean because various feedback mechanisms should result in characteristic regional patterns of variability although the instrumental record of climate variability in the tropics is essentially limited to the last few decades the stable isotopic composition of living corals provides an effective means for extending the instrumental observations here we present two coral isotopic records from the indonesian maritime continent and we use these records with other previously published records to describe i the relationship between western pacific and central pacific climate variability over the past century with special emphasis on the biennial band and ii the strength of the west east indian ocean dipole we find that the amplitude of the biennial cycle in the pacific did not vary inversely with the strength of enso el nino southern oscillation as might be expected from some models of monsoonal feedback on the central pacific instead the biennial variability was modulated on decadal timescales throughout much of the pacific we also show that the zonal oxygen isotopic gradient in the indian ocean coral records was significantly correlated with central pacific sea surface temperature on a variety of timescales thus it is likely that this coral dipole was a product of strong enso like teleconnections over the indian ocean as opposed to being the result of unique indian ocean or monsoonal dynamics

modulation of north pacific tropical cyclone activity by three phases of enso abstract tropical pacific ocean warming has been separated into two modes based on the spatial distribution of the maximum sea surface temperature sst anomaly an east pacific warming epw and a central pacific warming cpw when combined with east pacific cooling epc these three regimes are shown to have different impacts on tropical cyclone tc activity over the north pacific by differential modulation of both local thermodynamic factors and large scale circulation patterns in epw years the genesis and the track density of tcs tend to be enhanced over the southeastern part and suppressed in the northwestern part of the western pacific by strong westerly wind shear the extension of the monsoon trough and the weak wind shear over the central pacific increases the likelihood of tc activity to the east of the climatological mean tc genesis location in cpw years the tc activity is shifted to the west and is extended through the northwestern part of the western pacific the westward shifting of c

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

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

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

east asian monsoon variability since the mid holocene recorded in a high resolution absolute dated aragonite speleothem from eastern china abstract paleoclimatic conditions associated with the east asian monsoon are reconstructed for the mid to late holocene using 18o values 819 measurements from a precisely dated 10 230th dates aragonite stalagmite from lianhua cave hunan province china 18o values 1 6 to 7 0 are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation throughout this period the intensity of east asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the intertropical convergence zone itcz punctuating this first order trend are abrupt millennial to decadal scale fluctuations the most prominent of which occurred around 3337 5 yr bp and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of neoglacial conditions comparisons between the 18o values of stalagmite a1 and previously published data from stalagmite hs 4 from heshang cave and stalagmites d4 and da from dongge cave china demonstrate a similar regional response to changes in east asian monsoonal circulation several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the east asian monsoon during the holocene multi taper method mtm lomb scargle and single spectrum analysis ssa results reveal common periodicities that are unlikely to be artifacts of any single technique the periodicities expressed in the stalagmite 18o records occur at both solar and non solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi regular intervals which may indicate long term cyclicity that is unconstrained by the chronology of the record

global patterns of enso induced precipitation although there have been many analyses of el nino southern oscillation enso induced precipitation anomalies global patterns from these analyses remain incomplete here we combine recent satellite estimates of oceanic precipitation and historical rain gauge records to derive a global climatology of enso induced precipitation anomalies using empirical orthogonal function eof analyses the patterns suggest that the re arrangement of convection centers of the walker circulation during enso events induces large precipitation anomalies in the tropics while associated changes in the monsoon systems through the hadley cell over the pacific indian and atlantic oceans and their interactions with midlatitude westerlies generate coherent anomaly patterns over the extratropics our results can be used to evaluate climate models and forecast enso induced precipitation anomalies

