geometry and physical properties of the socorro new mexico magma bodies analysis of multichannel seismic reflection profiles gathered by the consortium for continental reflection profiling cocorp constrains the geometry and material properties of a proposed magma body located within the rio grande rift a new spectral ratio method is used to find the reflectivities of the proposed midcrustal intrusion large and spatially variable reflectivities support the interpretation of the reflector as an intrusive molten magma complex modeling of the reflectivity suggests that in one location the intrusion took the form of several thin 30 to 40 m thick layers seismic wave attenuation within the rift s midcrust is low

attenuation relationships of peak ground acceleration and velocity for crustal earthquakes in taiwan strong seismic ground motion data obtained by the taiwan strong motion instrumentation program tsmip and central mountain strong motion array cmsma are used to derive new attenuation relationships for the vertical and horizontal peak ground acceleration pga and peak ground velocity pgv for crustal earthquakes in taiwan more than 7900 three component accelerograms recorded from 51 crustal earthquakes in taiwan with m w magnitudes ranging from 4 0 to 7 1 have been analyzed to study the dependence of peak ground motion parameters on magnitude distance regional and local site effects through attenuation relationships we first found that for both pga and pgv the attenuation relationships decay faster with distance for the vertical component than for the horizontal component also the attenuation relationships decay faster with distance for the vertical pga than for the vertical pgv we further compared the attenuation relationships for three subregions chy iwa and nto and the whole taiwan region twn it is found that the chy area has higher ground motion either in pga or pgv than the other areas especially at near source distances this is because the chy area is located on a thick recent alluvial plain comparison of our new attenuation relationships with strong motion data from the 1999 chi chi earthquake m w 7 7 and the 2003 cheng kung earthquake m w 6 8 shows that the attenuation relationships developed for m w 7 can be extrapolated to make reasonable estimates of strong motion from larger m w 7 earthquakes finally we analyzed the residuals to investigate variations of pga and pgv with respect to site conditions the results show that 1 the residual contour maps especially for the pgv have high consistency with the regional geology and topography of taiwan 2 the pgv residual contours reveal that taipei basin changhua plain chianan plain pingtung valley ilan plain and taitung longitudinal valley have high residual values note that most major metropolitan areas all fall in high residual areas 3 the site classification based on geologic criteria by lee et al 2001 can be simplified into three classes that is class e for soft soils a combination of classes c and d for dense and stiff soils and class b for rocks these three site classes are mostly distributed respectively in the alluvial plains at an elevation less than 50 m in terraces and hills at an elevation less than 1000 m and in high mountainous areas

seismic wave propagation beneath the molucca sea arc arc collision zone indonesia abstract seismograms of earthquakes from the molucca sea arc arc collision zone recorded at local stations show a wide variety of coda envelope shapes and frequency contents some shallow depth less than 20 km events display large amplitude codas relative to primary body waves and lower frequency 2 4 cps than deeper events which contain frequencies up to 12 cps the shallowest events probably originate within the accretionary wedge of the collision zone and their signal characters at local stations indicate intense scattering within the highly deformed accretionary material the scattering attenuation for travel paths within the crust is high but must decrease with depth starting in the upper mantle resulting in a more efficient path between intermediate depth events and the stations a wide variation in the efficiency of s wave propagation from intermediate depth events suggests the presence of considerable heterogeneity in deeper structure of the collision zone

probability for simulating future earthquakes with mw 6 0 in taiwan for seismic hazard for the earthquake catalog from 1900 to 2008 in this study we use extreme value theory based on gumbel equation derivations to estimate the gutenberg richter a and b parameters for taiwan data are from the augmented homogenized in terms of moment magnitude historic catalog for taiwan the island is divided into grids of 0 2 latitude by 0 2 longitude and gumbel type 1 statistical analysis is applied the values of a and b are then used to determine the probability of large earthquakes m w 6 0 occurring at each grid the results show two relatively high probability paths for large earthquakes one extending from hsinchu southward to taichung chiayi and tainan in western taiwan and the other from ilan southward to hualian and taitung in eastern taiwan both of which are characterized by low b values it indicates that future earthquakes can be expected along these paths characterized by low b values additionally maximum peak ground acceleration and maximum peak ground velocity determined from respective attenuation laws and a gridding regimen of 0 1 latitude by 0 1 longitude for taiwan follow similar paths to that of the low b values

petrologic evolution of krakatau indonesia implications for a future activity abstract krakatau volcano is located along a n35e volcanic lineament running through the sunda straits indonesia its last activity has been characterized by successive phases each beginning with the construction of a cone and ending with its destruction and the formation of a caldera the two last pre and post 1883 cycles are well known but the more ancient ones are not so clearly defined lavas of krakatau belong to an andesitic series in which fractional crystallization plays the most important role the petrologic evolution is characterized by a cyclicity in good agreement with the structural evolution the succession is regular basalts basic andesites acid andesites dacites a gap between acid and basic andesites occurs in each cycle the destructive stages correspond to the occurrence of dacitic terms the anak cycle was characterized from 1927 to 1979 by basalts and basic andesites the 1981 eruption involved a more differentiated magma close to dacitic detailed study of the petrologic evolution since 1883 emphasizes the predominant role of fractional crystallization this process occurred during a very short period between 1979 and 1981 separation of labradorite augite olivine and magnetite from parental basic andesite may generate the dacitic descendant in a shallow reservoir p h 2 o estimated about 0 5 kbar implications for a future activity are considered