stable isotopes of oxygen and hydrogen in the truckee river pyramid lake surface water system 3 source of water vapor overlying pyramid lake during 1988 and 1989 a series of water vapor extractions were conducted in the pyramid lake basin to determine the source of moisture that overlies the lake calculations of the isotopic and water vapor balances were made from isotopic and meteorological data from the pyramid lake and reno nevada areas the results indicate that in the warm season most of the moisture that overlies the lake is derived from evaporation as opposed to advected moisture isotopic fluxes at the lake surface can be approximated by climatic data from the lake site which simplifies the calculation of this input in numerical simulations of the isotopic evolution of the lake the stable isotopic composition of a lake is a function of the volume weighted isotopic values of each component of the lake s hydrologic balance researchers have used the stable isotope history of a lake together with the volume weighted isotopic composition of easily measured components of the hydrologic balance to estimate the stable isotope values or amounts of less easily measured components of the hydrologic balance see iaea 1970 1979 it is usually relatively simple to quantify the amounts and isotopic compositions of components of the surface water system and the isotopic composition of groundwater it is often more difficult to quantify the amount and direction of groundwater transport across the sediment water interface and the amount and isotopic composition of lake surface evaporation the isotopic value of water evaporated from a lake is highly dependent on the isotopic value acknowledgments we express our appreciation to those who assisted in sampling including jim davis dan mosley and nancy vucinich special thanks to irving friedman who loaned us the copper traps used for water vapor extraction to carol kendall and tyler coplen who oversaw the isotopic analyses to james ashby who maintained the weather stations and to steve hostetler who extracted the meteorological data from the weather station database and stratified the wind data for the sutcliffc and northshore sites we also thank zell peterman steve hostetler and pieter tans for reviews of earlier versions of this manuscript

temporal change in attenuation intensity before and after the eastern yamanashi earthquake of 1983 in central japan a crutal earthquake of magnitude 6 0 took place on august 8 1983 in the middle of the kanto tokai microearthquake observation network of the national research center for disaster prevention in central japan by analyzing vertical seismograms of microearthquakes occurring in a small volume in the aftershock region we measured temporal change in attenuation intensity for a period from 22 months before to 9 months after the main shock attenuation change was estimated by using two different kinds of analyses in the first analysis station magnitude calculated from the maximum amplitude at each station was compared with the average of station magnitudes deviations of station magnitude from the average magnitude at five stations in the vicinity of the aftershock area are found to have increased after the main shock compared with that before in the second analysis s coda duration from the origin time was measured and was compared with the average magnitude the increase of s coda duration for the same average magnitude is found after the main shock at two stations close to the main shock epicenter the simplest interpretation of the results is that the attenuation intensity in the upper crust in the close vicinity of the focal region decreased after the main shock for frequencies f from 2 to 20 hz qs 1 1 4 10 2f 1 since other precursors appeared in the preparation stage it is possible to interpret the change in qs 1 as a precursor the attenuation intensity would have been anomalously large before the main shock

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

comparison of the structure of the itcz in the west pacific during the boreal summers of 1989 93 using amip simulations and ecmwf reanalysis the dynamic structure and interannual variability of the itcz in the western north pacific and east asia during the boreal summers of 1989 93 are investigated european centre for medium range weather forecasts ecmwf reanalyses are used to characterize the dynamical structure of the itcz the itcz structure in the national center for atmospheric research ncar community climate model 3 ccm3 6 and the national aeronautics and space administration nasa goddard institute of space studies giss si2000 gcm is also explored the itcz axis can be partitioned into three sections in the western north pacific and east asia the continental monsoon trough cmt in india the bay of bengal and indo china the oceanic monsoon trough omt in the pacific warm pool and the trade wind trough twt in the central pacific the confluence point cp is defined as an area where the broad cyclonic flow in omt changes to the easterly trades of the twt east of the cp both gcms simulate a weaker easterly trade wind regime with a broader itcz due to the dislocation of the pacific high to the west of the cp both gcms simulate a weaker cross equatorial flow and omt both models show skill in simulating the interannual variability of the location of the cp however for the peak enso warm phase years 1992 93 the spread among ensemble members of the cp longitude is comparable to the shift of ensemble mean cp location relative to 1989 that is the internal variability of each gcm is on the same order as the simulated interannual variability in this region

a record of the southern oscillation index for the past 2 000 years from precipitation proxies the el nino southern oscillation enso is a coupled ocean atmosphere climate phenomenon in the tropical pacific ocean the interannual climate variations have been shown to modify both the hadley and walker meridional and zonal atmospheric circulations with strong impacts on global climate 1 3 proxy based reconstructions of the southern oscillation index on a multi decadal scale have shown that the strength and frequency of el nino occurrences have varied over the past millennium 4 7 here we compile reconstructions of precipitation 8 15 from regions that experience substantial enso variability to extend the multidecadal scale southern oscillation index to include the past 2 000 years we find that the medieval warm period similar to ad 800 1300 was characterized by a negative index which indicates more el nino dominated conditions whereas during the little ice age similar to ad 1400 1850 more la nina dominated conditions prevailed the southern oscillation index we derive is significantly correlated with reconstructions of solar irradiance and mean northern hemisphere temperature fluctuations