a geophysical interpretation of the 1883 krakatau eruption abstract from the present submarine topography in the vicinity of the krakatau islands it is concluded that the focus of the large explosions was situated to the northwest of the present rakata island the channel between krakatau and sebesi islands was completely blocked by banks of volcanic material immediately after the eruptions and it is suggested that this material was mainly lithic fragments the explosion sequences of krakatau are deduced from the records of sea waves and air waves observed at jakarta the large tsunami was caused by the most violent explosion simultaneously with the largest air waves it is inferred that the origin of the tsunami was a sudden upheaval of the seawater due to a violent explosion and that the height of the tsunami near its source was 30 40 m energy of the explosion is estimated from analyses of the air waves as one order of magnitude greater than that of the 1956 bezymianny eruption thus the 1883 krakatau eruption may have caused explosive removal of more than 10 km3 of material the subsurface structure of krakatau islands after the 1883 eruption is deduced from gravity anomalies it is concluded that at the bottom of the caldera there are deposits of low density in the shape of an inverted cone 8 km in diameter and 1 km in depth from the residual gravity anomaly observed over the caldera one can estimate the mass deficiency there this allows estimates to be made as to the amount of ejecta although large uncertainties remain these data indicate that explosive removal of material was the main process responsible for the disappearance of the northern half of the former rakata krakatau island in the 1883 eruption

seismic evidence for magma in the vicinity of mt katmai alaska p wave traveltime delays of as much as 0 9 sec are consistently observed at one seismic station from local and regional earthquakes 70 to 150 km deep this station is on the southwest flank of mt trident the most recently active volcano within katmai national park alaska delays from local shallow earthquakes are typically less than 0 3 sec suggesting that most of the major delay results from anomalous material at depths of more than a few kilometers this station is located near the center of a bowlshaped low in the bouguer gravity field that is approximately 15 km in diameter and more than 25 mgals deep these anomalies suggest but do not prove the presence of considerable amounts of magma in the shallow part of the crust that could have been the source for all magma erupted in the vicinity of mt katmai and mt trident this century

estimated seismic intensity distributions for earthquakes in taiwan from 1900 to 2008 in this study we recreated peak ground accelerations pga and peak ground velocity pgv distributions for taiwan by applying the attenuation relations of liu and tsai 2005 to calculate the pga and pgv values for 1989 mw 5 0 earthquakes in a catalog of earthquakes from 1900 to 2008 with homogenized magnitude mw chen and tsai 2008 we further combined the pga and pgv values to obtain corresponding modified mercalli intensity mmi values wald quitoriano heaton kanamori et al 1999 and their spatial distributions and recurrence intervals we adopted a logarithmic functional form analogous to the gutenberg richter relation for seismicity to represent the annual frequency of seismic intensity parameters log10n a blog10pga log10n a blog10pgv and log10n a bi the regions with high pga and pgv values are often associated with low b values in these equations as it is well known that the mw 7 45 chi chi earthquake of 21 september 1999 had produced high pga values in excess of 0 9g and pgv values in excess of 300 cm s we used these relations to estimate the poisson probability distributions in taiwan for mmi viii i e pga 485g for recurrence intervals of 30 50 and 100 years the results show a wide range of differences in the poisson probability of mmi viii among different areas of taiwan for example for a 50 year interval this probability at 10 major cities in taiwan is as follows taipei 0 67 hsinchu 2 15 taichung 5 24 chiayi 24 35 tainan 1 61 kaohsiung 0 04 hengchun 4 94 ilan 17 67 hualien 37 04 and taitung 9 82 these esti mates should be of interest to city planners especially for earthquake preparedness planning

sunda strait and central sumatra fault sunda strait marks the limit between java trench frontal subduction and sumatra trench oblique subduction the right lateral central sumatra fault accommodates the oblique subduction it does not pass sunda strait but ends between sumatra and java in a complex pattern of dominantly normal faults associated with subsidence seismicity and volcanism we examine the implications of this phenomenon in sunda strait and in the adjacent fore arc basin and accretionary prism which underwent north south compression due to subduction as well as east west extension we propose that the strait is a consequence of the northwestward motion of the southwestern sumatra block along the central sumatra fault we also propose that the extensional zone in the sunda strait widens considerably to the southwest toward the trench and changes into a composite zone of deformation affected by strike slip as well as normal faulting

evidence of preferential directions for gravity wave propagation due to wind filtering in the middle atmosphere all sky tv images of wave structure in the near infrared hydroxyl oh nightglow emission were recorded over a 3 month period during may june and july 1988 from a high altitude site at the mountain research station 40 0 n 105 6 w 3050 m near nederland colorado well defined coherent wave patterns associated with the passage of short period 1 hour gravity waves were observed on a total of 22 occasions the wave motions exhibited similar spatial and temporal properties during each month but a distinct tendency for northward propagation 68 of the wave azimuths within 40 0 n with some eastward motion in may and june was observed throughout the campaign although it is theoretically well known that upward propagating gravity waves can be blocked at a critical layer produced by the interaction of the waves with the horizontal background wind observational evidence of this phenomenon is rare to investigate the possibility that the asymmetry in the wave propagation directions was caused by the critical layer a model based on mean climatological background winds and numerical tidal wave modes valid for any mid latitude site and time of the year was constructed to show the regions forbidden to upward gravity wave propagation from critical layer theory these blocking diagrams which vary with height and time were constructed for the oh altitude 87 km for the present paper comparison of the predicted i e least restricted and the observed directions of the wave motion show almost complete agreement this suggests that middle atmospheric winds can play an important role in determining the flux and the azimuthal distribution of short period waves reaching the upper atmosphere

generation mechanism of tsunamis from the 1883 krakatau eruption the 1883 eruption of krakatau generated a destructive tsunami which claimed about 34 000 lives we compute the generation and propagation of tsunamis from three models previously proposed they are 1 large scale caldera collapse of the northern part of krakatau island 2 emplacement of pyroclastic flow deposits 3 submarine explosion we numerically solve the non linear shallow water equations on actual bathymetry all three models displace the same volume 11 5 km 3 of water in different ways we compare the results of our computation with the observed tsunami waveforms at batavia and tsunami wave heights along the coasts of java and sumatra the comparison shows that the submarine explosion model of 1 to 5 min duration best explains the generation of the largest tsunami

crustal differentiation processes at krakatau volcano indonesia anak krakatau is a basaltic andesite cone that has grown following the famous caldera forming 1883 eruption of krakatau it breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week we present new major and trace element data combined with whole rock delta o 18 sr and nd isotope data for 1883 1993 and 2002 krakatau eruptive products and the surrounding crust bombs erupted from anak krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism plastic deformation and partial melting contact metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high temperature metamorphism and incorporation at mid to upper crustal depth energy constrained assimilation and fractional crystallization modelling of whole rock data suggests that the anak krakatau magmas have a genetic relationship with the 1883 eruption products the geochemical impact of crustal contaminants on whole rock compositions is apparently small and we conclude that low levels of assimilation of a quartzo feldspathic sediment are recorded in anak krakatau magmas plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning however and are also isotopically variable with a total range in sr 87 sr 86 of 0 center dot 7043 0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry this suggests that although shallow crustal assimilation appears to have had a limited effect on whole rock chemistry a complex late stage differentiation history is recorded within the magma s cargo of crystals and xenoliths

revisiting the ishimoto iida law for strong motion seismograms a case study at ceorka network japan abstract frequency distribution of the maximum amplitude of seismograms at a station exhibits a power law relation which is the ishimoto iida law ii law we investigate whether the ii law is applicable to modern strong motion seismograms distribution of maximum amplitudes records at stations of the committee of earthquake observation and research in the kansai area ceorka network western japan exhibits properties of the power law or the ii law the observation matches well with the prediction which is based on existing ground motion prediction equations for japan parameters of the observed ii law could be used in understanding the probabilities of future seismic hazard intuitively

interaction of zonal winds with the equatorial midnight pressure bulge in the earth s thermosphere empirical check of momentum balance a minimum is observed at midnight in the time variation of averaged zonal winds measured in situ near the equator at an average altitude of about 350 km and we inquire whether observations of the equatorial midnight pressure bulge are consistent with this feature the observed zonal wind maintains an eastward direction all night it increases steadily in the early evening reaching a maximum of about 160 m s at 2100 hrs local time lt dropping to a minimum of about 70 m s around 2400 lt then up to about 120 m s around 0300 lt decreasing thereafter and turning westward in the morning around 0500 lt the nighttime eastward ion drift at jicamarca averaged over periods of similar solar activity 1970 71 shows the same signature but generally with amplitude between 70 and 90 of the zonal wind amplitude the 1978 81 jicamarca ion drifts are similar except from 2400 to 0300 lt when they are about 30 larger than the in situ zonal wind averages the ion drift is used together with the measured zonal winds to estimate the ion drag effect in the momentum equation the pressure term of this equation is estimated using in situ measurements of the neutral temperature and density the pressure term is found to be large before 2100 lt 0 05 m s consistent with the steady increase in zonal wind before 2100lt drops rapidly to near zero roughly 0 005 m s before 2200 lt and then increases slowly beginning at 2300 to about 0 015 m s just before 0300 lt when it is observed to reverse the small pressure term observed from 2100 to 2400 lt is associated with the midnight pressure bulge and accounts for the decay of the wind from 160 m s at 2100lt to 70 m s at midnight the larger value at 0300lt is consistent with the second maximum in the wind it is found that the existing data sets are consistent in terms of zonal momentum balance the striking similarity between the zonal wind and the eastward ion drift is responsible for the small ion drag term before midnight which is required to maintain the large zonal winds observed