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

a predictability study of simulated north atlantic multidecadal variability the north atlantic is one of the few places on the globe where the atmosphere is linked to the deep ocean through air sea interaction while the internal variability of the atmosphere by itself is only predictable over a period of one to two weeks climate variations are potentially predictable for much longer periods of months or even years because of coupling with the ocean this work presents details from the first study to quantify the predictability for simulated multidecadal climate variability over the north atlantic the model used for this purpose is the gfdl coupled ocean atmosphere climate model used extensively for studies of global warming and natural climate variability this model contains fluctuations of the north atlantic and high latitude oceanic circulation with variability concentrated in the 40 60 year range oceanic predictability is quantified through analysis of the time dependent behavior of large scale empirical orthogonal function eof patterns for the meridional stream function dynamic topography 170 m temperature surface temperature and surface salinity the results indicate that predictability in the north atlantic depends on three main physical mechanisms the first involves the oceanic deep convection in the subpolar region which acts to integrate atmospheric fluctuations thus providing for a red noise oceanic response as elaborated by hasselmann the second involves the large scale dynamics of the thermohaline circulation which can cause the oceanic variations to have an oscillatory character on the multidecadal time scale the third involves nonlocal effects on the north atlantic arising from periodic anomalous fresh water transport advecting southward from the polar regions in the east greenland current when the multidecadal oscillatory variations of the thermohaline circulation are active the first and second eof patterns for the north atlantic dynamic topography have predictability time scales on the order of 10 20 y whereas eof 1 of sst has predictability time scales of 5 7 y when the thermohaline variability has weak multidecadal power the hasselmann mechanism is dominant and the predictability is reduced by at least a factor of two when the third mechanism is in an extreme phase the north atlantic dynamic topography patterns realize a 10 20 year predictability time scale additional analysis of sst in the greenland sea in a region associated with the southward propagating fresh water anomalies indicates the potential for decadal scale predictability for this high latitude region as well the model calculations also allow insight into regional variations of predictability which might be useful information for the design of a monitoring system for the north atlantic predictability appears to break down most rapidly in regions of active convection in the high latitude regions of the north atlantic

properties of scattered elastic waves in the lithosphere of kamchatka parameters and temporal variations abstract records of near earthquakes from the shipunsky station were used to estimate s wave absorption for seven frequency bands ranging from 0 4 to 24 hz three techniques were employed and three rows of consistent estimates were obtained two of the three techniques give estimates that are independent of q anisotropic scattering was studied by observing the broadening of the s wavelet the estimates obtained show that anisotropic scatter may be significant the time variation of the coda envelope shape was studied using the records of 1 s regional seismographs three epicentral regions were chosen in the kurile kamchatka zone where m 8 earthquakes have occurred time series of the parameter which is the anomaly of the logarithmic steepness of coda envelope were constructed for vertical and horizontal channels of several stations pronounced forerunner type variations of were revealed we show that the probable cause of these variations is a qs decrease in the vicinity of impending m 8 earthquake this decrease is about 20 with a lead time of about a year the forerunner anomaly is not of the bay type and recovers 1 2 years after a large earthquake

global survey of aftershock area expansion patterns we developed an objective method to define the aftershock areas of large earthquakes as a function of time after the main shock the definition is based upon the amount of energy released by aftershocks the spatial distribution of the energy release is first determined and is contoured the 1 day aftershock area is defined by a contour line corresponding to the energy release level of 10 15 6 ergs 100 km 2 day the 10 day 100 day and 1 y aftershock areas are similarly defined by contour lines corresponding to 10 14 8 10 14 0 and 10 13 5 ergs 100 km 2 day respectively we also define the expansion ratios at time t by the ratio of the aftershock area at t to that at 1 day using this method we study the aftershock area expansion patterns of 44 large m s 7 5 and five moderate shallow earthquakes which occurred from 1963 to 1980 each aftershock sequence is examined at four different times i e 1 day 10 days 100 days and 1 y after the main event we define the aftershock area expansion ratios and e by s 100 s 1 and l 100 l 1 respectively here s t and l t are the area and the length of the aftershock area respectively at time t our study suggests that a distinct regional variation of aftershock area expansion patterns is present it is strongly correlated with the tectonic environment in general the subduction zones of the mariana type have large expansion ratios and those of the chilean type have small expansion ratios some earthquakes that occurred in the areas of complex bathymetry such as aseismic ridges tend to have large expansion ratios these results can be explained in terms of an asperity model of fault zones in which a fault plane is represented by a distribution of strong spots called the asperities and weak zones surrounding the asperities the rupture immediately after the main shock mostly involves asperities after the main rupture is completed the stress change caused by the main shock gradually propagates outward into the surrounding weak zones this stress propagation manifests itself as expansion of aftershock activity in this simple picture if the fault zone is represented by relatively large asperities separated by small weak zones chilean type then little expansion of aftershock activity would be expected on the other hand if relatively small asperities are sparsely distributed mariana type significant expansion occurs the actual distribution of asperities is likely to be more complex than the two cases described above however we would expect that the expansion ratio is in general proportional to the spatial ratio of the total asperity area to the fault area