simultaneous assessment of the median annual seismicity rates and their dispersions for taiwan earthquakes in different depth ranges abstract the main purpose of this study is to apply an innovative approach to assess simultaneously the median annual seismicity rates and their dispersions for taiwan earthquakes in different depth ranges in this approach an alternative gutenberg richter g r relation is explicitly expressed in terms of both the logarithmic mean annual seismicity rate and its standard deviation instead of only by the arithmetic mean in the conventional g r relation seismicity data from 1975 to 2014 in a taiwan earthquake catalog with homogenized m w moment magnitudes are used in this study this catalog consists of high quality earthquake data originally obtained by the institute of earth sciences ies and the central weather bureau cwb the selected seismicity data set is shown to be complete for m w 3 0 the logarithmic mean annual seismicity rate and its standard deviation from the observed annual seismicity rates of individual years are obtained initially for different m w ranges it is shown subsequently that the logarithmic annual seismicity rates indeed possess a well behaved lognormal distribution it is further shown that our new approach has an added merit that tends to suppress the influences of anomalously high annual seismicity rates due to large numbers of aftershocks from major earthquake sequences finally the observed logarithmic mean annual seismicity rates with their standard deviations for 3 0 m w 5 0 are used to obtain the alternative gutenberg richter relations for different depth ranges the results are as follows log 10 n 5 75 0 90 m w 0 25 0 01 m w for focal depth 0 300 km log 10 n 5 78 0 94 m w 0 20 0 01 m w for focal depth 0 35 km log 10 n 4 72 0 89 m w 0 08 0 08 m w for focal depth 35 70 km log 10 n 4 69 0 88 m w 0 47 0 16 m w for focal depth 70 300 km in above equations log 10 n represents the logarithmic annual seismicity rate these g r relations give distinctly different values of the parameters a and b for taiwan earthquakes in different depth ranges these analytical equations can be readily used to obtain both the mean logarithmic annual seismicity rate and its standard deviation for any given m w as an example a numerical table presenting the corresponding median annual seismicity rates and their upper and lower bounds at median one standard deviation levels is given at the end this table offers a concise glance at the annual seismicity rates for taiwan earthquakes of various magnitudes and focal depths it is interesting to point out that the seismicity rate of crustal earthquakes which tends to contribute most hazards accounts for only about 74 of the overall seismicity rate in taiwan accordingly direct use of the entire earthquake catalog without differentiating focal depth ranges may result in substantial overestimates of potential seismic hazards

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

three dimensional vp vs variations for the coso region california recent seismological studies of the coso region of southeastern california document both low p wave velocities and abnormal sv attenuation in indian wells valley south of the pleistocene volcanics of the coso range in order to learn more about the physical nature of these colocated anomalies a tomographic inversion for the three dimensional variations of vp vs the ratio of compressional to shear velocity was performed iterative back projection of 2966 shear and compressional wave travel time residuals from local earthquakes recorded on vertical instruments reveals that vp vs is generally high at the surface and decreases systematically to 10 km depth superimposed on this trend are several large anomalies near devil s kitchen in the coso geothermal area vp vs values are very low near the surface consistent with measured values for steam dominated geothermal systems abnormally high values of vp vs are observed in portions of indian wells valley and also below the cactus peak rhyolite dome from 2 to 5 km in depth in indian wells valley the co occurrence of low p velocities low s velocities high vp vs and anomalous sv attenuation are indicative of subsurface partial melt because the inversion is based on vertical data only however the results cannot be considered conclusive only suggestive

evidence for orographic wave heating in the equatorial thermosphere at solar maximum fabry perot interferometer observations of equatorial 630 nm airglow thermospheric winds and temperatures were made at arequipa peru 16 5 s 71 5 w during the solar maximum years of 1989 and 1990 examination of the thermospheric winds measured from doppler shifts of the 630 nm airglow emission in the two directions east and west of arequipa shows that the zonal wind is often significantly weaker over the andes east than over the pacific west in winter between 19 lt and 24 lt the typical reductions in speed found were 40 to 70 m s in the same time period the temperature results show elevated values of 200 500 k for the three directions north east and zenith over mountainous terrain compared with those of the two directions west and south over water this effect fades near equinoctial periods examination of the standard deviation of the temperature ohservations for the five directions showed an increase in this value above the measurement error hy a factor of three for the direction toward the andes east but not for the direction over water south this elevation is consistent with wave activity as a source of the heating viscous dissipation of waves propagating into the thermosphere region from below is suggested as an explanation for the localized regions of heating