principal modes of rainfall sst variability of the asian summer monsoon a reassessment of the monsoon enso relationship abstract using global rainfall and sea surface temperature sst data for the past two decades 1979 98 the covariability of the asian summer monsoon asm and el nino southern oscillation enso was investigated the findings suggest three recurring rainfall sst coupled modes characterized by a pronounced biennial variability the first mode is associated with generally depressed rainfall over the western pacific and the maritime continent stemming from the eastward shift of the walker circulation during the growth phase of el nino the associated sst pattern consists of an east west sst seesaw across the pacific and another seesaw with opposite polarity over the indian ocean the second mode is associated with a growing la nina comprising mixed regional and basin scale rainfall and sst variability with abnormally warm water in the vicinity of the maritime continent and western pacific it possesses a pronounced low level west pacific anticyclone wpa near the philippines and exhibits large sub

is there a correlation between lithosphere structure and the statistical properties of seismicity the elastic parameters and the thickness of the lithospheric part of the mantle the lid are correlated with the seismicity of italy and surrounding areas through the estimation of several statistical parameters in particular the intensity of the flow of seismic events deprived of aftershocks reveals concentrations associated with large gradients in the lithospheric thickness the average depth of crustal shocks tends to be very shallow in areas of thin and soft low shear wave velocities lid the positive influence probably reflecting the thermal state in the lithosphere is very large in connection with the thin and soft lid and where strong gradients in lid thickness are observed and is small in connection with a thick and hard lid high shear wave velocities

extension of global creepex definition ms mb to local studies md ml the case of the italian region creepex defined as the systematic deviation of the magnitude of a single earthquake from the linear orthogonal regression between local magnitude ml and coda duration magnitude md calculated for the whole region is used as a measure of the frequency content of the seismic sources in the italian region predominantly high frequency events are found in the two areas of quaternary tectonic shortening in north central italy and in the calabrian arc this result confirmed by two independent statistical tests is in agreement with the global pattern obtained from the study of the regression between body wave magnitude mb and surface wave magnitude ms systematic shift to high frequencies in the energy release of seismic sources located in subduction zones and to low frequencies in zones of spreading the analysis of the correlation between the patterns of heat flow and of seismic source spectral properties indicates that these source properties in general do not reflect thermal conditions in the lithosphere but rather represent the result of tectonic processes

neo deterministic seismic hazard assessment for alborz region iran abstract seismic hazard maps for alborz region north of iran and adjacent areas are prepared using the neo deterministic seismic hazard assessment ndsha based on the computation of synthetic seismograms at the regional scale the study area is zoned according to different geophysical structural models delimited at the surface by polygons used to define the mechanical properties of the source site paths we have refined the velocity structures of iran as obtained from surface waves tomography to obtain the velocity structure of alborz region by applying the joint inversion of the p wave receiver functions prf and surface wave s dispersion the input data set consists of attenuation velocity structural models representing bedrock conditions seismogenic zones focal mechanisms and the catalog of past seismicity the seismic hazard expressed in terms of maximum displacement pgd maximum velocity pgv and design ground acceleration dga is extracted from the synthetic seismograms and mapped on a regular grid of 0 2 0 2 over the entire region the results of this first order ndsha zoning indicate a high seismic hazard in the alborz region and may represent an important knowledge basis towards detailed and comprehensive seismic microzonation studies

a method of studying variations in the clustering property of earthquakes application to the analysis of global seismicity we propose a formal algorithm for identification of aftershocks following a main event our approach is based on the analysis of the local statistics the number of events following the initial earthquake displayed as a function of distance and time by comparing this distribution with the random catalog we establish for several magnitude ranges spatiotemporal thresholds for detection of aftershocks high confidence thresholds correspond to the limit at which the number of events derived from the actual catalog corrected for the background seismicity exceeds by a factor of 10 the expected level of background seismicity marginal confidence thresholds correspond to the spatiotemporal boundary along which these two values are approximately equal after several iterations the final thresholds are derived the swarming parameter is defined as the number of aftershocks with a cut off lower magnitude range following an initial earthquake of certain magnitude if a correction for the recurrence law is applied we find that the swarming parameter is magnitude independent this allows us to apply this technique to the analysis of global seismicity using a catalog derived from the isc bulletin for the years from 1964 to 1975 we determine for shallow earthquakes the average values of the swarming parameter in 9 9 cells a global map produced in this manner shows a very wide range of variations in the swarming property undoubtedly reflecting variations in the local geological conditions triple junctions are among the areas with the highest swarming values at the present time there is an insufficient amount of data to study regional variations in the swarming property of deep earthquakes considering the clustering as a function of depth alone we find detectable swarming for two depth ranges from 100 to 250 km and from 450 to 650 km not a single aftershock has been detected among nearly 200 earthquakes withmb 5 in a depth range from 250 to 450 km the average swarming parameter for earthquakes deeper than 100 km is 10 times smaller than that for the shallow earthquakes

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

lessons learned from oxygen isotopes in modern precipitation applied to interpretation of speleothem records of paleoclimate from eastern asia abstract variability in oxygen isotope ratios collected from speleothems in chinese caves is often interpreted as a proxy for variability of precipitation summer precipitation seasonality of precipitation and or the proportion of 18o to 16o of annual total rainfall that is related to a strengthening or weakening of the east asian monsoon and in some cases to the indian monsoon we use modern reanalysis and station data to test whether precipitation and temperature variability over china can be related to changes in climate in these distant locales we find that annual and rainy season precipitation totals in each of central china south china and east india have correlation length scales of 500 km shorter than the distance between many speleothem records that share similar long term time variations in 18o values thus the short distances of correlation do not support though by themselves cannot refute the idea that apparently synchronous variations in 18o values at widely spaced 500 km caves in china are due to variations in annual precipitation amounts we also evaluate connections between climate variables and 18o values using available instrumental measurements of 18o values in precipitation these data from stations in the global network of isotopes in precipitation gnip show that monthly 18o values generally do not correlate well with either local precipitation amount or local temperature and the degree to which monthly 18o values do correlate with them varies from station to station for the few locations that do show significant correlations between 18o values and precipitation amount we estimate the differences in precipitation amount that would be required to account for peak to peak differences in 18o values in the speleothems from hulu and dongge caves assuming that 18o scales with the monthly amount of precipitation or with seasonal differences in precipitation insofar as the present day relationship between 18o values and monthly precipitation amounts can be applied to past conditions differences of at least 50 in mean annual precipitation would be required to explain the 18o variations on orbital time scales which are implausibly large and inconsistent with published gcm results similarly plausible amplitudes of seasonal cycles in amounts or in seasonal variations in 18o values can account for less than half of the 4 5 difference between glacial and interglacial 18o values from speleothems in china if seasonal cycles in precipitation account for the amplitudes of 18o values on paleoclimate timescales they might do so by extending or contracting the durations of seasons a frequency modulation of the annual cycle but not by simply varying the amplitudes of the monthly rainfall amounts or monthly average 18o values amplitude modulation allowing that several processes can affect seasonal variability in isotopic content we explore the possibility that one or more of the following processes contribute to variations in 18o values in chinese cave speleothems different source regions of the precipitation which bring different values of 18o in vapor different pathways between the moisture source and the paleorecord site along which exchange of 18o between vapor surface water and condensate might differ a different mix of processes involving condensation and evaporation within the atmosphere or different types of precipitation each may account for part of the range of 18o values revealed by speleothems and each might contribute to seasonal differences between past and present that do not scale with monthly or even seasonal precipitation amounts