neutral temperature anomaly in the equatorial thermosphere a source of vertical winds data obtained from the wats wind and temperature spectrometer instrument on de 2 dynamics explorer during high solar activity show new evidence for the presence of vertical winds of a significant magnitude in the equatorial thermosphere they reveal a latitudinal structure that can be related to the recently discovered phenomena of the equatorial temperature and wind anomaly etwa in the local evening hours the vertical winds usually are downward around the dip equator and collocated with the temperature minimum of etwa in general they are upward at about 24 dip latitude away from the dip equator and are collocated with the etwa temperature crests the magnitude of the vertical winds is in the 10 40 m s range it is proposed that the temperature and pressure ridges formed by the excess ion drag on the zonal winds around the two crests and ordered by the relatively lower ion drag at the trough of the well known equatorial ionization anomaly eia drive a new wind system in the meridional plane and that the measured vertical winds form part of this wind system

a catalog of taiwan earthquakes 1900 2006 with homogenized mw magnitudes taiwan has a relatively complete catalog of earthquakes since the first seismograph was installed in 1897 however due to changes in seismographic characteristics network coverage and observational practice the definition and procedure for magnitude determination were different during different time periods recognizing a complete catalog of earthquakes with consistent magnitudes is essential for delineating seismicity patterns and assessing seismic hazards for taiwan efforts have been made to convert the original magnitudes of earthquakes in taiwan based on various magnitude scales to a common m l or m s magnitude scale unfortunately the m l or m s magnitude scales chosen for previous studies all are subject to a fundamental limitation of saturation toward large earthquakes besides these studies are nearly two decades old in order to avoid this limitation and to follow the current trend we have chosen in this study to convert original magnitudes of various scales to a common m w scale in this study we used two independent methods for magnitude conversion in the first method we converted the original magnitudes to m w through empirical relations between these magnitudes and m w this magnitude is called the old m w in the second method we used the best fitting a and b values to convert the original magnitudes to m w this magnitude is called the new m w the converted m w magnitudes from both methods have resulted in significant improvements over the original magnitudes and are in good agreement with each other nevertheless by examining the log10 n versus m w plots we found better linearity and tighter overlap among different time periods for the new m w than for the old m w thus we chose the new m w as the unified magnitude for the catalog of taiwan earthquakes finally a list of 899 earthquakes from 1900 to 2006 with m w 5 5 is presented graphic 1 see the earthquake lists available in the electronic supplement to this article the list is considered complete for the whole period from 1900 to 2006 1 embed inline graphic 1 gif

seasonal variation in the occurrence time of the equatorial midnight temperature bulge we have reexamined incoherent scatter radar data on electron and ion temperature from the jicamarca radar observatory 12 s 77 w 1 n diplat for the period 1967 68 and early 1969 we find clear evidence of systematic nighttime temperature increases presumably associated with the midnight pressure bulge and the collapse of the middle latitude f region a significant new finding is that the temperature enhancements tend on the average to occur about two hours before midnight in the local summer and about one hour after midnight in the local winter the bulges appear in various shapes and the enhancement magnitudes vary considerably from barely detectable to many tens of degrees kelvin but show a definite tendency to be smaller in winter than in summer when increases of up to 200 k are sometimes observed changeover from summer to winter behavior occurs within two months or less around equinox our results are consistent with the hypothesis of a nighttime equatorial temperature bulge moving with the antisolar meridian but at jicamarca systematically centered 30 west of this meridian 2 hrs before midnight near the december solstice and 15 east of it near the june solstice our data have relevance to the questions of seasonal changes in the phase and amplitude of the tidal modes responsible for the midnight pressure and temperature bulge

p wave velocity variations in the coso region california derived from local earthquake travel times inversion of 4036 p wave travel time residuals from 429 local earthquakes using a tomographic scheme provides information about three dimensional upper crustal velocity variations in the indian wells valley coso region of southeastern california the residuals are calculated relative to a coso specific velocity model corrected for station elevation weighted and back projected along their ray paths through models defined with layers of blocks slowness variations in the surface layer reflect local geology including slow velocities for the sedimentary basins of indian wells and rose valleys and relatively fast velocities for the sierra nevada and argus mountains in the depth range of 3 5 km the inversion images an area of reduced compressional velocity in western and northern indian wells valley but finds no major velocity variations beneath the coso volcanic field to the north these results are consistent with a recent study of anomalous shear wave attenuation in the coso region between 5 and 10 km depth low velocity areas 7 slow appear at the southern end of the coso volcanics reaching east to the coso basin numerical tests of the inversion s resolution and sensitivity to noise indicate that these major anomalies are significant and well resolved while other apparent velocity variations in poorly sampled areas are probably artifacts the seismic data alone are not sufficient to uniquely characterize the physical state of these low velocity regions because of the coso region s history of pleistocene bimodal volcanism high heat flow geothermal activity geodetic deformation and seismic activity one possibility is to link the zones of decreased p velocity to contemporary magmatic activity

detection of magma bodies beneath krakatau volcano indonesia from anomalous shear waves abstract the seismograms of 14 local earthquakes recorded by a temporary network in the sunda strait were used to construct an image of shear wave attenuating bodies in the vicinity of the krakatau volcanic complex seismograms for all ray paths going beneath the krakatau complex show a diminution of the amplitude of s waves these diminutions cannot be attributed to source mechanisms or station effects combination of all ray paths although in limited number demonstrates that the attenuating body is located in two zones which are probably disconnected although the limited set of data available does not allow us to draw a definite conclusion the upper zone is about 9 km deep and the lower one is at least 22 km deep the upper zone contains probably numerous irregular pockets of magma the deep zone appears to be a very wide body related to the extensional nature of the sunda strait the existence of a large deep reservoir should be taken into account for the mitigation of future hazards

acoustic waves generated by gusty flow over hilly terrain 1 we examine the generation of acoustic waves by gusty flow over hilly terrain we use simple theoretical models of the interaction between terrain and eddies and a linear model of acoustic gravity wave propagation the calculations presented here suggest that over a dense array of geographically extensive sources orographically generated vertically propagating acoustic waves can be a significant cause of thermospheric heating this heating may account in good part for the thermospheric hot spot near the andes reported by meriwether et al 1996 1997

thermospheric gravity wave modes over low and equatorial latitudes during daytime 1 the small scale intensity fluctuations obtained from 56 days of observations of oi 630 0 nm dayglow emission intensities from mount abu 24 6 n 73 7 e dip latitude 19 09 n a station under the crest of equatorial ionization anomaly eia have been subjected to harmonic analysis to unravel different modes of atmospheric gravity waves agw similar analysis is carried out for 26 days of dayglow intensity data recorded from waltair 17 7 n 83 3 e dip latitude 10 09 n a low latitude station and for 8 days of available data from thumba 8 68 n 77 0 e dip latitude 0 45 n an equatorial station with the same objective the analysis reveals the relative dominance preferred mode of 0 5 1 0 hour periodic component over mount abu 2 0 2 5 hour periodic component over waltair and 1 0 1 5 hour component over thumba during geomagnetically quiet periods qualitative arguments have been propounded to explain the differences in the preferred modes over these places and it is suggested that the source responsible for the preferred modes may lie in the lower atmosphere further the analysis also indicates the presence of additional preferred modes over low latitudes during geomagnetically disturbed periods

estimating seismic hazards from the catalog of taiwan earthquakes from 1900 to 2014 in terms of maximum magnitude maximum expected earthquake magnitude is an important parameter when designing mitigation measures for seismic hazards this study calculated the maximum magnitude of potential earthquakes for each cell in a 0 1 0 1 grid of taiwan two zones vulnerable to maximum magnitudes of m w 6 0 which will cause extensive building damage were identified one extends from hsinchu southward to taichung nantou chiayi and tainan in western taiwan the other extends from ilan southward to hualian and taitung in eastern taiwan these zones are also characterized by low b values which are consistent with high peak ground shaking we also employed an innovative method to calculate at intervals of m w 0 5 the bounds and median of recurrence time for earthquakes of magnitude m w 6 0 8 0 in taiwan

application of the gauss theorem to the study of silicic calderas the calderas of la primavera los azufres and los humeros mexico abstract we explored applications including limitations of gauss s theorem to the study of silicic calderas first it enables us to determine the mass deficiency from calderas mass deficiency itself has also other potential applications it enables to make qualitative comparisons between calderas we can use the mass deficiency to test in a quick way and as a preliminary step to a formal gravity inversion for the feasibility of caldera types of simple geometry i e piston subsidence and funnel models this application can be done in a straightforward way once the mass deficiency has been determined for this purpose the mass deficiency is converted to the volume of material missing at the caldera subsequently for example this volume and the respective caldera diameter enable us to estimate the height of the cylinder fitting the piston subsidence model if the obtained parameters are congruent with the known geology and geophysical information then the model may be considered further in the inversion of the gravity data for the detailed structure other simple models i e the funnel model can also be analyzed in this way in particular when working with a piston subsidence caldera type the gauss theorem enables us to estimate the caldera collapse very difficult to obtain based on geologic information alone these possible uses of gauss s theorem are illustrated with the calderas of la primavera los azufres and los humeros caldera mexico the obtained mass deficiency from these calderas follow the linear mass deficiency diameter trend observed for other calderas in particular because of their diameters and mass deficiencies la primavera and krakatau calderas can be considered equiparable this comparison is of the most importance considering that la primavera is located in the neighbourhood of a metropolis guadalajara city since geophysical studies have already established a piston subsidence model for these calderas we assessed gauss s theorem used to estimate their collapses the respective estimated subsidences for la primavera 600 m los humeros 500 m and los azufres calderas 800 and 1200 m respectively are supported by borehole data these relatively small subsidences in relation to many calderas in western us can be explained by the presence of cylindrical to sub spherical magma chambers of smaller size than those underlying the western us calderas of yellowstone valles and long valley for example in an epicontinental setting of young quaternary rocks against precambrian cratonic basement in western us a reassessment of all the available geological and geophysical information was also done in particular the caldera limits were checked and corrected when necessary based on available 2 d gravity modeling gravity gradients and the location of the volcanic vents regional tectonic lineaments might explain many of the particular details of their structures la primavera caldera might have formed through a piecemeal subsidence controlled by the pre caldera tectonics los humeros caldera is an example of a caldera that evolved by incremental growth as the vulsiniani calderas in italy the los azufres caldera comprises two contiguous calderas emplaced in a regional tectonic depression