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

seismicity and seismic structure at okmok volcano alaska abstract okmok volcano is an active volcanic caldera located on the northeastern portion of umnak island in the aleutian arc with recent eruptions in 1997 and 2008 the okmok area had 900 locatable earthquakes between 2003 and june 2008 and an additional 600 earthquakes from the beginning of the 2008 eruption to mid 2009 providing an adequate dataset for seismic tomography to image the seismic velocity structure of okmok we apply waveform cross correlation using bispectrum verification and double difference tomography to a subset of these earthquakes we also perform p wave attenuation tomography using a spectral decay technique we examine the spatio temporal characteristics of seismicity in the opening sequence of the 2008 eruption to investigate the path of magma migration during the establishment of a new eruptive vent we also incorporate the new earthquake relocations and three dimensional 3d velocity model with first motion polarities to compute focal mechanisms for selected events in the 2008 pre eruptive and eruptive periods through these techniques we obtain precise relocations a well constrained 3d p wave velocity model and a marginally resolved s wave velocity model we image a main low vp and vs anomaly directly under the caldera consisting of a shallow zone at 0 2 km depth connected to a larger deeper zone that extends to about 6 km depth we find that areas of low qp are concentrated in the central to southwestern portion of the caldera and correspond fairly well with areas of low vp we interpret the deeper part of the low velocity anomaly 4 6 km depth beneath the caldera as a magma body this is consistent with results from ambient noise tomography and suggests that previous estimates of depth to okmok s magma chamber based only on geodetic data may be too shallow the distribution of events preceding the 2008 eruption suggest that a combination of overpressure in the zone surrounding the magma chamber and the introduction of new material from below were jointly responsible for the explosive eruption magma escaping from the top of the main magma chamber likely reacted with both a smaller shallow pod of magma and groundwater on its way up below the cone d area the earthquakes in the 2008 pre eruptive and eruptive periods are found to have a mixture of strike slip oblique normal and oblique thrust mechanisms with a dominant p axis orientation that is nearly perpendicular to the regional tectonic stress this may indicate that the stresses related to magmatic activity locally dominated regional tectonic forces during this time period

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

imaging preeruptive and coeruptive structural and mechanical changes of a volcano with ambient seismic noise 1 forecasting the location of an eruption is of primary importance for risk management in volcanic regions locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano using recent results in wave physics we develop an imaging procedure that is based on the sensitivity of multiply scattered waves to weak changes in heterogeneous media this procedure allows to locate changes in both mechanical and scattering properties of the studied medium we study ambient seismic noise from 19 broadband stations at the active volcano piton de la fournaise on reunion island recorded from june to december 2010 during this period two volcanic eruptions occurred at two different locations we calculate the noise cross correlations and study two types of changes in the coda apparent velocity variations related to changes in the elastic properties of the medium and waveform decoherence associated with variations in the scattering and thus the geological structures we observe that the temporal variations of both of these parameters provide potential precursors of volcanic eruptions at piton de la fournaise the locations determined from the preeruptive and coeruptive changes in both parameters are in good agreement with the actual eruptive activities these data demonstrate that the coda of ambient noise correlations contains deterministic information on the locations of the eruptive processes in an active volcano our analysis offers an original and significant constraint for the localization of forthcoming volcanic eruptions

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

temporal change in scattering and attenuation associated with the earthquake occurrence a review of recent studies on coda waves the study of coda waves has recently attracted increasing attention from seismologists this is due to the fact that it is viewed as a new means by which the stress accumulation stage preceding a large earthquake can be measured since the scattering paths nearly uniformly cover a fairly large region around the focus and observation stations compared with the direct ray paths to date we have had many reports on the temporal variation of the relation between coda duration and amplitude magnitude and that of the coda attenuationq 1 which is estimated from coda amplitude decay some of these have shown a precursor like behavior however others seem to have shown a coseismic change we have critically reviewed these reports and discussed what these observational facts tell us about the change in the heterogeneous crust we found significant temporal variations not only in the mean but also in the scatter ofq 1 associated with the mainshock occurrence the formation of new cracks the reopening and growing of existing cracks the interaction of these cracks and the pore water movement through these cracks might correspond to such variations in addition we may expect an inhomogeneous distribution of crack clusters in a fairly large region compared with the aftershock region the gradual appearance of such crack clusters seems to be the most plausible mechanism by which coda decay gradients are caused to largely scatter in the stress accumulation stage