how complete is the isc gem global earthquake catalog abstract the international seismological centre in collaboration with the global earthquake model effort has released a new global earthquake catalog covering the time period from 1900 through the end of 2009 in order to use this catalog for global earthquake studies i determined the magnitude of completeness m c as a function of time by dividing the earthquakes shallower than 60 km into seven time periods based on major changes in catalog processing and data availability and applying four objective methods to determine m c with uncertainties determined by nonparametric bootstrapping deeper events were divided into two time periods because of differences between the four methods the final m c was determined subjectively by examining the main features of each method in both the cumulative and binned magnitude frequency distributions the time periods and m c values for shallow events are 1900 1917 m c 7 7 1918 1939 m c 7 0 1940 1954 m c 6 8 1955 1963 m c 6 5 1964 1975 m c 6 0 1976 2003 m c 5 8 and 2004 2009 m c 5 7 using these m c values for the longest time periods for which they are valid e g 1918 2009 1940 2009 the shallow data fits a gutenberg richter distribution with b 1 05 and a 8 3 within 1 standard deviation and with no declustering the exception is for time periods that include 1900 1917 during which there are only 33 events with m m c and for those few data b 2 15 0 46 that result calls for further investigations for this time period ideally having a larger number of earthquakes for deep events the results are m c 7 1 for 1900 1963 although the early data are problematic and m c 5 7 for 1964 2009 for the later time period b 0 99 and a 7 3

maximum altitude penetration of atmospheric gravity waves observed during aloha 93 atmospheric gravity waves agws are subject to altitude propagation limits which are governed by the diffusion processes diffusion times and scales which exceed the wave period and wavelength define the limiting domain for agws an expression is presented which defines the upper altitude limit to which agws can propagate given vertical diffusion constraints of the atmosphere airglow lidar and radar measurements are combined to characterize the intrinsic agw parameters in the 80 105 km altitude region a subset of agws 17 observed by airglow imagers during the aloha 93 were made when simultaneous wind measurements were available and intrinsic wave parameters were calculated the limiting altitude of propagation for these measured monochromatic waves is calculated to range from 110 150 km with a mean limiting altitude of 130 km the altitude limit is necessarily lower for waves with short vertical wavelengths and longer intrinsic periods this observation is important for a large number of issues including energetic considerations regarding thermospheric heating in models which consider upward propagating agws and energy flux of tropospheric origin this limited data base should be expanded for statistical significance in future work

attenuation of p and s waves in a magma chamber in long valley caldera california shallow earthquakes around the southwest boundary of long valley caldera west of the hilton creek fault are characterized by lack of s waves at regional seismic network stations to the northwest north and northeast and p waves for these same station event combinations are deficient in frequencies higher than about 2 3 hz earthquakes east of the hilton creek fault and southeast of the caldera have normal p and s wave signatures at the same stations these effects are explained by propagation through a magma chamber in the south central part of long valley caldera at depth greater than 7 8 km

anomalous shear wave attenuation in the shallow crust beneath the coso volcanic region california we use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the coso volcanic geothermal area of eastern california sv and p wave amplitudes were measured from vertical component seismograms of earthquakes that occurred in the cososouthem sierra nevada region from july 1983 to august 1985 seismograms of 16 small earthquakes show sv amplitudes which are greatly diminished at some azimuths and takeoff angles indicating strong lateral variations in s wave attenuation in the area three dimensional images of the relative s wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data the results indicate regions within a 20 by 30 by 10 km volume of the shallow crust one shallower than 5 km that severely attenuate sv waves passing through them these anomalies lie beneath the indian wells valley 30 km south of the coso volcanic field and are coincident with the epicentral locations of recent earthquake swarms no anomalous attenuation is seen beneath the coso volcanic field above about 5 km depth geologic relations and the coincidence of anomalously slow p wave velocities suggest that the attenuation anomalies may be related to magmatism along the eastern sierra front

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

geometry of magma bodies beneath long valley california determined from anomalous earthquake signals one hundred and ninety two small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 13 km are used to map the subsurface geometry of magma bodies in the caldera seismograms of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals are absent and high frequency p wave energy is missing these anomalous ray paths intersect in an area of the south central caldera which we interpret to be a region of molten or partially molten rock this magma body lies between about 4 1 2 and at least 13 km depth and is 10 km long by 5 km wide beneath 7 km the magma appears to be relatively contiguous below 7 km and more dispersed above another magma body may be present in the northwest caldera coincident with an interpreted 7 8 km deep reflection from the top of a magma chamber

revised estimates for the volume of the late bronze age minoan eruption santorini greece the late bronze age minoan eruption of santorini greece occurred from within an existing caldera low temperature pyroclastic flow emplacement on shallow slopes outside the caldera can only be consistent with the caldera being filled with eruption products that are not preserved field observations and seismic reflection surveys suggest that this missing material has been downfaulted the volume of the caldera infill is estimated as 18 26 km 3 dense rock equivalent dre increasing the total of the minoan eruption deposits to 78 86 km 3 dre and making it the largest known holocene eruption this study highlights a general mechanism whereby caldera eruption volumes could be significantly underestimated

gravity wave momentum flux in the lower stratosphere over convection this work describes a method for estimating vertical fluxes of horizontal momentum carried by short horizontal scale gravity waves lambda sub x 10 100 km using aircraft measured winds in the lower stratosphere we utilize in situ wind vector and pressure altitude measurements provided by the meteorological measurement system mms on board the er 2 aircraft to compute the momentum flux vectors at the flight level above deep convection during the tropical experiment of the stratosphere troposphere exchange project step tropical data from flight 9 are presented here for illustration the vertical flux of horizontal momentum these observations points in opposite directions on either side of the location of a strong convective updraft in the cloud shield this property of internal gravity waves propagating from a central source compares favorably with previously described model results

did tsunami launched gravity waves trigger ionospheric turbulence over arecibo 1 we report on measurements of ionospheric plasma dynamics conducted at the arecibo observatory between 20 00 and 24 00 local time lt on december 25 and 26 2004 using the 430 mhz incoherent scatter radar isr for interpretive purposes these measurements are supported by data from two nearby ionosondes and global positioning system gps satellites the isr detected different ionospheric behaviors during the vertical transmission periods on the consecutive magnetically quiet nights on the night of december 25 the ionosphere descended smoothly and spread f signatures faded for about two hours on the following evening the bottomside ionosphere rose by 50 km inducing plasma irregularities and intense spread f alternating cycles of bottom side plasma rising and falling persisted through the remainder of the experiments we postulate that this sinusoidal behavior is a response to gravity waves propagating above puerto rico nearly simultaneous data from two nearby stations show that gps signals were modified by variations in total electron content tec indicating the presence of traveling ionospheric disturbances tids the december 26 experiments were conducted about a day after an mw 9 2 earthquake launched tsunami waves first across the indian then into the atlantic and pacific oceans we suggest that coupling at the tsunami sea air interface launched gravity waves that propagated for great distances beneath the mesopause gps data recorded tec variation in asia europe and the caribbean suggesting that tids were induced on a global scale at the wake of tsunami launched gravity waves energy from imperfectly ducted gravity waves leaked into the ionosphere partially over puerto rico the wind velocity field of these gravity waves caused local ionospheric plasma to rise seeding bottomside irregularities via the generalized rayleigh taylor instability

location and configuration of magma bodies beneath long valley california determined from anomalous earthquake signals recordings of 281 small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 15 km are used to map the subsurface geometry of shear wave attenuating bodies in the caldera signatures of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals have very low amplitudes and high frequency p and s wave energy is missing for the same station event combinations the volcanic and geothermal history of the region suggests that ray paths for these anomalous signals have passed through magma which absorbed much of the s wave energy and also attenuated the higher frequencies with over 1200 normal and anomalous ray paths through the caldera we have located two apparently massive magma bodies in the central and northwest caldera as well as two more dispersed magma areas in the southern caldera and beneath crowley lake the central magma body extends from 4 5 to at least 13 km beneath the surface and the northwest body is as shallow as 5 5 km these two magma bodies are probably connected below about 8 km secondary arrivals seen on select seismograms are tentatively interpreted as reverberations inside the central magma chamber and are consistent with the interpreted lateral extent of the magma the northwest and central magma bodies lie beneath the northwest and southeast corners of the caldera s resurgent dome and probably connect beneath the dome s center also the shallower parts of these magma bodies and the southern anomalous area lie beneath the surface expression of the medial graben faults suggesting that structural features seen at the surface of the valley may be related to magma location at depth

optical interferometric measurements of nighttime equatorial thermospheric winds at arequipa peru we obtained nighttime measurements of equatorial thermospheric wind dynamics at arequipa peru with an automated field widened fabry perot interferometer between april 1983 and august 1983 and reduced data from 62 nights significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed near the equinox between 2000 and 2300 lt the zonal wind component is eastward with an amplitude between 100 and 150 m s that gradually ebbs to zero by dawn the meridional component is generally small throughout the night in the winter months may august and at the winter solstice the zonal wind persists eastward throughout the night with speeds between 50 and 150 m s the meridional component is directed poleward southward toward the winter hemisphere with a speed of 50 75 m s that decays to zero by midnight comparison with the predictions of the national center for atmospheric research thermospheric general circulation model for equinoctial and solstice conditions shows good agreement we conclude that the observed seasonal changes are caused by the changing nature of the solar forcing function the arequipa results found the day to day variability in the winter thermospheric winds to be less than that found for the summer equatorial observations obtained at kwajalein interferometric measurements of the 630 0 nm intensity at equinox showed a major reduction of the emission lasting 1 or 2 hours in all directions but south shortly after evening twilight this decrease was not observed during winter