lava dome collapse detected using passive seismic interferometry 1 the collapse of the lava dome at the soufriere hills volcano on montserrat in july 2003 is the largest recorded in historical times i use noise correlation green s functions to measure the changes in seismic properties that resulted from this collapse continuous three component seismic data recorded at two pairs of stations were cross correlated to retrieve three component green s functions along two paths that intersect the volcanic edifice before and after the dome collapse particle motion analysis shows that the green s functions are dominated by rayleigh waves and are consistent with the expected green s tensor for a vertical point force source at one station recorded by a three component receiver at the other following the collapse there is a clear decorrelation and phase shift in the green s functions corresponding to a change in velocity of approximately 0 5 that can be interpreted in terms of the unloading of the lava dome

spatial and temporal correlation between coda q and seismicity in china a map of coda q at 1 hz q was constructed for china by analyzing more than 1000 seismograms from 80 seismic stations distributed throughout china the resultant contour map of q shows a strong correlation with the epicenters of historic great earthquakes in china the high q regions are devoid of the epicenters and the low q regions are full of them a remarkably linear relation was found between the logarithm of coda q and the maximum earthquake within the area sampled by coda waves radius of about 150 km from each station when we consider earthquakes which occurred from 1700 to present roughly speaking if q is 1000 m max is about 4 and if q is 100 m max is about 8 this relation will be very useful for siting critical facilities such as nuclear power plants and waste disposal sites we also found evidence in support of the migration of low q region coincident with the well known migration of high seismicity region over the distance of several hundred kilometers during the period of several hundred years if the migration is due to a diffusion process the diffusion constant is of the order of 100 km2 yr which agrees very well with those associated with the aftershock migration fluid injection and vp vs anomaly comparison of coda q with q1 estimated from the intensity data shows that they agree very well for q1 150 supporting the validity of the s to s single backscattering model for coda waves for q1 150 however coda q becomes constant independent of q1 this behavior is qualitatively consistent with numerical experiments of frankel and clayton and suggests that coda q may be measuring the intrinsic q of about 150 for these regions where q1 150 this limiting coda q value may depend on regions because coda q lower than 100 has been observed in some active regions in this study and also coda q as low as 30 to 40 has been reported in california mexico and italy

climate and hydrographic variability in the indo pacific warm pool during the last millennium planktonic foraminiferal mg ca and delta o 18 derived sea surface temperature and salinity records from the makassar strait indonesia show a long term cooling and freshening trend as well as considerable centennial scale variability during the last millennium the warmest temperatures and highest salinities occurred during the medieval warm period mwp while the coolest temperatures and lowest salinities occurred during the little ice age lia these changes in the western pacific along with observations from other high resolution records indicate a regionally coherent southern displacement of the inter tropical convergence zone during the lia with more arid conditions in the northern tropics and wetter conditions in the southern tropics

real time monitoring of relative velocity changes using ambient seismic noise at the piton de la fournaise volcano la reunion from january 2006 to june 2007 we present the results of a real time method based on coda wave interferometry from seismic noise cross correlation functions for relative seismic velocity variations monitoring on a volcanic edifice the ambient seismic noise at the piton de la fournaise volcano on la reunion island is analyzed from january 2006 to june 2007 during this period five eruptions occurred showing a great diversity in eruption duration intensity and eruptive fissure location two different methods are used to compute the velocity variations in order to compare their stability in quasi real time routine we compare the obtained velocity variations with the surface deformation observed by gps and extensometers networks this allows us to identify and quantify three major processes at the origin of seismic wave velocity variations in the edifice firstly the observed pre eruptive summit inflation is accompanied by a decrease in seismic velocity secondly the edifice deflation following the opening of an eruptive fissure is characterized by an increase of the velocity finally the summit caldera collapse generates a strong velocity drop coda wave interferometry from seismic noise cross correlation functions in quasi real time may allow us to forecast eruption and constrain the processes taking place in the volcanic plumbing system

friction and faulting editor s note combining the topics of rock friction and faulting in one volume is an expression of a certain optimism that information obtained on frictional properties which comes primarily from relatively small laboratory samples is relevant to slip on those faults of greatest interest to us the relatively large ones found in the earth probably most workers in this general area believe or hope that this is true but there is still debate concerning how much progress has been made in relating the laboratory measurements to the earth and how reasonable it is to expect that more progress can be made in the future the scientific fascination and challenges of these complex topics are enhanced by the possibility they offer for understanding the mechanics of earthquakes that may lead to a workable earthquake prediction program it is worth reflecting on the similarities and differences between the laboratory and the field settings and on what must be done to understand the mechanics of faulting using laboratory friction data the articles in this volume are representative of the types of studies that must be combined to attain this goal